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1.
We tested for rapid changes in photosynthate transport and partitioning in response to Lymantria dispar (L.) (Lepidoptera: Lymantriidae) (gypsy moth) herbivory in Populus nigra L. (Salicaceae). Transport and partitioning of [11C]-photosynthate from young mature leaves were measured in vivo before and 18 h after leaf chewing by gypsy moth larvae, which were caged on three older leaves. Following herbivory, there was an increase in export speed of recently fixed carbon from younger mature leaves. The increased export speed was due to a quicker transit time of 11C through the leaf, rather than a change in transport speed through the phloem. Additionally, basipetal partitioning of [11C]-photosynthate was increased following herbivory. Neither of these changes was observed in control plants. This enhancement of export occurs even though herbivores are well known to induce increases in carbon allocation to secondary metabolites within leaves. Our results demonstrate that the use of non-destructive imaging of 11C tracer is a powerful tool for examining plant responses to herbivory. Although the mechanisms underlying the rapid increase in carbon flux to stems and roots remain to be elucidated, our results raise the possibility of a coordinated whole plant response to herbivory. Thus, even when the herbivore specializes on only one plant tissue type, a whole plant approach may be key to understanding how plants respond to herbivory.  相似文献   

2.
Photosynthesis, growth, and carbon partitioning of vigorous coppice shoots were compared with the slower growing intact shoots of Populus maximowiczii × nigra L. MN9 to determine the relationship between carbon partitioning and photosynthetic rate. Relative height growth rate of coppice shoots was 2.2 times that of intact shoots with net photosynthetic rate 1.9 times that of intact shoots. Coppice leaves exported a larger proportion of newly-fixed assimilate (11% compared with 6%) after a 4-h chase. The greater export from coppice leaves was correlated with a greater proportion of [14C]-labelled photosynthate deposited as starch in stems 4 cm below the point of label application. Coppice leaf assimilate levels were reduced to 15% that of leaves on intact plants, but coppice leaves had twice the concentration of labelled sucrose. Carbohydrates constituted 55% of the water-soluble [14C]-labelled photosynthate in leaves of coppice shoots compared with 40% in intact shoots. The results suggest that carbon allocation and partitioning in coppice shoots were altered towards production and export of new assimilate, and support the hypothesis that photosynthetic rate is responsive to sink demand for assimilates.  相似文献   

3.
The photosynthetic rate of a decaploid genotype (1-16-2) of tall fescue ( Festuca arundinacea Schreb.) is about twice that of a common hexaploid genotype (V6-802) (Plant Physiol. 72: 16–21, 1983). Translocation of photosynthate out of the leaves is a possible means of regulating carbon assimilation. To evaluate this possibility, we have examined a) translocation velocity, b) time course of translocation from leaves, c) photoassimilate partitioning pattern into whole plants in pulse and chase experiments, and d) interveinal distances between two ploidy genotypes. Most of the 14C accumulated in sucrose, and the labelled carbon moved down the leaf blades at similar velocities (6 to 10 cm h−1) in both genotypes. Recent 14C assimilate was rapidly translocated from the fed area of the leaf blade. For example, the decaploid and the common hexaploid had translocated 40 and 26% of the 14C, respectively, at 6 h, and 79 and 49% of the 14C, respectively, at 24 h. Partitioning of 14C among plant organs was considerably different between the genotypes after a 24 h chase. For example, out of the total 14C recovered from the whole plant, the decaploid had retained 40% in the labelled leaf with 10, 33 and 29% in other leaves, stem bases and roots, respectively; whereas the hexaploid had retained 91% in the labelled leaf with 4, 3 and 2% in other leaves, stem bases and roots, respectively. However, the higher rate of translocation was correlated with greater interveinal distances in the decaploid genotype. These results suggested that the higher translocation percentage in the decaploid than the hexaploid genotype was due to greater sink activity.  相似文献   

4.
Water deficit and high temperature often occur simultaneously, but their effects on plants are usually investigated separately. The aim of this study was to test how interactions between water stress and nocturnal warming affect carbon allocation in the perennial grass, Leymus chinensis . Plant biomass, dry mass allocation, 14C partitioning and carbon isotope composition (δ13C) were measured. Severe and extreme water stress during nocturnal warming decreased the allocation of dry mass and 14C partitioning below ground to the roots, but moderate water stress significantly increased the below-ground allocation of dry mass and 14C, especially at the lower night temperature. The δ13C values were more positive at day/night temperatures of 30/20°C than at 30/25°C, and greater in the roots than in the leaves. By plotting the δ13C values of the leaves against the δ13C values of the roots, the slopes of regressions were steeper at low than at high night temperature, also indicating that nocturnal warming reduces carbon allocation below ground to the roots. The results suggest that nocturnal warming may weaken acclimation during water stress in this species by regulating carbon allocation between source and sink organs.  相似文献   

5.
We evaluated diurnal and seasonal patterns of carbon isotope composition of leaf dark-respired CO2 ( δ 13Cl) in the C3 perennial shrub velvet mesquite ( Prosopis velutina ) across flood plain and upland savanna ecosystems in the south-western USA. δ 13Cl of darkened leaves increased to maximum values late during daytime periods and declined gradually over night-time periods to minimum values at pre-dawn. The magnitude of the diurnal shift in δ 13Cl was strongly influenced by seasonal and habitat-related differences in soil water availability and leaf surface vapour pressure deficit. δ 13Cl and the cumulative flux-weighted δ 13C value of photosynthates were positively correlated, suggesting that progressive 13C enrichment of the CO2 evolved by darkened leaves during the daytime mainly resulted from short-term changes in photosynthetic 13C discrimination and associated shifts in the δ 13C signature of primary respiratory substrates. The 13C enrichment of dark-respired CO2 relative to photosynthates across habitats and seasons was 4 to 6‰ at the end of the daytime period (1800 h), but progressively declined to 0‰ by pre-dawn (0300 h). The origin of night-time and daytime variations in δ 13Cl is discussed in terms of the carbon source(s) feeding respiration and the drought-induced changes in carbon metabolism.  相似文献   

6.
The influence of microbial degradation on the 13C/12C isotope composition of aromatic hydrocarbons is presented using toluene as a model compound. Four different toluene-degrading bacterial strains grown in batch culture with oxygen, nitrate, ferric iron or sulphate as electron acceptors were studied as representatives of different environmental redox conditions potentially prevailing in contaminated aquifers. The biological degradation induced isotope shifts in the residual, non-degraded toluene fraction and the kinetic isotope fractionation factors αC for toluene degradation by Pseudomonas putida (1.0026 ± 0.00017), Thauera aromatica (1.0017 ± 0.00015), Geobacter metallireducens (1.0018 ± 0.00029) and the sulphate-reducing strain TRM1 (1.0017 ± 0.00016) were in the same range for all four species, although they use at least two different degradation pathways. A similar 13C/12C isotope fractionation factor (αC = 1.0015 ± 0.00015) was observed in situ in a non-sterile soil column in which toluene was degraded under sulphate-reducing conditions. No carbon isotope shifts resulting from soil–hydrocarbon interactions were observed in a non-degrading soil column control with aquifer material under the same conditions. The results imply that microbial degradation of toluene can produce a 13C/12C isotope fractionation in the residual hydrocarbon fraction under different environmental conditions.  相似文献   

7.
A toluene-degrading microbial consortium was enriched directly in a BTEX-contaminated aquifer under sulfate-reducing conditions using in situ microcosms consisting of toluene-loaded activated carbon pellets. Degradation of toluene and concomitant sulfide production by the consortium was subsequently demonstrated in laboratory microcosms. The consortium was physiologically and phylogenetically characterized by isotope tracer experiments using nonlabeled toluene, [13C]-α-toluene or [13C7]-toluene as growth substrates. Cells incubated with [13C]-α-toluene or [13C7]-toluene incorporated 8–15 at.%13C and 51–57 at.%13C into total lipid fatty acids, respectively, indicating a lower specific incorporation of 13C from [13C7]-toluene. In order to identify the toluene-assimilating bacteria, the incorporation of carbon from both [13C]-α-toluene and [13C7]-toluene into rRNA was analyzed by stable isotope probing. Time and buoyant density-resolved 16S rRNA gene-based terminal restriction fragment length polymorphism profiles, combined with cloning and sequencing, revealed that an uncultured bacterium (99% sequence similarity) related to the genus Desulfocapsa was the main toluene-degrading organism in the consortium. The ratio of the respective terminal restriction fragments changed over time, indicating trophic interactions within this consortium.  相似文献   

8.
1. Increased water motion is expected to reduce boundary layer diffusion resistance of autotrophs, thereby enabling greater isotopic discrimination against 13C such that lower δ13C values (ratio of 13C : 12C) should ensue. A field test of this hypothesis was undertaken by sampling benthic algae in streams of differing current speed.
2. Contrary to the expected negative relationship between δ13C and water motion, filamentous benthic algae were found to exhibit higher δ13C values in rapid water.
3. Under conditions of low current in the streams studied, concentrations of dissolved organic carbon as measured by water colour are elevated through the microbial decomposition of largely terrestrial organic matter. Photoassimilation of this respired carbon by benthic filamentous algae generates 13C‐depletion and lower δ13C values, and appears to be substantial enough in the streams used in the present study to override the competing influence of water motion on boundary layer thickness.  相似文献   

9.
1.  Applying Keeling plot techniques to derive δ13C of respiratory input in a closed non-equilibrated chamber can lead to large errors because steady-state diffusion rules are violated in a non-steady-state environment. To avoid these errors, respiratory δ13C can be derived using equilibrated closed chambers.
2.  We introduce a new method to obtain stem respired CO2δ13C (δst - r) with closed equilibrated stem chambers (E-SC). We present a theoretical model describing the equilibration process, test the model against field data and find excellent agreement. The method is further tested by comparing it with closed non-equilibrated stem chambers (NE-SC); we found no difference between these methods.
3.  Our theoretical model to describe CO2 diffusion from the respiratory pool into the chamber and the equation to derive the δ13C of the efflux are general. They could be applied to other ecosystem components (e.g. soils).
4.  Our method is easy to implement, cost effective, minimizes sources of error and allows for rigorous leak detection. One major limitation is its inability to detect rapid change; the equilibration process requires 15 ± 2 h. A second limitation is that it cannot be used for species that produce abundant pitch at sites of stem wounding (e.g. Pseudotsuga menziesii ).
5.  Investigating δ13C of CO2 respired by different ecosystem components is necessary to interpret δ13C of ecosystem respiration. This parameter has major implications with respect to global carbon cycle science.  相似文献   

10.
1.  The δ13C and δ15N signatures of zooplankton vary with dissolved organic carbon (DOC), but inconsistent and limited taxonomic resolution of previous studies have masked differences that may exist among orders, genera or species and are attributable to dietary and/or habitat differences. Here we investigate differences among the isotopic signatures of five zooplankton taxa ( Daphnia , Holopedium , large Calanoida, small Calanoida and Cyclopoida) in Precambrian shield lakes with a sixfold range of DOC concentration.
2.  δ13C signatures of Daphnia , small calanoids and large calanoids became more depleted with increasing lake DOC, whereas Holopedium and cyclopoid δ13C became enriched with increasing DOC concentration.
3.  The variability of δ13C and δ15N isotopic signatures among zooplankton groups was reduced in high-DOC, compared to low-DOC lakes, especially for δ13C. Differences in δ13C and POM-corrected δ15N accounted for up to 33.7% and 19.5% of the variance, respectively, among lakes of varying DOC concentration.
4.  The narrow range of signatures found in higher DOC lakes suggests that different taxa have similar food sources and/or habitats. In contrast, the wide range of signatures in low-DOC lakes suggests that different taxa are exploiting different food sources and/or habitats. Together with the variable trends in zooplankton isotopic signatures along our DOC gradient, these results suggest that food web dynamics within the zooplankton community of temperate lakes will change as climate and lake DOC concentrations change.  相似文献   

11.
Photosynthetic assimilation of CO2 is a primary source of carbon in soil and root exudates and can influence the community dynamics of rhizosphere organisms. Thus, if carbon partitioning is affected in transgenic crops, rhizosphere microbial communities may also be affected. In this study, the temporal effects of gene transformation on carbon partitioning in rice and rhizosphere microbial communities were investigated under greenhouse conditions using the 13C pulse-chase labeling method and phospholipid fatty acid (PLFA) analysis. The 13C contents in leaves of transgenic (Bt) and nontransgenic (Ck) rice were significantly different at the seedling, booting and heading stages. There were no detectable differences in 13C distribution in rice roots and rhizosphere microorganisms at any point during rice development. Although a significantly lower amount of Gram-positive bacterial PLFAs and a higher amount of Gram-negative bacterial PLFAs were observed in Bt rice rhizosphere as compared with Ck at all plant development stages, there were no significant differences in the amount of individual 13C-PLFA between Bt and Ck rhizospheres at any growing stage. These findings indicate that the insertion of cry1Ab and marker genes into rice had no persistent or adverse effect on the photosynthate distribution in rice or the microbial community composition in its rhizosphere.  相似文献   

12.
Abstract. Steady-state photosynthesis (Pn), post-illumination CO2 release rates (R), sucrose-phosphate synthase (SPS) activities, and levels of starch, sucrose and hexoses were measured in the source leaf of corn ( Zea mays L.) during a 16-h photoperiod at 800 μmol m 2 s 1. Pn and SPS activity remained constant. Carbohydrate pools increased at a linear rate, except the first and last hour of the photoperiod. Both the CO2 evolution rate at the moment of light removal (Rmax) and SPS activity decreased by one half after the onset of darkness (0 60 min). Sucrose diminished during this period by 40%, whereas the starch remained constant. Thereafter, starch mobilization began, followed by a gradual decline in leaf respiration. The average dark export rate was calculated to be 60% less than that during the day. Maintenance respiration (Rm) of an attached leaf after 48 h darkness was determined. Plants were illuminated for different intervals (e.g. 5, 10 or 20 min), each followed by dark periods sufficient for respiration to decline to Rm. The ratio of C assimilated in light to that released in dark was 6:1. After the 48-h dark period, the minimal period of illumination (Tmin) required to restore Pn and Rmax to the original level was determined. A mathematical analysis of the kinetics involved in the recovery of Pn and Rmax provided an estimate of turnover time (0.22h) and pool size 9.15 mmol m 2) for the newly fixed carbon.  相似文献   

13.
Warming climate could affect leaf-level carbon isotope composition (δ13C) through variations in photosynthetic gas exchange. However, it is still unclear to what extent variations in foliar δ13C can be used to detect changes in net primary productivity (NPP) because leaf physiology is only one of many determinants of stand productivity. We aim to examine how well site-mean foliar δ13C and stand NPP co-vary across large resource gradients using data obtained from the Tibetan Alpine Vegetation Transects (1900–4900 m, TAVT). The TAVT data indicated a robust negative correlation between foliar δ13C and NPP across ecosystems (NPP=−2.7224δ13C-67.738, r2=0.60, p<0.001). The mean foliar δ13C decreased with increasing annual precipitation and its covariation with mean temperature and soil organic carbon and nitrogen contents. The results were further confirmed by global literature data. Pooled δ13C data from global literature and this study explained 60% of variations in annual NPP both from TAVT-measures and MODIS-estimates across 67 sites. Our results appear to support a conceptual model relating foliar δ13C and nitrogen concentration (Nmass) to NPP, suggesting that: 1) there is a general (negative) relationship between δ13C and NPP across different water availability conditions; 2) in water-limited conditions, water availability has greater effects on NPP than Nmass; 3) when water is not limiting, NPP increases with increasing Nmass.  相似文献   

14.
The present study investigated the relative importance of leaf and root carbon input for soil invertebrates. Experimental plots were established at the Swiss Canopy Crane (SCC) site where the forest canopy was enriched with 13C depleted CO2 at a target CO2 concentration of c . 540 p.p.m. We exchanged litter between labelled and unlabelled areas resulting in four treatments: (i) leaf litter and roots labelled, (ii) only leaf litter labelled, (iii) only roots labelled and (iv) unlabelled controls. In plots with only 13C-labelled roots most of the soil invertebrates studied were significantly depleted in 13C, e.g. earthworms, chilopods, gastropods, diplurans, collembolans, mites and isopods, indicating that these taxa predominantly obtain their carbon from belowground input. In plots with only 13C-labelled leaf litter only three taxa, including, e.g. juvenile Glomeris spp. (Diplopoda), were significantly depleted in 13C suggesting that the majority of soil invertebrates obtain its carbon from roots. This is in stark contrast to the view that decomposer food webs are based on litter input from aboveground.  相似文献   

15.
Abstract— Glucose metabolism in the superior cervical ganglion for calves has been studied by incubating slices with [1-14C]-, [6-14C]- and [U-14C]-labelled glucose at 37°C and pH 7.4. Glucose utilization and the metabolic partitioning of glucose carbon in products during different incubation periods ranging from 5 to 60 min were determined by isotopic methods.
Separation and identification of labelled compounds have been achieved by anion and cation exchange chromatography as well as by TLC and enzymatic analyses.
From the data obtained a carbon balance could be constructed showing lactate to be the major product of glucose metabolism followed by CO2 and amino acids. Measuring the release of 14CO2 from differently 4C-labelled glucose, the existence of an active pentose phosphate pathway in the ganglion could be demonstrated although this pathway seems to contribute only to a small extent to glucose metabolism. The marked decrease of the C-U: C-6 and the C-U:C-1 ratios in 14CO2 observed in the course of incubation is discussed in terms of a time-dependent change in the rate of synthesis of amino acids which are directly connected with intermediates of the citric acid cycle.  相似文献   

16.
Seasonal patterns of [14C]-labeled photosynthate distribution within two intensively cultured Populus clones with contrasting phenology ( P. tristis × P. balsamifera cv. 'Tristis no. 1'; P. × euramericana cv. Eugenei) were investigated during the establishment year. During active shoot elongation upper mature leaves exported 14C acropetally to the expanding leaves and elongating internodes, and basipetally to the stem. Little 14C was exported to lower mature leaves or lateral branches. At budset the 14C export pattern shifted dramatically in the basipetal direction, i.e., to the lower stem, hardwood cutting, and roots. The timing of budset was the primary factor determining the differences between the clones, except that in all cases Tristis exported more 14C to the roots than Eugenei. After budset lower mature leaves had a similar export pattern to upper leaves, but the quantity of 14C exported to the roots was slightly higher. The results confirm the importance of autumn foliage for root growth in poplar. Clonal differences in seasonal patterns of photosynthate distribution offer potential for the poplar breeder seeking to match a clone's growth pattern with the specific growing season of the site.  相似文献   

17.
Abstract. In the marine environment, the range of values of carbon isotope fractionation between particulate tissue of phytoplankton and inorganic carbon can be more than 20‰ (− 35‰ < δ13C < − 14‰). This review considers the influence of seawater temperature, lipid content of phytoplanktonic cells, kinetic fractionation, and carbon pathway on δ13C values observed at sea.
In order to study the contribution of carboxylases (RUBISCO and the β-carboxylases phosphoenolpyruvate carboxylase, phosphoenoplpyruvate carboxykinase and pyruvate carboxylase) to variations of particulate δ13C values at sea, we present results obtained simultenously on carboxylase activities and δ13C in various environmental conditions. The lowest δ13C values are clearly associated with predominance of ribulose-1.5-bisphosphate carboxylase activity, but it was more difficult to explain the high δ13C values. Different hypotheses are discussed.  相似文献   

18.
Plantago lanceolata L. seedlings were grown in sand microcosm units over a 43‐day experimental period under two CO2 regimes (800 or 400 µmol mol−1) to investigate the effect of elevated atmospheric CO2 concentration on carbon partitioning and exudate release. Total organic carbon (TOC) content of the collected exudate material was measured throughout the experimental period. After 42 days growth the seedlings were labelled with [14C]‐CO2 and the fate of the label within the plant and its release by the roots monitored. Elevated CO2 significantly (P ≤ 0.001) enhanced shoot, root and total dry matter production although the R:S ratio was unaltered, suggesting no alteration in gross carbon partitioning. The cumulative release of TOC (in mg C) over 0‐42 days was unaltered by CO2 treatment however, when expressed as a percentage of net assimilated C, ambient‐grown plants released a significantly (P≤ 0.001) higher percentage from their roots compared to elevated CO2‐grown plants (i.e. 8 vs 3%). The distribution of 14C‐label was markedly altered by CO2 treatment with significantly (P≤ 0.001) greater per cent label partitioned to the roots under elevated CO2. This indicates increased partitioning of recent assimilate below‐ground under elevated CO2 treatment although there was no significant difference in the percentage of 14C‐label released by the roots. Comparison of plant C budgets based on 14C‐pulse‐chase methodology and TOC measurements is discussed.  相似文献   

19.
The sloughed skin from three captive manatees at Lowry Park Zoological Garden (Tampa, Florida) was examined over a period of one year to determine its stable carbon isotopic composition (δ13C). The food consumed by these manatees in a controlled diet was also sampled and its δ13C values determined. The sloughed skin δ13C values from the captive manatees were enriched by an average of +4.1%0 relative to lettuce (generally >98% of the diet) the animals consumed. δ13C values of the skin were shown to be related to changes in δ13C values of the lettuce.
The stable carbon isotopic composition of internal tissues (liver, kidney, and blubber) and skin from dead, stranded manatees was also determined. These values were compared to values of vegetation that manatees are known to eat in the wild. The δ13C values of the internal tissues and skin of wild manatees were consistent with the range of δ13C values of their expected diet.  相似文献   

20.
An application of stable carbon isotope analysis to the mechanistic interpretation of ultraviolet-B (UV-B) effects on growth inhibition is described that is particularly useful for small plants such as Arabidopsis thaliana that are not well suited for gas exchange studies. Many investigators use tissue δ13C, relative abundance of 13C and 12C, as a proxy for water use efficiency and as an indicator of environmental effects on stomatal behaviour and on photosynthesis during growth. Discrimination against 13C is enhanced by both high stomatal conductance and damage to photosynthetic machinery. Because the thinning of the stratospheric ozone layer is permitting more UV-B to enter the biosphere, the mechanisms of action of UV-B radiation on plants are of particular current interest. Arabidopsis thaliana wild-type Landsberg erecta (L er ) and the UV-B-sensitive mutant fah I , deficient in UV-absorbing sinapate esters, were grown in a controlled environment and exposed to UV-BBE doses of 0 or 6–7 kJ m−2 day−1. UV-B exposure decreased dry matter production and δ13C in both genotypes, but growth inhibition was generally greater in fah I than in L er . The fah I mutant also had less leaf greenness than L er . Changes in leaf tissue δ13C were detected before growth inhibition and were evident in treatments of both genotypes that did not cause marked growth effects. This suggests that the effects of UV-B contributing to increased carbon isotope discrimination in L er may have been primarily associated with high stomatal conductance, and in fah I with both high stomatal conductance and damage to photosynthetic machinery.  相似文献   

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