Response of two mangrove species to elevated temperatures: a comparative study on photosynthetic physiological sensitivity and acclimation to simulated climate warming.

As global warming intensifies, understanding the physiological and ecological responses of mangrove species to rising temperatures becomes crucial for predicting their future distribution and resilience. This study investigated the photosynthetic physiology, growth, and biomass allocation of seedlings of two mangrove species, Kandelia obovata and Bruguiera gymnorrhiza, under controlled temperature gradients of 22-32 °C, simulating IPCC projected warming scenarios. Key findings include a unimodal response of net photosynthesis to temperature, with species-specific optimal temperatures: K. obovata achieved its maximum net photosynthetic rate (9.25 ± 0.13 μmol m-2 s-1) at 30 °C, while B. gymnorrhiza peaked at 28 °C (7.44 ± 0.17 μmol m-2 s-1) and maintained a plateau at 30 °C. The maximum quantum efficiency of photosystem II increased by 33.87% in K. obovata at 30 °C and by 32.20% in B. gymnorrhiza at 32 °C relative to 22 °C. Warming significantly enhanced biomass accumulation in K. obovata, with total dry biomass increasing by 63.83% at 32 °C compared to 22 °C, while B. gymnorrhiza showed a 25.6% increase at 28 °C. The study highlights species-specific acclimation: K. obovata exhibits higher photosynthetic efficiency and biomass allocation plasticity, whereas B. gymnorrhiza demonstrates greater photoprotection and water-use efficiency. The strategies suggest that K. obovata may thrive under increased water availability, whereas conservative traits could enhance resilience to drought and heat stress for B. gymnorrhiza. These findings reveal a fundamental trade-off between growth and photosynthetic efficiency under warming. This mechanistic insight into mangrove acclimation improves our ability to forecast their responses to climate change and supports the development of targeted conservation strategies.