Intra-annual stability of spatial and temporal niche complementarity in temperate grasslands

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Within Subproject Plant Water Relations (SP8), we will address complementary resource use, one of the potential mechanisms explaining biodiversity-ecosystem functioning relationships. We will focus on water and light use, since here major gaps in knowledge still exist, despite the relevance of both resources for plant performance. We aim to identify temporal niches for water sourcing at the species level and for the first time quantify plant water relations along a diversity gradient in the main experiment (block 2), complementing on-going efforts to partition ecosystem water fluxes (task 1). We will determine the ecophysiological mechanisms in terms of light and water use that are the basis for any spatio-temporal resource complementarity (in the tracer and Ecotron experiments) (task 2). In addition, we will assess the temporal development of light and water use niches, their biochemical basis and relevance for C and N allocation in the new species-specific trait experiment (task 3). Our measurements based on plant ecophysiology (e.g., leaf water potentials, leaf gas exchange rates) will be complemented by the assessment of water- and light-related plant traits (e.g., leaf morphology, carbon allocation, leaf greenness), canopy light profiles as well as stable oxygen and hydrogen isotope analyses of plant xylem and soil water. Based on these different approaches, we will collect a unique dataset on light, and in particular, on water use, to quantify niche complementarity and its development over time as well as to identify the underlying ecophysiological mechanisms.