Forests are important centers for global carbon (C) and nitrogen (N) sequestration. Growing evidence suggests that tree species may impact rates of soil C and N cycling, but relatively few experiments have directly tested the effects of tree biodiversity on soil C and N storage. This study presents changes in soil C and N pools from the Forests and Biodiversity experiment (FAB) at the Cedar Creek Ecosystem Science Reserve, which consists of high density plots of one, two, five, or 12 tree species planted in a common soil. These tree species provide a broad range of functional diversity, including conifer and broadleaf species as well as ectomycorrhizal and arbuscular mycorrhizal species. Soils were collected from 66 plots in FAB, and we quantified the effects of species richness and functional diversity (i.e. leaf type and mycorrhizal fungi type) on C and N pools, aggregate size fractions, and fine root density using regression and ANOVA. To more directly assess the impacts of mycorrhizal fungi, we compared these data to previously collected estimates of phospholipid-derived fatty acids specific to arbuscular mycorrhizal fungi.
Results/Conclusions
Soil C and N pools both increased with increasing species richness(P = 0.04 and 0.1, respectively), though the trend with N was statistically insignificant. There were no clear effects of functional diversity. Soil macroaggregates (>250 μm diameter) were positively correlated with both soil C and N pools (P = 0.02) and tended to be higher under broadleaf trees (P = 0.06), though this was not statistically significant. There was no clear trend with species richness or mycorrhizal type. In the 12 species plots, which had relatively uniform understories, we found positive effects of AMF abundance on soil C and N pools (P = 0.03 and 0.01, respectively) and a probable but statistically insignificant positive effect on macroaggregate abundance (P = 0.06). This is particularly interesting as little research exists on the importance of AMF on aggregation in forest soils. As this experiment was planted only six years ago, our results highlight the potential for rapidly emerging effects of tree biodiversity on the storage of C and N in forest soils.