Convergence in hydraulic architecture, water relations and primary productivity amongst habitats and across seasons in Sydney

Abstract

Convergence in leaf traits across biomes demonstrates generality in plant functioning. Relationships between hydraulic architecture and photosynthesis are less well studied. We investigated convergence in minimum leaf water potential (Ψ_min), conductivity per sapwood area (k_s), Huber value (Hv) and xylem embolism and photosynthesis in four habitats across two seasons (summer and winter) in the Sydney region in heathland, woodland (ridge-top), woodland (below-ridge) and mangrove. Seasonality strongly influenced all parameters in all habitats. Winter Ψ_min values were lower than those for summer in the heathland and both woodland habitats but summer Ψ_min values were lower than those for winter in the mangrove. Summer k_s values were higher than winter values in all habitats, while Hv was higher in winter than summer for all habitats. Loss of conductance due to xylem embolism was larger in summer than winter in eight of 11 species. We also investigated relationships between the hydraulic parameters across habitats. There was a strong, significant inverse correlation between log-transformed Hv and log-transformed k_s, which held across the seasons. There were significant inverse correlations between Ψ_min and xylem embolism, which held within seasons but not across seasons. We found a strong, significant positive correlation between k_s and Ψ_min also within seasons but not across seasons and a significant negative correlation between xylem embolism and k_s for winter but only a weak negative correlation between xylem embolism and k_s for summer. We believe the seasonal patterns and relationships in hydraulic architecture and water relations are driven by the cost of efficient sapwood. This is demonstrated by the negative correlation between photosynthetic rate and k_s in winter.