RESEARCH & EVENTS
Update on orchard resilience to short-term water stress
Dane Thomas measuring transpiration rates .
SARDI Almond Production Research Team South Australian Research and Development Institute ( SARDI ), the research division of the Department of Primary Industries and Regions
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THE Autumn 2024 edition of In A Nutshell introduced SARDI ’ s work to assess the response of different rootstock and variety combinations to short-term periods of drought . In 2023 / 24 , a brief pre-harvest drought treatment was applied to five varieties grafted to 14 rootstocks in a section of SARDI ’ s rootstock compatibility screen . While it is too early to definitively point to rootstock differences , there were clear indications that varieties responded differently to the preharvest drought . Visual observations noted that both Vela and Nonpareil quickly wilted and dropped internal leaves . Shasta leaves appeared unaffected . Nonpareil also presented a degree of shoot tip death following the water stress . This did not occur in either Shasta or Vela . Nonpareil ’ s premature desiccation impacted kernel quality on affected shoots causing smaller and visually wrinkled nuts . Multiple plant physiology measures were collected before , during and after the drought treatment to complement these visual observations . One of these measures was stomatal conductance .
In A Nutshell - Winter 2024 Vol 25 Issue 2
Afternoon stomatal conductance measured in three varieties before , during and after a brief ( pre-harvest ) drought treatment .
What is stomatal conductance ? Stomatal conductance is the rate of gas exchange through the stomates ( leaf pores ). It relates to water vapour being lost through transpiration and carbon dioxide being absorbed to support photosynthesis . A common mechanism used by droughted plants to withstand periods of water stress is to close the stomates . This minimises transpiration and allows the plant to survive when water supply from the roots is restricted . However , closing the stomates also leads to lower photosynthetic rates , reducing carbon accumulation , higher leaf temperatures and slowing growth .
Stomatal conductance in droughted scion / rootstock trial Throughout the month-long study period , SARDI used a porometer to measure stomatal conductance twice on each measurement day , once in the morning ( 10am to 12noon ) and once in the afternoon ( 2pm to 4pm ). Repeated measures accounted for variation in plant water status driven by changes in temperature and relative humidity through the day .