Effects of Non-Uniform Salinity On Growth and Physiology of Citrus Seedlings.

Soil water content and salinity levels are not uniform in citrus groves, particularly with the use of micro-irrigation systems that water only a portion of the root zone.  An experiment using a split-root system of sour orange (Citrus aurantium) seedlings was designed to mimic non-uniform salinity under field conditions.  Growth and physiological parameters were evaluated when half or whole root systems were stressed with sodium chloride (NaCl).  This study was also designed to determine if the non-stressed portion of the root system would compensate for the decrease in water uptake by the stressed portion.

One or both halves of the root system of sour orange seedlings were treated for four months with nutrient solution adjusted with NaCl 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 by 45%.  Similarly, leaf water and osmotic potentials were 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 concentrations.  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.  The non-stressed portion of the root system compensated for the decrease in growth, water uptake, and physiological processes by the stressed portion.