Both CO2 and ozone increased the diseased leaf area of clone V5952 in Exp. 1 in the year 2000. The size of spots increased most under ozone fumigation, and the number of spots under ozone and CO2 + O3 fumigations. In clone K1659 all fumigation treatments decreased or had no effect on the DLA, or the number and size of the leaf spots. Also the number of fallen leaves under fumigation treatments was higher in clone V5952 than in clone K1659. Analysis of the year 2001 monitoring results is currently going on

Atmospheric nitrogen (N) deposition has a significant influence on soil organic carbon (SOC) accumulation in forest ecosystems. Microbial residues, as by-products of microbial anabolism, account for a significant fraction of soil C pools. However, how N deposition affects the accumulation of soil microbial residues in different forest biomes remains unclear. Here, we investigated the effects of six/seven-year N additions on microbial residues (amino sugar biomarkers) in eight forests from tropical to boreal zone in eastern China. Our results showed a minor change in the soil microbial residue concentrations but a significant change in the contribution of microbial residue-C to SOC after N addition. The contribution of fungal residue-C to SOC decreased under low N addition (50 kg N ha⁻¹ yr⁻¹) in the tropical secondary forest (−19%), but increased under high N addition (100 kg N ha⁻¹ yr⁻¹) in the temperate Korean pine mixed forest (+21%). The contribution of bacterial residue-C to SOC increased under the high N addition in the subtropical Castanopsis carlesii forest (+26%) and under the low N addition in the temperate birch forest (+38%), respectively. The responses of microbial residue-C in SOC to N addition depended on the changes in soil total N concentration and fungi to bacteria ratio under N addition and climate. Taken together, these findings provide the experimental evidence that N addition diversely regulates the formation and composition of microbial-derived C in SOC in forest ecosystems.

Airborne pollen measurements are the foundation of aerobiological research and provide essential raw data for various disciplines. Pollen itself should be considered a relevant factor in air quality. Symptom data shed light on the relationship of pollen allergy and pollination. The aim of this study is to assess the spatial variation of local, regional and national symptom datasets. Ten pollen season definitions are used to calculate the symptom load index for the birch and grass pollen seasons (2013–2014) in Austria. (1) Local, (2) regional and (3) national symptom datasets are used to examine spatial variations and a consistent pattern was found. In conclusion, national datasets are suitable for first insights where no sufficient local or regional dataset is available and season definitions based on percentages provide a practical solution, as they can be applied in regions with different pollen loads and produce more constant results.

To construct stomatal conductance models and estimate stomatal O3 uptake for Fagus crenata, Quercus serrata, Quercus mongolica var. crispula and Betula platyphylla, stomatal conductance (gs) was measured in seedlings of the four tree species. Better estimates of gs were made by incorporating the acute effects of O3 on gs into the models and the models could explain 34–52% of the variability in gs. Although the O3 concentration was relatively high in spring from April to May, COU of F. crenata, Q. serrata and Q. mongolica var. crispula were relatively low and the ratios of COU in spring to total COU in one year were 16.8% in all tree species because of low gs limited mainly by leaf pre-maturation and/or low temperature. The COU of B. platyphylla were relatively high mainly because of rapid leaf maturation and lower optimal temperature for stomatal opening.

Trees can improve air quality by capturing particles in their foliage. We determined the particle capture efficiencies of coniferous Pinus sylvestris and three broadleaved species: Betula pendula, Betula pubescens and Tilia vulgaris in a wind tunnel using NaCl particles. The importance of leaf surface structure, physiology and moderate soil drought on the particle capture efficiencies of the trees were determined. The results confirm earlier findings of more efficient particle capture by conifers compared to broadleaved plants. The particle capture efficiency of P. sylvestris (0.21%) was significantly higher than those of B. pubescens, T. vulgaris and B. pendula (0.083%, 0.047%, 0.043%, respectively). The small leaf size of P. sylvestris was the major characteristic that increased particle capture. Among the broadleaved species, low leaf wettability, low stomatal density and leaf hairiness increased particle capture. Moderate soil drought tended to increase particle capture efficiency of P. sylvestris.

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.

Betula papyrifera trees were exposed to elevated concentrations of CO2 (1.4 × ambient), O3 (1.2 × ambient) or CO2 + O3 at the Aspen Free-air CO2 Enrichment Experiment. The treatment effects on leaf surface characteristics were studied after nine years of tree exposure. CO2 and O3 increased epidermal cell size and reduced epidermal cell density but leaf size was not altered. Stomatal density remained unaffected, but stomatal index increased under elevated CO2. Cuticular ridges and epicuticular wax crystallites were less evident under CO2 and CO2 + O3. The increase in amorphous deposits, particularly under CO2 + O3, was associated with the appearance of elongated plate crystallites in stomatal chambers. Increased proportions of alkyl esters resulted from increased esterification of fatty acids and alcohols under elevated CO2 + O3. The combination of elevated CO2 and O3 resulted in different responses than expected under exposure to CO2 or O3 alone. The combined effects of CO2 and O3 on birch leaf surface characteristics cannot be predicted on the basis of studies examining each of these gases separately.

The forest hydrologic budget may be impacted by increasing CO2 and tropospheric O3. Efficient means to quantify such effects are beneficial. We hypothesized that changes in the balance of canopy interception, stem flow, and through-fall in the presence of elevated CO2 and O3 could be discerned using image analysis of leafless branches. We compared annual stem flow to the results of a computerized analysis of all branches from the 2002, 2004, and 2006 annual growth whorls of 97 ten-year-old trees from the Aspen Free-Air CO2 and O3 Enrichment (Aspen FACE) experiment in Rhinelander, WI. We found significant effects of elevated CO2 and O3 on some branch metrics, and that the branch metrics were useful for predicting stem flow from birch, but not aspen. The results of this study should contribute to development of techniques for efficient characterization of effects on the forest hydrologic budget of increasing CO2 and tropospheric O3. Canopy architecture and stem flow are affected by elevated CO2 and tropospheric O3.

Recent evidence from novel phytotron and free-air ozone (O3) fumigation experiments in Europe and America on forest tree species is highlighted in relation to previous chamber studies. Differences in O3 sensitivity between pioneer and climax species are examined and viewed for trees growing at the harsh alpine timberline ecotone. As O3 apparently counteracts positive effects of elevated CO2 and mitigates productivity increases, response is governed by genotype, competitors, and ontogeny rather than species per se. Complexity in O3 responsiveness increased under the influence of pathogens and herbivores. The new evidence does not conflict in principle with previous findings that, however, pointed to a low ecological significance. This new knowledge on trees' O3 responsiveness beyond the juvenile stage in plantations and forests nevertheless implies limited predictability due to complexity in biotic and abiotic interactions. Unravelling underlying mechanisms is mandatory for assessing O3 risks as an important component of climate change scenarios.