Poikilohydric Organisms Research Articles

Water relations and photosystem II efficiency of the intertidal macroalga Fucus virsoides

Intertidal macroalgae are sessile poikilohydric organisms exposed to desiccation stress during emersion. Water relations parameters are useful tools to evaluate an organism's capacity to withstand water scarcity conditions, but such information on marine intertidal macroalgae is scarce. We assessed the water relations of the intertidal relict Fucus virsoides, the unique Fucus species endemic to the Mediterranean. We combined measurements of water potential (Ψ) parameters derived from pressure-volume curves and chlorophyll a fluorescence (Fv/Fm) in juvenile and adult thalli sampled in three different dates between March and April 2023. F. virsoides exhibited remarkable water stress tolerance, as evidenced by the low water potential at turgor loss point (Ψtlp, -7.0 MPa on average), and the maintenance of high Fv/Fm at low water potentials indicating a prolonged maintenance of healthy physiological status. While no differences were observed between growth stages, Ψtlp, capacitance (C) and the bulk modulus of elasticity (ε) varied significantly according to the sampling dates, whereas the osmotic potential at full turgor did not significantly change. Ψ measured on thalli collected after a typical prolonged emersion period was markedly lower (−12.3 MPa on average) than the estimated Ψtlp, suggesting that the population is frequently undergoing turgor loss. Further investigations are required to determine environmental tolerance ranges based on water status characteristics to enhance our understanding of F. virsoides responses and vulnerability to climate change, thus providing insight into the possible causes of its widespread decline.

Modelling the carbon balance in bryophytes and lichens: Presentation of PoiCarb 1.0, a new model for explaining distribution patterns and predicting climate-change effects.

Bryophytes and lichens have important functional roles in many ecosystems. Insight into their CO2 -exchange responses to climatic conditions is essential for understanding current and predicting future productivity and biomass patterns, but responses are hard to quantify at time scales beyond instantaneous measurements. We present PoiCarb 1.0, a model to study how CO2 -exchange rates of these poikilohydric organisms change through time as a function of weather conditions. PoiCarb simulates diel fluctuations of CO2 exchange and estimates long-term carbon balances, identifying optimal and limiting climatic patterns. Modelled processes were net photosynthesis, dark respiration, evaporation and water uptake. Measured CO2 -exchange responses to light, temperature, atmospheric CO2 concentration, and thallus water content (calculated in a separate module) were used to parameterize the model's carbon module. We validated the model by comparing modelled diel courses of net CO2 exchange to such courses from field measurements on the tropical lichen Crocodia aurata. To demonstrate the model's usefulness, we simulated potential climate-change effects. Diel patterns were reproduced well, and the modelled and observed diel carbon balances were strongly positively correlated. Simulated warming effects via changes in metabolic rates were consistently negative, while effects via faster drying were variable, depending on the timing of hydration. Reproducing weather-dependent variation in diel carbon balances is a clear improvement compared to simply extrapolating short-term measurements or potential photosynthetic rates. Apart from predicting climate-change effects, future uses of PoiCarb include testing hypotheses about distribution patterns of poikilohydric organisms and guiding conservation strategies for species.

The Key Role of Cyclic Electron Flow in the Recovery of Photosynthesis in the Photobiont during Rehydration of the Lichen Cladonia stellaris

Lichens are poikilohydric organisms and an important part of the ecosystem. They show high desiccation tolerance, but the mechanism of dehydration resistance still needs to be studied. The photosynthesis recovery of the photobiont in rehydrated lichen Cladonia stellaris after 11-year desiccation was investigated by simultaneously monitoring both photosystem I and II (PSI and PSII) activities. The responses of the photochemical efficiency and relative electron transport rate (rETR) of PSI and PSII, and the quantum yield of the cyclic electron flow (CEF) were measured using a Dual-PAM-100 system. PSI recovered rapidly, but PSII hardly recovered in C. stellaris during rehydration. The maximal photochemical efficiency of PSII (Fv/Fm) was generally very low and reached about just 0.4 during the rehydration. These results indicated that PSII had restored little and was largely inactivated during rehydration. The quantum yield of PSI recovered quickly to almost 0.9 within 4 h and remained constant at nearly 1 thereafter. The results showed that the activation of the CEF in the early stages of rehydration helped the rapid recovery of PSI. The quantum yield of the CEF made up a considerable fraction of the quantum yield of PSI during rehydration. A regulated excess energy dissipation mechanism and non-photochemical quenching (NPQ) also recovered. However, the small extent of the recovery of the NPQ was not enough to dissipate the excess energy during rehydration, which may be responsible for the weak activity of PSII during rehydration. The results indicated that both CEF and NPQ were essential during the rehydration of the photobiont in C. stellaris. The methods used in the measurements of chlorophyll a fluorescence and P700+ absorbance changes in this study provided a speedy and simple way to detect the physiological characteristics of the photobionts of lichen during rehydration. This work improves our understanding of the mechanism behind lichen’s desiccation tolerance.

Life-stage dependent response of the epiphytic lichen Lobaria pulmonaria to climate

Lichens are poikilohydric organisms, whose internal water content tends to reflect external humidity conditions. After drying, they can reactivate their metabolic activity through water vapor uptake or liquid water input. Thus, lichen water-related functional traits are important as they are involved in the duration of the hydrated period. Models predicting the effect of environmental conditions on lichens are based mainly on the presence or absence of adult thalli. Nevertheless, ecological conditions required by lichens might vary during their life cycle, for example during propagule establishment or in the first stages of thallus development. Little is known about the different ecological requirements at the different development stages in lichens. In this work, we measured water holding capacity (WHC) and specific thallus mass (STM) of adult and juvenile thalli of the model species Lobaria pulmonaria along a climatic gradient to constrain the process-based model LiBry. The LiBry model allows accounting for the productivity of lichens with different physiological strategies under various environmental conditions. We simulated the activity and performance of adult and juvenile thalli in 9 regions of Italy and Corsica. The model was used to test if adult thalli of L. pulmonaria have a higher survival probability due to their higher aerodynamic resistance. In the current climatic condition, the LiBry model predicts a higher survival probability of adults with decreasing absolute survival rates of both life stages with increasing temperature. Adult thalli also result in having higher active time, STM, and relative growth rate (RGR). We discuss the main implications of our simulation outputs, provide future perspectives and possible implementations of the LiBry model.

Multiple drivers of large-scale lichen decline in boreal forest canopies.

Thin, hair‐like lichens (Alectoria, Bryoria, Usnea) form conspicuous epiphyte communities across the boreal biome. These poikilohydric organisms provide important ecosystem functions and are useful indicators of global change. We analyse how environmental drivers influence changes in occurrence and length of these lichens on Norway spruce (Picea abies) over 10 years in managed forests in Sweden using data from >6000 trees. Alectoria and Usnea showed strong declines in southern‐central regions, whereas Bryoria declined in northern regions. Overall, relative loss rates across the country ranged from 1.7% per year in Alectoria to 0.5% in Bryoria. These losses contrasted with increased length of Bryoria and Usnea in some regions. Occurrence trajectories (extinction, colonization, presence, absence) on remeasured trees correlated best with temperature, rain, nitrogen deposition, and stand age in multinomial logistic regression models. Our analysis strongly suggests that industrial forestry, in combination with nitrogen, is the main driver of lichen declines. Logging of forests with long continuity of tree cover, short rotation cycles, substrate limitation and low light in dense forests are harmful for lichens. Nitrogen deposition has decreased but is apparently still sufficiently high to prevent recovery. Warming correlated with occurrence trajectories of Alectoria and Bryoria, likely by altering hydration regimes and increasing respiration during autumn/winter. The large‐scale lichen decline on an important host has cascading effects on biodiversity and function of boreal forest canopies. Forest management must apply a broad spectrum of methods, including uneven‐aged continuous cover forestry and retention of large patches, to secure the ecosystem functions of these important canopy components under future climates. Our findings highlight interactions among drivers of lichen decline (forestry, nitrogen, climate), functional traits (dispersal, lichen colour, sensitivity to nitrogen, water storage), and population processes (extinction/colonization).

Optimising Artificial Moss Growth for Environmental Studies in the Mediterranean Area.

Bryophytes are poikilohydric organisms that play a key role in ecosystems, while some of them are also resistant to drought and environmental disturbances but present a slow growth rate. Moss culture in the laboratory can be a very useful tool for ecological restoration or the development of urban green spaces (roof and wall) in the Mediterranean region. Therefore, we aim to: (i) determine the optimal culture conditions for the growth of four moss species present in the Mediterranean climate, such as Bryum argenteum, Hypnum cupressiforme, Tortella nitida, and Tortella squarrosa; (ii) study the optimal growth conditions of the invasive moss Campylopus introflexus to find out if it can be a threat to native species. Photoperiod does not seem to cause any recognisable pattern in moss growth. However, temperature produces more linear but slower growth at 15 °C than at 20 and 25 °C. In addition, the lower temperature produced faster maximum cover values within 5–8 weeks, with at least 60% of the culture area covered. The study concludes that the culture of moss artificially in the organic gardening substrate without fertilisers is feasible and could be of great help for further use in environmental projects to restore degraded ecosystems or to facilitate urban green spaces in the Mediterranean area. Moreover, this study concludes that C. introflexus could successfully occupy the niche of other native moss species, especially in degraded areas, in a future global change scenario.

Coverage and Rainfall Response of Biological Soil Crusts Using Multi-Temporal Sentinel-2 Data in a Central European Temperate Dry Acid Grassland

Biological soil crusts (BSCs) are thin microbiological vegetation layers that naturally develop in unfavorable higher plant conditions (i.e., low precipitation rates and high temperatures) in global drylands. They consist of poikilohydric organisms capable of adjusting their metabolic activities depending on the water availability. However, they, and with them, their ecosystem functions, are endangered by climate change and land-use intensification. Remote sensing (RS)-based studies estimated the BSC cover in global drylands through various multispectral indices, and few of them correlated the BSCs’ activity response to rainfall. However, the allocation of BSCs is not limited to drylands only as there are areas beyond where smaller patches have developed under intense human impact and frequent disturbance. Yet, those areas were not addressed in RS-based studies, raising the question of whether the methods developed in extensive drylands can be transferred easily. Our temperate climate study area, the ‘Lieberoser Heide’ in northeastern Germany, is home to the country’s largest BSC-covered area. We applied a Random Forest (RF) classification model incorporating multispectral Sentinel-2 (S2) data, indices derived from them, and topographic information to spatiotemporally map the BSC cover for the first time in Central Europe. We further monitored the BSC response to rainfall events over a period of around five years (June 2015 to end of December 2020). Therefore, we combined datasets of gridded NDVI as a measure of photosynthetic activity with daily precipitation data and conducted a change detection analysis. With an overall accuracy of 98.9%, our classification proved satisfactory. Detected changes in BSC activity between dry and wet conditions were found to be significant. Our study emphasizes a high transferability of established methods from extensive drylands to BSC-covered areas in the temperate climate. Therefore, we consider our study to provide essential impulses so that RS-based biocrust mapping in the future will be applied beyond the global drylands.

Seasonal variation of antioxidant enzymatic responses in the desiccation-tolerant bryophyte Syntrichia ruralis (Hedw.) Web. & Mohr.

Bryophytes are poikilohydric organisms that can be used as model plants to study desiccation tolerance mechanisms. The main objective of this study was to examine the activities of the antioxidant enzymes ascorbate peroxidase (APX), catalase (CAT) and guaiacol peroxidase (POD) in the rehydrated and desiccated states in Syntrichia ruralis (Hedw.) Web. & Mohr. from two slopes, one North-east (NE) and one South-west (SW) facing and collected in different seasons. Our results showed seasonal variation in the enzymatic activities of APX, CAT and POD between the slopes in both the rehydrated and desiccated states. The mean value of all the activities of APX, CAT and POD and MDA contents (a measure of lipid peroxidation) tended to be higher in moss cushions collected from the NE compared to the SW facing slopes except in summer season. The mean values of all enzymatic activities were higher in desiccated states as compared with rehydrated states. Protein content has lower values in summer and winter season. Differences in the antioxidant activities of the mosses growing on the two slopes may reflect adaptations to desiccation stress.

Apparent electron transport rate – a non-invasive proxy of photosynthetic CO2 uptake in lichens

During desiccation, both apparent electron transport rate (ETRapp) and photosynthetic CO2 uptake peak when external water has evaporated. External water, causing suprasaturation, weakens the strong correlation between ETRapp and CO2 uptake. Lichens are poikilohydric organisms passively regulated by ambient conditions. In theory, apparent electron transport rate (ETRapp), estimated by photosystem II yield measured in light (ΦPSII), is a proxy of photosynthetic CO2 uptake. Hydration level, however, is a complicating factor, particularly during suprasaturation that strongly reduces CO2 diffusion. Here, the cephalolichen Lobaria pulmonaria and two chlorolichens Parmelia sulcata and Xanthoria aureola were excessively hydrated before photosynthetic CO2 uptake and ΦPSII using imaging fluorescence tools were simultaneously measured while drying at 200µmol photons m-2s-1. CO2 uptake peaked when hydration had declined to a level equivalent to their respective internal water holding capacity (WHCinternal) i.e., the water per thallus area after blotting external water. CO2 uptake and ETRapp in all species were highly correlated at hydration levels below WHCinternal, but weaker at higher hydration (chlorolichens) or absent (cephalolichen). Yet, at a specimen level for the two chlorolichens, the correlation was strong during suprasaturation. The CO2 uptake-ETRapp relationship did not differ between measured species, but may vary between other lichens because the slope depends on cortical transmittance and fraction of electrons not used for CO2 uptake. For new lichen species, calibration of ETRapp against CO2 uptake is therefore necessary. At intrathalline scales, ΦPSII during drying initially increased along thallus margins before reaching maximum values in central portions when hydration approached WHCinternal. WHCinternal represents the optimal hydration level for lichen photosynthesis. In conclusion, ETRapp is an easily measured and reliable proxy of CO2 uptake in thalli without external water but overestimates photosynthesis during suprasaturation.

Using Chlorophyll a Fluorescence Imaging to Select Desiccation-Tolerant Native Moss Species for Water-Sustainable Green Roofs

Green roofs have been more thoroughly investigated in the last few years due to the potential benefits they offer to ecosystems in urban areas (e.g., carbon sequestration, particle retention, heat island effect attenuation). However, current climate change models predict an increase in desertification, with an increase in temperature and decrease in rainfall, which means there is an increasing demand for green roofs with lower water consumption. Vegetation with very little water requirements, such as desiccation-tolerant mosses, has shown a potential to complement or substitute for vascular species, increasing the sustainability of lower water use in green roofs. In this study, we use chlorophyll a fluorescence imaging to screen for bryophytes with adequate physiology to be used in green roofs placed in at-risk areas with prolonged drought episodes. Apart from Hypnum cupressiforme, all selected species presented a high potential for use in those conditions, particularly Didymodon fallax, Grimmia lisae, Pleurochaete squarrosa, and Targionia hypophylla. Chlorophyll a fluorescence imaging technology proved to be a simple and non-invasive tool for a fast screening of these poikilohydric organisms, to be used in future studies of bryophyte biology, but more importantly in the green roof industry.

Spectral Response Assessment of Moss-Dominated Biological Soil Crust Coverage Under Dry and Wet Conditions

Biological soil crusts (BSCs) are a major functional vegetation unit, covering extensive parts of drylands worldwide. Therefore, several multispectral indices have been proposed to map the spatial distribution and coverage of BSCs. BSCs are composed of poikilohydric organisms, the activity of which is sensitive to water availability. However, studies on dry and wet BSCs have seldom considered the mixed coverage gradient that is representative of actual field conditions. In this study, in situ spectral data and photographs of 136 pairs of dry and wet plots were collected to determine the influence of moisture conditions on BSC coverage detection. Then, BSC spectral reflectance and continuum removal (CR) reflectance responses to wetting were analyzed. Finally, the responses of four commonly used indices (i.e., normalized difference vegetation index (NDVI); crust index (CI); biological soil crust index (BSCI); and band depth of absorption feature after CR in the red band, (BD_red)), calculated from in situ hyperspectral data resampled to two multispectral data channels (Landsat-8 and Sentinel-2), were compared in dry and wet conditions. The results indicate that: (i) on average, the estimated BSC coverage using red-green-blue (RGB) images is 14.98% higher in wet than in dry conditions (P < 0.001); (ii) CR reflectance features of wet BSCs are more obvious than those of dry BSCs in both red and red-edge bands; and (iii) NDVI, CI, and BSCI for BSC coverage of 0%–60% under dry and wet conditions are close to those of dry and wet bare sand, respectively. NDVI and BD_red cannot separate dead wood and BSC with low coverage. This study demonstrates that low-coverage moss-dominated BSC is not easily detected by the four indices. In the future, remote-sensing data obtained during the rainy season with red and red-edge bands should be considered to detect BSCs.

Disentangling functional trait variation and covariation in epiphytic lichens along a continent-wide latitudinal gradient.

Characterizing functional trait variation and covariation, and its drivers, is critical to understand the response of species to changing environmental conditions. Evolutionary and environmental factors determine how traits vary among and within species at multiple scales. However, disentangling their relative contribution is challenging and a comprehensive trait-environment framework addressing such questions is missing in lichens. We investigated the variation in nine traits related to photosynthetic performance, water use and nutrient acquisition applying phylogenetic comparative analyses in lichen epiphytic communities on beech across Europe. These poikilohydric organisms offer a valuable model owing to their inherent limitations to buffer contrasting environmental conditions. Photobiont type and growth form captured differences in certain physiological traits whose variation was largely determined by evolutionary processes (i.e. phylogenetic history), although the intraspecific component was non-negligible. Seasonal temperature fluctuations also had an impact on trait variation, while nitrogen content depended on photobiont type rather than nitrogen deposition. The inconsistency of trait covariation among and within species prevented establishing major resource use strategies in lichens. However, we did identify a general pattern related to the water-use strategy. Thus, to robustly unveil lichen responses under different climatic scenarios, it is necessary to incorporate both among and within-species trait variation and covariation.

Variability of water storage capacity in three lichen species

As poikilohydric organisms, lichens are capable of storing significant amounts of atmospheric water. Epiphytes that intercept rainfall change the amount and chemical composition of throughfall water, affecting water balance and microclimate of forest ecosystems. The aim of the study was to investigate the differences in the process of changes/increase in the amount of water in three lichen species: Evernia prunastrii, Hypogymnia tubulosa and Platismatia glauca. In the experiment, conducted under laboratory conditions, samples of thalli were wetted with constant doses of water and weighed in order to determine the amount of water storage capacity from simulated rainfall. The studied lichen species differed in terms of process dynamics and values of water storage capacity, probably due to the morphological structure of thalli. Average water retention was the highest in Platismatia glauca (33.58 %), lower in Evernia prunastrii (19.77 %) and the lowest in Hypogymnia tubulosa (15.38 %). Analyzed taxa with larger water storage capacity are also known to be more sensitive to air pollution.

Vertical variation in epiphytic cryptogam species richness and composition in a primeval Fagus sylvatica forest

AbstractQuestionBiodiversity surveys of epiphytic bryophytes and lichens on standing trees are mostly restricted to the lowermost 2 m, since sampling above this level is time‐consuming and therefore expensive. However, sampling only the stem base is likely to result in underestimation of forest epiphyte diversity, because microclimate and physico‐chemical site conditions, both of which vary with height above the ground, play important roles for poikilohydric organisms. We investigate variation in epiphyte diversity and composition along the vertical gradient in forests and discuss factors that may potentially account for height‐dependent distribution patterns.LocationMontane primeval beech forest Havešová in the Carpathians, eastern Slovakia.MethodsTen circular plots, each 500 m2, were selected randomly in an area severely affected by windfall. Epiphytes were sampled along the stems of recently uprooted trees, from base to the canopy. Mean Ellenberg indicator values (EIV) for light, moisture, acidity and nitrogen availability were used as surrogate variables for environmental interpretation of compositional patterns for sampling segments of 2 m along the stem.ResultsBy sampling only the lowest 2 m, 10% of the total bryophyte and 48% of the lichen species would have been missed. We detected systematic patterns of compositional variation for both groups along the vertical gradient. While pleurocarpous mosses and liverworts were mostly restricted to the stem base, acrocarpous mosses and crustose lichens occurred along the stem almost to the top. Foliose and fruticose lichens were concentrated at intermediate heights and in the upper canopy. Patterns of variation in EIVs suggested that increasing light availability, decreasing moisture and increasing inputs of acidic and nitrous substances are responsible for the compositional shifts along the vertical gradient.ConclusionsSampling only the stem base implies severe underestimation of the epiphyte diversity in temperate broad‐leaved forests. The middle and the upper parts of tree stems have distinctive compositions of epiphytic cryptogams, because microclimate and physico‐chemical site factors vary with height above the ground.

Rate of drying influences tolerance of low water contents in the moss Funaria hygrometrica (Funariaceae)

Desiccation tolerance (DT) in poikilohydric organisms is dependent upon four principal sequential factors, (1) the rate of drying (RoD), (2) the water content (WC) of the organism deriving from the equilibrating relative humidity (RHeq), (3) the duration of the desiccation event, and (4) the rate of rehydration (RoR). The first two factors are often combined in experiments as the “intensity” of desiccation, and thus the effect of one on the other is relatively unknown but likely to be important ecologically. We hypothesized that more protracted rates of drying should mitigate damage at lower equilibrating RHs in a known inducibly DT species. Cultured uniclonal shoots of the moss Funaria hygrometrica were dried at different RoDs (time from full turgor to leaf curling, from 0.067 to 120 h) at five different RHs (12, 33, 54, 75 and 93%), allowed to equilibrate at each RH, rehydrated and assessed using chlorophyll fluorescence at 0.5 and 24 h postrehydration. At 24 h postrehydration, shoots of F. hygrometrica subjected to a rapid-dry event (<10 min) were unable to recover to control levels of fluorescence (Fv/Fm and ΦPSII <80% of control levels) when equilibrated at RHeqs of ≤54%. Recovery was improved when the rate of drying was extended for more than ∼15 hours from full turgor to the onset of leaf curling at these RHeqs. When shoots were rapidly dried at RHeqs >54%, recovery was complete. At 0.5 h postrehydration, Fv/Fm levels indicated moderate damage at all RHeqs except 93%, with no mitigation of damage when the rate of drying was extended. Intensity of desiccation is normally construed as the ability to tolerate a combination of rate of drying × equilibrating RH. By varying the rate of drying across a range of RHeqs, F. hygrometrica is found to be able to tolerate all water contents tested, providing the rate of drying is extended to at least 15 h from full turgor to leaf curling. By adopting either the “step-down” approach to drying or the “wet substrate” technique used here, future studies on the desiccation tolerance of poikilohydric organisms can more accurately assess responses to desiccation stress.

Lichen diversity on tree trunks in tropical dry forests is highly influenced by host tree traits

Tropical dry forests have been recognized as one of the most threatened ecosystems in the world due to deforestation. These ecosystems harbour a high endemicity of epiphytes, which play a major role in the functioning of the forests. Lichens constitute an important fraction of the epiphytes. These poikilohydric organisms respond drastically to disturbance, which is strongly linked to humidity and light availability. We hypothesized that richness and species composition of lichens would be related to differences in forest structure (e.g., canopy openness) promoted by deforestation, and by host tree characteristics, due to the fact that dry forests generally have poor microclimatic stratification and low diversity of tree species. In this study, we assessed the richness and composition of epiphytic lichens on the trunks of 513 trees in undisturbed and disturbed dry forests of southern Ecuador. Both lichen composition and richness were highly correlated with tree species and host tree traits such as bark structure and tree diameter. Additionally, epiphytic lichen diversity was related to canopy cover and tree richness at different disturbance levels. We conclude that epiphytic lichen communities in seasonal dry tropical forests of Ecuador are mainly limited by host tree traits and tree species. Loss of epiphytic lichen species in the studied forests is particularly due to loss of host trees such as Cochlospermum vitifolium and Eriotheca ruizii, that maintain high species richness.

BtM, a Low-cost Open-source Datalogger to Estimate the Water Content of Nonvascular Cryptogams.

Communities of nonvascular cryptogams, such as mosses or lichens, are an important part of the Earth's biodiversity, contributing to the regulation of the carbon and nitrogen cycles in many ecosystems. Being poikilohydric organisms, they do not actively control their internal water content and need a humid environment to activate their metabolism. Therefore, studying water relationships of nonvascular cryptogams is crucial to understand both their diversity patterns and their functions in the ecosystems. We present the BtM datalogger, a low-cost open-source platform for the study of the water content of nonvascular cryptogams. The datalogger is designed to measure ambient temperature, humidity, and conductance from up to eight samples simultaneously. We provide a design for a printed circuit board (PCB), a detailed protocol to assemble the components, and the required source code. All this makes the assembly of the BtM datalogger accessible to any research group, even to those without previous specialized knowledge. Therefore, the design presented here has the potential to help popularize the use of this type of device among ecologists and field biologists.

Interactions of climate and solar irradiance can reverse the bioclimatic response of poikilohydric species: An experimental test for Flavoparmelia caperata

There is an increasing use of bioclimatic models to quantify the climate change response of bryophytes and lichens. The physiological performance of these poikilohydric organisms depends on ambient climatic conditions interacting with light availability. However, bioclimatic models have tended to follow a common practice of selecting temperature/precipitation variables without reference to light as a key functional constraint. In this study a growth chamber simulation was used to reconstruct patterns of temperature-moisture-light for the baseline and 2080s climates, affecting the performance of the lichen Flavoparmelia caperata for a high-latitude (56°N) temperate rainforest study site in Britain. The results demonstrate the importance of increased 2080s warmth and moisture under low winter light (possibly favoring respiration), and increased dormancy during drier and warmer summers (possibly reducing photosynthesis), resulting in negative growth (mass loss) for future climates. This is in direct contrast to the outcome of bioclimatic models applied to the same study site, which project increased environmental suitability based on a warmer and wetter climate (not considering irradiance). The study cautions that predictors for bioclimatic models should be chosen to reflect verified constraints in ecological performance (such as for growth), and especially for poikilohydric organisms this would include the interaction between ambient climate and light availability.

Soil moisture dynamics under two rainfall frequency treatments drive early spring CO2 gas exchange of lichen-dominated biocrusts in central Spain.

BackgroundBiocrusts, communities dominated by mosses, lichens, cyanobacteria, and other microorganisms, largely affect the carbon cycle of drylands. As poikilohydric organisms, their activity time is often limited to short hydration events. The photosynthetic and respiratory response of biocrusts to hydration events is not only determined by the overall amount of available water, but also by the frequency and size of individual rainfall pulses.MethodsWe experimentally assessed the carbon exchange of a biocrust community dominated by the lichen Diploschistes diacapsis in central Spain. We compared the effect of two simulated precipitation patterns providing the same overall amount of water, but with different pulse sizes and frequency (high frequency: five mm/day vs. low frequency: 15 mm/3 days), on net/gross photosynthesis and dark respiration.ResultsRadiation and soil temperature, together with the watering treatment, affected the rates of net and gross photosynthesis, as well as dark respiration. On average, the low frequency treatment showed a 46% ± 3% (mean ± 1 SE) lower rate of net photosynthesis, a 13% ± 7% lower rate of dark respiration, and a 24% ± 8% lower rate of gross photosynthesis. However, on the days when samples of both treatments were watered, no differences between their carbon fluxes were observed. The carbon flux response of D. diacapsis was modulated by the environmental conditions and was particularly dependent on the antecedent soil moisture.DiscussionIn line with other studies, we found a synergetic effect of individual pulse size, frequency, environmental conditions, and antecedent moisture on the carbon exchange fluxes of biocrusts. However, most studies on this subject were conducted in summer and they obtained results different from ours, so we conclude that there is a need for long-term experiments of manipulated precipitation impacts on the carbon exchange of biocrusts. This will enable a more complete assessment of the impacts of climate change-induced alterations in precipitation patterns on biocrust communities.

Comparative research of photosynthetic processes in selected poikilohydric organisms from Mediterranean and Central-European alpine habitats

Dehydration-induced decrease in photosynthetic activity was investigated in five poikilohydric autotrophs using chlorophyll fluorescence parameters recorded during controlled desiccation. For the study, two representatives of mosses from alpine zone (Rhizomnium punctatum, Rhytidiadelphus squarrosus) of the Jeseníky Mts. (Czech Republic) were used. Other two experimental species were mediterranean habitats liverwort (Pellia endiviifolia) and moss (Palustriella commutata), collected from under Woodwardia radicans canopy in the Nature Reserve Valle delle Ferriere (Italy). The last species was a liverwort (Marchantia polymorpha) collected from lowland site (Brno, Moravia, Czech Republic). We investigated the relationship between relative water content (RWC) and several chlorophyll fluorescence parameters evaluating primary photochemical processes of photosynthesis, such as effective quantum yield of photosynthetic processes in photosystem II (ΦPSII), and non-photochemical quenching (qN). With desiccation from fully wet (RWC = 100%) to dry state (RWC = 0%), ΦPSII exhibited a rapid (R. punctatum) and slow decline of ΦPSII (R. squarrosus, P. endiviifolia, M. polymorpha, and P. commutata). Shapes of dehydration-response curves were species-specific. RWC0.5, i.e. the RWC at which the sample showed half of maximum ΦPSII, reflected the species-specificity. It reached 65% in desiccation sensitive (R. punctatum), 53% and 43% in semi-tolerant (P. commutata and R. squarrosus), 24% and 18% in desiccation-tolerant species (P. endiviifolia and M. polymorpha). In all experimental species, non-photochemical quenching (qN) of absorbed light energy showed high values at RWC = 100% and a slight increase with desiccation. Steady state chlorophyll fluorescence (FS) remained high during desiccation and was not correlated with ΦPSII.