Effects of experimental warming and nitrogen addition on soil respiration and CH4 fluxes from crop rotations of winter wheat-soybean/fallow

Soil respiration showed clear seasonal fluctuations, with the largest emissions during summer and smallest in winter. Warming and nitrogen fertilization had no significant effects on total cumulative soil CO2 fluxes. Soil respiration was positively correlated with microbial biomass C, and microbial biomass C was not affected significantly by warming or nitrogen addition. The lack of significant effects of warming on soil respiration may have resulted from: (1) warming-induced soil drying offsetting the effects of soil temperature; or (2) adaption of soil respiration to increased temperature.