Document: BRE-3-32-15

Hydraulic architecture of seasonally dry rainforest tree species of differing leaf phenology from North Queensland, Australia.

CHOAT, B.* ^1,2, J.A.M.HOLTUM ¹, J.G.LULY ¹ and M.C.BALL ²

James Cook University ¹
Australian National University ²

Abstract:
Dry rainforest communities exist as scattered patches within the regionally dominant sclerophyll/savanna vegetation of tropical northern Australia. This landscape is exposed to a distinct wet/dry season pattern and thus a large variation in water availability and evaporative demand. We investigated how variations in hydraulic architecture influence vulnerability to embolism and the ability to survive seasonal drought in tree species of differing leaf phenology. Hydraulic architecture was examined in two evergreen species, Alphitonia excelsa and Austromyrtus bidwillii, and two deciduous species, Brachychiton australe and Cochlospermum gillivraei, growing naturally in a dry rainforest in North Queensland. B. australe and C. gillivraei had significantly wider vessels than the two evergreen species (mean vessel diameters of 176.1 m 3.9 and 120 m 4.1, respectively). There was also a significant difference in vessel diameter between the two evergreen species with values averaging 27.2 m 0.4 in A. bidwillii and 49.7 m 0.7 in A. excelsa. Intervessel pit membranes were examined using SEM. Diameters of intervessel pit membranes were greater in deciduous, averaging 5.4 m 0.2 in B. australe and 7.3 m 0.4 in C. gillivraei, than in evergreen species, averaging 3.2 m 0.1 in A. bidwillii and 3.5 m 0.4 in A. excelsa; however, pit membrane pores could not be detected to a resolution of 30 nm. Measurements of hydraulic conductivity revealed that the deciduous species were vulnerable to embolism at higher xylem than evergreen species. The evergreen species regularly experience < -4.0 MPa during the dry season, while the deciduous species lost their leaves once the daily minimum declines to values of approximately -2.0 MPa. These results indicate that for the species studies, hydraulic architecture and leaf phenology are part of an integrated response to seasonal drought.

Keywords: Hydraulic achitecture, Leaf Phenology, Vulnerability to embolism

This abstract is being presented at: 1:15 PM in session:
Oral Session #34: Water Relations in Trees.