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1.
Thomas M. Doherty-Bone Alison M. Dunn Caroline Liddell Lee E. Brown 《Biological invasions》2018,20(7):1799-1808
Invasive alien species have the potential to alter biodiversity and ecosystem processes. In freshwaters, detritus decomposition is a major ecosystem service but it remains uncertain whether invasive alien decapods process detritus differently to natives. This study examined leaf litter processing, and cascading effects on biofilms, by the European native white clawed crayfish (Austropotamobius pallipes) compared to two invasive alien decapod species: the American signal crayfish (Pacifastacus leniusculus) and the Chinese mitten crab (Eriocheir sinensis). Invasive alien decapods were responsible for higher leaf litter decomposition than the native. In comparison with native crayfish, invasive alien crab and crayfish showed higher rates of litter consumption, increased production of smaller leaf fragments, fine particulate organic matter (FPOM) and dissolved organic carbon. Nutrients (ammonia and soluble reactive phosphorous) derived from excretion (measured separately in the absence of biofilms) varied among decapod species, being lower for P. leniusculus. However, nutrient concentrations did not vary among species in the detritivory experiments with biofilm, implying nutrients were utilised for biofilm production and respiration as no differences in biomass were evident among decapod treatments. These results show invasive alien decapods have the potential to increase the magnitude of detrital processing to FPOM in rivers, but indirect impacts on primary producers due to nutrient release are uncertain based on this experimental context. 相似文献
2.
Importance of Shallow Water Habitats for Demersal Fishes and Decapod Crustaceans in Penobscot Bay, Maine 总被引:2,自引:0,他引:2
We characterized demersal fish and decapod crustacean habitats in 14 shallow (< 12m) areas in Penobscot Bay, Maine, by mapping the distribution of subtidal substrata with an acoustic sea bottom profiler. We identified the aquatic vegetation and the fishes and decapods associated with these habitats. Samples of fishes and decapods in each habitat were collected with a small beam trawl. The seabed at most of the stations sampled was composed of a mosaic of substrata. More species of fishes tow-1 and higher abundances of fishes and decapods were found in stations with vegetation present, particularly eelgrass, Zostera marina. Decapod species richness tow-1 was similar between vegetated and unvegetated habitats. Shallow habitats in Penobscot Bay were dominated by juvenile fishes and function as nursery areas. The greater species diversity and higher abundances of epibenthic fishes and decapod crustaceans observed in vegetated habitats, particularly beds of Zostera marina, compared with unvegetated areas in Penobscot Bay conform to the hypothesis that increased habitat complexity results in increased species richness and abundance.The first author is also senior author 相似文献
3.
The origin and early diversification of decapod crustaceans and their expansion from marine to continental environments are key events in arthropod evolution. Rare fossil decapods are known from the Palaeozoic, and the earliest eumalacostracans with undoubted decapod affinities are the Late Devonian Palaeopalaemon and Aciculopoda, found in offshore marine deposits. Here, we describe a new species of the shrimp Tealliocaris found in floodplain and temporary pond deposits from the Famennian (Late Devonian) of Belgium, together with a rare Palaeozoic assemblage of other crustaceans (conchostracans, notostracans and anostracans) and chelicerates (eurypterids). Tealliocaris walloniensis sp. nov. documents the earliest occurrence of continental decapod crustaceans and indicates that decapods have been part of continental ecosystems at least since the Late Devonian. 相似文献
4.
Spatial and temporal distribution of carbon isotopes in soil organic matter at the Dinghushan Biosphere Reserve, South China 总被引:6,自引:0,他引:6
Qingqiang Chen Chengde Shen Yanmin Sun Shaolin Peng Weixi Yi Zhi’an Li Mantao Jiang 《Plant and Soil》2005,273(1-2):115-128
The spatial and temporal distribution of carbon isotopes (13C, 14C) in soil organic matter (SOM) were studied based on SOM content, SOM 14C and SOM 13C of thinly layered soil samples for six soil profiles with different elevations at the Dinghushan Biosphere Reserve (DHSBR), South China. The results indicate that variations of SOM 13C with depth of the soil profiles at different elevations are controlled by soil development, and correlate well with SOM composition in terms of SOM compartments with different turnover rates, and SOM turnover processes at the DHSBR. The effect of carbon isotope fractionation was obvious during transformation of organic matter (OM) from plant debris to SOM in topsoil and SOM turnover processes after the topsoil was buried, which resulted in great increments of OM 13C, respectively. Increments of SOM 13C of topsoil from 13C of plant debris were controlled by SOM turnover rates. Both topsoil SOM 13C and plant debris 13C increase with elevation, indicating regular changes in vegetation species and composition with elevation, which is consistent with the vertical distribution of vegetation at the DHSBR. The six soil profiles at different elevations had similar characteristics in variations of SOM 13C with depth, alterations of SOM contents with depth and that SOM 14C apparent ages increasing with depth, respectively. These are presumably attributed to the regular distribution of different SOM compartments with depth because of their regular turnover during soil development. Depth with the maximal SOM 13C value is different in mechanism and magnitude with penetrating depth of 14C produced by nuclear explosion into atmosphere from 1952 to 1962, and both indicate controls of topography and vegetation on the distribution of SOM carbon isotopes with depth. Elevation exerts indirect controls on the spatial and temporal distribution of SOM carbon isotopes of the studied mountainous soil profiles at the DHSBR. This study shows that mountainous soil profiles at different elevations and with distinctive aboveground vegetation are presumably ideal sites for studies on soil carbon dynamics in different climatic-vegetation zones. 相似文献
5.
Carbon isotope ratios of soil organic matter and their use in assessing community composition changes in Curlew Valley,Utah 总被引:11,自引:0,他引:11
Summary Stable carbon isotope ratios of roots and soil organic matter were measured in Curlew Valley, Utah to determine if changes in the relative dominance of two shrub species had occurred in this salt-desert community. Measurements were made on soil cores along transects stretching from monospecific stands of Ceratoides lanata, a C3 shrub, to monospecific stands of Atriplex confertifolia, a C4 shrub. 13C values of roots and soil organic matter under Ceratoides cover appeared to be in equilibrium with the current plant community. By contrast, 13C values of roots and soils under Atriplex portions of the transects were more negative than would be expected for a C4-dominated community. These results indicate that a change in relative C3/C4 dominance has occurred, and suggest that the C4 shrub Atriplex confertifolia is increasing in importance in this salt-desert community. 相似文献
6.
Significance of instream autotrophs in trophic dynamics of the Upper Mississippi River 总被引:1,自引:0,他引:1
Trophic dynamics of large river–floodplain ecosystems are still not well understood despite development of several conceptual
models over the last 25 years. To help resolve questions about the relative contribution of algal and detrital organic matter
to food webs in the Upper Mississippi River, we (1) separated living and detrital components of ultrafine and fine transported
organic matter (UTOM and FTOM, respectively) by colloidal silica centrifugation; (2) identified stable isotope signatures
(δ13C and δ15N) for these two portions of transported organic matter and other potential organic matter sources; and (3) employed a multiple
source, dual-isotope mixing model to determine the relative contribution of major energy sources to primary consumers and
the potential contribution of basal sources to the biomass of secondary consumers. The δ13C and δ15N of living and detrital fractions of UTOM and FTOM were distinct, indicating clear differences in isotopic composition of
the algal and detrital fractions of transported organic matter. Living and detrital transported organic matter also differed
from other potential organic matter sources by either δ13C or δ15N. A six-source mixing model using both δ13C and δ15N indicated that algal transported organic matter was the major resource assimilated by primary consumers. The contribution
of detrital transported organic matter was small in most cases, but there were a small number of taxa for which it could potentially
contribute to more than half the assimilated diet. Colloidal dissolved organic matter, which includes heterotrophic bacteria,
accounted for only a small fraction of the organic matter assimilated by most primary consumers, indicating that coupling
between microbial processes and metazoan production is minimal. Terrestrial C3 litter from the floodplain forest floor and aquatic macrophytes were also relatively unimportant to the assimilated diet
of primary consumers. Application of the mixing model to compare basal source isotopic ratios to secondary consumers revealed
that most organic matter moving from primary to secondary consumers originated from algal TOM. Our findings indicate that
autochthonous organic matter is the major energy source supporting metazoan production in the main channel of this large river,
at least during the summer. This study joins a number of other investigations performed globally that indicate organic matter
originating from instream production of sestonic and benthic microalgae is a major driver in the trophic dynamics of large
river ecosystems. 相似文献
7.
The areal distribution of organic C contents, 13C values, total N and P and biogenic Si contents in surficial sediments were used to study the distribution, origin and diagenetic transformations of sedimented biogenic debris in the eutrophic subalpine Lake Bled (Slovenia), which for most of the yearhas an anoxic hypolimnion. The influence of an allochthonous input, restricted to the western basin, was clearly traced by higher organic C and total N and P contents, higher 13C values, and higher sedimentation rate in comparison to the eastern basin. The low 13C values of sedimentary organic matter in the major part of the lake, lower than the 13C values of different types of organic matter, suggest that this sedimentary organic matter is most probably the product of a microbial community and not a residue of primary production.The temporal variation of benthic diffusive fluxes of NH4, Si and PO4, derived from modelling the pore water profiles, was related to sedimentation of phytoplanktonic blooms, while the PO4 fluxes were also dependent on changing redox conditions at the sediment-water interface in the period of the winter-spring overtum. The removal of PO4 in pore waters is probably due to the adsorption of phosphate and precipitation of apatite and vivianite. The budget of C, N and P at the sediment-water interface revealed a high recycling efficiency (>70%), also confirmed by the rather uniform (or only slightly decreasing) vertical profiles of organic C, total N and P in sediment cores and C/N and C/P ratios. The percentage of biogenic Si recycling is low (<10%), suggesting its removal in sediments. 相似文献
8.
Origin and trophic importance of detritus-evidence from stable isotopes in the benthos of a small,temperate estuary 总被引:1,自引:0,他引:1
Ratios of 13C/12C and 15N/14N were measured in dissolved inorganic carbon (DIC), marginal vegetation, benthic macrodetritus (diameter > 1 mm) and selected invertebrate consumers in the Gamtoos estuary, South Africa to: (1) trace the provenance of benthic detrital deposits, and (2) determine the extent to which three abundant species of macroinvertebrates utilise this resource. DIC was strongly depleted in 13C with average 13C values (–9.5±0.5) being typical of limnetic waters. Benthic detrital particles (13C–24.1±0.3) originated mainly from marginal vegetation (13C–25.7±0.3), but their slightly elevated carbon ratio suggests additional input from 13C-rich sources-possibly C4 plants cultivated on the floodplain. Populations of the fossorial ghost shrimp Callianassa kraussi, the bentho-pelagic amphipod Grandidierella lignorum and the epifaunal crab Hymenosoma robiculare together account for 96% of total benthic biomass in the upper regions of this estuary. Marked differences in trophic niches were evident among these three consumer species. Ghost shrimp (13C –32.5±0.3) foraged by filter-feeding on fine suspended particulate organic matter (13C–31.2±0.5). Amphipods (13C–28.0±0.6) utilised some benthic detritus but fed mainly on suspended material. Only the relatively rare crabs (13C–23.8±1.5) appeared to utilise benthic detrital particles to any significant extent. In the benthic consumer community of the upper Gamtoos estuary, suspension feeders make up 98% of biomass and thus clearly dominate over deposit feeders. This can be traced to the low contribution of higher plants (c. 13%) to overall carbon production, and detritus originating from macrophytes is consequently relatively unimportant in supporting invertebrate secondary production in this particular system. 相似文献
9.
The Pantanal of Mato Grosso, Brazil, is a large, seasonal wetland, which exhibits high macrophyte productivity at the beginning of the rainy season, when the floodplain becomes flooded. During inundation, from December through May, there is rapid turnover of decomposing macrophyte litter, which is subsequently colonized and consumed by various organisms. In this paper, the variation in the carbon and nitrogen isotope signatures of decomposing macrophytes and detritus was determined to provide an isotopic baseline for the elucidation of higher trophic levels. Seven abundant macrophyte species, Cyperaceae sp., Pontederia lanceolata, Cabomba furcata, Salvinia auriculata, Eichhornia crassipes, Nymphaea amazonum and Paspalum repens, were exposed in mesocosm decomposition experiments lasting 21 or 100 days. Stable isotope ratios of carbon and nitrogen and the atomic C/N ratios were determined for decomposing plant material, particulate organic matter (POM), the microbial film, and aquatic invertebrate larvae. The 13C values for the macrophytes did not change during decomposition. However, the variability of 15N was high (range of ± 6 ) due to microbial activity. There was no consistent difference in the isotopic signatures of macrophytes and POM. C/N ratios decreased from 17 to 50 in macrophytes, to 7 to 12 in POM. The isotopic signatures and C/N ratios of the microbial film were the same as those of POM. We concluded that heterotrophic processes did not fractionate stable carbon isotopes but caused an increase in the variability of stable nitrogen ratios and a change in the C/N ratios in our experimental system. Therefore, it was not possible to distinguish fresh and senescent material or even POM when used as a food source. The 13C values of the aquatic larvae were closely coupled to those of the carbon source provided. 相似文献
10.
In southeastern Arizona, Prosopis juliflora (Swartz) DC. and Quercus emoryi Torr. are the dominant woody species at grassland/woodland boundaries. The stability of the grassland/woodland boundary in this region has been questioned, although there is no direct evidence to confirm that woodland is encroaching into grassland or vice versa. We used stable carbon isotope analysis of soil organic matter to investigate the direction and magnitude of vegetation change along this ecotone. 13C values of soil organic matter and roots along the ecotone indicated that both dominant woody species (C3) are recent components of former grasslands (C4), consistent with other reports of recent increases in woody plant abundance in grasslands and savannas throughout the world. Data on root biomass and soil organic matter suggest that this increase in woody plant abundance in grasslands and savannas may increase carbon storage in these ecosystems, with implications for the global carbon cycle. 相似文献
11.
Recorders of reef environment histories: stable isotopes in corals,giant clams,and calcareous algae 总被引:5,自引:0,他引:5
Paul Aharon 《Coral reefs (Online)》1991,10(2):71-90
Time-series 18O and 13C records from cohabiting massive coralPorites australiensis and giant clamTridacna gigas from the Great Barrier Reed of Australia, and from calcareous green algae in a core through modernHalimeda bioherm accreting in the eastern Java Sea, provide insights into the complex links between environmental factors and stable isotopes imprinted in these reef skeletal materials. The aragonitic coral and giant clam offer 20 years and 15 years of growth history, respectively. The giant clam yields mean 18O and 13C values of-0.5±0.5 and 2.2±0.2 (n=67), which agree well with the predicted equilibrium values. The coral yields mean 18O and 13C values of-5.6±0.5 and-1.8±0.7 (n=84), offering a striking example of kinetic and metabolic fractionation effects. Although both the coral and giant clam harbor symbionts and were exposed to a uniform ambient environment during their growth histories, their distinct isotopic compositions demonstrate dissimilar calcification pathways. The 18O records contain periodicities corresponding to the alternating annual density bands revealed by X-radiography and optical transmitted light. Attenuation of the 18O seasonal amplitudes occurring in the giant clam record 8 years after skeletal growth commenced is attributed to a changeover from fast to slow growth rates. Extreme seasonal 18O amplitudes of up to 2.2 discerned in both the coral and giant clam records exceed the equivalent seasonal temperature contrast in the reef environment, and are caused by the combined effect of rainfall and evaporation during the monsoon and dry seasons, respectively. Thus in addition of being useful temperature recorders, reef skeletal material of sufficient longevity, such asPorites andTridacna, may also indicate rainfall variations. Changing growth rates, determined from the annual growth bands, may exert a primary control on the coral 13C record which shows a remarkable negative shift of 1.7 over its growth history, by comparison with only 0.15 negative shift in the contemporaneous giant clam record. Use of coral 13C records as proxies of fossil fuel CO2 uptake by the ocean must be regarded with caution. The 18O and 13C records fromHalimeda are remarkably uniform over 1000 years of bioherm accretion history (18O=-1.7±0.2; 13C=3.9±0.1,n=28), in spite of variable Mg-calcite cements present in the utricles. Most of the cement infilling is probably syndepositional, and both theHalimeda aragonite and the Mg-calcite cements containign 12.3 mole % MgCO3 are deposited in isotopic equilibrium. Therefore, in favorable circumstances these algal skeletal remains may act as the shallow water analogs of benthic foraminifera in deep sea sediments in recording ambient sea water isotopic composition and temperature. 相似文献
12.
This paper reviews progress in understanding the processes which are important in elemental interactions and which influence organic matter composition of soils of the Great Plains in N. America. Comparison of grassland (semiarid) soils along environmental gradients and cultivation chrono- and toposequences with adjacent forest (subhumid) soils and consideration of the C/N/P/S ratios of organic matter of genetic horizons in the solum have emphasized the importance of movement of low molecular weight organic compounds in soil solution in addition to microbial degradation in the formulation of organic matter in soils. Phosphorus forms and transformations help to provide both an index on weathering and insight into textural influences. Use of 15N and 34S in combination with14C and other radioisotopes has provided valuable information on processes. Submicroscopy techniques in combination with cytoplasmic staining techniques have focussed attention in a realistic way on the mechanisms of organic matter stability. More attention must be paid to the catalytic role of soil inorganic constituents and selected minerals in the abiotic formation of stable organic matter. Conceptual and mathematical simulation models have an invaluable role in focussing attention on important processes and verifying hypotheses. 相似文献
13.
14.
Stable isotope ratios of soil carbonate and soil organic matter as indicators of forest invasion of prairie near Ames,Iowa 总被引:3,自引:0,他引:3
Stable isotope ratios of pedogenic carbonate and organic matter were measured in a prairie-transition-forest soil biosequence near Ames, Iowa to determine the vegetation succession. The modern vegetation is dominated by non-native C3 plants which have been introduced by agricultural practices. The 13C values of soil organic matter from the prairie and forest endmembers indicate C4 and C3 dominated ecosystems, respectively, during the accumulation of soil organic matter. Pedogenic carbonate from all soils, including rare pedogenic carbonate from the forested soil, has an average 13C of-2.0, indicating that the carbonate formed under a C4 vegetation. These results indicate that the ecosystem was a C4-dominated prairie and therefore suggest a recent arrival of forests and other C3 plants in the area. This study also implies that the primary features of the transitional Lester soil series, which has soil properties intermediate between Alfisols and Molisolls, formed under prairie conditions and were overprinted by an invading forest. 相似文献
15.
The 13C signature of organic carbon in estuarine bottom sediment in Louisiana Barataria Basin was used for estimating carbon flux from adjacent marsh. The stable carbon isotope composition of plants, soils and sediments from the basin were determined. The 13C content of marsh vegetation ranged from -26.3 to -27.8% for C3 freshwater vegetation in the upper basin to -13.0 to -13.3% for C4 vegetation in the lower basin. The 13C content of the highly organic marsh soils were similar to 13C content of vegetation present. The 13C content of organic carbon from bottom sediment of open water bodies ranged from 27.3 in the upper basin (freshwater) to 16.4 in bottom sediment of salt marsh ponds. The13C signature of organic carbon in bottom sediment from saline regions corresponded to the size of the body of water. The smaller salt marsh ponds contain sediment with 13C values close to that of the C4 plantSpartina alterniflora. Results suggest that phytoplankton rather thanSpartina alterniffora is the likely organic source in bottom sediment of the larger bay near the coast (e.g. Caminada Bay). 相似文献
16.
Evanilde Benedito cecilio Alexandre Leandro pereira Cássia Mônica sakuragui 《Environmental Biology of Fishes》2004,71(4):313-320
In this paper we analysed autotrophic sources of the carbon (
13C) and the trophic position (
15N) of Leporinus friderici in the influence area of Corumbá Reservoir, Brazil. We collected samples of muscles of fish from different sizes riparian vegetation, C4 grasses, zooplankton, periphyton and particulate organic carbon (POC). There were significant differences for the carbon isotope proportion found in muscles of L.friderici in the different size groups analysed. The highest values of
13C recorded for middle sized individuals is attributed to the large contribution of C4 plants in their diet. Small individuals sampled upstream also receive similar contribution from C4 plants. In contrast the same size group sampled downstream from the reservoir, has a much smaller of C4 plants. The
13C negative character of small individuals from downstream is due to the larger contribution of C3 plants (except periphyton). At larger sizes we found intermediate
13C values. The
15N proportions we found for each size group were not significantly different, however we found decreasing mean values with increasing size. The trophic level calculated from the dietary data was higher than that found with the
13C concentration in the muscle, except for small individuals, when the values were equal. 相似文献
17.
Ichiro Tayasu Toshio Nakamura Hirotaka Oda Fujio Hyodo Yoko Takematsu Takuya Abe 《Ecological Research》2002,17(2):195-206
Stable (13C and 15N) and radio- (14C, 137Cs and 210Pb) isotopes were determined for termites that
have been sampled from a dry evergreen forest in Thailand. A wood-feeding termite, Microcerotermes crassus, was separated from soil-feeders: Termes propinquus, Termes comis and Dicuspiditermes makhamensis by 13C and 15N values. The Termes group in Thailand had less diverse values in 13C and 15N than those in Australia, where the feeding habits of the Termes group are more diverse. Other soil-feeding termites produced similar 13C values, but a larger range in 15N values. 14C-percent modern carbon (pMC) values suggest that the soil-feeding termites used younger carbon than the wood-feeding termites, and this was consistent with the termites from Cameroon, central Africa. Values of 13C and 14C-pMC indicate that surface soil was used by a soil-feeding termite, D. makhamensis, in making the nest mounds, and deeper soil (10–30 cm) by a fungus-growing termite, Macrotermes carbonarius. 210Pb and 137Cs were scarcely incorporated into the termites, although 214Pb was recovered from the workers. The results suggest that stable- and radioisotopes are useful in the study of detritivorous animals, organic matter decomposition and ecosystem engineering.Takuya Abe - deceased. 相似文献
18.
Dehairs F. Rao R. G. Chandra Mohan P. Raman A.V. Marguillier S. Hellings L. 《Hydrobiologia》2000,431(2-3):225-241
Stable carbon isotopic composition and C/N ratio were used to trace the input of carbon associated with mangrove litter into the estuary of the Godavari–Gautami delta system and Kakinada bay (Andhra Pradesh, India). Suspended organic matter in the mangrove channels was more depleted in 13C (average 13C = –24.5) than in Kakinada bay which showed 13C values for suspended matter (average 13C = –22.7) closer to those expected for marine phytoplankton. Suspended organic matter from mangrove channels was enriched in nitrogen (average C/N atom ratio 12.7) and 13C (average 13C = –24.5) relative to mangrove leaf litter, which had a C/N ratio of 75 and a 13C value of –28. Lowest C/N ratios for suspended matter were observed during southwest monsoon when rainfall was highest. Although in general, mangrove litter fall was also lower during this period, no clear correlation was observed between litter fall and C/N ratio of suspended matter. In general, the composition of suspended matter pointed towards phytoplankton as a major component. Isotopic composition of zooplankton suggested selective feeding on 13C-enriched, marine phytoplankton in open Kakinada bay and on 13C-depleted organic matter, such as estuarine phytoplankton and mangrove litter, in the mangrove channels. From the 13C signature, it appeared that mangrove carbon was present to some extent in zooplankton and macrofauna from the mangrove mudflats and channels, but the signal rapidly decreased in Kakinada bay. Nitrogen isotopic composition of zooplankton and macrofauna indicated a progressive enrichment of 15N away from the mangrove forest towards the northern part of Kakinada bay, in approach of Kakinada city. This is thought to reflect input of anthropogenic nitrogen enriched in 15N and subsequent uptake of this enriched nitrogen into the aquatic food chain. 相似文献
19.
The aragonite constructions of the Black Sea are formed in a stable anaerobic zone and are a perfect object to study the natural mechanism of anaerobic methane oxidation. The most probable pathway of methane oxidation is its methanogen-mediated reaction with bicarbonates, dissolved in seawater, with the formation of water and acetate, which is then consumed by other components of the anaerobic community. Comparison of the 13C values of carbonate minerals and organic matter once more demonstrated that the formation of the organic matter of biomass is accompanied by intense fractionation of carbon isotopes, as a result of which the total organic matter of biomass acquires an extremely light isotopic composition, characterized by 13C values as low as –83.8. 相似文献
20.
15N abundance of surface soils,roots and mycorrhizas in profiles of European forest soils 总被引:6,自引:0,他引:6
Peter Högberg Lars Högbom Helga Schinkel Mona Högberg Christian Johannisson Håkan Wallmark 《Oecologia》1996,108(2):207-214
15N natural abundances of soil total N, roots and mycorrhizas were studied in surface soil profiles in coniferous and broadleaved forests along a transect from central to northern Europe. Under conditions of N limitation in Sweden, there was an increase in 15N of soil total N of up to 9% from the uppermost horizon of the organic mor layer down to the upper 0–5 cm of the mineral soil. The 15N of roots was only slightly lower than that of soil total N in the upper organic horizon, but further down roots were up to 5% depleted under such conditions. In experimentally N-enriched forest in Sweden, i.e. in plots which have received an average of c. 100 kg N ha–1 year–1 for 20 years and which retain less than 50% of this added N in the stand and the soil down to 20 cm depth, and in some forests in central Europe, the increase in 15N with depth in soil total N was smaller. An increase in 15N of the surface soil was even observed on experimentally N-enriched plots, although other data suggest that the N fertilizer added was depleted in15N. In such cases roots could be enriched in15N relative to soil total N, suggesting that labelling of the surface soil is via the pathway: — available pools of N-plant N-litter N. Under N-limiting conditions roots of different species sampled from the same soil horizon showed similar 15N. By contrast, in experimentally N-enriched forest 15N of roots increased in the sequence: ericaceous dwarf shrubs15N enriched compounds in fungal material, which could contribute to explain the observed 15N profiles if fungal material is enriched, because it is a precursor of stable organic matter and recalcitrant N. This could act in addition to the previous explanation of the isotopically lighter soil surface in forests: plant uptake of 15N-depleted N and its redeposition onto the soil surface by litter-fall. 相似文献