The temporal dynamics of soil properties and microbial community structure under capsicum monoculture

The adverse effects of long-term monoculture increasingly threaten the sustainable development of the capsicum industry, leading to soil degradation and yield decline. Although monoculture systems exhibit favorable economic benefits in the early years, these advantages gradually diminish and transform into negative impacts with prolonged cultivation. However, during this transition, the changes in soil physicochemical properties and microbial communities, as well as their potential coupling mechanisms, remain unclear. In this study, soils from capsicum monocultures of 1, 2, 7, and 11 years (Y1, Y2, Y7, and Y11) were used to examine the effects of monoculture duration on soil physicochemical properties and microbial communities. Results showed that with increasing years of monoculture, soil pH in Y2, Y7, and Y11 decreased by 0.03–0.33 units compared with Y1, whereas electrical conductivity (EC), available phosphorus (AP), available potassium (AK), and saturated hydraulic conductivity (SHC) increased by 48.49–87.48 %, 163.24–342.54 %, 43.25–71.57 %, and 80.0–240.0 %, respectively. In contrast, total nitrogen (TN) and soil organic matter (SOM) increased by 24.50 % and 44.44 %, respectively, in short-term monoculture (Y2) compared with Y1, but both gradually declined with increasing monoculture duration. Nitrate nitrogen (NO 3 − -N) and soil aggregate stability (WAS) remained relatively stable in the short term but declined markedly in the long term, with reductions of 69.30 % and 55.92 % in Y11 compared with Y1. In terms of microbial communities, short-term monoculture increased copiotrophic taxa (e.g., Proteobacteria , Mortierellomycota ), whereas long-term monoculture reduced oligotrophic taxa (e.g., Acidobacteriota , Rokubacteria ) and key nitrogen-cycling bacteria (e.g., Nitrospira ). Simultaneously, long-term monoculture decreased the average degree, network density, and proportion of positive correlations in bacterial and fungal networks, thereby reducing community structural stability. Structural equation modeling (SEM) further indicated that pH, WAS, and NO 3 − -N were the key factors influencing bacterial communities. These findings reveal that while short-term monoculture promotes nutrient release, long-term monoculture leads to nutrient imbalance, reduced aggregate stability, and disrupted microbial community structures, ultimately weakening carbon and nitrogen cycling functions and severely constraining the sustainable development of the capsicum industry. • Short-term monoculture promotes nutrient release; long-term monoculture leads to nutrient imbalance. • Short-term monoculture increases copiotrophs, while long-term reduces oligotrophs and key N-cyclers. • Sphingomonas in exacerbating denitrification and disrupting the nitrogen cycle. • Long-term monoculture reduces microbial network complexity, lowering soil structural stability.