BayCEER Workshop 2016

Community assembly processes and emerging diversity patterns in European grasslands along the hydrological gradient

O 3.1 in Water and the environment: From biosphere to geosphere

13.10.2016, 11:15-11:30, H36, NW III

European semi-natural grasslands are known to hold the world records of vascular plant species richness at small spatial grain sizes, but it remains a major challenge for ecological theory to explain how so many different species can co-exist together and why this apparently works particularly well in this habitat type. One possible explanation is that each species has a different ecological niche, and co-existence is promoted through spatio-temporal variation in environmental conditions, which prevents a single species to outcompete the others. Another idea is that resource competition in these systems is much lower than commonly assumed. Semi-natural grasslands exist from very wet through mesic to very dry conditions. This “hydrological gradient” is thus a suitable niche dimension to reach a deeper understanding of community assembly processes and emerging diversity patterns in European grasslands. In fact the hydrological gradient is not a single gradient, but is composed of two opposing stress gradients, one towards extreme drought (challenging the plants with water limitation) and one towards extreme wetness (challenging the plants with water logging and thus anoxia in the rooting zone).

Within the framework of the “Hydrological niche” initiative, we present a series of studies that address different aspects of plant community assembly along the hydrological gradient at different spatial and temporal scales, with a variety of complementary approaches. (a) In a mesocosm experiment conducted in 2016, we cultivated multi-species assemblages consisting of 20 grass and forb taxa with widely different moisture preferences under five moisture regimes from permanently waterlogged to extremely dry. We quantified aboveground biomass and survival of the individuals and assessed the within-species variability (i.e. phenotypic plasticity) between the treatments for several functional traits related to water use and stress reaction (plant height, SLA, LDMC, stomata density, minimal stomatal conductance, xylem width, aerenchym formation in the roots). (b) In an observational field study, we recorded vascular plant species occurrence in series of nested plots (0.0001, 0.001, 0.01, 0.1, 1, 10, 100 m²) in semi-natural grasslands around Bayreuth along the hydrological gradient. We used this dataset to assess which environmental factors drive the diversity patterns at different spatial scales as well as how functional composition (life form fractions and community-weighted means of relevant traits) change along the hydrological gradient. (c) In some of these field sites we also assessed water use efficiency (WUE) via the signature in stable isotopes of species that co-exist on 0.25 m² to see whether (i) co-occurring species under the same conditions are similar or dissimilar with respect to WUE and (ii) individuals of the same species show different WUE according to the site conditions. (d) Finally, we are going to take advantage of the European Vegetation Archive (EVA) to assess how grassland functional composition with respect to life forms, functional types (graminoids, legumes and non-legume forbs) and C-acquisition (C3, C4, CAM) varies systematically along climatic and edaphic moisture gradients.

Since these studies are all ongoing or emgerging, the talk will concentrate on illustrating the approaches and how they are interconnected, with some glimpses on first results.

Keywords: Plant ecology Biodiversity Hydrological niche Stress gradient Experiment Observational study Macroecology Ecoinformatics Plant functional traits Scale dependence Semi-natural grassland

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