Effects Of Salt-alkaline Mixed Stresses On Growth Of Kochia Sieversiana And Statistical Analysis

The formation of salt-alkaline soil included salinization and alkalinization.The increase of salinity was the character of salinization, and pH becoming high was the character of alkalinization. The aim of this experiment was to show the traits of salt-alkaline mixed stress on plant and the correlativity between saline stress and alkaline stress. The stress conditions of salt-alkalinized soil were simulated to investigate the features and acting factors of salt-alkaline mixed stress, using a natural salt-alkaline tolerant halophyte Kochia sieversiana. According to the features of salt-alkalinized soil in the northeast of China, various salt-alkali conditions with different salinities and pHs were established by mixing NaCl, NaHCO3, Na2SO4, and Na2CO3, in various proportions. The treatments included a salt concentration range of 80 to 400 mmol/L and pH values from 6.93 to 10.68. Seedlings of Kochia sieversiana were stressed under these salt-alkali conditions. Several physiological indices of seedlings stressed, including relative growth rate (RGR), water content, and others,were determined in order to analyze the characteristics of the stresses due to the salt-alkali mixes and their main stress factors.The results showed as followed:(1)The RGR, FW(fresh weight), and DW(dry weight) of Kochia sieversiana decreased with increasing salinity or pH (or alkalinity). This showed that the physiological responses of Kochia sieversiana to the salt-alkaline mixed stresses were closely correlated not only with salinity (the total concentration of stress salt), but also with the pH (or alkalinity).(2) The water content of Kochia sieversiana also decreased with increasing salinity or pH (or alkalinity). However, under the high salt-alkaline mixed stress, a relative water content is still remained in Kochia sieversiana, which is different from other plants.(3) Under the same salinity, RGR decreased with increasing pH. Under the same pH (or alkalinity), RGR decreased with increasing salinity. The alone deleterious effect of a high pH or salinity was significantly less than that of a combination of high pH and salinity. The buffer capacity of the treatment solution was taken as a stress factor in order to simplify the stress factor analysis.(4) The results of the statistical analysis showed that for the stress factors of the salt-alkaline mixed stress, [CO32- ] and [HCO3-] could be fully represented by the buffer capacity, and [Na+] could be fully represented by salinity, whereas [SO42- ] was negligible. Therefore, four factors, salinity, buffer capacity, pH and [Cl-] could reflect all of the stress factors. Perfect linear correlations were observed between all physiological indices and four stress factors by a regression analysis. Thus, the regression analysis showed it is reasonable to consider the four stress factors as the strength value of salt-alkaline mixed stress. Furthermore, the relationships between different physiological indices and various stress factors were shown to be different.Mixed salt-alkaline stress was different from simple saline stress, or simple alkaline stress in damaging to plants. The composition of mixed salt-alkali was more closed to natural salt-alkaline soil, so this research will contribute to improve the salt-alkaline soil.Abbreviations: RGR– relative growth rate; DW– dry weight; FW– fresh weight.