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 thestorage 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.