鼎湖山森林土壤活性碳及惰性碳沿海拔梯度的变化

对鼎湖山3个不同海拔高度下的沟谷雨林(LA)、低地常绿阔叶林(MA)和山地常绿阔叶林(UA)的土壤活性碳库和惰性碳库进行了研究。结果表明:(1)土壤总碳库仅在30—45 cm土层中存在显著差异且碳库大小随着海拔的增加而增加。(2)土壤微生物生物量碳(MBC)碳库在0—15 cm是LA和MA显著大于UA,在30—45 cm是MA和UA显著高于LA,在45—60 cm土层中MA最大。水溶性碳(WSOC)和颗粒碳(POC)碳库均不随海拔高度而改变。WSOC碳库占总碳库的百分比仅在30—45cm土层中存在差异且大小顺序为:LAUAMA,POC碳库占总碳库的百分比仅在土层15—30 cm上存在显著差异且MA比值最大。易氧化性碳(ROC)碳库及占总碳库百分比都是在表层土壤(0—15 cm)中产生显著变化,且UA极显著地大于LA和MA。(3)惰性碳(RC)碳库仅在深层土壤中存在显著差异且MA中RC碳库最大,UA次之,LA最小。RC碳库占总碳库比值仅在表层土壤0—15 cm存在显著差异且UA最大。表层土壤中ROC碳库和RC碳库占总碳库百分比的增加是导致中高海拔森林土壤总碳库最大的主要原因。(4)不同海拔高度上森林土壤理化性质与土壤碳库组成存在显著相关,土壤理化性质的改变是引起不同海拔高度森林土壤碳库组成变化的重要原因。

Altitudinal changes in active and recalcitrant soil carbon pools of forests in the Dinghu Mountains

Active and recalcitrant carbon (RC) fractions are two important components of soil organic carbon (SOC). The active SOC fractions with short turnover times, including microbial biomass carbon (MBC), water-soluble organic carbon (WSOC), particulate organic carbon (POC), and readily oxidizable carbon (ROC), are considered biologically available sources of carbon (C) and respond faster to environment changes than total SOC. Recalcitrant carbon with long turnover times may be indicative of the long-term positive feedback of soil decomposition in a warming world. Study of these two C fractions can help us to understand the dynamics of SOC. In this study, our aim was to evaluate the dynamics of SOC along an elevation gradient in Southern China. To this end, an experiment was conducted in the Dinghu Mountains (also called Dinghushan Nature Reserve) of subtropical China to investigate changes in the active and recalcitrant soil carbon pools in a ravine rainforest (LA), a lowland monsoon evergreen broadleaf forest (MA), and an upland monsoon evergreen broadleaf forest (UA), which represent low, middle, and high altitudes, respectively. In all three forests, active and recalcitrant C were measured at four soil depths (0-15, 15-30, 30-45, and 45-60 cm), and physicochemical properties of the soil were assessed. The results showed that water content, total nitrogen (N), hydrolysable-N, and available potassium decreased with an increase in altitudinal gradient. The C/N ratio similarly increased with an increase in altitudinal gradient, and the ratio was significantly higher in UA than in MA and LA. pH and bulk density were also highest in UA and were in the order of MA< LA< UA. The results also suggested that C stocks increased with an increase in altitudinal gradient; however, a significant difference among the three forest types was only found in the 30-45 cm soil layer. The MBC pool in the 0-15 cm soil layer was significantly higher in LA and MA than in UA; however, the pool in the 30-45 cm soil layer was significantly higher in MA and UA than in LA, and the highest value of MA was recorded in the 45-60 cm soil layer. In contrast, neither the WSOC pool nor the POC pool of the forests showed altitudinal variation. The percentage of WSOC pool to C stock in the 30-45 cm soil layer of the three forests was in the order of LA >UA >MA. The percentage of POC pool to C stock among the three forests differed significantly only in the 15-30 cm soil layer and the value was highest in MA. The size of the ROC pool and the percentage of ROC pool to C stock in the 0-15 cm soil layer were significantly higher in UA than in LA and MA. Among the three forests, the size of the RC pool was in the order of MA >UA >LA, although a significant difference was found only in the 30-45 cm and 45-60 cm soil layers. The percentage of RC pool to C stock in the 0-15 cm soil layer was highest in UA. In conclusion, the increasing ROC pool and the percentage of RC pool to C stock in the surface layer along the altitudinal gradient contribute to the largest stock of carbon in UA. Furthermore, the significant relationship between C fraction pools and soil physicochemical properties suggested that changes in soil physicochemical properties might be an important factor contributing to alterations in the C constitution of forests soils along the altitudinal gradient.