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Salinity reduces water use and nitrate-N-use efficiency of citrus

Lea-Cox, J.D., Syvertsen, J.P.
Annals of botany 1993 v.72 no.1 pp. 47-54
Citrus reticulata, Citrus limonia, salinity, water use efficiency, nitrate nitrogen, seedlings, sodium chloride, calcium chloride, isotope labeling, transpiration, nutrient uptake, chlorides, stems, roots, dry matter partitioning, shoots
Five-month-old Cleopatra mandarin (Citrus reticulata Blanco) (CM) and Volkamer lemon (Citrus volkameriana Ten. and Pasq.) (VL) seedlings were grown in a glasshouse in 2.3-1 pots of Candler fine sand. Plants were irrigated with either non-saline (ECe = 0.23 dS m-1) or saline (6.13 dS m-1) water using a 3:1 NaCl:CaCl2 solution over a 4-week period. A single application of K15NO3 (1964 atom % excess 15N) at 212 mg Nl-1, was substituted for a normal weekly fertilization after 3 weeks and plants were harvested 7 d later. The transpiration rate, uptake of nitrogen, growth and nitrogen-use efficiency (NUE) on a dry weight basis (mg d. wt mg-1 N) of both species was reduced by salinity. Based on growth, water-use and chloride (Cl) accumulation in leaves, VL was more salt-sensitive than CM, but 15N uptake was equally reduced by salinity in both species. Salinity reduced 15N uptake relatively more than shoot growth over the 7-d period, such that the 15NUE (mg d. wt/microgram-1 15N) of new shoot growth of both species increased. There was no evidence of Cl antagonism of nitrate (NO3) uptake but total plant 15NO3 uptake was positively correlated with whole plant transpiration in both species. Thus, it appears that reductions in NO3 uptake are more strongly related to reduced water use than to Cl antagonism from salt stress.