中亚热带4种森林类型土壤活性有机碳的季节动态特征

2011年12月至2012年9月, 在湘中丘陵区杉木(Cunninghamia lanceolata)人工林、马尾松(Pinus massoniana)-石栎(Lithocarpus glaber)针阔混交林、南酸枣(Choerospondias axillaries)落叶阔叶林、石栎(Lithocarpus glaber)-青冈(Cyclobalanopsis glauca)常绿阔叶林1 hm²的长期定位观测样地, 采集0-15 cm、15-30 cm土层土壤样品, 测定土壤微生物生物量碳(MBC)、可矿化有机碳(MOC)、易氧化有机碳(ROC)、水溶性有机碳(DOC)含量, 分析4种森林土壤MBC、MOC、ROC、DOC含量的季节变化特征, 为揭示天然林保护与恢复对土壤有机碳(SOC)库的影响机理过程提供基础数据。结果表明: 森林土壤MBC、MOC、ROC、DOC含量具有明显的季节动态, 且不同森林同一土壤活性有机碳组分的季节变化节律基本一致, MBC、MOC、ROC含量表现为夏、秋季较高, 春、冬季较低; DOC含量表现为春、夏、冬季较高, 秋季最低; 同一森林不同土壤活性有机碳组分含量的季节变化节律不同; 土壤MBC、MOC、ROC、DOC含量与土壤自然含水率、SOC、全N、水解N、全P (除杉木人工林土壤MBC、MOC、ROC外)、速效P含量显著或极显著正相关, 与土壤pH值、全K、速效K含量相关性不显著, 表明不同森林类型外源碳库投入和土壤理化性质的差异是导致不同森林类型土壤活性有机碳含量差异显著的主要原因, 该区域森林土壤活性有机碳各组分含量的季节变化与各森林类型组成树种生长节律及其土壤水分含量和SOC、N、P的可利用性, 以及土壤活性有机碳各组分的来源有关, 森林土壤MBC、MOC、ROC、DOC含量可作为衡量森林土壤C、N、P动态变化的敏感性指标。

Seasonal dynamics of active soil organic carbon in four subtropical forests in Southern China

Aims The objective of this paper was to quantify the seasonal variation of active soil organic carbon in the subtropical forests for better understanding of the underline mechanisms in controlling soil organic carbon storage and dynamics in natural and restored forests in the region. Methods The study was conducted in a one-hectare permanent plot at Dashanchong Forest Park in Changsha County, Hunan Province, China. Four types of subtropical forests were selected as our study sites: (1) Cunninghamia lanceolata plantation, (2) Pinus massoniana-Lithocarpus glaber mixed forest, (3) Choerospondias axillaries deciduous broad-leaved forest, and (4) L. glaber-Cyclobalanopsis glauca evergreen broad-leaved forest. The soil samples were taken from 0-15 cm and 15-30 cm depths within each of the forests from December 2011 to September 2012. Soil microbial biomass carbon (MBC), mineralized organic carbon (MOC), readily oxidized carbon (ROC), and dissolved organic carbon (DOC) were analyzed for their seasonal changes. Important findings There existed a considerable seasonal variations of soil MBC, MOC, ROC, DOC among the forests, with a similar patterns of active organic carbon fraction. Soil MBC, MOC and ROC were significantly higher in the summer and the autumn than those in the spring and winter, while soil DOC was higher in the spring, summer and winter than that in the autumn. The seasonal variations of different active organic carbon fractions appeared different within the same forest type. Significantly-positive correlations were found between soil MBC, MOC, ROC, DOC and soil moisture content, soil organic carbon (SOC), total N, hydrolysis N, total P (except for MBC, MOC and ROC in Cunninghamia lanceolata plantation), available P, but not between soil MBC, MOC, ROC, DOC concentrations and soil pH, total K and available K. The results indicated that the differences of exogenous carbon devotion, physicochemical properties were responsible for the significant differences of soil active organic carbon, and the growth rhythm of tree species, soil moisture content, the availability of nutrient (SOC, N and P), and the sources of soil active organic carbon fractions made a major contribution to seasonal variations of soil active organic carbon. Soil MBC, MOC, ROC, and DOC could be used as sensitivity indexes to assess the dynamics of soil C, N and P.