Impact of two hot and dry summers on the community structure and functional diversity of testate amoebae in an artificial bog, illustrating their use as bioindicators of peatland health

Ongoing climate warming threatens the survival of bogs at the warm/dry limit of their distribution (e.g. in central Europe), and jeopardises the restoration of damaged bogs even more. Because vegetation changes can be slow, early indicators of hydrological change such as testate amoebae are useful. We used testate amoeba community structure and community weighted mean of functional traits to monitor the impact of two very hot and dry summers on a small (around 100 m2) artificial peatland constructed in the botanic garden of Neuchâtel, Switzerland. We collected analogous samples in a naturally regenerating cutover peatland at 1000 m a.s.l. in the Jura Mountains as a reference. The comparison of living and dead assemblages in the botanic garden showed an increased representation of smaller testate amoeba taxa (Corythion dubium, small Euglypha sp.) with a small pseudostome (indicative of dry conditions) and a loss of mixotrophy in 2015, followed by a weaker further shift in 2016. Nevertheless, the testate amoeba community structure in 2016 still indicated a dry Sphagnum bog. Testate amoeba analysis allows rapid assessment of peatland health and/or restoration success. The comparison of living and dead assemblages makes it possible to observe changes within a season in a single sampling campaign

Diversity and soil chemical properties jointly explained the basal area in karst forest

IntroductionPlant diversity and soil chemical properties are important factors affecting the plant growth. We sought to compare the explanatory rates of diversity and soil chemical properties in explaining the variation of basal area in karst forests, and also sought to compare the relative importance of the niche complementarity and mass ratio hypotheses.MethodsOn the basis of linear regression and structural equation modelling, we examined the correlation between the basal area of plant communities and species diversity, functional diversity, phylogenetic diversity, the community-weighted mean (CWM) of traits, and soil chemical properties, using data obtained from 35 monitoring plots in southwest China.ResultsSpecies, functional, and phylogenetic diversities were all significantly correlated with the basal area of the plant community, among the indices of which, Faith’s phylogenetic diversity was found to have the greatest explanatory power for basal area. These plant diversity indices can better explain the variation in basal area than the CWM of traits, suggesting the niche complementarity hypothesis is more applicable than the mass ratio hypothesis. Moreover, soil chemical properties also have an equal important impact. Different chemical properties were found to show significant positive correlations with basal area, and their total effects on basal area were shown to be greater than the CWM of traits.DiscussionAttention should be paid to diversity and soil chemical properties. This study provides theoretical guidance for understanding biodiversity maintenance mechanisms and protecting karst forests

Diversity, functionality, and resilience under increasing harvesting intensities in woodlands of northern Patagonia

Sustainable forest management relies on the understanding of biodiversity response to disturbance and the ecological resilience of the system. The dynamic equilibrium hypothesis (DEM) predicts that site productivity will modulate the effects of disturbance gradient on biodiversity. Also, considering functional diversity (eco-morfo-phisicological traits related to resource usage) is needed to understand the effect of species gains and losses on ecosystem functionality. Here we assess the response of understory plant taxonomic and functional diversity to increasing harvesting intensities (0, 30, 50 and 70% of basal area removed) at three woodland sites of contrasting biomass growth (productivity) in northern Patagonia. Also, we assessed resilience based on comparisons with undisturbed treatments four years after initial harvest. In agreement with DEM, both taxonomic and functional diversity peaked at high, medium, or low harvesting intensities in the high-, medium-, or low-productivity site, respectively. Taxonomic composition was clearly determined by site productivity (biomass growth), while no pattern emerged for functional composition. Functional traits related to light use showed different responses: specific leaf area was only affected by site productivity while leaf chlorophyll content was affected by an interaction between harvesting intensity and site productivity. Interestingly, there was no effect of harvesting intensity on the resilience of taxonomic diversity and functional composition. Only for functional diversity, harvesting intensity was as important as site productivity. In the high and intermediate productivity sites the traits that characterizes the system were more resilient and resembled the control treatment after four years of low or high (but not intermediate) harvesting intensities. Our results support the use of the DEM on forest interventions and the importance of considering both taxonomic and functional composition, as the consideration of functional traits related to resource use strategies have different implications when considering the resilience of the system.info:eu-repo/semantics/acceptedVersio

Nuanced qualitative trait approaches reveal environmental filtering and phylogenetic constraints on lichen communities

We propose that a qualitative trait approach based on more detailed nuanced traits may reveal previously overlooked patterns, especially when combined with phylogenetic perspectives. By sampling epiphytic lichens and using a functional approach based on nuanced qualitative traits, such as a much greater resolution over photobiont identity, type of cortex, and chemical compounds, we evaluated the effects of environmental filtering and phylogenetic constraints on community assembly along a natural succession of Atlantic rainforest. We found changes in taxonomic, functional, and phylogenetic composition, structure, and diversity. Functional traits such as photobiont genera, type of cortex, reproductive structures, propagule size, and protection strategies showed strong responses to succession. Mature forests with a closed canopy impose strong environment filtering that is reflected in lichen species turnover, limiting diversity, but also holding different functional and phylogenetic composition. The use of a nuanced qualitative trait approach may overcome some of the limitations of using this type of traits and shows the importance of often-overlooked key lichen functional traits, including the presence of carbon-concentrating mechanisms in photobionts and cortex properties. Furthermore, this is the first study showing how patterns of phylogenetic assembly along forest succession structure lichen communities

Traits or species – space or environment

How communities are structured and the processes shaping species composition are among the basic questions in ecology. Knowledge about these processes is essential to predict changes in community composition in response to changes in for example climate or land use practices. Soil communities are considered to be both remarkably species-rich and to have many generalist species with seemingly similar niche requirements. Soil fauna composition shows a large variation even at small spatial scales and both local environment and spatial configuration of habitats are regarded as important forces shaping the community composition. In this thesis, I examine the factors influencing small-scale community composition of springtails (Collembola) in two habitats, a variable and dynamic salt marsh and a more stable mature pine forest. The functional traits of species determine both their responses to the environment and their effects on ecosystem processes. The current knowledge on environment - species - traits relationship is limited in spite of its potential importance for ecosystem function. I show that by combining perspectives from two closely linked theoretical frameworks – metacommunity ecology and community assembly theory – we get a better understanding of the important ecological factors operating in this system. I found that the factors influencing community composition was context dependent, but in a predictable way. In the environmentally variable habitat, salt marsh, with spatial and temporal heterogeneity, there was evidence of strong environmental filtering. Small-scale topography was the strongest predictor of community composition, likely due to disturbances restricting where habitat-generalists can persist. In contrast, in the more stable habitat, mature pine forest, environmental filtering appeared weaker and biotic interactions seemed to have a stronger impact. Coexisting species were more similar in traits related to resource utilisation and sensory ability than expected, and variation in species composition was explained mainly by spatial factors like the distance between samples, i.e. each local community seemed to depend on the composition of the surrounding communities

Climate Sensitivity of the Arid Scrublands on the Tibetan Plateau Mediated by Plant Nutrient Traits and Soil Nutrient Availability

Climate models predict the further intensification of global warming in the future. Drylands, as one of the most fragile ecosystems, are vulnerable to changes in temperature, precipitation, and drought extremes. However, it is still unclear how plant traits interact with soil properties to regulate drylands’ responses to seasonal and interannual climate change. The vegetation sensitivity index (VSI) of desert scrubs in the Qaidam Basin (NE Tibetan Plateau) was assessed by summarizing the relative contributions of temperature (SGST), precipitation (SGSP), and drought (temperature vegetation dryness index, STVDI) to the dynamics of the normalized difference vegetation index (NDVI) during plant growing months yearly from 2000 to 2015. Nutrient contents, including carbon, nitrogen, phosphorus, and potassium in topsoils and leaves of plants, were measured for seven types of desert scrub communities at 22 sites in the summer of 2016. Multiple linear and structural equation models were used to reveal how leaf and soil nutrient regimes affect desert scrubs’ sensitivity to climate variability. The results showed that total soil nitrogen (STN) and leaf carbon content (LC), respectively, explained 25.9% and 17.0% of the VSI variance across different scrub communities. Structural equation modeling (SEM) revealed that STN and total soil potassium (STK) mediated desert scrub’s VSI indirectly via SGST (with standardized path strength of −0.35 and +0.32, respectively) while LC indirectly via SGST and SGSP (with standardized path strength of −0.31 and −0.19, respectively). Neither soil nor leave nutrient contents alone could explain the VSI variance across different sites, except for the indirect influences of STN and STK via STVDI (−0.18 and 0.16, respectively). Overall, this study disentangled the relative importance of plant nutrient traits and soil nutrient availability in mediating the climatic sensitivity of desert scrubs in the Tibetan Plateau. Integrating soil nutrient availability with plant functional traits together is recommended to better understand the mechanisms behind dryland dynamics under global climate change

Spatiotemporal effects of climate on the relationship between tree diversity and forest ecosystem functioning

Worldwide, forest ecosystem functioning and plant diversity have been altered by global environmental change. Understanding the relationship between biodiversity and ecosystem functioning with long-term environmental change is important because maintaining diversity can mitigate the impacts of environmental change on ecosystem functioning. Here, I i) developed a concept that can elucidate how enhancing plant diversity may help mitigate global environmental change impacts on ecosystem functioning; ii) empirically tested this concept in natural forest systems by examining whether higher tree diversity enhances and reduces positive and negative impacts of long-term environmental change on forest biomass dynamics (biomass growth, loss, and net biomass change); iii) explored effects of spatial variations in climate on the relationship between tree functional diversity and forest biomass dynamics; and iv) investigated how spatial variations in climate mediate the impacts of long-term environmental change on tree functional composition. In order to establish the concept of how tree diversity can mitigate the impacts of global environmental change on forest ecosystem functioning, I reviewed the field of climate change effects on biodiversity-ecosystem functioning. I found mixed evidence for positive diversity effects on ecosystem functioning persistent before and after experiencing changes in climates within grassland communities, but strong support in the few studies conducted in forest ecosystems which are more stable and resilient at higher levels of diversity. I identify the importance of future research combining investigations into climate change impacts on ecosystem functionality with the B-EF. I concluded that biodiversity can hold certain potential to be a solution to mitigate environmental change impacts. Using inventory data of boreal forests of western Canada from 1958-2011, I revealed that aboveground biomass growth of species-rich forests increased with the calendar year but that of species-poor forests decreased. Moreover, species-rich forests experienced less aboveground biomass loss from tree mortality than species-poor forests. I found that the growth of species-rich forests, but not species-poor forests, was positively associated with elevated CO2. Mortality in species-poor forests increased more with decreasing water availability than species-rich forests. In contrast, growth decreased, and mortality increased as the climate warmed regardless of species diversity. The results of this study suggest that promoting high tree diversity may help reduce the climate and environmental change vulnerability of boreal forests