COMPARISON OF SOIL RESPIRATION IN BROAD_LEAVED KOREAN PINE FOREST AND RECLAIMED CROPLAND IN CHANGBAI MOUNTAINS, CHINA

Abstract

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 CO_(2). 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. 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 CO_(2) 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. 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 CO_(2) 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. Q_(10) values of soil respiration averaged 2.92 for forest plots and 3.07 for cropland plots, which may be overestimated. 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.