青藏高原不同类型草地土壤磷素分布及其影响因素

磷是限制草地生态系统生产力的关键性养分元素,阐明青藏高原草地土壤磷素分布特征及其影响因素对于维持该区域草地生态系统的可持续发展具有重要意义。沿青藏高原从西北至东南的水平样带采集不同类型草地(即草甸草原、典型草原和荒漠草原)的土壤样品,研究土壤全磷、有效磷、无机磷组分和有机磷组分的分布特征及其影响因素。结果表明:土壤全磷和有效磷含量以草甸草原最高,其次为荒漠草原和典型草原。各类型草地土壤的无机磷组成均以酸溶态无机磷为主;草甸草原土壤的有机磷组成以氢氧化钠态有机磷为主,而典型和荒漠草原土壤则以酸溶态有机磷为主。不同类型草地相比,草甸草原土壤的水溶态、碳酸氢钠态和氢氧化钠态无机磷以及各形态有机磷含量均显著高于典型和荒漠草原,而荒漠草原土壤的酸溶态无机磷含量显著高于草甸和典型草原。冗余分析指出,土壤有机碳、年均降雨量是影响全磷和有效磷的主要因子,年均降雨量和游离氧化铁是影响无机磷组分的主要因子,而pH、年均气温、地上生物量和年均降雨量是影响有机磷组分的主要因子;结构方程模型指出,草地类型对无机磷组分和有机磷组分都有直接的影响,年均温度和容重对无机磷组分也有直接的影响,而海拔、年均降水量和年均气温通过草地类型对无机磷组分和有机磷组分产生间接的影响。研究结果对于青藏高寒草地生态系统磷素养分的有效管理,进而实现该区域草地资源的可持续利用具有重要意义。

Soil Phosphorus Distribution and Its Influencing Factors in Different Grassland Types on the Qinghai-Tibet Plateau

Phosphorus is a key nutrient element limiting grassland ecosystem productivity. It is of great significance to clarify soil phosphorus distribution and its influencing factors for maintaining sustainable development of grassland ecosystem on the Qinghai-Tibet Plateau. In this study, we collected soil samples from different grassland types (i.e. meadow steppe, typical steppe, and desert steppe) along the horizontal transect of the Qinghai-Tibet Plateau from northwest to southeast. The distribution characteristics and influencing factors of soil total phosphorus, available phosphorus, and inorganic phosphorus and organic phosphorus fractions were investigated. The results showed that the total and available phosphorus contents in soil were the highest in meadow steppe, followed by desert steppe and typical steppe. The inorganic phosphorus fraction of all grassland types was dominated by acid-soluble inorganic phosphorus; the organic phosphorus fraction of meadow steppe soil was dominated by sodium hydroxide organic phosphorus, while acid-soluble organic phosphorus fraction was dominated in typical and desert steppe soils. Among different grassland types, the contents of water-soluble, sodium bicarbonate, sodium hydroxide inorganic phosphorus and various forms of organic phosphorus in the meadow steppe soil were significantly higher than those in the typical and desert steppes, while the content of acid-soluble inorganic phosphorus in the desert steppe soil was significantly higher than that in the typical and meadow steppes. Redundancy analysis showed that soil organic carbon, average annual rainfall were the main factors affecting the total and available phosphorus, average annual rainfall and free iron oxide were the main factors affecting inorganic phosphorus fractions, while pH, average annual temperature, above-ground biomass and average annual rainfall were the main factors affecting the organic phosphorus fractions. Structural equation model indicated that grassland type had a direct effect on both inorganic and organic phosphorus fractions, and annual average temperature and bulk density also had a direct effect on inorganic phosphorus fractions, while altitude, annual rainfall and annual average temperature had indirect effects on inorganic and organic phosphorus fractions through grassland types. The results of this study are of great significance for the effective management of soil phosphorus nutrient and the sustainable utilization of grassland resources on the Qinghai-Tibet Plateau.