| 1. |
- Barth, Sabine, 1974, et al.
(författare)
-
Water-Use-Efficiency of Forests Exposed to Elevated Carbon Dioxide and/or Elevated Tropospheric Ozone
- 2009
-
Ingår i: 8th International Carbon Dioxide Conference, Jena Germany, 13-19 September 2009.
-
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.
|
|
| 2. |
- Buker, P, et al.
(författare)
-
Comparison of different stomatal conductance algorithms for ozone flux modelling
- 2005
-
Ingår i: UNECE – Workshop “Critical Levels of Ozone: Further applying and developing the flux-based concept”, Obergurgl, 15-19 November 2005.
-
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.
|
|
| 3. |
- Carroll, M. A., et al.
(författare)
-
Reactive nitrogen oxide fluxes to a mixed hardwood forest
- 2008
-
Ingår i: International Geosphere-Biosphere Programme, Congress in May 2008.
-
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.
|
|
| 4. |
- Hogg, A., et al.
(författare)
-
Multi-year measurements of stomatal and non-stomatal fluxes
- 2007
-
Ingår i: American Geophysical Union, Meeting in San Francisco, 10–14 December 2007.
-
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.
|
|
| 5. |
- Hogg, A., et al.
(författare)
-
Stomatal and non-stomatal fluxes of ozone to a northern mixed hardwood forest
- 2007
-
Ingår i: Tellus Series B-Chemical and Physical Meteorology. - 0280-6509. ; 59:3, s. 514-525
-
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.
|
|
| 6. |
- Karlsson, Per Erik, 1957, et al.
(författare)
-
Evidence for Impacts of Near-ambient Ozone Concentrations on Vegetation in Southern Sweden
- 2009
-
Ingår i: Ambio. - : Royal Swedish Academy of Sciences. ; 38:8, s. 425-431
-
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.
|
|
| 7. |
- Karlsson, Per Erik, 1957, et al.
(författare)
-
Negative impact of ozone on the stem basal area increment of mature Norway spruce in south Sweden
- 2006
-
Ingår i: Forest Ecology and Management. - : Elsevier BV. - 0378-1127. ; 232:1-3, s. 146-151
-
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 (18008700 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.
|
|
| 8. |
- Karlsson, Per Erik, 1957, et al.
(författare)
-
Risk assessments for forest trees: The performance of the ozone flux versus the AOT concepts
- 2007
-
Ingår i: Environmental Pollution. - : Elsevier BV. - 0269-7491. ; 146:3, s. 608-616
-
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.
|
|
| 9. |
- Oksanen, E., et al.
(författare)
-
Northern environment predisposes birches to ozone damage
- 2007
-
Ingår i: Plant Biology. - : Wiley. - 1435-8603 .- 1438-8677. ; 9:2, s. 191-196
-
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.
|
|
| 10. |
- Uddling, Johan, 1972, et al.
(författare)
-
Changes in stomatal conductance and net photosynthesis during phenological development in spring wheat: implications for gas exchange modelling
- 2006
-
Ingår i: International Journal of Biometeorology. - : Springer Science and Business Media LLC. - 0020-7128 .- 1432-1254. ; 51:1, s. 37-48
-
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.
|
|
| 11. |
- Uddling, Johan, 1972, et al.
(författare)
-
Evaluating the relationship between leaf chlorophyll concentration and SPAD-502 chlorophyll meter readings
- 2007
-
Ingår i: Photosynthesis Research. - : Springer Science and Business Media LLC. - 0166-8595 .- 1573-5079. ; 91:3, s. 37-46
-
Tidskriftsartikel (refereegranskat)abstract
- Relationships between chlorophyll concentration ([chl]) and SPAD values were determined for birch, wheat, and potato. For all three species, the relationships were non-linear with an increasing slope with increasing SPAD. The relationships for birch and wheat were strong (r(2) similar to 0.9), while the potato relationship was comparatively weak (r(2) similar to 0.5). Birch and wheat had very similar relationships when the chlorophyll concentration was expressed per unit leaf area, but diverged when it was expressed per unit fresh weight. Furthermore, wheat showed similar SPAD-[chl] relationships for two different cultivars and during two different growing seasons. The curvilinear shape of the SPAD-[chl] relationships agreed well with the simulated effects of non-uniform chlorophyll distribution across the leaf surface and multiple scattering, causing deviations from linearity in the high and low SPAD range, respectively. The effect of non-uniformly distributed chlorophyll is likely to be more important in explaining the non-linearity in the empirical relationships, since the effect of scattering was predicted to be comparatively weak. The simulations were based on the algorithm for the calculation of SPAD-502 output values. We suggest that SPAD calibration curves should generally be parameterised as non-linear equations, and we hope that the relationships between [chl] and SPAD and the simulations of the present study can facilitate the interpretation of chlorophyll meter calibrations in relation to optical properties of leaves in future studies.
|
|
| 12. |
- Uddling, Johan, 1972, et al.
(författare)
-
Leaf and canopy conductance in aspen and aspen-birch forests under free-air enrichment of carbon dioxide and ozone
- 2009
-
Ingår i: Tree Physiology. - : Oxford University Press (OUP). - 0829-318X .- 1758-4469. ; 29:11, s. 1367-1380
-
Tidskriftsartikel (refereegranskat)abstract
- Increasing concentrations of atmospheric carbon dioxide (CO2) and tropospheric ozone (O-3) have the potential to affect tree physiology and structure, and hence forest feedbacks on climate. Here, we investigated how elevated concentrations of CO2 (+ 45%) and O-3 (+ 35%), alone and in combination, affected conductance for mass transfer at the leaf and canopy levels in pure aspen (Populus tremuloides Michx.) and in mixed aspen and birch (Betula papyrifera Marsh.) forests in the free-air CO2-O-3 enrichment experiment near Rhinelander, Wisconsin (Aspen FACE). The study was conducted during two growing seasons, when steady-state leaf area index (L) had been reached after > 6 years of exposure to CO2- and O-3-enrichment treatments. Canopy conductance (g(c)) was estimated from stand sap flux, while leaf-level conductance of sun leaves in the upper canopy was derived by three different and independent methods: sap flux and L in combination with vertical canopy modelling, leaf C-13 discrimination methodology in combination with photosynthesis modelling and leaf-level gas exchange. Regardless of the method used, the mean values of leaf-level conductance were higher in trees growing under elevated CO2 and/or O-3 than in trees growing in control plots, causing a CO2 x O-3 interaction that was statistically significant (P <= 0.10) for sap flux-and (for birch) C-13-derived leaf conductance. Canopy conductance was significantly increased by elevated CO2 but not significantly affected by elevated O-3. Investigation of a short-term gap in CO2 enrichment demonstrated a + 10% effect of transient exposure of elevated CO2-grown trees to ambient CO2 on g(c). All treatment effects were similar in pure aspen and mixed aspen-birch communities. These results demonstrate that short-term primary stomatal closure responses to elevated CO2 and O-3 were completely offset by long-term cumulative effects of these trace gases on tree and stand structure in determining canopy- and leaf-level conductance in pure aspen and mixed aspen-birch forests. Our results, together with the findings from other long-term FACE experiments with trees, suggest that model assumptions of large reductions in stomatal conductance under rising atmospheric CO2 are very uncertain for forests.
|
|
| 13. |
- Uddling, Johan, 1972, et al.
(författare)
-
Measuring and modelling stomatal conductance and photosynthesis in mature birch in Sweden
- 2005
-
Ingår i: Agricultural and Forest Meteorology. - : Elsevier BV. - 0168-1923. ; 132:1-2, s. 115-131
-
Tidskriftsartikel (refereegranskat)abstract
- Stomatal conductance (g(s)), net photosynthesis (A(n)) and twig water potential (Psi(t)) were measured in mature silver birch (Betula pendula) during 3 years in southern Sweden. Measurements from 2 years were used to parameterise three different gs models and measurements from a 3rd year were used to validate these models. Two different multiplicative stomatal models were used. In one of these, the gs response function for the water vapour pressure deficit (D) was fixed, while in the other the g, sensitivity to D increased with the accumulated time after sunrise with D above a certain threshold value. Furthermore, one combined stomatal-photosynthesis model (L-model) was used. The L-model was run either by using observations of photosynthesis as input data, or by predicting g(s) and photosynthesis simultaneously from environmental data. The model used to predict photosynthesis was parameterised from measurements of the photosynthetic responses to the photosynthetically active radiation, CO2 and temperature. The stomatal response functions of the L-model were parameterised using observations of photosynthesis as input data in order to make them independent of the performance of the photosynthesis model. The difference in model performance between the two multiplicative models was relatively small. The multiplicative stomatal models and the L-model were similarly successful in predicting g(s) when the L-model was driven by observations of photosynthesis. However, the L-model was considerably less successful when photosynthesis was predicted. Photosynthesis was systematically under- and overestimated at high and low Psi(t), respectively, causing errors in the prediction of g(s). In most situations, measurements of photosynthesis are not available and g(s) must be predicted from environmental data. In such cases, we conclude that the two multiplicative models are more successful in predicting gs in mature silver birch than the combined stomatal-photosynthesis model. (c) 2005 Elsevier B.V. All rights reserved.
|
|
| 14. |
- Uddling, Johan, 1972, et al.
(författare)
-
Ozone impairs autumnal resorption of nitrogen from birch (Betula pendula) leaves, causing an increase in whole-tree nitrogen loss through litter fall
- 2006
-
Ingår i: Tree Physiology. - 0829-318X. ; 26:1, s. 113-120
-
Tidskriftsartikel (refereegranskat)abstract
- Saplings of one half-sib family of birch, Betula pendula Roth, were exposed to three ozone concentrations (non-filtered air (NF); non-filtered air + 10-20 nmol O-3 mol(-1) (NF+); non-filtered air + 40-60 nmol O-3 mol(-1) (NF++)) in open-top chambers during two growing seasons from 1997 to 1998. Shed leaves were collected regularly during both growing seasons and, in 1998, the dry mass (DM) and nitrogen (N) concentrations ([N]) of the shed leaves were measured to quantify the total amount of N lost through litter fall. Dry mass and [N] were also determined in mid-August for attached, mature and non-senescent leaves, in order to estimate autumnal leaf N resorption efficiency and proportional leaf DM decrease. Net photosynthetic capacity was measured during August and September 1998, in a population of leaves that emerged in mid-July. Photosynthesis declined with increasing leaf age in the NF++ treatment, whereas it remained high throughout the measurement period in the NF and NF+ treatments. In both years, leaves abscised prematurely in the NF++ treatment, whereas this effect was only significant in 1998 in the NF+ treatment. There was a strong linear relationship between proportional leaf shedding and daylight ozone exposure above a threshold of 40 nmol mol(-1) (daylight AOT40) during the growing season. The resorption of N was significantly impaired by ozone, and the smaller autumnal decrease in leaf DM in elevated ozone concentrations suggested that the bulk resorption of leaf DM was also inhibited. Nitrogen resorption efficiencies were 81. 73 and 63% and leaf mass decreases were 45, 36 and 30% in the NF, NF+ and NF++ treatments, respectively. Compared with the NF treatment, total N loss through litter fall was increased by 16 and 122% in the NF+ and NF++ treatments, respectively. We conclude that ozone impaired N resorption from birch leaves before abscission, causing a substantial increase in whole-tree N loss through litter fall.
|
|
| 15. |
- Uddling, Johan, 1972, et al.
(författare)
-
Sap flux in pure aspen and mixed aspen-birch forests exposed to elevated concentrations of carbon dioxide and ozone
- 2008
-
Ingår i: Tree Physiology. - 0829-318X. ; 28:8, s. 1231-1243
-
Tidskriftsartikel (refereegranskat)abstract
- Elevated concentrations of atmospheric carbon dioxide ([CO2]) and tropospheric ozone ([O-3]) have the potential to affect tree physiology and structure and hence forest water use, which has implications for climate feedbacks. We investigated how a 40% increase above ambient values in [CO2] and [O-3], alone and in combination, affect tree water use of pure aspen and mixed aspen-birch forests in the free air CO2-O-3 enrichment experiment near Rhinelander, Wisconsin (Aspen FACE). Measurements of sap flux and canopy leaf area index (L) were made during two growing seasons, when steady-state L had been reached after more than 6 years of exposure to elevated [CO2] and [O-3]. Maximum stand-level sap flux wits not significantly affected by levated [O-3], but was increased by 18% by elevated [CO2] averaged across years, communities and O-3 regimes. Treatment effects were similar in pure aspen and mixed aspen-birch communities. Increased tree water use in response to elevated [CO2] was related to positive CO2 treatment effects on tree size and L (+40%). Tree water use was not reduced by elevated [O-3] despite strong negative O-3 treatment effects on tree size and L (-22%). Elevated [O-3] predisposed pure aspen stands to drought-induced Sap flux reductions, whereas increased tree water use in response to elevated [CO2] did not result in lower soil water content in the upper soil or decreasing sap flux relative to control values during dry periods. Maintenance of soil water content in the upper soil in the elevated [CO2] treatment was at least partly a function of enhanced soil water-holding capacity, probably a result of increased organic matter content from increased litter inputs. Our findings that larger trees growing in elevated [CO2] used more water and that tree size, but not maximal water use, was negatively affected by elevated [O-3] suggest that the long-term cumulative effects on stand Structure may be more important than the expected primary stomatal Closure responses to elevated [CO2] and [O-3] in determining stand-level water use under possible future atmospheric conditions.
|
|
| 16. |
- Uddling, Johan, 1972, et al.
(författare)
-
Source-sink balance of wheat determines responsiveness of grain production to increased [CO2] and water supply
- 2008
-
Ingår i: Agriculture Ecosystems & Environment. - : Elsevier BV. - 0167-8809. ; 127:3-4, s. 215-222
-
Tidskriftsartikel (refereegranskat)abstract
- Manipulation of source (flag-leaf removal) and sink (ear trimming) was conducted in a factorial CO2-irrigation field chamber experiment with spring wheat (Triticum aestivum L.) in south-west Sweden to test the hypothesis that responsiveness of grain production and biomass partitioning to CO2 concentration ([CO2]) and water supply is dependent on the source-sink balance of the plant. Negative effects of doubled [CO2] on both individual grain mass (IGM) and harvest index (HI) were strongly related to decreasing relative sink strength (i.e. increasing source:sink ratio), probably as a result of feedbacks from sink limitation on source activity under elevated [CO2] being relatively more important as relative sink strength decreases. Substantial down-regulation of photosynthetic capacity in elevated [CO2], resulted in lack of significant stimulation of grain yield (GY) of unmanipulated shoots growing under elevated [CO2]. GY was even reduced by elevated [CO2] in sink-manipulated shoots, implying that high source:sink ratio may result in a down-regulation of photosynthetic capacity that more than offsets the direct stimulating effect of elevated [CO2]. High irrigation positively affected IGM and HI in source-manipulated shoots only, probably as a result of the timing of irrigation treatment effects on soil moisture during, but not before, grain filling. Irrigation thus probably affected source activity during grain filling rather than potential sink capacity determined before and around anthesis, an effect that should be more pronounced for shoots with low source:sink ratio. We conclude that effects of [CO2] and irrigation on grain production and biomass partitioning of wheat are strongly modified by source-sink balance of the plant, and that sink limitation is a major constraint on CO2-induced GY enhancement of spring wheat under Scandinavian climatic conditions. These findings may explain earlier observations of decreased CO2 responsiveness of GY in modern wheat cultivars, with lower whole-plant sink strength before and around anthesis compared to old cultivars, and call into question current attempts of molecular plant breeding to maximise photosynthetic activity before and around anthesis in order to enhance GY in a world with rising atmospheric [CO2]. (C) 2008 Elsevier B.V. All rights reserved.
|
|
| 17. |
- Uddling, Johan, 1972, et al.
(författare)
-
Stomatal O3 uptake of forest trees under rising atmospheric CO2 and tropospheric O3
- 2008
-
Ingår i: Schaub M, Kaennel Dobbertin M, Steiner D (Eds) 2008. Air Pollution and Climate Change at Contrasting Altitude and Latitude. 23rd IUFRO Conference for Specialists in Air Pollution and Climate Change Effects on Forest Ecosystems. Murten, Switzerland, 7-12 Sept 2008. Abstracts. Birmensdorf, Swiss Federal Research Institute WSL. 162 pp..
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The rise in concentrations of atmospheric CO2 ([CO2]) and tropospheric O3 ([O3]) observed in recent decades and predicted for coming decades may portend large alterations in plant canopy function. Stomata respond to increased intercellular [CO2] by partially closing, and stomatal conductance (gs) was consistently reduced by both elevated [CO2] and elevated [O3] in shorter-term experiments with plants grown in controlled environments or field chambers. Based on these findings, combined stomatal-photosynthesis models, predicting decreased gs in response to increased [CO2], have been incorporated into the third generation of land surface models that are used in general circulation models. Such models have been employed to predict improved ecosystem hydrology, increased continental runoff and reduced stomatal uptake of O3 under rising atmospheric [CO2]. The Aspen FACE experiment in Rhinelander, Wisconsin USA, offers a unique opportunity to study fully acclimated long-term tree responses to elevated [CO2] and [O3], alone and in combination, under ecologically realistic conditions. Contrary to expectations, stand-level tree water-use of pure aspen and mixed aspen-birch communities was increased under elevated [CO2] and not significantly affected by [O3] treatment after canopy closure (Uddling et al. 2008). Here, we report on treatment effects on gs estimated by three independent methods: leaf-level gas exchange, sap flux in combination with within canopy scaling, and leaf tissue stable carbon isotope composition in combination with photosynthesis modelling. Regardless of method used, gs was always lowest in the control treatment (ambient [CO2] and ambient [O3]), but the only statistically significant treatment effect was that elevated [CO2] increased carbon isotope-derived gs. These results contrast with expectations as well as reports of reduced gs in an early phase of the experiment (Noormets et al. 2001), and suggest that long-term cumulative effects on stand structure and hydraulic efficiency may be more important than expected primary stomatal closure responses to elevated [CO2] and [O3] for determining gs under possible future atmospheric conditions. Results from FACE studies with trees are reviewed with respect to gs and tree water use and it is concluded that expectations and predictions of reduced O3 sensitivity of forests under rising [CO2] are unduly optimistic.
|
|
