Phenological season-dependent temperature effects on soil respiration in a subtropical Pinus massoniana forest

Abstract

Soil respiration (Rs) is a major flux of the carbon cycle in forest ecosystems, and time-scale-dependent variations in Rs are critical for evaluating carbon sequestration capacity, which is not fully understood. In this study, we investigated diurnal, phenological seasonal and annual variations in Rs over three years (2015–2017) in a Pinus massoniana forest in subtropical China based on automated Rs chamber measurements at hourly intervals. Soil temperature and moisture at the 5 cm soil depth were simultaneously measured, and precipitation data were collected to examine their influences on Rs. Our results showed that the daytime mean and total Rs were significantly higher than their respective nighttime counterparts over the course of a year. Daily Rs ranged from 0.42 to 4.63 µmol CO2m−2s−1, with the maximum value in August and the minimum value in February. The temperature sensitivity of Rs (Q10) did not significantly differ between daytime and nighttime, but it was significantly higher at the end-season (autumn) than during the nongrowing season. The effects of soil temperature but not soil moisture on Rs varied with phenological season, showing significant soil temperature effects in the active phenological seasons (spring and autumn) but not in the steady-state phenological seasons (growing season and nongrowing season). This seasonal-dependent temperature effect on Rs may be a result of the effect of rapidly changing temperature in spring and autumn on leaf phenology, plant growth and physiological activity, soil microbial and enzyme activity, and litter decomposition rate. Our results suggest that long-term data covering monthly, seasonal, and annual variations in Rs and its biotic and abiotic environments are needed for more precisely calculating and predicting the carbon balance of forest ecosystems on various time scales.