Coordination of pinna, petiole, and root anatomical traits in 24 tropical-subtropical fern species.

Ferns are primitive vascular plants with diverse morphologies and structures. Plant anatomical traits and their linkages can reflect adaptation to the environment; however, these remain are still poorly understood in ferns. The main objective of this study was to explore whether there was structural coordination among and within organs in fern species. We measured 16 hydraulically related anatomical traits of pinnae, petioles, and roots of 24 representative fern species from the tropical and subtropical forest understory and analyzed trait correlation networks. In addition, we examined phylogenetic signals for the anatomical traits and analyzed co-evolutionary relationships. These results indicated that stomatal density and all petiole anatomical traits exhibited significant phylogenetic signals. Evolutionary correlations were observed between the tracheid diameter and wall thickness of the petiole and between the water transport capacity of the petiole and stomatal density. Conversely, anatomical traits of roots (e.g., root diameter) showed no phylogenetic signals and were not significantly correlated with those of the pinnae and petioles, indicating a lack of structural coordination between the below- and above-ground organs. Unlike angiosperms, vein density is unrelated to stomatal density or pinna thickness in ferns. As root diameter decreased, the cortex-to-stele diameter ratio decreased significantly (enhanced water absorption) in angiosperms but remained unchanged in ferns. These differences lead to different responses of ferns to climate change and improve our knowledge of the water adaptation strategies of ferns.

Correlations between leaf economics, mechanical resistance and drought tolerance across 41 cycad species.

BACKGROUND AND AIMS: We conducted a comprehensive analysis of the functional traits of leaves (leaflets) of cycads. The aim of this study was to clarify the functional divergence between the earlier origin Cycadaceae and the later differentiated Zamiaceae, and the differences in trait associations between cycads and angiosperms. METHODS: We selected 20 Cycadaceae species and 21 Zamiaceae species from the same cycad garden in South China, and measured their leaf structure, economic traits, mechanical resistance (Fp) and leaf water potential at the turgor loss point (πtlp). In addition, we compiled a dataset of geographical distribution along with climatic variables for these cycad species, and some leaf traits of tropical-sub-tropical angiosperm woody species from the literature for comparison. KEY RESULTS: The results showed significantly contrasting leaf trait syndromes between the two families, with Zamiaceae species exhibiting thicker leaves, higher carbon investments and greater Fp than Cycadaceae species. Leaf thickness (LT) and πtlp were correlated with mean climatic variables in their native distribution ranges, indicating their evolutionary adaptation to environmental conditions. Compared with the leaves of angiosperms, the cycad leaves were thicker and tougher, and more tolerant to desiccation. Greater Fp was associated with a higher structural investment in both angiosperms and cycads; however, cycads showed lower Fp at a given leaf mass per area or LT than angiosperms. Enhancement of Fp led to more negative πtlp in angiosperms, but the opposite trend was observed in cycads. CONCLUSIONS: Our results reveal that variations in leaf traits of cycads are mainly influenced by taxonomy and the environment of their native range. We also demonstrate similar leaf functional associations in terms of economics, but different relationships with regard to mechanics and drought tolerance between cycads and angiosperms. This study expands our understanding of the ecological strategies and likely responses of cycads to future climate change.

Co-ordination between leaf biomechanical resistance and hydraulic safety across 30 sub-tropical woody species.

BACKGROUND AND AIMS: Leaf biomechanical resistance protects leaves from biotic and abiotic damage. Previous studies have revealed that enhancing leaf biomechanical resistance is costly for plant species and leads to an increase in leaf drought tolerance. We thus predicted that there is a functional correlation between leaf hydraulic safety and biomechanical characteristics. METHODS: We measured leaf morphological and anatomical traits, pressure-volume parameters, maximum leaf hydraulic conductance (Kleaf-max), leaf water potential at 50 % loss of hydraulic conductance (P50leaf), leaf hydraulic safety margin (SMleaf), and leaf force to tear (Ft) and punch (Fp) of 30 co-occurring woody species in a sub-tropical evergreen broadleaved forest. Linear regression analysis was performed to examine the relationships between biomechanical resistance and other leaf hydraulic traits. KEY RESULTS: We found that higher Ft and Fp values were significantly associated with a lower (more negative) P50leaf and a larger SMleaf, thereby confirming the correlation between leaf biomechanical resistance and hydraulic safety. However, leaf biomechanical resistance showed no correlation with Kleaf-max, although it was significantly and negatively correlated with leaf outside-xylem hydraulic conductance. In addition, we also found that there was a significant correlation between biomechanical resistance and the modulus of elasticity by excluding an outlier. CONCLUSIONS: The findings of this study reveal leaf biomechanical-hydraulic safety correlation in sub-tropical woody species.