Water table-temperature synergy drives maximal growth and photosynthesis in subtropical Sphagnum palustre under moderate regimes

Sphagnum mosses serve as a crucial carbon sequestration component in peatland ecosystems, and their carbon assimilation capacity is largely governed by growth rates under the interaction of the water table and temperature regulation. However, the optimal water table-temperature combination for Sphagnum growth remains a subject of ongoing debate. This study focused on Sphagnum palustre L, a dominant peat-forming species in the peatlands of southern China, to elucidate the ideal hydrothermal range for its growth and the associated physiological and ecological mechanisms through controlled laboratory culture experiments. Subsequent field surveys were conducted to further quantify the growth properties and biomass accumulation of artificially cultivated Sphagnum palustre L along natural gradients of temperature (15 °C, 25 °C, and 35 °C) and + 5 cm (high), -5 cm (medium), and − 15 cm (low) water table. Additionally, we evaluated the effect of artificial Sphagnum palustre L cultivation on the soil organic carbon content to assess its potential role in enhancing carbon sequestration. The results demonstrated that (1) under suitable moisture conditions (60%~80% field capacity), the photosynthetic performance reached the peak at 25℃(Fv/Fm>0.6), a with significant inhibition at 35℃ or 15℃. (2) Under the optimal water table-temperature combination (25 °C, -5 cm water table), chlorophyll a content increased by 30%, capitulum area increased by 376%, and plant height increased by 53%. (3) In contrast, combined high temperature and waterlogging stress (35 °C, + 5 cm) caused complete photosynthetic inhibition (Fv/Fm = 0), an undetectable chlorophyll a/b ratio, and a 25% reduction in capitulum area. (4) Biomass yield was maximal (600 kg·ha− 1·year− 1) at 25 °C/-5 cm and minimal (124 kg·ha− 1·year− 1) at 35 /+5 cm. with a significant positive correlation observed between yield and soil organic carbon across all experimental treatments. Our findings reveal that an optimal combination of moderate water table and temperature together maximizes subtropical Sphagnum palustre L growth and carbon sequestration. The observed suppression of PSII at high temperatures highlights the vulnerability of subtropical peatland carbon sinks to climate warming. The study provides key parameters for carbon cycle models and suggests practical strategies for peatland restoration through targeted water table management.