The role of topography and soil characteristics in the relationship between species richness and primary productivity in a Kansas grassland

Environmental conditions influence patterns of local-scale plant productivity and species richness. We sampled soils and plant communities at a topographicallydiverse, mid-successional old field site in Kansas to better understand the abiotic factors underlying a natural plant productivity gradient. We related soil texture, pH, percent nitrogen and carbon, and soil moisture to elevation, plant productivity, and species richness. Most soil qualities were significantly correlated with elevation. The four soil texture classes we identified — clay, silty clay, silty clay loam, and silt loam — were spatially clustered according to topography. The lowest elevation sites, characterized by high C and N, low pH, low light penetration, and soils containing more silt and sand which supported the most productive and least diverse plant communities. We suggest that topography drives spatial heterogeneity in soils at our site. We also suggest that although richness is influenced directly by the filtering effects of the abiotic environment on the species pool, the indirect effects environmental factors have on richness via biomass production are more important for governing plant species richness in our system.