不同种植模式橡胶林土壤磷转化对降水季节变化的响应机制

Changes in seasonal precipitation distribution are increasingly severe in tropical and subtropical areas, with intensified droughts in dry season while more storms in wet season. Phosphorus (P) is recognized as one of the most limiting nutrients for primary production in tropical forests because much of the soil P stocks are geochemically bound to iron and aluminum oxides in forms that are largely unavailable for plant uptake. It is very sensitive to soil moist and the change of plant community. However, our knowledge on the response of soil phosphorus transformation to seasonal precipitation changes in different agroforestry systems are poorly understood. The involved mechanisms of environmental regulation and microbial driving have not been well understood. Thus, this project aimed to investigate how the effects of seasonal precipitation change affects soil phosphorus transformation in the systems of rubber monoculture and mixtures with cover crops in a field experiment located in Hainan province.In the present project, phosphorous fractions, gross organic phosphorus mineralization rates and soil physico-chemical properties will be measured. The community structure, dominant population and function gene expression of soil phoD alkaline phosphatase gene and arbuscular mycorrhizal fungi will be explored using the techniques of soil molecular microbiology, such as Pyrosequencing and RT-qPCR. The purposes of this project are to quantitatively evaluate the capacity in soil phosphorus transformation in the systems of rubber monoculture and mixtures with different cover crops and to explore mechanisms on environmental and microbial driving. These results will consequently provide a scientific basis and practical guideline for P management of sustainable development in rubber forest in the present day and future climate conditions.

年降水量不变，干季越干、湿季越湿的降水季节变化是我国热带地区气候变化的显著特征。土壤磷是热带地区植物生长、微生物活性和生态系统生产力的重要限制因子。植被组成可能调节着磷转化对降水季节变化的响应，可是其内在机制尚缺乏研究。本项目拟以两种橡胶农林复合种植模式和单一种植模式为研究对象，开展降水季节变化的野外模拟实验，利用磷素分级和33P同位素标记法研究不同种植模式的橡胶林土壤磷素形态和有机磷矿化速率的季节和年际变化，揭示土壤磷形态变化规律及其相互转化机制；分析土壤小分子有机酸和主要理化性质，识别引起土壤磷转化的关键环境因素。利用高通量测序和RT-qPCR等手段，从DNA和RNA水平分析总的和活性的丛枝菌根真菌和溶磷细菌群落结构和基因表达，揭示降水季节变化和植被组成对土壤磷转化的微生物学机制。研究结果理论上将丰富降水季节变化对热带地区土壤磷转化影响的认识，实践上为橡胶林磷素管理提供科学依据。

年降水量不变，干季越干、湿季越湿的降水季节变化是我国热带地区气候变化的显著特征。土壤磷不仅是热带地区生态系统生产力的重要限制因子，而且环境问题也很突出。植被组成可能调节着磷转化对降水季节变化的响应，可是其内在机制尚缺乏研究。依托在海南儋州热带生态系统观测站建立的降水季节变化野外控制实验平台，设置对照、30%（干季减水30%，湿季增雨30%，全年降水量不变）、60%（干季减水60%，湿季增雨60%，全年降水量不变），橡胶单作和两种农林复合系统，测定了磷组分以及其它植物、土壤等影响因子；利用宏基因组测定了磷循环基因和微生物群落。研究表明：不管降雨强度和种植模式，热带土壤中等活性态磷含量最高，钙磷最低。雨季土壤闭蓄态磷含量均大于旱季。说明磷在雨季以惰性的组分被保留在土壤中。不同降雨强度对土壤中等活性态磷、团聚体内磷、钙磷和闭蓄态磷产生显著影响，而种植模式对团聚体磷和钙磷产生影响，且两者交互作用显著。铵态氮和 pH 与中等活性态磷，钙磷和闭蓄态磷之间是负相关，而土壤含水量、有机碳和速效磷是正相关；全氮、硝态氮和氧化还原电位与活性态磷和团聚体内磷是正相关。说明土壤环境的变化影响了土壤磷形态之间的转换。与自然降雨相比，低降雨强度豆科-橡胶林土壤酸性磷酸酶含量降低，而强降雨强度增加了土壤酸性磷酸酶活性。在低降雨强度条件下，与纯橡胶林相比，益智-橡胶林土壤酸性磷酸酶活性增加。土壤理化因子、植物特性和磷组分均对土壤细菌和真菌群落产生影响。且细菌群落受到植物特性较多，而真菌群落与土壤各个磷组分含量产生明显的相关关系。土壤磷的有效性主要是由凋落物、土壤理化因子和细根等因子控制。本项目标注发表研究论文6篇，培养博士研究生1名，硕士研究生2名，完成了研究目标。