Trade-offs between xylem hydraulic efficiency and mechanical strength in Chinese evergreen and deciduous savanna species

Abstract

Evergreen and deciduous species coexist in tropical dry forests and savannas, but differ in physiological mechanisms and life-history strategies. Hydraulic conductivity and mechanical support are two major functions of the xylems of woody plant species related to plant growth and survival. In the study, we measured sapwood-specific hydraulic conductivity (Ks), leaf-specific hydraulic conductivity (KL), modulus of rupture (MOR) and elasticity (MOE), xylem anatomical traits, and fiber contents in the xylems of 20 woody species with contrasting leaf phenology (evergreen vs. deciduous) in a Chinese savanna. Our results showed that deciduous species had significantly higher Ks and KL but lower MOR and MOE than evergreen species. Evergreen species experienced more negative seasonal minimum water potential (Pmin) than deciduous species during the dry season. Furthermore, we found trade-offs between xylem hydraulic efficiency and mechanical strength across species and within the evergreen and deciduous groups, and these trade-offs were modulated by structural and chemical traits. Both Ks and KL were significantly related to hydraulic weighted vessel diameter (Dh) across all species and within the deciduous group. Both MOR and MOE were significantly related to wood density (WD), neutral detergent fiber (NDF), and acid detergent fiber (ADF) across species and within evergreen and deciduous groups. Our findings demonstrated that Chinese evergreen and deciduous savanna species diverged in xylem hydraulic and mechanical functions, reflecting conservative and acquisitive life-history strategies for evergreen and deciduous species, respectively. This study provides new information to understand the hydraulic and biomechanical properties and ecological strategies of savanna species in long-term dry-hot environments.

Linkages among stem xylem transport, biomechanics, and storage in lianas and trees across three contrasting environments

“…Such anatomical trade-offs will determine the xylem functional tradeoffs (Zanne et al, 2010;Crivellaro et al, 2012;Zheng and Martínez-Cabrera, 2013;Janssen et al, 2020;Dória et al, 2022;Zhang et al, 2023a). As an example, K t was negatively related to MOE, also in line with earlier findings (Xiao et al, 2021;Pratt et al, 2021a;Zhang et al, 2022b).…”

“…In addition, the xylem mechanical strength is positively correlated with wood density (Onoda et al, 2010;Zhang et al, 2022b) and hydraulic safety (Pratt et al, 2007). However, the relationships between stem mechanical strength and its structural composition have rarely been tested (Zhang et al, 2022b).…”

“…Higher lignin content in the xylem can strengthen the mechanical support of the plants and also improve drought resistance (Pereira et al, 2017). In addition, the xylem mechanical strength is positively correlated with wood density (Onoda et al, 2010; Zhang et al, 2022b) and hydraulic safety (Pratt et al, 2007). However, the relationships between stem mechanical strength and its structural composition have rarely been tested (Zhang et al, 2022b).…”

“…One possible reason may be that due to the limited xylem space, an increase in the proportion of one cell type might lead to a decrease in the proportion of other cell types, resulting in trade‐offs among different functions (Pratt and Jacobsen, 2017; Plavcová et al, 2019). For example, there is a trade‐off between xylem hydraulic efficiency and mechanical strength across evergreen and deciduous species (Pratt et al, 2021a; Zhang et al, 2022b) and between water storage and mechanical strength (Pratt and Jacobsen, 2017; Chen et al, 2020). Although the study of xylem structure and its function trade‐offs can be helpful to understand plant ecological adaptation, a comprehensive study that includes potential associations and/or trade‐offs among xylem water transport, mechanical strength, and storage is still lacking.…”

China's subtropical deciduous plants are more sensitive to climate change than evergreen plants by flowering phenology

“…Deciduous plants, on the contrary, need new leaves to capture and use newly synthesized photosynthates to support flowering (Du et al., 2015). In response to environmental stresses, such as low temperatures, evergreen and deciduous plants adopt conservative and acquisitive functional strategies, respectively (Zhang et al., 2022). The low sensitivity of conservative species to environmental factors may also lead to late flowering.…”