| Pinus massoniana Lamb. is an important timber species and pioneer tree species of afforestation in southern China, and has high social, economic and ecological value. In recent years, normal growth of Pinus massoniana Lamb. has been severely constrained by the increase of active aluminum in soil results from the increase of soil acidification. How to improve aluminum-tolerant ability of Pinus massoniana Lamb. and repair Pinus massoniana Lamb. forest ecosystem under aluminum toxicity is an important scientific problem of Pinus massoniana Lamb. industry which need to solve currently. Using genetic breeding methods to improve aluminum-tolerant ability of plants and breed aluminum-tolerant genotype is an effective way to solve the problem. Thus, our study firstly had aluminum-tolerant screening among 29 Pinus massoniana Lamb. families（genotype） from different provenances, and selected 1-year-old seedlings of Guangdong No.5（aluminum-sensitive genotype） as materials on the basis of screening for further experiments. And we studied on the effect of aluminum stress on growth characteristics, physiological characteristics, nutrient absorption and transportation of Pinus massoniana Lamb. by hydroponics. Our study aimed at finding aluminum-tolerant genotype（family） of Pinus massoniana Lamb., revealed physiological and biochemical response mechanism of Pinus massoniana Lamb. under aluminum stress theoretically, and determined technical measures to relief soil aluminum toxicity on Pinus massoniana Lamb., and provided theoretical basis for the stabilization and high yield cultivation of Pinus massoniana Lamb. forest. The main results were as follows:1. The root growth of 29 Pinus massoniana Lamb. families had significant differences under aluminum stress, and the differences were mainly determined by genotype, not by difference in provenances. And according to cluster analysis based on relative root elongation under aluminum stress, 29 Pinus massoniana Lamb. families were classified into 3 categories: aluminum-tolerant genotype, intermediate aluminum-tolerant genotype and aluminum-sensitive genotype. The aluminum-tolerant genotype included Guangdong 22, Fujing 5, Guangxi 17 and Guangdong 10, and aluminum-sensitive genotype included Guangdong 5 and other 15 families.2. Aluminum stress had effect on the growth of Pinus massoniana Lamb.. It could inhibit height growth of Pinus massoniana Lamb., and the degree of inhibition increased as the increase of Al3+ concentration. And low concentration aluminum stress(0.2 mmol·L-1) could promote the growth of roots and stems to some extent, while high concentration aluminum stress could significantly inhibit the growth of roots and stems, and the inhibition of root growth were mainly on degree of branching and root area.3. Aluminum stress had a significant effect on physiological characteristics of Pinus massoniana Lamb. roots. It could significantly reduce activity of Pinus massoniana Lamb. root, promote accumulation of MDA in roots, and increase membrane lipid peroxidation. And proline and soluble sugar contents increased, along with the increase of Al3+ concentration gradually. However, aluminum stress had no significant effect on protein content in roots until Al3+ concentration reach 1.6 mmol·L-1. Furthermore, aluminum stress could inhibit the activity of POD in roots, and the degree of inhibition increased along with the increase of Al3+ concentration, only when the Al3+ concentration reach 1.6 mmol·L-1 the activity gone up again. And low concentration aluminum stress could increase the activity of SOD, while high concentration aluminum stress had no significant effect on it. In a word, when Al3+ concentrations reach 1.6 mmol·L-1, most physiological indicators of Pinus massoniana Lamb. roots appeared abnormal response which may resulted from the damage of root physiological functions and took effect on normal physiological activity of Pinus massoniana Lamb. roots.4. The effects of aluminum stress on physiological characteristics of Pinus massoniana Lamb. leaves depended on Al3+ concentration. Low concentration aluminum stress(<0.8 mmol·L-1) could promote synthesis of chlorophyll a and chlorophyll b and increase the ratio of chlorophyll a and chlorophyll b, while high concentration aluminum stress(≥0.8 mmol·L-1) could significantly decreased chlorophyll a contents, chlorophyll b contents and the ratio of chlorophyll a and chlorophyll b. And low concentration aluminum stress(0.2 mmol·L-1) could significantly reduce MDA contents in Pinus massoniana Lamb. leaves, but had a significant increase along with the increase of Al3+ concentration. Proline and protein contents increased along with the increase of Al3+ concentration. And soluble sugar contents reduced significantly at low concentration aluminum stress, and had no change along with the increase of Al3+ concentration until Al3+ concentration reach 1.6 mmol·L-1. Furthermore, when the concentration ≤ 0.8 mmol·L-1, as Al3+ concentration increased, SOD and POD activities showed a downward trend after the first rise, but activities of SOD and POD reduced significantly when Al3 + concentration > 0.8 mmol·L-1.5. Aluminum absorbing by roots were mostly accumulated in roots, and few were transported to stems and leaves. As Al3+ concentration increased, the accumulation of aluminum in roots, stems and leaves increased when Al3+ concentration less than 1.6 mmol·L-1. However, when Al3+ concentration greater than 1.6 mmol·L-1, the accumulation of aluminum in roots had a certain degree of decline, while had increase on that transport to stems and leaves, and aluminum transported to stems were more than that to leaves.6. Aluminum stress had significant effect on absorption and transportation of nutrients in Pinus massoniana Lamb.. Aluminum stress could promote absorption of P in root, but inhibit its upward transport. Low concentration aluminum stress(≤0.4 mmol·L-1) could promote absorption of Mg and transportation of K, Mg and P, while high concentrations aluminum stress(>0.4 mmol·L-1) showed inhibition on absorption and transportation of K, Ca and Mg. Furthermore, Aluminum stress showed significantly inhibition on absorption of Mn and Zn in root（showed promotion on absorption of Zn only at low concentration of Aluminum）, while had no effect on the absorption of Fe and Cu. And aluminum stress could inhibit the upward transport of Fe, Zn and Cu, but showed promotion on upward transport of Mn. |
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