Effects Of Simulated Warming On Soil Respiration,Nitrmcation And Denitrification In A Cropland

In order to investigate the effects of simulated warming on the key processes of soil respiration, soil carbon and nitrogen cycling in a cropland, a randomized block experiment including two treatments (simulated warming and control) was carried out in2011, a randomized block experiment including four treatments (simulated warming, control, acid rain, and warming and acid rain) was carried out in2012. A portable soil CO2fluxes system (LI-8100) was used to measure soil respiration rates. Soil CO2production rates, nitrification rates, denitrification rates were determined by using a Barometric Process Separation (BaPS) method. Soil temperature and soil moisture were simultaneously observed when measuring soil respiration rates. Root biomass, DOC, nitrite, sulfate and nitrate were observed after measuring soil CO2production rate, denitrification rate and nitrification rate.Results indicated that soil respiration rates under different treatments showed similar seasonal variability, in accordance with the variability in soil temperature. With the warming time increased, soil respiration rates during the soybean growth season were higher than the winter wheat season for simulated warming and control treatments in2011, and there was a good positive correlation between soil respiration and soil temperature. During the winter wheat soybean rotation growing season in2012, soil respiration for warming treatment was lower than control treatment, and soil respiration for warming and acid rain treatment was higher than acid rain treatment. Soil CO2production rates during the soybean growth season is significantly higher than those during the winter wheat growth season in2011. The effects of simulated warming on soil CO2production rates were significant during the soybean growth season but not significant during the wheat growth season. Soil CO2production rates for warming treatment is higher than control during the wheat growth season in2012, while soil CO2production rates for warming treatment is lower than control during the soybean growth season in2012. Soil CO2production rates for warming acid rain treatment was higher than acid rain treatment during the wheat soybean growth season in2012, indicating simulated warming increased soil CO2production rates. Soil respiration is significantly correlated with soil temperature. The temperature sensitivity (Q10) of soil respiration under the simulated warming treatments was significantly higher than that that under the control treatments during the winter wheat-soybean rotation growing season in2011and2012. Soil temperature and soil moisture were the key factors driving the interannual variability in soil respiration during the wheat-soybean rotation.Simulated warming significantly increased soil nitrification during the winter wheat-soybean rotation period; while simulated warming did not increase denitrification in2011. Simulated warming increased soil nitrification during the prophase period but did not increase soil nitrification during the later period for the winter wheat-soybean rotation period in2012. Simulated warming significantly increased soil nitrification compared to control. Simulated warming significantly increased soil denitrification during the winter wheat-soybean rotation period, and simulated warming and acid rain increased soil denitrification during the prophase period but did not increase soil nitrification. Our results indicated that simulated acid rain increased soil respiration during the winter wheat growth season, while significantly inhibited soil respiration during the soybean growth winter. During the winter wheat-soybean rotation simulated acid rain significantly increased soil respiration. Acid rain inhibited soil nitrification in the stage of prophase but promoted soil nitrification rate during the later growth period acid rain during the whole winter wheat-soybean rotation growth season.Further investigations suggested that, simulated warming did not affect root biomass, DOC, nitrite, sulfate and nitrate content in2011. The correlation between soil temperature and root biomass and between nitrite and sulfate was significant for warming treatment in2012. The correlation between DOC and soil moisture, and between DOC and soil temperature was significant for control treatment in2012. The correlation between soil respiration and soil temperature, between soil respiration and soil moisture, between DOC and soil moisture, between DOC and soil temperature was significantly for warming and acid rain treatment in2012. The correlation between soil respiration and root biomass, and between soil temperature and soil moisture was significant for acid rain treatment in2012.