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  • 1. Asplund, Johan
    et al.
    Johansson, Otilia
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Nybakken, Line
    Palmqvist, Kristin
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Gauslaa, Yngvar
    Simulated nitrogen deposition influences gastropod grazing in lichens2010In: Ecoscience, ISSN 1195-6860, Vol. 17, no 1, p. 83-89Article in journal (Refereed)
    Abstract [en]

    Lichens are often important photosynthetic organisms in oligotrophic environments where high-quality fodder plants are rare. A strong herbivore defence and/or low nutritional quality allows the accumulation of a high lichen biomass in such areas. However, it is not known how N deposition influences lichen palatability. This study analyzes possible changes in gastropod grazing preference after 3 months simulated N deposition on 3 foliose (Lobaria scrobiculata, Platismatia glauca, and Xanthoria aureola) and 1 pendulous lichen species (Alectoria sarmentosa). Lichens were daily irrigated in the field with rainwater containing 1.625 mM NH4NO3 from June to September, equivalent to a deposition of 50 kg N·ha-1·y-1. Irrigations applied at night, morning, or noon simulated different C-gain regimes. Afterwards in the lab, we offered 2 common lichen-feeding gastropods the choice between N-fertilized thalli and control thalli irrigated with artificial rainwater. The gastropods clearly preferred the unfertilized thalli of the 3 foliose species. For the pendulous A. sarmentosa, the gastropods preferred N-enriched thalli (irrigated at night) to controls. In conclusion, N-enrichment changes the palatability of lichens in species-specific ways.

  • 2.
    Dahlman, L
    et al.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Näsholm, T
    Palmqvist, K
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Growth, nitrogen uptake, and resource allocation in the two tripartite lichens Nephroma arcticum and Peltigera aphthosa during nitrogen stress2002In: New Phytologist, ISSN 0028-646X, Vol. 153, no 2, p. 307-315Article in journal (Refereed)
    Abstract [en]

     

    • The lichens were irrigated with different N forms, enriched in 15N to assess N uptake, during 3 months in the field, with a total N dosage of 500 mg m−2. Nitrogen deprivation was induced by removing the nitrogen-fixing cephalodia.

    • The lichens took up 11–134 mg N m−2 of the added N, corresponding to 1–4% of their total thallus N. Uptake was 4 times higher for NH4+ than for NO3, and the highest 15N concentrations were found in newly synthesized tissue. Both forms of N stress affected thallus expansion rates in both species.

    • It is concluded that the two lichens were able to maintain a balanced tissue N concentration despite large variations in N supply, and that assimilated N might be transported to growing apices. Alternatively, N assimilation from external sources might be greater in the margins than in the mature thallus. Thallus expansion was sensitive to N stress, apparently being tightly coupled to N assimilation.

  • 3.
    Dahlman, L
    et al.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Persson, J
    Näsholm, T
    Palmqvist, K
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Carbon and nitrogen distribution in the green algal lichens Hypogymnia physodes and and Platismatia glauca in relation to nutrient supply.2003In: Planta, ISSN 0032-0935, Vol. 217, no 1, p. 41-48Article in journal (Refereed)
  • 4.
    Dahlman, L
    et al.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Persson, J
    Palmqvist, K
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Näsholm, T
    Organic and inorganic nitrogen uptake in lichens2004In: Planta, Vol. 219, p. 459-467Article in journal (Refereed)
  • 5.
    Dahlman, Lena
    et al.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Palmqvist, Kristin
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Growth in two foliose tripartite lichens Nephroma arcticum and Peltigera aphthosa: empirical modelling of external versus internal factors2003In: Functional Ecology, ISSN 0269-8463, E-ISSN 1365-2435, Vol. 17, no 6, p. 821-831Article in journal (Refereed)
    Abstract [en]

    1 To assess how internal and external factors contribute to lichen growth, light, water and nutrient supplies were manipulated during 3 months in the field for the lichens Nephroma arcticum (L.) Torss. and Peltigera aphthosa (L.) Willd. Concomitant measures of weight and area gain, microclimatic conditions and investments in photobiont vs mycobiont tissue were also conducted.

    2 In both lichens ≈80% of the variation in weight gain was explained by a linear regression model including light received during wet active periods, chlorophyll a concentration and area gain. All three parameters had a positive effect on weight gain.

    3 About 80% of the variation in area gain was explained by a model including variation in weight gain, initial thallus specific weight, ergosterol and chitin concentration. The model was identical for the two lichens, with a positive effect of weight gain and thallus specific weight and a negative effect of ergosterol and chitin.

    4 Peltigera aphthosa grew faster than N. arcticum when exposed to the same environmental conditions. This could be explained by its higher chlorophyll a to ergosterol ratio, and a greater water-holding capacity prolonging the active time in light.

  • 6.
    Eriksson, Amanda
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Gauslaa, Yngvar
    Palmqvist, Kristin
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Ekström, Magnus
    Umeå University, Faculty of Social Sciences, Umeå School of Business and Economics (USBE), Statistics.
    Esseen, Per-Anders
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Morphology drives water storage traits in the globally widespreadlichen genus Usnea2018In: Fungal ecology, ISSN 1754-5048, E-ISSN 1878-0083, Vol. 35, p. 51-61Article in journal (Refereed)
    Abstract [en]

    Links between lichen morphology, internal/external water storage and distribution patterns are poorly known. We compared mass- (WC, % H2O) and area-based (WHC, mg H2O cm−2) hydration traits in seven pendent or shrubby Usnea species from oceanic to continental climates. All species held more external than internal water. Internal WHC and WC increased with specific thallus mass (STM, mg cm−2), while external WC decreased. Shrubby species had higher STM and total WHC than pendent ones. The continental Usnea hirta (shrubby) had the highest total and external storage; the suboceanic Usnea longissima (pendent) had the lowest internal storage. Morphology drives hydration traits and explains distributions of some Usnea species, but such traits did not distinguish oceanic from widespread species. Shrubby species maximize water storage and thus prolong hydration after rainfall events and/or hydration by dew. The low internal WHC in pendent species is likely an adaptation to frequent hydration in humid air.

  • 7.
    Esseen, Per-Anders
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Ekström, Magnus
    Umeå University, Faculty of Social Sciences, Umeå School of Business and Economics (USBE), Statistics.
    Westerlund, Bertil
    Palmqvist, Kristin
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jonsson, Bengt Gunnar
    Grafström, Anton
    Ståhl, Göran
    Broad-scale distribution of epiphytic hair lichens correlates more with climate and nitrogen deposition than with forest structure2016In: Canadian Journal of Forest Research, ISSN 0045-5067, E-ISSN 1208-6037, Vol. 46, no 11, p. 1348-1358Article in journal (Refereed)
    Abstract [en]

    Hair lichens are strongly influenced by forest structure at local scales, but their broad-scale distributions are less understood. We compared the occurrence and length of Alectoria sarmentosa (Ach.) Ach., Bryoria spp., and Usnea spp. in the lower canopy of > 5000 Picea abies (L.) Karst. trees within the National Forest Inventory across all productive forest in Sweden. We used logistic regression to analyse how climate, nitrogen deposition, and forest variables influence lichen occurrence. Distributions overlapped, but the distribution of Bryoria was more northern and that of Usnea was more southern, with Alectoria's distribution being intermediate. Lichen length increased towards northern regions, indicating better conditions for biomass accumulation. Logistic regression models had the highest pseudo R-2 value for Bryoria, followed by Alectoria. Temperature and nitrogen deposition had higher explanatory power than precipitation and forest variables. Multiple logistic regressions suggest that lichen genera respond differently to increases in several variables. Warming decreased the odds for Bryoria occurrence at all temperatures. Corresponding odds for Alectoria and Usnea decreased in warmer climates, but in colder climates, they increased. Nitrogen addition decreased the odds for Alectoria and Usnea occurrence under high deposition, but under low deposition, the odds increased. Our analyses suggest major shifts in the broad-scale distribution of hair lichens with changes in climate, nitrogen deposition, and forest management.

  • 8. Gaio-Oliveira, G
    et al.
    Dahlman, L
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Maguas, C
    Palmqvist, K
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Growth in relation to microclimatic conditions and physiological characteristics of four Lobaria pulmonaria populations in two contrasting habitats2004In: Ecography, Vol. 27, p. 75-86Article in journal (Refereed)
  • 9. Gaio-Oliveira, G
    et al.
    Dahlman, L
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Palmqvist, K
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Maguas, C
    Ammonium uptake in the nitrophytic lichen Xanthoria parietina (L.) Th. Fr. and its effects on vitality and balance between symbionts2004In: Lichenologist, Vol. 36, p. 75-86Article in journal (Refereed)
  • 10. Gaio-Oliveira, G
    et al.
    Dahlman, L
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Palmqvist, K
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Máguas, C
    Responses of the lichen Xanthoria parietina (L.) Th. Fr. to varying thallus nitrogen concentrations2005In: Lichenologist, Vol. 37, p. 171-179Article in journal (Refereed)
  • 11. Gaio-Oliveira, G
    et al.
    Moen, J
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Danell, Ö
    Palmqvist, K
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Effect of simulated reindeer grazing on the re-growth capacity of mat-forming lichens2006In: Basic and Applied Ecology, Vol. 7, p. 109-121Article in journal (Refereed)
  • 12. Gaio-Oliveira, Gisela
    et al.
    Dahlman, Lena
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Palmqvist, Kristin
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Martins-Loução, Maria Amélia
    Máguas, Cristina
    Nitrogen uptake in relation to excess supply and its effects on the lichens Evernia prunastri (L.) Ach and Xanthoria parietina (L.) Th. Fr.2005In: Planta, ISSN 0032-0935, Vol. 220, no 5, p. 794-803Article in journal (Refereed)
  • 13. Gauslaa , Y.
    et al.
    Palmqvist, Kristin
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Solhaug, K. A.
    Holien , H.
    Hilmo, O.
    Nybakken, L.
    Myhre, L.
    Ohlson, M.
    Growth of epiphytic old forest lichens across climatic and successional gradients2007In: Canadian Journal of Forest Research, ISSN 0045-5067, E-ISSN 1208-6037, Vol. 37, no 10, p. 1832-1845Article in journal (Refereed)
    Abstract [en]

    This paper aims to assess the influence of canopy cover on lichen growth in boreal forests along a regional forest gradient. Biomass and area gain, and some acclimation traits, were assessed in the old-forest lichens Lobaria pulmonaria (L.) Hoffm., Pseudocyphellaria crocata (L.) Vain., and Usnea longissima Ach. transplanted 110days in three successional Norway spruce (Picea abies (L.) Karst.) forest stands (clearcut, young, and old forest) repeated along a rainfall gradient (continental, suboceanic, and Atlantic zones) in Scandinavia. Lichen growth peaked in Atlantic rainforests with mean dry matter (DM) gain up to 36%-38%. The alectorioid lichen U. longissima showed the widest range of growth responses and no signs of chlorophyll degradation. Its highest DM gain consistently occurred in clearcuts, whereas the DM gain was close to zero in the shadiest young forest. The two foliose lichens L. pulmonaria and P. crocata exhibited maximal growth rates in old forests, but apparently growth was limited by low light even in old forests. Their DM gain was reduced in the most sun-exposed clearcuts due to chlorophyll degradation and was relatively high under closed young canopies, suggesting a better adaptation to shade. The lichen responses show that a high frequency and dominance of young and dense fast-growing forest stands at a landscape level are not compatible with large populations of these old-forest lichens and that a lack of lichens under an industrial forestry regime may not necessarily be determined by low dispersal efficiency only.

    Cet article a pour but d'évaluer l'influence du couvert de la canopée sur la croissance des lichens dans les forêts boréales le long d'un gradient forestier régional. Le gain en biomasse et en superficie ainsi que certains caractères d'acclimatation ont été évalués chez les lichens des forêts âgées, Lobaria pulmonaria (L.) Hoffm., Pseudocyphellaria crocata (L.) Vain. et Usnea longissima Ach., qui ont été transplantés pendant 110 jours dans trois peuplements d'épicéa commun (Picea abies (L.) Karst.) rendus à différents stades de succession (forêt coupée à blanc, jeune et vieille forêts). L'expérience a été répétée le long d'un gradient pluvial (zones continentale, subocéanique et atlantique) en Scandinavie. La croissance des lichens a culminé dans les forêts pluviales atlantiques avec un gain moyen en matière anhydre allant jusqu'à 36%-38%. Le lichen alectorioïde U. longissima a montré la plus vaste gamme de réponses en croissance végétative et aucun signe de dégradation de la chlorophylle. Son gain maximal en matière anhydre est survenu essentiellement dans les coupes à blanc alors qu'il était presque nul dans la jeune forêt la plus ombragée. Les deux lichens foliacés, L. pulmonaria et P. crocata, montraient des taux maximum de croissance dans les vieilles forêts, mais la croissance était apparemment limitée par la faible luminosité, même dans les forêts âgées. Leur gain en matière anhydre était réduit dans la plupart des coupes à blanc exposées au soleil à cause de la dégradation de la chlorophylle alors qu'il était relativement élevé sous les jeunes canopées fermées, ce qui indique une meilleure adaptation à l'ombre. La réponse des lichens montre qu'une fréquence élevée et une forte dominance de jeunes peuplements forestiers à croissance rapide à l'échelle du paysage ne sont pas compatibles avec de grandes populations de ces lichens, typiques des forêts matures, et que le manque de lichens sous un régime forestier industriel pourrait ne pas nécessairement être dû seulement à la faible efficacité de dispersion des lichens.

  • 14. Gauslaa, Yngvar
    et al.
    Palmqvist, Kristin
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Solhaug, Knut Asbjørn
    Hilmo, Olga
    Holien, Håkon
    Nybakken, Line
    Ohlson, Mikael
    Size-dependent growth of two old-growth associated macrolichen species2009In: New Phytologist, ISSN 0028-646X, E-ISSN 1469-8137, Vol. 181, no 3, p. 683-692Article in journal (Refereed)
    Abstract [en]

    Relationships between thallus size and growth variables were analysed for the foliose Lobaria pulmonaria and the pendulous Usnea longissima with the aim of elucidating their morphogenesis and the factors determining thallus area (A) versus biomass (dry weight (DW) gain. Size and growth data originated from a factorial transplantation experiment that included three boreal climate zones (Atlantic, suboceanic and continental), each with three successional forest stands (clear-cut, young and old). When A was replaced by the estimated photobiont layer area in an area-DW scatterplot including all thalli (n = 1080), the two separate species clusters merged into one, suggesting similar allocation patterns between photobionts and mycobionts across growth forms. During transplantation, stand-specific water availability boosted area gain in foliose transplants, consistent with a positive role of water in fungal expansion. In pendulous lichens, A gain greatly exceeded DW gain, particularly in small transplants. The A gain in U. longissima increased with increasing DW:A ratio, consistent with a reallocation of carbon, presumably mobilized from the dense central chord. Pendulous lichens with cylindrical photobiont layers harvest light from all sides. Rapid and flexible three-dimensional A gain allows the colonization of spaces between canopy branches to utilize temporary windows of light in a growing canopy. Foliose lichens with a two-dimensional photobiont layer have more coupled A and DW gains.

  • 15.
    Jansson, Ulrika
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Palmqvist, Kristin
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Esseen, Per-Anders
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Growth of the old forest lichen Usnea longissima in forest edges2009In: The Lichenologist, ISSN 0024-2829, E-ISSN 1096-1135, Vol. 41, no 6, p. 663-672Article in journal (Refereed)
    Abstract [en]

    The lichen Usnea longissima was used to examine how distance from forest edge and edge contrast influence growth of pendulous lichens. Thalli of two sizes (12 and 27 cm) were transplanted to the lower canopy of old Picea abies forest at 5, 25 and 100 m distance from cutovers. Sites represented three levels of edge contrast: high (clear-cut), intermediate (3 m tall saplings) and low (6-7 m tall young forest). Lichen growth was assessed as annual length and weight gain. Growth rates of intact thalli were size-dependent, with both growth variables being higher in long than in short thalli. Distance and edge contrast had significant effects on weight gain in long thalli but not in short ones. Weight gain in long thalli was twice as high near the edge (23%) compared to the forest interior (12%). The highest weight gain (31%) occurred at intermediate contrast edges with lower growth at both low (18%) and high contrast edges (20%). Chlorophyll a concentration was highest near the edge and positively correlated with weight gain, so growth was apparently stimulated by both increased photosynthetic capacity and higher light availability near the edge. The lower part of the canopy in forest edges apparently have favourable growth conditions for U. longissima with growth being influenced by vegetation on adjoining cutovers. Therefore growth responses can not explain the previously observed decline of pendulous lichens following edge creation. Our results suggest that vegetation buffers can improve conditions for pendulous lichens near forest edges.

  • 16.
    Johansson, Otilia
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Nordin, Annika
    Olofsson, Johan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Palmqvist, Kristin
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Responses of epiphytic lichens to an experimental whole-tree nitrogen-deposition gradient2010In: New Phytologist, ISSN 0028-646X, E-ISSN 1469-8137, Vol. 188, no 4, p. 1075-1084Article in journal (Refereed)
    Abstract [en]

    • Here, we examined the responses of the epiphytic lichens Alectoria sarmentosa and Platismatia glauca to increased atmospheric nitrogen (N) deposition in an old-growth boreal spruce forest, to assess the sensitivity of these species to N and define their critical N load. • Nitrogen deposition was simulated by irrigating 15 trees over a 3 yr period with water and isotopically labeled NH(4) NO(3) , providing N loads ranging from ambient to 50 kg N ha(-1)  yr(-1) . • Thallus N concentration increased in both species with increasing N load, and uptake rates of both NH(4) (+) and NO(3) (-) were similar. Photobiont concentration increased linearly with increased N in both species, saturating in A. sarmentosa in the third year at the highest N loads (25 and 50 kg ha(-1 ) yr(-1) ). The simulated N deposition decreased the phosphorus (P) concentration in A. sarmentosa, and increased the N : P ratio in both species. • Significant responses in lichen chemistry were detected to inputs of 12.5 kg N ha(-1)  yr(-1) or higher, suggesting that resources other than N limit lichens at higher N loads. However, the data also suggest that N saturation may be cumulative over time, even at low N.

  • 17.
    Johansson, Otilia
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Olofsson, Johan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Giesler, Reiner
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Palmqvist, Kristin
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Lichen responses to nitrogen and phosphorus additions can be explained by the different symbiont responses2011In: New Phytologist, ISSN 0028-646X, E-ISSN 1469-8137, Vol. 191, no 3, p. 795-805Article in journal (Refereed)
    Abstract [en]

    Responses to simulated nitrogen (N) deposition with or without added phosphorus (P) were investigated for three contrasting lichen species – the N-sensitive Alectoria sarmentosa, the more N-tolerant Platismatia glauca and the N2-fixing Lobaria pulmonaria– in a field experiment.

    To examine whether nutrient limitation differed between the photobiont and the mycobiont within the lichen, the biomass responses of the respective bionts were estimated.

    The lichenized algal cells were generally N-limited, because N-stimulated algal growth in all three species. The mycobiont was P-limited in one species (A. sarmentosa), but the growth response of the mycobionts was complex, as fungal growth is also dependent on a reliable carbon export from the photobiont, which may have been the reason for the decrease of the mycobiont with N addition in P. glauca.

    Our findings showed that P availability was an important factor when studying effects of N deposition, as P supply can both mitigate and intensify the negative effects of N on epiphytic lichens.

  • 18.
    Johansson, Otilia
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Palmqvist, Kristin
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Olofsson, Johan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Nitrogen deposition drives lichen community changes through differential species responses2012In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 18, no 8, p. 2626-2635Article in journal (Refereed)
    Abstract [en]

    Nitrogen (N) deposition has increased globally over the last 150 years and further increases are predicted. Epiphytic lichens decline in abundance and diversity in areas with high N loads, and the abundance of lichens decreases along gradients of increased deposition. Thus, although N is an essential nutrient for lichens, excessive loads may be detrimental for them. However, these gradients include many correlated pollutants and the mechanisms behind the decline are thus poorly known. The aim of this study was to assess effects of N deposition, alone, on the epiphytic lichen community composition in a naturally N-poor boreal forest. For this purpose, whole spruce trees were fertilized daily with N at five levels, equivalent to 0.6, 6, 12.5, 25, and 50 kg N ha-1 yr-1, during four consecutive growing seasons (20062009), and changes in the abundance of lichens were monitored each autumn from the preceding year (2005). The studied lichen communities were highly dynamic and responded strongly to the environmental perturbation. N deposition detectably altered the direction of succession and reduced the species richness of the epiphytic lichen communities, even at the lowest fertilization application (6 kg N ha-1 yr-1). The simulated N deposition caused significant changes in the abundance of Alectoria sarmentosa, Bryoria spp., and Hypogymnia physodes, which all increased at low N loads and decreased at high loads, but with species-specific optima. The rapid decline of A. sarmentosa may have been caused by the added nitrogen reducing the stability of the lichen thalli, possibly due to increases in the photobiont: mycobiont ratio or parasitic fungal attacks. We conclude that increases in nitrogen availability, per se, could be responsible for the reductions in lichen abundance and diversity observed along deposition gradients, and those community responses may be due to physiological responses of the individual species rather than changes in competitive interactions.

  • 19.
    Johansson, Otilia
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Palmqvist, Kristin
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Olofsson, Johan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Nitrogen drives lichen community changes through the different species responsesManuscript (preprint) (Other academic)
  • 20.
    Jonsson, Anna
    et al.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Moen, Jon
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Palmqvist, Kristin
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Predicting lichen hydration using biophysical models.2008In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 156, no 2, p. 259-73Article in journal (Refereed)
    Abstract [en]

    Two models for predicting the hydration status of lichens were developed as a first step towards a mechanistic lichen productivity model. A biophysical model included the water potential of the air, derived from measurements of air temperature, relative humidity and species-specific rate constants for desiccation and rehydration. A reduced physical model, included only the environmental parameters, assuming instantaneous equilibration between the lichen and the air. These models were developed using field and laboratory data for three green algal lichens; the foliose epiphytic Platismatia glauca (L.) W. Culb., the fruticose epiphytic Alectoria sarmentosa (Ach.) Ach., and the fruticose, terricolous and mat-forming Cladina rangiferina (L.) Weber ex Wigg. The models were compared and validated for the same three species using data from a habitat with a different microclimate. Both models predicted length and timing of lichen hydration periods with high accuracy for A. sarmentosa and P. glauca where near 100 percent of the total wet time was predicted by the biophysical and the physical model. Moreover, the models predicted an accurate timing of the total realized wet time for A. sarmentosa and P. glauca when the lichens were wet. The model accuracy was lower for C. rangiferina compared to the epiphytes, both for the total realized wet time and timing accuracy. The results demonstrate that the stochastic and continually varying hydration status of lichens can be simulated from biophysical data. Further development of these models to include also water related activity, light, and temperature conditions during the hydration events, will then be a potent tool to assess potential lichen productivity in landscapes and habitats of various microclimatic conditions.

  • 21.
    Jonsson Cabrajic, Anna V
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Moen, Jon
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Palmqvist, Kristin
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Predicting growth of mat-forming lichens on a landscape scale: comparing models with different complexities2010In: Ecography, ISSN 0906-7590, E-ISSN 1600-0587, Vol. 33, no 5, p. 949-960Article in journal (Refereed)
    Abstract [en]

    During the 20th century, forestry practices has adversely affected lichen-rich habitats. Mat-forming lichens are important components of the vegetation of boreal and arctic ecosystems and are the main reindeer forage during the winter. To support the long-term management of lichens in such habitats we developed models for predicting the growth of two common species. The lichens were transplanted across northern Scandinavia along a west-east gradient varying in precipitation, temperature and irradiance. Growth was recorded seasonally over 16 months and ranged from −4.8 to 34.6% and −12.7 to 34.7% dry weight change for Cetraria stellaris and Cladina islandica, respectively. Growth was light limited below canopies with more than ca 60% cover and highest at the more humid sites when light levels were optimal. The models were based on various meteorological parameters, irradiance, physiological data and lichen hydration status; the latter was derived from a recently developed lichen hydration model. Our models' abilities to predict growth, both annually and seasonally (i.e. in summer), were evaluated in relation to their complexity and their potential usefulness from a management perspective. One parameter related to irradiance (the logarithm of site openness) was valuable in the prediction of annual growth for both species and could, in combination with precipitation, explain 52% of the variation in annual growth for C. stellaris and, in combination with total wet time and the irradiance received while wet, explain 66% of the variation in annual growth for C. islandica. The best simplified model explained 43% of the variation in annual growth for C. stellaris, using stem basal area and the annual normal temperature, and 24% for C. islandica using basal area alone. It is concluded that ensuring sufficient irradiance below the forest canopy is of crucial importance in the long-term management of mat-forming lichens and that simplified models can be used to identify appropriate habitats.

  • 22.
    Jonsson Čabrajić, Anna V
    et al.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Lidén, Marlene
    Sveriges Lantbruksuniversitet, Umeå, Institutionen för Skogens ekologi och skötsel.
    Lundmark, Tomas
    Sveriges Lantbruksuniversitet, Umeå, Enheten för skoglig fältforskning.
    Ottosson-Löfvenius, Mikael
    Sveriges Lantbruksuniversitet, Umeå, Institutionen för Skogens ekologi och skötsel.
    Palmqvist, Kristin
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Modelling hydration and photosystem II activation in relation to in situ rain and humidity patterns: a tool to compare performance of rare an generalist epiphytic lichens2010In: Plant, Cell and Environment, ISSN 0140-7791, E-ISSN 1365-3040, Vol. 33, p. 840-850Article in journal (Refereed)
    Abstract [en]

    A dynamic water and activity model was developed to assess how efficiently lichens can exploit in situ rain and humid air. The capacity to rehydrate and activate photosynthesis [i.e. photosystem II (PSII)] by these water sources was compared among four hydrophilic and one generalist epiphytic lichen. Hydration status, potential (instant activation) and realized (delayed activation) day-light activity were simulated using a model based on species-specific hydration, PSII activation characteristics and in situ water content for Platismatia norvegica in three microclimatic scenarios. The results showed that delayed PSII activation could have profound effects on lichens' ability to exploit environmental water sources. During rain, realized activity was reduced by 19, 34 and 56% compared to simulations assuming instant activation for three hydrophilic lichens in the driest microclimate. During humid air, the reduction was 81% for the most extreme species and scenario, because of slow hydration and low equilibrium water content. Many and brief hydration events may thus hamper species with slow activation and fast desiccation kinetics. No evidence of compensation by a 'water-holding' morphology was observed among studied species. The developed model may provide a tool for identifying suitable habitats for long-term persistence of lichens with physiological constraints.

  • 23.
    Jonsson Čabrajić, Anna V
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Palmqvist, Kristin
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Wennergren, Uno
    Linköpings universitet, Institutionen för Fysik, Kemi och Biologi.
    Predicting local responses of epiphytic lichen vegetation to regional climate change scenariosManuscript (Other academic)
    Abstract [en]

    In northern Europe, projected climate change indicates annual warming and increased precipitation, especially during winter. The aim of this study was to assess potential responses to this of poikilohydric and epiphytic lichens that are closely coupled to the local atmospheric conditions, and consequently to climate change. Two scenarios, one moderate and another more intense emission scenario (SRES B2 and A2, respectively) for northern Europe, was used to assess regional climate changes. Both scenarios used the combination of projected changes in temperature (T), humidity (RH) and irradiance (I) towards the end of the 21st century. To generate local climate changes we used microclimate time series from 1993-94 of two contrasting habitats, an interior and an open site, and transformed them by superimposing the regional scenarios. We developed a physiological net carbon gain (NCG) model for Platismatia glauca on the responses of photosynthesis and respiration in relation to I, T and water content (WC), which was simulated by a lichen hydration model using RH and T, and growth. Carbon gain and growth was simulated for reference and the two climate local scenarios during one year, and validated against growth for the reference conditions. The growth response was two times higher at the lighter, exposed site compared to the interior site, in agreement with measured growth. However, the responses to climate change were not uniform locally or seasonally, mainly due to the changed patterns of hydration and whether irradiances were limiting or not during the wet periods. At the darker, interior site of the forest, growth was reduced due to climate change but was in contrast equal or increased at the lighter, exposed site. This was caused by a general increased growth during the more humid spring and a reduced or equal growth response during the drier summer and during the wetter, dark winter. The increasingly favored growth conditions at exposed sites will possibly favor lichens that can manage the potentially adverse effects of increased wind exposure at these sites. At darker sites, the lichens will likely be outcompeted by bryophytes that are better adapted to dark and wet conditions. It is thus likely that the realized niche of lichens will be reduced, with a shift in optimum abundance towards more exposed habitats, or even more reduced for pendulous lichens that are hampered by increased wind at the most exposed sites.

  • 24. Lidén, Marlene
    et al.
    Jonsson Čabrajić, Anna V
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Ottosson-Löfvenius, Mikael
    Palmqvist, Kristin
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Lundmark, Tomas
    Species-specific activation time-lags can explain habitat restrictions in hydrophiclic lichens2010In: Plant, Cell and Environment, ISSN 0140-7791, E-ISSN 1365-3040, Vol. 33, p. 851-862Article in journal (Refereed)
    Abstract [en]

    Photosystem II (PSII) activation after hydration with water or humid air was measured in four hydrophilic and a generalist lichen to test the hypothesis that slow activation might explain habitat restriction in the former group. For the hydrophilic species, activation was after 4 h nearly completed in Lobaria amplissima and Platismatia norvegica, while only c. 50% for Bryoria bicolor and Usnea longissima. The generalist Platismatia glauca was activated instantaneously. The effect of this on lichen field performance was investigated using a dynamic model separating the two water sources rain and humid air. Model simulations were made using the species-specific characteristics and climate data from 12 stream microhabitats. For U. longissima, slow PSII activation could reduce realized photosynthesis by a factor of five. Bryoria bicolor was almost as severely affected, while P. norvegica displayed moderate reductions. Lobaria amplissima displayed longer realized activity periods even in unfavourable microclimates, possibly because of a higher water loss resistance. Both close proximity to streams and presence of turbulent water had a positive impact on realized activity among the slowly activated species, coinciding with observed distribution patterns of hydrophilic species. The results presented here may thus partly explain observed habitat restrictions of rare hydrophilic lichens.

  • 25. Maaroufi, Nadia I
    et al.
    Nordin, Annika
    Hasselquist, Niles J
    Bach, Lisbet H
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Palmqvist, Kristin
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Gundale, Michael J
    Anthropogenic nitrogen deposition enhances carbon sequestration in boreal soils2015In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 21, no 8, p. 3169-3180Article in journal (Refereed)
    Abstract [en]

    It is proposed that carbon (C) sequestration in response to reactive nitrogen (N-r) deposition in boreal forests accounts for a large portion of the terrestrial sink for anthropogenic CO2 emissions. While studies have helped clarify the magnitude by which N-r deposition enhances C sequestration by forest vegetation, there remains a paucity of long-term experimental studies evaluating how soil C pools respond. We conducted a long-term experiment, maintained since 1996, consisting of three N addition levels (0, 12.5, and 50kgNha(-1)yr(-1)) in the boreal zone of northern Sweden to understand how atmospheric N-r deposition affects soil C accumulation, soil microbial communities, and soil respiration. We hypothesized that soil C sequestration will increase, and soil microbial biomass and soil respiration will decrease, with disproportionately large changes expected compared to low levels of N addition. Our data showed that the low N addition treatment caused a non-significant increase in the organic horizon C pool of similar to 15% and a significant increase of similar to 30% in response to the high N treatment relative to the control. The relationship between C sequestration and N addition in the organic horizon was linear, with a slope of 10kgCkg(-1)N. We also found a concomitant decrease in total microbial and fungal biomasses and a similar to 11% reduction in soil respiration in response to the high N treatment. Our data complement previous data from the same study system describing aboveground C sequestration, indicating a total ecosystem sequestration rate of 26kgCkg(-1)N. These estimates are far lower than suggested by some previous modeling studies, and thus will help improve and validate current modeling efforts aimed at separating the effect of multiple global change factors on the C balance of the boreal region.

  • 26. Maaroufi, Nadia I.
    et al.
    Nordin, Annika
    Palmqvist, Kristin
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Gundale, Michael J.
    Chronic Nitrogen Deposition Has a Minor Effect on the Quantity and Quality of Aboveground Litter in a Boreal Forest2016In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 11, no 8, article id e0162086Article in journal (Refereed)
    Abstract [en]

    There is evidence that anthropogenic nitrogen (N) deposition enhances carbon (C) sequestration in boreal soils. However, key underlying mechanisms explaining this increase have not been resolved. Two potentially important mechanisms are that aboveground litter production increases, or that litter quality changes in response to N enrichment. As such, our aim was to quantify whether simulated chronic N deposition caused changes in aboveground litter production or quality in a boreal forest. We conducted a long-term (17 years) stand-scale (0.1 ha) forest experiment, consisting of three N addition levels (0, 12.5, and 50 kg N ha(-1) yr(-1)) in northern Sweden, where background N deposition rates are very low. We measured the annual quantity of litter produced for 8 different litter categories, as well as their concentrations of C, N, phosphorus (P), lignin, cellulose and hemi-cellulose. Our results indicate that mosses were the only major litter component showing significant quantitative and qualitative alterations in response to the N additions, indicative of their ability to intercept a substantial portion of the N added. These effects were, however, offset by the other litter fractions where we found no changes in the total litter fluxes, or individual chemical constituents when all litter categories were summed. This study indicates that the current annual litter fluxes cannot explain the increase in soil C that has occurred in our study system in response to simulated chronic N application. These results suggest that other mechanisms are likely to explain the increased soil C accumulation rate we have observed, such as changes in soil microbial activity, or potentially transient changes in aboveground litter inputs that were no longer present at the time of our study.

  • 27. Maaroufi, Nadia I.
    et al.
    Nordin, Annika
    Palmqvist, Kristin
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Gundale, Michael J.
    Nitrogen enrichment impacts on boreal litter decomposition are driven by changes in soil microbiota rather than litter quality2017In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 7, article id 4083Article in journal (Refereed)
    Abstract [en]

    In nitrogen (N) limited boreal forests, N enrichment can impact litter decomposition by affecting litter quality and by changing the soil environment where litter decomposes. We investigated the importance of litter quality and soil factors on litter decomposition using a 2-year reciprocal transplant experiment for Picea abies needle litter, derived from plots subjected to 17 years of N addition, including control, low and high N treatments (ambient, 12.5 and 50 kg N ha(-1) yr(-1), respectively). Our data show that changes in soil factors were the main pathway through which N impacted litter decomposition, with rates reduced by approximate to 15% when placed in high N relative to control plots, regardless of litter origin. Litter decomposition was correlated to soil microbiota, with Picea abies litter decomposition positively correlated with gram negative and fungal functional groups. Our results suggest that previous findings of increase soil C accumulation in response to N deposition is likely to occur as a result of changes in soil microbiota rather than altered litter quality.

  • 28. Maaroufi, Nadia, I
    et al.
    Nordin, Annika
    Palmqvist, Kristin
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Hasselquist, Niles J.
    Forsmark, Benjamin
    Rosenstock, Nicholas P.
    Wallander, Hakan
    Gundale, Michael J.
    Anthropogenic nitrogen enrichment enhances soil carbon accumulation by impacting saprotrophs rather than ectomycorrhizal fungal activity2019In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, article id NBORG T, 1990, VEGETATIO, V90, P1 rg Bjorn, 1997, Environmental Reviews, V5, P1 ndahl Bjorn D., 2007, NEW PHYTOLOGIST, V173, P611 erer Noah, 2012, ISME JOURNAL, V6, P1007 sanen J., 2013, vegan: Community Ecology Package. R Package Version 2. 0-10, ndahl Bjorn D., 2010, ISME JOURNAL, V4, P872 ide Roger T., 2014, NEW PHYTOLOGIST, V201, P433Article in journal (Refereed)
    Abstract [en]

    There is evidence that anthropogenic nitrogen (N) deposition enhances carbon (C) sequestration in boreal forest soils. However, it is unclear how free-living saprotrophs (bacteria and fungi, SAP) and ectomycorrhizal (EM) fungi responses to N addition impact soil C dynamics. Our aim was to investigate how SAP and EM communities are impacted by N enrichment and to estimate whether these changes influence decay of litter and humus. We conducted a long-term experiment in northern Sweden, maintained since 2004, consisting of ambient, low N additions (0, 3, 6, and 12 kg N ha(-1) year(-1)) simulating current N deposition rates in the boreal region, as well as a high N addition (50 kg N ha(-1) year(-1)). Our data showed that long-term N enrichment impeded mass loss of litter, but not of humus, and only in response to the highest N addition treatment. Furthermore, our data showed that EM fungi reduced the mass of N and P in both substrates during the incubation period compared to when only SAP organisms were present. Low N additions had no effect on microbial community structure, while the high N addition decreased fungal and bacterial biomasses and altered EM fungi and SAP community composition. Actinomycetes were the only bacterial SAP to show increased biomass in response to the highest N addition. These results provide a mechanistic understanding of how anthropogenic N enrichment can influence soil C accumulation rates and suggest that current N deposition rates in the boreal region (<= 12 kg N ha(-1) year(-1)) are likely to have a minor impact on the soil microbial community and the decomposition of humus and litter.

  • 29. Maaroufi, Nadia, I
    et al.
    Palmqvist, Kristin
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Bach, Lisbet H.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Bokhorst, Stef
    Liess, Antonia
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Rydberg Laboratory of Applied Science, School of Business, Science and Engineering, Halmstad University, Halmstad, Sweden.
    Gundale, Michael J.
    Kardol, Paul
    Nordin, Annika
    Meunier, Cedric L.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Alfred-Wegener-Institut, Helmholtz-Zentrum für Polar- und Meeresforschung (AWI), Biologische Anstalt Helgoland, Helgoland, Germany.
    Nutrient optimization of tree growth alters structure and function of boreal soil food webs2018In: Forest Ecology and Management, ISSN 0378-1127, E-ISSN 1872-7042, Vol. 428, p. 46-56Article in journal (Refereed)
    Abstract [en]

    Nutrient optimization has been proposed as a way to increase boreal forest production, and involves chronic additions of liquid fertilizer with amounts of micro- and macro-nutrients adjusted annually to match tree nutritional requirements. We used a short-term (maintained since 2007) and a long-term (maintained since 1987) fertilization experiment in northern Sweden, in order to understand nutrient optimization effects on soil microbiota and mesofauna, and to explore the relationships between plant litter and microbial elemental stoichiometry. Soil microbes, soil fauna, and aboveground litter were collected from the control plots, and short- and long-term nutrient optimization plots. Correlation analyses revealed no relationships between microbial biomass and litter nutrient ratios. Litter C:N, C:P and N:P ratios declined in response to both optimization treatments; while only microbial C:P ratios declined in response to long-term nutrient optimization. Further, we found that both short- and long-term optimization treatments decreased total microbial, fungal, and bacterial PLFA biomass and shifted the microbial community structure towards a lower fungi:bacterial ratio. In contrast, abundances of most fungal- and bacterial-feeding soil biota were little affected by the nutrient optimization treatments. However, abundance of hemi-edaphic Collembola declined in response to the long-term nutrient optimization treatment. The relative abundances (%) of fungal-feeding and plant-feeding nematodes, respectively, declined and increased in response to both short-term and long-term treatments; bacterial-feeding nematodes increased relative to fungal feeders. Overall, our results demonstrate that long-term nutrient optimization aiming to increase forest production decreases litter C:N, C:P and N:P ratios, microbial C:P ratios and fungal biomass, whereas higher trophic levels are less affected.

  • 30. Nybakken, Line
    et al.
    Johansson, Otilia
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Palmqvist, Kristin
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Defensive compound concentration in boreal lichens in response to simulated nitrogen deposition2009In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 15, no 9, p. 2247-2260Article in journal (Refereed)
    Abstract [en]

    Nitrogen (N) deposition is expected to increase in northwestern Europe the next 50–100 years. The effects of higher N availability on lichens will presumably depend on their capacity to acquire carbon (C), that is, of the timing and duration of the wet and active state. If lichens respond like plants, their C and N status may affect their concentration of carbon-based secondary compounds (CBSCs), and thus their defence against herbivores, detrimental radiation, pathogens and parasites. In the present study we have manipulated N availability and timing and duration of the metabolically active state by spraying lichen transplants in an old spruce forest with rainwater or rainwater with added N corresponding to 50 kg N ha−1 yr−1. The spraying was applied either at night, in the morning or at noon to also investigate the effect of timing and duration of the active state. Concentrations of N, chlorophyll a (Chl a) and CBSCs were measured before and after one summer's spraying of 10 thalli in each of four different lichen species; Alectoria sarmentosa, Lobaria scrobiculata, Platismatia glauca, and Xanthoria aureola. The added N was readily taken up by all the lichen species. A. sarmentosa, P. glauca, and X. aureola increased their Chl a concentration in response to increased N, while L. scrobiculata increased Chl a in response to increased active time. None of the studied species reduced their concentration of secondary compounds during the experimental period, but in P. glauca the concentration of all compounds were significantly lower in N-treated thalli compared with those that got only rainwater. The results are consistent with a high degree of constitutive defence in three of four species, and we conclude that all the investigated lichens seem to have rather robust chemical defence systems despite considerable manipulation of the environmental conditions.

  • 31.
    Palmqvist, K
    et al.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Dahlman, L
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Responses of the green algal foliose lichen Platismatia glauca to increased nitrogen supply2006In: New Phytologist, Vol. 171, p. 343-356Article in journal (Refereed)
  • 32.
    Palmqvist, K
    et al.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Dahlman, L
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Valladares, F
    Tehler, A
    Sanches, LG
    Mattsson, J-E
    CO2 exchange and thallus nitrogen across 75 contrasting lichen associations from different climate zones.2002In: Oecologia, ISSN 0029-8549, Vol. 133, p. 295-306Article in journal (Refereed)
  • 33.
    Palmqvist, Kristin
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Dahlman, Lena
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jonsson, Anna
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Nash, T.H.
    The carbon economy of lichens2008In: Lichen Biology, 2nd edition / [ed] Thomas H. Nash, Cambridge: Cambridge University Press, 2008, 2, p. 182-215Chapter in book (Other academic)
  • 34.
    Palmqvist, Kristin
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Franklin, Oskar
    Nasholm, Torgny
    Symbiosis constraints: Strong mycobiont control limits nutrient response in lichens2017In: Ecology and Evolution, ISSN 2045-7758, E-ISSN 2045-7758, Vol. 7, no 18, p. 7420-7433Article in journal (Refereed)
    Abstract [en]

    Symbioses such as lichens are potentially threatened by drastic environmental changes. We used the lichen Peltigera aphthosaa symbiosis between a fungus (mycobiont), a green alga (Coccomyxa sp.), and N-2-fixing cyanobacteria (Nostoc sp.)as a model organism to assess the effects of environmental perturbations in nitrogen (N) or phosphorus (P). Growth, carbon (C) and N stable isotopes, CNP concentrations, and specific markers were analyzed in whole thalli and the partners after 4months of daily nutrient additions in the field. Thallus N was 40% higher in N-fertilized thalli, amino acid concentrations were twice as high, while fungal chitin but not ergosterol was lower. Nitrogen also resulted in a thicker algal layer and density, and a higher C-13 abundance in all three partners. Photosynthesis was not affected by either N or P. Thallus growth increased with light dose independent of fertilization regime. We conclude that faster algal growth compared to fungal lead to increased competition for light and CO2 among the Coccomyxa cells, and for C between alga and fungus, resulting in neither photosynthesis nor thallus growth responded to N fertilization. This suggests that the symbiotic lifestyle of lichens may prevent them from utilizing nutrient abundance to increase C assimilation and growth.

  • 35. Palmroth, Sari
    et al.
    Holm Bach, Lisbet
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Nordin, Annika
    Palmqvist, Kristin
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Nitrogen-addition effects on leaf traits and photosynthetic carbon gain of boreal forest understory shrubs2014In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 175, no 2, p. 457-470Article in journal (Refereed)
    Abstract [en]

    Boreal coniferous forests are characterized by fairly open canopies where understory vegetation is an important component of ecosystem C and N cycling. We used an ecophysiological approach to study the effects of N additions on uptake and partitioning of C and N in two dominant understory shrubs: deciduous Vaccinium myrtillus in a Picea abies stand and evergreen Vaccinium vitis-idaea in a Pinus sylvestris stand in northern Sweden. N was added to these stands for 16 and 8 years, respectively, at rates of 0, 12.5, and 50 kg N ha(-1) year(-1). N addition at the highest rate increased foliar N and chlorophyll concentrations in both understory species. Canopy cover of P. abies also increased, decreasing light availability and leaf mass per area of V. myrtillus. Among leaves of either shrub, foliar N content did not explain variation in light-saturated CO2 exchange rates. Instead photosynthetic capacity varied with stomatal conductance possibly reflecting plant hydraulic properties and within-site variation in water availability. Moreover, likely due to increased shading under P. abies and due to water limitations in the sandy soil under P. sylvestris, individuals of the two shrubs did not increase their biomass or shift their allocation between above- and belowground parts in response to N additions. Altogether, our results indicate that the understory shrubs in these systems show little response to N additions in terms of photosynthetic physiology or growth and that changes in their performance are mostly associated with responses of the tree canopy.

1 - 35 of 35
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