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1.
Stable carbon isotope composition (δ13C) of dry matter has been widely investigated as a selection tool in cereal breeding programmes. However, reports on the possibilities of using stable oxygen isotope composition (δ18O) as a yield predictor are very scarce and only in the absence of water stress. Indeed, it remains to be tested whether changes in phenology and stomatal conductance in response to water stress overrule the use of either δ13C or δ18O when water is limited. To answer this question, a set of 24 genotypes of bread wheat ( Triticum aestivum ) were assayed in two trials with different levels of deficit irrigation and a third trial under rainfed conditions in a Mediterranean climate (northwest Syria). Grain yield (GY) and phenology (duration from planting to anthesis and from anthesis to maturity) were recorded, and the δ13C and δ18O of grains were analysed to assess their suitability as GY predictors. Both δ13C and δ18O showed higher broad-sense heritabilities ( H 2) than GY. Genotype means of GY across trials were negatively correlated with δ13C, as previously reported, but not with δ18O. Both isotopes were correlated with grain filling duration, whereas δ18O was also strongly affected by crop duration from planting to anthesis. We concluded that δ18O of grains is not a proper physiological trait to breed for suboptimal water conditions, as its variability is almost entirely determined by crop phenology. In contrast, δ13C of grains, despite being also affected by phenology, still provides complementary information associated with GY.  相似文献   

2.
Abstract. Tree-ring indices (TRIs) of annual growth rings in stems of Douglas-fir ( Pseudotsuga menziesii ) growing near a copper smelter showed reduced growth during two multi-year time periods in the past. These periods coincided with World Wars I and II, which are known to represent periods of particularly high SO2 emissions from the smelter. Reduced growth was correlated with less negative stable carbon isotope composition (δ13C) in cellulose purified from wood formed in such years. Based on current models for 13C/12C in plants, these results indicate that exposure to air pollution resulted in reduced concentration of CO2 in the intercellular air spaces of the needles. This is consistent with the hypothesis that stomatal closure resulted in impaired photosynthesis and reduced growth during past episodes of high air pollution. The pollution-related change in δ13C was superimposed on a change with time in δ13C, independent of growth, by - 1.4 per mil from 1902 to 1984.  相似文献   

3.
The variations in δ 13C in both leaf carbohydrates (starch and sucrose) and CO2 respired in the dark from the cotyledonary leaves of Phaseolus vulgaris L. were investigated during a progressive drought. As expected, sucrose and starch became heavier (enriched in 13C) with decreasing stomatal conductance and decreasing p i/ p a during the first half (15 d) of the dehydration cycle. Thereafter, when stomata remained closed and leaf net photosynthesis was near zero, the tendency was reversed: the carbohydrates became lighter (depleted in 13C). This may be explained by increased p i/ p a but other possible explanations are also discussed. Interestingly, the variations in δ 13C of CO2 respired in the dark were correlated with those of sucrose for both well-watered and dehydrated plants. A linear relationship was obtained between δ 13C of CO2 respired in the dark and sucrose, respired CO2 always being enriched in 13C compared with sucrose by ≈ 6‰. The whole leaf organic matter was depleted in 13C compared with leaf carbohydrates by at least 1‰. These results suggest that: (i) a discrimination by ≈ 6‰ occurs during dark respiration processes releasing 13C-enriched CO2; and that (ii) this leads to 13C depletion in the remaining leaf material.  相似文献   

4.
Leaves of 407 individuals of Reaumuria soongorica (Pall.) Maxim. collected from the major distribution areas were measured to investigate the distribution characteristics of the stable carbon isotope in this desert plant, as well as correlations between δ^13C values and environmental factors. Results showed that δ^13C values in R. soongorica ranged from -22.77‰ to -29.85‰ and that the mean δ^13C value (-26.52‰) was higher than a previously reported δ^13C value for a different desert ecosystem. This indicates that R. soongorica belongs to the C3 photosynthetic pathway and has higher water use efficiency than other species. The correlations between δ^13C values and environmental factors demonstrated that the foliar δ^13C values in R. soongorica increased significantly with decreasing mean annual precipitation and mean relative humidity, and decreased with decreasing duration of sunshine and evaporation. The spatial distribution trend of δ^13C values in R. soongorica was not obvious and there was no significant correlation between the δ^13C values and mean annual temperature. We conclude that different distribution trends in δ^13C values for R. soongorica were likely caused by stomatal limitation rather than by nutrient-related changes in photosynthetic efficiency and that precipitation played an important role in the wide distribution range of R. soongorica. This pattern of δ^13C values for R. soongorica reinforced that it is a super-xerophil in terms of its adaptive strategies to a desert environment.  相似文献   

5.
1. Growth, density and δ13C of wood and leaf area were measured in two adjacent stands of 6 year-old Eucalyptus globulus growing in the 600–700 mm year–1 rainfall region of south-western Australia. Study sites were identical except for differences in the availability of water owing to physical properties of soil profiles and location of sites within the landscape.
2. Abundance of 13C (expressed as δ13C) in wood of trees growing on the drought-prone site (– 24·8‰±1·4) was greater than in other trees (– 25·8‰±1·2, P <0·001) throughout the 6 years and, with further development, the δ13C signatures of wood may become useful indices of drought-susceptibility in plantations within a few years of establishment. The seasonal pattern of δ13C of wood appeared to reflect seasonal variation in water availability and duration of cambial activity.
3. Basic density of wood of trees growing on the more drought-prone site (496±14·0 kg m–3) was reduced compared to other trees (554±5·3 kg m–3, P <0·001). δ13C of wood across boundaries of growth-rings suggested that drought stopped cambial activity resulting in less production of late wood and less dense wood.
4. The stand growing on the drought-prone site had reduced growth, wood yield and leaf area but identical specific leaf area. Annual growth was correlated with the previous season's rainfall. Together, these results suggested that within the same evaporative climate, drought reduces growth primarily by reducing leaf area and that there is a lag between onset of drought and reduced productivity.  相似文献   

6.
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   

7.
We developed and applied an ecosystem-scale model that calculated leaf CO2 assimilation, stomatal conductance, chloroplast CO2 concentration and the carbon isotope composition of carbohydrate formed during photosynthesis separately for sunlit and shaded leaves within multiple canopy layers. The ecosystem photosynthesis model was validated by comparison to leaf-level gas exchange measurements and estimates of ecosystem-scale photosynthesis from eddy covariance measurements made in a coastal Douglas-fir forest on Vancouver Island. A good agreement was also observed between modelled and measured δ 13C values of ecosystem-respired CO2 ( δ R). The modelled δ R values showed strong responses to variation in photosynthetic photon flux density (PPFD), air temperature, vapour pressure deficit (VPD) and available soil moisture in a manner consistent with leaf-level studies of photosynthetic 13C discrimination. Sensitivity tests were conducted to evaluate the effect of (1) changes in the lag between the time of CO2 fixation and the conversion of organic matter back to CO2; (2) shifts in the proportion of autotrophic and heterotrophic respiration; (3) isotope fractionation during respiration; and (4) environmentally induced changes in mesophyll conductance, on modelled δ R values. Our results indicated that δ R is a good proxy for canopy-level C c/ C a and 13C discrimination during photosynthetic gas exchange, and therefore has several applications in ecosystem physiology.  相似文献   

8.
Quantitative estimates of soil C input under ambient (35 Pa) and elevated (60 Pa) CO2-partial pressure (pCO2) were determined in a Free-Air Carbon dioxide Enrichment (FACE) experiment. To facilitate 13C-tracing, Trifolium repens L. was grown in a soil with an initial δ13C distinct by at least 5‰ from the δ13C of T. repens grown under ambient or elevated pCO2. A shift in δ13C of the soil organic C was detected after one growing season. Calculated new soil C inputs in soil under ambient and elevated pCO2 were 2 and 3 t ha–1, respectively. Our findings suggest that under elevated CO2 conditions, soil C sequestration may be altered by changes in plant biomass production and quality.  相似文献   

9.
1. Changes of δ13C and its relation to leaf development, biochemical content and water stress were monitored over a 2 year period in two co-occurring Mediterranean oak species: the deciduous Quercus pubescens and the evergreen Quercus ilex .
2. The time course of leaf δ13C showed different patterns in the two species. Young Q. pubescens leaves had a high δ13C and a marked decrease occurred during leaf growth. In contrast, leaves at budburst and maturity did not differ significantly in the case of Q. ilex . We suggest that the difference between δ13C of young leaves was linked to differential use of reserves of carbon compounds in the two species.
3. δ13C values of mature leaves were negatively correlated with minimum seasonal values of predawn water potential, suggesting that a functional adjustment to water resources occurred.
4. There was a significant correlation between individual δ13C values for two successive years. This interannual dependence showed that δ13C rankings between trees were constant through time.  相似文献   

10.
We investigated the extent to which plant water and nutrient status are affected by intraspecific competition intensity and microsite quality in a monodominant tussock grassland. Leaf gas exchange and stable isotope measurements were used to assess the water relations of Stipa tenacissima tussocks growing along a gradient of plant cover and soil depth in a semi-arid catchment of Southeast Spain. Stomatal conductance and photosynthetic rate decreased with increasing intensity of competition during the wet growing season, leading to foliar δ 18O and δ 13C enrichment. A high potential for runoff interception by upslope neighbours exerted strong detrimental effects on the water and phosphorus status of downslope S. tenacissima tussocks. Foliar δ 15N values became more enriched with increasing soil depth. Multiple stepwise regression showed that competition potential and/or rhizosphere soil depth accounted for large proportions of variance in foliar δ 13C, δ 18O and δ 15N among target tussocks (57, 37 and 64%, respectively). The results presented here highlight the key role that spatial redistribution of resources (water and nutrients) by runoff plays in semi-arid ecosystems. It is concluded that combined measurement of δ 13C, δ 18O and nutrient concentrations in bulk leaf tissue can provide insight into the intensity of competitive interactions occurring in natural plant communities.  相似文献   

11.
In outdoor common gardens, high latitude populations of deciduous tree species often display higher assimilation rates ( A ) than low latitude populations, but they accomplish less height. To test whether trends in A reflect adaptation to growing season length or, alternatively, are garden growth artefacts, we examined variation in height increment and ecophysiological traits in a range-wide collection of Populus balsamifera L. populations from 21 provenances, during unconstrained growth in a greenhouse. Rooted cuttings, maintained without resource limitation under 21 h photoperiod for 90 d, displayed increasing height growth, A , leaf mass per area and leaf N per area with latitude whereas stomatal conductance ( g s) showed no pattern. Water-use efficiency as indicated by both gas exchange and δ 13C increased with latitude, whereas photosynthetic nitrogen-use efficiency decreased. Differences in δ 13C were less than expected based on A/g s, suggesting coextensive variation in internal conductance ( g m). Analysis of A – C i curves on a subset of populations showed that high latitude genotypes had greater g m than low-latitude genotypes. We conclude that higher peak rates of height growth in high latitude genotypes of balsam poplar are supported by higher A , achieved partly through higher g m, to help compensate for a shorter growing season.  相似文献   

12.
We used stable carbon (δ13C) and nitrogen (δ15N) isotopes to assess the importance of benthic algae for the zooplankton individual growth in winter in a shallow, clear subarctic lake. The δ13C values of calanoid ( Eudiaptomus graciloides ) and cyclopoid ( Cyclops scutifer ) zooplankton in autumn suggest a food resource of pelagic origin during the ice-free period. The zooplankton δ13C values were high in spring compared to autumn. E. graciloides did not grow over winter and the change in δ13C was attributed to a decrease in lipid content during the winter. In contrast, the increase in δ13C values of C. scutifer over the winter was explained by their growth on organic carbon generated by benthic algae. The δ15N of the C. scutifer food resource during winter was low compared to δ15N of the benthic community, suggesting that organic matter generated by benthic algae was mainly channelled to zooplankton via 15N-depleted heterotrophic bacteria. The results demonstrate that benthic algae can sustain zooplankton metabolic demands and growth during long winters, which, in turn, may promote zooplankton growth on pelagic resources during the summer. Such multi-chain omnivory challenges the view of zooplankton as mainly dependent on internal primary production and stresses the importance of benthic resources for the productivity of plankton food webs in shallow lakes.  相似文献   

13.
Water-use efficiency and stable isotope composition were studied in three tropical tree species. Seedlings of Tectona grandis , Swietenia macrophylla and Platymiscium pinnatum were grown at either high or low water supply, and with or without added fertilizer. These three species previously exhibited low, intermediate and high whole-plant water-use efficiency ( TE ) when grown at high water supply in unfertilized soil. Responses of TE to water and nutrient availability varied among species. The TE was calculated as experiment-long dry matter production divided by cumulative water use. Species-specific offsets were observed in relationships between TE and whole-plant 13C discrimination (Δ13Cp). These offsets could be attributed to a breakdown in the relationship between Δ13Cp and the ratio of intercellular to ambient CO2 partial pressures ( c i/ c a) in P. pinnatum , and to variation among species in the leaf-to-air vapour pressure difference ( v ). Thus, a plot of v · TE against c i/ c a showed a general relationship among species. Relationships between δ 18O of stem dry matter and stomatal conductance ranged from strongly negative for S. macrophylla to no relationship for T. grandis . Results suggest inter-specific variation among tropical tree species in relationships between stable isotope ratios ( δ 13C and δ 18O) and the gas exchange processes thought to affect them.  相似文献   

14.
This study investigated the impact of lipid extraction, CaCO3 removal and of both treatments combined on fish tissue δ13C, δ15N and C:N ratio. Furthermore, the suitability of empirical δ13C lipid normalization and correction models was examined. δ15N was affected by lipid extraction (increase of up to 1·65‰) and by the combination of both treatments, while acidification alone showed no effect. The observed shift in δ15N represents a significant bias in trophic level estimates, i.e. lipid-extracted samples are not suitable for δ15N analysis. C:N and δ13C were significantly affected by lipid extraction, proportional to initial tissue lipid content. For both variables, rates of change with lipid content (ΔC:N and Δδ13C) were species specific. All tested lipid normalization and correction models produced biased estimates of fish tissue δ13C, probably due to a non-representative database and incorrect assumptions and generalizations the models were based on. Improved models need a priori more extensive and detailed studies of the relationships between lipid content, C:N and δ13C, as well as of the underlying biochemical processes.  相似文献   

15.
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   

16.
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   

17.
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   

18.
The influence of different feeding levels below and slightly above maintenance on whole body δ13C and δ15N values of Nile tilapia Oreochromis niloticus was examined. The energy budget of each fish was determined by indirect calorimetry. The δ13C values of the lipid-free material of Nile tilapia fed below and slightly above maintenance level did not differ between the feeding groups, but the δ13C values in the lipids and the δ15N values of the lipid-free material showed small but significant differences. Those fish with a negative lipid retention had significantly higher δ13C values in the lipid fraction compared to fish that synthesized fatty acids. There was a significant negative correlation between the amount of energy metabolized by the fish and both the δ13C values in the lipids and the δ15N values of the lipid-free material. Fasting and feeding below the maintenance level may influence the isotopic composition of animals and should therefore be considered in ecological and nutritional studies.  相似文献   

19.
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   

20.
Leaf δ13C is an indicator of water-use efficiency and provides useful information on the carbon and water balance of plants over longer periods. Variation in leaf δ13C between or within species is determined by plant physiological characteristics and environmental factors. We hypothesized that variation in leaf δ13C values among dominant species reflected ecosystem patterns controlled by large-scale environmental gradients, and that within-species variation indicates plant adaptability to environmental conditions. To test these hypotheses, we collected leaves of dominant species from six ecosystems across a horizontal vegetation transect on the Tibetan Plateau, as well as leaves of Kobresia pygmaea (herbaceous) throughout its distribution and leaves of two coniferous tree species ( Picea crassifolia, Abies fabri ) along an elevation gradient throughout their distribution in the Qilian Mountains and Gongga Mountains, respectively. Leaf δ13C of dominant species in the six ecosystems differed significantly, with values for evergreen coniferous13C values of the dominant species and of K. pygmaea were negatively correlated with annual precipitation along a water gradient, but leaf δ13C of A. fabri was not significantly correlated with precipitation in habitats without water-stress. This confirms that variation of δ13C between or within species reflects plant responses to environmental conditions. Leaf δ13C of the dominant species also reflected water patterns on the Tibetan Plateau, providing evidence that precipitation plays a primary role in controlling ecosystem changes from southeast to northwest on the Tibetan Plateau.  相似文献   

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