Fuentes, S., Mahadevan, M., Bonada, M., Skewes, M. and Cox, J.W. 2013. Night-time sap flow is parabolically linked to midday water potential for field grown almond trees. Irrigation Science. DOI: 10.1007/s00271-013-0403-3.
Similar results were found for nocturnal water uptake in grapevines from cultivars: Shiraz, Tempranillo and Cabernet Sauvignon.
Fuentes S., De Bei R., Collins M., Escalona J.M., Medrano H., Tyerman S. 2013. Night-time responses to water supply in grapevines (Vitis vinifera L.) under deficit irrigation and partial root-zone drying. Agricultural Water Management (Submitted).
Recent research has helped to break the paradigm stating that C3 and C4 plants do not transpire at night-time due to complete stomata closure. It has been shown that plant water losses by transpiration at night-time can reach levels between 10-60% compared to day-time depending on the level of aridity and water stress. Since night-time transpiration is not coupled to photosynthesis it contributes to decrease water use efficiency. Furthermore, for non-water stress situations, night-time transpiration is highly correlated to vapour pressure deficit. Therefore, considering that climate change models have forecasted that night-time temperatures will increase at a higher rate compared to diurnal temperatures, night-time transpiration might be exacerbated in future global warming scenarios. Considering these new insights from research, it is worrying that night-time transpiration has not been considered in evapotranspiration models neither for small scale (irrigation scheduling of crops) nor for large scales (catchments and forests water use estimations). This issue creates a big problem for water footprint, water balance and evapotranspiration estimations that affect growers, irrigation practitioners, catchment water modelling and government policy. Our research has helped to characterise the dynamics of night-time transpiration and water rehydration of plants to obtain amelioration strategies for crops to maximise water use efficiency under a challenging climate.
Figures below: Parabolic relationships found when comparing night-time water uptake by Almond trees (Sn) and tree water status measured as stem water potential (MPa). Figure 1 shows data taking the averaged values between probes located in the North-East and South West and Figure 2 shows data separating these probes. This example demonstrate that for larger trees it is important to have more than 1 set of probes to account for sap flow variability according to weather conditions and soil moisture.