红壤退化地森林恢复后土壤有机碳对土壤水库库容的影响

亚热带红壤侵蚀退化地实施生态恢复后生物生产力恢复迅速,但土壤尤其是土壤水库的功能并未获得同步恢复,导致土壤水库对于降水和地表径流的调节能力低下,区域性洪涝灾害和季节性干旱依然突出。采用野外调查和室内分析相结合的方式,研究了南方红壤侵蚀退化地典型植被恢复类型(马尾松与阔叶树复层林、木荷与马尾松混交林、阔叶混交林)0—60cm土层土壤水库各种库容差异,以及土壤总有机碳和活性有机碳密度分布特征,采用典型相关分析方法对土壤水库库容与土壤有机碳密度两组指标进行相关分析。结果表明:随着土层深度的增加,各森林恢复类型死库容呈上升趋势,兴利库容和最大有效库容呈下降趋势,防洪库容变化趋势不明显,木荷与马尾松混交林兴利库容略高。不同森林恢复类型同一土层土壤总有机碳密度均表现为马尾松与阔叶树复层林木荷与马尾松混交林阔叶混交林,而活性有机碳密度则以阔叶混交林最大。典型相关分析表明,土壤有机碳水平对土壤水库库容的增加具有显著的因果影响关系(P=0.01),其中对有机碳水平起到主导性贡献作用的是水溶性有机碳。因此,对于退化红壤地森林恢复初期,可通过适当密植和立体种植,提高林地生物量和土壤碳密度,并在马尾松等先锋树种针叶林分中补植阔叶乔灌木,以增加土壤活性有机碳含量,增大土壤水库容量,从而有利于土壤水库结构和功能以及退化生态系统的快速恢复。

Effects of soil organic carbon on soil reservoir capacity after forest restoration in degraded red soil

In a degraded red soil in subtropical China, the soil reservoir did not show a synchronized recovery with the rapid increase of biomass, resulting in frequent floods and droughts at the regional scale. The aim of this study was to determine the changes in soil organic carbon and soil reservoir capacity and their relationship following afforestation. Based on field investigations and lab assays, the differences of soil reservoir capacity in the 0-60 cm soil layer and the distribution characteristics of total organic carbon density and active organic carbon density were studied in three typical types of forest restoration in southern degraded red soil, i.e. Pinus massoniana and broad-leaved tree multiple layer forest(PB), Schima superba-Pinus massoniana mixed forest(SP), and broad-leaved mixed forest(BF). The correlation between soil reservoir capacity and soil organic carbon density was also analyzed using a canonical correlation analysis model. The results showed that with increased soil depth, all three forest restoration types exhibited growth trends in soil invalid capacity, while the storage capacity and the flood control capacity showed downward trends. However, the trend of flood control capacity was not obvious. Additionally, the storage capacity in the SP was higher than that in other forests. The total organic carbon density in the same layers was ranked as follows:PB > SP > BF. The active organic carbon density was largest in BF, suggesting that BF was propitious to the accumulation of active organic carbon. The soil organic carbon was positively correlated with soil reservoir capacity (P=0.01), and soil dissolved organic carbon played the dominant role for the increase of organic carbon levels. As a result, we could develop close-planting and stereoscopic planting appropriately to improve plant biomass and soil carbon density, and then interplant broad-leaved species with pioneer coniferous tree species such as Pinus massoniana at the early stage of forest restoration in degraded red soil. This strategy can increase the active soil organic carbon content and enhance soil reservoir capacity, which is conducive to the rapid recovery of the eroded soil and ecosystem.