Modulation of photosystem II heterogeneity and stomatal functioning contribute to sustaining photochemistry and photoprotection in mangroves exposed to a cold wave

Cold waves restrict the distribution of mangroves. This study examined the contribution of PSII heterogeneity and stomatal functioning to sustaining photochemistry and photoprotection in mangroves during a cold wave. We exposed eight populations of Kandelia obovata (cold-tolerant) and, Bruguiera gymnorhiza (cold-susceptible) from different latitudes to 27/20°C (favorable) and 10/3°C (chilling; simulated cold wave) day and night temperatures. Multiple trait responses imply that cold waves affected K. obovata the least. Significant changes in chlorophyll fluorescence transients (photosystem II [PSII]) with a slight decrease in the redox status of P700 (photosystem I [PSI]) imply a greater impact of a cold wave on PSII. During the cold wave, photochemical efficiency of PSII, efficiency of the water-splitting complex, light absorptance, stomatal pore area, cyclic electron flow, nonphotochemical quenching, and number of active PSIIα and PSII QB reducing centers decreased, while light transmittance, night respiration, and inactive PSII QB nonreducing, PSIIβ, and γ centers increased in both species. The population of K. obovata from the coldest latitudinal site (Fujian, China) was least affected by cold wave due to local evolutionary adaptations. Modulation of PSII heterogeneity and stomatal functioning is important to sustaining photochemistry and photoprotection in mangroves to cope with cold waves.