Ethylenediurea (EDU) effects on Japanese larch: an one growing season experiment with simulated regenerating communities and a four growing season application to individual saplings

Japanese larch (Larix kaempferi (Lamb.) Carr.) and its hybrid are economically important coniferous trees widely grown in the Northern Hemisphere. Ground-level ozone (O3) concentrations have increased since the pre-industrial era, and research projects showed that Japanese larch is susceptible to elevated O3 exposures. Therefore, methodologies are needed to (1) protect Japanese larch against O3 damage and (2) conduct biomonitoring of O3 in Japanese larch forests and, thus, monitor O3 risks to Japanese larch. For the first time, this study evaluates whether the synthetic chemical ethylenediurea (EDU) can protect Japanese larch against O3 damage, in two independent experiments. In the first experiment, seedling communities, simulating natural regeneration, were treated with EDU (0, 100, 200, and 400 mg L−1) and exposed to either ambient or elevated O3 in a growing season. In the second experiment, individually-grown saplings were treated with EDU (0, 200 and 400 mg L−1) and exposed to ambient O3 in two growing seasons and to elevated O3 in the succeeding two growing seasons. The two experiments revealed that EDU concentrations of 200–400 mg L−1 could protect Japanese larch seedling communities and individual saplings against O3-induced inhibition of growth and productivity. However, EDU concentrations ≤ 200 mg L−1 did offer only partial protection when seedling communities were coping with higher level of O3-induced stress, and only 400 mg EDU L−1 fully protected communities under higher stress. Therefore, we conclude that among the concentrations tested the concentration offering maximum protection to Japanese larch plants under high competition and O3-induced stress is that of 400 mg EDU L−1. The results of this study can provide a valuable resource of information for applied forestry in an O3-polluted world

Role of sesquiterpenes in biogenic new particle formation

Biogenic vapors form new particles in the atmosphere, affecting global climate. The contributions of monoterpenes and isoprene to new particle formation (NPF) have been extensively studied. However, sesquiterpenes have received little attention despite a potentially important role due to their high molecular weight. Via chamber experiments performed under atmospheric conditions, we report biogenic NPF resulting from the oxidation of pure mixtures of β-caryophyllene, α-pinene, and isoprene, which produces oxygenated compounds over a wide range of volatilities. We find that a class of vapors termed ultralow-volatility organic compounds (ULVOCs) are highly efficient nucleators and quantitatively determine NPF efficiency. When compared with a mixture of isoprene and monoterpene alone, adding only 2% sesquiterpene increases the ULVOC yield and doubles the formation rate. Thus, sesquiterpene emissions need to be included in assessments of global aerosol concentrations in pristine climates where biogenic NPF is expected to be a major source of cloud condensation nuclei

Molecular understanding of the suppression of new-particle formation by isoprene

Nucleation of atmospheric vapours produces more than half of global cloud condensation nuclei and so has an important influence on climate. Recent studies show that monoterpene (C10H16) oxidation yields highly oxygenated products that can nucleate with or without sulfuric acid. Monoterpenes are emitted mainly by trees, frequently together with isoprene (C5H8), which has the highest global emission of all organic vapours. Previous studies have shown that isoprene suppresses new-particle formation from monoterpenes, but the cause of this suppression is under debate. Here, in experiments performed under atmospheric conditions in the CERN CLOUD chamber, we show that isoprene reduces the yield of highly oxygenated dimers with 19 or 20 carbon atoms - which drive particle nucleation and early growth - while increasing the production of dimers with 14 or 15 carbon atoms. The dimers (termed C-20 and C-15, respectively) are produced by termination reactions between pairs of peroxy radicals (RO2 center dot) arising from monoterpenes or isoprene. Compared with pure monoterpene conditions, isoprene reduces nucleation rates at 1.7 nm (depending on the isoprene = monoterpene ratio) and approximately halves particle growth rates between 1.3 and 3.2 nm. However, above 3.2 nm, C-15 dimers contribute to secondary organic aerosol, and the growth rates are unaffected by isoprene. We further show that increased hydroxyl radical (OH center dot) reduces particle formation in our chemical system rather than enhances it as previously proposed, since it increases isoprene-derived RO2 center dot radicals that reduce C-20 formation. RO2 center dot termination emerges as the critical step that determines the highly oxygenated organic molecule (HOM) distribution and the corresponding nucleation capability. Species that reduce the C-20 yield, such as NO, HO2 and as we show isoprene, can thus effectively reduce biogenic nucleation and early growth. Therefore the formation rate of organic aerosol in a particular region of the atmosphere under study will vary according to the precise ambient conditions.Peer reviewe

Role of iodine oxoacids in atmospheric aerosol nucleation

Iodic acid (HIO₃) is known to form aerosol particles in coastal marine regions, but predicted nucleation and growth rates are lacking. Using the CERN CLOUD (Cosmics Leaving Outdoor Droplets) chamber, we find that the nucleation rates of HIO₃ particles are rapid, even exceeding sulfuric acid–ammonia rates under similar conditions. We also find that ion-induced nucleation involves IO₃⁻ and the sequential addition of HIO₃ and that it proceeds at the kinetic limit below +10°C. In contrast, neutral nucleation involves the repeated sequential addition of iodous acid (HIO₂) followed by HIO₃, showing that HIO₂ plays a key stabilizing role. Freshly formed particles are composed almost entirely of HIO₃, which drives rapid particle growth at the kinetic limit. Our measurements indicate that iodine oxoacid particle formation can compete with sulfuric acid in pristine regions of the atmosphere

Growth Characteristics of Two Promising Tree Species for Afforestation, Birch and Larch in the Northeastern Part of Asia

Re-vegetation is urgently needed to increase the carbon sink for moderating atmospheric CO2 by forest ecosystem, especially northeastern part of Asia with large population. We partly plant fast-growing species, such as birch (Betula spp.), larch (Larix spp.) and poplar (Populus spp.) in northeastern China. Especially, birch species are used for sap production; larch and its hybrid (F1) are promising species for timber production and increasing the carbon sink. For understanding these afforestation materials, we review the distribution of birch and larch species in China and northern Japan. They have deciduous leaf habit and typical light-demanding traits and are found in cool temperate climate regions. They can survive in infertile soil conditions and withstand drought even in the steeper slop. Both genera are considered as pioneer of secondary vegetation after disturbances. We mainly discuss on the growth habitat of birch and larch from the view point of taxonomy and their distribution, expecting to give some guidance for the potential plantation place of the two genera

Photosynthetic response of early and late leaves of white birch (Betula platyphylla var. japonica) grown under free-air ozone exposure

Betula platyphylla var.japonica (white birch) has heterophyllous leaves (i.e., early and late leaves) and is a typical pioneer tree species in northern Japan. Seedlings of white birch were exposed to ozone during two growing seasons, and measurements were carried out in the second year. Early leaves did not show an ozone-induced reduction in photosynthesis because of lower stomatal conductance resulting in higher avoidance capacity for ozone-induced stress. Also, an ozone-related increase in leaf nitrogen content may partly contribute to maintain the photosynthetic capacity in early leaves under elevated ozone in autumn. On the other hand, late leaves showed an ozone-induced decline of photosynthesis and early defoliation of leaves occurred. Also, smaller leaf size and higher stomatal density in late leaves were observed under elevated ozone. Differences in stress resistance to ozone may be related to differing functional roles of early and late leaves for birch species. (C) 2013 Elsevier Ltd. All rights reserved

Photosynthetic traits of Siebold's beech and oak saplings grown under free air ozone exposure in northern Japan

We set up a free-air ozone (O3) exposure system for determining the photosynthetic responses of Siebold’s beech (Fagus crenata) and oak (Quercus mongolica var. crispula) to O3 under field conditions. Ten-year-old saplings of beech and oak were exposed to an elevated O3 concentration (60 nmol mol-1) during daytime from 6 August to 11 November 2011. Ozone significantly reduced the net photosynthetic rate in leaves of both species in October, by 46% for beech and 15% for oak. In beech there were significant decreases in maximum rate of carboxylation, maximum rate of electron transport in photosynthesis, nitrogen content and photosynthetic nitrogen use efficiency, but not in oak. Stomatal limitation of photosynthesis was unaffected by O3. We therefore concluded photosynthesis in beech is more sensitive to O3 than that in oak, and the O3-induced reduction of photosynthetic activity in beech was due not to stomatal closure, but to biochemical limitation

Growth and Photosynthetic Responses of Cuttings of a Hybrid Larch (Larix gmelinii var. japonica x L. kaempferi) to Elevated Ozone and/or Carbon Dioxide

ABSTRACT:We studied the effects of elevated ozone ([O3]) and CO2 concentrations ([CO2]) on the growth and photosynthesis of the hybrid larch F1 (F1) and on its parents (the Dahurian larch and Japanese larch). F1 is a promising species for timber production in northeast Asia. Seedlings of the three species were grown in 16 open top chambers and were exposed to two levels of O3 (⁄10 ppb and 60 ppb for 7 h per day) in combination with two levels of CO2 (ambient and 600 ppm for daytime) over an entire growing season. Ozone reduced the growth as measured by height and diameter, and reduced the needle dry mass and net photosynthetic rate of F1, but had almost no effect on the Dahurian larch or Japanese larch. There was a significant increase in whole-plant dry mass induced by elevated [CO2] in F1 but not in the other two species. Photosynthetic acclimation to elevated [CO2] was observed in all species. The net photosynthetic rate measured at the growing [CO2] (i.e. 380 ppm for ambient treatment and 600 ppm for elevated CO2 treatment) was nevertheless greater in the seedlings of all species grown at elevated [CO2]. The high [CO2] partly compensated for the reduction of stem diameter growth of F1 at high [O3]; no similar trend was found in the other growth and photosynthetic parameters, or in the other species

Elevated CO2 enhances the growth of hybrid larch F-1 (Larix gmelinii var. japonica x L-kaempferi) seedlings and changes its biomass allocation

Elevated CO (2) enhances the photosynthesis and growth of hybrid larch F (1) seedlings. However, elevated CO (2) -induced change of tree shape may have risk to the other environmental stresses. The hybrid larch F-1 (Larix gmelinii var. japonica x L. kaempferi) is one of the most promising species for timber production as well as absorption of atmospheric CO2. To assess the ability of this species in the future high CO2 environment, we investigated the growth and photosynthetic response of hybrid larch F-1 seedlings to elevated CO2 concentration. Three-year-old seedlings of hybrid larch F-1 were grown on fertile brown forest soil or infertile volcanic ash soil, and exposed to 500 mu mol mol(-1) CO2 in a free-air CO2 enrichment system located in northern Japan for two growing seasons. Regardless of soil type, the exposure to elevated CO2 did not affect photosynthetic traits in the first and second growing seasons; a higher net photosynthetic rate was maintained under elevated CO2. Growth of the seedlings under elevated CO2 was greater than that under ambient CO2. We found that elevated CO2 induced a change in the shape of seedlings: small roots, slender-shaped stems and long-shoots. These results suggest that elevated CO2 stimulates the growth of hybrid larch F-1, although the change in tree shape may increase the risk of other stresses, such as strong winds, heavy snow, and nutrient deficiency