低磷环境下接种丛枝菌根真菌促进紫花苜蓿生长和磷素吸收的机理

  【目的】  磷极易被土壤吸附和固定，导致土壤中磷有效性较低。研究接种丛枝菌根真菌 (arbuscular mycorrhizal fungi, AMF) 和低磷处理两者交互对紫花苜蓿生长和磷吸收的影响，为提高碱性土壤中磷肥利用率提供理论依据。  【方法】  以黄绵土和紫花苜蓿 (Medicago sativa) 为试验材料进行盆栽试验。在施磷0、5、20 mg/kg (P0、P5、P20) 3个水平下，分别设接种和不接种丛枝菌根 Glomus mosseae BGC YN02 (+AMF、–AMF) 处理。植物生长120天后测定植株生物量、磷吸收量、AMF侵染率以及根际和非根际土壤的pH、土壤碱性磷酸酶活性、土壤有效磷含量、土壤微生物生物量磷，分析根际有机酸的组成与含量。  【结果】  +AMF处理中植物根系被AMF侵染，且施磷水平对侵染率没有显著影响；施磷和+AMF处理显著提高了植株地上部、地下部生物量以及磷含量，其中P20+AMF处理生物量和磷含量最高；根际有机酸总量随施磷水平上升而显著降低，但+AMF处理有机酸总量高于–AMF处理，其中柠檬酸和乙酸含量的变化较为明显；施磷和+AMF显著降低土壤碱性磷酸酶活性，增加土壤有效磷含量和微生物生物量磷，且低磷环境 (P0、P5) 下根际土壤碱性磷酸酶活性和微生物生物量磷均显著高于非根际土；P20处理显著降低磷利用效率和磷肥利用率，+AMF处理显著提高磷肥利用率。  【结论】  碱性土壤 (黄绵土) 中，AMF和紫花苜蓿根系能建立较好的共生关系，低施磷水平 (施磷量 ≤ 20 mg/kg) 对AMF侵染率没有显著影响。施磷和接种AMF均可以显著促进紫花苜蓿生长和磷吸收。低磷环境下，接种AMF可以扩大植物根系吸收范围，同时增强根际土壤碱性磷酸酶活性，促进根系分泌有机酸，特别是乙酸和柠檬酸，从而提高磷肥利用率。

Mechanisms of increasing alfalfa growth and phosphorus uptake by inoculation with arbuscular mycorrhizal fungal under low phosphorus application level

  【Objectives】  Phosphorus (P) is easily adsorbed and fixed by soil, resulting in low P availability in soil. This research investigated the interactive effects of AMF and low levels of P fertilizer on alfalfa growth and P-uptake to identify optimal methods for increasing P efficiency in alkaline soil.  【Methods】  A pot experiment was conducted using loessial soil and alfalfa (Medicago sativa) as test materials. The soil was treated with different P levels (0, 5 and 20 mg/kg, code as P0, P5, P20), and with AMF inoculation (20 g/L Glomus mosseae BGC YN02; +AMF) or without (–AMF). After 120 days of plant growth, the growth indices of alfalfa, P concentrations in alfalfa tissues, pH values, alkaline phosphatase activities, available P contents, and microbial biomass P in the rhizosphere and non-rhizosphere soil were analyzed. The composition and concentration of rhizosphere organic acids were also measured.  【Results】  In +AMF treatments, alfalfa roots were colonized by mycorrhiza, but P application rate had no significant effect on AMF root colonization. Both P application and AMF colonization significantly increased the dry mass and P concentrations of shoots and roots. The plant dry mass and P concentration in P20+AMF treatment were significantly higher than in the other treatments. The total amount of rhizosphere organic acids, especially citrate and acetate, in +AMF treatments decreased with increase in P application rate, but they were still significantly higher than those in ?AMF treatments. Phosphorus and AMF application significantly decreased soil alkaline phosphatase activity, but increased soil available-P and microbial biomass P contents. Alkaline phosphatase activity and microbial biomass P in rhizosphere were significantly higher than in non-rhizosphere. P20 trentment significantly decreased P-uptake efficiency and P-utilization efficiency, and +AMF significantly increased P-uptake efficiency.  【Conclusions】  AMF has a good symbiotic relationship with alfalfa roots in alkaline loessial soil. Low level of P application (≤ 20 mg/kg) has no significant effect on AMF root colonization. Both P application and AMF colonization could significantly stimulate the growth and P uptake of alfalfa. In low available P soil, inoculating AMF could broaden absorption area of root, increase alkaline phosphatase activity in rhizosphere and secretion of organic acids (especially citrate and acetate), and increase P-uptake efficiency.