Armidale, Australia
Armidale, Australia

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Zeppel M.J.B.,Macquarie University | Lewis J.D.,Fordham University | Lewis J.D.,University of Western Sydney | Medlyn B.,Macquarie University | And 8 more authors.
Tree Physiology | Year: 2011

Nocturnal water flux has been observed in trees under a variety of environmental conditions and can be a significant contributor to diel canopy water flux. Elevated atmospheric CO 2 (elevated [CO 2]) can have an important effect on day-time plant water fluxes, but it is not known whether it also affects nocturnal water fluxes. We examined the effects of elevated [CO 2] on nocturnal water flux of field-grown Eucalyptus saligna trees using sap flux through the tree stem expressed on a sapwood area (J s) and leaf area (E t) basis. After 19 months growth under well-watered conditions, drought was imposed by withholding water for 5 months in the summer, ending with a rain event that restored soil moisture. Reductions in J s and E t were observed during the severe drought period in the dry treatment under elevated [CO 2], but not during moderate- and post-drought periods. Elevated [CO 2] affected night-time sap flux density which included the stem recharge period, called 'total night flux' (19:00 to 05:00, J s,r), but not during the post-recharge period, which primarily consisted of canopy transpiration (23:00 to 05:00, J s,c). Elevated [CO 2] wet (EW) trees exhibited higher J s,r than ambient [CO 2] wet trees (AW) indicating greater water flux in elevated [CO 2] under well-watered conditions. However, under drought conditions, elevated [CO 2] dry (ED) trees exhibited significantly lower J s,r than ambient [CO 2] dry trees (AD), indicating less water flux during stem recharge under elevated [CO 2]. J s,c did not differ between ambient and elevated [CO 2]. Vapour pressure deficit (D) was clearly the major influence on night-time sap flux. D was positively correlated with J s,r and had its greatest impact on J s,r at high D in ambient [CO 2]. Our results suggest that elevated [CO 2] may reduce night-time water flux in E. saligna when soil water content is low and D is high. While elevated [CO 2] affected J s,r, it did not affect day-time water flux in wet soil, suggesting that the responses of J s,r to environmental factors cannot be directly inferred from day-time patterns. Changes in J s,r are likely to influence pre-dawn leaf water potential, and plant responses to water stress. Nocturnal fluxes are clearly important for predicting effects of climate change on forest physiology and hydrology. © 2011 The Author. Published by Oxford University Press. A ll rights reserved.

Duursma R.A.,University of Western Sydney | Barton C.V.M.,Forest Science Center | Eamus D.,University of Technology, Sydney | Medlyn B.E.,Macquarie University | And 5 more authors.
Tree Physiology | Year: 2011

Elevated atmospheric [CO 2] (eCa) often decreases stomatal conductance, which may delay the start of drought, as well as alleviate the effect of dry soil on plant water use and carbon uptake. We studied the interaction between drought and eCa in a whole-tree chamber experiment with Eucalyptus saligna. Trees were grown for 18 months in their Ca treatments before a 4-month dry-down. Trees grown in eCa were smaller than those grown in ambient Ca (aCa) due to an early growth setback that was maintained throughout the duration of the experiment. Pre-dawn leaf water potentials were not different between Ca treatments, but were lower in the drought treatment than the irrigated control. Counter to expectations, the drought treatment caused a larger reduction in canopy-average transpiration rates for trees in the eCa treatment compared with aCa. Total tree transpiration over the dry-down was positively correlated with the decrease in soil water storage, measured in the top 1.5 m, over the drying cycle; however, we could not close the water budget especially for the larger trees, suggesting soil water uptake below 1.5 m depth. Using neutron probe soil water measurements, we estimated fractional water uptake to a depth of 4.5 m and found that larger trees were able to extract more water from deep soil layers. These results highlight the interaction between rooting depth and response of tree water use to drought. The responses of tree water use to eCa involve interactions between tree size, root distribution and soil moisture availability that may override the expected direct effects of eCa. It is essential that these interactions be considered when interpreting experimental results. © 2011 The Author. Published by Oxford University Press. A ll rights reserved.

Baltzer J.,University of Waterloo | Patankar R.,University of Waterloo | Downey A.,ICT International | Downey A.,University of Western Australia | Quinton W.,University of Waterloo
Acta Horticulturae | Year: 2013

Boreal forests occupy latitudes that are expected to warm most dramatically over the coming decades, and evidence indicates that changes are already underway in these systems. Much of the boreal is underlain by permafrost, which can be expected to have important consequences for boreal forests as the climate warms. The southern margin of permafrost is especially susceptible to warming, since in this region, the permafrost is discontinuous, relatively thin (<10 m), warm and ice-rich. In the zone of discontinuous permafrost, permafrost forms the physical foundation on which trees develop, forming tree-covered peat plateaus. Trees in this system face two primary issues relating to ground ice: a) seasonal thaw of the active layer is not complete until July placing potential constraints on root function due to limited rooting space and low soil temperatures; and b) climate warming induced permafrost thaw is leading to ground surface subsidence, which destabilizes the trees, and waterlogging of soils, which may negatively impact root function. To investigate the impact of these cryotic processes on tree root function, we installed Heat Ratio Method (HRM) sap flow sensors on the roots of Picea mariana trees occurring on the edges of permafrost plateaus and in the interior of the plateau at the onset of active layer thaw. This allowed us to investigate seasonal changes in water uptake in response to increasing active layer thickness, which was remarkably stable throughout this period. In contrast, the location of trees in relation to degrading permafrost edges had marked impacts on root function. Specifically, trees on degrading edges had negligible sap flow rates that showed little or no diurnal pattern. However, when roots on the opposite side of the tree from the degrading edge were measured, sap flow rates comparable to the highest values from interior plateau trees were found. The relevance of these findings to permafrost thaw processes and local hydrology will be discussed. © ISHS 2013.

Forster M.A.,ICT International | Forster M.A.,University of Queensland
Tree Physiology | Year: 2014

Nocturnal sap flow (Qn) has been found to occur across many taxa, seasons and biomes. There is no general understanding as to how much Qn occurs and whether it is a significant contribution to total daily sap flow (Q). A synthesis of the literature and unpublished data was made to determine how significant is Qn, as a proportion of Q (%Q n), across seasons, biomes, phylogenetic groups and different thermometric sap flow methods. A total of 98 species were analysed to find that %Qn, on average, was 12.03% with the highest average dataset of 69.00%. There was significantly less %Qn in winter than in other temperate seasons, and significantly less %Qn in the wet season than in the dry season. The equatorial and tropical biomes had significantly higher %Qn than the warm temperate and nemoral biomes. The heat ratio method (HRM) and the thermal dissipation (TDP) method had significantly higher %Q n than the heat balance method. Additional analysis between HRM and TDP found HRM to have significantly higher %Qn in winter, wet season and various biomes. In all but one out of 246 cases Qn occurred, demonstrating that Qn is significant and needs to be carefully considered in sap flow and related studies. © 2014 The Author.

Doronila A.I.,University of Melbourne | Forster M.A.,ICT International | Forster M.A.,University of Queensland
International Journal of Phytoremediation | Year: 2015

Monitoring of trees with reliable technology is essential in phytoremediation. Sap flow instrumentation on three Eucalyptus species at a mine site in western Victoria, Australia, was used to determine which species is best suited to meet the goals of a phytoremediation project. Specifically, the aim of the monitoring was to determine which species could better tolerate the hypersaline soil, potentially lower saline ground water, and cope with expected hotter and drier weather given climate change scenarios. Over a summer period, average daily water use of E. cladocalyx was approximately six times greater than E. melliodora and four times greater than E. polybractea. During a three day heat wave event, E. cladocalyx was found to have a higher tolerance to extreme temperature. The optimal VPD / temperature for tree transpiration was 2.6 kPa / 26.2 °C for E. cladocalyx, 2.1 kPa / 23.9 °C for E. melliodora, and 2.0 kPa / 23.2 °C for E. polybractea. Through sap flow monitoring, it was determined that E. cladocalyx could better tolerate saline soils, hotter and drier weather, and had greater potential to lower saline ground water. © 2015, Taylor & Francis Group, LLC.

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