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1.
Because nitrogen and phosphorus are primary resources for plant, algal, and microbial production, increases in nutrient inputs
can markedly alter aquatic ecosystems. Coastal wetland plots at Belle W. Baruch Marine Field Laboratory (South Carolina, USA)
have been amended with nitrogen and phosphorus for ~20 years to determine the effects of nutrient loading on coastal wetlands.
We conducted a survey of δ15N and δ13C natural abundance in coastal wetland organic pools (sediment, vegetation) with long-term nutrient amendments (control, no
addition; nitrogen; phosphorus; and nitrogen + phosphorus additions). Additionally, we conducted laboratory assays to quantify
pore water nutrient availability and nitrification rates. Marsh vegetation (Spartina alterniflora) had enriched δ13C values (mean −14‰) relative to bulk sediment samples (mean −18‰). Nitrogen-amended plots (alone and in combination with
phosphorus) had enriched δ13C values in the surface sediment (0–5 cm; mean −16.1‰) relative to control (mean −16.5‰) and phosphorus-amended plots (mean
−16.8‰). Nitrogen-amended plots also had depleted δ15N in S. alterniflora leaf tissues (−3.3‰) and surface sediment samples (mean 2.1‰) relative to leaf tissues (mean 2.1‰) or sediment samples (mean
5.8‰) from control or phosphorus-only amended plots. Nitrate availability (as increased pore water concentration) was higher
in N-amended plots although ammonium availability did not differ. Phosphorus availability was higher only in phosphorus-only
amended plots. Overall, we found that long-term nutrient amendments to coastal wetlands significantly altered nutrient availability
and uptake rates as well as natural abundance of δ13C and δ15N in multiple organic matter sources. 相似文献
2.
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
3.
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
4.
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
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.
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
7.
Sediment organic matter (OM) and its stable carbon and nitrogen isotopes were studied in 12 Slovenian mountain lakes in the
Julian Alps. The lakes have different catchment areas and display a range of trophic states. Surface sediment atomic C/N ratios
ranged from 8.4 to 13.2. Based on these C/N ratios, we concluded that autochthonous OM dominates in these lakes and constitutes
approximately 65–92% of the total OM. Higher contributions of autochthonous OM sources were observed in lakes above the tree
line. Relatively constant C/N ratios in the deeper sediments suggest that degradation processes are most intense in the upper
few centimetres of the sediments and/or that remaining OM is relatively resistant to further degradation. Surface sediment
δ13C and δ15N values ranged from −36.1 to −14.1‰ and from −5.2 to +1.1‰, respectively. In sediment cores from seven lakes, higher δ13C and lower δ15N values characterize oligotrophic lakes situated above the tree line, whereas the reverse is true for eutrophic lakes below
the tree line that are also exposed to more anthropogenic impact. Carbon and nitrogen biogeochemical cycling differs considerably
among the lakes. Stratigraphic shifts in carbon, total nitrogen, C/N ratios and stable C and N isotopes in cores record changes
in inputs, and hence water column processes, as well as alterations in loading to the lakes. The stratigraphic variations
are also the result of post-depositional diagenetic changes in the upper few centimetres of sediment. All the lakes show impacts
from recent increases in atmospheric deposition of dissolved inorganic nitrogen. Application of sediment OM analysis thus
proved to be useful to reconstruct paleoecological changes in sensitive mountain lake ecosystems that are either natural and/or
anthropogenically derived. 相似文献
8.
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
9.
Autochthonous origin of semi-labile dissolved organic carbon in a large monomictic lake (Lake Biwa): carbon stable isotopic evidence 总被引:1,自引:0,他引:1
Koh Maki Chulgoo Kim Chikage Yoshimizu Ichiro Tayasu Toshihiro Miyajima Toshi Nagata 《Limnology》2010,11(2):143-153
Semi-labile dissolved organic carbon (DOC) plays an important role in the transport and hypolimnetic remineralization of carbon
in large freshwater lakes. However, sources of semi-labile DOC in lakes remain unclear. This study used a carbon stable isotope
approach to examine relative contributions of autochthonous and allochthonous sources to semi-labile DOC. Vertical and seasonal
variations in the concentration and carbon stable isotope ratio (δ13C) of DOC were determined in large (surface area 674 km2; maximum depth 104 m), monomictic Lake Biwa. A sharp vertical gradient of δ13C of DOC (δ13C-DOC) during the stratification period [mean ± standard error (SE) −25.5 ± 0.1 and −26.0 ± 0.0‰ in the epi- and hypolimnion,
respectively] indicated the accumulation of 13C-rich DOC in the epilimnion. Vertical mixing explained the intermediate values of δ13C-DOC (−25.7 ± 0.0‰) measured throughout the water column during the overturn period. Both DOC concentration and δ13C-DOC decreased in the hypolimnion during stratification, indicating selective remineralization of 13C-rich DOC. Using a two-component mixing model, we estimated the δ13C value of semi-labile DOC to be −22.2 ± 0.3‰, which was close to the δ13C of particulate organic carbon collected in the epilimnion during productive seasons (−22.7 ± 0.7‰) but much higher than
the δ13C-DOC in river waters (−26.5 ± 0.1‰). Semi-labile DOC appeared to be mainly autochthonous in origin, produced by planktonic
communities during productive seasons. The spatiotemporal uncoupling between production and remineralization of semi-labile
DOC implies that hypolimnetic oxygen consumption may be affected by pelagic primary production during productive seasons of
the preceding year. 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.
A recently described phloem-bleeding technique was used to study seasonal changes in δ13C, sugar levels and the amino acid:sugar balance of phloem translocate of 2- to 3-year old trees of Eucalyptus globulus at a rain-fed site (Eulup) and a waste-effluent-irrigated site (Albany) in south-west Australia. δ13C of phloem sap from the Eulup site fluctuated widely between winter (−27.6‰) and peak summer stress (−20.2‰), compared with
a much smaller range of −28.4 to −26.3 at Albany. Seasonal changes in sugar concentrations in sap fluctuated closely with
those of phloem δ13C, with highest concentrations and least negative δ13C values at times of greatest soil water deficit. Molar ratios of amino acids to sugars in phloem sap were similar between
plantations in winter through to early summer. They then remained high at the nitrogen-rich effluent-treated site, but fell
dramatically once soils dried out at Eulup. Mature leaf dry matter sampled at peak yearly stress (early autumn) showed more
negative δ13C values than concurrently harvested phloem sap or recently initiated shoot apex dry matter, presumably because the sampled
foliage had laid down its structural carbon earlier under relatively unstressed winter/spring conditions. Differences between
Albany and Eulup were much greater for δ13C of phloem and new apical dry matter than for dry matter of mature foliage. Comparisons of δ13C signatures of phloem sap carbon with those of dry matter of nascent xylem tissues showed seasonal fluctuations in δ13C of phloem translocate which were mirrored a month or so later by those for xylem carbon. δ13C analyses of trunk growth rings from Eulup and Albany showed well-defined seasonal oscillations over the first 2 or 3 years
of growth until irrigation commenced at Albany. Fluctuations in δ13C at the latter site then became noticeably less pronounced than at Eulup. Future use of phloem sap δ13C and solute analyses for studying seasonal water and nutrient status of E. globulus is discussed.
Received: 9 April 1998 / Accepted: 20 August 1998 相似文献
12.
Nitrogen and carbon isotope responses of Chinese cabbage and chrysanthemum to the application of liquid pig manure 总被引:2,自引:0,他引:2
Sang-Sun Lim Woo-Jung Choi Jin-Hyeob Kwak Jae-Woon Jung Scott X. Chang Han-Yong Kim Kwang-Sik Yoon Soo-Myung Choi 《Plant and Soil》2007,295(1-2):67-77
The effects of the liquid pig manure (LM) used in organic farming on the natural abundance of 15N and 13C signatures in plant tissues have not been studied. We hypothesized that application of LM will (1) increase δ15N of plant tissues due to the high δ15N of N in LM as compared with soil N or inorganic fertilizer N, and (2) increase δ13C of plant tissues as a result of high salt concentration in LM that decreases stomatal conductance of plants. To test these
hypotheses, variations in the δ15N and δ13C of Chinese cabbage (Brassica campestris L.) and chrysanthemum (Chrysanthemum morifolium Ramatuelle) with two different LMs (with δ15N of +15.6 and +18.2‰) applied at two rates (323 and 646 kg N ha-1 for cabbage and 150 and 300 kg N ha-1 for chrysanthemum), or urea (δ15N = -2.7‰) applied at the lower rate above for the respective species, in addition to the control (no N input) were investigated
through a 60-day pot experiment. Application of LM significantly increased plant tissue δ15N (range +9.4 to +14.9‰) over the urea (+3.2 to +3.3‰) or control (+6.8 to 7.7‰) treatments regardless of plant species, strongly
reflecting the δ15N of the N source. Plant tissue δ13C were not affected by the treatments for cabbage (range −30.8 to −30.2‰) or chrysanthemum (−27.3 to −26.8‰). However, cabbage
dry matter production decreased while its δ13C increased with increasing rate of LM application or increasing soil salinity (P < 0.05), suggesting that salinity stress caused by high rate of LM application likely decreased stomatal conductance and
limited growth of cabbage. Our study expanded the use of the δ15N technique in N source (organic vs. synthetic fertilizer) identification and suggested that plant tissue δ13C maybe a sensitive indicator of plant response to salinity stress caused by high LM application rates. 相似文献
13.
Using stable isotopes to study resource acquisition and allocation in procellariiform seabirds 总被引:1,自引:0,他引:1
Some procellariiform seabirds use a dual strategy for provisioning their chicks by alternating short (ST) and long (LT) foraging
trips. Parent birds gain mass during LT but they lose mass while increasing the chick feeding frequency during ST. Self-feeding
during LT is crucial for the success of ST because firstly most of the energy used during ST is likely to be derived from
the energy stored during LT and secondly self-feeding during ST is presumed to be negligible. Self-feeding by adult procellariiforms
is thus a key issue to understand allocation processes but it is still poorly known. We tested these predictions by using
the stable isotope (δ15N and δ13C) technique on birds’ plasma and prey with the short-tailed shearwater Puffinus tenuirostris breeding at Tasmania as a model. Parent shearwaters returning to the colony after a LT have an Antarctic/subantarctic δ13C signature in their plasma (−23.8‰), thus indicating that they fed in cold waters, far away from their breeding colony, for
their own maintenance. Parent birds returning to the colony after a ST also have a distant Antarctic/subantarctic δ13C signature in their plasma (−24.3‰), thus verifying that self-feeding is negligible during ST and that birds fast at that
time, using energy stores built up in cold waters. Plasma δ15N values of adults (8.8‰) indicates they mainly prey upon zooplankton-eating organisms, probably mesopelagic myctophid fishes.
A simple isotopic mixing model estimates that they consume by mass 87% myctophids and 13% subantarctic krill when self-feeding.
Finally and as expected, the carbon isotopic signature of chick plasma (−22.2‰) was intermediate between those of high- and
low-latitude marine organisms and is thus in agreement with chicks being fed with a large diversity of prey species caught
by adult birds from Antarctic to Tasmanian waters. One main consequence of this system is that reproduction of a Tasmanian
species is controlled by resources available at great distances from the breeding colony that drive allocation decisions of
parent birds. 相似文献
14.
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
15.
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
16.
Rivers link oceans with the land, creating global hot spots of carbon processing in coastal seas. Coastlines around the world
are dominated by sandy beaches, but beaches are unusual in that they are thought to rely almost exclusively on marine imports
for food. No significant connections to terrestrial production having been demonstrated. By contrast, we isotopically traced
carbon and nitrogen pathways leading to clams (Donax deltoides) on beaches. Clams from areas influenced by river plumes had significantly different isotope signatures (δ13C: −18.5 to −20.2‰; δ15N: 8.3–10.0‰) compared with clams remote from plumes (δ13C: −17.5 to −19.5‰; δ15N: 7.6–8.7‰), showing that terrestrial carbon and sewage, both delivered in river plumes, penetrate beach food webs. This
is a novel mechanism of trophic subsidy in marine intertidal systems, linking the world’s largest shore ecosystem to continental
watersheds. The same clams also carry pollution signatures of sewage discharged into rivers, demonstrating that coastal rivers
connect ecosystems in unexpected ways and transfer contaminants across the land–ocean boundary. The links we demonstrate between
terrigenous matter and the largest of all marine intertidal ecosystems are significant given the immense social, cultural,
and economic values of beaches to humans and the predicted consequences of altered river discharge to coastal seas caused
by global climate change. 相似文献
17.
The genus Ramaria is composed of several subgenera that often correspond to specific trophic strategies. Because carbon and nitrogen isotopes
can be used to assess fungal trophic status and nitrogen sources, we accordingly carried out an extensive survey of isotopic
patterns in archived specimens of Ramaria from Germany and other locations. Isotopic patterns in species generally corresponded to subgeneric affiliations and to the
range of different potential substrates, with fungi fruiting on wood and litter (subgenera Asteroramaria and Lentoramaria) much lower in δ15N (≈−3‰) than ectomycorrhizal taxa (≈12‰) (subgenus Ramaria) or taxa fruiting on soil (≈13‰) (subgenus Echinoramaria). Conversely, fungi fruiting on wood and litter were higher in δ13C (−23‰) than those fruiting on soil (≈−27‰), with ectomycorrhizal fungi intermediate (≈−24.5‰). Fungi colonizing mineral
soil horizons were about 3‰ enriched in 15N relative to those colonizing both mineral and organic horizons. The high δ15N and low δ13C signatures of taxa fruiting on soil remains unexplained. The high degree of fidelity of isotopic signatures with subgeneric
classifications and life history traits suggests that sporocarps are good integrators of patterns of carbon and nitrogen cycling
for specific taxa. Archived specimens represent a useful trove of life history information that could be mined without requiring
extensive supporting isotopic data from other ecosystem pools. 相似文献
18.
Understanding what governs patterns of soil δ15N and δ13C is limited by the absence of these data assembled throughout the development of individual ecosystems. These patterns are important because stable isotopes of soil organic N and C are integrative indicators of biogeochemical processing of soil organic matter. We examined δ15N of soil organic matter (δ15NSOM) and δ13CSOM of archived soil samples across four decades from four depths of an aggrading forest in southeastern USA. The site supports an old-field pine forest in which the N cycle is affected by former agricultural fertilization, massive accumulation of soil N by aggrading trees over four decades, and small to insignificant fluxes of N via NH3 volatilization, nitrification, and denitrification. We examine isotopic data and the N and C dynamics of this ecosystem to evaluate mechanisms driving isotopic shifts over time. With forest development, δ13CSOM became depth-dependent. This trend resulted from a decline of ~2‰ in the surficial 15 cm of mineral soil to −26.0‰, due to organic matter inputs from forest vegetation. Deeper layers exhibited relatively little trend in δ13CSOM with time. In contrast, δ15NSOM was most dynamic in deeper layers. During the four decades of forest development, the deepest layer (35–60 cm) reached a maximum δ15N value of 9.1‰, increasing by 7.6‰. The transfer of >800 kg ha−1 of soil organic N into aggrading vegetation and the forest floor and the apparent large proportion of ectomycorrhizal (ECM) fungi in these soils suggest that fractionation via microbial transformations must be the major process changing δ15N in these soils. Accretion of isotopically enriched compounds derived from microbial cells (i.e., ECM fungi) likely promote isotopic enrichment of soils over time. The work indicates the rapid rate at which ecosystem development can impart δ15NSOM and δ13CSOM signatures associated with undisturbed soil profiles. 相似文献
19.
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
20.
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