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1.
1. Increasing carbon dioxide concentration (E: 680 μl CO2 litre–1 vs ambient, A: 355 μl CO2 litre–1) around late-successional Alpine sedge communities of the Swiss Central Alps (2450 m) for four growing seasons (1992–1995) had no detectable effect on symbiotic N2 fixation in Trifolium alpinum —the sole N2-fixing plant species in these communities (74 ± 30 mg N m–2 year–1, A and E plots pooled).
2. This result is based on data collected in the fourth growing season showing that elevated CO2 had no effect on Trifolium above-ground biomass (4·4 ± 1·7 g m–2, A and E plots pooled, n = 24) or N content per unit land area (124 ± 51 mg N m–2, A and E pooled), or on the percentage of N Trifolium derived from the atmosphere through symbiotic N2 fixation (%Ndfa: 61·0 ± 4·1 across A and E plots) estimated using the 15N dilution method.
3. Thus, it appears that N inputs to this ecosystem via symbiotic N2 fixation will not be dramatically affected in the foreseeable future even as atmospheric CO2 continues to rise.  相似文献   

2.
A direct comparison of treatment uniformity and CO2 use of pure and prediluted free-air CO2 enrichment (FACE) systems was conducted in a forest ecosystem. A vertical release pure CO2 fumigation system was superimposed on an existing prediluted CO2 fumigation system and operated on alternate days. The FACE system using prediluted CO2 fumigation technology exhibited less temporal and spatial variability than the pure CO2 fumigation system. The pure CO2 fumigation system tended to over-fumigate the upwind portions of the plot and used 25% more CO2 than the prediluted CO2 fumigation system. The increased CO2 use by the pure CO2 system was exacerbated at low wind speeds. It is not clear if this phenomenon will also be observed in plots with smaller diameters and low-stature vegetation.  相似文献   

3.
1. There have been no reports of the long-term responses of the desiccation-tolerant (DT) plants to elevated CO2. Xerophyta scabrida is a DT woody shrub, which loses chlorophylls and thylakoids during desiccation: a so-called poikilochlorophyllous desiccation-tolerant species (PDT). When the leaves of X. scabria are allowed to desiccate, the species shows many of the normal features of (P)DT plants.
2. However, the duration of photosynthesis in X. scabria is prolonged by 300% when the measurements are made at 700 as opposed to 350p.p.m. CO2. The implication is that the carboxylating enzymes must still have been active at this time to enable appreciable photosynthetic activity. This response could have far-reaching implications for the success of such species in a future climate.
3. Lichens and mosses, representing the homoiochlorophyllous DTs (HDT), retain their chlorophyll content and photosynthetic apparatus during desiccation. We show the desiccation responses of two common HDT species ( Cladonia convoluta and Tortula ruralis ) to elevated CO2 for comparison. Both HDT species showed increased net CO2 uptake in the material grown at high CO2 by more than 30% in moss and by more than 50% in lichen. It is concluded that desiccation-tolerant plants will be among the main beneficiaries of a high CO2 future.  相似文献   

4.
Carbon and water fluxes in a calcareous grassland under elevated CO2   总被引:3,自引:2,他引:1  
1. As part of a long-term study of the effects of elevated CO2 on biodiversity and ecosystem function in a calcareous grassland, we measured ecosystem carbon dioxide and water-vapour fluxes over 24-h periods during the 1994 and 1995 growing seasons. Data were used to derive CO2 and H2O gas-exchange response functions to quantum flux density (QFD).
2. The relative increase in net ecosystem CO2 flux (NEC) owing to CO2 enrichment increased as QFD rose. Daytime NEC at high QFD under elevated CO2 increased by 25% to 60%, with the greatest increases in the spring and after mowing in June when above-ground biomass was lowest. There was much less stimulation of NEC in early June and again in October when the canopy was fully developed. Night-time NEC was not significantly altered under elevated CO2.
3. Short-term reversal of CO2 concentrations between treatments after two seasons of CO2 exposure provided evidence for a 50% downward adjustment of NEC expressed per unit above-ground plant dry weight. However, when expressed on a land area basis, this difference disappeared because of a c. 20% increase in above-ground biomass under elevated CO2.
4. Ecosystem evapotranspiration (ET) was not significantly altered by elevated CO2 when averaged over all measurement dates and positions. However, ET was reduced 3–18% at high QFD in plots at the top of the slope at our study site. In summary, CO2 enrichment resulted in a large stimulation of ecosystem CO2 capture, especially during periods of a large demand of carbon in relationship to its supply, and resulted in a relatively small and variable effect on ecosystem water consumption.  相似文献   

5.
Aims:  The objective of this study is to develop kinetic models based on batch experiments describing the growth, CO2 consumption, and H2 production of Anabaena variabilis ATCC 29413-UTM as functions of irradiance and CO2 concentration.
Methods and Results:  A parametric experimental study is performed for irradiances from 1120 to 16100 lux and for initial CO2 mole fractions from 0·03 to 0·20 in argon at pH 7·0 ± 0·4 with nitrate in the medium. Kinetic models are successfully developed based on the Monod model and on a novel scaling analysis employing the CO2 consumption half-time as the time scale.
Conclusions:  Monod models predict the growth, CO2 consumption and O2 production within 30%. Moreover, the CO2 consumption half-time is an appropriate time scale for analysing all experimental data. In addition, the optimum initial CO2 mole fraction is 0·05 for maximum growth and CO2 consumption rates. Finally, the saturation irradiance is determined to be 5170 lux for CO2 consumption and growth whereas, the maximum H2 production rate occurs around 10 000 lux.
Significance and Impact of the Study:  The study presents kinetic models predicting the growth, CO2 consumption and H2 production of A. variabilis . The experimental and scaling analysis methods can be generalized to other micro-organisms.  相似文献   

6.
To study the influence of elevated CO2 and nitrogen (N) fertilization on wood properties and energy, Populus × euramericana trees were exposed to ambient CO2 (about 370 μmol mol−1 CO2) or elevated CO2 (about 550 μmol mol−1 CO2) using Free Air CO2 Enrichment (FACE) technology in combination with two N levels. Elevated CO2 was maintained for 5 years. After three growing seasons, the plantation was coppiced, one half of each experimental plot was fertilized and secondary sprouts were harvested after two growing seasons. Fourier transform infrared (FT-IR) spectra of wood revealed significant effects of both elevated CO2 and N fertilization on wood chemistry, in particular, significant increases in lignin and decreases in N content. These results were corroborated by chemical analysis. Neither elevated CO2 nor N fertilization affected the calorific value of wood, which was 19.3 MJ kg−1. N fertilization enhanced the energy production per land area by 16–69% because of higher aboveground woody biomass production than on nonfertilized land. Estimates indicate that high yielding poplar short rotation cultivation may significantly contribute as an alternative feedstock for energy production.  相似文献   

7.
Inorganic carbon limitation of photosynthesis in lake phytoplankton   总被引:5,自引:0,他引:5  
1. Inorganic carbon availability influences species composition of phytoplankton in acidic and highly alkaline lakes, whereas the overall influence on community photosynthesis and growth is subject to debate.
2. The influence of total dissolved inorganic carbon (DIC) and free CO2 on community photosynthesis was studied in six Danish lakes during the summer of 1995. The lakes were selected to ensure a wide range of chlorophyll a concentrations (1–120 μg l–1), pH (5.6–9.6) and DIC concentration (0.02–2.5 m m ). Photosynthesis experiments were performed using the 14C technique in CO2-manipulated water samples, either by changing the pH or by adding/removing CO2.
3. Lake waters were naturally CO2 supersaturated during most of the experimental period and inorganic carbon limitation of photosynthetic rates did not occur under ambient conditions. However, photosynthesis by phytoplankton in lakes with low and intermediate DIC concentrations was seriously restricted when CO2 concentrations declined. Similarly, photosynthesis was limited by low CO2 concentrations during phytoplankton blooms in the hardwater alkaline lakes.  相似文献   

8.
Free Air CO2 Enrichment (FACE) systems are used to fumigate unconfined field plots with CO2. As these installations can treat a sufficiently large area without interfering with natural climatic conditions, they are considered important tools for global change research worldwide. However, there is general consensus that elevated capital costs of existing FACE systems as well as high running costs may prevent their application at the required level of scale. A new and small FACE system that was designed to reduce both capital costs and CO2 use, is described in this paper. Due to its intermediate size (8 m diameter) between the smaller Mini-FACE systems that were developed in Italy and the larger systems designed by the Brookhaven National Laboratory in the USA, it was named Mid-FACE. The Mid-FACE was at first developed as a prototype and then used to enrich field grown potato crops in a CO2 concentration gradient experimental design. Technical details of a Mid-FACE prototype and of the operational set-up are presented in this paper together with performance data in terms of temporal and spatial control of CO2 concentrations within the experimental area.  相似文献   

9.
The effects of elevated atmospheric CO2 (560 p.p.m.) and subsequent plant responses on the soil microbial community composition associated with trembling aspen was assessed through the classification of 6996 complete ribosomal DNA sequences amplified from the Rhinelander WI free-air CO2 and O3 enrichment (FACE) experiments microbial community metagenome. This in-depth comparative analysis provides an unprecedented, detailed and deep branching profile of population changes incurred as a response to this environmental perturbation. Total bacterial and eukaryotic abundance does not change; however, an increase in heterotrophic decomposers and ectomycorrhizal fungi is observed. Nitrate reducers of the domain bacteria and archaea, of the phylum Crenarchaea , potentially implicated in ammonium oxidation, significantly decreased with elevated CO2. These changes in soil biota are evidence for altered interactions between trembling aspen and the microorganisms in its surrounding soil, and support the theory that greater plant detritus production under elevated CO2 significantly alters soil microbial community composition.  相似文献   

10.
In situ responses to elevated CO2 in tropical forest understorey plants   总被引:3,自引:1,他引:2  
1. Plants growing in deep shade and high temperature, such as in the understorey of humid tropical forests, have been predicted to be particularly sensitive to rising atmospheric CO2. We tested this hypothesis in five species whose microhabitat quantum flux density (QFD) was documented as a covariable. After 7 (tree seedlings of Tachigalia versicolor and Beilschmiedia pendula ) and 18 months (shrubs Piper cordulatum and Psychotria limonensis, and grass Pharus latifolius ) of elevated CO2 treatment ( c. 700 μl litre–1) under mean QFD of less than 11 μmol m–2 s–1, all species produced more biomass (25–76%) under elevated CO2.
2. Total plant biomass tended to increase with microhabitat QFD (daytime means varying from 5 to 11μmol m–2 s–1) but the relative stimulation by elevated CO2 was higher at low QFD except in Pharus .
3. Non-structural carbohydrate concentrations in leaves increased significantly in Pharus (+ 27%) and Tachigalia (+ 40%).
4. The data support the hypothesis that tropical plants growing near the photosynthetic light compensation point are responsive to elevated CO2. An improved plant carbon balance in deep shade is likely to influence understorey plant recruitment and competition as atmospheric CO2 continues to rise.  相似文献   

11.
1 In a glasshouse experiment we studied the effect of raised CO2 concentration (720 p.p.m.) on CH4 emission at natural boreal peat temperatures using intact cores of boreal peat with living vascular plants and Sphagnum mosses. After the end of the growing season half of the cores were kept unnaturally warm (17–20 °C). The potential for CH4 production and oxidation was measured at the end of the emission experiment.
2 The vascular cores ('Sedge') consisted of a moss layer with sedges, and the moss cores (' Sphagnum ') of Sphagnum mosses (some sedge seedlings were removed by cutting). Methane efflux was 6–12 times higher from the Sedge cores than from the Sphagnum cores. The release of CH 4 from Sedge cores increased with increasing temperature of the peat and decreased with decreasing temperature. Methane efflux from Sphagnum cores was quite stable independent of the peat temperatures.
3 In both Sedge and Sphagnum samples, CO2 treatment doubled the potential CH4 production but had no effect on the potential CH4 oxidation. A raised concentration of CO2 increased CH4 efflux weakly and only at the highest peat temperatures (17–20 °C).
4 The results suggest that in cool regions, such as boreal wetlands, temperature would restrict decomposition of the extra substrates probably derived from enhanced primary production of mire vegetation under raised CO2 concentrations, and would thus retard any consequent increase in CH4 emission.  相似文献   

12.
1. The affinity of photosynthesis for CO2 is calculated here as the initial slope of net-photosynthetic rate against concentration of CO2. The affinity for CO2 for pairs of freshwater macrophytes with similar leaf morphology but able or unable to use HCO3 as a carbon source was compared.
2. Species restricted to CO2 had a higher affinity for CO2 than species that were also able to use HCO3 when rates were expressed on the basis of area, dry mass and content of chlorophyll a .
3. Published values for the affinity for CO2 and the concentration of CO2 which half-saturated rate of photosynthesis were compiled and compared. Despite a large range of values, affinity for CO2 was greater for species restricted to CO2 than for those also able to use HCO3 and statistically different when the slope was expressed on the basis of dry mass and chlorophyll a content.
4. The difference in affinity is consistent with predicted benefits of a high permeability to CO2 for species relying on passive diffusion of CO2 and a lower permeability for species able to use HCO3 in order to reduce efflux of CO2 from a high internal concentration generated by active transport.
5. The implications of the different affinities are discussed in terms of species distribution.  相似文献   

13.
1. Experimental grassland communities (turves) were exposed to elevated (60 Pa) and ambient (35 Pa) CO2 partial pressures (pCO2) in a Free-Air Carbon Dioxide Enrichment (FACE) experiment between 30 March 1995 and 4 July 1996. The vegetation was cut once during the experiment prior to the final harvest (harvest 2).
2. No significant treatment effects on total plant biomass at the whole turf level were detected, although biomass was typically about 25% higher under fumigation in year 1 and about 15% higher in year 2.
3. Biomass for two of the six sown species was significantly higher at harvest 2 than at harvest 1. There were no significant differences between individual species' biomass under the two CO2 treatments at either harvest 1 or 2 or in terms of overall cumulative biomass. However, in four of the five sown species in both years biomass tended to be higher in the fumigated than in the control rings ( Cerastium holosteiodes, Phleum pratense, Plantago lanceolata and Poa trivialis ). In contrast, Lolium perenne showed increased biomass under the control treatment relative to the fumigated treatment in both years. Owing to the high variance both within and between rings for each of the two treatments the statistical power of most, but not all, of the analyses carried out was poor.
4. The relative proportions of each species in the turves under fumigated and control treatments was broadly similar after the first summer, with differences in the second year being mainly owing to the negative response of L. perenne to CO2 fumigation.  相似文献   

14.
Abstract. A controlled-environment chamber constructed from a standard chest freezer was used to grow and measure the CO2 exchange of small stands of lettuce ( Lactuca sativa L. ev. Ambassador). The chamber, with horizontal air flow, provided good control of air temperature ( c. 6 to 16°C), irradiance (0–300 μmol PAR m 2S1 and CO2 (350–1000 μmol mol−1). The photosynthetic response to changes in these variables was measured using an inexpensive CO2 dosing system which recorded the input rate required to maintain a constant concentration of CO2 (to ± 2.5%). Characteristis of the growth environment and the changes in response to temperature and irradiance are described.  相似文献   

15.
Results from free-air CO2 enrichment (FACE) experiments in temperate climates indicate that the response of forest net primary productivity (NPP) to elevated CO2 might be highly conserved across a broad range of productivities. In this study, we show that the LPJ-GUESS dynamic vegetation model reproduces the magnitude of the NPP enhancement at temperate forest FACE experiments. A global application of the model suggests that the response found in the experiments might also be representative of the average response of forests globally. However, the predicted NPP enhancement in tropical forests is more than twice as high as in boreal forests, suggesting that currently available FACE results are not applicable to these ecosystems. The modeled geographic pattern is to a large extent driven by the temperature dependence of the relative affinities of the primary assimilation enzyme (Rubisco) for CO2 and O2.  相似文献   

16.
Abstract: In the present study, we used the eddy covariance method to measure CO2 exchange between the atmosphere and an alpine shrubland meadow ecosystem (37°36'N, 101°18'E; 3 250 m a.s.l.) on the Qinghai-Tibetan Plateau, China, during the growing season in 2003, from 20 April to 30 September. This meadow is dominated by formations of Potentilla fruticosa L. The soil is Mol-Cryic Cambisols. During the study period, the meadow was not grazed. The maximum rates of CO2 uptake and release derived from the diurnal course of CO2 flux were -9.38 and 5.02 μmol·m-2·s-1, respectively. The largest daily CO2 uptake was 1.7 g C·m-2·d-1 on 14 July, which is less than half that of an alpine Kobresia meadow ecosystem at similar latitudes. Daily CO2 uptake during the measurement period indicated that the alpine shrubland meadow ecosystem may behave as a sink of atmospheric CO2 during the growing season. The daytime CO2 uptake was correlated exponentially or linearly with the daily photo synthetic photon flux density each month. The daytime average water use efficiency of the ecosystem was 6.47 mg CO2/g H2O. The efficiency of the ecosystem increased with a decrease in vapor pressure deficit.
(Managing editor: Ya-Qin HAN)  相似文献   

17.
1. Ten herbaceous species were grown over a 4-month period under ambient (360 μmol mol–1) and elevated (610 μmol mol–1) atmospheric CO2 conditions. Plants were inoculated with the arbuscular mycorrhizal (AM) fungus Glomus mosseae and given a phosphorus (P) supply which was not immediately available to the plants.
2. Multiple harvests were taken in order to determine whether the effect of elevated CO2 on mycorrhizal colonization and phosphorus inflow was independent of its effect on plant growth.
3. All species grew faster under elevated CO2 and carbon partitioning was altered, generally in favour of the shoots. All species responded similarly to elevated CO2.
4. Elevated CO2 did not affect the percentage of root length colonized by AM fungi, but the total amount of colonized root length was increased, because the plants were bigger.
5. Elevated CO2 increased total P content, but had little or no effect on P concentration. At a given age, P inflow was stimulated by elevated CO2, but when root length was taken into account the CO2 effect disappeared.
6. In these host species there is no evidence for a direct effect of elevated CO2 on mycorrhizal functioning, because both internal mycorrhizal colonization and P inflow are unaffected.
7. Future research should concentrate on the potential for carbon flow to the soil via the external mycelial network.  相似文献   

18.
Yield of wheat across a subambient carbon dioxide gradient   总被引:1,自引:0,他引:1  
Yields and yield components of two cultivars of day-neutral spring wheat ( Triticum aestivum L.) were assessed along a gradient of daytime carbon dioxide (CO2) concentrations from about 200 to near 350 μmol CO2 (mol air)–1 in a 38 m-long controlled environment chamber. The range in CO2 concentration studied approximates that of Earth's atmosphere since the last ice age. This 75% rise in CO2 concentration increased grain yields more than 200% under well-watered conditions and by 80–150% when wheat was grown without additions of water during the last half of the 100-day growing season. The 27% increase in CO2 from the pre-industrial level of 150 years ago (275 μmol mol–1) to near the current concentration (350 μmol mol–1) increased grain yields of 'Yaqui 54' and 'Seri M82' spring wheats by 55% and 53%, respectively, under well-watered conditions. Yield increased because of greater numbers of grains per spike, rather than heavier grains or numbers of spikes per plant. Water use increased little with CO2 concentration, resulting in improved water use efficiency as CO2 rose. Data suggest that rising CO2 concentration contributed to the substantial increase in average wheat yields in the U.S. during recent decades.  相似文献   

19.
The influence of the root holoparasitic angiosperm Orobanche minor Sm. on the biomass, photosynthesis, carbohydrate and nitrogen content of Trifolium repens L. was determined for plants grown at two CO2 concentrations (350 and 550 μmol mol−1). Infected plants accumulated less biomass than their uninfected counterparts, although early in the association there was a transient stimulation of growth. Infection also influenced biomass allocation both between tissues (infected plants had lower root:shoot ratios) and within tissues:infected roots were considerably thicker before the point of parasite attachment and thinner below. Higher concentrations of starch were also found in roots above the point of attachment, particularly for plants grown in elevated CO2. Elevated CO2 stimulated the growth of T. repens only during the early stages of development. There was a significant interaction between infection and CO2 on growth, with infected plants showing a greater response, such that elevated CO2 partly alleviated the effects of the parasite on host growth. Elevated CO2 did not affect total O. minor biomass per host, the number of individual parasites supported by each host, or their time of attachment to the host root system. Photosynthesis was stimulated by elevated CO2 but was unaffected by O. minor . There was no evidence of down-regulation of photosynthesis in T. repens grown at elevated CO2 in either infected or uninfected plants. The data are discussed with regard to the influence of elevated CO2 on other parasitic angiosperm-host associations and factors which control plant responses to elevated CO2.  相似文献   

20.
1. We tested the hypothesis that the net partitioning of dry mass and dry mass:area relationships is unaltered when plants are grown at elevated atmospheric CO2 concentrations.
2. The total dry mass of Dactylis glomerata, Bellis perennis and Trifolium repens was higher for plants in 700 compared to 350 μmol CO2 mol–1 when grown hydroponically in controlled-environment cabinets.
3. Shoot:root ratios were higher and leaf area ratios and specific leaf areas lower in all species grown at elevated CO2. Leaf mass ratio was higher in plants of B. perennis and D. glomerata grown at elevated CO2.
4. Whilst these data suggest that CO2 alters the net partitioning of dry mass and dry mass:leaf area relationships, allometric comparisons of the components of dry mass and leaf area suggest at most a small effect of CO2. CO2 changed only two of a total of 12 allometric coefficients we calculated for the three species: ν relating shoot to root dry mass was higher in D. glomerata , whilst ν relating leaf area to total dry mass was lower in T. repens .
5. CO2 alone has very little effect on partitioning when the size of the plant is taken into account.  相似文献   

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