Simulating nectarine tree transpiration and dynamic water storage from responses of leaf conductance to light and sap flow to stem water potential and vapor pressure deficit

作者：Paudel Indira; Naor Amos; Gal Yoni; Cohen Shabtai^*

来源：Tree Physiology, 2015, 35(4): 425-438.

DOI：10.1093/treephys/tpu113

• capacitance
• isohydric behavior

For isohydric trees mid-day water uptake is stable and depends on soil water status, reflected in pre-dawn leaf water potential (Psi(pd)) and mid-day stem water potential (Psi(md)), tree hydraulic conductance and a more-or-less constant leaf water potential (Psi(l)) for much of the day, maintained by the stomata. Stabilization of Psi(l) can be represented by a linear relationship between canopy resistance (R-c) and vapor pressure deficit (D), and the slope (BD) is proportional to the steady-state water uptake. By analyzing sap flow (SF), meteorological and Psi(md) measurements during a series of wetting and drying (D/W) cycles in a nectarine orchard, we found that for the range of Psi(md) relevant for irrigated orchards the slope of the relationship of R-c to D, BD is a linear function of Psi(md). R-c was simulated using the above relationships, and its changes in the morning and evening were simulated using a rectangular hyperbolic relationship between leaf conductance and photosynthetic irradiance, fitted to leaf-level measurements. The latter was integrated with one-leaf, two-leaf and integrative radiation models, and the latter gave the best results. Simulated R-c was used in the Penman-Monteith equation to simulate tree transpiration, which was validated by comparing with SF from a separate data set. The model gave accurate estimates of diurnal and daily total tree transpiration for the range of Psi(md)s used in regular and deficit irrigation. Diurnal changes in tree water content were determined from the difference between simulated transpiration and measured SF. Changes in water content caused a time lag of 90-105 min between transpiration and SF for Psi(md) between -0.8 and -1.55 MPa, and water depletion reached 3 l h(-1) before noon. Estimated mean diurnal changes in water content were 5.5 l day(-1) tree(-1) at Psi(md) of -0.9 MPa and increased to 12.5 l day(-1) tree(-1) at -1.45 MPa, equivalent to 6.5 and 16.5% of daily tree water use, respectively. Sixteen percent of the dynamic water volume was in the leaves. Inversion of the model shows that Psi(md) can be predicted from D and R-c, which may have some importance for irrigation management to maintain target values of Psi(md). That relationship will be explored in future research.

• 出版日期2015-4