Abstract
Water and nitrogen are usually considered to be the limiting factors for growth of trees on urban streets. We demonstrated that the leaf carbon isotope ratio (δ13C) is a good indicator of long-term water stress of various species (Zelkowa serrata, Platanus occidentalis, Cinnamomun camphora, Sophora japonica, Ginkgo biloba), resulting from low intercellular carbon dioxide concentrations in water stress treatments in green house experiments. It is well known that the leaf carbon isotope ratio is negatively correlated with intercellular carbon dioxide concentrations in various kinds of plants. On the other hand, leaf nitrogen content is thought to be an indicator of nitrogen supply for street trees, because leaf nitrogen content increases as soil nutrients become enriched. The simultanuous measurements of δ13C and nitrogen content of leaves by automatic stable isotope analyzer suggested that the growth of street trees was limited by soil nitrogen, rather than soil water, during June to September, 1994, in Toyota city.
