Response of Split-Root Sour Orange Seedlings to NaCl and Polyethylene Glycol Stresses

Publisher Website
Google Scholar
Abstract
Soil water cotent and salinity levels are seldom uniform in the field, particularly with the use of micro-irrigation systems that may water only a portion of the root zone. For studying non-uniform salinity, a split-root experiment was designed to evaluate growth and water relations when half of the root system of sour orange (Citrus aurantium) seedlings was stressed with sodium chloride (NaCl) or polyethylene glycol (PEG). This study also determined if non-stressed portions of the root system compensated for the decrease in water uptake by the stressed portions. One or both halves of the root system were treated for four months with nutrient solution adjusted with NaCl or PEG to osmotic potentials of −0.10, −0.20, or −0.35 MPa. Shoot dry weight was reduced by only 9% when half of the root system was irrigated with saline solution at −0.10 MPa, but with both halves of the root system at −0.10 MPa, shoot and root dry weights were reduced as much as 45%. Similarly, leaf water and osmotic potentials were also more disturbed under uniform salinity than under non-uniform salinity conditions. Plant growth, leaf water potential, osmotic potential, stomatal conductance, and evapotranspiration decreased with increasing NaCl and PEG concentrations in the nutrient solution. Turgor potential and leaf thickness increased in response to NaCl treatments. Microscopic examination showed that the increase in leaf thickness was due to the development of larger cells in the spongy mesophyll. Shoot growth did not correlate with the average osmotic potential of the two root halves. Seedlings with one stressed half-root system had shoot dry weight and leaf water potential values closer to those of the non-stressed control than to those with the completely stressed root system.