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Endophytic fungus alleviates soil sickness in peanut crops by improving the carbon metabolism and rhizosphere bacterial diversity

China is a major peanut-producing country, with an annual planting area of approximately 5 million hectares, accounting for 35% of all oil crops. Because of the limited amount of arable land and a need to intensify regional agroindustrialization, peanut plants have generally been continuously monocropped on a large scale in main peanut producing areas of China. Long-term consecutive monoculture can give rise to soil sickness, which serve as a typical negative plant-soil feedback response that results in reductions in the quantity and quality of peanut yield. Soil microorganisms are considered to be key drivers for agroecosystem function and sustainability. Alteration of soil microbial communities can affect the metabolic functions performed by the communities and then feedback on crops growth and health. Therefore, how to effectively improve the carbon metabolism and diversity of soil microbial community is considered to be an important requirement for alleviating soil sickness and establishing the sustainability of peanut production.  Recently, the team led by Prof. Chuan-Chao Dai from the College of Life Sciences, Nanjing Normal University has published their findings in the Microbial Ecology (https://doi.org/10.1007/s00248-020-01555-0).

Endophytic fungi are important organisms that live in healthy plant tissues without causing any harmful effects to their hosts; their ecological functions have attracted increasing amounts of attention. The researchers found that endophytic fungus Phomopsis liquidambaris colonization could significantly alter the composition of peanut root exudates. Further study observed that peanut root exudates produced by endophytic fungus colonization mainly improved the carbon metabolism and rhizosphere bacterial community in long-term continuous cropping soils. Amendment of soil with P. liquidambaris-colonized root exudates effectively increased carbon metabolic richness and diversity indexes, and stimulated certain species of the rhizosphere bacterial community. Specifically, these root exudates increased the levels of potentially beneficial rhizosphere bacteria and decreased the abundance of soil-borne pathogen. The promotive effects on growth performance of continuous cropping peanut were mainly attributed to modifications of root exudate components caused by P. liquidambaris colonization. Therefore, carbon metabolism and rhizosphere bacterial diversity can be significantly improved by root exudates derived from P. liquidambaris colonization, which might be beneficial for alleviating soil sickness in long-term monoculture fields.

The first author is Xing-Guang Xie, a postdoctoral researcher at the College of Life Sciences, and the corresponding address is Nanjing Normal University. This work was financially supported by the National Natural Science Foundation of China (31870478), the Program for Jiangsu Excellent Scientific and Technological Innovation team (17CXTD00014) and a project funded by the Priority Academic Program Development (PAPD) of the Jiangsu Higher Education Institutions of China. In addition, Xing-Guang Xie was supported by a Postdoctoral Research Funding Program of Jiangsu Province (211100B62003).

A model in which endophytic fungus P. liquidambaris colonization alleviates soil sickness of continuous cropping peanuts by affecting root exudates. P. liquidambaris colonization can significantly change the root exudate components of continuous cropping peanuts. The secretion of specific root exudates from P. liquidambaris-colonized roots can effectively improve soil microbial carbon metabolism and community structure (especially the rhizosphere bacterial community composition), which helps to alleviate the soil sickness and promote the growth of continuous cropping peanuts.