长白山红松针阔混交林与开垦农田土壤呼吸作用比较

 利用静态箱式法测定长白山红松（Pinus koraiensis）针阔混交林及其开垦农田的土壤呼吸作用。结果表明，两者土壤呼吸作用的日动态和季节动态均主要受温度影响，农田土壤呼吸作用的日变化极值出现时间较林地提前，最大值出现在12∶00左右，比林地提前6 h左右，最小值在凌晨5∶00 左右，早于林地2～3 h；在生长季，土壤呼吸速率与10 cm土壤含水量关系不显著，而与土壤5 cm温度呈显著的指数关系；农田土壤温度高于林地，但在整个生长季（5～9月）林地土壤释放CO₂量(2 674.4 g·m^－2)约为农田(1 285.3 g·m^－2)的2倍；观测期间，农田土壤呼吸速率占 林地的比例范围在23.4%～76.3%之间，说明土壤呼吸作用还受不同土地利用方式下植被类型等的影响。农田和红松针阔混交林土壤呼吸作用的Q₁₀值分别为3.07和2.92，农田土壤呼吸作用的Q₁₀ 值估计可能偏大。森林转变为农田后，环境、生物因子以及土壤养分含量和物理性质发生改变，共同影响土壤呼吸作用的强度和动态特征。

COMPARISON OF SOIL RESPIRATION IN BROAD-LEAVED KOREAN PINE FOREST AND RECLAIMED CROPLAND IN CHANGBAI MOUNTAINS, CHINA

Background and Aims Soil respiration is a major flux in the global carbon cycle. A small change in soil respiration may result in a large increase of atmospheric CO₂. Land conversion has the greatest impact on the terrestrial ecosystems among the components of global change, but the effects on soil respiration are inadequately understood. Our objective was to examine the response of soil respiration to conversion from forests to agricultural lands, using broad-leaved Korean pine forest and reclaimed cropland in the Changbai Mountains.  Methods We used an Infra-red Gas Analyser (IGA) linked to a 50 cm×50 cm×15 cm chamber without a bottom. Three 50 cm×50 cm steel frames were inserted to a soil depth of 3-5 cm in randomly selected plots one day prior to measurement. When measuring, the chamber was put on the steel frame to make a closed container capturing CO₂ from the soil surface and piping the gas of chamber through the IGA. We repeated measurements every 15 days during the growing seasons from 2003 to 2005.  Key Results Diurnal and seasonal variations of soil respiration were mainly affected by soil temperatures. Soil respiration rate reached a maximum around noon in cropland plots, about six hours earlier than that in forest plots. Minimum rates occurred at 5∶00 am in cropland plots and 7∶00-8∶00 am in forest plots. Diurnal variations were driven mostly by temperature. During the growing season, soil respiration had a statistically significant exponential relationship with soil temperatures at 5 cm depth, but was weakly correlated with soil volumetric water contents at 10 cm depth. Although soil temperatures in cropland plots were higher than those in forest plots, soil CO₂ efflux in forest was about twice that in cropland during the growing season (May to September). During the period of measurement, soil respiration rate of cropland ranged from 23.4% to 76.3% that of forest. Therefore, vegetation types were another factor affecting soil respiration due to the change of land-use. Q₁₀ values of soil respiration averaged 2. 92 for forest plots and 3.07 for cropland plots, which may be overestimated.  Conclusions Differences in soil respiration rates and patterns between forests and croplands result from changes in abiotic and biotic factors, including soil physicochemical properties, due to land-use change.