| 1. |
- Barth, Sabine, 1974, et al.
(författare)
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Water-Use-Efficiency of Forests Exposed to Elevated Carbon Dioxide and/or Elevated Tropospheric Ozone
- 2009
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Ingår i: 8th International Carbon Dioxide Conference, Jena Germany, 13-19 September 2009.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Effects of a 40-50% increase of ambient CO2 and O3, alone and in combination, on pure aspen and mixed aspen-birch forests were examined in the free air CO2-O3 enrichment experiment near Rhinelander, Wisconsin, USA (Aspen FACE). These atmospheric conditions represent the prediction for 2050. Trees exposed to elevated CO2 showed a significant increase in tree size, leave area index (LAI) and fine root production, while elevated O3 reduced tree size and LAI but not fine root biomass after 7 years of exposure (King et al. 2005). Measurements of sap flux and yearly stem wood production were made in 2004 and 2006, after >6 years of experimental treatments and after steady-state LAI had been reached. Water use efficiency (WUE) was determined as a function of yearly stem wood production and sap flux during the active growing seasons, between DOY 168-249.
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| 2. |
- Buker, P, et al.
(författare)
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Comparison of different stomatal conductance algorithms for ozone flux modelling
- 2005
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Ingår i: UNECE – Workshop “Critical Levels of Ozone: Further applying and developing the flux-based concept”, Obergurgl, 15-19 November 2005.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Two widely used algorithms for modelling stomatal conductance (gs) were compared in order to evaluate the approach leading to the most realistic predictions of stomatal fluxes to vegetated surfaces: a multiplicative algorithm initially developed by Jarvis (1976) and refined by Emberson et al. (2000) (DO3SE ) and a photosynthesis-based Ball&Berry-type algorithm developed by Nikolov et al. (1995) (LEAFC3). Both models were parameterised for several crop and tree species (wheat, grapevine, Scots pine, beech and birch) and have been applied to various datasets – with the main focus on wheat - representing different European regions (North, Central and South Europe). A sensitivity analysis has been carried out for both models to evaluate the dependence of gs on the meteorological parameters temperature, photosynthetic active radiation and vapour pressure deficit. Furthermore, in order to test whether a general species-specific parameterisation can account for differences in gs due to plants growing under different climatic conditions throughout Europe, the models have been re-parameterised for local meteorological conditions. A direct comparison of both models showed that the net photosynthetic-based model required more detailed meteorological (e.g. ambient CO2-concentration, dew-point temperature) and plant-physiological (e.g. Vcmax and Jmax) input parameters while not delivering a substantially higher R2 when comparing measured and modelled gs. The relative weakness of the multiplicative model lies in its dependence on the maximum stomatal conductance (gmax), whereas the photosynthesis-based model is not taking into account phenology-related changes in gs. Furthermore, the results show that an equally close relationship between gs and net photosynthetic rate throughout the entire growing season is questionable. We conclude that the multiplicative approach is favourable for calculating stomatal fluxes on a wider scale (e.g. within EMEP-deposition model), whereas the photosynthesis-based approach is a potential alternative for modelling fluxes on a local scale.
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| 3. |
- Carroll, M. A., et al.
(författare)
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Reactive nitrogen oxide fluxes to a mixed hardwood forest
- 2008
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Ingår i: International Geosphere-Biosphere Programme, Congress in May 2008.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Measurements of NOx (nitric oxide and nitrogen dioxide) mixing ratios and fluxes (20 May – 1 September) and NOy mixing ratios and fluxes (9 August – 1 September) were made at a northern mixed hardwood forest located at the University of Michigan Biological Station in northern Michigan, USA (45.5 deg N, 84.7 deg W, elevation 238 m) in 2005. During the 15-week period of NOx measurements, the site received flow from two dominant flow regimes: the north-northwest (ozone 20 – 40 ppbv) and the south-southwest (ozone 40 – 100 ppbv) approximately 26% and 27% of the time, respectively. Typical ambient NOx and NOy levels ranged from 0.5 – 2.4 ppbv and 0.5 to 3 ppbv, respectively. NO and NOy fluxes were found to be strongly diurnal with mid-day maximum downward fluxes of 0.5 – 2 and 1 – 2 μmole per square meter per hour, respectively, and nighttime fluxes at or near zero. In contrast, NO2 fluxes were small and upward during the morning, small and downward during the afternoon, and at or near zero at night. NOx fluxes were found to be essentially zero throughout the day and night. If all of the NOy deposition in this study were in the form of nitric acid, it would increase the available nutrient nitrate input to the forest by 8% over measured wet nitrate deposition.
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| 4. |
- Hogg, A., et al.
(författare)
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Multi-year measurements of stomatal and non-stomatal fluxes
- 2007
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Ingår i: American Geophysical Union, Meeting in San Francisco, 10–14 December 2007.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Measurements of ozone, sensible heat, and latent heat fluxes, as well as relative humidity, temperature, pressure, wind speed, leaf area index, ambient ozone, and plant physiological parameters were made at a northern mixed hardwood forest located at the University of Michigan Biological Station (UMBS) in northern Michigan during the growing seasons 2002 through 2005. The ozone measurements were used to calculate total ozone flux and partitioning between stomatal and non-stomatal sinks. Total ozone flux varied diurnally with downward flux reaching -100 μmol m-2 h-1 at midday, at or near zero at night. Mean daytime canopy conductance varied over the four years: 0.39 mol m-2 s-1 (2002), 0.41 mol m-2 s-1 (2003), 0.52 mol m-2 s-1 (2004), and 0.43 mol m-2 s-1 (2005). Stomatal conductance showed expected patterns of behavior with respect to photosynthetic photon flux density (PPFD) and vapor pressure deficit (VPD). Estimated peak growing season stomatal ozone burden (flux) was 2.9 x105 nmol m-2 in 2002, 5.6 x105 nmol m-2 in 2003, 6.6 x105 nmol m-2 in 2004, and 4.1 x105 nmol m-2 in 2005. Non-stomatal conductance for ozone increased monotonically with increasing PPFD, and increased with temperature before falling off again at high temperature. Daytime non-stomatal ozone sinks were large and varied with time and environmental drivers. Daytime non-stomatal ozone conductance accounted for as much as 61% (2002), 31% (2003), 36% (2004), or 57% (2005) of canopy conductance, with the non-stomatal partition representing 4.2x105 nmol m-2 (2002), 2.0x105 nmol m-2 (2003), 3.5x105 nmol m-2 (2004), 3.5x105 nmol m-2 (2005) of the flux. Non-stomatal ozone conductance was strongly diurnal and a significant proportion of total canopy conductance.
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| 5. |
- Hogg, A., et al.
(författare)
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Stomatal and non-stomatal fluxes of ozone to a northern mixed hardwood forest
- 2007
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Ingår i: Tellus Series B-Chemical and Physical Meteorology. - 0280-6509. ; 59:3, s. 514-525
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Tidskriftsartikel (refereegranskat)abstract
- Measurements of ozone, sensible heat, and latent heat fluxes and plant physiological parameters were made at a northern mixed hardwood forest located at the University of Michigan Biological Station in northern Michigan from June 27 to September 28, 2002. These measurements were used to calculate total ozone flux and partitioning between stomatal and non-stomatal sinks. Total ozone flux varied diurnally with maximum values reaching 100 mu mol m(-2) h(-1) at midday and minimums at or near zero at night. Mean daytime canopy conductance was 0.5 mol m(-2) s(-1). During daytime, non-stomatal ozone conductance accounted for as much as 66% of canopy conductance, with the non-stomatal sink representing 63% of the ozone flux. Stomatal conductance showed expected patterns of behaviour with respect to photosynthetic photon flux density (PPFD) and vapour pressure defecit (VPD). Non-stomatal conductance for ozone increased monotonically with increasing PPFD, increased with temperature (T) before falling off again at high T, and behaved similarly for VPD. Day-time non-stomatal ozone sinks are large and vary with time and environmental drivers, particularly PPFD and T. This information is crucial to deriving mechanistic models that can simulate ozone uptake by different vegetation types.
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| 6. |
- Karlsson, Per Erik, 1957, et al.
(författare)
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Evidence for Impacts of Near-ambient Ozone Concentrations on Vegetation in Southern Sweden
- 2009
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Ingår i: Ambio. - : Royal Swedish Academy of Sciences. ; 38:8, s. 425-431
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Tidskriftsartikel (refereegranskat)abstract
- Substantial impacts of near-ambient ozone concentrations on agricultural crops, trees, and seminatural vegetation are demonstrated for southern Sweden. Impacts of ambient ozone levels (2–15 μL L-¹ hr annual accumulated ozone exposure over a threshold of 40 nL L-¹ [AOT40]) range from a 2%–10% reduction for trees (e.g., leaf chlorophyll, tree growth) up to a 15% reduction for crops (e.g., yield, wheat/potato). Visible leaf injury on bioindicator plants caused by ambient ozone levels has been clearly demonstrated. The humid climatic conditions in Sweden promote high rates of leaf ozone uptake at a certain ozone concentration. This likely explains the comparatively large ozone impacts found for vegetation in southern Sweden at relatively low ozone concentrations in the air. It is important that the future methods used for the representation of ozone impacts on vegetation across Europe are based on the leaf ozone uptake concept and not on concentration-based exposure indices, such as AOT40.
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| 7. |
- Karlsson, Per Erik, 1957, et al.
(författare)
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Negative impact of ozone on the stem basal area increment of mature Norway spruce in south Sweden
- 2006
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Ingår i: Forest Ecology and Management. - : Elsevier BV. - 0378-1127. ; 232:1-3, s. 146-151
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Tidskriftsartikel (refereegranskat)abstract
- The relative annual basal area increment of mature Norway spruce trees in south-central Sweden during 9 years was used as the response variable and analysed in relation to ozone exposure, meteorological conditions, soil moisture and stand characteristics. The method used was a modified multiple regression analysis, allowing for dependencies between observations from the same plots. The selected statistical model explained 91% of the variation in the annual relative basal area increment. The strongest explanatory variable was the stand basal area, followed by the temperature sum and the soil moisture index. After these three variables, the ozone index was the most important variable. Its effect was negative and highly significant. The average daylight ozone concentration gave a slightly better model fit as compared to the accumulated exposure during daylight hours above a threshold of 40 nmol mol−1 (AOT40). The predicted effect of ozone within the range of annual ozone exposures found in this study (1800–8700 nmol mol−1 h AOT40), was in absolute values a 0.8% decrease in the relative annual basal area increment. This could be compared with the mean relative annual increment measured during the study period of 4.6%. Our results provide statistical evidence that ground level ozone can have a negative impact on the stem growth of mature Norway spruce trees under field conditions.
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| 8. |
- Karlsson, Per Erik, 1957, et al.
(författare)
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Risk assessments for forest trees: The performance of the ozone flux versus the AOT concepts
- 2007
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Ingår i: Environmental Pollution. - : Elsevier BV. - 0269-7491. ; 146:3, s. 608-616
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Tidskriftsartikel (refereegranskat)abstract
- Published ozone exposure-response relationships from experimental studies with young trees performed at different sites across Europe were re-analysed in order to test the performance of ozone exposure indices based on AOTX (Accumulated exposure Over a Threshold of X nmol mol(-1)) and AF(st)Y (Accumulated Stomatal Flux above a threshold of Y nmol m(-2) s(-1)). AF(st)1.6 was superior, as compared to AOT40, for explaining biomass reductions, when ozone sensitive species with differing leaf morphology were included in the analysis, while this was not the case for less sensitive species. A re-analysis of data with young black cherry trees, subject to different irrigation regimes, indicated that leaf visible injuries were more strongly related to the estimated stomatal ozone uptake, as compared to the ozone concentration in the air. Experimental data with different clones of silver birch indicated that leaf thickness was also an important factor influencing the development of ozone induced leaf visible injury. (c) 2006 Elsevier Ltd. All rights reserved.
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| 9. |
- Oksanen, E., et al.
(författare)
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Northern environment predisposes birches to ozone damage
- 2007
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Ingår i: Plant Biology. - : Wiley. - 1435-8603 .- 1438-8677. ; 9:2, s. 191-196
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Tidskriftsartikel (refereegranskat)abstract
- Ozone sensitivity of silver birch (Betula pendula Roth) has been thoroughly investigated since early 1990's in Finland. in our long-term open-field experiments the annual percentage reduction in basal diameter and stem volume increment were the best non-destructive growth indicators for ozone impact when plotted against AOTX. Remarkable differences in defence strategies, stomatal conductance, and defence compounds (phenolics), clearly indicate that external exposure indices are ineffective for accurate risk assessment for birch. For flux-based approaches, site-specific values for g(max) and g(dark) are necessary, and determinants for cletoxification capacity, ageing of leaves, and cumulative ozone impact would be needed for further model development. increasing CO2 seems to counteract negative ozone responses in birch, whereas exposure to springtime frost may seriously exacerbate ozone damage in northern conditions. Therefore, we need to proceed towards incorporating the most important climate change factors in any attempts for ozone risk assessment.
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| 10. |
- Uddling, Johan, 1972, et al.
(författare)
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Changes in stomatal conductance and net photosynthesis during phenological development in spring wheat: implications for gas exchange modelling
- 2006
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Ingår i: International Journal of Biometeorology. - : Springer Science and Business Media LLC. - 0020-7128 .- 1432-1254. ; 51:1, s. 37-48
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Tidskriftsartikel (refereegranskat)abstract
- Gas exchange was measured from 1 month before the onset of anthesis until the end of grain filling in field-grown spring wheat, Triticum aestivum L., cv. Vinjett, in southern Sweden. Two g (s) models were parameterised using these data: one Jarvis-type multiplicative g (s) model (J-model), and one combined stomatal-photosynthesis model (L-model). In addition, the multiplicative g (s) model parameterisation for wheat used within the European Monitoring and Evaluation Programme (EMEP-model) was tested and evaluated. The J-model performed well (R-2=0.77), with no systematic pattern of the residuals plotted against the driving variables. The L-model explained a larger proportion of the variation in g (s) data when observations of A (n) were used as input data (R-2=0.71) compared to when A (n) was modelled (R-2=0.53). In both cases there was a systematic model failure, with g (s) being over- and underestimated before and after anthesis, respectively. This pattern was caused by the non-parallel changes in g (s) and A (n) during plant phenological development, with A (n) both peaking and starting to decline earlier as compared to g (s) . The EMEP-model accounted for 41% of the variation in g (s) data, with g (s) being underestimated after anthesis. We conclude that, under the climatic conditions prevailing in southern Scandinavia, the performance of the combined stomatal-photosynthesis approach is hampered by the non-parallel changes in g (s) and A (n), and that the phenology function of the EMEP-model, having a sharp local maximum at anthesis, should be replaced by a function with a broad non-limiting period after anthesis.
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