Soil Carbon Chemical Composition and Diversity Mediate Fungal and Bacterial Population Carbon Utilization Capacities.

Studies show a strong role of plant species and functional richness in regulating belowground processes. Diverse plant communities, in theory, contribute chemically diverse carbon (C) inputs to soils and, likewise, species-poor communities contribute a more limited array of compounds to soil. We hypothesize that such differences in C composition and diversity could be one mechanism by which plant diversity structures the niche availability for soil microorganisms. However, effects of plant richness on soil carbon composition and carbon diversity and its relationship to microbial carbon-use phenotypes are largely unknown.

We collected rhizosphere soils from two plant species, Lespedeza capitata (LC) and Andropogon gerardii (AG) grown in either low (monoculture) or high (16 species) diversity assemblages from the long-term biodiversity experiment at Cedar Creek Ecosystem Science Reserve, USA. We created culture collections of 59 isolates of the soil fungus, Fusarium, and 80 isolates of the soil bacterium, Streptomyces and measured growth of isolates on 91 individual C compounds using the Biolog^TM method. We measured soil C chemistry using pyrolysis GC-MS in the same plots.

The composition of rhizosphere soil C chemistry was significantly different between monocultures and high diversity assemblages (r² = 0.28; P = 0.033). In LC plots, C utilization profiles of Streptomyces and Fusarium were highly correlated with soil aromatic, protein, and phenolic compounds. In AG plots, C utilization differed among Streptomyces and Fusarium were related most C groups. Together these data present a potential mechanism by which plant diversity may structure functional niche diversity in microbial communities.