Time matters for plant diversity effects on nitrate leaching from temperate grassland

In biodiversity-ecosystem functioning experiments, plant diversity increases biomass production mainly because of complementary resource use. We determined the influence of seasonality and time since conversion from fertilized arable land to unfertilized grassland on the plant diversity-nitrate leaching relationship. NO3-N concentrations in soil solution, water contents in the main rooting zone, and climate data were measured between 2003 and 2006 in a grassland plant diversity experiment in Jena, Germany which consists of 82 plots with 1-60 plant species and 1-4 plant functional groups (legumes, grasses, non-leguminous tall herbs, and non-leguminous small herbs). To cope with data gaps and uneven sampling intervals, water contents were simulated with Bayesian statistical models, based on the measured data. Downward water fluxes were modeled with a deterministic water balance model. Monthly NO3-N fluxes were calculated as NO3-N concentration times downward water flux and statistically analyzed. The statistical results were confirmed with the help of a completely simulated NO3-N leaching data set without any data gaps. Plant species richness quantitatively decreased NO3-N leaching in winter, when leaching was highest, more than in summer. The presence of legumes increased and the presence of grasses decreased NO3-N leaching. The presence of small herbs decreased NO3-N leaching and this effect strengthened with time. We conclude that especially shortly after land-use change from fertilized arable land to unfertilized grassland, NO3-N leaching can be reduced if species-rich mixtures without legumes are established. (C) 2015 Elsevier B.V. All rights reserved.