PS 46-27
Ectomycorrhizal diversity declines across a nitrogen deposition gradient in a Mediterranean forest
Nitrogen (N) deposition from anthropogenic sources can cause large changes to the diversity of plants and soil organisms in affected ecosystems. Ectomycorrhizal fungi, important soil mutualists for many woody plants, have been particularly sensitive to chronic N-deposition in boreal and temperate forests. I asked whether this pattern also holds in a forest with a Mediterranean climate where differences such as seasonal drought may reduce the impact of additional nitrogen. in the San Bernardino Mountains northeast of Los Angeles, CA. I sampled 11 Ponderosa pine stands that were similar in elevation, rainfall, and soil type , but occurred along a gradient of N-deposition (3.5kgN/ha- >15 kgN/ha) In December of 2013 (during the rainy season for Ponderosa pine in Mediterranean climates), I sampled the ectomycorrhizal community by collecting root cores, and measured the relative production of ectomycorrhizal mycelium using in-growth bags that had incubated from early September 2013 to mid-December 2013.
Results/Conclusions
The chronic N-deposition present across the San Bernardino national forest reduced ectomycorrhizal species richness and altered the community structure of ectomycorrhizal fungi. Similarly, there was a small reduction in the amount of extramatrical mycelium present in in-growth bags. The response of community structure to N-deposition is consistent with results form more mesic forest systems. However, the relatively small magnitude of response in this study may be due to a record drought year in California.