Variation in soil microbial properties and their contribution to soil carbon storage under long-term fertilization and organic amendments

Soil organic carbon (SOC) sequestration is well known as one of effective strategies for mitigating atmospheric greenhouse effect and sustainable development of global agriculture. Chinese semiarid Loess Plateau accounts for one-third of the arable land in China and provides food for more than 100 million people at present, therefore, fertilization and organic amendment are the crucial management strategies in Loess Plateau accounts for sustainable farming systems. However, long-term reliance on chemical fertilizers has gradually led to a decline in soil quality and soil organic matter (SOM) depletion. As the key driver of multiple biogeochemical processes, soil microbial communities can not only regulate soil health but also facilitate carbon sequestration in intensive agriculture.
The objective of this dissertation was to evaluate the long-term impact of fertilization management on soil physicochemical characteristics, SOC storage and the contribution of microbial community activities to SOC sequestration. In this study, we performed an 27-year field experiment with four fertilization treatments (CK: no fertilization management; NP: inorganic fertilizers application alone; NPS: inorganic fertilization plus the incorporation of maize straw; NPM: inorganic fertilization plus the incorporation of composted cow manure), and an incubation experiment (300 days) of classified aggregates (> 5 mm, 2–5 mm, 1–2 mm, 0.25–1 mm or < 0.25 mm) with 13C-labeled maize straw application.
The results showed that microbial biomass had close relationships with both soil chemical and physical properties, and soil chemical properties explained a larger proportion of variation of microbial biomass than physical ones. The different fertilization managements could cause changes in the explanation of soil chemical and physical properties to the microbial community. Fungal variables (fungal, AM biomass, and F/B ratio) and enzyme activities (BXYL and LAP) were significantly correlated with SOC content in macro-aggregates (> 0.25 mm), but not in micro-aggregates (< 0.25 mm). In addition, organic amendment significantly reduced the impact of inorganic fertilizer on the growth of the microbial community. Fungi and G– bacteria contributed greatly to increasing C accumulation in > 2 mm aggregates, while G+ bacteria were more important in < 2 mm aggregates. Overall, the activities of microorganisms in independent aggregates contributed to inner C accumulation under straw application, which was closely associated with aggregate sizes under the straw application.
Therefore, the results above showed that organic amendment can help improve soil physicochemical properties and alter microbial community composition, and improve the contribution of the microbial process to SOC storage at aggregate scale compared with chemical fertilization. Those results indicated that organic amendment can contribute to agricultural SOC sequestration and sustainable farming in Loess Plateau.