Response of Mexican Lime to Partial Rootzone-drying: A Water-saving Strategy

The effects of alternate and fixed partial rootzone drying (PRD) on leaf gas exchange and water use efficiency (WUE) of citrus were evaluated. Three-year-old split-root potted Mexican Lime trees were grown in a greenhouse. Two irrigation trials were developed, and three treatments were applied in each trial. In the first trial, the treatments were: a) well-watered trees, where both rootzone halves were watered with 50% crop evapotranspiration (ET_c) each day (Control1); b) one half of the rootzone received no water while the other half was daily irrigated with 100% ET_c (fixed PRD, FPRD1); and c) one half of the rootzone was allowed to dry while the other half was irrigated with 100% ET_c by alternating wet and dry halves every two weeks (alternate PRD, APRD1). In the second trial, the distribution of water in the three treatments was the same (control, fixed PRD, and alternate PRD) but water was applied every three days so that every treatment received 300% ET_c in every irrigation event.  The FPRD1 plants used 16.3% significantly less water than Control1. Whole plant WUE was higher in APRD1 plants than in Control1 and FPRD1 plants. Leaf abscisic acid (ABA) concentration in FPRD1 plants was higher than in Control1 plants. FPRD2 and APRD2 plants used 14.7% and 17.3% less water than Control2 plants, respectively. Leaf ABA concentration was significantly higher in FPRD 2 and APRD2 plants than in Control2 plants, but there were no differences in stomatal conductance among treatments. PRD did not affect other leaf gas exchange or growth parameters since all treatments had similar CO₂ assimilation, and leaf area development. Thus, PRD treatments FPRD1, FPRD2 and APRD2 resulted in water savings without compromising growth.