冬小麦叶片气孔导度模型水分响应函数的参数化

Parameterization of water response functions in leaf stomatal conductance model for winter wheat

植物气孔导度模型的水分响应函数用来模拟水分胁迫对气孔导度的影响过程,是模拟缺水环境下植物与大气间水、碳交换过程的关键算法。水分响应函数包括空气湿度响应函数和土壤湿度(或植物水势)响应函数,该研究基于田间实验观测,分析了冬小麦(Triticum aestivum)叶片气孔导度对不同空气饱和差和不同土壤体积含水量或叶水势的响应规律。一个土壤水分梯度的田间处理在中国科学院禹城综合试验站实施,不同水分胁迫下的冬小麦叶片气体交换过程和气孔导度以及其他的温湿度数据被观测,同时观测了土壤含水量和叶水势。实验数据表明,冬小麦叶片气孔导度对空气饱和差的响应呈现双曲线规律,变化趋势显示大约1kPa空气饱和差是一个有用的阈值,在小于1kPa时,冬小麦气孔导度对空气饱和差变化反应敏感,而大于1kPa后则反应缓慢;分析土壤体积含水量与中午叶片气孔导度的关系发现,中午叶片气孔导度随土壤含水量增加大致呈现线性增加趋势,但在平均土壤体积含水量大于大约25%以后,气孔导度不再明显增加,而是维持在较高导度值上下波动;冬小麦中午叶片水势与相应的气孔导度之间,随着叶水势的增加,气孔导度呈现增加趋势。根据冬小麦气孔导度对空气湿度、土壤湿度和叶水势的响应规律,研究分别采用双曲线和幂指数形式拟合了水汽响应函数,用三段线性方程拟合了土壤湿度响应函数和植物水势响应函数,得到的参数可以为模型模拟冬小麦的各类水、热、碳交换过程采用。

Aims Water response functions in leaf stomatal conductance models are used to simulate the effects of water stress on stomatal conductance.Especially under a water-limited environment,the water response function is a critical method for modeling gas exchange between plant and air.Winter wheat（Triticum aestivum） is an important crop grown under water-limited environment in North China.Our objective is to determine the responses of stomatal conductance of winter wheat to vapor humidity,soil water content and leaf water potential and to determine the appropriate water response functions for winter wheat in North China based on field experiments.Methods Field experiments were carried out at Yucheng Comprehensive Station.Eight water treatment plots were set up to produce different degrees of water stress on winter wheat.Leaf gas exchange and stomatal conductance were measured,along with other environmental and water factors.We analyzed relationships between leaf stomatal conductance and air vapor humidity,soil water content and leaf water potential.Important findings Leaf stomatal conductance of winter wheat decreased with increasing air vapor pressure deficit（VPD）.About 1 kPa in VPD is a valuable threshold value for winter wheat.When VPD is 1 kPa,leaf stomatal conductance decreases rapidly with increasing VPD.But when VPD is 1 kPa,leaf stomatal conductance decreases slightly even with a large VPD increase.A hyperbolic function can simulate the response of stomatal conductance of winter wheat to VPD.Midday leaf stomatal conductance linearly increases when soil water content increases,but the maximum threshold is about 25% of mean soil water volumetric contents,above which leaf stomatal conductance fluctuates in high conductance and does not show a simple increasing trend.A similar relationship between midday leaf stomatal conductance and soil water content occurs between midday leaf water potential and midday leaf stomatal conductance,where the maximum threshold in midday leaf water potential is about-1 MPa when the leaf stomatal conductance becomes relatively stable.We obtained the vapor humidityresponse function for winter wheat in hyperbolic and power exponent forms based on our field experimental data by data-fitting methods.We also obtained the soil water content response function and leaf water potential response function in simple linear form.These water response functions are useful for the application on modelling surface processes for winter wheat,especially in North China.