Weak Tradeoff and Strong Segmentation Among Plant Hydraulic Traits During Seasonal Variation in Four Woody Species

Abstract

Plants may maintain long-term xylem function via efficiency-safety tradeoff and segmentation. Most studies focus on the growing season and community level. We studied species with different efficiency-safety tradeoff strategies, <i>Quercus acutissima</i>, <i>Robinia pseudoacacia</i>, <i>Vitex negundo</i> var. <i>heterophylla</i>, and <i>Rhus typhina</i>, to determine the seasonality of this mechanism. We separated their branches into perennial shoots and terminal twigs and monitored their midday water potential (Ψ_md), relative water content (RWC), stem-specific hydraulic conductivity (K_s), loss of 12, 50, and 88% of maximum efficiency (i.e., P₁₂, P₅₀, P₈₈) for 2 years. There were no correlations between water relations (Ψ_md, RWC, K_s) and embolism resistance traits (P₁₂, P₅₀, P₈₈) but they significantly differed between the perennial shoots and terminal twigs. All species had weak annual hydraulic efficiency-safety tradeoff but strong segmentation between the perennial shoots and the terminal twigs. <i>R. pseudoacacia</i> used a high-efficiency, low-safety strategy, whereas <i>R. typhina</i> used a high-safety, low-efficiency strategy. <i>Q. acutissima</i> and <i>V. negundo</i> var. <i>heterophylla</i> alternated these strategies. This mechanism provides a potential basis for habitat partitioning and niche divergence in the changing warm temperate zone environment.