SOIL CO2 EFFLUX IN RELATION TO SOIL TEMPERATURE AND RELATIVE HUMIDITY IN GMELINA, MAHOGANY AND PINE STANDS IN MALAYSIA

Soil CO2 efflux in mature plots of Gmelina arborea and Swietenia macrophylla (exotic broad-leaved trees) and Pinus caribaea (exotic conifer) was measured monthly in relation to soil temperature, air temperature and relative humidity from January till March 2016. Soil bulk density, pH, total C, total N and soil organic C were also measured at 0-15 and 15-30 cm depths. Soil CO2 efflux was significantly different between plots: gmelina > mahogany > pine (0.76 +/- 0.04, 0.49 +/- 0.02 and 0.40 +/- 0.01 g CO2 m(-2) h(-1) respectively). Regression analysis revealed significant positive correlation of soil CO2 efflux with soil temperature in the gmelina plot but no correlation with soil relative humidity in all three plots. Significant negative correlation was found between soil CO2 efflux and soil temperature in the pine plot, which indicated the influence of other factors on soil CO2 efflux in that plot. Monthly variations in soil relative humidity and soil properties of gmelina and pine plots were examined for possible influences on soil CO2 efflux and temperature sensitivity (Q(10)). Q(10) of soil CO2 efflux in the gmelina plot (1.19) was far higher than in the mahogany and pine plots (0.79 and 0.70 respectively).