Soil pH buffer capacity of tea garden with different planting years. A Simulation of Salt and Alkali Mixed Ecological Conditions and Analysis of Their Stress Factors in the Seedlings of Aneurolepidium chinense RESEARCHES ON THE THRESHOLD OF ALUMINUM TOXICITY AND THE DECLINE OF CHINESE FIR PLANTATION IN HILLY AREA AROUND THE SICHUAN BASIN Effects of different acidic materials on pH value of calcareous soil Effects of al穔ali-stress on Aneurolepidium chinense and Helianthus annuus