Impact of soil nitrate and chloride content on transpiration of crop plants (Acronym: “An-Trans”)

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In many parts of Europe, agriculture is facing two major challenges: crop plants are likely to encounter progressive soil water scarcity and, at the same time, crops in some areas must be supplied with less nitrogen to prevent groundwater and surface water pollution by nitrates. Both challenges are interrelated, since low soil water availability will reduce transpiration and the mass-flow driven uptake of nutrients such as nitrate (NO3−) and chloride (Cl−). In return, the uptake, i.e. the presence of NO3− and Cl− in the leaf, has been shown to affect stomatal movements and thus will have an important impact on water usage by crops. In the envisaged project, the relationship between the soil NO3−-to-Cl− ratio and stomatal movements will be studied on two crop plants; the dicotyledonous legume broad bean and the cereal barley. Both crops are likely to differ in their dependence on NO3− and Cl− for regulation of the stomatal conductance, since stomatal closure in barley depends on NO3− in the apoplast, while this requirement has not been found for dicotyledonous plants. Moreover, it is not known if barley or broad bean guard cells prefer the uptake of NO3− over Cl−, to drive stomatal opening.The project will study the impact of the NO3−-to-Cl− ratio in the soil on stomata in four work packages (WPs), which span the range of experiment with whole plants (WP1) via ion, metabolite and hormone analysis (WP2), single cell experiments (WP3) to the analysis of single transport proteins (WP4). In WP1, the relation between different NO3−-to-Cl− ratios in the soil will be linked to the ability of our model plants to regulate both stomatal movements and leaf hydration. In WP2, we will study to which extend different NO3−-to-Cl− ratios affect the ion, metabolite and hormone (ABA) concentration of the leaf apoplast and the guard cell symplast, while WP3 will show to which extend the anion composition (NO3−, Cl−) can affect stomatal movements. We will test if guard cells of broad bean and barley prefer NO3−, or Cl−, to accompany the osmotic processes that drive stomatal movements. Finally, WP4 will focus on the role of NPF transporters in the uptake NO3− and Cl− into guard cells and the SLAC1-like anion channels that can release these anions. While SLAC1-like channels have been shown to play a major role in regulation of stomatal movements, only little information is available for uptake of NO3− and Cl− into guard cells by NPF-proteins. The results of our project will help to predict both the impact of progressive soil drying and a reduction of NO3−-N input in soils on transpiration by dicotyledonous and cereal crop plants. In this way, mechanistic information is provided that can be integrated into breeding programs for crops with superb regulatory capabilities for stomatal conductance and water consumption.