Spatial and seasonal variations in soil respiration in a subtropical forest in Okinawa, Japan

Abstract

AbstractTo clarify soil respiration (soil CO2 efflux, Rs) characteristics in a subtropical evergreen broad‐leaved natural forest in Yambaru, Okinawa, Japan, we examined spatiotemporal variation in Rs and its determining factors. We then compared yearly Rs with the value in other forests. The spatial variation in Rs (coefficient of variation [CV] = 38.9%) was not significantly related to temperature or soil water content but was evidently dependent on ground surface litter coverage. Rs was greater in summer (ca. 7–10 μmol m−2 s−1), and its seasonal variation was exponentially related to soil temperature (Q10 = 2.16). As a function of soil temperature, we estimated a yearly mean stand‐scale Rs of 5.17 μmol m−2 s−1, and a total carbon efflux from the soil of 1959 g C m−2 year−1 for 2014. Despite showing similar seasonal patterns as those in temporal forests, the Rs in this ecosystem is very high throughout the year, and the yearly value is much higher for natural mature forests. A mass balance approach suggests that the large amount of belowground carbon allocation of plants contributed to the high CO2 emissions from the soils.