Effect of Aerial Environment and Soil Water Potential on the Transpiration and Energy Status of Water in Wheat Plants¹

Abstract

Water stress is an important factor limiting wheat (Triticum aestivum L.) growth on the Canadian prairies. To determine the effect of evaporative demand and soil water potential on transpiration and leaf water status, Thatcher wheat was grown under four combinations of air temperature and relative humidity in a loam and a clay soil. Transpiration rate, leaf water potential, leaf water content, and soil water potential were determined. The relationship between transpiration rate and soil water potential depended on evaporative demand and soil texture. The decline in the transpiration rate from its maximum commenced at higher soil water potentials under conditions of higher evaporative demand and was more gradual on the clay than on the loam soil, presumably due to the higher capillary conductivity of the former. Permanent wilting occurred at soil water potentials of —20 to —25 bars on the loam soil and at —45 to —50 bars on the clay soil. At these potentials the capillary conductivities of both soils were about equal. Resistance to Water flow in the plant decreased with increased temperature, while changes in relative humidity had no consistent effect. The total resistance to water movement in the plant and the soil increased with decreasing soil water potential and decreasing air temperature. The relationship between leaf water potential and relative water content was affected by aerial environment and soil texture.

Simulating water uptake in the root zone with a microscopic-scale model of root extraction

“…These results reveal that the diurnal cycle of root water potential is very sensitive to the combination of climatic demand [81], water content in the soil [77] and type of soil: during the day, the potential gradients between soil and roots increase whereas, during the night, these gradients decrease to return to equilibrium [44]. The minimal root water potential of each day is lower and lower because a drying soil is correlated to a decrease in soil hydraulic conductivity [97] . It is worth noting that gradients between root and soil water potential are very different, depending on the type of soil.…”

Plant hydraulic transport controls transpiration sensitivity to soil water stress

“…Several other factors not covered in this work could exacerbate the differences between β and PHM predictions. We expect plant capacitance (already incorporated into some TBMs; Xu et al, 2016;Christoffersen et al, 2016) will likely cause further deviations from β. PHMs with capacitance are expected to introduce hysteresis into transpiration downregulation (Zhang et al, 2014) in transport-limited systems that existing β are not equipped to capture. However, this hysteretic behavior may diminish in a high-conductance (i.e., soil-limited) system, because plant and soil water potentials will quickly equilibrate, so β may still be an adequate alternative to a PHM.…”

Een ecofysiologische benadering van ‘schade’, geïllustreerd aan het systeem tarwe, bruine roest en kafjesbruin

“…The maximum of b/k in EW was 500 days. Yang and De Jong (1972) published values for R pl for wheat growing in an artificial environment, ranging from 32 to 59 X 10 3 days. At EW, W, M, and D, the values of b/k were 500, 590, 1000, and 5000 days, or c. 1 %, 1.2%, 2% and 10% of R pl , respectively, and these values were entered into the calculation.…”

“…boundary. As soil-water potential declines, the resistance to water movement in the soil becomes an important part of the overall resistance to water flow (Rijtema, 1965;Yang and De Jong, 1972).…”