Spatiotemporal variations of carbon-water-hydraulic risk for Pinus tabuliformis Carrière Plantations on the Loess Plateau under future climate change

As a native perennial tree, Pinus tabuliformis Carrière (PT) has been widely planted on the Chinese Loess Plateau for ecological restoration. However, the impacts of climate-change on water resources pose a new challenge to the sustainability of restored ecosystems. To clarify the plantation carbon sequestration and water consumption, as well as their underlying physiological mechanisms, this study coupled the integrated BBGC-Sperry model with CMIP6 meteorological data under SSP1–2.6, SSP2–4.5, and SSP5–8.5. Daily transpiration, soil water content, and leaf water potential, along with multi-site total growing-season transpiration and aboveground biomass data, were used to validate the BBGC-Sperry model. The validated model was used to simulate the dynamics of annual mean NPP, annual mean actual evapotranspiration (ET) and annual average percentage loss of whole-plant hydraulic conductance (APLK) for PT plantations at 130 meteorological stations on the Loess Plateau. We integrated a “carbon-water-hydraulic risk index” (CWHRI) based on NPP, ET, and drought-induced mortality risk probability (DMRP) to assess ecosystem sustainability. These simulations covered the baseline period (2000–2024) and three future periods (2025–2049, NFP; 2050–2074, MFP; and 2075–2099, FFP) under three Shared Socioeconomic Pathways (SSP1–2.6, SSP2–4.5, and SSP5–8.5). The results indicate that compared with the baseline period, the annual mean NPP is projected to decrease by 4 %–27 % under all scenario–period combinations, except for the FFP under SSP5–8.5, where it will increase by 8 %. Annual mean ET and APLK are projected to increase from 0.05 %–61 % and 13 %–84 %, respectively, with the smallest increases under SSP1–2.6 with the NFP and the largest under SSP5–8.5 with the FFP. The CWHRI is projected to decline by 23 %–44 %, and exhibit a southeast-to-northwest decreasing gradient, which is dominated by NPP, with a secondary contribution from water-related environmental factors. These findings indicate the rising DMRP of PT plantations will threaten the sustainability of restored ecosystems on the Loess Plateau in the future.