Belowground Productivity and Biodiversity: The Effect of Soil Conditions and Species Diversity On Fine Root Biomass Distribution In a Broadleaf Forest Ecosystem.

It is clear that both nutrients and roots are unevenly distributed in natural environments, and that roots tend to proliferate in areas of nutrient enrichment. If carbon allocation by plants maximizes resource use, fine root biomass accrual should be higher in small, nutrient-rich spots. Additionally, increased species richness could be expected in areas with higher nutrient availability. Alternatively, it is possible that species are strongly segregated spatially and that variation in root biomass corresponds with differences in overall biomass among coexisting species. We tested these hypotheses measuring fine root biomass and soil conditions from >130 soil samples in a relatively undisturbed broadleaf forest in northeastern Ohio. Moreover, we used molecular techniques to identify root systems and assess the number of species coexisting in the same soil core. Our results indicated 1) no evidence of spatial segregation, either vertically or horizontally, among the most dominant species in the forest, and 2) a positive non-linear relationship between resource availability, species richness and fine root biomass, which suggests an intensive competition for resources at relatively small scales. We further explored the idea that functional or phylogenetic dimensions of diversity could be related to biomass accumulation. We found 3) a positive relationship between root biomass and phylogenetic diversity, even after correcting by nutrient availability, suggesting that the identity of species was important in the effectiveness of resource use in this tree community. Our results highlight the importance of the belowground component in understanding ecological processes such as biomass accrual, and the need to incorporate multiple dimensions of biodiversity to better understand the relationship between biodiversity and ecosystem productivity.