持续放牧和围封对科尔沁退化沙地草地碳截存的影响

研究了科尔沁退化沙地草地持续放牧和围封恢复下土壤-植物系统的碳(C)贮存,以揭示草地管理对C动态的影响.结果表明,0～15cm土壤OC和植物系统贮存的C(包括初级生产固定的C,立枯和地表凋落物C和根系C)贮量大小为:围封10年草地(584g·m^-2和309 g·m^-2)＞围封5年草地(524g·m^-2和146g·m^-2)＞持续放牧草地(493g·m^-2和95 g·m^-2).在围封10年,围封5年和持续放牧草地中,0～15cm土壤贮存C分别占各自土壤-植物系统C的65.3%,78.2%和83.9%.在风蚀严重的科尔沁沙地,持续放牧对植被,土壤及其周围环境有极严重的恶化作用.采取围封恢复措施后,植被恢复和凋落物积累使土壤免遭风蚀,也显著增加了土壤有机质的输入,因而显著作用于大气C的截存.但排除家畜放牧的长期围封使植物C向土壤C的再循环受到限制,截存的大部分C以凋落物的形式积存在土壤表面,需进一步深入研究围封的时间尺度.研究结果表明,退化沙地草地在采取有效的保护措施后,可以由C源变为C汇.

Influences of Grazing and Exclosure on Carbon Sequestration in Degraded Sandy Grassland, Inner Mongolia, North China

Very little is known about the effects of continuous grazing and exclosure on carbon sequestration in semi-arid sandy grassland of North China. Soil-plant system carbon in representative degraded sandy grassland in Horqin sandy steppe (N42 degrees 58', E 120 degrees 42') was measured. Three situations were compared: continuous grazing (CG), exclosure for 5 years (5EX) and exclosure for 10 years (10EX). Ground cover increased from the CG (35%) to the 5EX (63%) and to the 10EX (81%), and accordingly soil organic carbon and total plant components carbon increased from the CG (493 g.m-2 and 95 g.m-2) to the 5EX (524 g.m-2 and 146 g.m-2) and to the 10EX (584 g.m-2 and 309 g.m-2). In terms of the distribution of carbon in plant-soil system, 65.3%, 78.2% and 83.9% of plant-soil carbon was in soils at 0-15 cm in the 10EX site, in the 5EX site and in the CG site, respectively. The results suggested that continuous grazing in the erosion-prone sandy grassland was very detrimental to vegetation, soil and surrounding environment. Under exclosure conditions, vegetation restoration and litter accumulation not only effectively protected soil from loss through wind erosion, but also significantly increased plant-soil system carbon storage, and thus sequestration of atmospheric carbon. However, the recycling of aboveground plant carbon to the soil was restricted when grazing was excluded and a large part of carbon sequestrated was immobilized in plant litter accumulating on the soil surface. Further research on time scale for exclosure is needed. It is concluded that the degraded sandy grassland could contribute to significant carbon sequestration with the implementation of protecting practices.