Model Test Study On Alleviation Of Effect Of Nutritional Stress On The Regeneration Of Chinese Fir Plantation In Solution Culture

Three-month-old seedlings of Chinese fir (Cunninghamia laceolatd) were grown in solution culture at pH 4.0 for 80 days with ImM Al to evaluate the effects of varying concentration of Ca, P, NH4+-N or NO3"-N in solution on seedlings growth. The effects on morphological indexes (including fresh weight, dry weight, shoot length, root length and relative elongation ratio), physiological indexes (including MDA content and POD activity), chemical composition of seedlings and concentrations of total and monomeric Al in solution were submitted to statistical analysis and compared. The results indicate:Extensive growth problems of varying severity occurred on Chinese fir seedlings in normal nutrient solution added ImM Al. The Al toxicity could be alleviated by increasing Ca, P, NH4+-N or NCV-N supply. Which were partially associated with the increased ionic strength caused by higher nutrient elements concentration. The main beneficial effects of each nutrient element on seedlings growth under Al stress were different.Significant positive correlations were found between seedlings weight or shoot length and solution Ca/Al molar ratio. MDA content, POD activity and tissue Al increased with the decreasing molar ratio. Tissue Al was at a low level and solution Tol-Al at a high one compared to other treatments among the experiment. The positive effect of Ca concentration on Chinese fir seedlings confirmed the existence of a protective action of Ca against Al toxicity. The protective mechanism attributed to antagonism between Ca and Al and the adverse effect of Ca on the cellular physiology in comparison with Al. In this experiment, Ca/Al ^2.8086 (molar ratio) was the critical ratio.The beneficial effect of high P/A1 molar ratio on Chinese fir seedlings growth under Al stress was similar to Ca/Al. Except a larger proportion of the Al remained in tissue and a lower solution Tol-Al concentration. The direct effect in alleviating Al toxicity of solution P was associated with the detoxification caused by the chelation between P and Al. In the experiment solution P/A1^4.5089 was the critical ratio.Growth of Chinese fir seedlings was improved by increased solution NH4+-N supply. Solution NH4+-N/A1^4. 7087 was critical molar ratio. But the beneficial effects ofNH4+-N/A1 on root morphology and POD activity were less effective compared to Ca or P. Alleviation of Al toxicity by NH4+-N was probably bound to the direct inhibition of A13+ uptake by NH4+.Solution NO3--N could mitigate some of the adverse effect of Al on Chinese fir seedlings growth. MDA content and tissue Al decreased with increasing solution NOs'-N. But there were no direct relationships between each indexes and solution NOs'-N/Al molar ratio. Higher correlated coefficients (still not significant) were found between solution ionic strength and each growth index. The amelioration could not be related to the induced solution pH increase by N(V absorption but probably solely attributable to increase in ionic strength.