Ectomycorrhizal communities in temperate forest ecosystems: Does diversity decrease along an increasing natural nitrogen gradient?

Background/Question/Methods In nutrient poor soils of temperate forest ecosystems, niche partitioning within the ectomycorrhizal fungal (EMF) community is driven by heterogeneity in the underlying geochemical makeup of the soil, vegetative feedback mechanisms, and other abiotic-biotic interactions. If low nutrient soils increase the diversity of EMF species, one would expect fungal diversity to decrease as nutrient levels increase. Therefore, we hypothesized that species richness and diversity would decrease as nitrogen (N) availability increased across a natural N availability gradient. In order to test this hypothesis, we collected 144 soil cores from eight sites over a two year period within the Bartlett Experimental Forest in Bartlett, New Hampshire. Site selection was based on foliar N as a proxy for soil N with values ranging from 0.8-2.3%. Two approaches were applied to capture the EMF species 1) ectomycorrhizal root tips were identified using a combined morphotype/RFLP/sequencing approach (n=498) 2) the fungal community within the soil was characterized using cloning and sequencing techniques (n=199). Results/Conclusions Rarefied species accumulation curves and estimates of species richness and evenness were estimated. PIE estimates of species evenness was high at all sites (.89-.99). Species richness of ectomycorrhizal root tips was not significantly different between sites. However, the combined effort of sampling ectomcorrhizal root tips and soil revealed a pattern of increasing species richness along the nitrogen gradient. The high species richness and evenness across all sites indicates that EMF communities maintain high levels of diversity at all nitrogen levels. These data also reveal the importance of sampling both the soil community and those colonizing root tips.