Effects of NaCl and Zn on Growth and Nutrient Elements Uptake of Cotton

Brackish water distributes widely in arid area of Northwest China and the NaCl and trace element contents in brackish water are higher than those in fresh water. Cotton (Gossypium hirsutum L.) is likely to be affected by simultaneous NaCl and manganese toxicity stress when irrigated with brackish water. The crop yields including cotton (Gossypium hirsutum L.) are usually reduced by poor quality of irrigation water or the low contents of nutrient elements in soil. Many experiments indicate that some salinities in irrigation water or soil will affect the cotton growth and yield, and the predominant salt damage to cotton plant is from sodium (Na⁺). Meanwhile proper nutrient supply for cotton plant, especially trace elements for cotton, is important. Cotton diseases and abnormal growth are caused by lack or excess of trace elements. However, it remains beyond our full understanding as to the combined effect of salinity and trace elements on cotton growth and its uptake of nutrient elements. Thus we selected the trace element zinc which is sensitive to cotton growth, and conducted a pot experiment including 24 different treatments in irrigation with 6 NaCl levels (0 mmol/L, 5 mmol/L, 15 mmol/L, 25 mmol/L, 35 mmol/L and 45 mmol/L) and 4 Zn levels (0.192 0 μmol/L, 0.767 6 μmol/L, 3.068 0 μmol/L and 12.272 0 μmol/L) in three replicates randomly in a greenhouse at Wuhan Botanical Garden, Chinese Academy of Sciences. During the experiment, cotton growth of different treatments was measured every ten days after germination and cotton plants were harvested 197 days after sowing. The cotton bolls were harvested and air dried and weighted the wool without seeds to calculate the lint yields. Cotton samples of roots, stems, leaves and fruits were brushed to remove the sand and dusts, rinsed with deionized water; oven dried at 70 ℃ for two days and weighed dry weight. The dry matters of cotton for each treatment were triturated and sampled 0.5 g for acid digestion. Twenty-seven elements were measured in triplicate by ICP-OES (ICAP6300, Thermo Scientific, England). Nine of the 27 elements i.e. K, Ca, Mg, Na, B, Cu, Fe, Mn and Zn (cotton nutrient elements) are chosen for analysis in this paper. The results show that salinity promoted cotton root, steam growth and cotton lint yields when electrical conductivities (EC) of irrigation water fell in the range of 2.90 to 3.95 dS/m in the zinc deficiency environment. While in the zinc-rich environment, salinity inhibited cotton lint yields when EC was greater than 5.04 dS/m. Cotton plant vegetative growth become faster when Zn concentration of irrigation water in the range of 0.192 to 3.068 μmol/L, while when Zn concentration was greater than 0.767 μmol/L would cause cotton plant lint yields decline. Analysis of variance among cotton growth, root and stem dry weight parameters revealed significant influence by salinity effect but not by Zn. Cotton lint yield parameters revealed that the effect of Zn was more obvious than salinity. Interactive effect on cotton growth and yield between NaCl and Zn in the irrigation water was not observed but antagonistic effect was observed. Contents of nutrient elements Ca, K, Mg, B and Fe, in cotton leaves were higher than those in other organizations. Nutrient elements Cu and Zn in cotton bolls were higher than other organizations. Nutrient elements Na and Mn were not so movable that they are easily accumulated in roots. Zn concentration levels in irrigation water under salinity stress affected the nutrient elements uptake of cotton, caused different contents of nutrient elements in cotton, and then influenced cotton growth and yields.