| 其他摘要 | In southwest China, there exists one of the largest karstic areas in the world, developed with diverse karstic landforms. In this area, soil and water loss is serious. The ecosystems in the karstic areas of southwest China are fragile, due to the slow soil-formation rate of limestone, complex hydrological structure, and soil loss through surface and underground ways. In past several decades, people living in these areas irrationally used the land, which resulted in serious loss of soil and finally in intensive rocky desertification. The seriously degraded ecosystems have lost their production capacity, and are unable to support the living of human. The soil is critical to restoration of degraded ecosystem, and it is important to understand the properties of soils and the biogeochemical cycling of nutrients, such as carbon, sulfur and nitrogen, in the soil-plant systems. Accordingly, studies on biogeochemical features and nutrient cycling of the soils in different degraded ecosystems are necessary for us to get better understanding of the ecological processes and to help manage the ecosystems. It has been demonstrated that the biogeochemical cycling of sulfur affects that of carbon. The coupled cycling of sulfur and carbon is the key for us to understand the nutrient cycling processes and their eco-environmental effects in the karstic ecological systems. In order to get knowledge about carbon and sulfur cycling signatures and the processes affecting the cycling, this work studied the basic chemical, physical, and biological characteristics, variation in stable isotope composition (δ13CSOC、δ13CSIC、δ34SSO4、δ34SSOS) of soil profiles developed on sandstone and limestone in hill slop. Several conclusions have been reached as follows. The sandstone and limestone soils have different pH values: the former has lower pH values than the latter. Along the soil profiles, the soil pH values decrease with increasing depth. The difference in soil pH values between these two soil types should be ascribed to the different mineralogical and chemical compositions. The soil organic carbon (SOC) contents of the sandstone and limestone soils are not obviously different, varying between 3.1~79.7 g?kg-1 and 8.2~73.3 g?kg-1, respectively. The soil profiles from the top down to the lower site show different SOC contents, generally with higher SOC contents in the profile in the lower site compared to the upper site, which should be resulted from topography, different vegetation cover. The two types of soil profiles show higher SOC contents in tope soil and much lower SOC contents in the deep soil. The δ13CSOC values of the sandstone and limestone soil profiles are between -25.4‰~-20.7‰ and -23.2‰~ -18.8‰, respectively. All of the soil profiles show a general slight decrease of the δ13CSOC values from tope soil to the deep soil. However, the detailed variations in the δ13CSOC values especially for the tope soils are complex. Except for two sandstone soil profiles, all of the other soil profiles show δ13CSOC values increasing from the surface soil to the soil at 20-40cm depths, and the δ13CSOC values of soils at lower depths show gradually decrease trend with decreasing soil depths. The variation signatures of the δ13CSOC values along the soil profiles can be explained in terms of SOC decomposition, input of different plant type (C3 and C4 type plants), and soil erosion at upper and accumulation at the lower site. The soil inorganic carbon (SIC) in limestone soils shows higher δ13CSIC values than that in the limestone soils. The sandstone soil profiles show a general decrease in δ13CSIC value from top to bottom soils. Compared to the SIC in the limestone soil, the SIC in the sandstone soils is mainly derived from organic carbon decomposition and expiration of plant roots, and the carbonate in the soils is mainly secondary. The difference in variation of the δ13CSIC values in different soils indicate the different source of SIC, different extents of organic carbon decomposition, and different cycling processes in the different typ . |
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