PARENT SESSION
Oral Session #63: Plant Ecology: Water Relations. Presiding: J. Cleverly.
Thursday, August 9, 2001. 8:00 AM to 12:00 PM. Hall of Ideas H.

Variation in the vulnerability of woody plants to xylem cavitation: relationships with climate, water transport and taxonomy.

Maherali, Hafiz¹, Pockman, William², Jackson, Robert¹, ^{1 2}

ABSTRACT- Although clear links between vulnerability to xylem cavitation and dessication tolerance have been demonstrated, all plants are not uniformly resistant to xylem cavitation and considerable interspecific variation exists. To understand the adaptive significance of this variation, and examine the potential for trade-offs with other traits, we studied the relationships among xylem vulnerability to cavitation, mean annual precipitation (MAP) and water transport traits in a taxonomic context. We compiled a database for 178 species representing 50 families and seven biomes. Vulnerability to cavitation, expressed as the xylem tension at which 50% of conductivity was lost (₅₀), varied from -0.18 to -14.1 MPa. Across climates, resistance to cavitation conformed to adaptive expectations. On average, trees in wet tropical forests were more vulnerable to cavitation (₅₀ = -0.76 MPa) than shrubs in desert biomes (₅₀ = -4.21 MPa). Interspecific variation in the vulnerability of xylem to cavitation was greater in dry (< 500 mm MAP) than in wet climates (>1500 mm MAP) weakening the correlation between species ₅₀ and MAP (r² = 0.24). Correlations between species ₅₀ and water transport traits (K_S, K_L, g_S) were weak (r² < 0.10) and a trade-off between ₅₀ and K_S was only evident in mean comparisons of conifers and angiosperms. We conclude that although vulnerability to xylem cavitation is associated with moisture availability, it is only one of a suite of traits important for drought tolerance in woody plants.

KEY WORDS: Xylem, Cavitation, Climate, Evolution