Nutrient enrichment is one of the main drivers of global change. The main causes are fertilization in increasingly intensive agricultural schemes and wide-spread anthropogenic combustion processes. Although it has repeatedly been shown that nutrient pollution is one of the main culprits for biodiversity loss in natural and semi-natural ecosystems worldwide, most studies have focused on effects on above-ground biodiversity. Nevertheless, there is growing evidence suggesting far reaching effects of nutrient enrichment on below-ground biodiversity as well. Using 454-sequencing of soil and root samples, we studied the arbuscular mycorrhizal communities (AMF) of 15 different plant species and 138 grassland plots across 8 European countries. The grassland plots were located in 20 calcareous and 18 acid grassland sites along orthogonal gradients of atmospheric nitrogen deposition and soil phosphorus levels. Additionally, we also studied the orchid mycorrhizal communities of four orchid species and the ericoid mycorrhizal communities of two Ericaceae present in a subset of these grasslands.
Results/Conclusions
We found that nitrogen deposition was significantly negatively related to the number of AMF taxa, suggesting a possible loss of over half the AMF diversity following an increase of nitrogen deposition from 5 to 25 kg N ha-1 year-1. Independent of the effect of nitrogen deposition, we found that soil phosphorus was also negatively related to the number of AMF taxa, reflecting a similar drop in plant species richness found in earlier studies. These negative relationships were consistent across both types of grassland, and we found similar patterns for both the orchid and the ericoid mycorrhizae. Our results suggest that diversity of mycorrhizae is crucially dependent on the extant levels of nutrient pollution. Importantly, as mycorrhizae constitute key below-ground symbionts, their loss may have far reaching ramifications for ecosystem functioning in an era of ever-increasing nutrient pollution.