福建省不同耕地土壤和土地利用类型对“碳源/汇”的贡献差异研究

STUDY ON THE DIFFERENCE OF CONTRIBUTIONS MADE BY VARIOUS CROPLAND SOIL AND LAND USE TYPES TO CARBON SOURCE/SINK IN FUJIAN PROVINCE,CHINA

农田生态系统无论作为全球温室气体的"源"还是"汇",均对大气CO2浓度的年际变化产生重要影响。以我国亚热带地区——福建省不同地理位置的闽侯县、浦城县、同安县和永定县为典型研究区,利用这4个县1982年23 869个样点和2008年12 521个样点实测数据建立的1∶5万土壤类型-土地利用方式数据库,分析了近30年来福建省不同土类、亚类、土属和土地利用方式耕地有机碳密度变化,并利用尺度上推的方法估算了全省两期耕地土壤有机碳储量。结果表明,近30年来福建省耕地总体上表现为弱的"碳汇",土壤有机碳密度和储量分别上升了0.24 kg m-2和4.26 Tg,但不同土壤类型和土地利用方式在"碳汇/源"中的贡献程度差异很大。从土壤类型来看,紫色土、酸性紫色土和石灰泥田分别在土类、亚类和土属级别中的"碳汇"贡献最大,有机碳密度分别提高了0.63、0.63和1.25 kg m-2;而滨海盐土、滨海盐土和黄泥砂土则分别在土类、亚类和土属级别中的"碳源"贡献最大,有机碳密度分别下降了0.59、0.59和1.08 kg m-2。从土地利用方式来看,灌溉水田是全省最主要的"碳汇",有机碳密度提高了0.27 kg m-2,而水浇地是全省最主要的"碳源",有机碳密度下降了0.36 kg m-2。因此,在今后的福建省农田土壤有机碳管理政策中应重点考虑有机碳密度下降、面积较大的土壤类型及土地利用方式的有效管理。

No matter whether a farmland ecosystem acts as source or sink of global greenhouse gases, it has an important impact on annual variation of the concentration of carbon dioxide in the atmosphere. In this study, four counties, namely Minhou, Pucheng, Tongan and Yongding, located in different geographical locations in Fujian Province, subtropical China, were selected as typical study zones. Based on the data of field measurements at 23 869 sampling site in 1982 and 12 521 sampling sites in 2008, scattered in these four counties, a 1：50 000 database of soil type-land use pattern was established, analysis was carried out of changes in organic carbon density in the farmlands of Fujian in the past 30 years as affected by group, sub-group, genus and land use of the soils, and estimation was done of the soil organic carbon storages in the farmlands of the province in these two historical periods, using the scaling up method. Results show that the farm- lands in Fujian as a whole acted as a weak carbon sink in the past 30 years, with carbon density and carbon storage in- creased by C O. 24 kg m^-2 and 4.26 Tg, respectively. Contribution of the farmland ecosystems to the ＂ carbon sink/ source＂ varied sharply with soil type and landuse pattern. When speaking of soil types, purplish soil, acid purplish soil and calcic mud field contributed the greatest to the ＂carbon sink＂ in soil group, soil subgroup and soil genu, respectively, with organic carbon density increased by C 0.63, 0.63 and 1.25 kg m^-2, respectively; while coastal solonchaks, coastal solonchaks and yellow sandy soil were the major contributors to the ＂carbon source＂ in soil group, soil subgroup and soil genu, respectively, with organic carbon density decreased by C 0.59, 0.59 and 1.08 kg m^-2, respectively. In terms of land use, irrigated paddy fields were the major carbon sink in the province with organic carbon density increased by C 0.27 kg m^-2 ;while irrigated uplands the main carbon source with organic carbon density decreased by C O. 36 kg m^-2 The findings suggest that in formulating policies for management of soil organic carbon in farmlands of Fujian in the years to come, priority should be given to effective management measures for the types of soils and the patterns of land use that are large in area and cause organic carbon density to decrease.