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1.
The fate of assimilated carbon during drought: impacts on respiration in Amazon rainforests 总被引:1,自引:0,他引:1
Meir P Metcalfe DB Costa AC Fisher RA 《Philosophical transactions of the Royal Society of London. Series B, Biological sciences》2008,363(1498):1849-1855
Interannual variations in CO2 exchange across Amazonia, as deduced from atmospheric inversions, correlate with El Niño occurrence. They are thought to result from changes in net ecosystem exchange and fire incidence that are both related to drought intensity. Alterations to net ecosystem production (NEP) are caused by changes in gross primary production (GPP) and ecosystem respiration (Reco). Here, we analyse observations of the components of Reco (leaves, live and dead woody tissue, and soil) to provide first estimates of changes in Reco during short-term (seasonal to interannual) moisture limitation. Although photosynthesis declines if moisture availability is limiting, leaf dark respiration is generally maintained, potentially acclimating upwards in the longer term. If leaf area is lost, then short-term canopy-scale respiratory effluxes from wood and leaves are likely to decline. Using a moderate short-term drying scenario where soil moisture limitation leads to a loss of 0.5 m2 m−2 yr−1 in leaf area index, we estimate a reduction in respiratory CO2 efflux from leaves and live woody tissue of 1.0 (±0.4) t C ha−1 yr−1. Necromass decomposition declines during drought, but mortality increases; the median mortality increase following a strong El Niño is 1.1% (n=46 tropical rainforest plots) and yields an estimated net short-term increase in necromass CO2 efflux of 0.13–0.18 t C ha−1 yr−1. Soil respiration is strongly sensitive to moisture limitation over the short term, but not to associated temperature increases. This effect is underestimated in many models but can lead to estimated reductions in CO2 efflux of 2.0 (±0.5) t C ha−1 yr−1. Thus, the majority of short-term respiratory responses to drought point to a decline in Reco, an outcome that contradicts recent regional-scale modelling of NEP. NEP varies with both GPP and Reco but robust moisture response functions are clearly needed to improve quantification of the role of Reco in influencing regional-scale CO2 emissions from Amazonia. 相似文献
2.
A new estimation of global soil greenhouse gas fluxes using a simple data-oriented model 总被引:2,自引:0,他引:2
S Hashimoto 《PloS one》2012,7(8):e41962
Soil greenhouse gas fluxes (particularly CO2, CH4, and N2O) play important roles in climate change. However, despite the importance of these soil greenhouse gases, the number of reports on global soil greenhouse gas fluxes is limited. Here, new estimates are presented for global soil CO2 emission (total soil respiration), CH4 uptake, and N2O emission fluxes, using a simple data-oriented model. The estimated global fluxes for CO2 emission, CH4 uptake, and N2O emission were 78 Pg C yr−1 (Monte Carlo 95% confidence interval, 64–95 Pg C yr−1), 18 Tg C yr−1 (11–23 Tg C yr−1), and 4.4 Tg N yr−1 (1.4–11.1 Tg N yr−1), respectively. Tropical regions were the largest contributor of all of the gases, particularly the CO2 and N2O fluxes. The soil CO2 and N2O fluxes had more pronounced seasonal patterns than the soil CH4 flux. The collected estimates, including both the previous and the present estimates, demonstrate that the means of the best estimates from each study were 79 Pg C yr−1 (291 Pg CO2 yr−1; coefficient of variation, CV = 13%, N = 6) for CO2, 21 Tg C yr−1 (29 Tg CH4 yr−1; CV = 24%, N = 24) for CH4, and 7.8 Tg N yr−1 (12.2 Tg N2O yr−1; CV = 38%, N = 11) for N2O. For N2O, the mean of the estimates that was calculated by excluding the earliest two estimates was 6.6 Tg N yr−1 (10.4 Tg N2O yr−1; CV = 22%, N = 9). The reported estimates vary and have large degrees of uncertainty but their overall magnitudes are in general agreement. To further minimize the uncertainty of soil greenhouse gas flux estimates, it is necessary to build global databases and identify key processes in describing global soil greenhouse gas fluxes. 相似文献
3.
The effect of light on the tricarboxylic Acid cycle in green leaves: I. Relative rates of the cycle in the dark and the light 总被引:3,自引:3,他引:0
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Excised green leaves of mung bean (Phaseolus aureus L. var. Mungo) were used to determine the effect of light on the rate of endogenous respiration via the tricarboxylic acid cycle. Illumination with white light at an intensity of 0.043 gram calories cm−2min−1 (approximately 8600 lux) of visible radiation (400-700 nm) gave a rate of apparent photosynthesis, measured as net CO2 uptake, of 21 mg CO2 dm−2hr−1 which was about 11-fold greater than the rate of dark respiration. The feeding of 14CO2 or 14C-labeled acids of the tricarboxylic acid cycle in the dark for 2 hours was established as a suitable method for labeling mitochondrial pools of cycle intermediates. 相似文献
4.
Precipitation and temperature are important drivers of soil respiration. The role of moisture and temperature are generally explored at seasonal or inter-annual timescales; however, significant variability also occurs on hourly to daily time-scales. We used small (1.54 m2), throughfall exclusion shelters to evaluate the role soil moisture and temperature as temporal controls on soil CO2 efflux from a humid tropical forest in Puerto Rico. We measured hourly soil CO2 efflux, temperature and moisture in control and exclusion plots (n = 6) for 6-months. The variance of each time series was analyzed using orthonormal wavelet transformation and Haar-wavelet coherence. We found strong negative coherence between soil moisture and soil respiration in control plots corresponding to a two-day periodicity. Across all plots, there was a significant parabolic relationship between soil moisture and soil CO2 efflux with peak soil respiration occurring at volumetric soil moisture of approximately 0.375 m3/m3. We additionally found a weak positive coherence between CO2 and temperature at longer time-scales and a significant positive relationship between soil temperature and CO2 efflux when the analysis was limited to the control plots. The coherence between CO2 and both temperature and soil moisture were reduced in exclusion plots. The reduced CO2 response to temperature in exclusion plots suggests that the positive effect of temperature on CO2 is constrained by soil moisture availability. 相似文献
5.
Estimating the Excess Investment in
Ribulose-1,5-Bisphosphate
Carboxylase/Oxygenase in
Leaves of Spring Wheat Grown under Elevated
CO2
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Julian C. Theobald Rowan A.C. Mitchell Martin A.J. Parry David W. Lawlor 《Plant physiology》1998,118(3):945-955
Wheat (Triticum aestivum L.) was grown under CO2 partial pressures of 36 and 70 Pa with two N-application regimes. Responses of photosynthesis to varying CO2 partial pressure were fitted to estimate the maximal carboxylation rate and the nonphotorespiratory respiration rate in flag and preceding leaves. The maximal carboxylation rate was proportional to ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) content, and the light-saturated photosynthetic rate at 70 Pa CO2 was proportional to the thylakoid ATP-synthase content. Potential photosynthetic rates at 70 Pa CO2 were calculated and compared with the observed values to estimate excess investment in Rubisco. The excess was greater in leaves grown with high N application than in those grown with low N application and declined as the leaves senesced. The fraction of Rubisco that was estimated to be in excess was strongly dependent on leaf N content, increasing from approximately 5% in leaves with 1 g N m−2 to approximately 40% in leaves with 2 g N m−2. Growth at elevated CO2 usually decreased the excess somewhat but only as a consequence of a general reduction in leaf N, since relationships between the amount of components and N content were unaffected by CO2. We conclude that there is scope for improving the N-use efficiency of C3 crop species under elevated CO2 conditions. 相似文献
6.
Perry JR Voight BF Yengo L Amin N Dupuis J Ganser M Grallert H Navarro P Li M Qi L Steinthorsdottir V Scott RA Almgren P Arking DE Aulchenko Y Balkau B Benediktsson R Bergman RN Boerwinkle E Bonnycastle L Burtt NP Campbell H Charpentier G Collins FS Gieger C Green T Hadjadj S Hattersley AT Herder C Hofman A Johnson AD Kottgen A Kraft P Labrune Y Langenberg C Manning AK Mohlke KL Morris AP Oostra B Pankow J Petersen AK Pramstaller PP Prokopenko I Rathmann W Rayner W Roden M Rudan I Rybin D 《PLoS genetics》2012,8(5):e1002741
Common diseases such as type 2 diabetes are phenotypically heterogeneous. Obesity is a major risk factor for type 2 diabetes, but patients vary appreciably in body mass index. We hypothesized that the genetic predisposition to the disease may be different in lean (BMI<25 Kg/m2) compared to obese cases (BMI≥30 Kg/m2). We performed two case-control genome-wide studies using two accepted cut-offs for defining individuals as overweight or obese. We used 2,112 lean type 2 diabetes cases (BMI<25 kg/m2) or 4,123 obese cases (BMI≥30 kg/m2), and 54,412 un-stratified controls. Replication was performed in 2,881 lean cases or 8,702 obese cases, and 18,957 un-stratified controls. To assess the effects of known signals, we tested the individual and combined effects of SNPs representing 36 type 2 diabetes loci. After combining data from discovery and replication datasets, we identified two signals not previously reported in Europeans. A variant (rs8090011) in the LAMA1 gene was associated with type 2 diabetes in lean cases (P = 8.4×10−9, OR = 1.13 [95% CI 1.09–1.18]), and this association was stronger than that in obese cases (P = 0.04, OR = 1.03 [95% CI 1.00–1.06]). A variant in HMG20A—previously identified in South Asians but not Europeans—was associated with type 2 diabetes in obese cases (P = 1.3×10−8, OR = 1.11 [95% CI 1.07–1.15]), although this association was not significantly stronger than that in lean cases (P = 0.02, OR = 1.09 [95% CI 1.02–1.17]). For 36 known type 2 diabetes loci, 29 had a larger odds ratio in the lean compared to obese (binomial P = 0.0002). In the lean analysis, we observed a weighted per-risk allele OR = 1.13 [95% CI 1.10–1.17], P = 3.2×10−14. This was larger than the same model fitted in the obese analysis where the OR = 1.06 [95% CI 1.05–1.08], P = 2.2×10−16. This study provides evidence that stratification of type 2 diabetes cases by BMI may help identify additional risk variants and that lean cases may have a stronger genetic predisposition to type 2 diabetes. 相似文献
7.
Deforestation in the tropics is an important source of carbon C release to the atmosphere. To provide a sound scientific base for efforts taken to reduce emissions from deforestation and degradation (REDD+) good estimates of C stocks and fluxes are important. We present components of the C balance for selectively logged lowland tropical dipterocarp rainforest in the Malua Forest Reserve of Sabah, Malaysian Borneo. Total organic C in this area was 167.9 Mg C ha−1±3.8 (SD), including: Total aboveground (TAGC: 55%; 91.9 Mg C ha−1±2.9 SEM) and belowground carbon in trees (TBGC: 10%; 16.5 Mg C ha−1±0.5 SEM), deadwood (8%; 13.2 Mg C ha−1±3.5 SEM) and soil organic matter (SOM: 24%; 39.6 Mg C ha−1±0.9 SEM), understory vegetation (3%; 5.1 Mg C ha−1±1.7 SEM), standing litter (<1%; 0.7 Mg C ha−1±0.1 SEM) and fine root biomass (<1%; 0.9 Mg C ha−1±0.1 SEM). Fluxes included litterfall, a proxy for leaf net primary productivity (4.9 Mg C ha−1 yr−1±0.1 SEM), and soil respiration, a measure for heterotrophic ecosystem respiration (28.6 Mg C ha−1 yr−1±1.2 SEM). The missing estimates necessary to close the C balance are wood net primary productivity and autotrophic respiration.Twenty-two years after logging TAGC stocks were 28% lower compared to unlogged forest (128 Mg C ha−1±13.4 SEM); a combined weighted average mean reduction due to selective logging of −57.8 Mg C ha−1 (with 95% CI −75.5 to −40.2). Based on the findings we conclude that selective logging decreased the dipterocarp stock by 55–66%. Silvicultural treatments may have the potential to accelerate the recovery of dipterocarp C stocks to pre-logging levels. 相似文献
8.
Ribulose-1,5-Bisphosphate Carboxylase/Oxygenase Content,
Assimilatory Charge, and Mesophyll Conductance in Leaves
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The content of
ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco)
(Et; EC 4.1.1.39) measured in different-aged
leaves of sunflower (Helianthus annuus) and other plants
grown under different light intensities, varied from 2 to 75 μmol
active sites m−2. Mesophyll conductance (μ) was measured
under 1.5% O2, as well as postillumination CO2
uptake (assimilatory charge, a gas-exchange measure of the
ribulose-1,5-bisphosphate pool). The dependence of μ on
Et saturated at
Et = 30 μmol active sites m−2
and μ = 11 mm s−1 in high-light-grown leaves. In
low-light-grown leaves the dependence tended toward saturation at
similar Et but reached a μ of only 6 to 8
mm s−1. μ was proportional to the assimilatory charge,
with the proportionality constant (specific carboxylation efficiency)
between 0.04 and 0.075 μm−1
s−1. Our data show that the saturation of the relationship
between Et and μ is caused by three
limiting components: (a) the physical diffusion resistance (a minor
limitation), (b) less than full activation of Rubisco (related to
Rubisco activase and the slower diffusibility of Rubisco at high
protein concentrations in the stroma), and (c) chloroplast metabolites,
especially 3-phosphoglyceric acid and free inorganic phosphate, which
control the reaction kinetics of ribulose-1,5-bisphosphate
carboxylation by competitive binding to active sites.Rubisco (EC 4.1.1.39) catalyzes the irreversible carboxylation of
RuBP to form two PGA molecules (in this work the oxygenase reaction was
not active since a low O2 concentration was
used). RuBP carboxylation is the major rate-determining reaction in
photosynthetic CO2 assimilation. All factors that
influence the photosynthetic rate do so by influencing the activity of
Rubisco and the concentration of its substrates,
CO2 and RuBP. Et in
leaves may be as high as 75 μmol m−2, and for
the extracted enzyme
Km(CO2) = 9.4
μm (Makino et al., 1985a) and
Km(RuBP) = 30 to 40 μm (Yeoh
et al., 1981). In leaves photosynthesizing under atmospheric
conditions, the concentration of RuBP may increase to 10 to 15
mm (Badger et al., 1984; Sharkey et al., 1986), but the
concentration of CO2 is usually about 4 to 8
μm in leaf intercellular spaces, depending on stomatal
conductance. This CO2 concentration is well below
the Km(CO2) of the
enzyme, and it is the initial slope of the kinetic curve
VM/Km(CO2),
termed carboxylation conductance, that becomes important.rc limits the
CO2-fixation rate in series with the other
resistances, rg and
rmd. The carboxylation rates are usually
expressed in relation to Ci or
Cw. Cc is
usually about 20% to 30% lower than Cw
because of concentration decrease generated by the carboxylation flux
on rmd. Considering the above, the
carboxylation conductance in intact leaves in vivo may be found as the
initial slope of the A versus Cc
graph at low Cc values. If
Cc cannot be calculated because
rmd is unknown, the closest approximation
is a plot of A versus Cw or
A versus Ci. The true parameters
of the carboxylase can be found only from experiments carried out in
nonphotorespiratory conditions (1%–2% O2);
otherwise the competing oxygenase reaction consumes a part of RuBP and
partially inhibits carboxylase activity.Because of technical problems with the measurement of A
versus Cw relationships, in many studies
only the net photosynthetic rate under atmospheric conditions (21%
O2) was related to Rubisco activity or content.
Nevertheless, good correlation has been found (Makino et al., 1983;
Hudson et al., 1992; Jacob and Lawlor, 1992; Jiang and Rodermel, 1995;
Nakano et al., 1997). These results indicated that the level of Rubisco
protein could be a limiting factor in photosynthesis throughout the
life span of the leaf under natural environmental conditions. On the
other hand, when Rubisco levels in leaves exceeded 4 g
m−2 (60 μmol m−2), the
in vivo Rubisco activity (measured as photosynthesis under
pCi = 20 to 30 Pa and 21%
O2) became curvilinearly correlated with
Et (Makino et al., 1994, 1997). When
measurements were made over the whole life span of wheat leaves, the
measured rates of photosynthesis were lower in young leaves, which had
high protein content, than would have been expected from the amount and
activity of Rubisco (Lawlor et al., 1989).During senescence the decrease in Rubisco activity was initially
greater than the decrease in net photosynthesis (Hall et al., 1978). In
a willow canopy, Rubisco-specific activity was higher when the apparent
Et (N content in leaves) was smaller
(Vapaavuori and Vuorinen, 1989). A similar nonlinearity was found in
our previous experiments (Eichelmann and Laisk, 1990), in which we
obtained a saturating relationship when Et
exceeded 30 μmol m−2. In the latter work the
initial slope of the A versus Cw
curves under nonphotorespiratory conditions (1.5% O2)
was assumed to represent the Rubisco activity in vivo and was compared
with the Et. We discovered that growth
light had the strongest influence on the saturation of the relationship
between μ and Et. In the present work we
present insight into this relationship, using not only plants grown
under different light intensities but also leaves adapted to different
light intensities. 相似文献
9.
Hall LM Moran CN Milne GR Wilson J MacFarlane NG Forouhi NG Hariharan N Salt IP Sattar N Gill JM 《PloS one》2010,5(12):e14197
Background
South Asians are more insulin resistant than Europeans, which cannot be fully explained by differences in adiposity. We investigated whether differences in oxidative capacity and capacity for fatty acid utilisation in South Asians might contribute, using a range of whole-body and skeletal muscle measures.Methodology/Principal Findings
Twenty men of South Asian ethnic origin and 20 age and BMI-matched men of white European descent underwent exercise and metabolic testing and provided a muscle biopsy to determine expression of oxidative and lipid metabolism genes and of insulin signalling proteins. In analyses adjusted for age, BMI, fat mass and physical activity, South Asians, compared to Europeans, exhibited; reduced insulin sensitivity by 26% (p = 0.010); lower VO2max (40.6±6.6 vs 52.4±5.7 ml.kg−1.min−1, p = 0.001); and reduced fat oxidation during submaximal exercise at the same relative (3.77±2.02 vs 6.55±2.60 mg.kg−1.min−1 at 55% VO2max, p = 0.013), and absolute (3.46±2.20 vs 6.00±1.93 mg.kg−1.min−1 at 25 ml O2.kg−1.min−1, p = 0.021), exercise intensities. South Asians exhibited significantly higher skeletal muscle gene expression of CPT1A and FASN and significantly lower skeletal muscle protein expression of PI3K and PKB Ser473 phosphorylation. Fat oxidation during submaximal exercise and VO2max both correlated significantly with insulin sensitivity index and PKB Ser473 phosphorylation, with VO2max or fat oxidation during exercise explaining 10–13% of the variance in insulin sensitivity index, independent of age, body composition and physical activity.Conclusions/Significance
These data indicate that reduced oxidative capacity and capacity for fatty acid utilisation at the whole body level are key features of the insulin resistant phenotype observed in South Asians, but that this is not the consequence of reduced skeletal muscle expression of oxidative and lipid metabolism genes. 相似文献10.
As a consequence to hypobaric hypoxic exposure skeletal muscle atrophy is often reported. The underlying mechanism has been suggested to involve a decrease in protein synthesis in order to conserve O2. With the aim to challenge this hypothesis, we applied a primed, constant infusion of 1-13C-leucine in nine healthy male subjects at sea level and subsequently at high-altitude (4559 m) after 7–9 days of acclimatization. Physical activity levels and food and energy intake were controlled prior to the two experimental conditions with the aim to standardize these confounding factors. Blood samples and expired breath samples were collected hourly during the 4 hour trial and vastus lateralis muscle biopsies obtained at 1 and 4 hours after tracer priming in the overnight fasted state. Myofibrillar protein synthesis rate was doubled; 0.041±0.018 at sea-level to 0.080±0.018%⋅hr−1 (p<0.05) when acclimatized to high altitude. The sarcoplasmic protein synthesis rate was in contrast unaffected by altitude exposure; 0.052±0.019 at sea-level to 0.059±0.010%⋅hr−1 (p>0.05). Trends to increments in whole body protein kinetics were seen: Degradation rate elevated from 2.51±0.21 at sea level to 2.73±0.13 µmol⋅kg−1⋅min−1 (p = 0.05) at high altitude and synthesis rate similar; 2.24±0.20 at sea level and 2.43±0.13 µmol⋅kg−1⋅min−1 (p>0.05) at altitude. We conclude that whole body amino acid flux is increased due to an elevated protein turnover rate. Resting skeletal muscle myocontractile protein synthesis rate was concomitantly elevated by high-altitude induced hypoxia, whereas the sarcoplasmic protein synthesis rate was unaffected by hypoxia. These changed responses may lead to divergent adaptation over the course of prolonged exposure. 相似文献
11.
Palstra AP Tudorache C Rovira M Brittijn SA Burgerhout E van den Thillart GE Spaink HP Planas JV 《PloS one》2010,5(12):e14483
Background
Zebrafish has been largely accepted as a vertebrate multidisciplinary model but its usefulness as a model for exercise physiology has been hampered by the scarce knowledge on its swimming economy, optimal swimming speeds and cost of transport. Therefore, we have performed individual and group-wise swimming experiments to quantify swimming economy and to demonstrate the exercise effects on growth in adult zebrafish.Methodology/Principal Findings
Individual zebrafish (n = 10) were able to swim at a critical swimming speed (Ucrit) of 0.548±0.007 m s−1 or 18.0 standard body lengths (BL) s−1. The optimal swimming speed (Uopt) at which energetic efficiency is highest was 0.396±0.019 m s−1 (13.0 BL s−1) corresponding to 72.26±0.29% of Ucrit. The cost of transport at optimal swimming speed (COTopt) was 25.23±4.03 µmol g−1 m−1. A group-wise experiment was conducted with zebrafish (n = 83) swimming at Uopt for 6 h day−1 for 5 days week−1 for 4 weeks vs. zebrafish (n = 84) that rested during this period. Swimming zebrafish increased their total body length by 5.6% and body weight by 41.1% as compared to resting fish. For the first time, a highly significant exercise-induced growth is demonstrated in adult zebrafish. Expression analysis of a set of muscle growth marker genes revealed clear regulatory roles in relation to swimming-enhanced growth for genes such as growth hormone receptor b (ghrb), insulin-like growth factor 1 receptor a (igf1ra), troponin C (stnnc), slow myosin heavy chain 1 (smyhc1), troponin I2 (tnni2), myosin heavy polypeptide 2 (myhz2) and myostatin (mstnb).Conclusions/Significance
From the results of our study we can conclude that zebrafish can be used as an exercise model for enhanced growth, with implications in basic, biomedical and applied sciences, such as aquaculture. 相似文献12.
Schuldt K Kretz CC Timmann C Sievertsen J Ehmen C Esser C Loag W Ansong D Dering C Evans J Ziegler A May J Krammer PH Agbenyega T Horstmann RD 《PLoS genetics》2011,7(5):e1002066
Human genetics and immune responses are considered to critically influence the outcome of malaria infections including life-threatening syndromes caused by Plasmodium falciparum. An important role in immune regulation is assigned to the apoptosis-signaling cell surface receptor CD95 (Fas, APO-1), encoded by the gene FAS. Here, a candidate-gene association study including variant discovery at the FAS gene locus was carried out in a case-control group comprising 1,195 pediatric cases of severe falciparum malaria and 769 unaffected controls from a region highly endemic for malaria in Ghana, West Africa. We found the A allele of c.−436C>A (rs9658676) located in the promoter region of FAS to be significantly associated with protection from severe childhood malaria (odds ratio 0.71, 95% confidence interval 0.58–0.88, pempirical = 0.02) and confirmed this finding in a replication group of 1,412 additional severe malaria cases and 2,659 community controls from the same geographic area. The combined analysis resulted in an odds ratio of 0.71 (95% confidence interval 0.62–0.80, p = 1.8×10−7, n = 6035). The association applied to c.−436AA homozygotes (odds ratio 0.47, 95% confidence interval 0.36–0.60) and to a lesser extent to c.−436AC heterozygotes (odds ratio 0.73, 95% confidence interval 0.63–0.84), and also to all phenotypic subgroups studied, including severe malaria anemia, cerebral malaria, and other malaria complications. Quantitative FACS analyses assessing CD95 surface expression of peripheral blood mononuclear cells of naïve donors showed a significantly higher proportion of CD69+CD95+ cells among persons homozygous for the protective A allele compared to AC heterozygotes and CC homozygotes, indicating a functional role of the associated CD95 variant, possibly in supporting lymphocyte apoptosis. 相似文献
13.
Heterotrophic soil microorganisms rely on carbon (C) allocated belowground in plant production, but belowground C allocation (BCA) by plants is a poorly quantified part of ecosystem C cycling, especially, in peat soil. We applied a C balance approach to quantify BCA in a mixed conifer-red maple (Acer rubrum) forest on deep peat soil. Direct measurements of CH4 and CO2 fluxes across the soil surface (soil respiration), production of fine and small plant roots, and aboveground litterfall were used to estimate respiration by roots, by mycorrhizae and by free-living soil microorganisms. Measurements occurred in two consecutive years. Soil respiration rates averaged 1.2 bm μmol m? 2 s? 1 for CO2 and 0.58 nmol m? 2 s? 1 for CH4 (371 to 403 g C m? 2 year? 1). Carbon in aboveground litter (144 g C m? 2 year? 1) was 84% greater than C in root production (78 g C m? 2 year? 1). Complementary in vitro assays located high rates of anaerobic microbial activity, including methanogenesis, in a dense layer of roots overlying the peat soil and in large-sized fragments within the peat matrix. Large-sized fragments were decomposing roots and aboveground leaf and twig litter, indicating that relatively fresh plant production supported most of the anaerobic microbial activity. Respiration by free-living soil microorganisms in deep peat accounted for, at most, 29 to 38 g C m? 2 year? 1. These data emphasize the close coupling between plant production, ecosystem-level C cycling and soil microbial ecology, which BCA can help reveal. 相似文献
14.
Soil respiration and the hydrolysis of fluorescein diacetate (FDA) as a measure of total microbial activity were investigated
in central Korea, at three sites that had been changed from abandoned agricultural lands to natural vegetation: rice field
conversion to forest (RF), crop field conversion to shrub (CS), and indigenous forest (IF). Seasonal variations in soil respiration
were affected by soil temperature and, to a lesser extent, by photosynthetically active radiation (PAR) and soil moisture.
The mean annual rate of soil respiration (g CO2 m-2 hr-1) was highest at CS (0.36), followed by IF (0.29) and RF (0.28), whereas the total annual soil respiration (kg CO2 m-2 yr-1) was 2.82 for CS, 2.46 for IF, and 2.40 for RF. Mean annual FDA hydrolysis (μg FDA min-1 g-1 dry soil) was higher at RS (4.56) and IF (4.61) than at CS (3.65). At all three land-use change sites, soil respiration was
only very weakly correlated with FDA hydrolysis. 相似文献
15.
Photosynthesis and Carbon Partitioning in Transgenic Tobacco Plants Deficient in Leaf Cytosolic Pyruvate Kinase 总被引:4,自引:1,他引:3
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Bernard Grodzinski Jirong Jiao Vicki L. Knowles William C. Plaxton 《Plant physiology》1999,120(3):887-896
Whole-plant diurnal C exchange analysis provided a noninvasive estimation of daily net C gain in transgenic tobacco (Nicotiana tabacum L.) plants deficient in leaf cytosolic pyruvate kinase (PKc−). PKc− plants cultivated under a low light intensity (100 μmol m−2 s−1) were previously shown to exhibit markedly reduced root growth, as well as delayed shoot and flower development when compared with plants having wild-type levels of PKc (PKc+). PKc− and PKc+ source leaves showed a similar net C gain, photosynthesis over a range of light intensities, and a capacity to export newly fixed 14CO2 during photosynthesis. However, during growth under low light the nighttime, export of previously fixed 14CO2 by fully expanded PKc− leaves was 40% lower, whereas concurrent respiratory 14CO2 evolution was 40% higher than that of PKc+ leaves. This provides a rationale for the reduced root growth of the PKc− plants grown at low irradiance. Leaf photosynthetic and export characteristics in PKc− and PKc+ plants raised in a greenhouse during winter months resembled those of plants grown in chambers at low irradiance. The data suggest that PKc in source leaves has a critical role in regulating nighttime respiration particularly when the available pool of photoassimilates for export and leaf respiratory processes are low. 相似文献
16.
Annual cycles of water vapour and carbon dioxide fluxes in and above a boreal aspen forest 总被引:10,自引:0,他引:10
T. A. BLACK G. DEN HARTOG † H. H. NEUMANN † P.D. BLANKEN P.C. YANG C. RUSSELL ‡ Z. NESIC X. LEE § S. G. CHEN R. STAEBLER† M. D. NOVAK 《Global Change Biology》1996,2(3):219-229
Water vapour and CO2 fluxes were measured using the eddy correlation method above and below the overstorey of a 21-m tall aspen stand in the boreal forest of central Saskatchewan as part of the Boreal Ecosystem-Atmosphere Study (BOREAS). Measurements were made at the 39.5-m and 4-m heights using 3-dimensional sonic anemometers (Kaijo-Denki and Solent, respectively) and closed-path gas analysers (LI-COR 6262) with 6-m and 4.7-m long heated sampling tubing, respectively. Continuous measurements were made from early October to mid-November 1993 and from early February to late-September 1994. Soil CO2 flux (respiration) was measured using a LI-COR 6000-09 soil chamber and soil evaporation was measured using Iysimetry. The leaf area index of the aspen and hazelnut understorey reached 1.8 and 3.3, respectively. The maximum daily evapotranspiration (E) rate was 5–6 mm d?1. Following leaf-out the hazelnut and soil accounted for 22% of the forest E. The estimated total E was 403 mm for 1994. About 88% of the precipitation in 1994 was lost as evapotranspiration. During the growing season, the magnitude of half-hourly eddy fluxes of CO2 from the atmosphere into the forest reached 1.2 mg CO2 m?2 s?1 (33 μmol C m?2 s?1) during the daytime. Downward eddy fluxes at the 4-m height were observed when the hazelnut was growing rapidly in June and July. Under well-ventilated night-time conditions, the eddy fluxes of CO2 above the aspen and hazelnut, corrected for canopy storage, increased exponentially with soil temperature at the 2-cm depth. Estimates of daytime respiration rates using these relationships agreed well with soil chamber measurements. During the 1994 growing season, the cumulative net ecosystem exchange (NEE) was -3.5 t C ha?1 y?1 (a net gain by the system). For 1994, cumulative NEE, ecosystem respiration (R) and gross ecosystem photosynthesis (GEP = R - NEE) were estimated to be -1.3, 8.9 and 10.2 t C ha?1 y?1 respectively. Gross photosynthesis of the hazelnut was 32% of GEP. 相似文献
17.
Serrano-Sánchez JA Delgado-Guerra S Olmedillas H Guadalupe-Grau A Arteaga-Ortiz R Sanchis-Moysi J Dorado C Calbet JA 《PloS one》2010,5(10):e13435
Background
To determine if there is an association between physical activity assessed by the short version of the International Physical Activity Questionnaire (IPAQ) and cardiorespiratory and muscular fitness.Methodology/Principal Findings
One hundred and eighty-two young males (age range: 20–55 years) completed the short form of the IPAQ to assess physical activity. Body composition (dual-energy X-Ray absorptiometry), muscular fitness (static and dynamic muscle force and power, vertical jump height, running speed [30 m sprint], anaerobic capacity [300 m running test]) and cardiorespiratory fitness (estimated VO2max: 20 m shuttle run test) were also determined in all subjects.Activity-related energy expenditure of moderate and vigorous intensity (EEPAmoderate and EEPAvigorous, respectively) was inversely associated with indices of adiposity (r = −0.21 to −0.37, P<0.05). Cardiorespiratory fitness (VO2max) was positively associated with LogEEPAmoderate (r = 0.26, P<0.05) and LogEEPAvigorous (r = 0.27). However, no association between VO2max with LogEEPAmoderate, LogEPPAvigorous and LogEEPAtotal was observed after adjusting for the percentage of body fat. Multiple stepwise regression analysis to predict VO2max from LogEEPAwalking, LogEEPAmoderate, LogEEPAvigorous, LogEEPAtotal, age and percentage of body fat (%fat) showed that the %fat alone explained 62% of the variance in VO2max and that the age added another 10%, while the other variables did not add predictive value to the model [VO2max = 129.6−(25.1× Log %fat) − (34.0× Log age); SEE: 4.3 ml.kg−1. min−1; R2 = 0.72 (P<0.05)]. No positive association between muscular fitness-related variables and physical activity was observed, even after adjusting for body fat or body fat and age.Conclusions/Significance
Adiposity and age are the strongest predictors of VO2max in healthy men. The energy expended in moderate and vigorous physical activities is inversely associated with adiposity. Muscular fitness does not appear to be associated with physical activity as assessed by the IPAQ. 相似文献18.
Michael G. Ryan Stith T. Gower Robert M. Hubbard Richard H. Waring Henry L. Gholz Wendell P. Cropper Jr Steven W. Running 《Oecologia》1995,101(2):133-140
We estimate maintenance respiration for boles of four temperate conifers (ponderosa pine, western hemlock, red pine, and slash pine) from CO2 efflux measurements in autumn, when construction respiration is low or negligible. Maintenance respiration of stems was linearly related to sapwood volume for all species; at 10°C, respiration per unit sapwood volume ranged from 4.8 to 8.3 mol CO2 m–3 s–1. For all sites combined, respiration increased exponentially with temperature (Q
10
=1.7, r
2=0.78). We estimate that maintenance respiration of aboveground woody tissues of these conifers consumes 52–162 g C m–2 y–1, or 5–13% of net daytime carbon assimilation annually. The fraction of annual net daytime carbon fixation used for stem maintenance respiration increased linearly with the average annual temperature of the site. 相似文献
19.
Zhang XM Zhong R Liu L Wang Y Yuan JX Wang P Sun C Zhang Z Song WG Miao XP 《PloS one》2011,6(7):e21894
Background
Over-expression and increased activity of cyclooxygenase (COX)-2 induced by smoking has been implicated in the development of cancer. This study aimed to explore the interaction between smoking and functional polymorphisms of COX-2 in modulation of gastric cardia adenocarcinoma (GCA) risk.Methods and Findings
Three COX-2 polymorphisms, including –1195G>A (rs689466), –765G>C (rs20417), and 587Gly>Arg (rs3218625), were genotyped in 357 GCA patients and 985 controls. In the multivariate logistic regression analysis, we found that the –1195AA, –765GC, and 587Arg/Arg genotypes were associated with increased risk of GCA (OR = 1.50, 95% CI = 1.05–2.13; OR = 2.06, 95% CI = 1.29–3.29 and OR = 1.67, 95% CI = 1.04–2.66, respectively). Haplotype association analysis showed that compared with G−1195-G−765- GGly587Arg, the A−1195-C−765-AGly587Arg conferred an increased risk of GCA (OR = 2.49, 95% CI = 1.54–4.01). Moreover, significant multiplicative interactions were observed between smoking and these three polymorphisms of –1195G>A, –765G>C, and 587Gly>Arg, even after correction by false discovery rate (FDR) method for multiple comparisons (FDR-P interaction = 0.006, 5.239×10−4 and 0.017, respectively). Similarly, haplotypes incorporating these three polymorphisms also showed significant interaction with smoking in the development of GCA (P for multiplicative interaction = 2.65×10−6).Conclusion
These findings indicated that the functional polymorphisms of COX-2, in interaction with smoking, may play a substantial role in the development of GCA. 相似文献20.
NT Krarup N Grarup K Banasik M Friedrichsen K Færch CH Sandholt T Jørgensen P Poulsen DR Witte A Vaag T Sørensen O Pedersen T Hansen 《PloS one》2012,7(7):e40376