Responses of gas-exchange rates and water relations to annual fluctuations of weather in three species of urban street trees.
The frequency of extreme weather has been rising in recent years. A 3-year study of street trees was undertaken in Tokyo to determine whether: (i) street trees suffer from severe water stress in unusually hot summer; (ii) species respond differently to such climatic fluctuations; and (iii) street trees are also affected by nitrogen (N) deficiency, photoinhibition and aerosol pollution. During the study period (2010-12), midsummers of 2010 and 2012 were unusually hot (2.4-2.8 °C higher maximum temperature than the long-term mean) and dry (6-56% precipitation of the mean). In all species, street trees exhibited substantially decreased photosynthetic rate in the extremely hot summer in 2012 compared with the average summer in 2011. However, because of a more conservative stomatal regulation (stomatal closure at higher leaf water potential) in the hot summer, apparent symptoms of hydraulic failure were not observed in street trees even in 2012. Compared with Prunus × yedoensis and Zelkova serrata, Ginkgo biloba, a gymnosperm, was high in stomatal conductance and midday leaf water potential even under street conditions in the unusually hot summer, suggesting that the species had higher drought resistance than the other species and was less susceptible to urban street conditions. This lower susceptibility might be ascribed to the combination of higher soil-to-leaf hydraulic conductance and more conservative water use. Aside from meteorological conditions, N deficiency affected street trees significantly, whereas photoinhibition and aerosol pollution had little effect. The internal CO2 and δ(13)C suggested that both water and N limited the net photosynthetic rate of street trees simultaneously, but water was more limiting. From these results, we concluded that the potential risk of hydraulic failure caused by climatic extremes could be low in urban street trees in temperate regions. However, the size of the safety margin might be different between species.
School of Social Information Studies, Otsuma Women's University, 2-7-1 Karakida, Tama, Tokyo 206-8540, Japan Department of Biological Sciences, Graduate School of Science and Engineering, Tokyo Metropolitan University, Minamiosawa 1-1, Hachioji, Tokyo 192-0397, Japan osone.yk@gmail.com.
Yoko
Y
Osone
Department of Biological Sciences, Graduate School of Science and Engineering, Tokyo Metropolitan University, Minamiosawa 1-1, Hachioji, Tokyo 192-0397, Japan.
Satoko
S
Kawarasaki
Center for Ecological Research, Kyoto University, 2-509-3 Hirano, Otsu, Shiga 520-2113, Japan.
Atsushi
A
Ishida
Forestry and Forest Products Research Institute, 1 Matsunosato, Tsukuba 305-8687, Japan.
Satoshi
S
Kikuchi
School of Social Information Studies, Otsuma Women's University, 2-7-1 Karakida, Tama, Tokyo 206-8540, Japan.
Akari
A
Shimizu
Forestry and Forest Products Research Institute, 1 Matsunosato, Tsukuba 305-8687, Japan.
Kenichi
K
Yazaki
Forestry and Forest Products Research Institute, 1 Matsunosato, Tsukuba 305-8687, Japan Japan Forest Technology Association, Chiyoda, Tokyo 102-0085, Japan.
Shin-Ichi
S
Aikawa
Graduate School of Agriculture, Tokyo University of Agriculture and Technology, Fuchu, Tokyo 183-8509, Japan Graduate School of Fisheries Science and Environmental Studies, Nagasaki University, Nagasaki 852-8521, Japan.
Masahiro
M
Yamaguchi
Institute of Agriculture, Tokyo University of Agriculture and Technology, Fuchu, Tokyo 183-8509, Japan.
Takeshi
T
Izuta
School of Social Information Studies, Otsuma Women's University, 2-7-1 Karakida, Tama, Tokyo 206-8540, Japan.
Genki I
GI
Matsumoto
D002247:Carbon Isotopes; D002947:Cities; D003681:Dehydration; D055864:Droughts; D020441:Ginkgo biloba / Q000502:physiology; D006358:Hot Temperature; D010788:Photosynthesis; D018515:Plant Leaves / Q000502:physiology*; D018526:Plant Transpiration; D027861:Prunus / Q000502:physiology; D014197:Trees / Q000502:physiology*; D034401:Ulmaceae / Q000502:physiology
D002247:Carbon Isotopes
carbon isotopes; extreme weather; photosynthesis; roadside trees; stomatal conductance; summer heat; water potential