雅砻江下游干热河谷表土化学风化及其控制因子

化学风化是地表岩石矿物向土壤释放营养元素同时形成土壤粘粒组分的地球化学过程，这一过程使土壤具有生态环境功能。本文选择采集青藏高原东南缘的雅砻江下游不同地貌部位和植物群落的表土样品并分析其粒度组成和地球化学特征。结果表明：研究区表土粒度组成以粉砂为主（46.68%），其次是砂粒（34.05%）和粘粒（19.28%）；元素组成以Si、Al和Fe为主；K、P和Si相对于上陆壳亏损，与区内沉积岩为主的岩石分布特征一致。研究区表土粘粒含量和化学蚀变指数（CIA）存在明显的空间差异：海拔 < 1300 m、坡度较大的南部谷坡地表土粘粒平均含量为6.51%，CIA平均为65，处于脱Ca、Na的中等风化阶段早期；海拔>2400 m、坡度平缓的西部坡地和宽谷地表土粘粒含量达39.21%，CIA平均达86，风化程度较高。母岩、海拔、坡度和土壤总氮含量对表土CIA值的贡献依次是57.34%、23.46%、10.33%和6.87%。显然，母岩性质是控制研究区表土化学风化过程的主要因素，地貌条件（海拔和坡度）是驱动化学风化过程最重要的外部因素，且海拔高度的影响大于坡度；生物作用对CIA值有一定的贡献。本研究可为深入探讨干热河谷地区土壤生物地球化学过程提供基础数据。

The chemical weathering and its controlling factors of topsoil in the hot-dry valley of the lower Yalongjiang River

Rocks/minerals chemical weathering is a superficial geochemical process in which releasing nutrient elements to soil and forming clay minerals in the soil, and simultaneously developing eco-environmental functions of soil. In this study, we selected 10 community plots, located respectively in the different slopes and mountain rift basins (26°32'~34°05'N, 96°52'~102°48'E) with elevation ranging from 1000 m to 3000 m in the lower reaches of the Yalongjiang River on the southeastern Qinghai-Tibetan Plateau, including grassland, savanna, mixed woodland, Leucaena leucocephala woodland, coniferous and broad-leaved mixed forest land, Pinus yunnanensis woodland, wide-valley grassland, corn field, mango orchard and apple orchard, etc., and collected its topsoil samples, respectively. The grain size composition and mineral elemental composition were analyzed, the proxies of grain size and geochemical parameters and the methods of correlation analysis and ridge regression analysis were employed. The objectives of this study were to explore the evolution trend of the topsoil chemical weathering; to quantify the contributions of major controlling factors to the topsoil chemical weathering; and to evaluate the carbon sink potential of the topsoil chemical weathering in the hot-dry valleys of the southwestern China. The results show that the spatial differences of the topsoil chemical weathering intensity resulted in significant spatial heterogeneity of the topsoil grain size composition in the study area. In the south of the study area with lower altitude (below 1300 m) and steeper slope, including grassland, savanna, mixed woodland, Leucaena leucocephala woodland, corn field and mango orchard, the grain size of the topsoil occurs more coarse (mean grain size ranging from 3.94 φ to 6.35 φ) and merely 6.51% of clay content. The topsoil is characterized by relatively weak eco-environmental function. However, in the western study area with higher elevation (above 2400 m) and gentle slope, including wide-valley grassland, Pinus yunnanensis woodland, coniferous and broad-leaved mixed forest land and apple orchard, the grain size of the topsoil exists more finer (mean grain size ranging from 7.91 φ to 8.57 φ) and higher clay content (39.21%). Hence, the topsoil is characterized by stronger eco-environmental function.