Sweet sorghum (Sorghum bicolor L. Moench) has significant cultivation potential in arid and saline–alkaline regions due to its drought and salt tolerance. This study aims to evaluate the mechanisms by which increased soil salinity and reduced irrigation affect the growth, aboveground biomass, and stem sugar content of sweet sorghum. A two-year field experiment was conducted, with four salinity levels (CK: 4.17 dS/m, S1: 5.83 dS/m, S2: 7.50 dS/m, and S3: 9.17 dS/m) and three irrigation levels (W1: 90 mm, W2: 70 mm, and W3: 50 mm). The results showed that increased salinity and reduced irrigation significantly reduced both the emergence rate and aboveground biomass, with the decreases in the emergence rate ranging from 11.0% to 36.2% and the reductions in the aboveground biomass ranging from 15.9% to 43.8%. Additionally, increased soil salinity led to reductions in stem sugar content of 6.3% (S1), 8.8% (S2), and 12.8% (S3), respectively. The results also indicated that photosynthetic efficiency, including the net photosynthetic rate (Pn), stomatal conductance (Gs), and chlorophyll content (SPAD), was significantly hindered under increased water and salt stress, with the Pn decreasing by up to 50.4% and the SPAD values decreasing by up to 36.3% under the highest stress conditions. These findings underscore the adverse impacts of increased soil salinity and reduced irrigation on sweet sorghum’s growth, photosynthetic performance, and sugar accumulation, offering critical insights for optimizing its cultivation in arid and saline environments.

The Chinese Loess Plateau is a vast semi-arid landscape that has experienced substantial vegetation recovery through afforestation since the late twentieth century, altering the regional carbon cycle and contributing to China’s carbon neutrality efforts. However, large-scale quantification of carbon storage (CS) remains challenging in this heterogeneous and erosion-prone landscape. In this study, the PLUS land-use simulation model was coupled with an InVEST-based carbon storage accounting framework, and multi-source remote sensing and field survey data were integrated to quantify historical carbon storage from 1980 to 2020 and predict carbon storage in 2040 under three future land-use scenarios: natural development (ND), cultivated land protection (CLP), and ecological protection (EP). The results showed that NDVI exhibited a distinct southeast-to-northwest gradient, with peak values (>0.8) in the southeastern tablelands, where CS reached 10.27 ± 4.20 kg C m⁻². Carbon storage increased from 1980 to 2020, primarily due to afforestation, with higher CS in the humid southeastern plateau and lower CS in the arid northwest. Scenario simulation showed that CS maintained a baseline level of 7.07 ± 3.81 kg C m⁻² under the ND scenario, increased slightly to 7.08 ± 3.77 kg C m⁻² under the CLP scenario, and reached the highest value of 7.10 ± 3.80 kg C m⁻² under the EP scenario. SEM-based mechanism analysis indicated that topography exerted the strongest direct influence on CS, followed by vegetation, climate, and socioeconomic factors. These findings suggest that water availability and topographic constraints strongly regulate CS in semi-arid regions, while land-use policy can still modify CS through scenario-dependent land-use change.