Abstract

The relationship between plant diversity and nitrate leaching into groundwater was investigated in a Mid-European semi-natural grassland ecosystem. An experimental approach was used to directly manipulate plant diversity in the field, and to control for influences of environmental differences among habitats. Species loss was simulated by establishing grassland communities of 16, 8, 4, 2, 1 and 0 plant species, while simultaneously manipulating three functional groups (grasses, legumes, non-legume herbs). Every diversity treatment was replicated with several different species mixtures. Nitrate leaching was determined by continuous extraction of soil solution below the rooting zone and modeling of seepage rates. NO3- concentration in the soil solution was highly variable within each level of diversity. In bare ground plots and several low diversity mixtures containing legumes, nitrate concentrations were higher than the official EU threshold value for drinking water of 50 mg l-1, with maximum values of up to 350 mg l-1 measured in clover monocultures. Total annual loss of nitrate was highly dependent on the specific species composition of the communities; plots with legumes lost significantly more NO3- than plots without them. Generally, leaching decreased with increasing diversity, because, for plots containing legumes, higher species richness led to a balance between fixation and uptake of N. Aboveground biomass had no influence on nitrate loss, whereas leaching was negatively correlated with increasing root biomass. The abundance of legumes within a community, litter decomposition rates and net nitrification were all positively correlated with total NO3- loss. The results suggest that low diverse grass-clover mixtures of ley-farming systems may be detrimental for groundwater quality, especially if the grass species used are not well established or have a short annual period of vegetative growth

Keywords

BIODEPTH; biodiversity; ecosystem functioning; ecosystem processes; functional groups; grassland; legumes; nitrate leaching; species richness

Published in

Ecology
2003, volume: 84, number: 6, pages: 1539-1552
Publisher: Ecological Society of America

Authors' information