The single and interactive effects of aluminium and low pH, or Ca/Al ratios on red pine seedlings

Acid deposition has been one of the major environmental pollution problems for longer than 50 years, since the 1970s. Investigation on the interactive effects of aluminum (Al) and low pH or Ca/Al ratios on red pine (Pinus densiflora Sieb. and Zucc.) has been required but lacking. In the present study, needles of red pine seedlings exposed to Al treatments with solution pH 4.0 and 3.5 exhibited purplish leaf characteristics of Al toxicity. The dry weights of the needle and whole plant, and the current needle elongation were linearly reduced with Al concentrations from 0, 13 to 26 ppm. Results show that red pine is an intermediate species in sensitivity to Al and is insensitive to low pH. However, the synergistic interactions of low pH treatments with the elevated Al were significant. Al toxicity to red pine was significantly enlarged with reduced pH. The root length and whole plant length were significantly decreased at 1:10 of Ca/Al ratios (p < 0.05), but Al phytotoxicity was completely lost when the Ca/Al molar ratio was 10:1. Liming is still an applicable measure to remediate acidification problems by natural or anthropogenic factors such as acid deposition.