Responses of gas-exchange rates and water relations to annual fluctuations of weather in three species of urban street trees

Abstract

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.

Magnolia grandiflora L. shows better responses to drought than Magnolia × soulangeana in urban environment

“…Similarly to our findings, many studies observed significantly reduced A rates in urban areas, which are characterized by limited water availability (Percival et al 2006, Osone et al 2014 and sealed surfaces (Wang et al 2019). The reduction of A under drought has been addressed to the protective mechanism of plants to avoid damage due to dehydration and hydraulic failure (Osone et al 2014).…”

Multiple Proxy Estimates of Atmospheric CO2 from an Early Paleocene Rainforest

“…The mean stomatal density for G. biloba, 80.7 ± 1.4 mm -2 , is similar to most published values (McElwain and Chaloner, 1996;Beerling et al, 1998;Chen et al, 2001;Pandey et al, 2003;Sun et al, 2003;Smith et al, 2010;Osone et al, 2014), which range from ~61 -98 mm -2 . (Note that some of these values are estimated from plots.)…”

“…I find a mean photosynthetic rate for G. biloba of 8.19 ± 0.24 μmol m -2 s -1 (Table 5.3). This rate is similar to that found for the species in at least one other study (Pandey et al, 2003), and lower than the rates measured by Osone et al (2014), but higher than many other published values (Beerling et al, 1998;Leigh et al, 2011;Franks et al, 2014) which are all close to 5 μmol m -2 s -1 . My mean stomatal conductance for G. biloba is similar to published values (Leigh et al, 2011;P.…”

The dynamics of carbon stored in xylem sapwood to drought-induced hydraulic stress in mature trees

“…The stored carbon in sapwood would contribute to the homeostasis of forest ecosystems with reducing the hydraulic failure-induced forest die-offs. Such a mechanism is responsible for ongoing cases of forest die-offs for heating and drying in urban forests 38 . Under the chronic shortage in carbon resources induced by the progressing global changes, forest ecosystem may not be able to maintain the homeostasis.…”