Manganese toxicity as indicated by visible foliar symptoms of Japanese white birch (Betula platyphylla var. japonica)

For the purpose of a field diagnosis of Mn toxicity, we showed the possibil ity of using visible foliar symptoms of Japanese white birch (Betula platyp hylla var. japonica Hara) as indicator. To examine the relationship between the expression of visible symptoms and leaf Mn concentrations, white birch seedlings were grown under four different Mn levels: 1 mg Mn l(-1) as cont rol, 10, 50 and 100 mg Mn l(-1). Foliar symptoms of Mn toxicity for white b irch were: (1) chlorosis at entire young leaves in the 50 and 100 mg Mn l(- 1) treatments; and (2) brown speckles at the leaf marginal and interveinal area for old leaves in the treatments greater than 1 mg Mn l(-1). Mn prefer ably accumulated into the leaf marginal and interveinal area, where the bro wn speckles were observed. The mechanism determining the expression of symp toms seems to be associated with the physiological state related to leaf ag e as well as Mn distribution and concentration within a leaf. (C) 2000 Else vier Science Ltd. All rights reserved.