紫色丘陵区玉米-大豆套作系统根际解磷菌活化土壤难溶磷的生化机制

Microorganisms play an important role in the regulation of soil P availability. Previous studies showed that maize-soybean relay intercropping can improve soil phosphorus availability by interspecific root interactions. However, the response of soil microbial diversity to soil environmental factors in this model and the regulation mechanism of phosphorus availability are not clear. This project takes maize- soybean relay intercropping system in purple hilly area as the research object, base on the field experiment, using the classical microbiological methods of cultivation, clone, and gene identification, combine with the technology of high-throughput sequencing, to analysis the microbial diversity and abundance of phosphate solubilizing bacteria (PSB) in maize and soybean rhizosphere soil under different cropping patterns. Take a root box inoculation experiment to analysis the relationship between the colonization rate of PSB strains in soil and soil P fractions, as well as plant P uptake, so as to select high effiency PSB strains, which are suitable for maize-soybean relay intercropping system in southwest of China. Using HPLC method to determine the varieties and quantity of organic acid in PSB exudates, combine with the determination results of root distribution, root exudates, soil phosphatase activity and other relative soil environmental indicators, to find the key influencing factors on phosphate solubilizing capacity of PSB in maize-soybean intercropping system. Finally, to clarify the biochemical mechanism of sparingly available phosphorus mobilization by rhizosphere soil PSB in maize-soybean relay intercropping system according to above results. This project has important scientific significance and practical value to promote the sustainable use of soil phosphorus in farmland.

微生物对土壤磷有效性的调控起至关重要的重要作用。前期研究表明玉米-大豆套作因作物种间根系交互作用有利于提高土壤磷有效性，但该模式根际土壤微生物多样性对土壤环境因子的响应及其对磷有效性的调控机制尚不明确。本项目以紫色丘陵区玉米-大豆套作系统为研究对象，拟利用田间定位试验，采用培养、克隆、基因鉴定等经典微生物学方法，结合高通量测序技术，比较不同栽培模式下玉米和大豆根际土壤微生物多样性及解磷菌丰度；利用根箱接种试验，分析解磷菌在土壤中的定殖率与土壤磷素组分及植株吸磷量之间的关系，筛选出适宜西南地区玉米-大豆套作体系的高效解磷菌株；采用HPLC法测定解磷菌分泌的有机酸种类和数量，结合根系分布规律及分泌物种类和数量、土壤磷酸酶活性等指标测定，找出套作系统中影响解磷菌解磷能力的关键因子。最终阐明玉米-大豆套作系统根际解磷菌活化土壤难溶磷的生化机制，对促进农田土壤磷可持续利用具有重要科学意义和实践价值。

玉米-大豆套作因作物种间根系交互作用有利于提高土壤磷有效性，但该模式根际土壤微生物多样性及潜在解磷微生物对磷有效性的调控机制尚不明确。本项目以玉米-大豆套作系统为研究对象，比较研究了种植模式和施磷对玉米和大豆根际土壤微生物多样性的影响；从雅安、仁寿、崇州试验基地套作大豆根际土中筛选出了9株高效解磷菌株，并利用盆栽试验验证了其中3株解磷菌对玉米植株的促生效果；联合接种丛枝菌根真菌和解磷细菌以探索玉米-大豆复合种植系统减施磷肥的潜力。研究结果表明种植模式比磷肥施用对作物根际土微生物多样性影响更大。从套作大豆根际土中筛选出的Y9、R1、R7和R9分别属于芽孢杆菌，Y5、Y7、C8、C9和C10分别属于新鞘氨醇菌、水稻科萨克氏菌、肠杆菌、拉尔斯顿菌和假单胞菌。这些菌株能有效利用Ca3(PO4)2，菌株Y7、Y9和C9活化后的水溶性磷含量分别高达380.96 µg mL-1、388.62 µg mL-1和381.30 µg mL-1。HPLC结果表明，各菌株均能分泌大量的有机酸，包括草酸、丙二酸、柠檬酸和琥珀酸。所有菌株都分泌IAA并产生铁载体。菌株Y9分泌的IAA含量高达26.17μg mL-1；菌株C8的铁载体活性最高，达64.5个单位。与未接种的对照相比，接种解磷菌的种子具有较高的发芽率和生根数。混合接种PSBs可以提高土壤酸性磷酸酶活性、有效磷和植物对磷的吸收。不规则噬根菌（Rhizophagus irregularis）定殖的根系能够促进植物的发育，链霉菌（Streptomyces sp）和巨大芽孢杆菌（Bacillus megaterium）两种细菌菌株辅助AMF的生长促进了根系生长和磷吸收。AMF和PGPB菌剂与适量磷肥协同施用，在不影响作物产量的情况下，可活化土壤难溶磷，使玉米-大豆间作系统磷肥用量减少50%，减少土壤磷素积累。本项目阐明的套作大豆根际土解磷菌活化土壤难溶磷的生化机制及其对相邻作物玉米的实际促生效果，对促进土壤磷可持续利用具有重要科学意义和实践价值。