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1.
The interspecific variability of sunlit leaf carbon isotope composition (δ13C), an indicator of leaf intrinsic water-use efficiency (WUE, CO2 assimilation rate/leaf conductance for water vapour), was investigated in canopy trees of three lowland rainforest stands
in French Guiana, differing in floristic composition and in soil drainage characteristics, but subjected to similar climatic
conditions. We sampled leaves with a rifle from 406 trees in total, representing 102 species. Eighteen species were common
to the three stands. Mean species δ13C varied over a 6.0‰ range within each stand, corresponding to WUE varying over about a threefold range. Species occurring
in at least two stands displayed remarkably stable δ13C values, suggesting a close genetic control of species δ13C. Marked differences in species δ13C values were found with respect to: (1) the leaf phenology pattern (average δ13C=–29.7‰ and –31.0‰ in deciduous-leaved and evergreen-leaved species, respectively), and (2) different types of shade tolerance
defined by features reflecting the plasticity of growth dynamics with respect to contrasting light conditions. Heliophilic
species exhibited more negative δ13C values (average δ13C=–30.5‰) (i.e. lower WUE) than hemitolerant species (–29.3‰). However, tolerant species (–31.4‰) displayed even more negative
δ13C values than heliophilic ones. We could not provide a straightforward ecophysiological interpretation of this result. The
negative relationship found between species δ13C and midday leaf water potential (Ψwm) suggests that low δ13C is associated with high whole tree leaf specific hydraulic conductance. Canopy carbon isotope discrimination (Δ
A
) calculated from the basal area-weighed integral of the species δ13C values was similar in the three stands (average Δ
A
=23.1‰), despite differences in stand species composition and soil drainage type, reflecting the similar proportions of the
three different shade-tolerance types among stands.
Received: 30 November 1999 / Accepted: 23 March 2000 相似文献
2.
Coupling 13C natural abundance and 14C pulse labelling enabled us to investigate the dependence of 13C fractionation on assimilate partitioning between shoots, roots, exudates, and CO2 respired by maize roots. The amount of recently assimilated C in these four pools was controlled by three levels of nutrient
supply: full nutrient supply (NS), 10 times diluted nutrient supply (DNS), and deionised water (DW). After pulse labelling
of maize shoots in a 14CO2 atmosphere, 14C was traced to determine the amounts of recently assimilated C in the four pools and the δ13C values of the four pools were measured. Increasing amounts of recently assimilated C in the roots (from 8% to 10% of recovered
14C in NS and DNS treatments) led to a 0.3‰ 13C enrichment from NS to DNS treatments. A further increase of C allocation in the roots (from 10% to 13% of recovered 14C in DNS and DW treatments) resulted in an additional enrichment of the roots from DNS to DW treatments by 0.3‰. These findings
support the hypothesis that 13C enrichment in a pool increases with an increasing amount of C transferred into that pool. δ13C of CO2 evolved by root respiration was similar to that of the roots in DNS and DW treatments. However, if the amount of recently
assimilated C in root respiration was reduced (NS treatment), the respired CO2 became 0.7‰ 13C depleted compared to roots. Increasing amounts of recently assimilated C in the CO2 from NS via DNS to DW treatments resulted in a 1.6‰ δ13C increase of root respired CO2 from NS to DW treatments. Thus, for both pools, i.e. roots and root respiration, increasing amounts of recently assimilated
C in the pool led to a δ13C increase. In DW and DNS plants there was no 13C fractionation between roots and exudates. However, high nutrient supply decreased the amount of recently assimilated C in
exudates compared to the other two treatments and led to a 5.3‰ 13C enrichment in exudates compared to roots. We conclude that 13C discrimination between plant pools and within processes such as exudation and root respiration is not constant but strongly
depends on the amount of C in the respective pool and on partitioning of recently assimilated C between plant pools.
Section Editor: H. Lambers 相似文献
3.
Spatial patterns of foliar stable carbon isotope compositions of C<Subscript>3</Subscript> plant species in the Loess Plateau of China 总被引:1,自引:0,他引:1
The spatial pattern of foliar stable carbon isotope compositions (δ13C) of dominant species and their relationships with environmental factors in seven sites, Yangling, Yongshou, Tongchuan, Fuxian,
Ansai, Mizhi and Shenmu, standing from south to north in the Loess Plateau of China, was studied. The results showed that
in the 121 C3 plant samples collected from the Loess Plateau, the foliar δ13C value ranged from −22.66‰ to −30.70‰, averaging −27.04‰. The foliar δ13C value varied significantly (P<0.01) among the seven sites, and the average δ13C value increased by about 1.69‰ from Yangling in the south to Shenmu in the north as climatic drought increased. There was
a significant difference in foliar δ13C value among three life-forms categorized from all the plant samples in the Loess Plateau (P<0.001). The trees (−26.74‰) and shrubs (−26.68‰) had similar mean δ13C values, both significantly (P<0.05) higher than the mean δ13C value of herbages (−27.69‰). It was shown that the trees and shrubs had higher WUEs and employed more conservative water-use
patterns to survive drier habitats in the Loess Plateau. Of all the C3 species in the Loess Plateau, the foliar δ13C values were significantly and negatively correlated with the mean annual rainfall (P<0.001) and mean annual temperature (P<0.05), while being significantly and positively correlated with the latitude (P<0.001) and the annual solar radiation (P<0.01). In general, the foliar δ13C values increased as the latitude and solar radiation increased and the rainfall and temperature decreased. The annual rainfall
as the main influencing factor could explain 13.3% of the spatial variations in foliar δ13C value. A 100 mm increment in annual rainfall would result in a decrease by 0.88‰ in foliar δ13C values. 相似文献
4.
Discrimination between12C and13C by marine plants 总被引:2,自引:0,他引:2
Summary The natural abundance13C/12C ratios (as δ13C) of organic matter of marine macroalgae from Fife and Angus (East Scotland) were measured for comparison with the species'
ability to use CO2 and HCO
3
-
for photosynthesis, as deduced from previously published pH-drift measurements. There was a clear difference in δ13C values for species able or unable to use HCO
3
-
. Six species of Chlorophyta, 12 species of Phaeophyta and 8 species of Rhodophyta that the pH-drift data suggested could
use HCO
3
-
had δ13C values in the range -8.81‰ to -22.55‰. A further 6 species of Rhodophyta which the pH-drift data suggested could only use
CO2 had δ13C values in the range -29.90‰ to-34.51‰. One of these six species (Lomentaria articulata) is intertidal; the other five are subtidal and so have no access to atmospheric CO2 to complicate the analysis. For these species, calculations based on the measured δ13C of the algae, the δ13C of CO2 in seawater, and the known13C/12C discrimination of CO2 diffusion and RUBISCO carboxylation suggest that only 15–21% of the limitation to photosynthesisin situ results from CO2 diffusion from the bulk medium to the plastids; the remaining 79–85% is associated with carboxylation reactions (and, via
feedback effects, down-stream processes). This analysis has been extended for one of these five species,Delesseria sanguinea, by incorporating data onin situ specific growth rates, respiratory rates measured in the laboratory, and applying Fick's law of diffusion to calculate a
boundary layer thickness of 17–24 μm. This value is reasonable for aDelesseria sanguinea frondin situ. For HCO
3
-
-using marine macroalgae the range of δ13C values measured can be accommodated by a CO2 efflux from algal cells which range from 0.306 of the gross HCO
3
-
influx forEnteromorpha intestinalis (δ13C=-8.81‰) in a rockpool to 0.787 forChondrus crispus (δ13C=-22.55‰). The relatively high computed CO2 efflux for those HCO
3
-
-users with the more negative δ13C values implies a relatively high photon cost of C assimilation; the observed photon costs can be accommodated by assuming
coupled, energy-independent inorganic carbon influx and efflux. The observed δ13C values are also interpreted in terms of water movement regimes and obtaining CO2 from the atmosphere. Published δ13C values for freshwater macrophytes were compared with the ability of the species to use CO2 and HCO
3
-
and again there was an apparent separation in δ13C values for these two groups. δ13C values obtained for marine macroalgae for which no pH-drift data are available permit predictions, as yet untested, as to
whether they use predominantly CO2 or HCO
3
- 相似文献
5.
The mechanisms behind the 13C enrichment of organic matter with increasing soil depth in forests are unclear. To determine if 13C discrimination during respiration could contribute to this pattern, we compared δ13C signatures of respired CO2 from sieved mineral soil, litter layer and litterfall with measurements of δ13C and δ15N of mineral soil, litter layer, litterfall, roots and fungal mycelia sampled from a 68-year-old Norway spruce forest stand
planted on previously cultivated land. Because the land was subjected to ploughing before establishment of the forest stand,
shifts in δ13C in the top 20 cm reflect processes that have been active since the beginning of the reforestation process. As 13C-depleted organic matter accumulated in the upper soil, a 1.0‰ δ13C gradient from −28.5‰ in the litter layer to −27.6‰ at a depth of 2–6 cm was formed. This can be explained by the 1‰ drop
in δ13C of atmospheric CO2 since the beginning of reforestation together with the mixing of new C (forest) and old C (farmland). However, the isotopic
change of the atmospheric CO2 explains only a portion of the additional 1.0‰ increase in δ13C below a depth of 20 cm. The δ13C of the respired CO2 was similar to that of the organic matter in the upper soil layers but became increasingly 13C enriched with depth, up to 2.5‰ relative to the organic matter. We hypothesise that this 13C enrichment of the CO2 as well as the residual increase in δ13C of the organic matter below a soil depth of 20 cm results from the increased contribution of 13C-enriched microbially derived C with depth. Our results suggest that 13C discrimination during microbial respiration does not contribute to the 13C enrichment of organic matter in soils. We therefore recommend that these results should be taken into consideration when
natural variations in δ13C of respired CO2 are used to separate different components of soil respiration or ecosystem respiration. 相似文献
6.
Voigt CC Grasse P Rex K Hetz SK Speakman JR 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2008,178(1):9-16
We analysed the stable carbon isotope ratio in exhaled CO2 (δ13Cbreath) of free-ranging vampires to assess the type of metabolized substrate (endogenous or exogenous substrate) and its origin,
i.e. whether the carbon atoms came from a C4 food web (grass and cattle) or the C3 food web in which they were captured (a rainforest remnant and its mammals). For an improved understanding of factors influencing
the δ13Cbreath of vampires, we conducted feeding experiments with captive animals. The mean δ13Cbreath of starved bats was depleted in 13C in relation to the diet by 4.6‰ (n = 10). Once fed with blood, δ13Cbreath levelled off within a short time approximately 2.2‰ above the stable carbon isotope signature of the diet. The median time
required to exchange 50% of the carbon atoms in exhaled CO2 with carbon atoms from the ingested blood was 18.6 min (mean 29.5 ± 19.0 min, n = 5). The average δ13C of wing membrane and fur in free-ranging vampire bats suggested that bats almost exclusively foraged for cattle blood during
the past weeks. The δ13Cbreath of the same bats averaged −19.1‰. Given that all free-ranging vampires were starving and that the δ13C of cattle was more in enriched in 13C by 5–6‰ than the δ13Cbreath of vampires, we conclude that the vampire bats of our study metabolised fat that was predominantly built from carbon atoms
originating from cattle blood. Since δ13C of wing membrane and fur integrates over weeks and months respectively and δ13Cbreath over hours and days, we also conclude that vampire bats of the studied population consistently ignored rainforest mammals
and chose cattle as their prey during and prior to our study. 相似文献
7.
Researchers will be able to use stable isotope analysis to study community structure in an efficient way, without a need for extensive calibrations, if isotopic enrichment values are consistent, or if variation in enrichment values can be predicted. In this study, we generated an experimental data set of δ15N and δ13C enrichment means for 22 terrestrial herbivorous arthropods feeding on 18 different host plants. Mean enrichments observed across a single trophic transfer (plants to herbivores) were −0.53±0.26‰ for δ13C (range: −3.47‰ to 1.89‰) and 1.88±0.37‰ for δ15N (range: −0.20‰ to 6.59‰). The mean δ13C enrichment was significantly lower than that reported in recent literature surveys, whereas the mean δ15N enrichment was not significantly different. The experimental data set provided no support for recent hypotheses advanced to explain variation in enrichment values, including the proposed roles for consumer feeding mode, development type, and diet C:N ratio. A larger data set, formed by combining our experimental data with data from the literature, did suggest possible roles for feeding mode, nitrogen recycling, herbivore life stage, and host plant type. Our results indicate that species enrichment values are variable even in this relatively narrow defined group of organisms and that our ability to predict enrichment values of terrestrial herbivorous arthropods based on physiological, ecological, or taxonomic traits is low. The primary implications are that (1) mean enrichment may have to be measured empirically for each trophic link of interest, rather than relying on estimates from a broad survey of animal taxa and (2) the advantage of using stable isotope analysis to probe animal communities that are recalcitrant to other modes of study will be somewhat diminished as a consequence.Electronic Supplementary Material Supplementary material is available for this article at 相似文献
8.
Long-term management plans for restoration of natural flow conditions through the Everglades increase the importance of understanding
potential nutrient impacts of increased freshwater delivery on Florida Bay biogeochemistry. Planktonic communities respond
quickly to changes in water quality, thus spatial variability in community composition and relationships to nutrient parameters
must be understood in order to evaluate future downstream impacts of modifications to Everglades hydrology. Here we present
initial results combining flow cytometry analyses of phytoplankton and bacterial populations (0.1–50 μm size fraction) with measurements of δ13C and δ15N composition and dissolved inorganic nutrient concentrations to explore proxies for planktonic species assemblage compositions
and nutrient cycling. Particulate organic material in the 0.1–50 μm size fraction was collected from five stations in Northeastern and Western Florida Bay to characterize spatial variability
in species assemblage and stable isotopic composition. A dense bloom of the picocyanobacterium, Synechococcus elongatus, was observed at Western Florida Bay sites. Smaller Synechococcus sp. were present at Northeast sites in much lower abundance. Bacteria and detrital particles were also more abundant at Western
Florida Bay stations than in the northeast region. The highest abundance of detritus occurred at Trout Creek, which receives
freshwater discharge from the Everglades through Taylor Slough. In terms of nutrient availability and stable isotopic values,
the S. elongatus population in the Western bay corresponded to low DIN (0.5 μM NH
4
+
; 0.2 μM NO
3
−
) concentrations and depleted δ15N signatures ranging from +0.3 to +0.8‰, suggesting that the bloom supported high productivity levels through N2-fixation. δ15N values from the Northeast bay were more enriched (+2.0 to +3.0‰), characteristic of N-recycling. δ13C values were similar for all marine Florida Bay stations, ranging from −17.6 to −14.4‰, however were more depleted at the
mangrove ecotone station (−25.5 to −22.3‰). The difference in the isotopic values reflects differences in carbon sources.
These findings imply that variations in resource availability and nutrient sources exert significant control over planktonic
community composition, which is reflected by stable isotopic signatures. 相似文献
9.
The natural relationship13C/12C determined in three soil profiles under grass vegetation indicated a depletion in organic13C at depth: theδ
13C was between −18‰ and −15‰ in the A horizons and ranged from −18 to −22‰ at depth. Previous work showed that in forest soils,
whereδ
13C was near −28‰ in the upper horizon, there was, on the contrary, a relative enrichment of the lower strata. This meant thatδ
13C, initially different in the various topsoils, became more equal at depth. Comparison between dark, deep horizons (sombric
horizons), which are certainly of illuvial origine, would confirm this:δ
13C of grassland and a forest sombric horizon were almost equal at around −22‰. These results might mean that, in natural ecosystems,
the isotopic carbon composition of the soil underlying humus would be independent of the vegetation type. This would have
practical implications for the use of13C as a tracer for soil organic matter studies. 相似文献
10.
In theory, carbon is highly mobile in aquatic systems. Recent evidence from carbon stable isotopes of crabs (Parasesarma erythrodactyla and Australoplax tridentata), however, shows that in subtropical Australian waters, measurable carbon movement between adjacent mangrove and saltmarsh habitats is limited to no more than a few metres. We tested whether the pattern in crab δ13C values across mangrove and saltmarsh habitats was explained by crab movement, or the movement of particulate organic matter. We estimated crab movement in a mark–recapture program using an array of pitfall traps on 13 transects (a total of 65 traps) covering an area of 600 m2 across the interface of these two habitats. Over a 19-day period, the majority of crabs (91% for P. erythrodactyla, 93% for A. tridentata) moved <2 m from the place of initial capture. Crab movement cannot, therefore, explain the patterns in δ13C values of crabs. δ13C values of detritus collected at 2-m intervals across the same habitat interface fitted a sigmoidal curve of a similar form to that fitting the δ13C values of crabs. δ13C values of detritus were 2–4‰ more depleted in saltmarsh (−18.5±0.6‰), and 4–7‰ more depleted in mangroves (−25.9±0.1‰) than δ13C values of crabs recorded previously in each habitat. Assimilation by crabs of very small detrital fragments or microphytobenthos, more enriched in 13C, may explain the disparity in δ13C values. Nevertheless, the pattern in δ13C values of detritus suggests that crabs obtain their carbon from up to several metres away, but without themselves foraging more then a metre or so from their burrow. Such detailed measurements of carbon movement in estuaries provide a spatially explicit understanding of the functioning of food webs in saltmarsh and mangrove habitats. 相似文献
11.
Primary production by phytoplankton in the eutrophic Mikawa Bay, Japan, was studied by simultaneous measurements of natural
carbon isotope ratio (δ
13C) and short-term carbon uptake rates (13C tracer study) of size-fractionated nannoplankton (<10 μm) and net plankton (>10 μm) samples. Short-term photosynthetic rates,
which represent the physiological state of algae, were variable regardless of standing stock sizes. Theδ
13C values of particulate organic carbon (POC) in June and July displayed horizontal variations for both the net plankton fraction
(−19.8 to −12.7‰) and the nannoplankton fraction (−22.0 to −12.8‰). For both fractions, low concentrations of POC had more
negativeδ
13C values (−22 to −18‰). Highδ
13C values for the net plankton were found when POC concentrations were much higher, due to red tide. This suggests that the
increase in algal standing crop for the net plankton fraction resulted from accelerated photosynthetic activity. However the
nannoplankton fractions with higher POC values have relatively lowδ
13C values. 相似文献
12.
Desert plants have unique strategies for survival and growth to cope with the limited water availability in arid regions.
The stable carbon isotope (δ
13C) provides an integrated measurement of internal plant physiological and external environmental properties affecting photosynthetic
gas exchange and water use efficiency. The δ
13C values of 84 species in the Junggar Basin were categorized into two groups (ranged from −30.1 to −23.3‰ for C3 and −14.9 to −9.9‰ for C4 species, respectively). No life form differences in δ
13C values were detected in C3 (p = 0.78) and C4 plants (p = 0.63). Small differences among life forms were observed in δ
13C values in C4 species with shrubs slightly depleted (−13.3‰) relative to perennials (−13.1‰) and annuals (−12.5‰). These differences suggested
that δ
13C value could not represent a plant functional group classification based on life forms in C4 plants in extremely arid regions. Ephemerals are all using C3 photosynthetic pathway and no significant differences (p = 0.92) in δ
13C values were observed between annuals (−26.5‰) and perennials (−26.4‰). The δ
13C values of Tulipa iliensis (an important ephemeral species distributed widely in the Junggar Basin) among nine natural populations were positively correlated
with leaf (r
2 = 0.46, p = 0.046) and soil (r
2 = 0.67, p = 0.007) total nitrogen content, and negatively correlated with leaf (r
2 = 0.48, p = 0.039) and soil (r
2 = 0.79, p = 0.001) water content. This indicated that the variation in δ
13C values of T. iliensis was probably caused by both water availability associated stomatal openness and nitrogen availability associated photosynthetic
capacity. T. iliensis is very sensitive to water and nitrogen availability in soil. 相似文献
13.
Peter D. Erskine Dana M. Bergstrom Susanne Schmidt George R. Stewart Craig E. Tweedie Justine D. Shaw 《Oecologia》1998,117(1-2):187-193
Plants collected from diverse sites on subantarctic Macquarie Island varied by up to 30‰ in their leaf δ15N values. 15N natural abundance of plants, soils, animal excrement and atmospheric ammonia suggest that the majority of nitrogen utilised
by plants growing in the vicinity of animal colonies or burrows is animal-derived. Plants growing near scavengers and animal
higher in the food chain had highly enriched δ15N values (mean = 12.9‰), reflecting the highly enriched signature of these animals' excrement, while plants growing near nesting
penguins and albatross, which have an intermediate food chain position, had less enriched δ15N values (>6‰). Vegetation in areas affected by rabbits had lower δ15N values (mean = 1.2‰), while the highly depleted δ15N values (below −5‰) of plants at upland plateau sites inland of penguin colonies, suggested that a portion of their nitrogen
is derived from ammonia (mean 15N =−10‰) lost during the degradation of penguin guano. Vegetation in a remote area had δ15N values near −2‰. These results contrast with arctic and subarctic studies that attribute large variations in plant 15N values to nitrogen partitioning in nitrogen-limited environments. Here, plant 15N reflects the 15N of the likely nitrogen sources utilised by plants.
Received: 18 December 1997 / Accepted: 13 June 1998 相似文献
14.
Influence of stand structure on carbon-13 of vegetation, soils, and canopy air within deciduous and evergreen forests in Utah, United States 总被引:15,自引:0,他引:15
Carbon isotope ratios (δ13C) were studied in evergreen and deciduous forest ecosystems in semi-arid Utah (Pinus contorta, Populus tremuloides, Acer negundo and Acer grandidentatum). Measurements were taken in four to five stands of each forest ecosystem differing in overstory leaf area index (LAI) during
two consecutive growing seasons. The δ13Cleaf (and carbon isotope discrimination) of understory vegetation in the evergreen stands (LAI 1.5–2.2) did not differ among canopies
with increasing LAI, whereas understory in the deciduous stands (LAI 1.5–4.5) exhibited strongly decreasing δ13Cleaf values (increasing carbon isotope discrimination) with increasing LAI. The δ13C values of needles and leaves at the top of the canopy were relatively constant over the entire LAI range, indicating no
change in intrinsic water-use efficiency with overstory LAI. In all canopies, δ13Cleaf decreased with decreasing height above the forest floor, primarily due to physiological changes affecting c
i/c
a (> 60%) and to a minor extent due to δ13C of canopy air (< 40%). This intra-canopy depletion of δ13Cleaf was lowest in the open stand (1‰) and greatest in the denser stands (4.5‰). Although overstory δ13Cleaf did not change with canopy LAI, δ13C of soil organic carbon increased with increasing LAI in Pinus contorta and Populus tremuloides ecosystems. In addition, δ13C of decomposing organic carbon became increasingly enriched over time (by 1.7–2.9‰) for all deciduous and evergreen dry temperate
forests. The δ13Ccanopy of CO2 in canopy air varied temporally and spatially in all forest stands. Vertical canopy gradients of δ13Ccanopy, and [CO2]canopy were larger in the deciduous Populus tremuloides than in the evergreen Pinu contorta stands of similar LAI. In a very wet and cool year, ecosystem discrimination (Δe) was similar for both deciduous Populus tremulodies (18.0 ± 0.7‰) and evergreen Pinus contorta (18.3 ± 0.9‰) stands. Gradients of δ13Ccanopy and [CO2]canopy were larger in denser Acer spp. stands than those in the open stand. However, 13C enrichment above and photosynthetic draw-down of [CO2]canopy below tropospheric baseline values were larger in the open than in the dense stands, due to the presence of a vigorous understory
vegetation. Seasonal patterns of the relationship δ13Ccanopy versus 1/[CO2]canopy were strongly influenced by precipitation and air temperature during the growing season. Estimates of Δe for Acer spp. did not show a significant effect of stand structure, and averaged 16.8 ± 0.5‰ in 1933 and 17.4 ± 0.7‰ in 1994. However,
Δe varied seasonally with small fluctuations for the open stand (2‰), but more pronounced changes for the dense stand (5‰).
Received: 15 April 1996 / Accepted: 19 October 1996 相似文献
15.
Interseasonal comparison of CO2 concentrations, isotopic composition, and carbon dynamics in an Amazonian rainforest (French Guiana) 总被引:2,自引:0,他引:2
Canopy CO2 concentrations in a tropical rainforest in French Guiana were measured continuously for 5 days during the 1994 dry season
and the 1995 wet season. Carbon dioxide concentrations ([CO2]) throughout the canopy (0.02–38 m) showed a distinct daily pattern, were well-stratified and decreased with increasing height
into the canopy. During both seasons, daytime [CO2] in the upper and middle canopy decreased on average 7–10 μmol mol−1 below tropospheric baseline values measured at Barbados. Within the main part of the canopy (≥ 0.7 m), [CO2] did not differ between the wet and dry seasons. In contrast, [CO2] below 0.7 m were generally higher during the dry season, resulting in larger [CO2] gradients. Supporting this observation, soil CO2 efflux was on average higher during the dry season than during the wet season, either due to diffusive limitations and/or
to oxygen deficiency of root and microbial respiration. Soil respiration rates decreased by 40% after strong rain events,
resulting in a rapid decrease in canopy [CO2] immediately above the forest floor of about 50␣μmol mol−1. Temporal and spatial variations in [CO2]canopy were reflected in changes of δ13Ccanopy and δ18Ocanopy values. Tight relationships were observed between δ13C and δ18O of canopy CO2 during both seasons (r
2 > 0.86). The most depleted δ13Ccanopy and δ18Ocanopy values were measured immediately above the forest floor (δ13C = −16.4‰; δ18O = 39.1‰ SMOW). Gradients in the isotope ratios of CO2 between the top of the canopy and the forest floor ranged between 2.0‰ and 6.3‰ for δ13C, and between 1.0‰ and 3.5‰ for δ18O. The δ13Cleaf and calculated c
i/c
a of foliage at three different positions were similar for the dry and wet seasons indicating that the canopy maintained a
constant ratio of photosynthesis to stomatal conductance. About 20% of the differences in δ13Cleaf within the canopy was accounted for by source air effects, the remaining 80% must be due to changes in c
i/c
a. Plotting 1/[CO2] vs. the corresponding δ13C ratios resulted in very tight, linear relationships (r
2 = 0.99), with no significant differences between the two seasons, suggesting negligible seasonal variability in turbulent
mixing relative to ecosystem gas exchange. The intercepts of these relationships that should be indicative of the δ13C of respired sources were close to the measured δ13C of soil respired CO2 and to the δ13C of litter and soil organic matter. Estimates of carbon isotope discrimination of the entire ecosystem, Δe, were calculated as 20.3‰ during the dry season and as 20.5‰ during the wet season.
Received: 3 March 1996 / Accepted: 19 October 1996 相似文献
16.
Food web structure of a shallow eutrophic lake (Lake Taihu,China) assessed by stable isotope analysis 总被引:1,自引:0,他引:1
Lake Taihu is a large, shallow, and eutrophic lake in China. It has provided local communities with valuable fisheries for
centuries, but little is known of the trophodynamics, or of its faunal communities. Carbon and nitrogen isotopic composition
was used to assess its trophic pathways and the food web structure [food sources and trophic levels (TL)]. Basal food sources
were distinguishable based on their δ13C values, ranging from −27.2 to −15.2‰. Consumers were also well separated in δ13C (−26.9 to −17.9‰ for invertebrates and −25.7 to −18.1‰ for fishes), which allowed for an effective discrimination of carbon
sources between these fauna. An average trophic enrichment factor of 3.4‰ was used to calculate the TLs based on δ15N of zooplankton, with results indicating a food web having four TLs. Although δ15N values overlap and cover a large range within trophic compartments, the isotopic signatures of the species assessed revealed
a general trend of 15N enrichment with increasing TL. Stable isotope signatures were also used to establish a general food web scheme in which
five main trophic pathways were analyzed. 相似文献
17.
Palaeozoic cold seep carbonates from Europe and North Africa—an integrated isotopic and geochemical approach 总被引:1,自引:0,他引:1
In this paper, we report the highest and lowest carbon isotope values known from Palaeozoic carbonate rocks. These unusual δ13C values (−50 to +23.5‰) are due to microbial methanogenesis and methanotrophy in Silurian to Carboniferous carbonates. Trace elements were used to decipher the primary mineralogy of the carbonate cements. Very high Sr values and low amounts of Mg, Fe and Mn point toward aragonite precursors, whereas high Fe and Mn values are indicative of primary calcites and allow reconstruction of the redox conditions. Four carbonate deposits are described from the Meseta and the Antiatlas of Morocco, the Pyrenees (France) and the Harz mountains (Germany). The highest δ13C values in concretion below the uppermost Silurian Spinatrypa Mound (Moroccan Meseta) give evidence, that CO2 was produced during methanogenesis. δ13C values between −10 and −32‰indicate that the formation of microbial carbonates and cements in the Middle Devonian Hollard Mound (Antiatlas) and in the Lower Carboniferous sediments of the Iberg (Harz) formed at thermogenetic methane or petroleum seeps. The Late Bashkirian carbonate mound of the High Pyrenees (Tantes Mound) is the first Palaeozoic carbonate with seepage fluids being dominated by biogenic methane. Matrix carbonates exhibit δ13C values as low as −34‰. In some parts, voids make up more than 50 vol% of the mound. They are filled with several generations of cement. The earliest void filling is isopachous fibrous cement, which represents former aragonite. Most negative δ13C values of −50‰were measured in these isopachous fibrous cements. The difference of 55‰in δ13C values between normal sediments and early aragonite cements can only be explained by the contribution of CO2 from anaerobic oxidation of biogenic methane in a cold seep setting. 相似文献
18.
Our objective was to evaluate the relative importance of gradients in light intensity and the isotopic composition of atmospheric
CO2 for variation in leaf carbon isotope ratios within a Pinus resinosa forest. In addition, we measured photosynthetic gas exchange and leaf carbon isotope ratios on four understory species (Dryopteris carthusiana, Epipactus helleborine, Hieracium floribundum, Rhamnus frangula), in order to estimate the consequence of the variation in the understory light microclimate for carbon gain in these plants.
During midday, CO2 concentration was relatively constant at vertical positions ranging from 15 m to 3 m above ground. Only at positions below
3 m was CO2 concentration significantly elevated above that measured at 15 m. Based on the strong linear relationship between changes
in CO2 concentration and δ13C values for air samples collected during a diurnal cycle, we calculated the expected vertical profile for the carbon isotope
ratio of atmospheric CO2 within the forest. These calculations indicated that leaves at 3 m height and above were exposed to CO2 of approximately the same isotopic composition during daylight periods. There was no significant difference between the daily
mean δ13C values at 15 m (–7.77‰) and 3 m (–7.89‰), but atmospheric CO2 was significantly depleted in 13C closer to the ground surface, with daily average δ13C values of –8.85‰ at 5 cm above ground. The light intensity gradient in the forest was substantial, with average photosynthetically
active radiation (PAR) on the forest floor approximately 6% of that received at the top of the canopy. In contrast, there
were only minor changes in air temperature, and so it is likely that the leaf-air vapour pressure difference was relatively
constant from the top of the canopy to the forest floor. For red pine and elm tree samples, there was a significant correlation
between leaf δ13C value and the height at which the leaf sample was collected. Leaf tissue sampled near the forest floor, on average, had
lower δ13C values than samples collected near the top of the canopy. We suggest that the average light intensity gradient through the
canopy was the major factor influencing vertical changes in tree leaf δ13C values. In addition, there was a wide range of variation (greater than 4‰) among the four understory plant species for average
leaf δ13C values. Measurements of leaf gas exchange, under natural light conditions and with supplemental light, were used to estimate
the influence of the light microclimate on the observed variation in leaf carbon isotope ratios in the understory plants.
Our data suggest that one species, Epipactus helleborine, gained a substantial fraction of carbon during sunflecks.
Received: 21 March 1996 / Accepted: 13 August 1996 相似文献
19.
S. I. Kiyashko T. A. Velivetskaya A. V. Ignatiev 《Russian Journal of Marine Biology》2011,37(4):297-302
Stable isotope ratios of sulfur (34S/32S), carbon (13C/12C), and nitrogen (15N/14N) were analyzed in the soft tissues of 12 common species of fish from the near-shore waters of the Peter the Great Bay in
the Sea of Japan. The average δ13C values of individual species varied from −20.7‰ for planktivorous fish to −16.8‰ for benthivorous fish, reflecting the growing
relative contribution of benthic primary producers to fish nutrition. The majority of the various species representatives
studied can be assigned to one trophic level, as indicated by their narrow range of δ15N values (9.9 to 12.6‰). Large interspecific variations were found in the sulfur stable isotope ratios of fish (the mean δ34S values ranged from 11.2 to 19.5‰). This is the result of the different contributions to fish nutrition of infaunal invertebrates
that are depleted in 34S due to the microbial food chain of the bottom sediments. 相似文献
20.
The relative abundance of carbon isotope (δ13C) was measured in four C3 species (Sophora viccifolia, Quercus liaotungensis, Ostryopsis davidiana and Zizyphus jujuba var. spinosa) of the Loess Plateau in China from the 1930’s to 2002. The results showed that the δ13C values in the four species varied from −25.05‰ to −29.75‰ with their a average at −27.04‰. A decrease in the δ13C value with time was found in all the four species, which indicating that the water use efficiencies (WUEs) of all the measured
species declined during 70 years. However, the decrease in δ13C value differed among the four species with its significant decreases measured in two of the species, Sophora viciifolia and Quercus liaotungensis, its relatively significant decrease found in Ostryopsis davidiana, and its slight decrease appearing in Zizyphus jujuba var. spinosa. in the δ13C values in the four species decreased by 14.65 ‰, 14.46‰, 11.99‰ and 2.44‰, respectively. The different species were shown
to have different sensitivities to climatic change, and Zizyphus jujuba var. spinosa was found to be the most drought-tolerant species of the four, which had a high WUE. 相似文献