Abstract
Low P availability is a vital constraint for nodulation and efficient N2 fixation of legume, including soybean. To elucidate the mechanisms involved in nodule adaption to low P availability under legume/cereal intercropping systems, two experiments consisting of three cropping patterns (monocropped soybean, monocropped maize, soybean/maize intercropping) were studied under both sufficient- and deficient-P levels. Our results demonstrated that intercropped soybean with maize showed a higher nodulation and N2 fixation efficiency under low P availability than monocropped soybean as evidenced by improvement in the number, dry weight and nitrogenase activity of nodules. These differences might be attributed to increase in P level in intercropping-induced nodules under low P supply, which was caused by the elevated activities of phytase and acid phosphatases in intercropping-induced nodules. Additionally, the enhanced expression of phytase gene in nodules supplied with deficient P level coincided with an increase in phytase and acid phosphatase activities. Our results revealed a mechanism for how intercropped maize stimulated nodulation and N2 fixation of soybean under P deficient environments, where enhanced synthesis of phytase and acid phosphatases in intercropping-induced nodules, and stimulated nodulation and N2 fixation.
Highlights
Low P availability is a vital constraint for nodulation and efficient N2 fixation of legume, including soybean
A reduction in P supply resulted in a significant decrease in dry matter (DM) accumulation in shoots and roots in both maize and soybean
Root DM was more affected than shoot DM under deficient P conditions in soybean
Summary
Low P availability is a vital constraint for nodulation and efficient N2 fixation of legume, including soybean. Our results demonstrated that intercropped soybean with maize showed a higher nodulation and N2 fixation efficiency under low P availability than monocropped soybean as evidenced by improvement in the number, dry weight and nitrogenase activity of nodules. These differences might be attributed to increase in P level in intercropping-induced nodules under low P supply, which was caused by the elevated activities of phytase and acid phosphatases in intercropping-induced nodules. Significant increase in synthesis and secretion of acid phosphatases in legume respond to P stress to stimulate effective utilization of internal and external phosphorus, under legume/cereal intercropping patterns consisting of faba bean/maize and peanut/maize[27,28,29]. How intercropped cereal induced the synthesis of phytase and acid phosphatases in nodules by root–root interaction under P stressful environments and their specific role in affecting nodular P level remain poorly documented
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