Salinity level influenced morpho-physiology and nutrient uptake of young citrus rootstocks

Abstract

Soil and irrigation water salinity are major limiting factor to citrus industry in arid environments. The objective of this study was to assess the effects of different salt stress levels on growth and ion uptake of three-month-old citrus rootstocks; sour orange (Citrus aurantium) and Volkamer lemon (Citrus volkameriana). Six levels of NaCl-salinity were used, 0.7 (control), 2, 4, 8, 12 and 15 dS m^-1. Salinity increment from 2.0 to 15.0 dS m^-1 significantly reduced seedlings height, stem diameter, leaf area, root dry weight, leaf relative water content, chlorophyll content index and chlorophyll fluorescence by one to three folds. In addition, leaf and root N concentration reduced by 10%-50%, P 6%-50%, K 8%-47%, Ca⁺² 7%-51% and Mg⁺² 7%-50% when salt stress in the irrigation water increased from 2.0 to 15.0 dS m^-1. Conversely, salt stress increment (2.0-15.0 dS m^-1) increased leaf stomatal resistance (5 folds), proline concentration (1 fold), Na⁺ and Cl^- in the leaf (10 fold) and root (4 fold) when compared to control (0.7 dS m^-1). In term of rootstock, Volkamer had higher seedling height, stem diameter, and root constituents (length, fresh and dry weight) than sour orange. While sour orange had higher leaf Cl^-, Ca⁺² and Mg⁺², Volkamer lemon had higher N, Na⁺, K⁺, and P. However, root nutrient (N, Na⁺, Cl^-, P and Mg⁺²) from Volkamer had consistently higher concentration compared to sour orange at 4.0, 8.0, 12.0 and 15.0 dS m^-1. Therefore, we believe that the Volkamer rootstock is more tolerant to salt stress than sour orange.

Keywords: Ions uptake; Lemon; NaCl; Salt stress; Sour orange.

Fig. 1

Effect of different salinity levels (0.7 (control, 2.0, 4.0, 8, 12, 15 dS m⁻¹) on shoot and root of (A) Volkamer lemon and (B) sour orange rootstocks. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)

Fig. 2

Root length, fresh and dry weight of sour orange (SO) and Volkamer lemon (Vol) under different salinity levels. Different letters indicate significant differences between treatments at p < 0.05. Data represents mean of 4 seedlings.

Fig. 3

Leaf nutrient concentration of sour orange (SO) and Volkamer lemon (Vol) under different salinity levels. Data represents mean of 4 seedlings.

Fig. 4

Root nutrient concentration of sour orange (SO) and Volkamer lemon (Vol) under different salinity levels. Data represents mean of 4 seedlings.