Stem and leaf hydraulic properties are finely coordinated in three tropical rain forest tree species

Abstract

Coordination of stem and leaf hydraulic traits allows terrestrial plants to maintain safe water status under limited water supply. Tropical rain forests, one of the world's most productive biomes, are vulnerable to drought and potentially threatened by increased aridity due to global climate change. However, the relationship of stem and leaf traits within the plant hydraulic continuum remains understudied, particularly in tropical species. We studied within-plant hydraulic coordination between stems and leaves in three tropical lowland rain forest tree species by analyses of hydraulic vulnerability [hydraulic methods and ultrasonic emission (UE) analysis], pressure-volume relations and in situ pre-dawn and midday water potentials (Ψ). We found finely coordinated stem and leaf hydraulic features, with a strategy of sacrificing leaves in favour of stems. Fifty percent of hydraulic conductivity (P50 ) was lost at -2.1 to -3.1 MPa in stems and at -1.7 to -2.2 MPa in leaves. UE analysis corresponded to hydraulic measurements. Safety margins (leaf P50 - stem P50 ) were very narrow at -0.4 to -1.4 MPa. Pressure-volume analysis and in situ Ψ indicated safe water status in stems but risk of hydraulic failure in leaves. Our study shows that stem and leaf hydraulics were finely tuned to avoid embolism formation in the xylem.

Evidence for Hydraulic Vulnerability Segmentation and Lack of Xylem Refilling under Tension

“…Resistance to embolism is indeed tightly linked to xylem anatomy at the interspecific level (Lens et al, 2011): air bubbles nucleating onto cell walls and propagate through pores of pit membrane (Jansen et al, 2009;Schenk et al, 2015). Through the gradient in water potential and hydraulic vulnerability segmentation, leaves and petioles isolate perennial parts of the plant from more negative water potentials and hydraulic failure under water deficit in grapevine (as demonstrated in this study) and some tropical tree species (Nolf et al, 2015).…”

“…If leaves or petioles were more vulnerable to embolism than branches and the trunk, then they would be far more likely to suffer embolism during periods of water stress. This would allow petioles, leaves (Nolf et al, 2015), or even young branches (Rood et al, 2000) to become embolized without significant impacts on the trunk and larger branches. In grapevine, petioles have been described as extremely sensitive to cavitation (C 50 of approximately 21 MPa; Zufferey et al, 2011).…”

Wood density, but not leaf hydraulic architecture, is associated with drought tolerance in clones of Coffea canephora

“…A close coordination of stem and leaf hydraulic traits has been observed in tropical tree species, which can result in proper maintenance of safe water status, particularly under limited water availability (Santiago et al 2004;Nolf et al 2015). Here, some apparent coordination between xylem structural properties at the stem and leaf levels was observed under control conditions, reflected by the clustering of traits (VD L and VD S ; Fig.…”

Herb Hydraulics: Inter- and Intraspecific Variation in Three Ranunculus Species

“…Thresholds were computed after fitting the reparameterized Weibull function (Ogle et al, 2009) (Nolf et al, 2015). Although some of these species also had very vulnerable leaves at P k50 of 21 MPa or greater (Hao et al, 2008;Chen et al, 2009;Blackman et al, 2012;Guyot et al, 2012), the majority of previously studied species exhibited P k50 of 21.5 MPa or less and down to 24.3 MPa (Sack and Holbrook, 2006;Blackman et al, 2010;Johnson et al, 2012;Nardini et al, 2012;Bucci et al, 2013).…”