Climate-associated Variation in the Response of Bermudagrass (Cynodon dactylon) to Exogenous Hydrogen Sulfide Under Shade Stress

Shade stress reduces light availability and limits plant growth and development. Hydrogen sulfide (H 2 S) participates in plant stress responses, but whether H 2 S-related shade responses vary among bermudagrass accessions from different origin-site environments remains unclear. Seven Cynodon dactylon accessions collected from different sites in China were exposed to shade stress (a 50% reduction in natural sunlight intensity outdoors) and treated with NaHS (an H 2 S donor) and hypotaurine (an H 2 S scavenger). Shade stress reduced dry weight, fresh weight, net photosynthetic rate, stomatal conductance, and Fv/Fm, and increased reactive oxygen species accumulation and membrane damage. Compared with plants exposed to shade stress alone, NaHS-treated plants showed higher endogenous H 2 S content, biomass, gas-exchange parameters, and APX, POD, and SOD activities, together with lower H 2 O 2 , O 2 − , MDA, and reduced electrolyte leakage. Hypotaurine showed the opposite pattern relative to NaHS. Across the seven accessions, H₂S content, biomass, gas exchange, and antioxidant activity in NaHS-treated plants under shade were associated with collection-site climatic variables, including sunshine duration, precipitation, mean annual temperature, and altitude, along the longitudinal gradient. These results suggest that exogenous H 2 S is associated with improved shade responses in bermudagrass, and that accession-level variation in this response may be related to origin-site environmental conditions.