A Study Of The Effects Of Simulated Acid Rain On Soil Respiration In A Secondary Forest

A simulated acid rain (SAR) experiment was conducted in a northern subtropical natural secondary forest from March2010to January2012. A portable soil CO2fluxes system was used to measure soil respiration rates. Soil respiration and heterotrophic respiration were simultaneously measured. Autotrophic respiration was calculated as the difference between soil respiration (Rs) and heterotrophic respiration (Rh). Four SAR treatments, which were CK (dionized water), T1(pH=4.0), T2(pH=3.0) and T3(pH=2.0), were set up in field. Soil temperature and moisture were also measured during respiration measurements. Results indicated that Rh increased with the increase of Rs; a natural logrithmatic equation, which is Rh=1.37751n(Rs)+0.875, could be employed to explain the relationship between Rh and Rs. It could explain90.5%(R2=0.905) variations in Rh. Significantly exponential relationships between Rs/Rh/Ra and soil temperature were observed. The exponential equations with temperature explained about81.6%,80.8%and56.1%variations in Rs, Rh and Ra, respectively, with the p values less than0.01.Mean soil respiration rates for CK, T1, T2and T3treatments were2.86.2.73%2.69.3.05μmol·(m2·s)-1, respectively, in2010, while they were2.24.2.23.2.22.2.16μmol·(m2·s)-1, respectively, in2011. Mean soil respiration rates for CK, T1, T2and T3treatments during the whole measurement period were2.54.2.48.2.45.2.59μmol·(m2·s)-1, respectively. The result showed that SAR did not significantly affect Rs in the northern subtropical natural secondary forest. A Logrithmatic equation could be employed to explained the relationship between Rs and soil temperature; the equation can explain81.6%.76.3%.77.8%and80.4%variations in Rs Q10represents the temperature sensitivity of soil respiration. The Q10values for CK, T1, T2and T3treatments were2.74.2.92.2.73.2.87, respectively. Acid rain did not reduce the Q10values.Mean soil heterotrophic respiration rates for CK, T1, T2and T3treatments were2.00.2.30.2.71.2.48umol·(m2·s)-1, respectively, in2010, while they were1.64.1.79.1.86.1.86μmol·(m2·s)-1, respectively, in2011. Mean soil respiration rates for CK, T1, T2and T3treatments during the whole measurement period were1.81、2.04.2.27、2.16μmol(m2·s)-1, respectively. The acid rain treatment increased Rh. significantly exponential relationships between Rh under different acid rain treatments and soil temperature existed. The Q10values for CK, T1, T2and T3treatments were2.47,2.42,2.68,2.55, respectively. The relationship between Rh under different different acid rain and soil temperature and moisture could be described by the following equations:RCK=0.346e(0.075t+1.093w),RT1=0.456e(0.073t+0.626w), RT2=0.462e(0.082t+0.331w), RT3=0.484e(0.069t+0.891w), where RCk, RT1, RT2and RT3were heterotrophic respiration rates for CK, T1, T2and T3treatments, respectively, and t and w were soil temperature and moisture, respectively. These equations explained83.2%、84.1%.82.9%.79.1%variations in soil heterotrophic respiration for CK, T1, T2and T3treatments, respectively.Ra can be calculated as the difference by Rs and Rh. As no significant differences in Ra were found among3SAR treatments, Ra rates for the three treatments were pooled into one group. Thus, here, there were2groups, which were Ra_CK and R a_SAR, respectively. Respiration rates for Ra_CK and R a_SAR were0.765and0.544μmol·(m2·s)-1, respectively. SAR significantly reduced Ra. Significantly exponential relationships between Ra and soil temperature also existed for both CK and SAR groups. The Q10values are3.572and4.302for both CK and SAR groups, respectively. The relationship between Ra and soil temperature and moisture could be described by the following equations:Ra_CK=0.106e(0.098t+0.428w) and R a SAR=0.054e(0.127t+0.614w)...