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Relationships between sap flow and water potential in woody or perennial plants on islands of the Great Barrier Reef
Author(s) -
ALLAWAY W. G.,
PITMAN M. G.,
STOREY R.,
TYERMAN S.
Publication year - 1981
Publication title -
plant, cell and environment
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.646
H-Index - 200
eISSN - 1365-3040
pISSN - 0140-7791
DOI - 10.1111/1365-3040.ep11604561
Subject(s) - shoot , xylem , transpiration , biology , botany , vapour pressure deficit , perennial plant , horticulture , photosynthesis
. This paper describes studies on trees of Pisonia grandis , bushes of Argusia argentea , and the perennial herb Melanthera biflora , growing on One Tree Island, a coral cay of the Great Barrier Reef with ‘soil’ of coarse coral rubble. Water potential (Ψ b , measured on small shoots with a pressure chamber), sap flow, stomatal conductance, vapour pressure deficit and photon flux density were monitored over day/night cycles. Sap flow and Ψ b responded to changes in light and humidity. From these experiments good linear correlations were found between sap flow in a shoot and Ψ b of similar adjacent shoots. The linearity suggests that the resistance to sap flow is constant as Ψ b varies. The correlation, however, does not indicate a causal relationship between Ψ b of an individual shoot on the plant and its sap flow. Ψ b was only slightly different in shaded shoots from those in sunshine, although sap flow would be expected to differ between them. Enclosing shoots and so reducing their transpiration and sap flow to very low rates resulted in only small changes in Ψ b of the enclosed shoots; Tb of such enclosed shoots should closely approximate that of the xylem at the point of shoot attachment. From these results it is suggested that the resistance to water flow in shoot and leaf xylem is small compared to the resistance further down the plant, in the root or at the root/soil interface. Shoot xylem water potential would be similar for all parts of the plant, and in such plants the water potential of shoots in the shade would be determined by the overall water use of the plant.