Soil microbial necromass carbon contributions to soil organic carbon after three decades of citrus cultivation.

Introduction: Citrus is one of the most economically significant fruits globally, and soil organic carbon (SOC) plays a central role in maintaining soil health and fertility. Consequently, enhancing SOC content directly influences both the yield and quality of citrus crops. However, the sources of SOC in citrus orchards and their mechanisms of contribution remains poorly understood. Methods: This study investigated citrus soils from orchards of varying planting ages by collecting 0-20 cm soil samples. We analyzed amino sugars, glomalin, particulate organic carbon (POC), and mineral-bound organic carbon (MAOC) to examine the source of microbial residue carbon and its contribution to SOC. Results: The results revealed a significant decrease in microbial residue carbon (MNC), fungal residue carbon (FNC), and bacterial residue carbon (BNC) with increasing orchard age ( Discussion: These findings offered novel insights into the mechanisms through which intensive citrus cultivation influences microbial necromass contributions to SOC. This study also highlighted the negative impacts of long-term citrus cultivation on soil microbial necromass and offered recommendations for the rehabilitation of aging orchards.