Effect of thinning on partitioned soil respiration in a young Pinus tabulaeformis plantation during growing season

Understanding soil respiration (Rs) response to thinning is an important component of our understanding of belowground carbon (C) dynamics and evaluating effects of forest management on C cycling. Therefore, we partitioned Rs into heterotrophic respiration (Rh) and autotrophic respiration (Ra) using trenched plots in a 20 year-old Pinus tabulaeformis plantation, subjected to varying thinning intensities, in Shanxi Province, China. Soil respiration was measured using an infrared gas exchange analyzer in untrenched and trenched plots. Rates of soil respiration were measured twice a month from May to October in 2011 and 2012, while soil temperature and moisture were obtained using temperature and moisture probes and data loggers. Rs was measured in untrenched plots and Rh in trenched plots. Mean Rs and Rh values were significantly greater in stands subjected to heavy thinning (HT) (Rs = 2.79 μmol CO2 m−2 s−1, Rh = 2.24 μmol CO2 m−2 s−1) than in the control (CK) (Rs = 2.29 μmol CO2 m−2 s−1, Rh = 1.81 μmol CO2 m−2 s−1) and low thinned stand (LT) (Rs = 2.48 μmol CO2 m−2 s−1, Rh = 1.80 μmol CO2 m−2 s−1). The mean Ra was greater in the thinned stands (Ra = 0.69, 0.58, 0.55 μmol CO2 m−2 s−1 in LT, moderate thinned stand (MT) and HT) than CK (Ra = 0.48 μmol CO2 m−2 s−1), possibly the result of increased productivity and root growth in thinned stands. The relative proportion of Rh to Rs averaged 71.6-79.7% over the four thinned stands. Temperature sensitivity (Q10) values of Rh ranged from 2.16 to 2.75 in the various thinning intensities, with the highest Q10 value in the control stand. Temperature sensitivity of Ra was also affected by thinning ranging from 1.34 to 1.84. The model with the best fitted temperature and moisture factors explained 66.7-77.3% of the variation in Rh and 30.2-46.4% in Ra among the four thinned stands during two growing seasons.