Ecological differentiation in xylem cavitation resistance is associated with stem and leaf structural traits

Abstract

Cavitation resistance is a critical determinant of drought tolerance in tropical tree species, but little is known of its association with life history strategies, particularly for seasonal dry forests, a system critically driven by variation in water availability. We analysed vulnerability curves for saplings of 13 tropical dry forest tree species differing in life history and leaf phenology. We examined how vulnerability to cavitation (P50) related to dry season leaf water potentials and stem and leaf traits. P50-values ranged from -0.8 to -6.2 MPa, with pioneers on average 38% more vulnerable to cavitation than shade-tolerants. Vulnerability to cavitation was related to structural traits conferring tissue stress vulnerability, being negatively correlated with wood density, and surprisingly maximum vessel length. Vulnerability to cavitation was negatively related to the Hubervalue and leaf dry matter content, and positively with leaf size. It was not related to SLA. We found a strong trade-off between cavitation resistance and hydraulic efficiency. Most species in the field were operating at leaf water potentials well above their P50, but pioneers and deciduous species had smaller hydraulic safety margins than shade-tolerants and evergreens. A trade-off between hydraulic safety and efficiency underlies ecological differentiation across these tropical dry forest tree species.

Groundwater-dependent ecosystems: recent insights from satellite and field-based studies

“…Leaf water potential at turgor loss is recognised as a physiological measure of plant sensitivity to water stress (McDowell et al, 2008). Similarly, measurements of vulnerability to xylem cavitation and safety margins are critical determinants of drought tolerance (Markesteijn et al, 2011;Sperry et al, 2008). Safety margins are equal to the difference between minimum daily branch water potential and PLC 50 Sperry et al, 2008).…”

Do community-weighted mean functional traits reflect optimal strategies?

“…Electronic supplementary material, appendix S1 provides details on trait measurements. Briefly, WD (g cm 23 ) is related to a growth/ mortality trade-off; low WD confers rapid growth, high hydraulic conductance and low investment in structural materials [8], whereas high WD is associated with resistance to drought-induced cavitation and low mortality [10,28]. LMA (g cm 22 ) is positively related to leaf lifespan and, more generally, to variation in lifehistory strategies ranging from fast growth and high mortality by rapid photosynthetic return on carbon investment (low LMA) to slow growth and low mortality by retaining nutrients for a longer time (high LMA) [5].…”

“…For instance, CWM values of tree wood density (WD; g cm 23 ) and leaf mass per area (LMA ¼ 1/specific leaf area (SLA); g m 22 ) generally decline with increasing precipitation [5,8]. Because these traits correspond to resource acquisition and utilization strategies [9,10], these trait-environment relationships can be interpreted in terms of physiological trade-offs related to resource availability (i.e. drought resistance and resource conservation in dry conditions versus rapid growth and resource acquisition when water is abundant).…”

Going Back to Basics: Importance of Ecophysiology when Choosing Functional Traits for Studying Communities and Ecosystems

“…For instance, ecophysiological approaches, even when not labeled as functional ecology, have been successfully used in studies on species distribution (Borchert 1994), functional convergence (Grime 1977;Wright et al 2002), species interactions (Wardle et al 1998), mechanism of coexistence (Markesteijn et al 2011), environmental filtering (Grime 1977;Borchert 1994), ecosystem processes/services (Wardle et al 1998) and conservation biology (Wikelski & Cooke 2006). …”