Soil Respiration From The Northern Subtropical Secondary Forest, Farmland And Effects Of Environmental Problem On It

This forest soil respiration experiment was conducted in a northern subtropical natural secondary forest from March 2009 to November 2010. Farmland soil respiration experiment was carried out in agrometeorological experimental station of NanJing University of Information Science & Technology from March 2009 to November 2010. A portable soil CO2 fluxes system was used to measure soil respiration rates. Results showed that forest and farmland soil respiration had significant seasonal variation patterns. Mean soil respiration rates for natural secondary forest and farmland were (3.05±0.12), (2.66±0.20). Independent t-test analysis showed that there were no significant differences (p>0.05) in soil respiration rates among natural secondary forest and farmland. During the experimental period, natural secondary forest and farmland soil respiration showed an exponential relationship with soil temperature. The Q10 values (the respiratory flux at one temperature over the flux at a temperature 10℃lower) were 2.61,1.65 for natural secondary forest and farmland soil respiration. The temperature sensitivity of natural secondary forest soil respiration was higher than that of farmland soil respiration.In order to investigate the effects of acid rain on forest soil respiration, a simulated acid rain experiment was conducted in a northern subtropical natural secondary forest from March 2009 to January 2010. Acid rain treatments included CK(pH=6.4,deionized water), T1(pH=4.5), T2(pH=3.5) and T3(pH=2.5). A portable soil CO2 fluxes system was used to measure soil respiration rates. Results showed that soil respiration among all treatments had significant seasonal variation patterns. Mean soil respiration rates for CK, T1, T2 and T3 treatments were (3.20±0.21), (3.34±0.30), (3.51±0.06), (2.99±0.23)μmol·m2·s)-1, respectively. The experimental period was divided into three parts, which were non-growth period 1 (from February,2009 to April,2009), growth period (from Mary,2009 to October, 2009), non-growth period 2 (from November,2009 to January,2010), respectively. A paired t-test analysis showed that simulated acid rain did not inhibit soil respiration, T1 and T2 even promoted soil respiration in slow growing period 1; T3 significantly inhibited soil respiration during the growth period; simulated acid rain also promoted soil respiration during the non-growth period 2.Only T3 significantly inhibited soil respiration during the whole experimental period. During the whole experimental period, soil respiration showed an exponential relationship with soil temperature for each of the treatment. The Q10 values were 3.04,2.73,2.83 and 2.51 for CK, T1, T2, T3 treatments, respectively. Simulated acid rain significantly reduced the temperature sensitivity of soil respiration in the northern subtropical natural secondary forest.Field experiments were carried out in a winter wheat farmland, in order to investigate the effects of elevated ozone concentration on soil respiration. Three ozone concentration treatments, which were CK, T1 (100 nL·L-1) and T2 (150 nL·L-1), were arranged using open top chambers (OTCs). A portable soil CO2 fluxes system was used to measure soil respiration rates. Results indicated that there were no significant differences (p>0.05) in soil respiration rates among CK,T1 and T2 treatments. Mean soil respriation rates for CK,T1 and T2 treatments were (5.36±0.72), (5.08±0.04), (4.94±0.18)μmol·(m2·s)-1, respectively.During the experimental period, soil respiration showed an exponential relationship with soil temperature for each of the treatment. The Q10 values were 1.72,1.58 and 1.51 for CK, T1 and T2 treatments, respectively. This study indicated that elevated ozone concentration did not significantly affect soil respiration rates in the winter wheat farmland. Elevated ozone concentration, however, significantly reduced the temperature sensitivity of soil respiration.