Alleviating Effects Of Calcium And Phosphorus On Aluminum Toxicity In Chinese Fir Seedlings And Its Mechanism

Chinese fir is extremely important timber species in southern China. With the continuous development of society, the demand for Chinese fir is increasing and becoming more and more important in social economy. However, on the background of most acidic soil in southern area and increasing soil acidification, aluminum in such type of soil is easier to dissolve and becomes active aluminum, leading to the increasing risk of aluminum toxicity in Chinese fir. Aluminum toxicity is one of the main factors limiting the growth of Chinese fir. It is an urgent task to alleviate aluminum toxicity. Therefore, the aim of this paper was to study the effects of calcium and phosphorus at different levels on the growth of Chinese fir under 150mg/kg aluminum stress by using soil culture and orthogonal design.1 year old seedlings of Chinese firs were used as plant material.The changes and the relationship in rhizosphere soil pH, chemical forms of aluminum in soil, growth as well as chemical and physiological index in Chinese fir were analyzed based on the results. This study will provide more information about the methods to alleviate aluminum toxicity in Chinese fir and related theoretical basis, promoting the sustainable development of Chinese fir plantation. The main results were as follows.1. The rhizosphere environment in Chinese fir was significantly altered. The results showed that the soil pH of all treatment was changed at different degree under the treatment of calcium and phosphorus as compared with the control. Soil pH was raised, while the chemical forms of aluminum in rhizosphere were changed significantly. The chemical forms of aluminum were decreased significantly and even more under the mixed treatment of calcium and phosphorus. Multiple comparisons and variance analysis showed that calcium and phosphorous had a significant effect on pH and chemical forms of aluminum in rhizosphere soil. There was a significant or very significant effect of the interaction between calcium and phosphorus on the different chemical forms of aluminum in soil; Variance analysis of showed that calcium was the main factor effecting on pH in rhizosphere soil and chemical forms of aluminum, followed by the interaction of calcium and phosphorus;2. Growth of Chinese fir was improved after the rhizosphere environment had been altered. In general, it showed promotion effect, whereas the content of aluminum in leave was decreased. The corresponding treatment was not always the same when the maximum growth index or the lowest aluminum content in leave was obtained. Variance analysis showed that there was a significant effect of the interaction of calcium and phosphorus on seedling height, while there was a significant effect of calcium, phosphorus and their interaction on aluminum content in leave;3. There was a decrease in MDA content and an increase in soluble protein content at different degree under the treatment of calcium and phosphorus. MDA content was the lowest under low or high calcium treatment, while soluble protein content had a significant increase under the mixed treatment of calcium and phosphorus. Variance analysis showed that there was a very significant effect of calcium and the interaction between calcium and phosphorus on both of above indexes. Calcium was the main factor, followed by the interaction between calcium and phosphorus, and the phosphorus was the least one.4. Chlorophyll content in leave of Chinese fir and related index of chlorophyll fluorescence were improved at deferent degree under the treatment of calcium and phosphorus. Calcium treatment had significant effects on chlorophyll a, chlorophyll b, total content of chlorophyll, maximum fluorescence and initial fluorescence. Variance analysis showed that there was a very significant effect of the interaction between calcium and phosphorus on chlorophyll a, chlorophyll b, total content of chlorophyll, while effect of phosphorus was the least. Calcium was the main factor of maximum fluorescence Fm and initial fluorescence Fo. The interaction between calcium and phosphorus had a largest effect on PS Ⅱ potential activity. Chlorophyll a showed more sensible to the treatment of calcium and phosphorus than chlorophyll b.5. The correlation analysis between each index showed that the changes of each index under the treatments of calcium and phosphorus had closely internal relation with each other. Soil pH in rhizosphere area was very significantly negatively correlated with content of exchangeable aluminum, whereas it had a very significantely positive correlation with monomer hydroxyl-aluminum and humic acid aluminum. Exchangeable aluminum content had a very significantely negative correlation with monomer hydroxyl-aluminum and humic acid aluminum, whereas it had a very significantely positive correlation with aluminum and MDA in leave of Chinese fir. It also had a very significantely negative correlation with water content, soluble protein and maximum fluorescence. Aluminum content in leave had a very significantely positive correlation with MDA, whereas it showed a very significantely negative correlation with soluble protein. It also had a significantely negative correlation with seedling height, ground diameter, water content, chlorophyll a, total chlorophyll, maximum fluorescence and potential activity. Above results indicated that the alteration in rhizosphere environment may be the main factor improving the growth and physiological and biochemical character, consequently alleviating the aluminum toxicity in Chinese fir to some extent.