Effects of long-term fertilization on soil mineral-associated organic carbon and particulate organic carbon across agricultural systems in China: a meta-analysis

Abstract Long-term fertilization is a key factor influencing soil carbon components. While long-term fertilization generally increases soil organic carbon (SOC), it remains unclear whether mineral-associated organic carbon (MAOC) and particulate organic carbon (POC) exhibit threshold effects to fertilization duration. We conducted a meta-analysis of 234 field observation datasets from China to assess the impact of long-term fertilization regimes on soil carbon components. The results showed that long-term application of organic fertilizer increased POC content by 119% and MAOC content by 24%. When the duration of fertilization exceeded 30 years, the response of fMAOC (the proportion of MAOC in SOC) shifted from negative to positive. Importance analysis indicated that changes in POC were closely associated with carbon input and K fertilizer application, whereas MAOC was more sensitive to mean annual precipitation, initial organic carbon content, and fertilization duration. POC increased more in lower initial organic carbon, while MAOC increased more markedly under organic fertilization or combined application of organic and mineral fertilizers. POC accumulated rapidly during the first 23 years of fertilization and subsequently reached a plateau, whereas MAOC began to increase persistently only after 28 years, exhibiting a clear nonlinear, stage-dependent response. This study provides quantitative evidence for threshold responses of soil organic carbon fractions to fertilization duration and elucidates the stage-specific dynamic characteristics of POC and MAOC. These findings offer a theoretical basis for developing phased and precision fertilization strategies aimed at enhancing POC in the short term and stabilizing MAOC in the long term to promote carbon sequestration.