滇南喀斯特断陷盆地土地利用方式对土壤有机碳及其活性组分的影响

土地利用方式是影响土壤有机碳库的重要因素，为探究喀斯特断陷盆地土壤有机碳库对土地利用方式及环境因素的响应，以滇南喀斯特地区5种典型土地利用方式(耕地、草地、灌丛、人工林、天然林)为研究对象，分析不同土地利用方式土壤有机碳(SOC)及活性有机碳(LOC)组分，即可溶性有机碳(DOC)、易氧化性有机碳(EOC)及微生物量碳(MBC)的含量、储量及分配比例在土壤垂直剖面(0-60 cm)的变化特征。结果表明：5种土地利用方式的SOC含量随土层深度的增加逐渐降低，其储量依次为灌丛(191.77 t/hm²)、草地(166.86 t/hm²)、耕地(142.47 t/hm²)、人工林(134.31 t/hm²)和天然林(102.62 t/hm²)；EOC和MBC的平均含量及储量均以草地及灌丛最高、人工林及天然林次之，二者在土壤垂直剖面上与SOC含量的变化特征一致，但EOC和MBC含量在土层间的下降幅度大于SOC；土地利用方式和土层深度对DOC无显著影响(P>0.05)；活性有机碳的分配比例受土地利用方式及土层深度的显著影响(P<0.01)，其中人工林的EOC/SOC和MBC/SOC显著低于草地、灌丛及天然林。通径分析指出SOC和EOC主要受C/P比、全磷、砂粒和交换性钙的影响，砂粒和C/P比是影响MBC的主要因子。研究阐明在喀斯特断陷盆地地区EOC和MBC对土地利用方式的响应比SOC更敏感。另外，今后在土壤碳库的研究中应更多关注土壤磷和物理结构对其的影响。

Effects of land use types on soil organic carbon and soil labile organic carbon in karst faulted basin of southern Yunnan

Land use types are important factor affecting soil organic carbon pool by regulating carbon fluxes between the terrestrial biosphere and atmosphere. Five typical land use types including farmland, grassland, shrubland, artificial forest and natural forest were selected to explore the responses of soil organic carbon pool to land use types and environmental factors in the karst faulted basin, China. The contents, stocks and distribution ratios of soil organic carbon (SOC) and labile organic carbon (LOC), namely dissolve organic carbon (DOC), easily oxidated carbon (EOC) and microbial biomass carbon (MBC), were analyzed along soil profiles (0-60 cm) under different land use types. The results showed that the SOC contents was 4.83-69.01 g/kg, which decreased with soil depths under the five land use types. The SOC stocks under five land use types were in descending order of shrubland (191.77 t/hm²), grassland (166.86 t/hm²), farmland (142.47 t/hm²), artificial forest (134.31 t/hm²) and natural forest (102.62 t/hm²). The contents and stocks of EOC and MBC were the highest in grassland and shrubland on average, followed by artificial forest and natural forest. The variation characteristics of EOC and MBC in the soil profile were consistent with SOC, but the decline rates of EOC and MBC contents in soil layers were obviously higher than SOC. Land use types and soil depths had no significant effects on DOC contents with a range of 0.84-1.62 g/kg under the five land use types. The ratios of labile organic carbon to soil organic carbon were affected by land use types and soil depths (P<0.01). The EOC/SOC and MBC/SOC ratios of artificial forest were lower than those of grassland, shrubland and natural forest. Pearson correlation analysis showed that SOC was positively correlated with LOC (P<0.01). In addition, SOC and LOC were positively correlated with total nitrogen, C/P ratio, C/N ratio, exchangeable calcium, soil water content, clay, sand and so on (P<0.05). Path analysis further identified that the variation in the SOC and EOC were significantly related to the changes of C/P ratio, total phosphorus, sand and exchangeable calcium and MBC was mainly influenced by sand and C/P ratio. These findings suggested that the land use types had significant effects on SOC, EOC and MBC contents and the responses of EOC and MBC to land use types were more sensitive than SOC in karst faulted basins. Moreover, more attention should be paid to soil physical structure and phosphorus availability in the future research on soil organic carbon pool.