Sirkku Manninen

Ozone sensitivity of wild field layer plant species of northern Europe. A review

The increasing tropospheric ozone (O3) concentration constitutes a potential threat to nature. Plants are known to react to O3, but knowledge of the sensitivity and type of responses of different species and plant communities is widely lacking. This review focuses on the ecological effects of O3 on northern wild field layer plant species. Most of the 65 species examined thus far have proven to be quite tolerant of O3. Visible symptoms were observed in 54% of the 61 species studied, and growth reduction in 31% of the 55 species studied for growth. There were no signs to suggest that certain families or vegetation types are more sensitive or tolerant than others. There were, however, clear differences in sensitivity between the different species. It seems that forbs are usually more sensitive than grasses. It should be kept in mind, however, that we still lack knowledge on the responses of many common and abundant key species. The long-term effects are also far from clear. Hardly any field examinations have been carried out on the effects of O3 on plant communities.

Urbanization-related changes in European aspen (Populus tremula L.): Leaf traits and litter decomposition

We investigated foliar and litter responses of European aspen (Populus tremula L.) to urbanization, including factors such as increased temperature, moisture stress and nitrogen (N) deposition. Leaf samples were collected in 2006-2008 from three urban and three rural forest stands in the Helsinki Metropolitan Area, southern Finland, and reciprocal litter transplantations were established between urban and rural sites. Urban leaves exhibited a higher amount of epicuticular waxes and N concentration, and a lower C:N ratio than rural ones, but there was no difference in specific leaf area. Urban litter had a slightly higher N concentration, lower concentrations of lignin and total phenolics, and was more palatable to a macrofaunal decomposer. Moreover, litter decay was faster at the urban site and for urban litter. Urbanization thus resulted in foliar acclimatization in terms of increased amount of epicuticular waxes, as well as in accelerated decomposition of the N-richer leaf litter.

Effect of 3 years' free-air exposure to elevated ozone on mature Norway spruce (Picea abies (L) Karst.) needle epicuticular wax physicochemical characteristics

We examined the effect of ozone (O(3)) on Norway spruce (Picea abies) needle epicuticular wax over three seasons at the Kranzberg Ozone Fumigation Experiment. Exposure to 2x ambient O(3) ranged from 64.5 to 74.2 microl O(3) l(-1) h AOT40, and 117.1 to 123.2 nl O(3) l(-1) 4th highest daily maximum 8-h average O(3) concentration. The proportion of current-year needle surface covered by wax tubes, tube aggregates, and plates decreased (P=0.011) under 2x O(3). Epistomatal chambers had increased deposits of amorphous wax. Proportion of secondary alcohols varied due to year (P=0.004) and O(3) treatment (P=0.029). Secondary alcohols were reduced by 9.1% under 2x O(3). Exposure to 2x O(3) increased (P=0.037) proportions of fatty acids by 29%. Opposing trends in secondary alcohols and fatty acids indicate a direct action of O(3) on wax biosynthesis. These results demonstrate O(3)-induced changes in biologically important needle surface characteristics of 50-year-old field-grown trees.

Mesocosms mimic natural meadows as regards greenhouse gas fluxes and potential activities of nitrifying and denitrifying bacteria

The objective of this study was to determine whether a planted mesocosm mimics a natural habitat in terms of N2O and CH4 fluxes, soil characteristics and potential nitrification and denitrification activities. We compared mesocosms in unchambered open-field plots and in open-top chambers with nonfiltered ambient air with three natural meadows that had similar soil characteristics and species composition. The N2O fluxes in the mesocosms were very similar to the fluxes in the three natural meadows. There were no marked differences in potential nitrification and denitrification activities between the mesocosms and the natural meadows, either. Only the CH4 fluxes differed slightly between the mesocosms and some of the natural meadows. Therefore, it seems that the mesocosms compared rather well to natural habitats. The open-top chambers modified only the soil water content, the values being higher in the unchambered plots than in the chambered plots. These results thus suggest that the open-top chamber experiment enables estimates of greenhouse gas and potential activities of nitrifying and denitrifying bacteria in unfertilized Finnish meadows, in spite of the chamber effects on the soil water content.

Northern Plants and Ozone

Abstract Forests in northern Fennoscandia are mainly composed of the O3-sensitive species—Scots pine and downy, mountain, and silver birches. Seminatural vegetation also contributes to biodiversity, carbon cycling, and ecosystem services as a part of forests, mires, meadows, and road verges. Fumigation experiments show that current O3 concentrations of 30–50 ppb reduce plant biomass production and reproduction. Visible foliar injury is attributable to peak O3 concentrations and relates to fast phenological development and high growth rate. Trees can acclimate to O3-induced water stress by producing more xeromorphic leaves or needles. The direct effects of O3 on grassland vegetation also translate to changes in the structure and size of the soil microbial community, and ecosystem N cycling. It is necessary to reduce the emission of O3 precursors and maintain high biodiversity to protect northern ecosystems. Regular, systematic, countrywide monitoring and validation as well as quantification of the effects of O3 on plants in the Nordic countries are also necessary.

Near-ambient Ozone Concentrations Reduce the Vigor of Betula and Populus Species in Finland

Abstract In this review the main growth responses of Finnish birch (Betula pendula, B. pubescens) and aspen species (Populus tremula and P. tremuloides × P. tremula) are correlated with ozone exposure, indicated as the AOT40 value. Data are derived from 23 different laboratory, open-top chamber, and free-air fumigation experiments. Our results indicate that these tree species are sensitive to increasing ozone concentrations, though high intraspecific variation exists. The roots are the most vulnerable targets in both genera. These growth reductions, determined from trees grown under optimal nutrient and water supply, were generally accompanied by increased visible foliar injuries, carbon allocation toward defensive compounds, reduced carbohydrate contents of leaves, impaired photosynthesis processes, disturbances in stomatal function, and earlier autumn senescence. Because both genera have shown complex ozone defense and response mechanisms, which are modified by variable environmental conditions, a mechanistically based approach is necessary for accurate ozone risk assessment.

Management mitigates the impact of urbanization on meadow vegetation

Urban regions often contain remnants of ecologically valuable habitats. Whilst meadow habitats have been recognized as ecologically important and much studied, little attention has been given to meadow assemblages of urban locations. We studied the effects of meadow type, urbanization level, and management on vascular plant species richness, field layer diversity and soil chemistry in 18 grassland sites in the Helsinki Metropolitan Area (60°E, 25°N), on the southern coast of Finland during the summer of 2007. We recorded a total of 252 species, though the average number of species per m2 was only 12.6. The negative effects of urbanization on forbs seemed to result in particular from increased soil nitrate (NO3- -N) concentration. The highest NO3- -N and Fe concentrations and ratios of total inorganic nitrogen (Ntot) to phosphorus (P) and potassium (K), were recorded from the soils of urban rocky meadows. Management by mowing decreased soil NO3- -N and Fe concentrations, ratios of Ntot:P and Ntot:K, and increased species richness and diversity. Elevated NOx deposition is considered as a major driver of urbanization effects on vegetation, though changes in soil pH and metal concentrations, such as zinc (Zn), may also negatively affect the frequency of both forbs and grasses. This study shows that regular management by mowing and removal of hay mitigates these effects. We also recommend increasing the provision of dry meadows and maintaining more areas of supplementary semi-natural grassland habitats in urban green space as concrete measures for the conservation of dry meadow assemblages and urban biodiversity.

Differences in ozone response between two Finnish wild strawberry populations

Abstract The sensitivity of two Finnish wild strawberry ( Fragaria vesca ) populations of seed origin (Kainuu 64°N, 27°E; Etela-Hame 61°N, 25°E) to slightly elevated tropospheric O 3 was studied during two summers in open-top chambers (OTC; NF=non-filtered air and NF+O 3 =non-filtered air+supplemental O 3 ) and on open-field plots (AA=ambient air). The hypothesis was that the southern Finnish population may be less O 3 sensitive, as the ambient O 3 levels are higher there and, consequently, some selection may already have occurred. The seedlings were moved to an experimental field and planted into a mixture of humus and sand (3:1) without growing pots on 11 June 1998. In the northern areas, elevated O 3 concentrations are episodic, and we hence fumigated the NF+O 3 plants for 8 h a day on 5 days a week as follows: ambient air+30 ppb in June, ambient air+20 ppb in July and ambient air+10 ppb in August. The accumulated exposure over a threshold of 40 ppb reached 5040 ppb h in the NF+O 3 OTCs in June–August 1998, but only 1156 ppb h by mid-August in 1999, when the fumigations were started on 23 June. During the first summer, the shoot (−16%) and root (−13%) biomasses in the NF+O 3 strawberries of the Kainuu population decreased, whereas those in the NF+O 3 strawberries of the Etela-Hame population increased (+22 and +20%, respectively). However, there was no difference in the runner biomass between the populations. On the whole, the AA plants had the highest biomass in summer 1998. This pointed to a noteworthy chamber effect. In 1999, the proportion of fruiting plants was markedly higher in the NF+O 3 -treated Kainuu population than in the Etela-Hame population. The average number of red, yellow and brown leaves was also higher in the NF+O 3 plants of the Kainuu population than in those of the Etela-Hame population or in the NF plants of the Kainuu population. However, the differences were not statistically significant due to large variation in the number of discoloured leaves between the individual plants in the NF+O 3 treatment, particularly in the Kainuu population. The results thus suggest that the Kainuu population was more sensitive to O 3 than the Etela-Hame population and responded to an O 3 exposure far below the proposed critical level of 7000 ppb h.

Nitrogen deposition does not enhance Sphagnum decomposition.

Long-term additions of nitrogen (N) to peatlands have altered bryophyte growth, species dominance, N content in peat and peat water, and often resulted in enhanced Sphagnum decomposition rate. However, these results have mainly been derived from experiments in which N was applied as ammonium nitrate (NH4NO3), neglecting the fact that in polluted areas, wet deposition may be dominated either by NO3(-) or NH4(+). We studied effects of elevated wet deposition of NO3(-) vs. NH4(+) alone (8 or 56kgNha(-1)yr(-1) over and above the background of 8kgNha(-1)yr(-1) for 5 to 11years) or combined with phosphorus (P) and potassium (K) on Sphagnum quality for decomposers, mass loss, and associated changes in hummock pore water in an ombrotrophic bog (Whim). Adding N, especially as NH4(+), increased N concentration in Sphagnum, but did not enhance mass loss from Sphagnum. Mass loss seemed to depend mainly on moss species and climatic factors. Only high applications of N affected hummock pore water chemistry, which varied considerably over time. Overall, C and N cycling in this N treated bog appeared to be decoupled. We conclude that moss species, seasonal and annual variation in climatic factors, direct negative effects of N (NH4(+) toxicity) on Sphagnum production, and indirect effects (increase in pH and changes in plant species dominance under elevated NO3(-) alone and with PK) drive Sphagnum decomposition and hummock C and N dynamics at Whim.

Consequences of long-term severe industrial pollution for aboveground carbon and nitrogen pools in northern taiga forests at local and regional scales

Boreal coniferous forests act as an important sink for atmospheric carbon dioxide. The overall tree carbon (C) sink in the forests of Europe has increased during the past decades, especially due to management and elevated nitrogen (N) deposition; however, industrial atmospheric pollution, primarily sulphur dioxide and heavy metals, still negatively affect forest biomass production at different spatial scales. We report local and regional changes in forest aboveground biomass, C and N concentrations in plant tissues, and C and N pools caused by long-term atmospheric emissions from a large point source, the nickel-copper smelter in Monchegorsk, in north-western Russia. An increase in pollution load (assessed as Cu concentration in forest litter) caused C to increase in foliage but C remained unchanged in wood, while N decreased in foliage and increased in wood, demonstrating strong effects of pollution on resource translocation between green and woody tissues. The aboveground C and N pools were primarily governed by plant biomass, which strongly decreased with an increase in pollution load. In our study sites (located 1.6-39.7 km from the smelter) living aboveground plant biomass was 76 to 4888 gm(-2), and C and N pools ranged 35-2333 g C m(-2) and 0.5-35.1 g N m(-2), respectively. We estimate that the aboveground plant biomass is reduced due to chronic exposure to industrial air pollution over an area of about 107,200 km2, and the total (aboveground and belowground) loss of phytomass C stock amounts to 4.24×10(13) g C. Our results emphasize the need to account for the overall impact of industrial polluters on ecosystem C and N pools when assessing the C and N dynamics in northern boreal forests because of the marked long-term negative effects of their emissions on structure and productivity of plant communities.