Partial consistency of net primary productivity and water-carbon use efficiency in response to climate change among three plantations

Currently, most research focuses on changes in forest productivity and evapotranspiration, while relatively less attention has been paid to water and carbon use efficiency and their future trends. This knowledge gap hinders a comprehensive understanding of the dynamic processes and interactions between water and carbon cycles within forest ecosystems. This study aimed to calibrate the parameters of the Biome-BGC model using net primary productivity (NPP) derived from tree-ring data of three plantations. The model was employed to simulate and predict the trends of NPP, evapotranspiration (ET), carbon use efficiency (CUE), and water use efficiency (WUE) under different climate scenarios, analyzing their consistent responses to climate change. The results showed that the simulated NPP (NPPs) from the Biome-BGC model showed a highly significant correlation with the measured NPP (NPPm) in mature plantations, with the regression slope close to 1:1, indicating the model’s accuracy in simulating ecological variables of mature plantations. Under three climate scenarios, the NPPs, ETs, and WUEs of Mongolian pine were significantly higher than the baseline, while CUEs decreased. For black locust and Chinese fir, NPPs, ETs, and CUEs significantly decreased, while WUEs exhibited complex changes, with black locust showing a significant increase in WUEs under the RCP2.6 scenario. The impacts of all four variables were more pronounced in the far future compared to the near future. For the same species, the responses of NPP, ET, and water-carbon use efficiency to climate change were generally consistent across most sites, though some divergence occurred due to local environmental conditions. In the future, CUEs is predicted to decrease across all sites and scenarios, suggesting that carbon consumption through respiration will exceed carbon fixation through photosynthesis, potentially exacerbating future climate warming via negative feedback. Clustering results revealed that as climate change intensifies, the three plantations developed distinct climate response patterns, although consistency within the same species was not absolute. The simulation and prediction results of this study provide valuable scientific insights for the sustainable management of plantations.