Extensive use of polyethylene plastic mulch (PM) boosts crop productivity in rainfed Northwest China but causes severe soil pollution. Consequently, biodegradable plastic mulch (DM) and straw mulching (full-coverage, CM; strip, SM) have emerged as eco-friendly alternatives. However, their trade-offs regarding soil hydrothermal regulation and yield formation under varying rainfall regimes remain unclear. A two-year field experiment (2023–2024) investigated five treatments (PM, DM, CM, SM, and control CK) on soil hydrothermal status, photosynthetic characteristics, and potato yield. Results indicated that mulching significantly altered the hydrothermal environment: film mulching (PM, DM) warmed the soil, whereas straw mulching (CM, SM) cooled it. Both strategies increased soil water content (10.5–15.8%), with film and straw mulching proving more effective in wet and dry years, respectively. While all mulching practices improved photosynthesis compared to CK, temporal divergence occurred: film mulching promoted early-stage activity, while straw mulching sustained late-stage capacity. Film mulching maximized biomass and yield, particularly in the wetter year (46.4–48.0% increase). Conversely, straw mulching optimized commercial tuber rates and yield stability in the drier year. Crucially, partial least squares structural equation modeling revealed that optimized soil water status and hydrothermal balance were the primary drivers of dry matter accumulation and yield improvement, while photosynthetic capacity acted as a regulated physiological trait dependent on water availability. In conclusion, while PM and DM offer high immediate yields, CM and SM provide a superior balance among yield stability, commercial quality, and agro-ecological sustainability. • Film mulching enhanced early-stage photosynthetic capacity, whereas straw mulching sustained functional leaf duration in the late growth stages. • PLS-SEM identified optimized soil water status and hydrothermal balance as primary drivers of dry matter accumulation and final yield. • Straw mulching improved commercial tuber rates and yield stability, particularly under water-limited conditions.
LI et al. (Sun,) studied this question.