Research progresses of soil microorganisms driven nutrient coupling cycles in fluvo-aquic soils of China

Scientific fertilization is a pivotal step towards sustainable increase of crop yield without the expense of agroecosystem health. The knowledge on the process of nutrient cycle driven by soil microbes is of great help to evaluate and guide scientific fertilizations. Although mounting investigations had been conducted on the influences of fertilization strategies on soil microorganisms in recent years, they are mainly limited to the cycling of single nutrient involved into soil microorganisms. In view of the integrity and inseparability of nutrients cycling, the related knowledge on their interaction and coordination with microbial processes would greatly contribute to the comprehensive understanding of the influences that fertilizations bring to agroecosystem. Therefore, revealing the nutrients cycling mediated by soil microorganisms will help us to understand the soil nutrient cycling process and guide scientific fertilization. This paper reviews the findings of the group of Prof. Xiangui Lin, in Institute of Soil Science, Chinese Academy of Sciences. Based on a long-term fertilizer experiment located in Fengqiu Agro-Ecological Experimental Station, they have systematically investigated carbon (C), nitrogen (N), phosphorus (P) nutrients cycling and their interactions in association with microbial processes, using soil microbiology, molecular ecology, microcalorimetric and isotopic determination technique, etc. The results indicated that the fluvo-aquic soil is mainly limited by phosphorous. Application of phosphorous fertilizers enhanced microbial biomass carbon content, invertase activity, urease activity, respiration rate and microbial metabolic activity in the soil, which could ensure nutrient transformation in the soil and nutrient uptake of crop, as a result increasing sink effects of carbon and nitrogen. On the contrary, if phosphorus fertilization is deficient, even with application of other nutrients such as nitrogen, soil microbial metabolic efficiency still remains low. More carbon and nitrogen will be lost by microbial metabolic processes, which are not conducive to soil carbon and nitrogen accumulation, consequently leading to poor soil quality and intensified environmental pollution. In addition to the response and feedback of soil microorganisms to nutrients in fluvo-aquic soil, this paper further reveals the microbial mechanisms of the coupling of carbon and phosphorus, and summarizes as " P deficiency leads to C consumption, C supply results in P activation”. Long-term P deficiency significantly increased the net mineralization of exogenous carbon, which reduced the retention of exogenous C into the soil organic carbon pool mediated by microbial transformation, possibly due to a higher C loss into the atmosphere in the form of CO₂. The addition of exogenous C could stimulate microbial proliferation in P-deficient soils, especially P solubilizing microorganisms. The process can shift P from relatively unavailable soil-bound pools into microbial biomass pools through pool cycling; potentially increase soil available P content for crops. Finally, this review looks forward to the future of soil nutrients cycling mediated by soil microorganisms in cropland. These cognitions will deepen the understanding of scientific fertilization and help to guide the regulation of soil microorganisms and better serve the farmland ecosystem.