Emissions of volatile organic compounds and leaf structural characteristics of European aspen (Populus tremula) grown under elevated ozone and temperature

Abstract

Northern forest trees are challenged to adapt to changing climate, including global warming and increasing tropospheric ozone (O(3)) concentrations. Both elevated O(3) and temperature can cause significant changes in volatile organic compound (VOC) emissions as well as in leaf anatomy that can be related to adaptation or increased stress tolerance, or are signs of damage. Impacts of moderately elevated O(3) (1.3x ambient) and temperature (ambient + 1 degrees C), alone and in combination, on VOC emissions and leaf structure of two genotypes (2.2 and 5.2) of European aspen (Populus tremula L.) were studied in an open-field experiment in summer 2007. The impact of O(3) on measured variables was minor, but elevated temperature significantly increased emissions of total monoterpenes and green leaf volatiles. Genotypic differences in the responses to warming treatment were also observed. alpha-Pinene emission, which has been suggested to protect plants from elevated temperature, increased from genotype 5.2 only. Isoprene emission from genotype 2.2 decreased, whereas genotype 5.2 was able to retain high isoprene emission level also under elevated temperature. Elevated temperature also caused formation of thinner leaves, which was related to thinning of epidermis, palisade and spongy layers as well as reduced area of palisade cells. We consider aspen genotype 5.2 to have better potential for adaptation to increasing temperature because of thicker photosynthetic active palisade layer and higher isoprene and alpha-pinene emission levels compared to genotype 2.2. Our results show that even a moderate elevation in temperature is efficient enough to cause notable changes in VOC emissions and leaf structure of these aspen genotypes, possibly indicating the effort of the saplings to adapt to changing climate.

Leaf anatomy, BVOC emission and CO2exchange of arctic plants following snow addition and summer warming

“…Hartikainen et al, 2009Hartikainen et al, , 2014. This indicates the sensitivity and significance of leaf anatomy in plant acclimation.…”

“…Empetrum hermaphroditum additionally showed a decreased palisade:spongy mesophyll ratio in response to the OTC treatment, which corresponds to the warming responses in Cassiope tetragona, B. nana and Salix arctica in Schollert et al (2015). As the palisade mesophyll has a high potential for photosynthesis (Monson and Baldocchi, 2014b) and BVOC synthesis (Hartikainen et al, 2009), a lower palisade:spongy mesophyll ratio might partly explain why the OTCs led to only a few increases in BVOC emission from E. hermaphroditum.…”

“…For example, Schollert et al (2015) showed that thickening of leaf and palisade tissue and thinning of the epidermis explained increased isoprene emissions in the deciduous shrubs Betula nana and Salix arctica. Hartikainen et al (2009Hartikainen et al ( , 2014 suggested that thinning of the epidermis by warming enhanced BVOC emissions from Populus tremula and Betula pendula leaves. The study by Kivim€ aenp€ a€ a et al (2016) revealed that higher numbers of terpene-storing structures explained increased terpenoid emissions by warming, elevated O 3 and higher nitrogen availability in Scots pine (Pinus sylvestris), an evergreen conifer.…”

“…Anatomical changes can develop within weeks, and several studies on environmental change have observed modifications in leaf anatomy of deciduous species already during the first growing season for leaves developed under e.g. elevated temperature, nitrogen fertilization, drought or elevated O 3 levels (P€ a€ akkönen and Holopainen, 1995;P€ a€ akkönen et al, 1998;Hartikainen et al, 2009Hartikainen et al, , 2014. However, to our knowledge, the impacts of snow depth on leaf anatomy, indirectly caused by e.g.…”

Effects of ozone on isoprene emission from two major <i>Quercus</i> species native to East Asia

“…Very few studies have been conducted on the long-term effects of ozone on isoprene emission Calfapietra et al, 2007;Calfapietra et al, 2008;Hartikainen et al, 2009;Yuan et al, 2016 . When aspen Populus tremuloides was exposed to 1.5 ambient concentration of ozone over a long term by using a free-air CO 2 enrichment FACE facility, the isoprene emission rate decreased by 25 under elevated O 3 in the O 3 -sensitive clone and only slightly decreased in the O 3 -tolerant clone Calfapietra et al, 2008 .…”