Impact of Long-Term Fertilization on Agroecosystem Multifunctionality and Yield in Loess Plateau, China

Resource enhancements have been shown to affect ecosystem functions that are central to biogeochemical cycling. However, knowledge gaps still remain regarding how changes in soil microbial communities are impacted by long-term fertilization and the influence of long-term fertilization on agroecosystem multifunctionality, and the mechanism how the shifts of soil microbial community drives agroecosystem functions and ultimately yields. We chose buckwheat (Fagopyrum esculentum Moench.) to evaluate how agroecosystem functions in terms of element cycles driven by soil microbial communities finally impact yields, with seven fertilizer applications: control with no fertilizer (CK); nitrogen (N); phosphorus (P); N and P (NP); manure (M); M and N (MN); and M, N, and P (MNP) since 1983 in the Loess Plateau, China. Yields at MNP were significantly higher than that of other treatments. The threshold elemental C:N ratio was higher, in comparison to the C:N of soil from each treatment, whereas the threshold elemental ratio of C:P was lower than the soil C:P from each treatment, suggesting that the microbes were suppressed by C and P. This equilibrium of microbial nutrient demands and soil resource supplementation was balanced by increasing the alkaline phosphatase (AP) and β-1,4-glucosidase (BG) activity (range: 71.89 to 117.11, and 782.14 to 1164.58 nmol g^− 1 h^− 1, respectively). In addition, fertilizer application impacted soil total and bacterial phospholipid fatty acid (PLFA) contents. MN and MNP promoted the multifunctionality and element cycling (C, N, and P) in soil ecosystem. And soil multifunctionality and P cycling index was positively linked with soil microbial community composition. From structural equation model, both soil microbial C and P limitation state altered soil total PLFA, thus affecting C cycles and yield.