This paper incorporates the cumulative effect of water stress, in a phenomenological model of stomatal conductance of upper canopy foliage (g su ) for Eucalyptus globulus and Eucalyptus nitens. Maximum observed stomatal conductance of irrigated trees was moderated by three functions describing the response of g su to light, air temperature and vapour pressure deficit. This model explained 70% of the variation in g su of irrigated trees using the same parameter values for both species. Daily total conductance was calculated for rainfed (G su,R ) and irrigated (G su,I ) trees. Linear relationships between the ratio of G su,R /G su,I (f(W)) and pre-dawn water potential explained only 46 and 30%, respectively, of variation in f(W) for E. globulus and E. nitens. The average value of pre-dawn water potential for the preceding x days (S ⌿x ) was calculated for a range of values of x. When x was 8 for E. globulus and 20 for E. nitens a single exponential decay function accounted for 70% of variation in f(W) for both species. This result and the number of days over which it was necessary to calculate (S ⌿x ) were consistent with previous studies of the leaf water relations, canopy and sapwood development, and stomatal behaviour of the two species.
Early patterns of growth and water use of Eucalyptus globulus subsp globulus Labill. and Eucalyptus nitens (Deane and Maiden) Maiden were measured for the first four years in a plantation established on a low rainfall site in south-east Tasmania. Half the plantation was irrigated to maintain soil water deficits at levels where available water did not limit growth: the other half was subjected to a series of water stress cycles which were interrupted by rainfall or terminated by supplementary irrigation to end severe drought stress.Height of E. globulus was greater than that of E. nitens irrespective of water status. For both height and diameter, differences due to levels of available water remained insignificant until the third year of growth. Increments in volume were significantly higher in E. globulus than E. nitens in the third and fourth year of growth and these differences were more apparent in the rainfed than the irrigated treatment. However there were no differences in water use between species for either treatment in the second, third or fourth year of growth. Maximum rates of growth were associated with total water use just above pan evaporation.The ratio of water use (mm water) to volume increment (m 3 ) was always lower for E. globulus than E. nitens. It was concluded that E. globulus was more suited to sites where moderate water stress is experienced as part of the normal annual growing cycle.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.