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1.
Increased mercury in forest soils under elevated carbon dioxide 总被引:1,自引:0,他引:1
Fossil fuel combustion is the primary anthropogenic source of both CO2 and Hg to the atmosphere. On a global scale, most Hg that enters ecosystems is derived from atmospheric Hg that deposits
onto the land surface. Increasing concentrations of atmospheric CO2 may affect Hg deposition to terrestrial systems and storage in soils through CO2-mediated changes in plant and soil properties. We show, using free-air CO2 enrichment (FACE) experiments, that soil Hg concentrations are almost 30% greater under elevated atmospheric CO2 in two temperate forests. There were no direct CO2 effects, however, on litterfall, throughfall or stemflow Hg inputs. Soil Hg was positively correlated with percent soil organic
matter (SOM), suggesting that CO2-mediated changes in SOM have influenced soil Hg concentrations. Through its impacts on SOM, elevated atmospheric CO2 may increase the Hg storage capacity of soils and modulate the movement of Hg through the biosphere. Such effects of rising
CO2, ones that transcend the typically studied effects on C and nutrient cycling, are an important next phase for research on
global environmental change. 相似文献
2.
Hill PW Marshall C Williams GG Blum H Harmens H Jones DL Farrar JF 《The New phytologist》2007,173(4):766-777
Prediction of the impact of climate change requires the response of carbon (C) flow in plant-soil systems to increased CO(2) to be understood. A mechanism by which grassland C sequestration might be altered was investigated by pulse-labelling Lolium perenne swards, which had been subject to CO(2) enrichment and two levels of nitrogen (N) fertilization for 10 yr, with (14)CO(2). Over a 6-d period 40-80% of the (14)C pulse was exported from mature leaves, 1-2% remained in roots, 2-7% was lost as below-ground respiration, 0.1% was recovered in soil solution, and 0.2-1.5% in soil. Swards under elevated CO(2) with the lower N supply fixed more (14)C than swards grown in ambient CO(2), exported more fixed (14)C below ground and respired less than their high-N counterparts. Sward cutting reduced root (14)C, but plants in elevated CO(2) still retained 80% more (14)C below ground than those in ambient CO(2). The potential for below-ground C sequestration in grasslands is enhanced under elevated CO(2), but any increase is likely to be small and dependent upon grassland management. 相似文献
3.
Growth and maintenance components of leaf respiration of cotton grown in elevated carbon dioxide partial pressure 总被引:9,自引:4,他引:9
Elevated atmospheric carbon dioxide partial pressures have been shown to have variable direct and indirect effects on plant respiration rates. In this study, growth, leaf respiration, and leaf nitrogen and carbohydrate partitioning were measured in Gossypium hirsutum L. grown in 35 and 65 Pa CO2 for 30d. Growth and maintenance coefficients of leaf respiration were estimated using gas exchange techniques both at night and during the day. Elevated CO2 stimulated biomass production (107%) and net photo-synthetic rates (35–50%). Total day-time respiration (Rd) was not significantly affected by growth CO2 partial pressure. However, night respiration (Rn) of leaves grown in 65 Pa CO2 was significantly greater than that of plants grown in 35 Pa CO2. Correlation of Rd and Rn with leaf expansion rates indicated that plants in both CO2 treatments had equivalent growth respiration coefficients but maintenance respiration was significantly greater in elevated CO2. Increased maintenance coefficients in elevated CO2 appeared to be related to increased starch accumulation rather than to changes in leaf nitrogen. 相似文献
4.
The aspen free-air CO2 and O3 enrichment (FACTS II–FACE) study in Rhinelander, Wisconsin, USA, is designed to understand the mechanisms by which young northern deciduous forest ecosystems respond to elevated atmospheric carbon dioxide (CO2) and elevated tropospheric ozone (O3) in a replicated, factorial, field experiment. Soil respiration is the second largest flux of carbon (C) in these ecosystems, and the objective of this study was to understand how soil respiration responded to the experimental treatments as these fast-growing stands of pure aspen and birch + aspen approached maximum leaf area. Rates of soil respiration were typically lowest in the elevated O3 treatment. Elevated CO2 significantly stimulated soil respiration (8–26%) compared to the control treatment in both community types over all three growing seasons. In years 6–7 of the experiment, the greatest rates of soil respiration occurred in the interaction treatment (CO2 + O3), and rates of soil respiration were 15–25% greater in this treatment than in the elevated CO2 treatment, depending on year and community type. Two of the treatments, elevated CO2 and elevated CO2 + O3, were fumigated with 13C-depleted CO2, and in these two treatments we used standard isotope mixing models to understand the proportions of new and old C in soil respiration. During the peak of the growing season, C fixed since the initiation of the experiment in 1998 (new C) accounted for 60–80% of total soil respiration. The isotope measurements independently confirmed that more new C was respired from the interaction treatment compared to the elevated CO2 treatment. A period of low soil moisture late in the 2003 growing season resulted in soil respiration with an isotopic signature 4–6‰ enriched in 13C compared to sample dates when the percentage soil moisture was higher. In 2004, an extended period of low soil moisture during August and early September, punctuated by a significant rainfall event, resulted in soil respiration that was temporarily 4–6‰ more depleted in 13C. Up to 50% of the Earth’s forests will see elevated concentrations of both CO2 and O3 in the coming decades and these interacting atmospheric trace gases stimulated soil respiration in this study. 相似文献
5.
The experimental data presented here relate to the question of whether terrestrial ecosystems will sequester more C in their soils, litter and biomass as atmospheric CO2 concentrations rise. Similar to our previous study with relatively fertile growth conditions (Körner and Arnone 1992), we constructed four rather nutrient-limited model communities of moist tropical plant species in greenhouses (approximately 7 m2 each). Plant communities were composed of seven species (77 individuals per community) representing major taxonomic groups and various life forms found in the moist tropics. Two ecosystems were exposed to 340 l CO2 l–1 and two to 610 l l–1 for 530 days of humid tropical growth conditions. In order to permit precise determination of C deposition in the soil, plant communities were initially established in C-free unwashed quartz sand. Soils were then amended with known amounts of organic matter (containing C and nutrients). Mineral nutrients were also supplied over the course of the experiment as timed-release full-balance fertilizer pellets. Soils represented by far the largest repositories for fixed C in all ecosystems. Almost 5 times more C (ca. 80% of net C fixation) was sequestered in the soil than in the biomass, but this did not differ between CO2 treatments. In addition, at the whole-ecosystem level we found a remarkably small and statistically non-significant increase in C sequestration (+4%; the sum of C accretion in the soil, biomass, litter and necromass). Total community biomass more than quadrupled during the experiment, but at harvest was, on average, only 8% greater (i.e. 6% per year; n.s.) under elevated CO2, mainly due to increased root biomass (+15%, P=0.12). Time courses of leaf area index of all ecosystems suggested that canopy expansion was approaching steady state by the time systems were harvested. Net primary productivity (NPP) of all ecosystems-i.e. annual accumulation of biomass, necromass, and leaf litter (but not plant-derived soil organic matter)-averaged 815 and 910 g m–2 year–1 at ambient and elevated CO2, respectively. These NPPs are remarkably similar to those of many natural moist tropical forested ecosystems. At the same time net productivity of soil organic matter reached 7000 g dry matter equivalent per m2 and year (i.e. 3500 g C m–2 year–1). Very slight yet statistically significant CO2-induced shifts in the abundance of groups of species occurred by the end of the experiment, with one group of species (Elettaria cardamomum, Ficus benjamina, F. pumila, Epipremnum pinnatum) gaining slightly, and another group (Ctenanthe lubbersiana, Heliconia humilis, Cecropia peltata) losing. Our results show that: (1) enormous amounts of C can be deposited in the ground which are normally not accounted for in estimates of NPP and net ecosystem productivity; (2) any enhancement of C sequestration under elevated atmospheric CO2 may be substantially smaller than is believed will occur (yet still very important), especially under growth conditions which permit close to natural NPP; and (3) species dominance in plant communities is likely to change under elevated CO2, but that changes may occur rather slowly. 相似文献
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A. H. Fitter G. K. Self J. Wolfenden M. M. I. van Vuuren T. K. Brown L. Williamson J. D. Graves D. Robinson 《Plant and Soil》1995,187(2):299-306
An essential component of an understanding of carbon flux is the quantification of movement through the root carbon pool. Although estimates have been made using radiocarbon, the use of minirhizotrons provides a direct measurement of rates of root birth and death. We have measured root demographic parameters under a semi-natural grassland and for wheat. The grassland was studied along a natural altitudinal gradient in northern England, and similar turf from the site was grown in elevated CO2 in solardomes. Root biomass was enhanced under elevated CO2. Root birth and death rates were both increased to a similar extent in elevated CO2, so that the throughput of carbon was greater than in ambient CO2, but root half-lives were shorter under elevated CO2 only under a Juncus/Nardus sward on a peaty gley soil, and not under a Festuca turf on a brown earth soil. In a separate experiment, wheat also responded to elevated CO2 by increased root production, and there was a marked shift towards surface rooting: root development at a depth of 80–85 cm was both reduced and delayed. In conjunction with published results for trees, these data suggest that the impact of elevated CO2 will be system-dependent, affecting the spatio-temporal pattern of root growth in some ecosystems and the rate of turnover in others. Turrnover is also sensitive to temperature, soil fertility and other environmental variables, all of which are likely to change in tandem with atmospheric CO2 concentrations. Differences in turnover and time and location of rhizodeposition may have a large effect on rates of carbon cycling. 相似文献
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Fluxes of nitrous oxide, methane and carbon dioxide were measured from soils under ambient (350 µL L-1) and enhanced (600 µL L-1) carbon dioxide partial pressures (pCO2) at the Free Air Carbon Dioxide Enrichment (FACE) experiment, Eidgenössische Technische Hochschule (ETH), Eschikon, Switzerland in July 1995, using a GC housed in a mobile laboratory. Measurements were made in plots of Lolium perenne maintained under high N input. During the data collection period N fertiliser was applied at a rate of 14 g m-2 of N. Elevated pCO2 appeared to result in an increased (27%) output of N2O, thought to be the consequence of enhanced root-derived available soil C, acting as an energy source for denitrification. The climate, agricultural practices and soils at the FACE experiment combined to give rise to some of the largest N2O emissions recorded for any terrestrial ecosystem. The amount of CO2–C being lost from the control plot was higher (10%) than for the enhanced CO2 plot, and is the reverse of that predicted. The control plot oxidised consistently more CH4 than the enhanced plot, oxidising 25.5 ± 0.8 µg m-2 hr-1 of CH4 for the control plot, with an average of 8.5 ± 0.4 µg m-2 hr-1 of CH4 for the enhanced CO2 plot. This suggests that elevated pCO2 may lead to a feedback whereby less CH4 is removed from the atmosphere. Despite the limited nature of the current study (in time and space), the observations made here on the interactions of elevated pCO2 and soil trace gas release suggest that significant interactions are occurring. The feedbacks involved could have importance at the global scale. 相似文献
10.
Temperate grasslands contribute about 20% to the global C budget. Elevation of atmospheric CO2 concentration (pCO2) could lead to additional C sequestration into these ecosystems. Microbial‐derived C in the soil comprising about 1–5% of total soil organic carbon may be an important ‘pool’ for long‐term storage of C under future increased atmospheric CO2 concentrations. In our study, the impact of elevated pCO2 on bacterial‐ and fungal‐derived C in the soil of Lolium perenne pastures was investigated under free air carbon dioxide enrichment (FACE) conditions. For 7 years, L. perenne swards were exposed to ambient and elevated pCO2 (36 and 60 Pa pCO2, respectively). The additional CO2 in the FACE plots was depleted in 13C compared with ambient plots, so that ‘new’ (<7 years) C inputs in the form of microbial‐derived residues could be determined by means of stable C isotope analysis. Amino sugars in soil are reliable organic biomarkers for indicating the presence of microbial‐derived residues, with particular amino sugars indicative of either bacterial or fungal origin. It is assumed that amino sugars are stabilized to a significant extent in soil, and so may play an important role in long‐term C storage. In our study, we were also able to discriminate between ‘old’ (> 7 years) and ‘new’ microbial‐derived C using compound‐specific δ13C analysis of individual amino sugars. This new tool was very useful in investigating the potential for C storage in microbial‐derived residues and the turnover of this C in soil under increased atmospheric pCO2. The 13C signature of individual amino sugars varied between ?17.4‰ and ?39.6‰, and was up to 11.5% depleted in 13C in the FACE plots when compared with the bulk δ13C value of the native C3 L. perenne soil. New amino sugars in the bulk soil contributed up to 16% to the overall amino sugar pool after the first year and between 62% and 125% after 7 years of exposure to elevated pCO2. Amounts of new glucosamine increased by the greatest amount (16–125%) during the experiment, followed by mannosamine (?9% to 107%), muramic acid (?11% to 97%), and galactosamine (15–62%). Proportions of new amino sugars in particle size fractions varied between 38% for muramic acid in the clay fraction and 100% for glucosamine and galactosamine in the coarse sand fraction. Summarizing, during the 7‐year period, amino sugars constituted only between 0.9% and 1.6% of the total SOC content. Therefore, their absolute significance for long‐term C sequestration is limited. Additionally new amino sugars were only sequestered in the silt fraction upon elevated pCO2 exposure while amino sugar concentrations in the clay fraction decreased. Overall, amino sugar concentrations in bulk soil did not change significantly upon exposure to elevated pCO2. The calculated mean residence time of amino sugars was surprisingly low varying between 6 and 90 years in the bulk soil, and between 3 and 30 years in the particle size fractions, representing soil organic matter pools with different but relatively low turnover times. Therefore, compound‐specific δ13C analysis of individual amino sugars clearly revealed a high amino sugar turnover despite more or less constant amino sugar concentrations over a 7 years period of exposure to elevated pCO2. 相似文献
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Castor bean (Ricinus communis L.) plants were grown for 5–7 weeks in a controlled environment at 350 μl l−1 or 700 μl l−1 CO2. Carbon assimilation, assimilate deposition, dark respiration and assimilate mobilization were measured in leaves 2, 3 and
4 (counted from the base of the plant), and a balance sheet of carbon input and export was elaborated for both CO2 concentrations. Carbon dioxide assimilation was nearly constant over the illumination period, with only a slight depression
occurring at the end of the day in mature source leaves, not in young source leaves. Assimilation was ca. 40% higher at 700 μl l−1 than at 350 μl l−1 CO2. The source leaves increased steadily in weight per unit area during the first 3 weeks, more at 700 μl l−1 than at 350 μl l−1 CO2. On top of an irreversible weight increase, there was a large gain in dry weight during the day, which was reversed during
the night. This reversible weight gain was constant over the life time of the leaf and ca. 80% higher at 700 μl l−1 than at 350 μl l−1. Most of it was due to carbohydrates. The carbon content (as a percentage) was not altered by the CO2 treatment. Respiration was 25% higher in high-CO2 plants when based on leaf area, but the same when based on dry weight. The rate of carbon export via the phloem was the same
during the daytime in plants grown at 350 μl l−1 and 700 μl l−1 CO2. During the night the low-CO2 plants had only 50% of the daytime export rate, in contrast to the high-CO2 plants which maintained the high export rate. It was concluded that the phloem loading system is saturated during the daytime
in both CO2 regimes, whereas during the night the assimilate supply is reduced in plants in the normal CO2 concentration. Two-thirds of the carbon exported from the leaves was permanently incorporated as plant dry matter in the
residual plant parts. This “assimilation efficiency” was the same for both CO2 regimes. It is speculated that under 350 μl l−1 CO2 the growing Ricinus plant operates at sink limitation during the day and at source limitation during the night.
Received: 2 February 1999 / Accepted: 19 April 1999 相似文献
13.
HIROYUKI SHIMONO MASUMI OKADA MEGURU INOUE HIROFUMI NAKAMURA KAZUHIKO KOBAYASHI TOSHIHIRO HASEGAWA 《Plant, cell & environment》2010,33(3):322-331
Understanding of leaf stomatal responses to the atmospheric CO2 concentration, [CO2], is essential for accurate prediction of plant water use under future climates. However, limited information is available for the diurnal and seasonal changes in stomatal conductance (gs) under elevated [CO2]. We examined the factors responsible for variations in gs under elevated [CO2] with three rice cultivars grown in an open‐field environment under flooded conditions during two growing seasons (a total of 2140 individual measurements). Conductance of all cultivars was generally higher in the morning and around noon than in the afternoon, and elevated [CO2] decreased gs by up to 64% over the 2 years (significantly on 26 out of 38 measurement days), with a mean gs decrease of 23%. We plotted the gs variations against three parameters from the Ball‐Berry model and two revised versions of the model, and all parameters explained the gs variations well at each [CO2] in the morning and around noon (R2 > 0.68), but could not explain these variations in the afternoon (R2 < 0.33). The present results provide an important basis for modelling future water use in rice production. 相似文献
14.
Summary Seeds of Gliricidia sepium (Jacq.) Walp., a tree native to seasonal tropical forests of Central America, were inoculated with N-fixing Rhizobium bacteria and grown in growth chambers for 71 days to investigate interactive effects of atmospheric CO2 and plant N status on early seedling growth, nodulation, and N accretion. Seedlings were grown with CO2 partial pressures of 350 and 650 bar (current ambient and a predicted partial pressure of the mid-21st century) and with plus N or minus N nutrient solutions to control soil N status. Of particular interest was seedling response to CO2 when grown without available soil N, a condition in which seedlings initially experienced severe N deficiency because bacterial N-fixation was the sole source of N. Biomass of leaves, stems, and roots increased significantly with CO2 enrichment (by 32%, 15% and 26%, respectively) provided seedlings were supplied with N fertilizer. Leaf biomass of N-deficient seedlings was increased 50% by CO2 enrichment but there was little indication that photosynthate translocation from leaves to roots or that plant N (fixed by Rhizobium) was altered by elevated CO2. In seedlings supplied with soil N, elevated CO2 increased average nodule weight, total nodule weight per plant, and the amount of leaf nitrogen provided by N-fixation (as indicated by leaf 15N). While CO2 enrichment reduced the N concentration of some plant tissues, whole plant N accretion increased. Results support the contention that increasing atmospheric CO2 partial pressures will enhance productivity and N-fixing activity of N-fixing tree seedlings, but that the magnitude of early seedling response to CO2 will depend greatly on plant and soil nutrient status. 相似文献