Soil CO2 Flux in Different Types of Forests Under a Subtropical Microclimatic Environment

The flux of carbon dioxide (CO2) from soil surface presents an important component of carbon (C) cycle in terrestrial ecosystems and is controlled by a number of biotic and abiotic factors. In order to better understand characteristics of soil CO2 flux (FCO2) in subtropical forests, soil FCO2 rates were quantified in five adjacent forest types (camphor tree forest, Masson pine forest, mixed camphor tree and Masson pine forest, Chinese sweet gum forest, and slash pine forest) at the Tianjiling National Park in Changsha, Hunan Province, in subtropical China, from January to December 2010. The influences of soil temperature (T-soil), volumetric soil water content (theta(soil)), soil pH, soil organic carbon (SOC) and soil C/nitrogen (N) ratio on soil FCO2 rates were also investigated. The annual mean soil FCO2 rate varied with the forest types. The soil FCO2 rate was the highest in the camphor tree forest (3.53 +/- 0.51 [mu mol m(-2) s(-1)), followed by, in order, the mixed, Masson pine, Chinese sweet gum, and slash pine forests (1.53 +/- 0.25 mu mol m(-2) s(1)). Soil FCO2 rates from the five forest types followed a similar seasonal pattern with the maximum values occurring in summer (July and August) and the minimum values during winter (December and January). Soil FCO2 rates were correlated to T-soil and soil, but the relationships were only significant for T-soil. No correlations were found between soil FCO2 rates and other selected soil properties, such as soil pH, SOC, and C/N ratio, in the examined forest types. Our results indicated that soil FCO2 rates were much higher in the evergreen broadleaved forest than coniferous forest under the same microclimatic environment in the study region.