根系吸水模型模拟覆膜旱作水稻气孔导度

为构建覆膜旱作水稻根系吸水模型,进一步改进气孔导度模型,该文在湖北十堰开展包含3个水分处理(淹水、覆膜湿润和覆膜旱作栽培)的田间试验,分析覆膜旱作水稻蒸腾(根系吸水)与根长之间的关系,在此基础上建立覆膜旱作水稻根系吸水模型,并将其代替彭曼(Penman-Monteith,PM)方程来估算蒸腾强度,进而与脱落酸(abscisic acid,ABA)参与调控的气孔导度模型耦合,模拟覆膜旱作条件下水稻气孔导度的日变化过程。结果表明,水稻蒸腾与根长呈线性正比关系(R~2=0.96,P0.05),据此建立的根系吸水模型可以较好地模拟覆膜旱作水稻的蒸腾(根系吸水)规律,使蒸腾强度模拟值和实测值间的相对误差基本控制在15%以内;经改进后的Tardieu-Davies气孔导度模型(TD模型)可有效描述不同土层根系吸水流中的ABA浓度及不同根系层ABA的合成对木质部蒸腾流中总ABA含量的贡献,可较好地模拟气孔导度的日变化过程。改进TD模型大大提高了模拟精度,使相对误差不超过7.0%。该研究可为覆膜旱作水稻生理节水机理和水分利用效率评估提供一定的理论依据。

Modeling stomatal conductance using root-water-uptake in ground cover rice production system

Abstract: Ground cover rice production system (GCRPS) has attracted great attention. The rice root system of GCRPS is under water stress, it is necessary to establish root water uptake models to quantify its root-water-uptake. The aim of this study was to investigate the relationship between transpiration (i.e. root-water-uptake) and root length, and thereupon to establish a root-water-uptake model under GCRPS. Furthermore, the Penman-Monteith (PM) equation was replaced by the validated root water uptake model to estimate transpiration rate and improve the traditional stomatal conductance model proposed by Tardieu-Davies (TD) in this study. A field experiment with 3 irrigation levels (named as TPRPS, GCRPSsat and GCRPS80%) was conducted in 2013 at Shiyan, Hubei province. Each treatment was designed and replicated 3 times in 9 plots, with an area of 9×10 m2. For treatment TPRPS, a water layer of 2-5 cm in thickness was always maintained on the soil beds. For GCRPSsat, soil water content in the root zone was kept close to saturation by completely filling the furrows with water but without water layer on the soil beds. For GCRPS80%, the management was the same way as that for GCRPSsat before mid-tillering stage, and then transient irrigation was intermittently implemented through the furrows to keep soil water content in the root zone between 80%-100% of field water-water holding capacity. A seepage-proof material was laid around each plot to the depth of 80 cm to avoid lateral percolation between neighbor plots. Five soil beds in each plot were built for planting rice, with the space of 26×18 cm2. Small furrows (15 cm in width and depth) were dug around each soil bed. The water saving characteristics of GCRPS were analyzed as a function of the measured soil water conditions, water input and consumption, and plant parameters regarding root growth and physical parameter were also determined. The soil water content under GCRPS was measured with a capacitance probe. Roots in each soil layer were washed via a sieve and analyzed for root length. Stomatal conductance of flag leaves were measured using a portable photosynthesis system. Experimental results showed that the potential transpiration rate was linearly proportional to the total root length of rice (R2=0.96, P<0.05). The root-water-uptake model established on the linear relationship simulated the dynamics of transpiration under GCRPS successfully, with the relative errors between simulated and measured transpiration rates less than 15%. The PM equation was replaced by the validated root water uptake model to estimate transpiration rate and to improve the TD model. The daily dynamics of stomatal conductance under GCRPS was simulated with the improved TD model by combining the established root water uptake model. The improved TD model was applied to estimate the ABA concentration of root water flow in various soil layers and evaluate the contribution of ABA synthesized in each root layer to that in transpiration flow in xylem. Compared with the traditional TD model, the improved TD model simulated the daily dynamics of stomatal conductance more accurately, with relative error less than 7.0% and root mean square error of 0.02 mol/(m2·s). This study can provide valuable information for understanding the physiological water saving mechanism and water use efficiency evaluation of GCRPS.