The life state of smooth vetch regulates the seasonal dynamics of microbial nutrient limitations in citrus orchards

Abstract Cover crops improve soil fertility in orchard ecosystems, however, the response of soil microbial metabolism to fruit tree interactions with cover legumes at different stages of the life cycle remains uncertain, thereby limiting our understanding of the mechanisms that regulate nutrient cycling in orchards with cover crop management. Here, the characteristics of microbial energy (carbon, C) and nutrient (nitrogen, N or phosphorus, P) metabolism in the citrus rhizosphere and bulk soil in orchards were analyzed with two managements, that is, smooth vetch ( Vicia villosa Roth var. glabresens Koch) cover and clean tillage, using an extracellular enzymatic stoichiometry model. Microbial C limitation was significantly reduced by cover during the vetch growing season owing to the resulting higher plant root C and soil organic C content. Competition for N between plants and microbes in the bulk soil might lead to significant microbial N limitation in covered orchards during the vetch‐decomposition season, presumably owing to a significant increase in citrus root N and a concomitant decrease in bulk soil total N. Partial least squares path modeling showed that citrus root nutrient contents negatively affected microbial C limitation, while soil nutrients negatively affected microbial relative nutrient limitation in covered orchards. Conversely, both effects were reversed by tillage. Smooth vetch cover mitigated microbial C limitation, and the microbial relative N/P limitation was also influenced by the life state of smooth vetch. Our study highlights the importance of changes in microbial metabolism driven by seasonal nutrient dynamics for understanding soil nutrient cycling and optimizing cover‐legumes management in orchards.