Soil respiration and its components partitioning in the typical forest ecosystems at the transitional area from the northern subtropics to warm temperate, China

In order to ascertain the carbon emission rate and soil respiration response by its components to changing soil temperature and water content in the five typical forest stands at the transitional area from the northern subtropics to warm temperate, the root-excluded quadrates by trenching were set up to partition soil respiration components and the soil temperature, soil water content and respiration rate in each plot were simultaneously measured over the whole year experiment. The results indicate that respiration rates of the total soil respiration and its different components are higher in summer and autumn than that in spring and winter. The respiration rate is largely controlled by soil temperature when soil temperature is below 15 ℃, while it is clearly limited by soil water content when soil temperature is above 15 ℃ and soil water content is below 0.20 kg·kg-1. However, it is simultaneously affected by both soil temperature and soil water content when soil temperature is above 15 ℃ and soil water content is above 0.20 kg·kg-1. Soil temperature and soil water content can account for 80.36%—94.94% and 7.20%—48.45% of seasonal variation in respiration rates, respectively, suggesting that the effect of soil temperature on soil respiration is greater than that of soil water content. The Q10 values for autotrophic respiration, soil respiration and heterotrophic respiration are 2.49—2.82 , 2.30—2.44 and 2.09—2.35, respectively, in the five stands. The temperature sensitivity of autotrophic respiration is the highest, followed by soil respiration and the heterotrophic respiration is the lowest, regardless of stands. The contribution rates of daily autotrophic respiration in Quercus aliena var.acuteserrata young stand, Quercus aliena var.acuteserrata old stand, broadleaf/coniferous mixed stand, broadleaf mixed forest and Quercus variabilis stand are 35.19%—57.73%, 28.73%—49.24%, 28.67%—49.82%, 24.24%—41.70% and 30.07%—46.22%, respectively. Their annual amounts of carbon release through soil respiration are 1105.15, 779.12, 821.23, 912.19 gC ·m-2·a-1and 899.50 gC·m-2·a-1, respectively. Their annual contribution percentages of autotrophic respiration are 52.89%, 39.77%, 44.17%, 38.15% and 43.26%, respectively, while if taking account of fine root decomposition in root-excluded quadrates, their annual contribution rates of autotrophic respiration increase to 65.56%, 47.95%, 53.80%, 46.83% and 53.86%, respectively. The statistical analysis indicates there is no significant differences in soil respiration rate and the heterotrophic respiration rate among the five stands (p0.05), but the significant differences occur in the autotrophic respiration rate (p0.05). The live fine root biomass accounts for 94.71%of the difference of autotrophic respiration rates among the five stands.