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1.
To identify the controls on dissolved organic carbon (DOC) production, we incubated soils from 18 sites, a mixture of 52 forest
floor and peats and 41 upper mineral soil samples, at three temperatures (3, 10, and 22°C) for over a year and measured DOC
concentration in the leachate and carbon dioxide (CO2) production from the samples. Concentrations of DOC in the leachate were in the range encountered in field soils (<2 to >50 mg l−1). There was a decline in DOC production during the incubation, with initial rates averaging 0.03–0.06 mg DOC g−1 soil C day−1, falling to averages of 0.01 mg g−1 soil C day−1; the rate of decline was not strongly related to temperature. Cumulative DOC production rates over the 395 days ranged from
less than 0.01 to 0.12 mg g−1 soil C day−1 (0.5–47.6 mg g−1 soil C), with an average of 0.021 mg g−1 soil C day−1 (8.2 mg g−1 soil C). DOC production rate was weakly related to temperature, equivalent to Q10 values of 0.9 to 1.2 for mineral samples and 1.2 to 1.9 for organic samples. Rates of DOC production in the organic samples
were correlated with cellulose (positively) and lignin (negatively) proportion in the organic matter, whereas in the mineral
samples C and nitrogen (N) provided positive correlations. The partitioning of C released into CO2–C and DOC showed a quotient (CO2–C:DOC) that varied widely among the samples, from 1 to 146. The regression coefficient of CO2–C:DOC production (log10 transformed) ranged from 0.3 to 0.7, all significantly less than 1. At high rates of DOC production, a smaller proportion
of CO2 is produced. The CO2–C:DOC quotient was dependent on incubation temperature: in the organic soil samples, the CO2–C:DOC quotient rose from an average of 6 at 3 to 16 at 22°C and in the mineral samples the rise was from 7 to 27. The CO2–C:DOC quotient was related to soil pH in the organic samples and C and N forms in the mineral samples. 相似文献
2.
Sue C. Ebanks Michael J. O’Donnell Martin Grosell 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2010,180(7):953-965
Embryos of the freshwater common pond snail Lymnaea stagnalis develop to hatch within 10 days under control conditions (22°C, Miami-Dade tap water) and this development is impaired by
removal of ambient calcium. In contrast, embryos did not exhibit dependence upon an ambient HCO3
−/CO3
2− source, developing and hatching in HCO3
−/CO3
2−-free water at rates comparable to controls. Post-metamorphic, shell-laying embryos exhibited a significant saturation-type
calcium uptake as a function of increasing ambient calcium concentration. However, changes in ambient bicarbonate concentration
did not influence calcium or apparent titratable alkalinity uptake. There was a distinct shift from no significant flux in
pre-metamorphic embryos to net uptake of calcium in post-metamorphic stages as indicated by an increased uptake from the micro-environment
surrounding the egg mass and increased net uptake in 24-h, whole egg mass flux measurements. Furthermore, HCO3
−/CO3
2− acquisition as measured by titratable alkalinity flux is at least partially attributable to an endogenous carbonate source
that is associated with acid extrusion. Thus, calcium requirements for embryonic shell formation are met via uptake but HCO3
−/CO3
2−, which is also necessary for shell formation is acquired in part from endogenous sources with no detectable correlation to
ambient HCO3
−/CO3
2− availability. 相似文献
3.
Carbon acquisition by diatoms 总被引:2,自引:0,他引:2
Diatoms are responsible for up to 40% of primary productivity in the ocean, and complete genome sequences are available for
two species. However, there are very significant gaps in our understanding of how diatoms take up and assimilate inorganic
C. Diatom plastids originate from secondary endosymbiosis with a red alga and their Form ID Rubisco (ribulose-1,5-bisphosphate
carboxylase-oxygenase) from horizontal gene transfer, which means that embryophyte paradigms can only give general guidance
as to their C acquisition mechanisms. Although diatom Rubiscos have relatively high CO2 affinity and CO2/O2 selectivity, the low diffusion coefficient for CO2 in water has the potential to restrict the rate of photosynthesis. Diatoms growing in their natural aquatic habitats operate
inorganic C concentrating mechanisms (CCMs), which provide a steady-state CO2 concentration around Rubisco higher than that in the medium. How these CCMs work is still a matter of debate. However, it
is known that both CO2 and HCO3− are taken up, and an obvious but as yet unproven possibility is that active transport of these species across the plasmalemma
and/or the four-membrane plastid envelope is the basis of the CCM. In one marine diatom there is evidence of C4-like biochemistry which could act as, or be part of, a CCM. Alternative mechanisms which have not been eliminated include
the production of CO2 from HCO3− at low pH maintained by a H+ pump, in a compartment close to that containing Rubisco. 相似文献
4.
Response of soil respiration to simulated N deposition in a disturbed and a rehabilitated tropical forest in southern China 总被引:3,自引:1,他引:2
Jiangming Mo Wei Zhang Weixing Zhu Yunting Fang Dejun Li Ping Zhao 《Plant and Soil》2007,296(1-2):125-135
Responses of soil respiration (CO2 emission) to simulated N deposition were studied in a disturbed (reforested forest with previous understory and litter harvesting)
and a rehabilitated (reforested forest with no understory and litter harvesting) tropical forest in southern China from October
2005 to September 2006. The objectives of the study were to test the following hypotheses: (1) soil respiration is higher
in rehabilitated forest than in disturbed forest; (2) soil respiration in both rehabilitated and disturbed tropical forests
is stimulated by N additions; and (3) soil respiration is more sensitive to N addition in disturbed forest than in rehabilitated
forest due to relatively low soil nutrient status in the former, resulting from different previous human disturbance. Static
chamber and gas chromatography techniques were employed to quantify the soil respiration, following different N treatments
(Control, no N addition; Low-N, 5 g N m−2 year−1; Medium-N, 10 g N m−2 year−1), which had been applied continuously for 26 months before the respiration measurement. Results showed that soil respiration
exhibited a strong seasonal pattern, with the highest rates observed in the hot and wet growing season (April–September) and
the lowest rates in winter (December–February) in both rehabilitated and disturbed forests. Soil respiration rates exhibited
significant positive exponential relationship with soil temperature and significant positive linear relationship with soil
moisture. Soil respiration was also significantly higher in the rehabilitated forest than in the disturbed forest. Annual
mean soil respiration rate in the rehabilitated forest was 20% lower in low-N plots (71 ± 4 mg CO2-C m−2 h−1) and 10% lower in medium-N plots (80 ± 4 mg CO2-C m−2 h−1) than in the control plots (89 ± 5 mg CO2-C m−2 h−1), and the differences between the control and low-N or medium-N treatments were statistically significant. In disturbed forest,
annual mean soil respiration rate was 5% lower in low-N plots (63 ± 3 mg CO2-C m−2 h−1) and 8% lower in medium-N plots (61 ± 3 mg CO2-C m−2 h−1) than in the control plots (66 ± 4 mg CO2-C m−2 h−1), but the differences among treatments were not significant. The depressed effects of experimental N deposition occurred
mostly in the hot and wet growing season. Our results suggest that response of soil respiration to elevated N deposition in
the reforested tropical forests may vary depending on the status of human disturbance.
Responsible Editor: Hans Lambers. 相似文献
5.
Carbon Dioxide Variation in a Hardwood Forest Stream: An Integrative Measure of Whole Catchment Soil Respiration 总被引:8,自引:3,他引:5
The concentration of CO2 in stream water is a product of not only instream metabolism but also upland, riparian, and groundwater processes and as
such can provide an integrative measure of whole catchment soil respiration. Using a 5-year dataset of pH, alkalinity, Ca2+, and Mg2+ in surface water of the West Fork of Walker Branch in eastern Tennessee in conjunction with a hydrological flowpath chemistry
model, we investigated how CO2 concentrations and respiration rates in stream, bedrock, and soil environments vary seasonally and interannually. Dissolved
inorganic carbon concentration was highest in summer and autumn (P < 0.05) although the proportion as free CO2 (pCO2) did not vary seasonally (P > 0.05). Over the 5 years, pCO2 was always supersaturated with respect to the atmosphere ranging from 374 to 3626 ppmv (1.0- to 10.1-fold greater than atmospheric
equilibrium), and CO2 evasion from the stream to the atmosphere ranged from 146 to 353 mmol m−2 d−1. Whereas pCO2 in surface water exhibited little intra-annual or interannual variation, distinct seasonal patterns in soil and bedrock pCO2 were revealed by the catchment CO2 model. Seasonally, soil pCO2 increased from a winter low of 8167 ppmv to a summer high of 27,068 ppmv. Driven by the seasonal variation in gas levels,
evasion of CO2 from soils to the atmosphere ranged from 83 mmol m−2 d−1 in winter to 287 mmol m−2 d−1 in summer. The seasonal variation in soil CO2 tracked soil temperature (r
2= 0.46, P < 0.001) and model-derived estimates of CO2 evasion rate from soils agreed with previously reported fluxes measured using chambers (Pearson correlation coefficient =
0.62, P < 0.05) supporting the model assumptions. Although rates of CO2 evasion were similar between the stream and soils, the overall rate of evasion from the channel was only 0.4% of the 70,752
mol/d that evaded from soils due to the vastly different areas of the two subsystems. Our model provides a means to assess
whole catchment CO2 dynamics from easily collected and measured stream-water samples and an approach to study catchment scale variation in soil
ecosystem respiration.
Received 24 July 1997; accepted 14 November 1997. 相似文献
6.
The effects of Aporrectodea caliginosa earthworms on both carbon dioxide (CO2) accumulation in and emissions from soil, as well as the simultaneous impact of earthworms on soil microbiological properties
were investigated in a microcosm experiment carried out over 5.5 months. Concentration of CO2 in soil air was greater at a depth of 15 cm when compared with a depth of 5 cm, but varied during the season both in control
and earthworm-inhabited chambers. Peaks of CO2 concentrations at both depths occurred in both treatments during August, approximately 80 days after the experiment started.
Generally, the presence of earthworms increased the CO2 concentration at 15-cm depth. Larger CO2 emissions were consistently recorded in conjunction with higher amounts of CO2 in soil air when chambers were inhabited by earthworms. The total CO2 emissions during the experimental period covering 161 days were estimated at 118 g CO2-C m−2 and 99 g CO2-C m−2 from chambers with and without earthworms respectively. Moreover, the presence of earthworms increased microbial biomass
in the centre and at the bottom of chambers, and enhanced both dehydrogenase activity and nitrifying enzyme activity in the
soils. We suggest that the effect of earthworms on both the enhanced soil accumulation of CO2 as well as emissions of CO2 was mostly indirect, due to the impacts of earthworms on soil microbial community. 相似文献
7.
The impact of seawater saturation state and bicarbonate ion concentration on calcification by new recruits of two Atlantic corals 总被引:1,自引:0,他引:1
Rising concentrations of atmospheric CO2 are changing the carbonate chemistry of the oceans, a process known as ocean acidification (OA). Absorption of this CO2 by the surface oceans is increasing the amount of total dissolved inorganic carbon (DIC) and bicarbonate ion (HCO3
−) available for marine calcification yet is simultaneously lowering the seawater pH and carbonate ion concentration ([CO3
2−]), and thus the saturation state of seawater with respect to aragonite (Ωar). We investigated the relative importance of [HCO3
−] versus [CO3
2−] for early calcification by new recruits (primary polyps settled from zooxanthellate larvae) of two tropical coral species,
Favia fragum and Porites astreoides. The polyps were reared over a range of Ωar values, which were manipulated by both acid-addition at constant pCO2 (decreased total [HCO3
−] and [CO3
2−]) and by pCO2 elevation at constant alkalinity (increased [HCO3
−], decreased [CO3
2−]). Calcification after 2 weeks was quantified by weighing the complete skeleton (corallite) accreted by each polyp over the
course of the experiment. Both species exhibited the same negative response to decreasing [CO3
2−] whether Ωar was lowered by acid-addition or by pCO2 elevation—calcification did not follow total DIC or [HCO3
−]. Nevertheless, the calcification response to decreasing [CO3
2−] was nonlinear. A statistically significant decrease in calcification was only detected between Ωar = <2.5 and Ωar = 1.1–1.5, where calcification of new recruits was reduced by 22–37% per 1.0 decrease in Ωar. Our results differ from many previous studies that report a linear coral calcification response to OA, and from those showing
that calcification increases with increasing [HCO3
−]. Clearly, the coral calcification response to OA is variable and complex. A deeper understanding of the biomineralization
mechanisms and environmental conditions underlying these variable responses is needed to support informed predictions about
future OA impacts on corals and coral reefs. 相似文献
8.
Lubomír Adamec 《Ecological Research》2009,24(2):327-333
Aquatic carnivorous plants usually grow in shallow dystrophic waters poor in inorganic N and P. Utricularia australis was chosen as a model plant for its prolific distribution and great ecological plasticity. The photosynthetic CO2 compensation point and factors associated with investment in carnivory and capture of prey were measured in 17 U. australis micropopulations in Třeboň basin, Czech Republic, together with water chemistry factors at these sites differing greatly
in their trophic level, water hardness, and prey availability. Apical shoot growth rate was estimated at some oligotrophic
sites. The micropopulations differed greatly in the proportion of traps with animal prey (2.7–70%, mean 26%), trap proportion
to total biomass (1.4–42%, mean 26%), mean trap biomass (0.7–63 μg trap−1, mean 19 μg), and maximum trap size (1–3 mm, mean 2.0 mm). CO2 compensation points ranged from 0.7 to 6.1 μM (mean 2.6 μM). A weak HCO3
− use (compensation point 0.51 mM) was found in plants growing in alkaline water. Trap biomass proportion did not correlate
significantly with prey capture and CO2 compensation points with ambient [CO2]. A very rapid apical growth (2.5–4.2 new nodes day−1) occurred in sand pits. Thus, HCO3
− use in U. australis can be induced by growing at very high pH. CO2 compensation points resembled those known in other aquatic non-carnivorous plants. They did not reflect carnivory. In spite
of very rapid apical shoot growth, the relative growth rate of U. australis can be zero in oligotrophic habitats without prey. 相似文献
9.
Effect of Increased Carbon Dioxide and Temperature on Runoff Chemistry at a Forested Catchment in Southern Norway (CLIMEX Project) 总被引:3,自引:1,他引:2
Richard F. Wright 《Ecosystems》1998,1(2):216-225
CLIMEX (Climate Change Experiment) is an integrated, whole-ecosystem research project that focuses on the response of forest
ecosystems at the catchment scale to increased CO2 and temperature. KIM catchment (860 m2) is completely enclosed by a transparent greenhouse, receives deacidifed “clean” rain, and has elevated CO2 (560 ppmv) and elevated air temperature (3°–5°C above ambient). The uppermost 20% of the catchment is partitioned off, is
not subject to changed CO2 or temperature, and serves as an untreated control. Fluxes of nitrate and ammonium in runoff from KIM catchment increased
from 2 mmol m−
2 y−
1 each in the 3 years before treatment to 6 and 3 mmol m−
2 y−
1, respectively, in the 3 years after treatment (May 1994–April 1997), despite a 15 mmol m−
2 y−
1 decrease in N dry deposition due to the sealing of the walls to the enclosure. N flux in runoff from three reference catchments
and the control section did not change. The net loss of inorganic N was thus about 20 mmol m−
2 treated soil y−
1. There were no changes in organic N or total organic carbon in runoff. The ecosystem switched from a net sink to a net source
of inorganic nitrogen (N). The increased loss of N may be due to accelerated decomposition of soil organic matter induced
by higher temperature. Due to many decades of N deposition from long-range transported pollutants, the ecosystem prior to
treatment was N saturated. If global change induces persistent losses of inorganic N on a regional scale, the result may be
a significant increase in nitrate concentrations in fresh waters and N loading to coastal marine ecosystems. In regions with
acid sensitive waters, such as southern Norway, the increased nitrate release caused by global change may offset improvements
achieved by reduced sulfur and N deposition.
Received 15 October 1997; accepted 18 November 1997. 相似文献
10.
We used sugar maple litter double-labeled with 13C and 15N to quantify fluxes of carbon (C) and nitrogen (N) between litter and soil in a northern hardwood forest and the retention
of litter C and N in soil. Two cohorts of litter were compared, one in which the label was preferentially incorporated into
non-structural tissue and the other structural tissue. Loss of 13C from this litter generally followed dry mass and total C loss whereas loss of 15N (20–30% in 1 year) was accompanied by large increases of total N content of this decaying litter (26–32%). Enrichment of
13C and 15N was detected in soil down to 10–15 cm depth. After 6 months of decay (November–May) 36–43% of the 13C released from the litter was recovered in the soil, with no differences between the structural and non-structural labeled
litter. By October the percentage recovery of litter 13C in soil was much lower (16%). The C released from litter and remaining in soil organic matter (SOM) after 1 year represented
over 30 g C m−2 y−1 of SOM accumulation. Recovery of litter 15N in soil was much higher than for C (over 90%) and in May 15N was mostly in organic horizons whereas by October it was mostly in 0–10 cm mineral soil. A small proportion of this N was
recovered as inorganic N (2–6%). Recovery of 15N in microbial biomass was higher in May (13–15%) than in October (about 5%). The C:N ratio of the SOM and microbial biomass
derived from the labeled litter was much higher for the structural than the non-structural litter and for the forest floor
than mineral SOM, illustrating the interactive role of substrates and microbial activity in regulating the C:N stoichiometry
of forest SOM formation. These results for a forest ecosystem long exposed to chronically high atmospheric N deposition (ca.
10 kg N ha−1 y−1) suggest possible mechanisms of N retention in soil: increased organic N leaching from fresh litter and reduced fungal transport
of N from soil to decaying litter may promote N stabilization in mineral SOM even at a relatively low C:N ratio. 相似文献
11.
Steve F. Perry Marvin H. Braun Janet Genz Branka Vulesevic Josi Taylor Martin Grosell Kathleen M. Gilmour 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2010,180(8):1213-1225
The plainfin midshipman (Porichthys notatus) possesses an aglomerular kidney and like other marine teleosts, secretes base into the intestine to aid water absorption.
Each of these features could potentially influence acid–base regulation during respiratory acidosis either by facilitating
or constraining HCO3
− accumulation, respectively. Thus, in the present study, we evaluated the capacity of P. notatus to regulate blood acid–base status during exposure to increasing levels of hypercapnia (nominally 1–5% CO2). Fish exhibited a well-developed ability to increase plasma HCO3
− levels with values of 39.8 ± 2.8 mmol l−1 being achieved at the most severe stage of hypercapnic exposure (arterial blood PCO2 = 21.9 ± 1.7 mmHg). Consequently, blood pH, while lowered by 0.15 units (pH = 7.63 ± 0.06) during the final step of hypercapnia,
was regulated far above values predicted by chemical buffering (predicted pH = 7.0). The accumulation of plasma HCO3
− during hypercapnia was associated with marked increases in branchial net acid excretion (J
NETH+) owing exclusively to increases in the titratable alkalinity component; total ammonia excretion was actually reduced during
hypercapnia. The increase in J
NETH+ was accompanied by increases in branchial carbonic anhydrase (CA) enzymatic activity (2.8×) and CA protein levels (1.6×);
branchial Na+/K+-ATPase activity was unaffected. Rectal fluids sampled from control fish contained on average HCO3
− concentrations of 92.2 ± 4.8 mmol l−1. At the highest level of hypercapnia, rectal fluid HCO3
− levels were increased significantly to 141.8 ± 7.4 mmol l−1 but returned to control levels during post-hypercapnia recovery (96.0 ± 13.2 mmol l−1). Thus, the impressive accumulation of plasma HCO3
− to compensate for hypercapnic acidosis occurred against a backdrop of increasing intestinal HCO3
− excretion. Based on in vitro measurements of intestinal base secretion in Ussing chambers, it would appear that P. notatus did not respond by minimizing base loss during hypercapnia; the increases in base flux across the intestinal epithelium in
response to alterations in serosal HCO3
− concentration were similar in preparations obtained from control or hypercapnic fish. Fish returned to normocapnia developed
profound metabolic alkalosis owing to unusually slow clearance of the accumulated plasma HCO3
−. The apparent inability of P. notatus to effectively excrete HCO3
− following hypercapnia may reflect its aglomerular (i.e., non-filtering) kidney coupled with the normally low rates of urine
production in marine teleosts. 相似文献
12.
Highly productive papyrus (Cyperus papyrus L.) wetlands dominate many permanently flooded areas of tropical East Africa; however, the cycling of carbon and water within
these ecosystems is poorly understood. The objective of this study was to utilise Eddy Covariance (EC) techniques to measure
the fluxes of carbon dioxide and water vapour between papyrus vegetation and the atmosphere in a wetland located near Jinja,
Uganda on the Northern shore of Lake Victoria. Peak, midday rates of photosynthetic CO2 net assimilation were approximately 40 μmol CO2 m−2 s−1, while night time losses through respiration ranged between 10 and 20 μmol CO2 m−2 s−1. Numerical integration of the flux data suggests that papyrus wetlands have the potential to sequester approximately 0.48 kg C m−2 y−1. The average daily water vapour flux from the papyrus vegetation through canopy evapotranspiration was approximately 4.75 kg
H2O m−2 d−1, which is approximately 25% higher than water loss through evaporation from open water. 相似文献
13.
Late-successional forests in the upper Great Lakes region are susceptible to nitrogen (N) saturation and subsequent nitrate
(NO3−) leaching loss. Endemic wind disturbances (i.e., treefall gaps) alter tree uptake and soil N dynamics; and, gaps are particular
susceptible to NO3− leaching loss. Inorganic N was measured throughout two snow-free periods in throughfall, forest floor leachates, and mineral
soil leachates in gaps (300–2,000 m2, 6–9 years old), gap-edges, and closed forest plots in late-successional northern hardwood, hemlock, and northern hardwood–hemlock
stands. Differences in forest water inorganic N among gaps, edges, and closed forest plots were consistent across these cover
types: NO3− inputs in throughfall were significantly greater in undisturbed forest plots compared with gaps and edges; forest floor leachate
NO3− was significantly greater in gaps compared to edges and closed forest plots; and soil leachate NO3− was significantly greater in gaps compared to the closed forest. Significant differences in forest water ammonium and pH
were not detected. Compared to suspected N-saturated forests with high soil NO3− leaching, undisturbed forest plots in these late-successional forests are not losing NO3− (net annual gain of 2.8 kg ha−1) and are likely not N-saturated. Net annual NO3− losses were observed in gaps (1.3 kg ha−1) and gap-edges (0.2 kg ha−1), but we suspect these N leaching losses are a result of decreased plant uptake and increased soil N mineralization associated
with disturbance, and not N-saturation. 相似文献
14.
Philip A. Fay Alexia M. Kelley Andrew C. Procter Dafeng Hui Virginia L. Jin Robert B. Jackson Hyrum B. Johnson H. Wayne Polley 《Ecosystems》2009,12(5):699-714
Field studies of atmospheric CO2 effects on ecosystems usually include few levels of CO2 and a single soil type, making it difficult to ascertain the shape of responses to increasing CO2 or to generalize across soil types. The Lysimeter CO2 Gradient (LYCOG) chambers were constructed to maintain a linear gradient of atmospheric CO2 (~250 to 500 μl l−1) on grassland vegetation established on intact soil monoliths from three soil series. The chambers maintained a linear daytime
CO2 gradient from 263 μl l−1 at the subambient end of the gradient to 502 μl l−1 at the superambient end, as well as a linear nighttime CO2 gradient. Temperature variation within the chambers affected aboveground biomass and evapotranspiration, but the effects
of temperature were small compared to the expected effects of CO2. Aboveground biomass on Austin soils was 40% less than on Bastrop and Houston soils. Biomass differences between soils resulted
from variation in biomass of Sorghastrum nutans, Bouteloua curtipendula, Schizachyrium scoparium (C4 grasses), and Solidago canadensis (C3 forb), suggesting the CO2 sensitivity of these species may differ among soils. Evapotranspiration did not differ among the soils, but the CO2 sensitivity of leaf-level photosynthesis and water use efficiency in S. canadensis was greater on Houston and Bastrop than on Austin soils, whereas the CO2 sensitivity of soil CO2 efflux was greater on Bastrop soils than on Austin or Houston soils. The effects of soil type on CO2 sensitivity may be smaller for some processes that are tightly coupled to microclimate. LYCOG is useful for discerning the
effects of soil type on the CO2 sensitivity of ecosystem function in grasslands.
Author Contributions: PF conceived study, analyzed data, and wrote the paper. AK, AP analyzed data. DH, VJ, RJ, HJ, and WP
conceived study, and conducted research. 相似文献
15.
N2O, CH4 and CO2 emissions from seasonal tropical rainforests and a rubber plantation in Southwest China 总被引:2,自引:1,他引:1
Christian Werner Xunhua Zheng Janwei Tang Baohua Xie Chunyan Liu Ralf Kiese Klaus Butterbach-Bahl 《Plant and Soil》2006,289(1-2):335-353
The main focus of this study was to evaluate the effects of soil moisture and temperature on temporal variation of N2O, CO2 and CH4 soil-atmosphere exchange at a primary seasonal tropical rainforest (PF) site in Southwest China and to compare these fluxes with fluxes from a secondary forest (SF) and a rubber plantation (RP) site. Agroforestry systems, such as rubber plantations, are increasingly replacing primary and secondary forest systems in tropical Southwest China and thus effect the N2O emission in these regions on a landscape level. The mean N2O emission at site PF was 6.0 ± 0.1 SE μg N m−2 h−1. Fluxes of N2O increased from <5 μg N m−2 h−1 during dry season conditions to up to 24.5 μg N m−2 h−1 with re-wetting of the soil by the onset of first rainfall events. Comparable fluxes of N2O were measured in the SF and RP sites, where mean N2O emissions were 7.3 ± 0.7 SE μg N m−2 h−1 and 4.1 ± 0.5 SE μg N m−2 h−1, respectively. The dependency of N2O fluxes on soil moisture levels was demonstrated in a watering experiment, however, artificial rainfall only influenced the timing of N2O emission peaks, not the total amount of N2O emitted. For all sites, significant positive correlations existed between N2O emissions and both soil moisture and soil temperature. Mean CH4 uptake rates were highest at the PF site (−29.5 ± 0.3 SE μg C m−2 h−1), slightly lower at the SF site (−25.6 ± 1.3 SE μg C m−2 h−1) and lowest for the RP site (−5.7 ± 0.5 SE μg C m−2 h−1). At all sites, CH4 uptake rates were negatively correlated with soil moisture, which was also reflected in the lower uptake rates measured in the watering experiment. In contrast to N2O emissions, CH4 uptake did not significantly correlate with soil temperature at the SF and RP sites, and only weakly correlated at the PF site. Over the 2 month measurement period, CO2 emissions at the PF site increased significantly from 50 mg C m−2 h−1 up to 100 mg C m−2 h−1 (mean value 68.8 ± 0.8 SE mg C m−2 h−1), whereas CO2 emissions at the SF and RP site where quite stable and varied only slightly around mean values of 38.0 ± 1.8 SE mg C m−2 h−1 (SF) and 34.9 ± 1.1 SE mg C m−2 h−1 (RP). A dependency of soil CO2 emissions on changes in soil water content could be demonstrated for all sites, thus, the watering experiment revealed significantly higher CO2 emissions as compared to control chambers. Correlation of CO2 emissions with soil temperature was significant at the PF site, but weak at the SF and not evident at the RP site. Even though we demonstrated that N and C trace gas fluxes significantly varied on subdaily and daily scales, weekly measurements would be sufficient if only the sink/ source strength of non-managed tropical forest sites needs to be identified. 相似文献
16.
The effects of elevated [CO2] (700 μl l−1 [CO2]) and temperature increase (+3 °C) on carbon accumulation in a grassland soil were studied at two N-fertiliser supplies (160
and 530 kgN ha−1 year−1) in a long-term experiment (2.5 years) on well established ryegrass swards (Lolium perenne L.,) supplied with the same amounts
of irrigation water. For all experimental treatments, the C:N ratio of the top soil organic matter fractions increased with
their particle size. Elevated CO2 concentration increased the C:N ratios of the below-ground phytomass and of the macro-organic matter. A supplemental fertiliser
N or a 3 °C increase in elevated [CO2] reduced it. At the last sampling date, elevated [CO2] did not affect the C:N ratio of the soil organic matter fractions, but increased significantly the accumulation of roots
and of macro-organic matter above 200 μm (MOM). An increased N-fertiliser supply stimulated the accumulation of the non harvested
plant phytomass and of the OM between 2 and 50 μm, without positive effect on the macro-organic matter >200 μm. Elevated [CO22] increased C accumulation in the OM fractions above 50 μm by +2.1 tC ha−1, on average, whereas increasing the fertiliser N supply led to an average supplemental accumulation of +0.8 tC ha−1. There was no significant effect of a 3 °C temperature increase under elevated [CO2] on C accumulation in the OM fractions above 50 μm.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
17.
Soil carbon storage, litterfall and CO2 efflux in fertilized and unfertilized larch (Larix leptolepis) plantations 总被引:1,自引:0,他引:1
Choonsig Kim 《Ecological Research》2008,23(4):757-763
This study evaluated the effects of forest fertilization on the forest carbon (C) dynamics in a 36-year-old larch (Larix leptolepis) plantation in Korea. Above- and below-ground C storage, litterfall, root decomposition and soil CO2 efflux rates after fertilization were measured for 2 years. Fertilizers were applied to the forest floor at rates of 112 kg
N ha−1 year−1, 75 kg P ha−1 year−1 and 37 kg K ha−1 year−1 for 2 years (May 2002, 2003). There was no significant difference in the above-ground C storage between fertilized (41.20 Mg C
ha−1) and unfertilized (42.25 Mg C ha−1) plots, and the C increment was similar between the fertilized (1.65 Mg C ha−1 year−1) and unfertilized (1.52 Mg C ha−1 year−1) plots. There was no significant difference in the soil C storage between the fertilized and unfertilized plots at each soil
depth (0–15, 15–30 and 30–50 cm). The organic C inputs due to litterfall ranged from 1.57 Mg C ha−1 year−1 for fertilized to 1.68 Mg C ha−1 year−1 for unfertilized plots. There was no significant difference in the needle litter decomposition rates between the fertilized
and unfertilized plots, while the decomposition of roots with 1–2 mm diameters increased significantly with the fertilization
relative to the unfertilized plots. The mean annual soil CO2 efflux rates for the 2 years were similar between the fertilized (0.38 g CO2 m−2 h−1) and unfertilized (0.40 g CO2 m−2 h−1) plots, which corresponded with the similar fluctuation in the organic carbon (litterfall, needle and root decomposition)
and soil environmental parameters (soil temperature and soil water content). These results indicate that little effect on
the C dynamics of the larch plantation could be attributed to the 2-year short-term fertilization trials and/or the soil fertility
in the mature coniferous plantation used in this study. 相似文献
18.
Mizue Ohashi Tomo’omi Kumagai Tomonori Kume Koichiro Gyokusen Taku M. Saitoh Masakazu Suzuki 《Biogeochemistry》2008,90(3):275-289
Although soil carbon dioxide (CO2) efflux from tropical forests may play an important role in global carbon (C) balance, our knowledge of the fluctuations
and factors controlling soil CO2 efflux in the Asian tropics is still poor. This study characterizes the temporal and spatial variability in soil CO2 efflux in relation to temperature/moisture content and estimates annual efflux from the forest floor in an aseasonal intact
tropical rainforest in Sarawak, Malaysia. Soil CO2 efflux varied widely in space; the range of variation averaged 17.4 μmol m−2 s−1 in total. While most CO2 flux rates were under 10 μmol m−2 s−1, exceptionally high fluxes were observed sporadically at several sampling points. Semivariogram analysis revealed little
spatial dependence in soil CO2 efflux. Temperature explained nearly half of the spatial heterogeneity, but the effect varied with time. Seasonal variation
in CO2 efflux had no fixed pattern, but was significantly correlated with soil moisture content. The correlation coefficient with
soil moisture content (SMC) at 30 and 60 cm depth was higher than at 10 cm depths. The annual soil CO2 efflux, estimated from the relationship between CO2 efflux and SMC at 30 cm depth, was 165 mol m−2 year−1 (1,986 g C m−2 year−1). As this area is known to suffer severe drought every 4–5 years caused by the El Nino-Southern Oscillation, the results
suggest that an unpredictable dry period might affect soil CO2 efflux, leading an annual variation in soil C balance. 相似文献
19.
Inorganic Carbon Uptake during Photosynthesis : II. Uptake by Isolated Asparagus Mesophyll Cells during Isotopic Disequilibrium 总被引:3,自引:3,他引:0
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The species of inorganic carbon (CO2 or HCO3−) taken up a source of substrate for photosynthetic fixation by isolated Asparagus sprengeri mesophyll cells is investigated. Discrimination between CO2 or HCO3− transport, during steady state photosynthesis, is achieved by monitoring the changes (by 14C fixation) which occur in the specific activity of the intracellular pool of inorganic carbon when the inorganic carbon present in the suspending medium is in a state of isotopic disequilibrium. Quantitative comparisons between theoretical (CO2 or HCO3− transport) and experimental time-courses of 14C incorporation, over the pH range of 5.2 to 7.5, indicate that the specific activity of extracellular CO2, rather than HCO3−, is the appropriate predictor of the intracellular specific activity. It is concluded, therefore, that CO2 is the major source of exogenous inorganic carbon taken up by Asparagus cells. However, at high pH (8.5), a component of net DIC uptake may be attributable to HCO3− transport, as the incorporation of 14C during isotopic disequilibrium exceeds the maximum possible incorporation predicted on the basis of CO2 uptake alone. The contribution of HCO3− to net inorganic carbon uptake (pH 8.5) is variable, ranging from 5 to 16%, but is independent of the extracellular HCO3− concentration. The evidence for direct HCO3− transport is subject to alternative explanations and must, therefore, be regarded as equivocal. Nonlinear regression analysis of the rate of 14C incorporation as a function of time indicates the presence of a small extracellular resistance to the diffusion of CO2, which is partially alleviated by a high extracellular concentration of HCO3−. 相似文献
20.
Photosynthesis and Inorganic Carbon Usage by the Marine Cyanobacterium, Synechococcus sp 总被引:38,自引:25,他引:13
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The marine cyanobacterium, Synechococcus sp. Nägeli (strain RRIMP N1) changes its affinity for external inorganic carbon used in photosynthesis, depending on the concentration of CO2 provided during growth. The high affinity for CO2 + HCO3− of air-grown cells (K½ < 80 nanomoles [pH 8.2]) would seem to be the result of the presence of an inducible mechanism which concentrates inorganic carbon (and thus CO2) within the cells. Silicone-oil centrifugation experiments indicate that the inorganic carbon concentration inside suitably induced cells may be in excess of 1,000-fold greater than that in the surrounding medium, and that this accumulation is dependent upon light energy. The quantum requirements for O2 evolution appear to be some 2-fold greater for low CO2-grown cells, compared with high CO2-grown cells. This presumably is due to the diversion of greater amounts of light energy into inorganic carbon transport in these cells.
A number of experimental approaches to the question of whether CO2 or HCO3− is primarily utilized by the inorganic carbon transport system in these cells show that in fact both species are capable of acting as substrate. CO2, however, is more readily taken up when provided at an equivalent concentration to HCO3−. This discovery suggests that the mechanistic basis for the inorganic carbon concentrating system may not be a simple HCO3− pump as has been suggested. It is clear, however, that during steady-state photosynthesis in seawater equilibrated with air, HCO3− uptake into the cell is the primary source of internal inorganic carbon.
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