Effects of potassium and sodium supply on drought-adaptive mechanisms in Eucalyptus grandis plantations.

A basic understanding of nutrition effects on the mechanisms involved in tree response to drought is essential under a future drier climate., A large-scale throughfall exclusion experiment was set up in Brazil to gain an insight into the effects of potassium ( K) and sodium ( Na) nutrition on tree structural and physiological adjustments to water deficit., Regardless of the water supply, K and Na supply greatly increased growth and leaf area index ( LAI) of Eucalyptus grandis trees over the first 3 yr after planting. Excluding 37% of throughfall reduced above-ground biomass accumulation in the third year after planting for K- supplied trees only. E. grandis trees were scarcely sensitive to drought as a result of the utilization of water stored in deep soil layers after clear-cutting the previous plantation. Trees coped with water restriction through stomatal closure (isohydrodynamic behavior), osmotic adjustment and decrease in LAI. Additionally, droughted trees showed higher phloem sap sugar concentrations., K and Na supply increased maximum stomatal conductance, and the high water requirements of fertilized trees increased water stress during dry periods. Fertilization regimes should be revisited in a future drier climate in order to find the right balance between improving tree growth and limiting water shortage. [ABSTRACT FROM AUTHOR]