黄土丘陵区土地利用变化对深层土壤活性碳组分的影响

Effects of Land Use Change on Soil Active Organic Carbon in Deep Soils in Hilly Loess Plateau Region of Northwest China

土壤活性有机碳组分对土地利用变化的响应规律已成为当前土壤碳和养分循环研究的一个热点.本文以黄土丘陵子午岭林区为研究区,通过分析天然乔木林转变为人工乔木林、天然乔木林转变为农田,天然灌木林转变为农田以及撂荒后土壤活性有机碳含量及其在土壤剖面上分布的差异,与浅层(0~60 cm)土壤对比,分析土地利用变化对深层土壤(60~200 cm)活性有机碳组分的影响.结果表明:1土壤易氧化性碳(LOC)和土壤微生物量碳(MBC)含量主要集中在0~60 cm土层,分别占0~200 cm土层含量的49%~66%和71%~84%.不同土地利用类型0~60 cm土层LOC和MBC含量差异显著,深层土壤含量差异不显著.2土地利用变化对土壤活性有机碳影响显著,浅层比深层反映敏感.天然乔木林转变成人工乔木林和农田、天然灌木林转变成撂荒地和农田这4种土地利用转变方式下,浅层土壤LOC分别减少了10%、60%、29%、40%,深层分别减少了9%、21%、12%、1%;浅层土壤MBC分别减少了24%、73%、23%、56%,深层土壤MBC分别减少了25%、18%、8%、11%.3土地利用变化改变了活性有机碳占总有机碳的分配比例.天然乔木林和天然灌木林转变成农田浅层土壤LOC/SOC比例增加,深层差异不大;天然灌木林转变为农田,浅层土壤MBC/SOC降低,深层差异不大.结果说明土壤活性有机碳含量和分配比例受土地利用变化的影响,与浅层相比,深层土壤有机碳具有较大的稳定性.

Response of soil active organic carbon to land-use change has become a hot topic in current soil carbon and nutrient cycling study. Soil active organic carbon distribution characteristics in soil profile under four land-use types were investigated in Ziwuling forest zone of the Hilly Loess Plateau region. The four types of land-use changes included natural woodland converted into artificial woodland,natural woodland converted into cropland,natural shrubland converted into cropland and natural shrubland converted into revegetated grassland. Effects of land-use changes on soil active organic carbon in deep soil layers( 60-200 cm) were explored by comparison with the shallow soil layers( 0-60 cm). The results showed that: 1The labile organic carbon( LOC) and microbial carbon( MBC) content were mainly concentrated in the shallow 0-60 cm soil,which accounted for 49%-66% and 71%-84% of soil active organic carbon in the profile( 0-200 cm) under different land-use types. Soil active organic carbon content in shallow soil was significantly varied for the land-use changes types,while no obvious difference was observed in soil active organic carbon in deep soil layer. 2Land-use changes exerted significant influence on soil active organic carbon,the active organic carbon in shallow soil was more sensitive than that in deep soil. The four types of land-use changes,including natural woodland to planted woodland,natural woodland to cropland,natural shrubland to revegetated grassland and natural shrubland to cropland,LOC in shallow soil was reduced by 10%,60%,29%,40%,and LOC in the deep layer was decreased by 9%,21%,12%,1%,respectively. MBC in the shallow soil was reduced by 24%,73%,23%,56%,and that in the deep layer was decreased by 25%,18%,8% and 11%,respectively. 3 Land-use changes altered the distribution ratio of active organic carbon in soil profile. The ratio between LOC and SOC in shallow soil increased when natural woodland and shrubland were converted into farmland,but no obvious difference was observed in deep soil. The ratio of MBC /SOC in shallow soil decreased when natural shrubland was converted into farmland,also,no significant difference was detected in the ratio of MBC / SOC for other land-use change types. The results suggested that land-use change exerted significant influence on soil active organic carbon content and distribution proportion in soil profile. Soil organic carbon in deep soil was more stable than that in shallow soil.