The Effect Of Rhizosphere Aeration On Ecophysiological Characteristics Of Cotton Seedlings Under Salt Stress

The experiments were performed with hydroponically cultured plants to ensure intact observation of roots and easy osygen control. In this paper, the effect of rhizosphere ventilation and salt stress on the growth of cotton seedings cultivated in nutrient solution was studied. The experiments were divided into five different levels of salt stress(0、100、200、300、400 mmol·L-1 NaCl) and two ventilation conditions(ventilation- O2 content is more than 7 mg·L-1 in culture solutions and no ventilation-O2 content is below 0.3 mg·L-1 in culture solutions) and 10 combinations of treatments.The changes in the growth, photosynthetic performance index, chlorophyll fluorescence, the water potential, osmotic potential of plant water status, Na+, K+content, ash content, calorific value, as well as leaf construction cost in cotton seedling were examined to investigate the effect of rhizosphere ventilation on the growth of cotton under salt stress. The results are as follows:(1) The effect of rhizosphere ventilation on the growth of cotton seedling undersalt stressThe growth rate, plant height, leaf area and dry weight all declined under salt stress; poor ventilation also lead to a decline in the plant height and dry weight. A further comparison of the effect of rhizosphere ventilation and the combined effect of rhizosphere ventilation with salt stress showed that the effect of salt stress on plant height and total biomass is significant, whereas the effect of rhizosphere ventilation on root volume, root biomass and root-shoot ration was even more significant. The adverse effect of salt stress was mainly exhibited on stems and leaves, while that of the rhizosphere ventilation was mainly exhibited on root growth. In addition, the variations in cotton seedlings in terms of plant height, root volume, leaf area, root biomass and total biomass in the rhizosphere ventilation conditions is much smaller than those in seedlings without ventilation. It is suggested that rhizosphere ventilation could lead to an increase in plantlet height, leaf area, dry weight, alleviating the adverse effect of salt stresses.(2) The effect of rhizosphere ventilation on plant water status and ion contentof cotton seedling under salt stressSalt stress and hypoxia stress can improve the moisture of cotton seedlings,reducing leaf water potential, osmotic potential. The salt stress lead to a increse in Na+content and Na+/K+, and a decline in the content of K+ in roots, stems and leaves.Rhizosphere environment ventilation treatment can lead to a decline in Na+accumulation, a increase in the content of K+ and a decline in Na+/K+, stimulate the osmotic regulation of cotton, so as to enhance the resistance of cotton.(3) Effect of rhizosphere ventilation on the photosynthetic perfotmance indexand chlorophyll fluorescence of cotton seedling under salt stressHypoxia stress result in a increase in Fo, ABS/RC, a significant decline in Fv,Fv/Fm, Fv/Fo; Low conceatration NaCl treatment had a less effect on fluorescence parameters. Fo, Fv, ABS/RC, Fv/Fm, and Fv/Fo change slightly, but fluorescence parameters significantly reduced with the increase of NaCl concentration. Salt stress and hypoxia stress lead a decline in net photosynthetic rate. Rhizosphere ventilation can reduce the damage of salt stress on cotton leaves photosynthetic organs, improve photosynthetic activity of mesophyll cells and eventually improve the photosynthetic ability of cotton.(4) The effect of rhizosphere ventilation on ash content, calorific value and leafconstruction cost of cotton seedling under salt stressThe ash content was significantly higher, but the calorific value were significantly lower in leaves with rhizosphere ventilation than in leaves under anoxia conditions with no salt or low salt stress, showing that the rhizosphere ventilation can promote the absorption of mineral elements and plant growth. Under higher concentration of salt stress, the ash content increased and the calorific value declined because of the plant photosynthesis was suppressed and the accumulation of photosynthate significantly reduced as a result of anoxia. Further analysis found that salt stress and low oxygen stress lead to a decline in leaf construction cost. It is suggested that rhizosphere ventilation could enhance the resistance of cotton seedlings to stress. However, in theory, the reduction of construction costs did not match with the increase of the growth rate in this experiment. Further study is needed for this reason.To sum up: the rhizosphere ventilation can alleviate the adverse effect of salt stresses on the photosynthesis and the growth in cotton seedlings, promote the absorption of mineral elements by the plants.