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1.
A global survey of carbon isotope discrimination in plants from high altitude   总被引:55,自引:0,他引:55  
Summary Carbon 13/12 isotope ratios have been determined from leaves of a hundred C3 plant species (or ecotypes) from all major mountain ranges of the globe, avoiding drought stressed areas. A general increase in 13C content was found with increasing altitude, i.e. overall discrimination against the heavy isotope is reduced at high elevation. The steepest decline of discrimination is observed in taxa typically ranging to highest elevations (e.g. the genus Ranunculus). Mean 13C for all samples collected between 2500 and 5600 m altitude is-26.15 compared to the lowland average of-28.80 (P<0.001). Forbs from highest elevations reach-24. According to theory of 13C discrimination this indicates decreasing relative limitation of carbon uptake by carboxylation. In other words, we estimate that the ratio of internal to external partial pressure of CO2 (p i /p a )in leaves of high elevation plants is lower than in leaves of low altitude. These results confirm recent gas exchange analyses in high and low elevation plants.  相似文献   

2.
Carbon isotope effects were investigated for the reaction catalyzed by the glycine decarboxylase complex (GDC; EC 2.1.2.10). Mitochondria isolated from leaves of pea (Pisum sativum L.) and spinach (Spinacia oleracea L.) were incubated with glycine, and the CO2 evolved was analyzed for the carbon isotope ratio (δ13C). Within the range of parameters tested (temperature, pH, combination of cofactors NAD+, ADP, pyridoxal 5-phosphate), carbon isotope shifts of CO2 relative to the C1-carboxyl carbon of glycine varied from +14‰ to −7‰. The maximum effect of cofactors was observed for NAD+, the removal of which resulted in a strong 12C enrichment of the CO2 evolved. This indicates the possibility of isotope effects with both positive and negative signs in the GDC reaction. The measurement of δ13C in the leaves of the GDC-deficient barley (Hordeum vulgare L.) mutant (LaPr 87/30) plants indicated that photorespiratory carbon isotope fractionation, opposite in sign when compared to the carbon isotope effect during CO2 photoassimilation, takes place in vivo. Thus the key reaction of photorespiration catalyzed by GDC, together with the key reaction of CO2 fixation catalyzed by ribulose-1,5-bisphosphate carboxylase, both contribute to carbon isotope fractionation in photosynthesis. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献   

3.
Summary Stable carbon isotope ratio analysis is a powerful technique in tracing ecosystem carbon flows, especially those between primary and secondary producers. The distinctive 13C/12C ratios of plant species tend to pass along the food chain with little further fractionation, hence the stable carbon isotope composition of an animal is an important clue to what it has eaten. We compared the stable carbon isotope composition of plants and insects in an old field in Georgia. Of the dominant plants in the old field, 6 were C4 species and had 13C1 values of-10.9 to 12.9, and 7 were C3 species with values of-27.3 to-29.1. Insects known to be feeding on only one plant species had 13C values within 1 of the isotopic composition of the plant. Wasp larvae parasitizing two insect species had 13C values 1.3 and 1.7 higher than that of the food plant. A variety of insects of unknown food habits collected on monospecific and mixed species plant stands in the old field had 13C values ranging from-10.1 to-30.0. Two species of leafhopper and a grasshopper had isotopic compositions within the range of C4 plant values; a tortoise beetle and a lace bug had isotopic compositions within C3 plant values. Other insects had intermediate 13C values, suggesting a mixed diet composed of both C3 and C4 plants. The carbon isotopic ratios of field collected insects appears to be a useful qualitative indicator of their feeding preference.  相似文献   

4.
13C discrimination during CO2 assimilation by the terrestrial biosphere   总被引:1,自引:0,他引:1  
Estimates of the extent of the discrimination against13CO2 during photosynthesis (A) on a global basis were made using gridded data sets of temperature, precipitation, elevation, humidity and vegetation type. Stomatal responses to leaf-to-air vapour mole fraction difference (D, leaf-to-air vapour pressure difference divided by atmospheric pressure) were first determined by a literature review and by assuming that stomatal behaviour results in the optimisation of plant water use in relation to carbon gain. Using monthly time steps, modelled stomatal responses toD were used to calculate the ratio of stomatal cavity to ambient CO2 mole fractions and then, in association with leaf internal conductances, to calculate A. Weighted according to gross primary productivity (GPP, annual net CO2 asimilation per unit ground area), estimated A for C3 biomes ranged from 12.9 for xerophytic woods and shrub to 19.6 for cool/cold deciduous forest, with an average value from C3 plants of 17.8. This is slightly less than the commonly used values of 18–20. For C4 plants the average modelled discrimination was 3.6, again slightly less than would be calculated from C4 plant dry matter carbon isotopic composition (yielding around 5). From our model we estimate that, on a global basis, 21% of GPP is by C4 plants and for the terrestrial biosphere as a whole we calculate an average isotope discrimination during photosynthesis of 14.8. There are large variations in A across the globe, the largest of which are associated with the precence or absence of C4 plants. Due to longitudinal variations in A, there are problems in using latitudinally averaged terrestrial carbon isotope discriminations to calculate the ratio of net oceanic to net terrestrial carbon fluxes.  相似文献   

5.
The study deals with a comparative analysis of the relative abundances of the carbon isotopes 12C and 13C in the metabolites and biomass of the Burkholderia sp. BS3702 and Pseudomonas putida BS202-p strains capable of utilizing aliphatic (n-hexadecane) and aromatic (naphthalene) hydrocarbons as sources of carbon and energy. The isotope compositions of the carbon dioxide, biomass, and exometabolites produced during the growth of Burkholderia sp. BS3702 on n-hexadecane (13C = –44.6 ± 0.2) were characterized by the values of 13CCO 2 = –50.2 ± 0.4, 13Cbiom = –46.6 ± 0.4, and 13Cexo = –41.5 ± 0.4, respectively. The isotope compositions of the carbon dioxide, biomass, and exometabolites produced during the growth of the same bacterial strain on naphthalene (13C = –21 ± 0.4) were characterized by the isotope effects 13CCO 2 = –24.1 ± 0.4, 13Cbiom = –19.2 ± 0.4, and 13Cexo = –19.1 ± 0.4, respectively. The possibility of using the isotope composition of metabolic carbon dioxide for the rapid monitoring of the microbial degradation of petroleum hydrocarbons in the environment is discussed.  相似文献   

6.
Phaseolus vulgaris (cv. Hawkesbury Wonder) was grown over a range of NaCl concentrations (0–150 mM), and the effects on growth, ion relations and photosynthetic performance were examined. Dry and fresh weight decreased with increasing external NaCl concentration while the root/shoot ratio increased. The Cl- concentration of leaf tissue increased linearly with increasing external NaCl concentration, as did K+ concentration, although to a lesser degree. Increases in leaf Na+ concentration occurred only at the higher external NaCl concentrations (100 mM). Increases in leaf Cl- were primarily balanced by increases in K+ and Na+. X-ray microanalysis of leaf cells from salinized plants showed that Cl- concentration was high in both the cell vacuole and chloroplast-cytoplasm (250–300 mM in both compartments for the most stressed plants), indicating a lack of effective intracellular ion compartmentation in this species. Salinity had little effect on the total nitrogen and ribulose-1,5-bisphosphate (RuBP) carboxylase (EC 4.1.1.39) content per unit leaf area. Chlorophyll per unit leaf area was reduced considerably by salt stress, however. Stomatal conductance declined substantially with salt stress such that the intercellular CO2 concentration (C i) was reduced by up to 30%. Salinization of plants was found to alter the 13C value of leaves of Phaseolus by up to 5 and this change agreed quantitatively with that predicted by the theory relating carbon-isotope fractionation to the corresponding measured intercellular CO2 concentration. Salt stress also brought about a reduction in photosynthetic CO2 fixation independent of altered diffusional limitations. The initial slope of the photosynthesis versus C i response declined with salinity stress, indicating that the apparent in-vivo activity of RuBP carboxylase was decreased by up to 40% at high leaf Cl- concentrations. The quantum yield for net CO2 uptake was also reduced by salt stress.Abbreviations and symbols A net CO2 assimilation rate - C a ambient CO2 concentration - C i intercellular CO2 concentration - RuBP ribulose-1,5-bisphosphate - 13C ratio of 13C to 12C relative to standard limestone  相似文献   

7.
Summary Hemiepiphytic species in the genera Clusia and Ficus were investigated to study their mode of photosynthetic metabolism when growing under natural conditions. Despite growing sympatrically in many areas and having the same growth habit, some Clusia species show Crassulacean acid metabolism (CAM) whereas all species of Ficus investigated are C3. This conclusion is based on diurnal CO2 fixation patterns, diurnal stomatal conductances, diurnal titratable acidity fluctuations, and 13C isotope ratios. Clusia minor, growing in the savannas adjacent to Barinas, Venezuela, shows all aspects of Crassulacean acid metabolism (CAM) on the basis of nocturnal gas exchange, stomatal conductance, total titratable acidity, and carbon isotope composition when measured during the dry season (February 1986). During the wet season (June 1986), the plants shifted to C3-type gas exchange with all CO2 uptake occurring during the daylight hours. The carbon isotope composition of new growth was-28 to-29 typical of C3 plants.  相似文献   

8.
Short-term measurements of instantaneous carbon-isotope discrimination have been determined from mass-spectrometric analyses of CO2 collected online during gas exchange for the epiphytic bromeliad Tillandsia utriculata L. Using this technique, the isotopic signature of CO2 exchange for each phase of Crassulacean acid metabolism (CAM) has been characterised. During night-time fixation of CO2 (Phase I), discrimination () ranged from 4.4 to 6.6, equivalent to an effective carbon-isotope ratio (13C) of –12.3 to –14.5 versus Pee Dee Belemnite (PDB). These values reflected the gross photosynthetic balance between net CO2 uptake and refixation of respiratory CO2, characteristic of CAM in the Bromeliaceae. When for the relative proportion of external (p a ) and internal (p i) CO2 is taken into account, calculated p i/p a decreased during the later part of the dark period from 0.68 to 0.48. Measurements of during Phase II, early in the light period, showed the transition between C4 and C3 pathways, with carboxylation being increasingly dominated by ribulose bisphosphate carboxylase (Rubisco) as increased from 10.5 to 21.2 During decarboxylation in the light period (Phase III), CO2 leaked out of the leaf and the inherent discrimination of Rubisco was expressed. The value of calculated from on-line measurements (64.4) showed that the CO2 lost was considerably enriched in 13C, and this was confirmed by direct analysis of the CO2 diffusing out into a CO2-free atmosphere ( 13C = + 51.6 versus PDB). Instantaneous discrimination was characteristic of the C3 pathway during Phase IV (late in the light period), but a reduction in showed an increasing contribution from phosphoenolpyruvate carboxylase. The results from this non-invasive technique confirm the observations that double carboxylation involving both phosphoenolpyruvate carboxylase and Rubisco occurs during the transient phases of CAM (II and IV) in the light period.Abbreviations and Symbols CAM Crassulacean acid metabolism - H+ (dawn-dusk) variation in titratable acidity - 13C carbonisotope ratio of plant organic material, relative to Pee Dee Belemnite (vs. PDB) - discrimination against 13CO2, - p i, p a internal, external partial pressures of CO2 - Rubisco ribulose1,5-bisphosphate carboxylase - PAR photosynthetically active radiation - PEPCase phosphoenolpyruvate carboxylase We are grateful for financial support in respect of research grants (GR3/5360, GR3/6419) and a studentship awarded by the Natural Environment Research Council, UK.  相似文献   

9.
The CO2 concentration of the atmosphere has increased by almost 30% in the past two centuries, with most of the increase (>5 Pa) during the past 60 years. Controlled environment studies of crop plants dependent on the C3 photosynthetic pathway indicate that an increase of this magnitude would enhance net photosynthesis, reduce stomatal conductance, and increase the difference in CO2 concentration across the stomata, i.e., CO2 concentration outside the leaf to that within (c a-c i). Here we report evidence, based on stable isotope composition of tree rings from three species of field-grown, native conifer trees, that the trees have indeed responded. However, rather than increasing c a-c i, intercellular CO2 concentrations have shifted upward to match the rise in atmospheric concentrations, holding c a-c i constant. No differences were detected among Douglas-fir (Pseudotsuga menziesii), ponderosa pine (Pinus ponderosa), or western white pine (Pinus monticola). The values of c a-c i were inferred from stable carbon isotope ratio (13C) of tree ring holocellulose adjusted for the 0.6–2.6 difference between holocellulose and whole sapwood. The cellulose extraction removed contaminants deposited in the tree ring after it formed and the adjustment corrected for the enrichment of cellulose relative to whole tissue. The whole sapwood values were then adjusted for bublished estimates of past atmospheric 13CO2 and CO2 concentrations. To avoid confounding tree age with CO2, cellulose deposited by saplings in the 1980s was compared to cellulose deposited in the inner rings of nature trees when the mature trees were saplings, between 1910–1929 and 1941–1970; thus saplings were compared to saplings. In a separate analysis, the juvenile effect, which describes the tendency for 13C to increase in the first decades of a tree's life, was quantified independent of source CO2 effects. This study provides evidence that conifers have undergone adjustments in the intercellular CO2 concentration that have maintained c a-c i constant. Based on these results and others, we suggest that c a-c i, which has also been referred to as the intrinsic water-use efficiency, should be considered a homeostatic gas-exchange set point for these conifer species.  相似文献   

10.
Summary Seedlings of two mangrove species, Avicennia marina and Aegiceras corniculatum, were grown in a range of salinities and humidities in controlled environment chambers, and Phaseolus vulgaris plants were grown in the glasshouse. The fractionation of carbon isotopes in the three species was correlated with the ratio of intercellular and ambient partial pressures of CO2. The results are consistent with fractionation being due both to diffusion in air and to carboxylation in the leaf. It was concluded that the latter process discriminates against 13CO2 relative to 12CO2 by about 27.  相似文献   

11.
The relative contribution of autotrophic carbon sources (aquatic macrophytes, flooded forest, phytoplankton) for heterotrophic bacterioplankton was evaluated in a floodplain lake of the Central Amazon. Stable carbon isotopes (13C) were used as tracers. Values of 13C of different autotrophic sources were compared to those of dissolved organic carbon (DOC) and those of bacterially produced CO2.The percentage of carbon derived from C4 macrophytes for bacterially produced CO2 was the highest, on average 89%. The average 13C value of CO2 from bacterial respiration was –18.5 ± 3.3. Considering a fractionation of CO2 of 3 by bacterial respiration, 13C value was –15.5, near C4 macrophyte 13C value (–13.1).The average value of total DOC 13C was –26.8 ± 2.4. The percentage of C4 macrophytes carbon for total DOC was on average 17%. Considering that bacteria consume mainly carbon from macrophytes, the dominance of C3 plants for total DOC probably reflects a faster consumption of the former source, rather than a major contribution of the latter source.Heterotrophic bacterioplankton in the floodplain may be an important link in the aquatic food web, transferring the carbon from C4 macrophytes to the consumers.  相似文献   

12.
Online carbon isotope discrimination (Δ) and leaf gas exchange measurements were made with control and salt-stressed Zea mays and Andropogon glomeratus, two NADP-ME type C4 grasses. Linear relationships between Δ and pi/pa (the ratio of intercellular to atmospheric CO2 partial pressure) were found for control plants which agreed well with theoretical models describing carbon isotope discrimination in C4 plants. These data provided estimates of , the proportion of CO2 fixed by phosphoenolpyruvate carboxylase which leaks out of the bundle sheath and the component of fractionation due to diffusion in air. Salt-stressed plants had wider variation in Δ for the same or less range in pi/pa. Additional work indicated Δ changed independently of pi/pa in both water- and salt-stressed plants, suggesting a possible diurnal change in as plant water status changed linked to a decrease in the activity of the C3 photosynthetic pathway relative to C4 pathway activity. The possible effect of stress-induced changes in on organic matter δ13 C of C4 plants is apt to be most apparent in chronically stressed environments.  相似文献   

13.
Choi  Woo-Jung  Lee  Sang-Mo  Ro  Hee-Myong  Kim  Kyoung-Cheol  Yoo  Sun-Ho 《Plant and Soil》2002,245(2):223-232
To investigate the effect of inorganic fertilizer and composted manure amendments on the N isotope composition (delta 15N) of crop and soil, maize (Zea mays L.) was cultivated under greenhouse conditions for 30, 40, 50, 60, and 70 days. Composted pig manure (delta 15N= +13.9) and urea (-2.3) were applied at 0 and 0 kg N ha–1 (C0U0), 0 and 150 kg N ha–1 (C0U2), 150 and 0 kg N ha–1 (C2U0), and 75 and 75 kg N ha–1 (C1U1), respectively. The delta 15N of total soil-N was not affected by both amendments, but delta 15N of NH+ 4 and NO 3 provided some information on the N isotope fractionation in soil. During the early growth stage, significant differences (P < 0.05) in delta 15N among maize subjected to different treatments were observed. After 30 days of growth, the delta 15N values of maize were +6.6 for C0U0, +1.1 for C0U2, +7.7 for C2U0, and +4.5 for C1U1. However, effects of urea and composted manure application on maize delta 15N progressively decreased with increasing growth period, probably due to isotope fractionation accompanying N losses and increased uptake of soil-derived N by maize. After 70 days of growth, delta 15N of leaves and grains of maize amended with composted pig manure were significantly (P < 0.05) higher than those with urea. The temporal variations in delta 15N of maize amended with urea and composted manure indicate that plant delta 15N is generally not a good tracer for N sources applied to field. Our data can be used in validation of delta 15N fractionation models in relation to N source inputs.  相似文献   

14.
On-line instantaneous carbon isotope discrimination was measured in conjunction with net uptake of CO2 in leaves of exposed and shaded plants of the C3-CAM intermediate Clusia minor growing under natural conditions in Trinidad. At the end of the rainy season (late January-early February, 1992) C3 photosynthesis predominated although exposed leaves recaptured a small proportion of respiratory CO2 at night for the synthesis of malic acid. Citric acid was the major organic acid accumulated by exposed leaves at this time with a citric: malic acid ratio of 11:1. Values of instantaneous discrimination () in exposed leaves during the wet season rose from 17.1 shortly after dawn to 22.7 around mid-day just before stomata closed, suggesting that most CO2 was fixed by Rubisco at this time. During the late afternoon, instantaneous declined from 22.2 to 17, probably reflecting the limited contribution from PEPc activity and an increase in diffusional resistance to CO2 in exposed leaves. Shaded leaves showed no CAM activity and CO2 uptake proceeded throughout the day in the wet season. The decrease in instantaneous from 27 in the morning to 19.2 in the late afternoon was therefore entirely due to diffusional limitation. Leaves sampled in the dry season (mid-March, 1992) had by now induced full CAM activity with both malic and citric acids accumulated overnight and stomata closed for 4–5 h over the middle of the day. Values of instantaneous measured over the first 3 h after dawn (6.4–9.1) indicated that C4 carboxylation dominated CO2 uptake for most of the morning when rates of photosynthesis were maximal, implying that under natural conditions, the down regulation of PEPc in phase II occurs much more slowly than laboratory-based studies have suggested. The contribution from C3 carboxylation to CO2 uptake during phase II was most marked in leaves which accumulated lower quantities of organic acids overnight. In exposed leaves, measurements of instantaneous during the late afternoon illustrated the transition from C3 to C4 carboxylation with stomata remaining open during the transition from dusk into the dark period. Uptake of CO2 by shaded leaves during the late afternoon however appeared to be predominantly limited by decreased stomatal conductance. The short-term measurements of instantaneous were subsequently integrated over 24 h in order to predict the leaf carbon isotope ratios (p) and to compare this with the p measured for leaf organic material. Whilst there was close agreement between predicted and measured p for plants sampled in the wet season, during the dry season the predicted carbon isotope ratios were 5–9 higher than the measured isotope ratios. During the annual cycle of leaf growth most carbon was fixed via the C3 pathway although CAM clearly plays an important role in maintaining photochemical integrity in the dry season.  相似文献   

15.
Summary The ratio of deuterium to hydrogen (expressed as D) in hydrogen released as water during the combustion of dried plant material was examined. The D value (metabolic hydrogen) determined on plant materials grown under controlled conditions is correlated with pathways of photosynthetic carbon metabolism. C3 plants show mean D values of-132 for shoots and -117 for roots; C4 plants show mean D values of -91 for shoots and-77 for roots and CAM plants a D value of-75 for roots and shoots. The difference between the D value of shoot material from C3 and C4 plants was confirmed in species growing under a range of glasshouse conditions. This difference in D value between C3 and C4 species does not appear to be due to differences in the D value (tissue water) in the plants as a result of physical fractionation of hydrogen isotopes during transpiration. In C3 and C4 plants the hydrogen isotope discrimination is in the same direction as the carbon isotope discrimination and factors contributing to the difference in D values are discussed. In CAM plants grown in the laboratory or collected from the field D values range from-75 to +50 and are correlated with 13C values. When deprived of water, the D value (metabolic hydrogen) in both soluble and insoluble material in leaves of Kalanchoe daigremontiana Hamet et Perr., becomes less negative. These changes may reflect the deuterium enrichment of tissue water during transpiration, or in field conditions, may reflect the different D value of available water in areas of increasing aridity. Whatever the origin of the variable D value in CAM plants, this parameter may be a useful index of the water relations of these plants under natural conditions.  相似文献   

16.
Vodnik  D.  Pfanz  H.  Maček  I.  Kastelec  D.  Lojen  S.  Batič  F. 《Photosynthetica》2002,40(4):575-579
High abundance of cockspur (Echinochloa crus-galli) at the geothermal carbon dioxide spring area in Staveinci indicates that this species is able to grow under widely varying CO2 concentrations. Living cockspur plants can even be found very close to gas-releasing vents where growth is significantly reduced. Plant height correlated well with CO2 exposure. The 13C value of the CO2 spring air was –3.9 and 13C values of high-, medium-, and low-CO2 plants were –10.14, –10.44, and –11.95 , respectively. Stomatal response directly followed the prevailing CO2 concentrations, with the highest reduction of stomatal conductance in high CO2 concentration grown plants. Analysis of the curves relating net photosynthetic rate to intercellular CO2 concentration (P N-Ci curves) revealed higher CO2 compensation concentration in plants growing at higher CO2 concentration. This indicates adjustment of respiration and photosynthetic carbon assimilation according to the prevailing CO2 concentrations during germination and growth. There was no difference in other photosynthetic parameters measured.  相似文献   

17.
Summary Fifty-four species of the Chenopodiaceae in Israel were examined for their anatomical features, 13C values, habitat and phytogeographical distribution. 17 species have 13C values between -20 and -30and non-Kranz anatomy (NK) and are therefore considered as C3 plants. 37 species have 13C values between -10 and -18 and Kranz or C4-Suaeda type anatomy and are therefore considered as C4 plants. Some C4 plants have leaf structure which seems to be intermediate between the Kranz and the C4-Suaeda type of leaf anatomy.The segregation of the species into photosynthetic groups shows tribal and phytogeographical grouping. Most of the C3 Chenopods are either mesoruderal plants or coastal halophytes, with a distribution area which covers the Euro-Siberian as well as the Mediterranean phytogeographical regions. The C4 Chenopods are mainly desert or steppe xerohalophytes with a distribution area which includes the Saharo-Arabian and/or Irano-Turanian phytogeographical regions.  相似文献   

18.
Summary A method of monitoring and collecting CO2 samples in the field has been developed which has been used to study both temporal and spatial variations in canopy CO2 isotopic signatures in two contrasting tropical forest formations in Trinidad. These have been related to vertical gradients in the carbon isotope ratio (13C) of organic material in conjunction with measurements of other environmental parameters. The 13C of leaf material from two canopies showed a gradient with respect to height, more negative values being found low in the understorey. The deciduous secondary forest, (Simla) showed a difference of 4.6 and the semi-evergreen seasonal canopy (Aripo), 2.8. The range of 13C values at Simla was 4 less negative than those at Aripo. In order to relate these measurements to the interaction between diffusion or carboxylation limitation, and source CO2 effects, variations in environmental parameters through the canopy have been compared with changes in CO2 partial pressure (P a) and isotopic composition 13C throughout the day during the dry season. Values of P a20 m above the ground at Aripo varied from 380 vpm at dawn to 340 vpm at midday, at which time the partial pressure 15 cm above the ground was 375 vpm. The CO2 partial pressure did not stabilise during the course of the day, and there was good correlation (r 2=0.82) between a and P a, with more negative values of a occuring in the understorey. Diuraal changes of 2 were evident at all canopy positions. In the more open canopy at Simla, these gradients were similar, but less marked. Leaf-air vapour pressure deficit (VPD) showed no relationship with height, possibly as a result of minimal water flux from both the soil and the canopy due to low soil water content; VPD was 1.5 kPa higher at midday than dawn. A 3° C temperature gradient between the understorey and upper canopy was observed at Aripo but not in the more open Simla canopy. CO2 partial pressure stabilised for only 4 h in the middle of the day, while other parameters showed no stable period. The proportion of floor respired CO2 reassimilated at Aripo has been calculated as 26%, 19%, and 8% for the periods 0600–1000, 1000–1400, and 1400–1800 hours. In order to quantify source CO2 effects, measurements of the environmental parameters and assimilation rate must be made at all canopy positions and throughout the day.  相似文献   

19.
Summary The temperature dependence of the oxygen isotope fractionation factor during respiration has been examined for two different microorganisms, namelyTorulopsis utilis andEscherichia coli K12 representing a yeast and a bacterium, respectively. The investigation covered a temperature range of 18° C, that is from 16° C to 34° C forT. utilis and from 19° C to 37° C forE. coli K12. Within this temperature range the fractionation factor ofT. utilis increases by 0.18; an insignificant change ( 10° C = 0.063;r = 0.067), whereas withE. coli K 12 an increase of 1.12; has been observed ( 10° C = 0.6;r = 0.55).  相似文献   

20.
MacFadden BJ  Higgins P 《Oecologia》2004,140(1):169-182
Middle Miocene mammals are known from ~15 million-year-old sediments exposed along the Panama Canal of Central America, a region that otherwise has an exceedingly poor terrestrial fossil record. These land mammals, which represent a part of the ancient terrestrial herbivore community, include an oreodont Merycochoerus matthewi, small camel-like protoceratid artiodactyl Paratoceras wardi, two horses Anchitherium clarencei and Archaeohippus sp., and two rhinos Menoceras barbouri and Floridaceras whitei. Bulk and serial carbon and oxygen isotope analyses of the tooth enamel carbonate allow reconstruction of the ancient climate and ecology of these fossil mammals. Ancient Panama had an equable climate with seasonal temperature and rainfall fluctuations less than those seen today. The middle Miocene terrestrial community consisted predominantly, or exclusively, of C3 plants, i.e., there is no evidence for C4 grasses. Statistically different mean carbon isotope values for the mammalian herbivores indicate niche partitioning of the C3 plant food resources. The range of individual carbon isotope analyses, i.e., 13C from –15.9 to –10.1, indicates herbivores feeding on diverse plants from different habitats with extrapolated 13C values of –29.9 to –24.2, possibly ranging from dense forest to more open country woodland. The ecological niches of individual mammalian herbivore species were differentiated either by diet or body size.  相似文献   

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