红壤侵蚀地不同人工恢复林对土壤总有机碳和活性有机碳的影响

土壤有机碳尤其是活性有机碳可快速反映土壤肥力和土壤质量的恢复程度。研究了南方红壤侵蚀地3种典型人工恢复林(马尾松与阔叶复层林(Pinus massoniana-broadleaved multiple layer forest(PB))、木荷与马尾松混交林(Schima superba-Pinus massoniana mixed forest(SP))、阔叶混交林(broad-leaved mixed forest(BF)))土壤(0—60 cm)总有机碳和不同活性有机碳的垂直分布特征及其差异。结果表明:不同恢复林分土壤总有机碳(SOC)含量和有机碳储量均表现为PBSPBF,均随土层深度的增加而逐渐降低;土壤表层有机碳富集系数为0.49—0.55,表明表层土壤具有较高的有机碳恢复水平和保持强度。不同林分土壤易氧化有机碳(ROC)、水溶性有机碳(DOC)和微生物量碳(MBC)含量变化范围为0.92—9.17 g/kg、535.89—800.46 mg/kg和27.24—261.31 mg/kg,且均随土层深度的增加而降低,土壤活性有机碳含量总体以BF较高。土壤活性有机碳分配比例以ROC/SOC最高,DOC/SOC次之,MBC/SOC最低,且随土层深度的增加,ROC/SOC的值呈逐渐降低趋势,DOC/SOC的值却呈逐渐升高趋势,MBC/SOC(微生物熵)则变化规律不明显;不同林分间土壤活性有机碳分配比例以BF最高,表明阔叶混交林更有利于活性碳的积累。因此,对于红壤侵蚀地森林恢复初期,可适当密植和立体种植,以提高土壤碳储量和土壤肥力,并在马尾松等先锋树种林分中补植阔叶树种,以增加土壤活性有机碳含量,从而有利于退化生态系统土壤速效养分和土壤功能的快速恢复。

Effects of artificially restored forests on soil organic carbon and active organic carbon in eroded red soil

Measuring soil organic carbon (SOC), especially active organic carbon, can be used to quickly evaluate the recovery of soil fertility and quality. Therefore, we performed field and laboratory experiments to investigate the vertical distribution of total and active organic carbon in different layers (0-60 cm) of eroded red soil in three typical artificially restored forests, i.e., Pinus massoniana-broadleaved multiple layer forest (PB), Schima superba-Pinus massoniana mixed forest (SP), and broad-leaved mixed forest (BF). The SOC and organic carbon storage in different forests decreased with increasing soil depth and were ranked as follows:PB > SP > BF. The accumulation coefficients of surface SOC ranged from 0.49 to 0.55, which indicated that the surface soil had a high capacity to recover and maintain organic carbon. Soil readily oxidized organic carbon (ROC), dissolved organic carbon (DOC), and microbial biomass carbon (MBC) were calculated as 0.92-9.17 g/kg, 535.89-800.46 mg/kg, and 27.24-261.31 mg/kg, respectively, exhibiting reductions with the increasing soil depth. The content of active organic carbon was generally higher in the BF; and ROC constituted the largest proportion of active organic carbon (i.e., ROC/SOC), followed by DOC (i.e., DOC/SOC), whereas MBC accounted for the smallest proportion (i.e., MBC/SOC). As soil depth increased, ROC/SOC and DOC/SOC exhibited decreasing and increasing trends, respectively, whereas MBC/SOC (microorganism entropy) varied erratically. The allocation to ROC/SOC was higher in the BF than in the other two forest types, which suggested that broad-leaved mixed forest is prone to the accumulation of active organic carbon. Therefore, we could develop dense planting and stereoscopic planting techniques to use at early stages of forest restoration, in order to improve the carbon density and fertility of degraded red soil, and broad-leaved species could be planted into pioneer coniferous forests, such as those dominated by Pinus massoniana, in order to increase the active organic carbon content and, therefore, facilitate the recovery of available nutrients and soil function.