Application of organic manure as a potential strategy to alleviate the limitation of microbial resources in soybean rhizospheric and bulk soils

Abstract

The development and vigor of soil microorganisms in terrestrial ecosystems are frequently constrained by the limited availability of essential elements such as carbon (C), nitrogen (N), and phosphorus (P). In this study, we investigated the impact of long-term application of varying levels of organic manure, low (7.5 Mg ha−1 yr−1), moderate (15.0 Mg ha−1 yr−1), and high (22.5 Mg ha−1 yr−1), on the stoichiometry of enzymes and the structures of the microbial communities in soybean rhizospheric and bulk soils. The main goal of this research was to examine how soil microbial resource limitations in the rhizosphere respond to different long-term fertilization strategies. The soil enzymatic activities were quantified, and the structure of the microbial community was assessed by analyzing phospholipid fatty acid profiles. When compared to the bulk soil, the rhizospheric soil had significant increases in microbial biomass carbon (MBC), nitrogen (MBN), and phosphorus (MBP), with MBC increasing by 54.19 to 72.86%, MBN by 47.30 to 48.17%, and MBP by 17.37 to 208.47%. Compared with the unfertilized control (CK), the total microbial biomasses of the rhizospheric (increased by 22.80 to 90.82%) and bulk soils (increased by 10.57 to 60.54%) both exhibited increases with the application of organic manure, and the rhizospheric biomass was higher than that of bulk soil. Compared with bulk soil, the activities of C-, N- and P-acquiring enzymes of rhizospheric soil increased by 22.49, 14.88, and 29.45% under high levels of organic manure, respectively. Analyses of vector length, vector angle, and scatter plots revealed that both rhizospheric and bulk soils exhibited limitations in terms of both carbon (C) and phosphorus (P) availability. The results of partial least-squares path modelling indicated that the rhizospheric soil exhibited a more pronounced response to the rate of manure application than the bulk soil. The varying reactions of rhizospheric and bulk soils to the extended application of organic manure underscore the crucial function of the rhizosphere in mitigating limitations related to microbial resources, particularly in the context of different organic manure application rates.