Cao, K.-F. | bioRxiv Science

bioRxiv2023

Stomatal dynamics are regulated by leaf hydraulic traits and guard cell anatomy in nine true mangrove species

Stomatal regulation is critical for mangroves to survive water deficits and highly fluctuating ambient water availability in the hyper-saline intertidal zone. Despite the importance of stomatal regulation in mangroves very little is known about stomatal sensitivity to vapour pressure deficit (VPD), and the co-ordination of this trait with stomatal morphology and leaf hydraulic traits in these species. We measured the stomatal response to a step increase in vapour pressure deficit (VPD) in situ, stomatal anatomy, leaf hydraulic vulnerability and pressure-volume traits in nine true mangrove species of five families. We aimed to answer two questions: (1) Does stomatal morphology determine stomatal dynamics in response to a high VPD in mangroves and (2) do leaf hydraulic traits influence stomatal sensitivity to VPD in mangroves? We found that the stomata of mangrove plants highly sensitive to VPD, and that species with higher maximum stomatal conductance had slower stomatal responses to an increase in VPD, and that stomatal density and size were correlated with the speed of stomatal closure at high VPD across the closely-related species. We also found that a higher leaf capacitance (Cleaf) and more resistance to leaf hydraulic vulnerability were associated with slower stomatal responses to an increase in VPD. Our results demonstrate that the dynamics of the stomatal response to an increase in VPD are regulated by leaf hydraulic traits and stomatal morphology. Our work provides a quantitative framework to better understand stomatal regulation in mangroves in an environment with highly dynamic water availability.

ecology↗

bioRxiv2022

Mangroves deviate from other angiosperms in their genome size, leaf cell size, and cell packing density relationships

Background and AimsWhile genome size limits the minimum sizes and maximum numbers of cells that can be packed into a given leaf volume, mature cell sizes can be substantially larger than their meristematic precursors and vary in response to abiotic conditions. Mangroves are iconic examples of how abiotic conditions can influence the evolution of plant phenotypes. MethodsHere, we examined the coordination between genome size, leaf cell sizes, and cell packing densities, and leaf size in 13 mangrove species across four sites. Four of these species occurred at more than one site, allowing us to test the effect of climate on leaf anatomy. ResultsWe found that genome sizes of mangroves were very small compared to other angiosperms, and, like other angiosperms, mangrove cells were always larger than the minimum size defined by genome size. Increasing mean annual temperature of a growth site led to higher packing densities of veins (Dv) and stomata (Ds) and smaller epidermal cells but had no effect on stomatal size. Contrary to other angiosperms, mangroves exhibited (1) a negative relationship between guard cell size and genome size; (2) epidermal cells that were smaller than stomata, and (3) coordination between Dv and Ds that was not mediated by epidermal cell size. Furthermore, mangrove epidermal cell sizes and packing densities covaried with leaf size. ConclusionsWhile mangroves exhibited coordination between veins and stomata and attained a maximum theoretical stomatal conductance similar to other angiosperms, the tissue-level tradeoffs underlying these similar relationships across species and environments was markedly different, perhaps indicative of the unique structural and physiological adaptations of mangroves to their stressful environments.

ecology↗