贡嘎山东坡土壤磷的生物地球化学循环过程与海拔分异

Mountains are special areas for the research of Critical Zone (CZ) in the earth’s surface. Mountains have distinct advantages to understand the biogeochemical cycling processes, spatial difference and driving mechanisms of nutrients under different conditions of soil development, climate and vegetation types. In last few years, the significance of phosphorus (P) in terrestrial ecosystems has been increasingly highlighted; however, the biogeochemical cycling processes of P still need to be lucubrated. In this proposed project, the biogeochemical cycling and spatial differences of P in soils along an altitudinal gradient (2000-4200 m above sea level) will be deciphered in the Hailuogou valley of the eastern slope of Gongga Mountain by the field investigation as well as the designed experiments including litter decomposition experiment, soil translocation experiment and nutrients addition experiment. Moreover, the high-throughput pyrosequencing, magnetic resonance imaging (MRI), oxygen isotope analysis of phosphate, phosphorus fraction analysis, etc. will be applied. The purposes are to understand the distribution characteristics of soil P, its fractions and formation mechanisms; to clarify the driving functions of plants and microbes on the soil P biogeochemical cycling; to probe into the distribution and formation mechanisms of soil organic P and its fractions along the altitudinal gradient; and ultimately illuminate the altitudinal patterns, processes and mechanisms of the biogeochemical cycling of soil P in the mountain ecosystem. The results of this project will be benefit for understanding the P biogeochemical cycling in terrestrial ecosystems, and the role and function of the CZ in the biogeochemical cycling of P. Meanwhile, this project will also provide theoretical basis for the ecological conservation and development and ecological barrier construction in mountain regions of southwestern China.

山地是地表关键带研究的重要区域，具有在有限空间内开展不同土壤发育程度、气候和植被类型条件下养分元素生物地球化学循环的空间分异、过程及驱动机制研究的优势。磷（P）在陆地生态系统中的重要作用日益显现，其生物地球化学循环过程尚需深入研究。本项目拟选取贡嘎山东坡海螺沟海拔2000-4200m，开展土壤P的生物地球化学循环和海拔分异研究，利用高通量测序、核磁共振、磷酸根氧同位素分析、P形态分析等技术，野外调查结合凋落物分解实验、土体置换实验及元素添加控制实验等，弄清研究区土壤P及其生物有效性的空间分布特征及形成机制；阐明植物、微生物对山地土壤P的生物地球化学循环的驱动作用；探讨土壤有机P及其形态的海拔分布特征并分析其矿化过程和驱动机制；在此基础上阐明山地土壤P生物地球化学循环的过程、机制及海拔分异规律。为探讨P的生物地球化学循环与地表关键带功能发挥、为西南山地生态保育和生态屏障建设提供理论基础。

磷是维持陆地生态系统稳定的重要养分元素之一，了解其不同土壤发育程度、气候和植被类型条件下生物地球化学循环的空间分异、过程及驱动机制，是当前研究的热点和难点。项目通过原位观测和控制实验对贡嘎山东坡海螺沟土壤磷的生物地球化学循环海拔分异进行了研究，并探讨了形成海拔分异的地球化学和生物作用机制。研究表明：贡嘎山东坡海螺沟土壤磷的生物地球化学循环呈现出明显的海拔分异特征，以原生矿物磷分解和淋溶为主的地球化学作用的强度随着海拔的升高呈现为抛物线型；以吸收和通过凋落物归还的植物对磷的生物循环，随植被类型变化产生较大差异，生物循环效率随海拔升高逐渐降低。微生物解磷作用及微生物量磷均呈现出抛物线型特征，在峨眉冷杉磷带最高。在季节上，无论是地球化学作用还是生物作用，均呈现出明显差异，生长季显著大于非生长季。上述生物地球化学循环海拔差异的形成机制，除环境因素外，地球化学和生物作用至关重要，而地球化学作用过程中同时有生物参与。高海拔区（3600m以上），原生矿物磷的溶解过程是土壤磷生物地球化学循环的主要过程，低分子量有机酸和微生物的参与控制了溶磷速率。中低海拔区（3600m以下）原生矿物磷的分解和有机磷矿化归还是土壤磷生物地球化学循环的主要过程。淋溶作用的强弱，不仅影响了土壤总磷的分布特征，更重要的是在这一过程中造成了生物有效磷的流失。凋落物分解对土壤磷的归还是针叶林和针阔混交林带土壤生物有效磷的重要来源，分解速率和归还量受微生物群落结构及其分泌的酶所控制。以植物低分子量有机酸螯合反应、微生物磷酸酶水解有机磷为主的生物化学作用控制着亚高山针叶林和针阔混交林的磷循环。研究成果对维持陆地生态系统稳定、提升初始生产力和在贫瘠地区生态恢复提供理论依据。