Long-Term Increase and Shifting Predictor Contributions of Net Ecosystem Production in Moso Bamboo Forests Across Anji County, China

Subtropical bamboo forests are important carbon sinks, yet long-term regional assessments of their net ecosystem production (NEP) and associated factor contributions remain scarce. Here, using approximately 646 km2 of mapped Moso bamboo (Phyllostachys pubescens) in Anji County, China, we generated a monthly NEP reconstruction on a 500 m output grid for 2003–2022 by integrating eddy covariance observations, meteorological data, and multi-source remote sensing products within an automated machine learning framework. Bamboo NEP showed weak overall spatial heterogeneity but followed a clear unimodal elevational pattern, with the highest carbon sequestration at mid-elevations (342–550 m). Regional carbon uptake peaked in summer and reached a minimum in winter, consistent with bamboo phenology. Annual mean NEP was 0.43 Tg C yr−1 and increased significantly over the study period (3.35 Gg C yr−2, p < 0.001), with 95.8% of bamboo pixels exhibiting upward trends. Negative modeled anomalies coincided with drought years, whereas the biennial growth cycle of Moso bamboo had little effect on annual NEP at the regional scale. SHapley Additive exPlanations (SHAP) shows that long-term NEP enhancement was dominated by canopy vegetation indices and exhibited a descriptive transition around 2013, when the leading control changed from solar radiation to vegetation conditions. Structural equation modeling (SEM) further showed statistical pathways in which meteorological variables were associated with modeled NEP partly through vegetation indicators. These findings reveal a sustained strengthening of the regional bamboo carbon sink and identify shifting controls on its long-term variability, providing a scientific basis for carbon sink management in subtropical bamboo forests under climate change.