Effects of soil acidification on Asian trees

Abstract

Acid deposition is a serious environmental problem in Asia and may adversely affect Asian tree species due to soil acidification, the leaching of nutrients essential for normal plant growth from rhizospheric soil, and enhancement of the solubility of toxic metals such as aluminum (Al) and manganese (Mn) in the soil solution. The results of limited experimental studies indicate that soil acidification increases the concentrations of Al and Mn in the soil solution and reduces the growth, physiological functions such as net photosynthetic rate, and concentrations of nutrients such as Ca and Mg in several Asian forest tree species such as Cryptomeria japonica, Pinus densiflora, Betula platyphylla, Fagus crenata, and Pinus massoniana. A relatively low pH of culture solution below 3.5 reduces fresh and dry-weight growth and increases the concentrations of Ca and Mg in the shoots of Asian tree species such as C. japonica. Excessive Al or Mn in soil solution or water culture medium reduces fresh and dry-weight growth, shoot water content, and concentrations of Ca and Mg in the shoots and roots of Asian tree species such as C. japonica and P. densiflora. The extent of the negative effects of Al on growth, physiological functions, and water and nutrient status is greater than that of Mn when the concentrations of both elements in water culture medium are the same. Because the atmospheric deposition of acid substances is increasing in Asian countries, further studies are needed to elucidate the effects of soil acidification on many Asian forest tree species.