Comparative study on anatomical traits and gas exchange responses due to belowground hypoxic stress and thermal stress in three tropical seagrasses

Anatomical adaptations of mangroves to the intertidal environment and their dynamic responses to various stresses

Mangroves are intertidal plants that survive extreme environmental conditions through unique adaptations. Various reviews on diverse physiological and biochemical stress responses of mangroves have been published recently. However, a review of how mangroves respond anatomically to stresses is lacking. This review presents major mangrove anatomical adaptations and their modifications in response to dynamic environmental stresses such as high salinity, flooding, extreme temperatures, varying light intensities, and pollution. The available research shows that plasticity of Casparian strips and suberin lamellae, variations in vessel architecture, formation of aerenchyma, thickening of the cuticle, and changes in the size and structure of salt glands occur in response to various stresses. Mangrove species show different responses correlated with the diversity and intensity of the stresses they face. The flexibility of these anatomical adaptations represents a key feature that determines the survival and fitness of mangroves. However, studies demonstrating these mechanisms in detail are relatively scarce, highlighting the need for further research. An in-depth understanding of the structural adaptations of individual mangrove species could contribute to appropriate species selection in mangrove conservation and restoration activities.

Comparative effects of heat stress on photosynthesis and oxidative stress in Halophila ovalis and Thalassia hemprichii under different light conditions

This study investigated the physiological responses of two tropical seagrass species, Halophila ovalis and Thalassia hemprichii, to heat stress under varying light conditions in a controlled 5-day experiment. The experimental design included four treatments: control, saturating light, heat stress under sub-saturating light, and heat stress under saturating light (combined stress). We assessed various parameters, including chlorophyll fluorescence, levels of reactive oxygen species (ROS), antioxidant enzyme activities, and growth rates. In H. ovalis, heat stress resulted in a significant reduction in the maximum quantum yield of photosystem II (Fv/Fm) regardless of the light condition. However, the effects of heat stress on the effective quantum yield of photosystem II (ɸPSII) were more pronounced under saturating light conditions. In T. hemprichii, saturating irradiance exacerbated the heat stress effects on Fv/Fm and ɸPSII, although the overall photoinhibition was less severe than in H. ovalis. Heat stress led to ROS accumulation in H. ovalis and reduced the activity of superoxide dismutase (SOD) and ascorbate peroxidase in the sub-saturating light condition. Conversely, T. hemprichii exhibited elevated SOD activity under saturating light. Heat stress suppressed the growth of both seagrass species, regardless of the light environment. The Biomarker Response Index indicated that H. ovalis displayed severe effects in the heat stress treatment under both light conditions, while T. hemprichii exhibited moderate effects in sub-saturating light and major effects in saturating light conditions. However, the Effect Addition Index revealed an antagonistic interaction between heat stress and high light in both seagrass species. This study underscores the intricate responses of seagrasses, emphasizing the importance of considering both local and global stressors when assessing their vulnerability.