黄土台塬不同土地利用方式下土壤有机碳分解特性

Decomposition of Soil Organic Carbon in Loess Tableland Relative to Type of Land Use

为了探讨土地利用方式对土壤有机碳分解的影响,以黄土台塬的乔木林地、灌木林地、天然草地和耕地等不同植被类型土壤为研究对象,对土壤有机碳矿化分解特征进行分析.结果表明,不同土地利用方式下土壤有机碳含量、有机碳密度、土壤可矿化碳含量和有机碳矿化速率均表现为天然草地和灌木林地较高,耕地最低;而土壤有机碳矿化率和呼吸速率表现为耕地和乔灌混交林地较高,灌木林地和天然草地较低.在土壤孵化的1 575 h内,不同土地利用方式下土壤矿化过程均可划分为4 个阶段：0.5～5 h（第1 阶段）、5～111 h（第2 阶段）、111～399h（第3 阶段）和399～1 575 h（第4 阶段）;前399 h 是可矿化碳排放的主要时段,前111 h 是土壤可矿化碳排放速率最大且排放速率下降速度最快的主要时段;总体上,土壤可矿化碳累积排放量随培养时间的延长呈增加趋势,可矿化碳累积排放速率则逐渐降低.土壤有机碳矿化速率随土层深度的增加而递减.土壤有机碳矿化分解速率与有机碳总量有关,土壤呼吸与有机碳总量、矿化碳总量相关性不显著（P〉0.05）.

In order to explore effects of land use on decomposition of soil organic carbon in the Loess Plateau, soil sam.ples were collected from lands different in land use, woodlot, shrubland, natural grassland and farmland for analysis of soilorganic carbon and its mineralization characteristics. Results show that no matter whether in soil organic carbon content,organic carbon density, mineralizable carbon content and organic carbon mineralization rate, natural grassland, shrublandand forestland are all higher than farmland; while in soil organic carbon mineralization rate and soil respiration rate, farm.land and arbor.shrub land are higher than natural grassland and shrubland. During the 1 575 h of soil incubation, soil min.eralization, regardless of land use,can be divided into four phases： 0.5-5 h （first phase）, 5-111 h （second phase）,111-399 h （third phase）, 399-1 575 （fourth phase）. The first 399 h is the main period when minerlizable carbon is e.mitted; during the first 111 h, soil mineralization carbon emission rate peaks and drops the fastest too; as a whole, cumu.lative soil mineralizable carbon emission increased and cumulative emissions rate gradually decreased with the incubationgoing on. Soil organic carbon mineralization rate is closely related to the content of total organic carbon, and soil respirationis not so related to the content of total organic carbon or total mineralized carbon.