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Abstract

The impact of species richness and functional diversity of plants on ecosystem water vapor fluxes has been little investigated. To address this knowledge gap, we combined a lysimeter setup in a controlled environment facility (Ecotron) with large ecosystem samples/ monoliths originating from a long-term biodiversity experiment (“The Jena Experiment”) and a modelling approach. We aimed at (1) quantifying the impact of plant species richness (4 vs. 16 species) on day- and night-time ecosystem water vapor fluxes, (2) partitioning ecosystem evapotranspiration into evaporation and plant transpiration using the Shuttleworth and Accepted Article This article is protected by copyright. All rights reserved. Wallace (SW) energy partitioning model, and (3) identifying the most parsimonious predictors of water vapor fluxes using plant functional trait-based metrics such as functional diversity and community weighted means. Day-time measured and modeled evapotranspiration were significantly higher in the higher diversity treatment suggesting increased water acquisition. The SW model suggests that at low plant species richness, a higher proportion of the available energy was diverted to evaporation (a non-productive flux), while at higher species richness the proportion of ecosystem transpiration (a productivity-related water flux) increased. While it is well established that LAI controls ecosystem transpiration, here we also identified that the diversity of leaf nitrogen concentration among species in a community is a consistent predictor of ecosystem water vapor fluxes during day-time. The results provide evidence that, at the peak of the growing season, higher LAI and lower percentage of bare ground at high plant diversity diverts more of the available water to transpiration – a flux closely coupled with photosynthesis and productivity. Higher rates of transpiration presumably contribute to the positive effect of diversity on productivity.