Some physiological properties of Cryptomeria japonica leaves from Kanto, Japan: potential factors causing tree decline

Abstract

Japanese cedar (Cryptomeria japonica D. Don) has been declining in urban areas of Japan. We examined if the decline was associated with physiological deterioration of leaves and resulting water stress. Leaves from three locations (severe decline, slight decline, and healthy) were analyzed for minimum transpiration rates (MT), amounts of epicuticular wax (EW), contact angles (CA), fractions of unhealthy stomata (US), cuticular thickness, and leaching of elements (LE). Anthropogenic elements (e.g., antimony (Sb)) in aerosols on the leaves were also analyzed by neutron activation analysis. MT, US, and amounts of Sb were 2, 15, and 10 times greater, respectively, at the severe decline location compared with the healthy location. LE was also greater at the severe decline location than at the slight decline and healthy locations. In contrast, CA was greatest at the healthy location and least at the severe decline location. MT correlated with the values obtained from a linear trinomial function that included EW, CA, and US as variables (r = 0.872, P < 0.01), and US correlated with amounts of Sb in aerosols (r = 0.939, P < 0.01). Therefore, it is likely that the deterioration of epicuticular wax and stomatal unhealthiness resulting mainly from clogging with aerosols, in combination with environmental aridification, have placed C. japonica under chronic and sometimes fatal water stress, causing tree decline.