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  • 1
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Water availability limits plant growth and production in almost all terrestrial ecosystems. However, biomes differ substantially in sensitivity of aboveground net primary production (ANPP) to between-year variation in precipitation. Average rain-use efficiency (RUE; ANPP/precipitation) also ...
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  • 2
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: Bryophytes blanket the floor of temperate rainforests in New Zealand and may influence a number of important ecosystem processes, including carbon cycling. Their contribution to forest floor carbon exchange was determined in a mature, undisturbed podocarp-broadleaved forest in New Zealand, dominated by 100–400-year-old rimu (Dacrydium cupressimum) trees. Eight species of mosses and 13 species of liverworts contributed to the 62% cover of the diverse forest floor community. The bryophyte community developed a relatively thin (depth 〈30 mm), but dense, canopy that experienced elevated CO2 partial pressures (median 46.6 Pa immediately below the bryophyte canopy) relative to the surrounding air (median 37.6 Pa at 100 mm above the canopy). Light-saturated rates of net CO2 exchange from 14 microcosms collected from the forest floor were highly variable; the maximum rate of net uptake (bryophyte photosynthesis – whole-plant respiration) per unit ground area at saturating irradiance was 1.9 μmol m−2 s−1 and in one microcosm, the net rate of CO2 exchange was negative (respiration). CO2 exchange for all microcosms was strongly dependent on water content. The average water content in the microcosms ranged from 1375% when fully saturated to 250% when air-dried. Reduction in water content across this range resulted in an average decrease of 85% in net CO2 uptake per unit ground area.The results from the microcosms were used in a model to estimate annual carbon exchange for the forest floor. This model incorporated hourly variability in average irradiance reaching the forest floor, water content of the bryophyte layer, and air and soil temperature. The annual net carbon uptake by forest floor bryophytes was 103 g m−2, compared to annual carbon efflux from the forest floor (bryophyte and soil respiration) of −1010 g m−2. To put this in perspective of the magnitude of the components of CO2 exchange for the forest floor, the bryophyte layer reclaimed an amount of CO2 equivalent to only about 10% of forest floor respiration (bryophyte plus soil) or ∼11% of soil respiration. The contribution of forest floor bryophytes to productivity in this temperate rainforest was much smaller than in boreal forests, possibly because of differences in species composition and environmental limitations to photosynthesis. Because of their close dependence on water table depth, the contribution of the bryophyte community to ecosystem CO2 exchange may be highly responsive to rapid changes in climate.
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  • 3
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: Measurements of photosynthesis and respiration were made on leaves in summer in a Quercus rubra L. canopy at approximately hourly intervals throughout 5 days and nights. Leaves were selected in the upper canopy in fully sunlit conditions (upper) and in the lower canopy (lower). In addition, leaves in the upper canopy were shaded (upper shaded) to decrease photosynthesis rates. The data were used to test the hypothesis that total night-time respiration is dependent on total photosynthesis during the previous day and that the response is mediated through changes in storage in carbohydrate pools. Measurements were made on clear sunny days with similar solar irradiance and air temperature, except for the last day when temperature, especially at night, was lower than that for the previous days. Maximum rates of photosynthesis in the upper leaves (18.7 μmol m−2 s−1) were approximately four times higher than those in the lower leaves (4.3 μmol m−2 s−1) and maximum photosynthesis rates in the upper shaded leaves (8.0 μmol m−2 s−1) were about half those in the upper leaves. There was a strong linear relationship between total night-time respiration and total photosynthesis during the previous day when rates of respiration were normalized to a fixed temperature of 20°C, removing the effects of temperature from this relationship. Measurements of specific leaf area, nitrogen and chlorophyll concentration and calculations of the maximum rate of carboxylation activity, Vcmax, were not significantly different between upper and upper shaded leaves 5 days after the shading treatment was started. There were small, but significant decreases in the rate of apparent maximum electron transport at saturating irradiance, Jmax (P〉0.05), and light use efficiency, ɛ (P〈0.05), for upper shaded leaves compared with those for upper leaves. This suggests that the duration of shading in the experiment was sufficient to initiate changes in the electron transport, but not the carboxylation processes of photosynthesis. Support for the hypothesis was provided from analysis of soluble sugar and starch concentrations in leaves. Respiration rates in the upper shaded leaves were lower than those expected from a relationship between respiration and soluble sugar concentration for fully exposed upper and lower leaves. However, there was no similar difference in starch concentrations. This suggests that shading for the duration of several days did not affect sugar concentrations but reduced starch concentrations in leaves, leading to lower rates of respiration at night. A model was used to quantify the significance of the findings on estimated canopy CO2 exchange for the full growing season. Introducing respiration as a function of total photosynthesis on the previous day resulted in a decrease in growing season night-time respiration by 23% compared with the value when respiration was held constant. This highlights the need for a process-based approach linking respiration to photosynthesis when modelling long-term carbon exchange in forest ecosystems.
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  • 4
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: Estimation of leaf photosynthetic rate (A) from leaf nitrogen content (N) is both conceptually and numerically important in models of plant, ecosystem, and biosphere responses to global change. The relationship between A and N has been studied extensively at ambient CO2 but much less at elevated CO2. This study was designed to (i) assess whether the A–N relationship was more similar for species within than between community and vegetation types, and (ii) examine how growth at elevated CO2 affects the A–N relationship. Data were obtained for 39 C3 species grown at ambient CO2 and 10 C3 species grown at ambient and elevated CO2. A regression model was applied to each species as well as to species pooled within different community and vegetation types. Cluster analysis of the regression coefficients indicated that species measured at ambient CO2 did not separate into distinct groups matching community or vegetation type. Instead, most community and vegetation types shared the same general parameter space for regression coefficients. Growth at elevated CO2 increased photosynthetic nitrogen use efficiency for pines and deciduous trees. When species were pooled by vegetation type, the A–N relationship for deciduous trees expressed on a leaf-mass basis was not altered by elevated CO2, while the intercept increased for pines. When regression coefficients were averaged to give mean responses for different vegetation types, elevated CO2 increased the intercept and the slope for deciduous trees but increased only the intercept for pines. There were no statistical differences between the pines and deciduous trees for the effect of CO2. Generalizations about the effect of elevated CO2 on the A–N relationship, and differences between pines and deciduous trees will be enhanced as more data become available.
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  • 5
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Global change biology 2 (1996), S. 0 
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: Trees growing in natural systems undergo seasonal changes in environmental factors that generate seasonal differences in net photosynthetic rates. To examine how seasonal changes in the environment affect the response of net photosynthetic rates to elevated CO2, we grew Pinus taeda L. seedlings for three growing seasons in open-top chambers continuously maintained at either ambient or ambient + 30 Pa CO2. Seedlings were grown in the ground, under natural conditions of light, temperature nd nutrient and water availability. Photosynthetic capacity was measured bimonthly using net photosynthetic rate vs. intercellular CO2 partial pressure (A-Ci) curves. Maximum Rubisco activity (Vcmax) and ribulose 1,5-bisphosphate regeneration capacity mediated by electron transport (Jmax) and phosphate regeneration (PiRC) were calculated from A-Ci curves using a biochemically based model. Rubisco activity, activation state and content, and leaf carbohydrate, chlorophyll and nitrogen concentrations were measured concurrently with photosynthesis measurements. This paper presents results from the second and third years of treatment.Mean leaf nitrogen concentrations ranged from 13.7 to 23.8 mg g−1, indicating that seedlings were not nitrogen deficient. Relative to ambient CO2 seedlings, elevated CO2 increased light-saturated net photosynthetic rates 60–110% during the summer, but 〈 30% during the winter. A relatively strong correlation between leaf temperature and the relative response of net photosynthetic rates to elevated CO2 suggests a strong effect of leaf temperature. During the third growing season, elevated CO2 reduced Rubisco activity 30% relative to ambient CO2 seedlings, nearly completely balancing Rubisco and RuBP-regeneration regulation of photosynthesis. However, reductions in Rubisco activity did not eliminate the seasonal pattern in the relative response of net photosynthetic rates to elevated CO2. These results indicate that seasonal differences in the relative response of net photosynthetic rates to elevated CO2 are likely to occur in natural systems.
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  • 6
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Ltd
    Global change biology 5 (1999), S. 0 
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: Interactive effects of CO2 and water availability have been predicted to alter the competitive relationships between C3 and C4 species over geological and contemporary time scales. We tested the effects of drought and CO2 partial pressures (pCO2) ranging from values of the Pleistocene to those predicted for the future on the physiology and growth of model C3 and C4 species. We grew co-occurring Abutilon theophrasti (C3) and Amaranthus retroflexus (C4) in monoculture at 18 (Pleistocene), 27 (preindustrial), 35 (current), and 70 (future) Pa CO2 under conditions of high light and nutrient availability. After 27 days of growth, water was withheld from randomly chosen plants of each species until visible wilting occurred. Under well-watered conditions, low pCO2 that occurred during the Pleistocene was highly limiting to C3 photosynthesis and growth, and C3 plants showed increased photosynthesis and growth with increasing pCO2 between the Pleistocene and future CO2 values. Well-watered C4 plants exhibited increased photosynthesis in response to increasing pCO2, but total mass and leaf area were unaffected by pCO2. In response to drought, C3 plants dropped a large amount of leaf area and maintained relatively high leaf water potential in remaining leaves, whereas C4 plants retained greater leaf area, but at a lower leaf water potential. Furthermore, drought-treated C3 plants grown at 18 Pa CO2 retained relatively greater leaf area than C3 plants grown at higher pCO2 and exhibited a delay in the reduction of stomatal conductance that may have occurred in response to severe carbon limitations. The C4 plants grown at 70 Pa CO2 showed lower relative reductions in net photosynthesis by the end of the drought compared to plants at lower pCO2, indicating that CO2 enrichment may alleviate drought effects in C4 plants. At the Pleistocene pCO2, C3 and C4 plants showed similar relative recovery from drought for leaf area and biomass production, whereas C4 plants showed higher recovery than C3 plants at current and elevated pCO2. Based on these model systems, we conclude that C3 species may not have been at a disadvantage relative to C4 species in response to low CO2 and severe drought during the Pleistocene. Furthermore, C4 species may have an advantage over C3 species in response to increasing atmospheric CO2 and more frequent and severe droughts.
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  • 7
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Onions were grown in environmentally controlled growth chambers for 85 days to investigate the effect of relatively low light intensity (350 µmol m−2 s−1) at two different total irradiance periods (12-h and 24-h photoperiods) on growth and photosynthetic performance. To test whether photosynthetic downregulation occurred due to carbohydrate feedback, we used onions that differed in bulb-forming capacity. Allium fistulosum (L. cv. ‘Kinka’) is a non-bulbing onion, with potentially limited carbohydrate storage capacity, while Allium cepa (L. cv. ‘Cal 296’) is a bulb-forming onion with possibly greater carbohydrate storage capacity. In A. fistulosum, photosynthetic downregulation was observed in 24-h plants as indicated by reductions in the light- and CO2-saturated photosynthetic capacity (Asat and Amax, respectively) by 26%, reduced maximum rate of carboxylation (Vcmax) by ribulose-1,5-biphosphate carboxylase/oxygenase (Rubisco) by 33%, reduced maximum rate of electron transport (Jmax) by 27% and 3-fold higher foliar sugar concentration. In contrast, the photosynthetic and biochemical capacity of A. cepa was not affected by exposure to 24-h photoperiod, presumably because substantial amounts of foliar carbohydrates were re-allocated to bulbs. In 24-h A. cepa, up to 84% of total plant mass was allocated to bulbs, while in 12-h plants, more mass was allocated to leaves. Production of greater leaf area in 12-h plants compared with 24-h plants compensated for lower total daily irradiance such that 12-h and 24-h plants of both species exhibited similar daily total leaf net CO2 exchange and plant mass at the end of the experiment.
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  • 8
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 101 (1997), S. 0 
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Radioisotopic and spectrophotometric assays for ribulose-1,5-bisphosphate carboxy-lase/oxygenase (Rubisco) initial and final activities and Rubisco content were compared in plants chronically exposed to ozone (O3) in a greenhouse and the field. In a greenhouse experiment, Glycine max was treated in exposure chambers with either charcoal-filtered air (CF air) or 100 nl O3 1−1 for 6 h daily during vegetative growth. Samples were collected after 7 days of exposure. In a field experiment, G. max was treated in open-top chambers with either CF air or nonfiltered air with O3 added at 1.5 times ambient O3 for 12 h daily. Average daily O3 concentrations were 21 and 92 nl T1 in the CF and O3 treatments, respectively. Samples were collected during vegetative and reproductive growth. Both assays generally yielded comparable Rubisco initial and final activities for greenhouse-grown plants regardless of the O3 treatment. However for field-grown plants, Rubisco initial and final activities averaged 15 and 23% lower when assayed by the spectrophotometric rather than the radioisotopic method. For Rubisco content estimated by the spectrophotometric method, lower r2 values for the regression of Rubisco activity vs concentratio of carboxyarabinitol-1,5-bisphos-phate were observed in O3 than in CF-treated plants. Both assays yielded comparable Rubisco contents in the greenhouse and in the field although the variation was larger with the spectrophotometric method in field-grown plants. Growth conditions, field vs greenhouse, were more critical to the spectrophotometric assay performance than the O3 treatments for measurement of Rubisco activity and content.
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  • 9
    ISSN: 1432-1939
    Keywords: Key wordsPinus taeda ; Stomatal conductance ; Elevated CO2 ; Whole-plant water use
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract While photosynthetic responses of C3 plants to elevated CO2 are fairly well documented, whole-plant water use under such conditions has been less intensively studied. Woody species, in particular, have exhibited highly variable stomatal responses to high CO2 as determined by leaf-level measurements. In this study, sap flux of Pinus taeda L. saplings was periodically monitored during the 4th year of an open-top chamber CO2 fumigation experiment. Water use per unit sapwood area did not differ between treatments. Furthermore, the ratio of leaf area to sapwood area did not change under high CO2, so that average canopy stomatal conductance (on a unit leaf area basis) remained unaffected by the CO2 treatment. Thus, the only effect of high CO2 was to increase whole-plant water use by increasing sapling leaf area and associated conducting sapwood area. Such an effect may not directly translate to forest-level responses as the feedback effects of higher leaf area at the canopy scale cannot be incorporated in a chamber study. These feedbacks include the potential effect of higher leaf area index on rainfall and light interception, both of which may reduce average stomatal conductance in intact forest canopies.
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  • 10
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