Hydraulic architecture, water relations and vulnerability to cavitation of Clusia uvitana Pittier: a C3-CAM tropical hemiepiphyte

Authors


  • *

    Correspondence should be addressed to M. T. Tyree, Proctor Maple Research Center, P.O. Box 233. Underhill Center, VT 05490, USA.

SUMMARY

Clusia uvitana Pittíer (Clusiacea) is a tropical hemiepiphyte that has been shown to display a high plasticity in the expression of CAM in response to the environment. When water is available CO2 is taken up mostly during the- day. This study of the water relations and hydraulic architecture has revealed that leaf water potentials, £ ranged from 0-7 to -0.9 MPa and changed very little with time or water availability. The absolute hydraulic conductivity of stem segments (K,) and the specific conductivity (K1) were comparable to many other temperate and tropical species, but the leaf specificity conductivity (K1) was 1/3 to 1/30 that of many other species. So stems supported high leaf areas per unit of hydraulic conductivity. C uvitana was very vulnerable to cavitation, reaching 50 % loss of hydraulic conductivity at stem £=1.3 MPa. The species survives in spite of low K1 and high xylem vulnerability, because the CAM physiology insures low transpiration rates and high ability to evade dehydration.

Abbreviations
AL & AW

leaf area and sapwood area, respectively (m2)

D

wod diameter (mm)

xp/ds

pressure potential gradient in xylem

E

evaporative flux density

Kh

hydraulic conductivity of stem segments (kg s−1 m MPa−1)

KL

leaf sepcific conductivity of stem segments (kg s−1 m−1 MPa−1)

Km & Ki

maximum and initial Kh, respectively

Ks

specific conductivity of stem segments (kg s−1 m−1 MPa−1)

PLC

percent loss hydraulic conductivity

VC

vulnerability curve

ψ

water potential (MPa)

ψp

turgor pressure potential (MPa)

ψxp

xylem pressure potential (MPa)

ψπ

osmotic potential (MPa).

Ancillary