Antagonistic effect of Mn and NaCl in irrigation water on cotton growth and yield

The stresses of salinity and some trace elements along with the mutual relations on plant growth and yield have been well investigated and well documented in the literature. The combined effects of the two factors can be additive, antagonistic or synergistic. A soilless culture experiment was conducted to better understand the combined effects of manganese (Mn) and salinity (NaCl) on cotton growth and yield in a greenhouse at Wuhan Botanical Garden, Chinese Academy of Sciences. There were 30 orthogonal tests with six NaCl-levels and five Mn-levels in three random replicates. NaCl was added to solutions to create six NaCl-levels of concentration (0, 5 mmol·L^-1, 15 mmol·L^-1, 25 mmol·L^-1, 35 mmol·L^-1, 45 mmol·L^-1) to form six electrical conductivities (EC) (2.36 dS·m^-1, 2.90 dS·m^-1, 3.95 dS·m^-1, 5.04 dS·m^-1, 6.11 dS·m^-1, 7.17 dS·m^-1, respectively). The Mn factor was at five levels where MnCl2 was added to solutions to create five Mn-levels of concentration (4.5 μmol·L^-1, 9 μmol·L^-1, 18 μmol·L^-1, 36 μmol·L^-1, 72 μmol·L^-1). Cotton growth, yield, dry weight and element content were measured. The results showed that salinity inhibited cotton growth but promoted cotton yield when NaCl concentration increased from 15 mmol·L^-1 to 45 mmol·L^-1. Cotton vegetative growth was at the best when NaCl concentration of irrigation water was 15 25 mmol·L ^-1. Dry weight of cotton roots and shoots decreased with increasing salinity as NaCl concentration of irrigation water increased from 25 mmol·L^-1 to 45 mmol·L^-1. The maximum growth and yield occurred when Mn concentration was 36 μmol·L^-1. Mn and salinity had a significant impact on Na and Mn accumulation in cotton leaf. Salinity promoted Na accumulation but inhibited Mn accumulation in cotton leaves. The contents of Na decreased and Mn increased in cotton leaves when Mn concentration levels in irrigation water increased from 18 μmol·L^-1to 72 μmol·L^-1. In order to independently compare the effects of salinity and Mn on cotton, growth and yield of cotton were analyzed in a two-way ANOVA analysis using the MATLAB7.6.0.324 (R2008a) software. The results showed that there were no significant influences of the interactions between salinity and Mn on cotton growth and yield. Thus the effects of the main treatments on cotton growth and yield could be presented and discussed independently. The Abbott equation was used to analyze the combined effects of Mn and salinity on cotton growth and yield and the results showed a negative relationship between Mn and salinity. In other words, the toxic effects on the growth and yield of cotton were less severe for combined Mn and salinity than the expected effects of the individual factors added together.