ABSTRACT

Soil acidification caused by acid mine drainage, metalliferous and monmetalliferous ores, and acid deposition near coal combustion power plants and other industry facilities has induced many degraded lands and forest declines. Soil solution aluminum (Al) concentrations are identified to increase exponentially with increases in hydrogen ion concentration below 5.5 (Magistad, 1925). It is well established that high Al concentrations in soil solutions can damage sensitive plants. Al toxicity was considered as a cause of forest decline (Ulrich et al., 1980). Effects of Al on tree growth have given rise to concern about forest decline in Europe, North America, and Eastern Asia (Cronan and Shonfield, 1979; Miyake et al., 1991). Soil acidification reduced the growth of red pine seedlings and soil analysis showed that the Al concentrations were elevated with soil pH reduction (Shan et al., in press). Trees are different in sensitivity to Al or low pH. Therefore, it was asked whether toxicity of Al and low pH was greater to red pine seedlings in the acidified soils. It is necessary to study the interactive effects of low pH, Al toxicity, and calcium (Ca) on plants for the remediation and revegetation in these damaged lands. Toxicity due to low pH or Al per se is difficult to show because of complex soil chemistry and lack of a good understanding of ion uptake by roots in any case. In solution culture, because the concentrations of Al and other elements can be controlled, the single and combined effects of Al, low pH, or Ca/AI ratio can be examined. The present study was therefore undertaken to determine single and interactive effects of Al, low pH, or Ca/AI ratio on growth of red pine (Pinus densiflora Sieb. and Zucc.) seedlings through a solution culture experiment.