Estimating sunflower canopy conductance under the influence of soil salinity

Abstract

Canopy conductance (gc) is the key parameter to quantify eco-hydrology processes. Salinity stress is one of the most important abiotic stresses to growth of crops in arid and semi-arid areas. Understanding the influence of salinity on stomatal movement and accurately describing gc under salt stress are of great significance to quantify agro-hydrology processes affected by salt. Therefore, we measured stomata conductance (gs) of sunflower leaves at different growth stages and soil salinity conditions in two consecutive years. At the same time, the evapotranspiration above canopy and the dynamic changes of soil moisture and salinity in root zone were continuously monitored. It was found that under the same meteorological conditions, leaf gs decreased with the increase of soil salt content. Relatively, gs was more sensitive to salt at seedling and maturity stages than at budding and flowering stages. Furthermore, an empirical formula describing the effect of soil salinity on gs was added to the Jarvis multi-factor multiplication gs model, which used leaf area index (LAI) as a parameter to express the salt tolerance of different growth stages. Effective LAI was used to upgrade the model from leaf scale to canopy scale. gc calculated by Penman-Monteith equation using the farmland canopy evapotranspiration measured by the eddy covariance system was used to evaluate the applicability of model. The results showed that the model could simulate gc well on both the half-hour and the daily average scale. Nash-Sutcliffe efficiency coefficient of the daily average scale model was about 0.65, and determination coefficient of the simulation results of different scales in two years were all above 0.66. Our findings could improve the understanding of influence of salinity on stomatal movement in such areas and provided a basis for simulating canopy evapotranspiration and photosynthesis under salt stress.