Long-term organic fertilization improves the productivity of kiwifruit (Actinidia chinensis Planch.) through increasing rhizosphere microbial diversity and network complexity

The effects of organic soil amendments on rhizosphere microbial communities have been studied in many crop species. However, there is little research on rhizosphere microbial communities in kiwifruit (Actinidia chinensis Planch.), which is a valuable fruit tree species. Therefore, the objective of this study was to explore changes in community composition and co-occurrence networks of bacteria and fungi in the rhizosphere of kiwifruit under long-term organic fertilization regimes. Organic amendments (mainly pig and sheep dung compost) were applied at rates of 10, 20, and 40 Mg ha−1 y−1 over 9 years, with chemical fertilizers (N 287.5, P 115 kg ha−1 y−1, and K 115 kg ha−1 y−1) applied as the control. Results showed that in addition to soil pH and nutrients (e.g., carbon and nitrogen), the yield and quality of kiwifruit were improved by the application of organic amendments compared with the control. Organic amendments also increased bacterial diversity and relative abundance of plant growth-promoting bacteria (including Pseudomonas, Chrysosporium, and Burkholderia) in the rhizosphere of kiwifruit. Conversely, the relative abundance of plant pathogenic fungi (including Fusarium) was reduced due to the application of organic amendments. Network analysis indicated that organic amendments stimulated the formation of functional groups and activated antagonism or mutualism between microbial taxa. Spearman's correlation analysis revealed that the relative abundance of potentially beneficial microorganisms including Burkholderia and Devosia was positively correlated with fruit yield or quality. In conclusion, long-term organic fertilization regimes might improve the productivity of kiwifruit by increasing rhizosphere microbial diversity and network complexity.