冰川退缩迹地成土过程中土壤有机磷的矿化及其关键机理

The content of inorganic phosphorus (P) decreases and organic P increases with soil development. The mineralization of organic P becomes an important source of bioavailable P for natural ecosystems. However, knowledge about rate and mechanisms of mineralization of organic P during pedogenesis is still scarce. This proposed project will investigate the processes of mineralization of soil organic P in the Hailuogou Glacier chronosequence, Mount Gongga. Specifically, the rate of organic P and its variations will be measured by 33-P isotope dilution technique in four selected sites with different exposure age (60, 128, 580 and 1500 year-old) in the chronosequence. The contribution of inorganic P from mineralization of organic P to bioavailable P pool in soil will be evaluated. The effects of soil properties and plants on the mineralization of organic P will be investigated by combining results of an incubation experiment and in situ observation. The role of microorganisms in mineralization of organic P will be revealed at the gene level by functional gene microarray and enzyme activities. The direct and/or indirect effects of various abiotic and biotic factors on mineralization of organic P will be quantified by using structural equation models. The results of this project will be helpful to understand the mechanisms of biogeochemical cycling of P during the pedogenesis and relationship between cycling of nutrients and plant succession.

成土过程中土壤无机磷（Pi）逐渐减少，有机磷（Po）逐渐积累，Po矿化释放的Pi因而成为自然生态系统有效P的重要来源。然而，目前仍不清楚成土过程中Po矿化的速率和关键机理。本项目拟利用贡嘎山冰川退缩迹地土壤年代序列，在前期Po形态研究的基础上，开展原位监测和室内培养实验，采用33-P同位素稀释技术，定量解析Po矿化速率及其随成土过程的变化特征，评估Po矿化对土壤有效P库的贡献；结合Po矿化速率实验，开展有机酸添加实验，同时对比分析根际与非根际土中有机酸及Po的异同，明确成土作用和有机酸对Po矿化的影响；利用酶活性和微生物功能基因芯片等技术，从基因水平上阐明微生物对Po矿化的作用机理；利用结构方程模型定量解析多种环境和生物因素对Po矿化速率的直接或间接影响，揭示成土过程中Po矿化的关键机理。研究成果既有利于阐明成土过程中P的生物地球化学循环机制，也有助于揭示养分循环与植被演替之间的关系。

基于贡嘎山东坡海螺沟冰川退缩迹地土壤年代序列，原位观测与室内培养实验相结合，利用31P核磁共振、功能基因芯片和酶学等技术，查明了成土过程中土壤有机磷（Po）的矿化速率，发现土壤Po净矿化速率随土壤年龄的增加呈上升趋势，由60年样点的54 mg P·m-2·a-1逐渐上升至1460年的902 mg P·m-2·a-1；60–130年样点，Po矿化速率为有效磷库的36–49%，540–1460年样点，Po矿化速率为有效磷库的1.39–1.93倍。分析了成土作用和植物根系分泌物对土壤Po矿化的影响，发现成土作用导致的粘土矿物的增加抑制了土壤Po的矿化速率，而根系分泌的羧化物提高了Po的矿化速率，但是，二者相互作用对矿化速率的影响还受到底物有效性和酶活性的影响。从基因水平上阐释了微生物活动对Po矿化的作用机理，发现phoC基因和酸性磷酸酶活性随成土年龄逐渐增加，而phoD和碱性磷酸酶活性呈相反趋势；phoC基因占9个P循环功能基因的比例从最初期的约40%增长至最后样点的约90%。揭示了成土过程中土壤Po矿化的关键机理，将海螺沟冰川退缩区土壤Po矿化机理分为两个模式：在中-低速阶段，由于土壤颗粒对Po的吸附能力较为有限，植物根际羧化物对Po的释放作用相对较小；酸性和碱性磷酸酶共同作用是这一阶段土壤Po被矿化的关键机理。在高速阶段，土壤颗粒对Po的吸附能力相对提高，植物根际羧化物对Po的配位交换-释放、酸性磷酸酶对Po的水解是这一阶段土壤Po被矿化的关键机理。提出了原位条件下识别植物活化磷能力的技术方法。共发表同行评议的学术论文8篇，其中SCI论文7篇，联合出版专著1部，申报发明专利1项；其中一篇学术论文获得由Journal of Plant Ecology颁发的首届JPE Best Paper award。研究成果不仅加深了对成土过程中P生物地球化学循环机理的认识，为阐明成土过程的生物学机制提供了案例，而且可为科学合理利用土壤有机磷库提供依据。