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1.
Abstract
Freshwater ecosystems derive organic carbon from both allochthonous and autochthonous sources. We studied the relative contributions
of different carbon sources to zooplankton in a small, polyhumic, steeply stratified lake, using six replicate surface-to-sediment
enclosures established during summer and autumn 2004. We added 13C-enriched bicarbonate to the epilimnion of half the enclosures for three weeks during each season and monitored carbon stable
isotope ratios of DIC, DOC, POC and Daphnia, along with physical, chemical and biological variables. During summer, 13C-enriched DIC (δ13C up to 44 ± 7.2‰) was soon taken up by phytoplankton (δ13C up to −5.1 ± 13.6‰) and was transmitted to Daphnia (δ13C up to −1.7 ± 7.2‰), demonstrating consumption of phytoplankton. In contrast, during autumn, 13C-enriched DIC (δ13C up to 56.3 ± 9.8‰) was not transmitted to Daphnia, whose δ13C became progressively lower (δ13C down to −45.6 ± 3.3‰) concomitant with decreasing methane concentration. Outputs from a model suggested phytoplankton contributed
64–84% of Daphnia diet during summer, whereas a calculated pelagic carbon mass balance indicated only 30–40% could have come from phytoplankton.
Although autumn primary production was negligible, zooplankton biomass persisted at the summer level. The model suggested
methanotrophic bacteria contributed 64–87% of Daphnia diet during autumn, although the calculated carbon mass balance indicated a contribution of 37–112%. Thus methanotrophic
bacteria could supply virtually all the carbon requirement of Daphnia during autumn in this lake. The strongly 13C-depleted Daphnia values, together with the outputs from the models and the calculated carbon mass balance showed that methanotrophic bacteria
can be a greater carbon source for Daphnia in lakes than previously suspected. 相似文献
2.
We report abundance of 13C and 15N contents in terrestrial plants (mosses, lichens, liverworts, algae and grasses) from the area of Barton Peninsula (King
George Island, maritime Antarctic). The investigated plants show a wide range of δ13C and δ15N values between −29.0 and −20.0‰ and between −15.3 and 22.8‰, respectively. The King George Island terrestrial plants show
species specificity of both carbon and nitrogen isotope compositions, probably due to differences in plant physiology and
biochemistry, related to their sources and in part to water availability. Carbon isotope compositions of Antarctic terrestrial
plants are typical of the C3 photosynthetic pathway. Lichens are characterized by the widest carbon isotope range, from −29.0 to −20.0‰. However, the
average δ13C value of lichens is the highest (−23.6 ± 2.8‰) among King George Island plants, followed by grasses (−25.6 ± 1.7‰), mosses
(−25.9 ± 1.6‰), liverworts (−26.3 ± 0.5‰) and algae (−26.3 ± 1.2‰), partly related to habitats controlled by water availability.
The δ15N values of moss samples range widest (−9.0 to 22.8‰, with an average of 4.6 ± 6.6‰). Lichens are on the average most depleted
in 15N (mean = −7.4 ± 6.4‰), whereas algae are most enriched in 15N (10.0 ± 3.3‰). The broad range of nitrogen isotope compositions suggest that the N source for these Antarctic terrestrial
plants is spatially much variable, with the local presence of seabird colonies being particularly significant. 相似文献
3.
We studied the nutritional modes of the orchid Serapias strictiflora and its mycorrhizal fungus Epulorhiza sp. using the differences in carbon isotopic composition (δ13C) of C3 orchid and C4 maize tissues. We found that if cultivated in substrate lacking any organic compounds, the mycorrhizal extraradical mycelia
(δ13C = −26.3 ± 0.2 ‰) developed well, despite being fully dependent on nutrition from orchid roots (δ13C = −28.6 ± 0.1 ‰). If the mycorrhizal fungus had additional access to and colonized decaying maize roots (δ13C = −14.6 ± 0.1 ‰), its isotopic composition (δ13C = −21.6 ± 0.4 ‰) reflected a mixture of biotrophy and saprotrophy. No statistically significant differences in δ13C of new storage tubers were found between Epulorhiza-associated orchids with (δ13C = -28.2 ± 0.1 ‰) and without access to maize roots (δ13C = −28.6 ± 0.2 ‰). We conclude that autotrophy is the predominant nutritional mode of mature S. strictiflora plants and that they supply their mycorrhizal fungus with substantial amount of carbon (69 ± 3 % of the fungus demand), even
if the fungus feeds saprotrophically. 相似文献
4.
In marine food web studies, stable isotopes of nitrogen (δ15N) and carbon (δ13C) are widely used to estimate organisms’ trophic levels (TL) and carbon sources, respectively. For smaller organisms, whole
specimens are commonly analyzed. However, this “bulk method” involves several pitfalls since different tissues may fractionate
stable isotopes differently. We compared the δ15N and δ13C values of exoskeleton versus soft tissue, in relation to whole specimens, of three common Arctic amphipods in Svalbard waters:
the benthic Anonyx nugax, the sympagic (ice-associated) Gammarus wilkitzkii and the pelagic Themisto libellula. The δ15N values of the exoskeletons were significantly lower than those of the soft tissues for A. nugax (10.5 ± 0.7‰ vs. 15.7 ± 0.7‰), G. wilkitzkii (3.3 ± 0.3‰ vs. 8.3 ± 0.4‰) and T. libellula (8.6 ± 0.3‰ vs.10.8 ± 0.3‰). The differences in δ13C values between exoskeletons and soft tissues were insignificant, except for A. nugax (−21.2 ± 0.2‰ vs. −20.3 ± 0.2‰, respectively). The δ15N values of whole organisms were between those of the exoskeletons and the soft tissues, being similarly enriched in 15N as the exoskeletons (except G. wilkitzkii) and depleted in 15N by 1.2–3.7‰ compared to the soft tissues. The δ15N-derived TLs of the soft tissues agreed best with the known feeding preferences of the three amphipods, which suggest a potential
underestimation of 0.5–1.0 TL when stable isotope analyses are performed on whole crustaceans with thick exoskeletons. The
insignificant or small differences in δ13C values among exoskeletons, soft tissues and whole specimens, however, suggest low probability for misinterpretations of
crustaceans’ primary carbon source in marine ecosystems with distinctly different δ13C-carbon sources. 相似文献
5.
The δ15N and δ13C values of particulate organic material (POM) were analyzed from 35 sites in the Florida Keys over the time interval 2000
to 2002. The sites within the study area were delineated into nine transects stretching from Key West to Key Largo. Each transect
consisted of three to five sites extending from close to the Keys to the edge of the reef tract. The POM had mean δ15N and δ13C values of +3.6‰ (σ = ±3.2‰) and −19.9‰ (σ = ±0.6‰) respectively. Over the study period there were no statistically significant
changes in δ15N, δ13C, or C:N. For the majority of the sampling dates, the δ13C values showed a distinct inshore (δ13C = −18.3‰, σ = ±1.0‰) to offshore gradient (δ13C = −21.4, σ = ±0.9‰). In contrast, the δ15N values showed no consistent patterns related to the distance from land. The more positive δ13C values of the nearshore samples suggest that the source of the carbon and the nitrogen in the POM in the nearshore was mainly
derived from the degradation of seagrass detritus and not from the input of anthropogenically derived material from the Florida
Keys. In contrast, the POM on the outer reef was dominated by marine plankton. As mineralization and nitrification of the
organic nitrogen pool are major contributors to the dissolved inorganic nitrogen in the water column, it is unlikely that
variations in the δ15N of the algae and other benthic organisms reported in the Florida Keys are related to the input of sewage. 相似文献
6.
Giedrius Trakimas Timothy D. Jardine Rūta Barisevi?iūt? Andrius Garbaras Raminta Skipityt? Vidmantas Remeikis 《Hydrobiologia》2011,675(1):87-95
During migrations and ontogeny amphibians change their habitat and feeding, and thus are important in linking terrestrial
and aquatic ecosystems. We measured δ
13C and δ
15N values of early stages (egg, embryo, tadpole) and toes of adult frogs Rana temporaria, collected from a small wetland in Lithuania. We compared the isotopic composition of these tissues with potential food sources,
excrements of tadpoles, and filled intestinal tracts. We found that δ
13C values in R. temporaria tadpoles were markedly depleted in comparison to adults, eggs or embryos, demonstrating a terrestrial to aquatic shift in
energy sources. After the onset of feeding, tadpoles approached isotopic equilibrium with available food (algae and litter).
Tadpoles had higher δ
15N than both algae and litter, differing by 3.6 and 2.4‰, respectively, and similar δ
13C to these sources. However, tadpole excrements and body tissue diverged, with mean δ
13C values of excrements (−30.3 ± 1.6‰ SD) more similar to litter (−31.7 ± 1.2‰ SD) and body tissue δ
13C (−34.8 ± 0.7‰ SD) more similar to algae (−34.2 ± 4.1‰ SD). This suggests that algal resources are critical in early life
stages of this anuran, particularly at stages characterized by high growth and low development (stages: 25–35). 相似文献
7.
The C isotope composition of leaf dark-respired CO2 (δ13Cl) integrates short-term metabolic responses to environmental change and is potentially recorded in the isotopic signature
of ecosystem-level respiration. Species differences in photosynthetic pathway, resource acquisition and allocation patterns,
and associated isotopic fractionations at metabolic branch points can influence δ13Cl, and differences are likely to be modified by seasonal variation in drought intensity. We measured δ13Cl in two deep-rooted C3 trees (Prosopis velutina and Celtis reticulata), and two relatively shallow-rooted perennial herbs (a C3 dicot Viguiera dentata and a C4 grass Sporobolus wrightii) in a floodplain savanna ecosystem in southeastern Arizona, USA during the dry pre-monsoon and wet monsoon seasons. δ13Cl decreased during the nighttime and reached minimum values at pre-dawn in all species. The magnitude of nocturnal shift in
δ13Cl differed among species and between pre-monsoon and monsoon seasons. During the pre-monsoon season, the magnitude of the nocturnal
shift in δ13Cl in the deep-rooted C3 trees P. velutina (2.8 ± 0.4‰) and C. reticulata (2.9 ± 0.2‰) was greater than in the C3 herb V. dentata (1.8 ± 0.4‰) and C4 grass S. wrightii (2.2 ± 0.4‰). The nocturnal shift in δ13Cl in V. dentata and S. wrightii increased to 3.2 ± 0.1‰ and 4.6 ± 0.6‰, respectively, during the monsoon season, but in C3 trees did not change significantly from pre-monsoon values. Cumulative daytime net CO2 uptake was positively correlated with the magnitude of the nocturnal decline in δ13Cl across all species, suggesting that nocturnal δ13Cl may be controlled by 13C/12C fractionations associated with C substrate availability and C metabolite partitioning. Nocturnal patterns of δ13Cl in dominant plant species in the semiarid savanna apparently have predictable responses to seasonal changes in water availability,
which is important for interpreting and modeling the C isotope signature of ecosystem-respired CO2. 相似文献
8.
Roberto Bertoni Cristiana Callieri Gianluca Corno Serena Rasconi Emanuele Caravati Mario Contesini 《Hydrobiologia》2010,644(1):279-287
We analysed the long-term dynamics (1980–2007) of hypolimnetic and epilimnetic bacterial abundances and organic carbon concentrations,
both dissolved (DOC) and particulate (POC), in the deep holo-oligomictic Lake Maggiore, included in the Southern Alpine Lakes
Long-Term Ecological Research (LTER) site. During the 28 years of investigation, bacterial abundance and POC concentrations
did not decrease with declining phosphorus concentrations, while DOC concentrations showed a pronounced decrease in the epi-
and hypolimnion. We used the annual mean total lake heat content and total annual precipitation as climate-related variables,
and in-lake total phosphorus as a proxy for trophic state. The model (forward stepwise regression, FSR) showed that reduced
anthropogenic pressure was more significant than climate change in driving the trend in DOC concentrations. Bacterial dynamics
in the hypolimnion mirrored the fluctuations observed in the epilimnion, but average cell abundance was three times lower.
The FSR model indicates that bacterial number variability was dependent on POC in the epilimnion and DOC in the hypolimnion.
In the hypolimnion, cell biovolumes for rod and coccal morphotypes were significantly larger than in the epilimnion. 相似文献
9.
A stable carbon isotope study of dissolved inorganic carbon cycling in a softwater lake 总被引:3,自引:0,他引:3
Andrew L. Herczeg 《Biogeochemistry》1987,4(3):231-263
The dissolved inorganic carbon (DIC) cycle in a softwater lake was studied using natural variations of the stable isotopes of carbon,12C and13C. During summer stratification there was a progressive decrease in epilimnion DIC concentration with a concomitant increase in 13CDIC), due to preferential uptake of12C by phytoplankton and a change in the dominant CO2 source from inflow andin situ oxidation to invasion from the atmosphere. There was an increase in hypolimnion DIC concentration throughout summer with a concomitant general decrease in 13CDIC from oxidation of the isotopically light particulate organic carbon that sank down through the thermocline from the epilimnion.Mass balance calculations of DI12C and DI13C in the epilimnion for the summer (June 23–September 25) yield a mean rate of net conversion of DIC to organic carbon (Corg) of 430 ± 150 moles d-1 (6.5 ± 1.8 m moles m-2 d-1. Net CO2 invasion from the atmosphere was 420 ± 120 moles d-1 (6.2 ± 1.8 m moles m-2 d-1) with an exchange coefficient of 0.6 ± 0.3m d-1. These results imply that at least for the summer months the phytoplankton obtained about 90% of their carbon from atmosphere CO2. About 50% of CO2 invasion and conversion to Corg for the summer occurred during a two week interval in mid-summer.DIC concentration increased in the hypolimnion at a rate of 350 ± 70 moles DIC d-1 during summer stratification. The amount of DIC added to the hypolimnion was equivalent to 75 ± 20% of net conversion of DIC to Corg in the euphotic zone over spring and summer implying rapid degradation of POC in the hypolimnion. The 13C of DIC added to the deep water (-22.) was too heavy to have been derived from oxidation of particulate organic carbon alone. About 20% of the added DIC must have diffused from hypolimnetic sediments where relatively heavy CO2 (-7) was produced by a combination of POC oxidation and as a by-product of methanogenesis. 相似文献
10.
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
11.
In semi-arid regions, where plants using both C3 and C4 photosynthetic pathways are common, the stable C isotope ratio (δ13C) of ecosystem respiration (δ13CR) is strongly variable seasonally and inter-annually. Improved understanding of physiological and environmental controls over
these variations will improve C cycle models that rely on the isotopic composition of atmospheric CO2. We hypothesized that timing of precipitation events and antecedent moisture interact with activity of C3 and C4 grasses to determine net ecosystem CO2 exchange (NEE) and δ13CR. Field measurements included CO2 and δ13C fluxes from the whole ecosystem and from patches of different plant communities, biomass and δ13C of plants and soils over the 2000 and 2001 growing seasons. NEE shifted from C source to sink in response to rainfall events,
but this shift occurred after a time lag of up to 2 weeks if a dry period preceded the rainfall. The seasonal average of δ13CR was higher in 2000 (−16‰) than 2001 (20‰), probably due to drier conditions during the 2000 growing season (79.7 mm of precipitation
from April up to and including July) than in 2001 (189 mm). During moist conditions, δ13C averaged −22‰ from C3 patches, −16‰ from C4 patches, and −19‰ from mixed C3 and C4 patches. However, during dry conditions the apparent spatial differences were not obvious, suggesting reduced autotrophic
activity in C4 grasses with shallow rooting depth, soon after the onset of dry conditions. Air and soil temperatures were negatively correlated
with δ13CR; vapor pressure deficit was a poor predictor of δ13CR, in contrast to more mesic ecosystems. Responses of respiration components to precipitation pulses were explained by differences
in soil moisture thresholds between C3 and C4 species. Stable isotopic composition of respiration in semi-arid ecosystems is more temporally and spatially variable than
in mesic ecosystems owing to dynamic aspects of pulse precipitation episodes and biological drivers. 相似文献
12.
Estimates of diet derived from stable isotope analyses are sensitive to the accuracy of corrections made for diet-tissue fractionation.
In particular, diet-tissue fractionation in reindeer Rangifer tarandus may be expected to differ significantly from the generic values often used in stable isotope dietary calculations, given
the known values obtained from other ungulates and the complex digestive system and nutrient recycling characteristic of the
species. We fed domestic reindeer a homogenous artificial diet of known isotopic value in order to directly determine diet-tissue
isotopic fractionation of carbon and nitrogen, the main elements used in stable isotope dietary analyses. Diet-tissue fractionation
values for blood plasma were +3.5 ± 0.1‰ (δ13C) and +4.2 ± 0.3‰ (δ15N). Diet-tissue fractionation values for whole blood were +3.7 ± 0.2‰ (δ13C) and +2.5 ± 0.3‰ (δ15N). Metabolic turnover rates were clearly sufficient for complete tissue replacement over the period of artificial feeding
for blood plasma, but may not have been so for whole blood, especially for δ15N. Our values, except for whole blood δ15N, differ considerably from the generic values often used in dietary studies and interspecific comparisons of trophic niche.
The results underline the importance of obtaining as specific as possible fractionation values for the species, tissue, and
in some cases sex and physiological status of animals under examination, and the potential problems associated with assuming
‘generic’ fractionation values when comparing species, especially where digestive processes are dissimilar. 相似文献
13.
Martin Merino-Ibarra Emiliano Monroy-Ríos Gloria Vilaclara Fermin S. Castillo Margarita E. Gallegos Jorge Ramírez-Zierold 《Aquatic Ecology》2008,42(3):335-345
Valle de Bravo (VB) is a tropical reservoir located (19°21′30″ N, 100°11′00″ W) in the highlands of Mexico. The reservoir
is daily swept by strong (7.4 m s−1 mean speed) diurnal (12:00–19:00 h) winds that blow along its two main arms. As expected from its fetch (6.9 km) and its
depth (21.1 m mean), the reservoir behaves as a warm monomictic water body. During 2001, VB was stratified from February to
October, and well mixed from November to January. Its mean temperature was 19.9°C; the maximum found was 23.8°C in the epilimnion,
while a minimum of 17.8°C was registered during mixing. VB exhibited a thermal regime similar to other water bodies of the
Mexican tropical highlands, except for a steady increase of its hypolimnetic temperature during stratification, which is attributed
to entrainment of epilimnetic water into the hypolimnion. During stratification, the hypolimnion was anoxic, while the whole
water column remained under-saturated (60%) during mixing. The flushing time is 2.2 years. Mineralization and total alkalinity
are low, which allows strong changes in pH. Ammonia remained low (2.4 μmol l−1 mean) in the epilimnion, but reached up to 60 μmol l−1 in the hypolimnion. Soluble reactive phosphorous had a mean of 0.28 μmol l−1 in the epilimnion and a mean of 1.25 μmol l−1 in the hypolimnion. Nitrate exhibited maxima (up to 21 μmol l−1) during mixing, and also in the metalimnion (2 μmol l−1) during stratification. Low dissolved inorganic nitrogen indicated nitrogen limitation during stratification. Eutrophication
is an emerging problem in VB, where cyanobacteria dominate during stratification. At VB chlorophyll a is low during mixing (mean of 9 μg l−1), and high during stratification (mean 21 μg l−1), when blooms (up to 88 μg l−1) are frequent. This pattern is similar to that found in other eutrophic tropical water bodies. We propose that in VB the
wind regime causes vertical displacements of the thermocline (0.58–1.10 m hr−1) and boundary mixing, enhancing the productivity during the stratification period in this tropical reservoir. 相似文献
14.
During microbial breakdown of leaf litter a fraction of the C lost by the litter is not released to the atmosphere as CO2 but remains in the soil as microbial byproducts. The amount of this fraction and the factors influencing its size are not
yet clearly known. We performed a laboratory experiment to quantify the flow of C from decaying litter into the soil, by means
of stable C isotopes, and tested its dependence on litter chemical properties. Three sets of 13C-depleted leaf litter (Liquidambar styraciflua L., Cercis canadensis L. and Pinus taeda L.) were incubated in the laboratory in jars containing 13C-enriched soil (i.e. formed C4 vegetation). Four jars containing soil only were used as a control. Litter chemical properties
were measured using thermogravimetry (Tg) and pyrolysis–gas chromatography/mass spectrometry–combustion interface–isotope
ratio mass spectrometry (Py–GC/MS–C–IRMS). The respiration rates and the δ13C of the respired CO2 were measured at regular intervals. After 8 months of incubation, soils incubated with both L. styraciflua and C. canadensis showed a significant change in δ13C (δ13Cfinal = −20.2 ± 0.4‰ and −19.5 ± 0.5‰, respectively) with respect to the initial value (δ13Cinitial = −17.7 ± 0.3‰); the same did not hold for soil incubated with P. taeda (δ13Cfinal:−18.1 ± 0.5‰). The percentages of litter-derived C in soil over the total C loss were not statistically different from one
litter species to another. This suggests that there is no dependence of the percentage of C input into the soil (over the
total C loss) on litter quality and that the fractional loss of leaf litter C is dependent only on the microbial assimilation
efficiency. The percentage of litter-derived C in soil was estimated to be 13 ± 3% of total C loss. 相似文献
15.
James Nelson Jeffrey Chanton Felicia Coleman Christopher Koenig 《Environmental Biology of Fishes》2011,90(3):243-252
To determine the feasibility of using stable isotopes to track diet shifts in wild gag, Mycteroperca microlepis, populations over seasonal timescales, we conducted a repeated measures diet-shift experiment on four adult gag held in the
laboratory. Fish were initially fed a diet of Atlantic mackerel, Scomber scombrus, (mean δ13C = −21.3‰ ± 0.2, n = 20) for a period of 56 days and then shifted to a diet of pinfish, Lagodon rhomboids, (mean δ13C = −16.6‰ ± 0.6, n = 20) for the 256 day experiment. We developed a non-lethal surgical procedure to obtain biopsies of the muscle, liver, and
gonad tissue monthly from the same four fish. We then determined the δ13C value of each tissue by isotope ratio mass spectrometry. For the gonad tissue we used the relationship between C/N and lipid
content to correct for the influence of lipids on δ13C value. We observed a significant shift in the δ13C values of all of the tissues sampled in the study. Carbon turnover rates varied among the three tissues, but the shift in
diet from mackerel to pinfish was clearly traceable through analysis of δ13C values. The turnover rates for muscle tissue were 0.005‰ day−1, and for gonad tissue was 0.009‰ day−1. Although it is generally thought that tissue turnover rates in ectotherms are driven primarily by growth, we found that
metabolic rate can be a major factor driving tissue turnover in adult gag. 相似文献
16.
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
17.
Sources and fates of dissolved organic carbon in lakes as determined by whole-lake carbon isotope additions 总被引:3,自引:0,他引:3
Darren L. Bade Stephen R. Carpenter Jonathan J. Cole Michael L. Pace Emma Kritzberg Matthew C. Van de Bogert Rose M. Cory Diane M. McKnight 《Biogeochemistry》2007,84(2):115-129
Four whole-lake inorganic 13C addition experiments were conducted in lakes of differing trophic status. Inorganic 13C addition enriched algal carbon in 13C and changed the C-DOC by +1.5‰ to +9.5‰, depending on the specific lake. This change in C-DOC represented a significant input of algal DOC that was not completely consumed by bacteria. We modeled the dynamics in
C-DOC to estimate the fluxes of algal and terrestrial carbon to and from the DOC pool, and determine the composition of the
standing stock. Two experiments in lightly stained, oligotrophic lakes indicated that algal production was the source of about
20% of the DOC pool. In the following year, the experiment was repeated in one of these lakes under conditions of nutrient
enrichment, and in a third, more humic lake. Algal contributions to the DOC pool were 40% in the nutrient enriched lake and
5% in the more humic lake. Spectroscopic and elemental analyses corroborated the presence of increased algal DOC in the nutrient
enriched lake. Natural abundance measurements of the C of DOC in 32 lakes also revealed the dual contributions of both terrestrial and algal carbon to DOC. From these results,
we suggest an approach for inferring the contribution of algal and terrestrial DOC using easily measurable parameters. 相似文献
18.
Retrospective investigations using carbon and nitrogen stable isotope composition of archived material have a great potential
for describing past effects of anthropogenic ecosystem alterations or natural shifts in ecosystems. In this study, we examined
the effects of two commonly used preservation substances of freshwater invertebrates, ethanol and lugol, on δ13C and δ15N of various planktonic and benthic taxa. For both isotopes, the average effect of fixation in ethanol was stronger than in
lugol, and the effects on δ13C were stronger than on δ15N (average ± SD: 1.18 ± 0.94 and −0.47 ± 0.99 for δ13C ethanol and lugol fixed samples, respectively, and 0.39 ± 0.68 and 0.17 ± 0.77 for δ15N, respectively). The changes in the isotopic composition were not dependent on the initial isotopic composition of each taxon,
but were related with concomitant changes in the carbon or nitrogen content. Application of a mass balance correction equation
to the fixed samples resulted in a significantly lower average effect of fixation in ethanol (0.01 ± 0.59 and 0.44 ± 0.65
for δ15N and δ13C, respectively), while corrections had little effect for lugol fixed samples (0.24 ± 0.53 and −0.39 ± 0.85, respectively).
For both isotopes and fixatives, corrections resulted in linear relationships between fixed vs. control samples, with slopes
and intercepts not significantly different from 1 and 0, respectively. Therefore, mass balance correction of stable isotopes
in fixed invertebrates is recommended for minimising the effects of fixation.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.
Handling editor: M. Power 相似文献
19.
Tom Moens Sandra Vanhove Ilse De Mesel Bea Kelemen Thierry Janssens Ann Dewicke Ann Vanreusel 《Polar Biology》2007,31(1):1-13
δ13C of nematode communities in 27 sites was analyzed, spanning a large depth range (from 130 to 2,021 m) in five Antarctic regions,
and compared to isotopic signatures of sediment organic matter. Sediment organic matter δ13C ranged from −24.4 to −21.9‰ without significant differences between regions, substrate types or depths. Nematode δ13C showed a larger range, from −34.6 to −19.3‰, and was more depleted than sediment organic matter typically by 1‰ and by up
to 3‰ in silty substrata. These, and the isotopically heavy meiofauna at some stations, suggest substantial selectivity of
some meiofauna for specific components of the sedimenting plankton. However, 13C-depletion in lipids and a potential contribution of chemoautotrophic carbon in the diet of the abundant genus Sabatieria may confound this interpretation. Carbon sources for Antarctic nematodes were also explored by means of an experiment in
which the fate of a fresh pulse of labile carbon to the benthos was followed. This organic carbon was remineralized at a rate
(11–20 mg C m−2 day−1) comparable to mineralization rates in continental slope sediments. There was no lag between sedimentation and mineralization;
uptake by nematodes, however, did show such a lag. Nematodes contributed negligibly to benthic carbon mineralization. 相似文献
20.
D. R. Bowling W. J. Massman S. M. Schaeffer S. P. Burns R. K. Monson M. W. Williams 《Biogeochemistry》2009,95(1):37-59
Considerable research has recently been devoted to understanding biogeochemical processes under winter snow cover, leading
to enhanced appreciation of the importance of many winter ecological processes. In this study, a comprehensive investigation
of the stable carbon isotope composition (δ13C) of CO2 within a high-elevation subalpine forest snowpack was conducted. Our goals were to study the δ13C of biological soil respiration under snow in winter, and to assess the relative importance of diffusion and advection (ventilation
by wind) for gas transport within snow. In agreement with other studies, we found evidence of an active microbial community
under a roughly 1-m deep snowpack during winter and into spring as it melted. Under-snow CO2 mole fractions were observed up to 3,500 μmol mol−1, and δ13C of CO2 varied from ~−22 to ~−8‰. The δ13C of soil respiration calculated from mixing relationships was −26 to −24‰, and although it varied in time, it was generally
close to that of the bulk organic horizon (−26.0‰). Subnivean CO2 and δ13C were quite dynamic in response to changes in soil temperature, liquid water availability, and wind events. No clear biologically-induced
isotopic changes were observed during periods when microbial activity and root/rhizosphere activity were expected to vary,
although such changes cannot be eliminated. There was clear evidence of isotopic enrichment associated with diffusive transport
as predicted by theory, but simple diffusive enrichment (4.4‰) was not observed. Instead, ventilation of the snowpack by sustained
wind events in the forest canopy led to changes in the diffusively-enriched gas profile. The isotopic influence of diffusion
on gases in the snowpack and litter was greatest at greater depths, due to the decreased relative contribution of advection
at depth. There were highly significant correlations between the apparent isotopic content of respiration from the soil with
wind speed and pressure. In summary, physical factors influencing gas transport substantially modified and potentially obscured
biological factors in their effects on δ13C of CO2 within this subalpine forest snowpack. 相似文献