Spatiotemporal dynamics of non-photosynthetic vegetation across China and their implications for carbon fluxes along climate gradients

Non-photosynthetic vegetation (NPV), comprising dead branches, fallen leaves, senescent stems, and plant residues, plays a critical role in regulating terrestrial carbon dynamics. However, conventional carbon models and remote sensing products frequently misclassify NPV as bare soil (BS), resulting in systematic underestimation of organic matter transfer, soil respiration, and soil carbon sink along climatic gradients. This misclassification introduces structural biases into carbon fluxes modeling and impedes accurate quantification of vegetation-soil carbon feedbacks. Here, we generated annual maximum NPV coverage (f_NPV) products for China at a 300 m spatial resolution for the period 2016–2024 by integrating Sentinel imagery with field observations. To better characterize ecosystem-level carbon fluxes, we propose a novel ecosystem carbon exchange flux (ECEF) index that integrates NPV, photosynthetic vegetation (PV), and BS. Nationally, the average annual f_NPV was 0.3679, with an annual increase of 0.0014 yr⁻¹. The highest values were observed in semi-arid to sub-humid regions (R_s), reaching 0.4235 with an annual increase of 0.0075 yr⁻¹. Boosted regression tree analysis identified quarterly temperature and precipitation as dominant climatic drivers, explaining 19.38% and 15.22% of the variance in f_NPV, respectively. Carbon sink strength varied along climate gradients, with ECEF values of 0.95 in humid regions and −0.47 in arid regions. Spatial analysis revealed a strong inverse correlation between ECEF and net ecosystem exchange (NEE) (Pearson’s r=−0.68, p<0.05, R²=0.46), supporting ECEF as a robust framework for estimating carbon fluxes across climatic regions. This model-based proxy provides a scalable approach for assessing ecosystem carbon dynamics in regions where direct flux measurements are sparse or unavailable. These findings emphasize the ecological significance of NPV in the terrestrial carbon cycle and underscore its essential role in improving carbon flux estimates under accelerating climate change.