Trade-off between shoot and root dry weight along with a steady CO2 assimilation rate ensures the survival of Eucalyptus camaldulensis under salt stress

Salt stress is a major challenge for reforestation in arid to semi-arid regions. Therefore the effect of salt stress was tested in 4-months-old saplings of Eucalyptus camaldulensis under controlled conditions. Individuals were subjected to three levels of salt stress (2, 8, 16 d.Sm-1) and several traits describing growth and dry weight production/allocation, as well as physiological attributes were measured. The results showed that salt stress had no impact on plant height or stem diameter. Number of leaves, number of branches, and leaf chlorophyll content decreased significantly under high salt stress treatment. Leaf dry weight decreased significantly, but root dry weight increased significantly from 6.22 to 8.24 g under high salt stress treatment. Total plant dry weight remained similar while the root/shoot ratio increased significantly under high salt stress treatment. The net CO2 assimilation rate remained stable at ~ 10.1 mmol.m-2.s-1 and stomatal conductance decreased significantly to 79 mmol.m-2.s-1 under high salt stress. Consequently, water use efficiency increased significantly to 3.25 mmol.mol-1 under high salt stress. Therefore we may conclude that the young Eucalyptus camaldulensis saplings can tolerate moderate salt stress by increasing dry weight allocation towards the root system and sustaining the CO2 assimilation rate.