The influence of transpiration on foliar accumulation of salt and nutrients under salinity in poplar (Populus × canescens).

Increasing salinity is one of the major drawbacks for plant growth. Besides the ion itself being toxic to plant cells, it greatly interferes with the supply of other macronutrients like potassium, calcium and magnesium. However, little is known about how sodium affects the translocation of these nutrients from the root to the shoot. The major driving force of this translocation process is thought to be the water flow through the xylem driven by transpiration. To dissect the effects of transpiration from those of salinity we compared salt stressed, ABA treated and combined salt- and ABA treated poplars with untreated controls. Salinity reduced the root content of major nutrients like K+, Ca2+ and Mg2+. Less Ca2+ and Mg2+ in the roots resulted in reduced leaf Ca2+ and leaf Mg2+ levels due to reduced stomatal conductance and reduced transpiration. Interestingly, leaf K+ levels were positively affected in leaves under salt stress although there was less K+ in the roots under salt. In response to ABA, transpiration was also decreased and Mg2+ and Ca2+ levels decreased comparably to the salt stress treatment, while K+ levels were not affected. Thus, our results suggest that loading and retention of leaf K+ is enhanced under salt stress compared to merely transpiration driven cation supply.