Non-destructive measurements such as Gs and recording of pot weight for the calculation of FTSW was undertaken each day on all twelve plants.
citriodora maintained full rates of Gs until the FTSW reached 50%.
exhibited a 20% decline at 45% FTSW (co-incident with the level of soil water availability at which Gs values fell), and pronounced reductions of 60% and 125% at FTSW levels of 15 and 5%, respectively (Fig.
citriodora leaves was more sensitive to the early stages of drought as a significant difference between the carbon isotope values of control and drought treatment leaves was apparent at 45%, and this upturn in d13C was increasingly evident as FTSW declined further; whereas, the leaves of Z.
The FTSW values for the threshold in decline of ARA ranged from 0.
40 FTSW while the threshold for ARA was shifted to a low value of 0.
Abbreviations: ARA, acetylene reduction assay; FTSW, fraction transpirable soil water.
The relationship between NTR and FTSW for each hybrid in response to a drying soil was first evaluated using the equation described by Muchow and Sinclair (1991) for maize:
In each experiment, a single curve was generated for each hybrid by combining the NTR and FTSW data from the individual plants.
To determine the FTSW point at which stomata began to close, the plateau regression procedures of PC SAS (SAS Institute, Inc.