RESEARCH & EVENTS
LEFT : Droughted Nonpareil ( wilted leaves and thinner canopy ). RIGHT : Fully irrigated Nonpareil .
It is expected that stomatal conductance would be lowest in the most water stressed trees . Drought sensitive scion / rootstock combinations would reduce stomatal conductance to conserve water ( at the expense of photosynthesis ) while drought tolerant combinations would maintain stomatal conductance ( to continue photosynthesis ) but at the expense of depleting soil water more quickly . Whilst differences between rootstocks were observed , the clearest differences were between varieties ( Nonpareil , Shasta and Vela ). The figure on page 30 compares a representative subset of afternoon stomatal conductance measurements taken from each variety before , during and after the application of the drought treatment . Note that stomatal conductance of control trees varied from day to day , depending on the climatic conditions , so it is the magnitude of change between fully watered and drought treatments that should be compared at any point in time . Measurements collected prior to the trial ( pre-drought ) and from nondroughted ( control ) trees indicated that Nonpareil leaves had higher stomatal conductance than Shasta and Vela when water supply was not limited . When the water stress was applied ( 23 to 26 January ), stomatal conductance of droughted Nonpareil reduced more dramatically compared to the well irrigated trees . The Nonpareil was also more sensitive to the water stress than either the Shasta or Vela . During the recovery phase , after the irrigation was restored , stomatal conductance of droughted Nonpareil trees also recovered more slowly than those of Shasta and Vela . Whilst these data complement visual observations of canopy health , it is important to note that stomatal conductance alone cannot be used to infer drought tolerance . SARDI continues to process corresponding datasets to better define tree response . These datasets include stem water potential , sap flow , soil moisture , canopy size , spectral and thermal
imagery and yield metrics . The integration of these datasets , together with a planned repeat of drought treatments in the first half of season 2025 , will assist in better defining the drought resistance of multiple rootstock / scion combinations .
More information If you are interested in visiting this demonstration trial or any of SARDI ’ s other trials at the ACE experimental orchard , please contact SARDI on 08 8595 9100 or the ABA on 08 8584 7053 .
Acknowledgment SARDI projects conducted at the ACE experimental orchard have been funded by Hort Innovation using the almond research and development levy with co-investment from the South Australian Government and contributions from the Australian Government . For more information on these funds and strategic levy investments visit horticulture . com . au .
industry . australianalmonds . com . au
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