Influence Of Different Adversity Stresses On Chinese Fir Seedlings' Physiological Indexes And Root Exudates

Chinese firs are one of the most important tree species in afforestation in the southern China .However continuous planting on the plot leads to soil depression, which causes a decline in production. Researchs showed that continuous planting may cause decline of soil PH value and fertility, it may also lead to other adverse consequence such as aggravation of aluminum toxicity and self toxicity. In this experiment, we used 1 year old Chinese fir seedlings as experimental materials, cultivated it in Hoagland nutrient solution and analysised the variation of physiological indexes such as SOD,POD,MDA and net photosynthetic rate under the stress of pH,nutrition,aluminum ion and m-hydroxy phthalic acid, In the mean time, its root exudates were collected using the method of CRETS, then identified it through GC-MS/LC-MS. We expected this research offer some theoretic foundation to the resolution of the barrier of continuous planting.1.As the extension of stress time, the activity of SOD in Chinese fir's seedlings declined rapidly under the stress of pH, the lower the pH was, the quicker it declined, so the activity of SOD was pH4.0pH4.5>pH5.0; under the condition of nutritional stress, it was: 1/8 concentration>1/4 concentration>1/2 concentration; under the condition of aluminum stress, it was: 2.5mMol/L>1.5mMol/L>0.5mMol/L;under the condition of m-hydroxy phthalic acid stress, it was: 200mg/L>100mg/L>50mg/L. Analysis of variance showed that the difference of the content of MDA between the blank and adversity stresses are extremely significant.4.Under the condition of pH stress, nutritional stress, aluminum stress and m-hydroxy phthalic acid stress, the net photosynthetic rate of chinese fir seedlings increased as time extended, the higher the concentration was, the higher it increased; so under the condition of pH stress, the net photosynthetic rate value was: pH4.0>pH4.5>pH5.0; under the condition of nutritional stress, it was: 1/8 concentration>1/4 concentration>1/2 concentration; under the condition of aluminum stress, it was: 2.5mMol/L>1.5mMol/L>0.5mMol/L;under the condition of m-hydroxy phthalic acid stress, it was: 200mg/L>100mg/L>50mg/L. Analysis of variance showed that the difference of the net photosynthetic rate between the blank and adversity stresses are extremely significant.5. Chinese fir seedlings'root exudates have a big change as time extended under different adversity stresses, the species and quantities of root exudates in initial stage were more than middle stage and last stage. Under the condition of pH stress, at the initial stage the root exudates mainly were esters, alkanes, phenolic and a small amount of organic acid, alcohols, ketones, amines, thiazoles, at the mid-and late stage, there were 4 esters, 1 alkane, 1 amine and 1 ketone; under the condition of nutritional stress, at the initial stage, the root exudates mainly were organic acids, alcohols, amines, alkanes, at the mid-and late stage, there were 4 esters, 1 alkane and 1 acohol; Under the condition of aluminum stress, at the initial stage the root exudates mainly were alkanes, esters, alcohols and a small amount of amines, amines, phenols, olefins, thiazoles, at the mid-and late stage, there were 2 esters and 2 alkanes; Under the condition of m-hydroxy phthalic acid stress, at the initial stage the root exudates mainly were alkanes, esters and a small amount of alcohols, phenols, ketones, at the mid-and late stage,there were 3 esters, 2 alkanes, 1 ketone and 1 amine.