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  • 1. Balogianni, Vasiliki G.
    et al.
    Blume-Werry, Gesche
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Wilson, Scott D.
    Root production in contrasting ecosystems: the impact of rhizotron sampling frequency2016Ingår i: Plant Ecology, ISSN 1385-0237, E-ISSN 1573-5052, Vol. 217, nr 11, s. 1359-1367Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Despite their critical role in every terrestrial ecosystem, fine root production and mortality have not been widely compared among systems due to the practical difficulties of belowground research. We examined fine root production and mortality among five contrasting sites: native and invaded grassland in eastern Montana, USA, aspen forest in southern Saskatchewan, Canada, and birch forest and tundra in northern Sweden. Additionally, we investigated the importance of minirhizotron sampling interval on measures of root production and mortality by comparing measures produced from 1-, 7-, 14-, and 21-day sample intervals. Root length and mortality varied significantly among sites, with invaded grassland having the greatest root length (> 2 x than any other site) and significantly greater root mortality than native grassland (54 %). In contrast, there were no significant differences in root production among the sites. Sample interval had no significant influence on root production or mortality. Minirhizotron sampling intervals up to 3 weeks did not underestimate the measures of root production and mortality in comparison to measures derived from shorter sampling intervals, regardless of the site studied. The results suggest that 3 weeks can be an accurate and efficient sample interval when studying root production and mortality with minirhizotrons.

  • 2.
    Dietrich, Anna L.
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Nilsson, Christer
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Jansson, Roland
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Restoration effects on germination and survival of plants in the riparian zone: a phytometer study2015Ingår i: Plant Ecology, ISSN 1385-0237, E-ISSN 1573-5052, Vol. 216, nr 3, s. 465-477Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Many streams that were channelized to facilitate timber floating in northern Sweden, have in recent years been restored by returning coarse sediment (cobbles and boulders) to the channel and reconnecting riparian with instream habitats. We asked if such restoration measures affect germination and survival of plants in the riparian zone, and if such potential effects depend on location in the catchment. We used a paired site approach, comparing the performance of Helianthus annuus (sunflower) phytometers (seeds and seedlings) in the riparian zone in channelized versus restored river reaches along climate and stream size gradients in the Vindel River catchment in northern Sweden. Phytometer survival, substrate availability, and soil nutrient content in large streams were enhanced by restoration, but overall, phytometer performance was negatively related to the length of the growing season, i.e. phytometers grew best at high altitudes and short growing seasons. This result may have been caused by less competition from the shorter and sparser neighbouring vegetation at these sites or to more frequent flooding events, enhancing retention of organic matter. Soil nutrient levels were lowest close to the coast and in large streams, probably due to deposition of mineral sediment. The higher availability of riparian habitat at restored than at channelized sites suggests that plant species richness and abundance may potentially increase after restoration. Seedling transplantation seems to be a preferable revegetation measure, because phytometer seedlings established better than seeds and survival was significantly higher at restored sites. The good plant performance at sites with short growing seasons and high altitudes suggests that, with limited resources, restoration measures should first be located to such sites.

  • 3.
    Graae, Bente J.
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Alsos, I.G.
    Ejrnaes, R.
    The impact of temperature regimes on development, dormancy breaking and germination of dwarf shrub seeds from arctic, alpine and boreal sites.2008Ingår i: Plant Ecology, ISSN 1385-0237, E-ISSN 1573-5052, Vol. 198, s. 275-284Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    It has been suggested that the infrequent sexual reproduction of arctic dwarf shrubs might be related to the harsh environmental conditions in which they live. If this is the case, then increases in temperature resulting from global climate change might drastically affect regeneration of arctic species. We examined whether recruitment of Empetrum nigrum ssp. hermaphroditum and Vaccinium uliginosum (hereafter E. nigrum and V. uliginosum) was affected by temperature during three reproductive stages: seed development, dormancy breakage and germination. Seeds were collected from an arctic, an alpine (only E. nigrum) and a boreal site with different climates; stored at different winter temperatures and incubated for germination at different temperatures. Seeds of V. uliginosum developed in the boreal region had a higher percentage germination than did seeds developed in the Arctic. In contrast, seeds of E. nigrum from the arctic site had a higher or similar percentage germination than did seeds from the alpine and boreal sites. Increased winter temperatures had no significant effect on resulting germination percentage of E. nigrum. However, V. uliginosum seeds from the arctic site suffered increased fungal attack (and thus decreased germination) when they were stratified under high winter temperatures. Seeds of both species increased germination with increased incubation temperatures. Our results suggest that both species would increase their germination in response to warmer summers. Longer summers might also favour the slow-germinating E. nigrum. However, increased winter temperatures might increase mortality due to fungal attack in V. uliginosum ecotypes that are not adapted to mild winters.

  • 4. Gundale, Michael J.
    et al.
    Sverker, Jennie
    Albrectsen, Benedicte R.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysiologisk botanik. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Umeå Plant Science Centre (UPSC).
    Nilsson, Marie-Charlotte
    Wardle, David A.
    Variation in protein complexation capacity among and within six plant species across a boreal forest chronosequence2010Ingår i: Plant Ecology, ISSN 1385-0237, E-ISSN 1573-5052, Vol. 211, nr 2, s. 253-266Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We investigated among and within species variation in several litter chemical properties, including protein complexation capacity (PCC), for six plant species across a boreal forest chronosequence in northern Sweden across which stand fertility declines sharply with stand age. We hypothesized (1) that evergreen species which dominate in late-successional stands would exhibit higher PCCs than deciduous species that dominate in young stands, (2) that individual species would increase their PCCs in response to nutrient limitation as succession proceeds, and (3) that differences in PCC among litter types would determine their interactive effects with proteins on soil N and C mineralization. The data demonstrated a high PCC, but a low PCC per unit of soluble phenol, for two deciduous species that dominate in early-successional high fertility stands, providing mixed support for our first hypothesis. No species demonstrated a significant correlation between their PCC and stand age, which did not support our second hypothesis. Finally, a soil incubation assay revealed that litter extracts for three of the six species had negative interactive effects with added proteins on N mineralization rates, and that all six species demonstrated positive interactive effects with protein on C mineralization. This pattern did not provide strong support for our third hypothesis, and suggests that N immobilization was likely a more important factor regulating N mineralization than stabilization of proteins into tannin complexes. These data suggest that multiple interactive mechanisms between litter extracts and proteins likely occur simultaneously to influence the availability of N in soils.

  • 5. Hughes, Francine MR
    et al.
    Johansson, Mats
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Xiong, Shaojun
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Carlborg, Elisabet
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Hawkins, Dawn
    Svedmark, Magnus
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Hayes, Adrian
    Goodall, Alexander
    Richards, Keith S
    Nilsson, Christer
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    The influence of hydrological regimes on sex ratios and spatial segregation of the sexes in two dioecious riparian shrub species in northern Sweden2010Ingår i: Plant Ecology, ISSN 1385-0237, E-ISSN 1573-5052, Vol. 208, nr 1, s. 77-92Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    River management practices have altered the hydrological regimes of many rivers and also altered the availability of regeneration niches for riparian species. We investigated the impact of changed hydrological regimes on the sex ratios and the Spatial Segregation of the Sexes (SSS) in the dioecious species Salix myrsinifolia Salisb.–phylicifolia L. and S. lapponum L. by studying the free-flowing Vindel River and the regulated Ume River in northern Sweden. We surveyed sex ratios of these species in 12 river reaches on the Vindel River and in 17 reaches on the Ume River. In addition, we surveyed the sex and location above mean river stage of 1,002 individuals across both river systems to investigate the SSS of both species. Cuttings were collected from male and female individuals of S. myrsinifolia–phylicifolia from both rivers and subjected to four different water table regimes in a greenhouse experiment to investigate growth response between the sexes. We found an M/F sex ratio in both river systems similar to the regional norm of 0.62 for S.myrsinifolia–phylicifolia and of 0.42 for S. lapponum. We found no evidence of SSS in either the free-flowing Vindel River or the regulated Ume River. In the greenhouse experiment, hydrological regime had a significant effect on shoot and root dry weight and on root length. Significantly higher shoot dry weights were found in females than in males and significantly different shoot and root dry weights were found between cuttings taken from the two rivers. We concluded that changed hydrological regimes are likely to alter dimensions of the regeneration niche and therefore to influence sex ratios and SSS at an early successional stage, making it difficult to find clear spatial patterns once these species reach maturity and can be sexed.

  • 6. Lemke, Isgard H.
    et al.
    Kolb, Annette
    Graae, Bente J.
    De Frenne, Pieter
    Acharya, Kamal P.
    Blandino, Cristina
    Brunet, Jorg
    Chabrerie, Olivier
    Cousins, Sara A. O.
    Decocq, Guillaume
    Heinken, Thilo
    Hermy, Martin
    Liira, Jaan
    Schmucki, Reto
    Shevtsova, Anna
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Verheyen, Kris
    Diekmann, Martin
    Patterns of phenotypic trait variation in two temperate forest herbs along a broad climatic gradient2015Ingår i: Plant Ecology, ISSN 1385-0237, E-ISSN 1573-5052, Vol. 216, nr 11, s. 1523-1536Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Phenotypic trait variation plays a major role in the response of plants to global environmental change, particularly in species with low migration capabilities and recruitment success. However, little is known about the variation of functional traits within populations and about differences in this variation on larger spatial scales. In a first approach, we therefore related trait expression to climate and local environmental conditions, studying two temperate forest herbs, Milium effusum and Stachys sylvatica, along a similar to 1800-2500 km latitudinal gradient. Within each of 9-10 regions in six European countries, we collected data from six populations of each species and recorded several variables in each region (temperature, precipitation) and population (light availability, soil parameters). For each plant, we measured height, leaf area, specific leaf area, seed mass and the number of seeds and examined environmental effects on within-population trait variation as well as on trait means. Most importantly, trait variation differed both between and within populations. Species, however, differed in their response. Intrapopulation variation in Milium was consistently positively affected by higher mean temperatures and precipitation as well as by more fertile local soil conditions, suggesting that more productive conditions may select for larger phenotypic variation. In Stachys, particularly light availability positively influenced trait variation, whereas local soil conditions had no consistent effects. Generally, our study emphasises that intra-population variation may differ considerably across larger scales-due to phenotypic plasticity and/or underlying genetic diversity-possibly affecting species response to global environmental change.

  • 7. Manzaneda , AJ
    et al.
    Sperens, Ulf
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi, miljö och geovetenskap.
    Garcia , MB
    Effects of microsite disturbances and herbivory on seedling performance in the perennial herb Helleborus foetidus (Ranunculaceae)2005Ingår i: Plant Ecology, ISSN 1385-0237, E-ISSN 1573-5052, Vol. 179, nr 1, s. 73-82Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The impact of small scale disturbances on the early seedling performance components of Helleborus foetidus (Ranunculaceae) was studied through a transplant experiment. The aims of this study were: (i) to determine if the herbivory pattern depends on microsite disturbance, by the analysis of two of its components, seedling encounter (the probability of at least one seedling being harmed) and seedling exploitation (the proportion of seedling tissue removed once encountered); (ii) to test if seedlings of H. foetidus in disturbed microsites will survive in a greater proportion than seedlings in undisturbed microsites; (iii) to investigate if seedling survival is correlated with the degree of herbivory. Microsite disturbances had a large effect on the herbivory pattern. Seedlings growing in undisturbed vegetation had a 2-fold higher likelihood of being grazed and suffered 1.38-fold higher damage than those growing in disturbed plots. At the end of this experiment, after fourteen months, only 10.4% of the seedlings transplanted were still alive due to seedling desiccation, but no differences on seedling survival were found between disturbed and undisturbed plots. The effect of herbivory and the interactive effect of herbivory and disturbance on seedling survival only reached statistical significance dependent upon site. We concluded that although small scale disturbances had a large impact on herbivory patterns; they had only a minor role in the early seedling survival of H. foetidus. Only locally, small scale disturbances showed an effect on seedling survival through herbivory. Abiotic factors like summer drought and spatial variations determined the early survival of H. foetidus seedlings to a major extent.

  • 8. Sorensen, Pernille
    et al.
    Lett, Signe
    Michelsen, Signe
    Moss-specific changes in nitrogen fixation following two decades of warming, shading, and fertilizer addition2012Ingår i: Plant Ecology, ISSN 1385-0237, E-ISSN 1573-5052, Vol. 213, nr 4, s. 695-706Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Climate warming will induce changes in Arctic ecosystem carbon balance, but besides climate, nitrogen availability is a critical controlling factor of carbon cycling. It is therefore essential to obtain knowledge on the influence of a changing climate on nitrogen fixation, as this process is the main source of new nitrogen to arctic ecosystems. In order to gain information on future nitrogen fixation rates in a changing climate, we studied the effects of two decades of warming with passive greenhouses, shading with sackcloth, and fertilization with NPK fertilizer on nitrogen fixation rates. To expand the knowledge on species-specific responses, we measured nitrogen fixation associated with two moss species: Hylocomium splendens and Aulacomnium turgidum. Our expectations of decreased nitrogen fixation rates in the fertilizer and shading treatments were met. However, contrary to our expectation of increased nitrogen fixation in the warming treatment, we observed either no change (Hylocomium) or a decrease (Aulacomnium) in fixation in the warmed plots. We hypothesize that this could be due to moss-specific responses or to long-term induced effects of the warming. For example, we observed that the soil temperature increase induced by the warming treatment was low and insignificant as vegetation height and total vascular plant cover of the warmed plots increased, and moss cover decreased. Hence, truly long-term studies lasting more than two decades provide insights on changes in key biogeochemical processes, which differ from more transient responses to warming in the Arctic.

  • 9.
    te Beest, Mariska
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Centre for Invasion Biology, Stellenbosch University, South Africa; Department of Conservation Ecology and Entomology, Stellenbosch University, South Africa.
    Esler, Karen J.
    Richardson, David M.
    Linking functional traits to impacts of invasive plant species: a case study2015Ingår i: Plant Ecology, ISSN 1385-0237, E-ISSN 1573-5052, Vol. 216, nr 2, s. 293-305Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Our understanding of the link between plant functional traits and ecological impact of invasive alien plant species is fragmentary and the mechanisms leading to impacts are poorly understood. Moreover, current knowledge is heavily biased to the temperate regions of the world and we know much less about traits and impacts of invaders in tropical and subtropical ecosystems. We studied two leaf traits of the invasive alien shrub Chromolaena odorata and the impacts of its invasion on native vegetation in savannas. We compared specific leaf area (SLA) and leaf area index (LAI) between C. odorata and native species and assessed how C. odorata differentially affects canopy light interception, soil moisture, soil nutrients, and litter accumulation compared to native species. We found that C. odorata has higher SLA and LAI than native species, lower light and moisture levels below its canopy, but higher nutrient levels and a higher litter accumulation rate. Because of its higher SLA, C. odorata grows faster, resulting in more biomass, increased litter accumulation and higher nutrient availability. Due to its high SLA and LAI, C. odorata intercepts more light and reduces available moisture more than do native trees due to higher transpiration rates, reducing the biomass of native understory vegetation. This study provides empirical evidence for strong links between plant functional traits and ecological impact of invasive plant species, highlighting the importance of traits in predicting ecosystem-level impacts of invasive plant species.

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