Abstract:

Using the experiences of researching on forest soil acidification both at home and abroad, collecting the data from hilly area around the sichuan basin, the pure Chinese fir(Cunninghamia lanceolata Lamb. Hook)second generation plantation was studied basing on the site classification. The rhizosphere soil pH(KCl), Al³⁺,Ca²⁺/Al³⁺, litter Ca²⁺/(Ca²⁺+Fe³⁺+Al³⁺)were selected as reference factors to study the cause of growth decline of Chinese fir plantation and the thresholds of aluminum toxicity. The results showed that the causes of decline of Chinese fir plantation were: (1)The tree species was not suitable to the bad site conditions; (2)Aluminum toxicity occurred in the stands with good or better site conditions. The thresholds were: pH≤4.18, Al³⁺≥31.66mg/kg, Ca²⁺/Al³⁺≤1.809mol/mol and Ca²⁺/(Ca²⁺+Fe³⁺+Al³⁺)≤0.55mol/mol.

Key words: Site type, Thresholds of aluminum toxicity, chinese fir plantaion, Buffer capacity