绿肥水溶性有机物影响红壤团聚体磷素转化的作用机制

Green manure incorporation is one of the main agricultural practices for improving soil fertility, during which dissolved organic matter (DOM) affects many soil processes. Therefore, effects of DOM extracted from green manure on phosphorus transformation in soil aggregates are critical environmental issues due to the fact that red soil has poor structure. In the present study, DOM extracted from green manure are used as to investigate phosphorus form distribution and transformation and the mechanisms of DOM-P competitive adsorption, and further to reveal the mechanisms of phosphatase metabolism, microbial biomass turnover and microbial community structure succession responding to phosphorus transformations in soil aggregates. Firstly, a sorption-desorption experiment is conducted to examine effects of DOM properties on adsorption and distribution of phosphorus in different soil aggregate sizes and DOM-P competitive adsorption mechanisms involved. Secondly, series of incubation are carried out to check effects of DOM application types and patterns on soil aggregate stability, and also the distribution and transformation of phosphorus in different aggregate sizes during soil aggregate formation process, aiming to reveal the underlying mechanisms of phosphatase metabolism, microbial biomass turnover and microbial community changes responding to P transformation during which. The results will provide reference data for further understanding of P fixation and release and more importantly, microbial transformation mechanisms at soil aggregate level, and to provide scientific basis for regulating the availability of phosphorus and guiding soil fertility improvement in red soils.

绿肥还田是红壤培肥方式之一，其水溶性有机物(DOM)性质活跃，同时红壤表层结构不良，使绿肥DOM对团聚体中磷转化的影响成为重要环境问题。本项目以红壤团聚体中磷形态分布与转化研究为核心，以DOM施用为手段，在深入研究团聚体粒级中磷形态与转化特征基础上，重点探究团聚体中DOM-磷竞争吸附及团聚过程中酶代谢、微生物生物量周转与微生物群落响应机制。首先采用吸附实验，研究不同绿肥DOM性质对团聚体粒级中磷吸附、形态分布影响，揭示磷形态分布特征与DOM性质的关系及DOM-磷竞争吸附机制；开展系列培养实验，研究DOM施用种类和施用方式对团聚体稳定性及团聚过程不同团聚体粒级中磷形态分布与转化的影响，揭示磷形态转化特征及DOM影响团聚过程中磷转化的酶代谢、微生物生物量周转与微生物群落响应机制。以期了解土壤团聚体水平的磷固持、释放特征和微生物转化机制，为调控红壤磷有效性和指导培肥改良提供科学依据。

绿肥还田可以培肥红壤、改善磷有效性，探讨其中水溶性有机物（DOM）影响团聚体水平的磷固持特征、团聚过程中不同粒级磷形态转化及其微生物响应机制，可为调控红壤磷有效性和指导培肥改良提供依据。主要研究内容与结果如下：.(1) 葡萄糖（Glu）、柠檬酸钠（Cit）、谷氨酸钠（Glut）模拟DOM，探讨干湿交替(4DW与DW)对P形态转化的影响。DOM添加提高有机磷矿化，磷活化与分解后的分配因DOM类型和DW次数不同：Cit和Glut将Biocarb-Po矿化后向Resin-P转移，Glu将其向NaOH-Pi转移；磷分解在4DW更大。16S rRNA、ITS2 rRNA、phoD基因丰度及细菌群落NMDS分析显示微生物对磷活化存在碳源类型差异。Rhizobium、Mesorhizobium、Pseudomonas、Bacillus、Streptomyces等是分解磷的优势属，不因碳源类型和水分存在差异。.(2) 探讨DOM对团聚体粒级中磷吸附的影响，0.25-1 mm的磷吸附量最大，DOM添加降低吸附量，>2 mm效果更佳；1-2 mm粒级有较高解吸率，添加DOM后更显著，同粒级油菜DOM中有更小吸附量与更大解吸率；DOM使最大吸附量Qm减小，油菜效果更佳，同处理不同粒级的Qm以> 2 mm最小，各粒级吸附能常数和最大缓冲能力以0.25-1 mm最大。吸附解吸程度差异归结为DOM自身性质。.(3) DOM添加后测定团聚过程中不同粒级团聚体中微生物生物量碳磷（MBC、MBP）与磷形态转化。添加油菜DOM后期有较高MBP及最大量各形态磷，原土中有显著更高的各种无机态磷，显著更低的各种有机形态磷。归因于油菜DOM中丰富基团以及原土与小粒径团聚体更易破碎，导致碳周转加速，对磷同化加强。.(4) 一或四次添加DOM到土壤，探讨添加方式对团聚过程中磷形态转化的影响。回归分析发现随培养进行更多形态磷活化成为有效磷组分。磷形态分级、OUT量及含phoD微生物群落NMDS分析显示DOM方式差异，且因团聚体粒级存在不确定。无机磷与Ralstonia、Mesorhizobium、Methylobacterium、Lysobacter、Streptomyces、Mycobacterium、Cupriavidus显著负相关，而Collimonas与有机磷正相关，磷形态与含量差异是微生物共同作用的结果