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Modeling lichen performance in relation to climate: scaling from thalli to landscapes
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
2009 (English)Doctoral thesis, comprehensive summary (Other academic)Alternative title
Modellering av lavars responser i förhållande till klimat : i skalan från bål till landskap (Swedish)
Abstract [en]

Lichens can colonize nearly all terrestrial habitats on earth and are functionally important in many ecosystems. Being poikilohydric, their active growth periods are restricted to periods when the thallus is hydrated from atmospheric water sources, such as rain, fog and high relative humidity. Since lichen hydration varies greatly over time lichen growth is therefore more difficult to model compared with, for example vascular plants with more even water supply.

I developed two models to predict lichen hydration under field conditions that incorporates the atmospheric water potential (Ψair), derived from air temperature and humidity, only or in combination with species-specific rehydration and desiccation rates. Using Ψair allows the prediction of hydration induced by several water sources. These models were very accurate for epiphytic lichens with a close coupling to atmospheric conditions, but they were less accurate for mat-forming lichens with substantial aerodynamic boundary layers. The hydration model was further developed to include photosynthetic activation for different species, in order to compare their performance under different micro-climatic scenarios. Water balance and activation rate had large effects on lichen activity and were positively related to habitats providing long hydration periods, for example close to streams. To study effects of climate change, a complete model for net carbon gain (photosynthesis minus respiratory losses) was developed for an epiphytic lichen with intricate responses to light, hydration and temperature. Simulation responses in different climate scenarios revealed that projected climate change on a regional scale resulted in varied local scale responses. At the lighter, exposed sites of a forest, the growth responses were positive, but were potentially negative at darker sites with closed canopy.

At the local scale, fluctuating hydration, summed irradiance when wet and Chlorophyll a are variables that predict lichen growth. However, at a landscape scale, these variables may be too detailed. We tested this for two terrestrial, mat-forming lichens and developed statistical models for lichen growth in the widest possible climatic gradient in northern Scandinavia, varying in light, temperature and precipitation. Light was the most important factor for high growth at the landscape scale, reaching saturation at a site openness of 40 %, equivalent to a basal tree area of 15 m2 ha -1 in this study. Thereafter, hydration was the next limiting factor, which could be well described by precipitation for one of the species. The simplest predictor was the normal temperature in July, which was negatively correlated with growth.

It was apparent that the predictive variables and their power varied at different scales. However, light and hydration are limiting at all scales, particularly by light conditions when lichens are wet. This implies that ensuring that there is sufficient light below the forest canopy is crucial for lichen growth, especially for mat-forming lichens. Hydrophilic lichens may be better preserved in open habitats with long hydration periods. It was shown that models can be powerful and “easy to use” tools to predict lichen responses in various habitats and under different climate scenarios. Models can therefore help to identify suitable habitats with optimal growth conditions, which is very important for the conservation and management of lichens and their habitats.

Abstract [sv]

 Lavar kan kolonisera nästan alla terrestriska habitat i världen och är funktionellt viktiga i många ekosystem. Eftersom lavar är poikilohydriska (växelblöta), är deras aktiva tillväxtperioder begränsade till den tid då bålen är blöt från atmosfäriska vattenkällor, såsom regn, dimma och hög relativ fuktighet. Eftersom lavars vatteninnehåll varierar stort över tid är lavars tillväxt svårare att modellera jämfört med till exempel kärlväxter, med en mer jämn vattentillgång.

Jag har utvecklat två fuktmodeller som förutsäger lavars vatteninnehåll i fält. Modellerna använder den atmosfäriska vattenpotentialen (Ψair), som erhålls från lufttemperatur och -fuktighet, antingen enbart eller i kombination med de artspecifika uppblötnings - och uttorkningshastigheterna. Genom att använda (Ψair) kan man förutsäga lavars vatteninnehåll från flera vattenkällor. Dessa modeller var mycket precisa för epifytiska lavar med en nära koppling till de atmosfäriska förhållandena, men fungerade mindre väl för mattlevande lavar med ett betydande gränsskikt. Fuktmodellen utvecklades ytterligare för att inkludera även fotosyntetisk aktivering av olika lavar, för att kunna jämföra deras aktivitet i olika mikroklimatiska scenarior. Vattenbalans och aktiveringshastighet hade stor effekt på på lavars aktivitet och var positivt relaterad till habitat med tillräckligt långa fuktperioder, till exempel habitat nära strömmande vatten. För att studera klimateffekter på lavar, utvecklade jag en total modell för nettoförvärv av kol (fotosyntes minus respiration) för en epifytisk lav med dess intrikata förhållande mellan ljus, fukt och temperatur. Simuleringar av modellen visade att lavens responser i förhållande till regionala klimatförändringar var kontrasterande på lokal nivå. Vid ljusa, öppna lokaler i skogen ökade tillväxten medan de potentiellt minskade vid mörka lokaler med ett mer slutet krontäcke.

På den lokala skalan kan fluktuerande vatteninnehåll, summerat ljus när laven är blöt, och klorofyll a- innehåll förutsäga lavars tillväxt. Men, på en landskapsskala kan dessa variabler vara för detaljerade. Vi testade detta för två terrestriska, mattlevande lavar och utvecklade en statistisk modell för lavars tillväxt i en så stor klimatgradient som möjligt i norra Skandinavien genom att variera ljus, temperatur och nederbörd. Ljus var den viktigaste faktorn för att nå hög tillväxt på landskapsnivå där en mättnad nåddes vid 40 % öppenhet i skogen, som motsvarade en grundyta på 15 m2 ha -1 i den här studien. Fuktigheten var den näst viktigaste begränsande faktorn och kunde beskrivas väl med nederbörd för en av arterna. Den mest lättanvända faktorn var normaltemperaturen för juli månad, som i sin tur var negativt korrelerad till tillväxt.

Det var tydligt att de prediktiva variablerna och deras förutsägande förmåga varierade med olika skalor. Ljus och fukt var begränsande på alla nivåer, speciellt av ljusförhållandena då lavarna är blöta. Detta innebär att tillräckligt höga ljusnivåer under krontäcket är avgörande för lavars tillväxt, speciellt mattlevande lavar. Hydrofila lavar torde bevaras bättre i öppna habitat med tillräckligt långa fuktperioder. Det var tydligt att modeller kan vara betydelsefulla och lättanvända verktyg för att förutsäga lavars responser i en bredd av habitat med olika mikroklimat. Modeller kan därför vara en hjälp för att identifiera lämpliga habitat med optimala tillväxtförhållanden och detta är viktigt för att bevara och sköta lavar och deras habitat.

Place, publisher, year, edition, pages
Umeå: Umeå universitet , 2009. , 38 p.
Keyword [en]
Lichen, growth, model, micro-climate, hydration, activation, photosynthesis, respiration
National Category
Ecology
Research subject
Ecological Botany
Identifiers
URN: urn:nbn:se:umu:diva-22526ISBN: 978-91-7264-744-2 (print)OAI: oai:DiVA.org:umu-22526DiVA: diva2:216855
Distributor:
Institutionen för ekologi, miljö och geovetenskap, 901 87, Umeå
Public defence
2009-06-04, Stora Hörsalen, KB3B1, KBC, Umeå universitet, Umeå, 10:00 (English)
Opponent
Supervisors
Available from: 2009-05-14 Created: 2009-05-12 Last updated: 2012-02-02Bibliographically approved
List of papers
1. Predicting lichen hydration using biophysical models.
Open this publication in new window or tab >>Predicting lichen hydration using biophysical models.
2008 (English)In: Oecologia, ISSN 0029-8549, Vol. 156, no 2, 259-73 p.Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Springer, 2008
Keyword
Biophysical Phenomena, Biophysics, Climate, Computer Simulation, Lichens/chemistry/*physiology, Models; Biological, Species Specificity, Sweden, Water/*analysis, Water Loss; Insensible/physiology
Identifiers
urn:nbn:se:umu:diva-11450 (URN)doi:10.1007/s00442-008-0990-5 (DOI)18305964 (PubMedID)
Available from: 2009-01-08 Created: 2009-01-08Bibliographically approved
2. 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 lichens
Open this publication in new window or tab >>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 lichens
Show others...
2010 (English)In: Plant, Cell and Environment, ISSN 0140-7791, E-ISSN 1365-3040, Vol. 33, 840-850 p.Article in journal (Refereed) Published
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.

Keyword
Bryoria bicolor, Lobaria amplissima, Platismatia glauca, Platismatia norvegica, Usnea longissima, habitat restrictions, photosynthetic activity, simulation, thallus water content, water potential
Identifiers
urn:nbn:se:umu:diva-32953 (URN)10.1111/j.1365-3040.2009.02110.x (DOI)000276618100014 ()
Available from: 2010-03-31 Created: 2010-03-31 Last updated: 2010-04-06Bibliographically approved
3. Species-specific activation time-lags can explain habitat restrictions in hydrophiclic lichens
Open this publication in new window or tab >>Species-specific activation time-lags can explain habitat restrictions in hydrophiclic lichens
Show others...
2010 (English)In: Plant, Cell and Environment, ISSN 0140-7791, E-ISSN 1365-3040, Vol. 33, 851-862 p.Article in journal (Refereed) Published
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.

Keyword
Bryoria bicolor, Lobaria amplissima, Platismatia glauca, Platismatia norvegica, Usnea longissima, hydrophilic epiphytic lichens, photosynthesis, photosystem II activation, suboceanic distributional patterns, water relations
Identifiers
urn:nbn:se:umu:diva-32954 (URN)10.1111/j.1365-3040.2009.02111.x (DOI)000276618100015 ()
Available from: 2010-03-31 Created: 2010-03-31 Last updated: 2012-02-02Bibliographically approved
4. Predicting local responses of epiphytic lichen vegetation to regional climate change scenarios
Open this publication in new window or tab >>Predicting local responses of epiphytic lichen vegetation to regional climate change scenarios
(English)Manuscript (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.

Keyword
epiphytic lichen, Platismatia glauca, climate change scenarios, net carbon gain model, simulation, respiration, photosynthesis, growth
National Category
Ecology
Research subject
Ecological Botany
Identifiers
urn:nbn:se:umu:diva-22542 (URN)
Available from: 2009-05-12 Created: 2009-05-12 Last updated: 2012-02-02Bibliographically approved
5. Predicting growth of mat-forming lichens on a landscape scale: comparing models with different complexities
Open this publication in new window or tab >>Predicting growth of mat-forming lichens on a landscape scale: comparing models with different complexities
2010 (English)In: Ecography, ISSN 0906-7590, E-ISSN 1600-0587, Vol. 33, no 5, 949-960 p.Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Wiley, 2010
Keyword
Arctic ecosystem, Boreal forest, Cetraria islandica, Chlorophyll, Cladina stellaris, Forest canopy, Irradiance, Landscape scale, Micro-climate, Water content
National Category
Ecology
Research subject
Ecological Botany
Identifiers
urn:nbn:se:umu:diva-22540 (URN)10.1111/j.1600-0587.2009.06079.x (DOI)000283690900015 ()
Available from: 2009-05-12 Created: 2009-05-12 Last updated: 2011-10-28Bibliographically approved

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