The Innovation Team of Fertilizer and Fertilization Technology of the Institute of Agricultural Resources and Regional Planning (IARRP) of the Chinese Academy of Agricultural Sciences (CAAS) systematically studied the potential of soil nitrogen fixation and related mechanisms under different fertilization systems based on long-term fertilization experiments in irrigated desert soil in Northwest China. The related results were published in the famous domestic journal "iMeta" under the title of "Synergistic effects of diazotrophs and arbuscular mycorrhizal fungi on soil biological nitrogen fixation after three decades of fertilization".

Biological nitrogen fixation is an important part of the nitrogen cycle in terrestrial ecosystems. Biological nitrogen fixation is a process that consumes energy and many nitrogen-fixing bacteria have the characteristics of facultative nutrition. In a eutrophic environment, effective nutrients will be preferentially used to maintain vegetative growth of nitrogen-fixing bacteria. In theory, a large amount of nitrogen fertilizer input in agricultural soil will reduce the nitrogen fixation function of nitrogen-fixing microorganisms and diminish their contribution to agricultural production.

The process of biological nitrogen fixation (especially the symbiotic nitrogen fixation of legume root nodules) is often regulated by mycorrhizal fungi (AMF), and recent studies suggested that AMF could also affect the autogenic nitrogen fixation activity of soil azotobacter by regulating the nutrient status of rhizosphere or hyphosphere. Although it has been reported that fertilization could change the interspecific relationship between nitrogen-fixing bacteria and AMF, the impact of changes in this relationship on soil autogenous nitrogen fixation is still unclear.

This study is different from the traditional knowledge where fertilization reduces the potential of soil autogenous nitrogen fixation. Long-term fertilization (especially green manuring) can promote soil autogenous nitrogen fixation. The functionality strengthening was mainly associated with the increase in the absolute abundance of diazotrophs and AMF and the relative abundance of the key ecological cluster of Module #0 (gained from the co‐occurrence network of diazotrophic and AMF species) with dominant diazotrophs such as Skermanella and Azospirillum. Furthermore, long-term fertilization (especially organic fertilization) weakened the synergistic relationship between nitrogen-fixing bacteria and AMF, implying that autogenous nitrogen fixation may no longer need the help of AMF for nutrient transport at high fertility levels.

However, the long-term green manuring strengthened the synergistic relationship between nitrogen-fixing bacteria and AMF in the key ecological cluster Module #0, and such a synergistic relationship was significantly and positively correlated with the potential of soil autogenous nitrogen fixation, which also supported that soil autogenous nitrogen fixation would be largely favored after the fertilized strategy of green manure. This paper provided the evidence that application of green manure endogenously drives soil autogenous nitrogen fixation, and laid the foundation for studying the relationship between soil autogenous nitrogen fixation and AMF.

Figure 1 Effects of long-term fertilization on soil autogenous nitrogen fixation potential, nitrogen-fixing bacteria and mycorrhizal fungal communities

Figure 2 The co-occurrence network characteristics of nitrogen-fixing bacteria and mycorrhizal fungi (A, B), the response of main ecological clusters to fertilization (C), Relative abundance of species with positive relationships between diazotrophs and AMF in the co‐occurrence network. (D)

Dr. Zhou Guopeng from the IARRP is the first author, and researcher Cao Weidong is the corresponding author. The research was co-funded by the National Key Research & Development Program of China (2021YFD1700200) and the earmarked fund for CARS‐Green manure (CARS‐22).

Citation format:

Zhou G.P, Fan K.K, Li G.L., Gao S.J., Chang D.N., Liang T., Li S., Liang H., Zhang J.D., Che Z.X., Cao W.D. 2023. Synergistic Effects of diazotrophs and arbuscular mycorrizal fungi on soil biological nitrogen fixation after three decades of fertilization. iMeta. e81.

Paper link: https://doi.org/10.1002/imt2.81.