The Role of Plant Diversity and Composition for Nitrate Leaching in Grasslands

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, while holding other environmental factors constant. Species loss was simulated by establishing grassland communities of 16, 8, 4, 2, 1, and 0 plant species, composed of 3, 2, or 1 functional groups (grasses, legumes, and 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. The concentration of nitrate 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 European Union threshold value for drinking water of 50 mg/L, with maximum values of up to 350 mg/L measured in Trifolium pratense monocultures. Total annual loss of nitrate was unaffected by the number of plant species or functional groups, but it was highly dependent on the specific species composition of the communities, and plots with legumes lost significantly more nitrate than plots without them. 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 nitrate loss. However, in those communities containing legumes, leaching decreased with increasing diversity, because higher species richness led to a reduction in legume dominance, to a reduced nitrate supply through nitrification, and to a complementary uptake of nitrate by grasses and non‐leguminous herbs. Based on these results, we expect that increasing the diversity of non‐leguminous species or functional groups would reduce the risk of nitrate leaching in low‐diversity grass–clover mixtures of ley‐farming systems, while allowing for a more efficient exploitation of the beneficial fertilization effect provided by legumes. Corresponding Editor: M. Loreau.

Soil biodiversity and soil community composition determine ecosystem multifunctionality

“…However, the loss of soil biodiversity may have indirectly resulted in changes in some ecosystem functions. Specifically, the effect of the different soil communities on plant productivity and diversity may have consequently indirectly influenced carbon sequestration and nutrient losses through leaching (43,44). Additionally we also assessed the effects of litter decomposition and N turnover on nutrient losses from the system.…”

Effect of four plant species on soil 15N-access and herbage yield in temporary agricultural grasslands

“…Plant available soil N is generally concentrated in the upper soil layers, but may leach to deeper layers, especially in grasslands that include legumes (Scherer-Lorenzen et al 2003) and under conditions with surplus precipitation (Thorup-Kristensen 2006). To improve soil N use efficiency in temporary grasslands, we propose the addition of deeprooting plant species to a mixture of perennial ryegrass and white clover, which are the most widespread forage plant species in temporary grasslands in a temperate climate (Moore 2003).…”

Plant growth and soil microbial community structure of legumes and grasses grown in monoculture or mixture

“…Bardgett et al (1998) and Wardle et al (1999) have reported that the abundance, activity, and composition of soil decomposer communities may vary markedly with differ-ent plant species, or specific functional plant groups such as legumes. Legumes can positively affect the microbial biomass due to high litter quality, that is, litter with a lower C/N ratio (Spehn et al, 2000;Scherer-Lorenzen et al, 2003;Bartelt-Ryser et al, 2005). Experiments of mixed versus monocultured plant species have demonstrated that plant mixtures can produce greater plant biomass (DeBell et al, 1997;Forrester et al, 2004), and improve nutrient cycling and soil fertility (Binkley et al, 1992(Binkley et al, , 2000Bauhus et al, 2000;Montagnini et al, 2000).…”