Spatial Heterogeneity Of Soil Respiration In A Subtropical Evergreen Broad-leaved Forest On Tiantong, Zhejiang

The concentration of CO2 in the atmosphere has risen from 285 ppmv in 1850 to 398 ppmv in 2012, since the industrial revolution began. As a consequence, the earth’s surface temperature has increased by about 0.78℃ over the past century and is projected to increase by another 1.1-6.4℃ by the end of this century. A large number of studies have shown that the dynamic change in global carbon cycle has a close relationship with climate change and human activities, especially the burning of fossil fuels and land use change. Terrestrial ecosystems, which were estimated to have sequestered nearly 30% of the C released by anthropogenic activities from 1960 to 2008, are an important link of atmospheric CO2 in the global carbon cycle and play a crucial role in mitigating climate change.However, whether the natural sink will be sustainable into the future is under debate due to the complex responses of terrestrial ecosystem to global change. Therefore, it is imperative to understand the response and feedback mechanisms of terrestrial ecosystems to climate change for guiding international efforts to stabilise CO2 concentration.Soil respiration is the second largest flux of carbon to the atmosphere in the terrestrial carbon cycle after gross primary production. Therefore, a correct measurement of soil respiration is essential to evaluate ecosystem carbon budget. However, it is difficult to accurately monitor soil respiration in natural ecosystems due to the high spatial and temporal variability. Thus, optimizing sampling strategy and the number of sampling points are necessary to investigate the carbon cycle in terrestrial ecosystems. In order to optimize sampling strategies and the number of sampling points of soil respiration measurements,we tested the effectiveness of random and stratified sampling with a Monte Carlo simulation with measured soil respiration rate in 99 soil collars (three plots) with a LI-8100 soil respiration system in a subtropical evergreen broad-leaf forest on Tiantong, Zhejiang province, from August 2013 to January 2014. The results showed that mean soil respiration was not significantly different among the different sampling strategies. However, the coefficient of variation (CV) of mean soil respiration decreased with sample size. Stratified sampling is an alternative to random sampling as a method to reduce the number of sampling points by 36.4% and CV by 16.7% in the sampling process compared to random sampling in growing season, respectively, and by 22.2% and 8.7% in non-growing season. The two different sampling strategies produced the similar mean value of R10 and Q10 values, which were 1.0 μmol CO2/m2s and 2.0, respectively. The CV of the parameters decreased with the sample size but insignificant difference between two different sampling strategies.To examine the effects of drought and disburbance on spatial heterogeinity of soil respiration, we measured soil respiration rates in the three treatments (drought, disturbance and control) with a LI-8100 soil respiration system from June 2013 to May 2014. The results showed that mean soil respiration was not significantly different among the different treatmens at this period. However, disturbance has a significant influence on the CV of mean soil respiration, which increased 100% in non-growing season. Disturbance has a significant influence on the Rio value and its CV, which increased by 33% and 109%, respectively, while drought only decreased the CV of R10 by about 48%. However, the Q10 value and its CV exhibited the different effects in respones to disturbance which decreased 20% and increased of 100%. Drought only decreased the CV of Q10 about 45%.