Plant carbon substrate supply regulated soil nitrogen dynamics in a tallgrass prairie in the Great Plains, USA: results of a clipping and shading experiment

Aims Land use management affects plant carbon (C) supply and soil environments and hence alters soil nitrogen (N) dynamics, with consequent feedbacks to terrestrial ecosystem productivity. The objective of this study was to better identify mechanisms by which land-use management (clipping and shading) regulates soil N in a tallgrass prairie, OK, USA. Methods We conducted 1-year clipping and shading experiment to investigate the effects of changes in land-use management (soil microclimates, plant C substrate supply and microbial activity) on soil inorganic N (NH4+ - N and NO3- - N), net N mineralization and nitrification in a tallgrass prairie. Important Findings Land-use management through clipping and/or shading significantly increased annual mean inorganic N, possibly due to lowered plant N uptake and decreased microbial N immobilization into biomass growth. Shading significantly increased annual mean mineralization rates (P < 0.05). Clipping slightly decreased annual mean N nitrification rates whereas shading significantly increased annual mean N nitrification rates. Soil microclimate significantly explained 36% of the variation in NO3- - N concentrations (P = 0.004). However, soil respiration, a predictor of plant C substrate supply and microbial activity, was negatively correlated with NH4+ - N concentrations (P = 0.0009), net N mineralization (P = 0.0037) and nitrification rates (P = 0.0028) across treatments. Our results suggest that change in C substrate supply and microbial activity under clipping and/or shading is a critical control on NH4+ - N, net N mineralization and nitrification rates, whereas clipping and shading-induced soil microclimate change can be important for NO3- - N variation in the tallgrass prairie.