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58 p r a c t i c a l w i n e r y & v i n e ya r d J U n e 2 0 1 4 g r a p e g r o w i n g Understanding the dynamics of night- time transpiration and water rehydra- tion of plants and grapevines has benefited from recent research, with the aim of obtaining amelioration strategies to maximize water-use efficiency for crops in challenging climates. R ecent research on grapevines has challenged the paradigm that C3 and C4 plants do not transpire at night due to complete stomata clo- sure. Grapevine water loss by transpira- tion at night can reach up to 50% of daytime transpiration, depending on the level of aridity and water stress. 19,20 C3 plants (including grapevines), which account for more than 95% of earth's plant species, use rubisco to make a three-carbon compound as the first sta- ble product of carbon fixation. C4 plants possess biochemical and anatomical mechanisms to raise the intercellular car- bon dioxide concentration at the site of fixation; this reduces (and sometimes eliminates) carbon losses by photorespi- ration. Both C3 and C4 plants were thought to close stomata at night. Since nighttime transpiration is not coupled with photosynthesis, it con- tributes to decreased water-use effi- ciency. Furthermore, when plants are not subjected to water stress, nighttime transpiration is highly correlated to vapor-pressure deficit. 18 Therefore, con- sidering climate change models have forecasted that nighttime temperatures will increase at a higher rate compared with diurnals, nighttime transpiration might be exacerbated in future global- warming scenarios. 11 Respecting new insights from research, it is a concern that nighttime transpira- tion has not been considered in small- s c a l e e v a p o t r a n s p i r a t i o n m o d e l s (irrigation scheduling of crops), nor for large-scale models (catchments and for- est water-use estimations). This creates a problem for water footprint, water bal- ance and evapotranspiration calculations that could potentially affect growers, irri- gation practitioners, water modeling for catchments and government policy. Implications for irrigation/water use C l i m at e - c h a n g e pr e d ic t io n s h ave prompted research into water conserva- tion, since important reductions in rain events in most agricultural areas have been forecasted. Australia is a water-def- icit country, and many areas of the conti- nent have experienced long periods of drought during the past two decades. Australia's agriculture and horticulture industries depend on water supplied by irrigation and use around 70% of the fresh water available. Therefore, much research has explored how to improve water-use efficiency (WUE) at the farm level. In the 1990s in Australia, two major irrigation strategies were developed: reg- ulated deficit irrigation (RDI) and partial root zone drying (PRD). These techniques can help to increase WUE by exploiting plant physiology-manipulation strategies according to the spatial and temporal dis- tribution of water application within the root zone. These techniques rely heavily on pressurized irrigation systems. Growth and wood thickening of trees and shrubs are enhanced with increased atmospheric CO 2 concentration due to higher photosynthesis and decreased Unseen process for local/global water footprint and water balance estimates in grapevines night time pL Ant wAter Loss Figure 1. Dynamics of nighttime water uptake (s n ) for almond trees (Berri, south Australia, season 2009–10). Fully irrigated trees (filled circles) and deficit-irrigated trees (clear circles) respond to water application either by irrigation or rain events. Arrows represent rain events with their magnitude equivalent to litres received per plant. 11 0 200 400 600 800 1000 1200 1400 0 10 20 30 40 50 60 70 24-Nov-09 04-Dec-09 14-Dec-09 24-Dec-09 03-Jan-10 13-Jan-10 23-Jan-10 02-Feb-10 12-Feb-10 22-Feb-10 04-Mar-10 14-Mar-10 24-Mar-10 I + Pp (L tree -1 day -1 ) S n (L tree -1 night -1 ) I + Pp (T100) I + Pp (T60) Sn (T100) Sn (T60) 70 60 50 40 30 20 10 0 11/24/09 12/04/09 12/14/09 12/24/09 01/03/10 01/13/10 01/23/10 02/02/10 02/12/10 02/22/10 03/04/10 03/14/10 03/24/10 1400 1200 1000 800 600 400 200 0 l + Pp (L tree -1 day -1 S n (L tree -1 night 1 ) Sigfredo Fuentes, 1 * Roberta De Bei 2 and Stephen Tyerman 2 1 University of Melbourne, Melbourne School of Land and Environment, Victoria, Australia; 2 School of Agriculture, Food and Wine and Waite Research Institute, University of Adelaide, Plant Research Centre, Waite Campus, Glen Osmond, SA, Australia; *Corresponding author: sfuentes@ unimelb.edu.au BY