Modelling water use efficiency in a dynamic environment: An example using Arabidopsis thaliana()

Intrinsic water use efficiency (W(i)), the ratio of net CO(2) assimilation (A) over stomatal conductance to water vapour (g(s)), is a complex trait used to assess plant performance. Improving W(i) could lead in theory to higher productivity or reduced water usage by the plant, but the physiological traits for improvement and their combined effects on W(i) have not been clearly identified. Under fluctuating light intensity, the temporal response of g(s) is an order of magnitude slower than A, which results in rapid variations in W(i). Compared to traditional approaches, our new model scales stoma behaviour at the leaf level to predict g(s) and A during a diurnal period, reproducing natural fluctuations of light intensity, in order to dissect W(i) into traits of interest. The results confirmed the importance of stomatal density and photosynthetic capacity on W(i) but also revealed the importance of incomplete stomatal closure under dark conditions as well as stomatal sensitivity to light intensity. The observed continuous decrease of A and g(s) over the diurnal period was successfully described by negative feedback of the accumulation of photosynthetic products. Investigation into the impact of leaf anatomy on temporal responses of A, g(s) and W(i) revealed that a high density of stomata produces the most rapid response of g(s) but may result in lower W(i).