Abstract
Biological nitrogen fixation (BNF) refers to a bacterially mediated process by which atmospheric N2is reduced, either symbiotically or non-symbiotically, into ammonia (NH3) in the presence of the enzyme complex nitrogenase. In N2-fixing grain legumes, BNF is often hampered under low phosphorus (P) availability. The P status of legumes, particularly nodules, as well as P availability in the rhizosphere, play a vital role in regulating BNF. Aside from increasing P availability via fertilization, other plant traits (i.e., extensive rooting system and their spatial distribution, hyper-nodulation, root exudates, rhizosphere acidification, and heterogeneity) contribute to greater P uptake and hence more effective BNF. The positive interaction between P availability and BNF can be exploited through beneficial soil P solubilizing microorganisms (PSM). These microorganisms can increase plant-available P by modifying either rhizosphere soil processes or promoting plant traits, which lead to increased P uptake by the production of plant growth-promoting substances, both of which could indirectly influence the efficiency of BNF in legumes. In this review, we report on the importance of microbial P bio-solubilization as a pathway for improving BNF in grain legumes via PSM and P solubilizing bacteria (PSB). Because BNF in legumes is a P-requiring agro-ecological process, the ability of soil PSB to synergize with the rhizobial strains is likely a key belowground process worth investigating for advanced research aiming to improve rhizosphere biological functions necessary for sustainable legume-based cropping systems.
Highlights
Legume crops play key roles both in food security and agro-ecosystems sustainability by providing several services at the food- and production-system levels (Stagnari et al, 2017)
Legume crops play a key role in integrated soil fertility management owing to their capacity to fix atmospheric N2 in association with rhizobia, which can lead to increased soil fertility and decreased dependence on N-fertilizers in low-input farming systems (Atienza and Rubiales, 2017; Vanlauwe et al, 2019)
Enhancing biological nitrogen fixation (BNF) in grain legumes via soil microorganisms not directly involved in BNF could be a propitious option for increasing the supply of affordable and eco-friendly protein for human consumption while improving the overall sustainability of cropping systems (Meena and Lal, 2018)
Summary
Legume crops play key roles both in food security and agro-ecosystems sustainability by providing several services at the food- and production-system levels (Stagnari et al, 2017). These positive effects were attributed to the synergies between PSM ( PSB) and N2 fixing bacteria, which resulted in enhanced BNF and increased nutrient use efficiency (Wani et al, 2007).
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