Phytohormonal homeostasis, chloroplast stability, and heat shock transcription pathways related to the adaptability of creeping bentgrass species to heat stress

Creeping bentgrass (Agrostis stolonifera) is a cool-season perennial turfgrass and is frequently utilized in high-quality turf areas. However, a poor to moderate resistance to heat stress limits its promotion and utilization in transitional and worm climate zones. The objectives of the study were to assess the heat tolerance of 18 creeping bentgrass genotypes in the field and to further uncover differential mechanisms of heat tolerance between heat-tolerant and heat-sensitive genotypes. The results showed that 18 different genotypes had different heat tolerance during summer months of 2021 and 2022. Among them, 13 M was identified as the best heat-tolerant cultivar based on the subordinate function values analysis of five physiological indicators. Under controlled growth conditions, heat stress significantly inhibited photosynthetic capacity and also accelerated oxidative damage and chlorophyll (Chl) degradation in both heat-tolerant 13 M and heat-sensitive PA4. However, as compared with heat-sensitive PA4, 13 M maintained significantly higher net photosynthetic rate, water use efficiency, and total antioxidant capacity as well as less Chl degradation and damage to chloroplast ultrastructure. Significantly higher contents of abscisic acid, cytokinin, gibberellin, and polyamines (spermine, spermidine, and putrescine) were also detected in 13 M than that in PA4 in the later stage of heat stress, but 13 M exhibited significantly lower indoleacetic acid content than PA4 during heat stress. In addition, heat-upregulated genes involved in heat shock transcriptional pathways were more pronounced in 13 M than in PA4. These findings indicated that better heat tolerance of 13 M could be related to more stable Chl metabolism, better photosynthetic and antioxidant capacities, endogenous hormonal homeostasis, and more effective heat shock transcriptional pathway. 13 M is more appropriate for planting in transitional and subtropical zones instead of widely used PA4.