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1.
W. Beyschlag S. Hanisch S. Friedrich A. Jentsch & C. Werner 《Plant biology (Stuttgart, Germany)》2009,11(5):713-724
δ15 N and total nitrogen content of above- and belowground tissues of 13 plant species from two successional stages (open pioneer community and ruderal grass stage) of a dry acidic grassland in Southern Germany were analysed, in order to evaluate whether resource use partitioning by niche separation and N input by N2 -fixing legumes are potential determinants for species coexistence and successional changes. Within each stage, plants from plots with different legume cover were compared. Soil inorganic N content, total plant biomass and δ15 N values of bulk plant material were significantly lower in the pioneer stage than in the ruderal grass community. The observed δ15 N differences were rather species- than site-specific. Within both stages, there were also species-specific differences in isotopic composition between above- and belowground plant dry matter. Species-specific δ15 N signatures may theoretically be explained by (i) isotopic fractionation during microbial-mediated soil N transformations; (ii) isotopic fractionation during plant N uptake or fractionation during plant–mycorrhiza transfer processes; (iii) differences in metabolic pathways and isotopic fractionation within the plant; or (iv) partitioning of available N resources (or pools) among plant groups or differential use of the same resources by different species, which seems to be the most probable route in the present case. A significant influence of N2 -fixing legumes on the N balance of the surrounding plant community was not detectable. This was confirmed by the results of an independent in situ removal experiment, showing that after 3 years there were no measurable differences in the frequency distribution between plots with and without N2 -fixing legumes. 相似文献
2.
Red clover, Trifolium pratense L., is the dominant forage legume in Sweden and is usually harvested twice per year, once in June and once in August. Two 15 N-based methods –15 N isotopic dilution (ID) and 15 N natural abundance (NA) – were used to study N2 fixation from spring until first harvest in late June, from first to second harvest in late August, and from second harvest until first frost in autumn in Umeå, Sweden. The material studied comprized three neighbouring fields carrying a first year ley, a second year ley and a third year ley. For the 15 N ID method, small amounts of highly enriched 15 N-nitrate were added to experimental plots. The non-legumes in the plots, essentially Phleum pratense L. together with Festuca pratensis L., served as reference plants for both the ID and 15 N NA measurements. Dry matter, N and 15 N were separately analysed in leaves (laminae), stems (including petioles), stubble and roots. The proportion of N derived from air (pNdfa) was then calculated for each plant part and for whole plants. Estimates of the proportion of N derived from N2 fixation (pNdfa) were always very high, usually ≥0.8. Generally, estimates of pNdfa obtained by the ID and NA methods were similar, but the ID method gave higher estimates of pNdfa than the NA method when the highest N2 fixation levels were recorded, at the August harvest. Regression analyses suggest that estimates of pNdfa in leaves could provide useful indications of pNdfa in shoots and whole T. pratense plants, thus avoiding the need for time-consuming root analyses. 相似文献
3.
Snow depth, soil freezing, and fluxes of carbon dioxide, nitrous oxide and methane in a northern hardwood forest 总被引:14,自引:0,他引:14
PETER M. GROFFMAN JANET P. HARDY† CHARLES T. DRISCOLL‡ TIMOTHY J. FAHEY§ 《Global Change Biology》2006,12(9):1748-1760
Soil–atmosphere fluxes of trace gases (especially nitrous oxide (N2 O)) can be significant during winter and at snowmelt. We investigated the effects of decreases in snow cover on soil freezing and trace gas fluxes at the Hubbard Brook Experimental Forest, a northern hardwood forest in New Hampshire, USA. We manipulated snow depth by shoveling to induce soil freezing, and measured fluxes of N2 O, methane (CH4 ) and carbon dioxide (CO2 ) in field chambers monthly (bi-weekly at snowmelt) in stands dominated by sugar maple or yellow birch. The snow manipulation and measurements were carried out in two winters (1997/1998 and 1998/1999) and measurements continued through 2000. Fluxes of CO2 and CH4 showed a strong seasonal pattern, with low rates in winter, but N2 O fluxes did not show strong seasonal variation. The snow manipulation induced soil freezing, increased N2 O flux and decreased CH4 uptake in both treatment years, especially during winter. Annual N2 O fluxes in sugar maple treatment plots were 207 and 99 mg N m−2 yr−1 in 1998 and 1999 vs. 105 and 42 in reference plots. Tree species had no effect on N2 O or CO2 fluxes, but CH4 uptake was higher in plots dominated by yellow birch than in plots dominated by sugar maple. Our results suggest that winter fluxes of N2 O are important and that winter climate change that decreases snow cover will increase soil:atmosphere N2 O fluxes from northern hardwood forests. 相似文献
4.
This study investigated the impact of lipid extraction, CaCO3 removal and of both treatments combined on fish tissue δ13 C, δ15 N and C:N ratio. Furthermore, the suitability of empirical δ13 C lipid normalization and correction models was examined. δ15 N was affected by lipid extraction (increase of up to 1·65‰) and by the combination of both treatments, while acidification alone showed no effect. The observed shift in δ15 N represents a significant bias in trophic level estimates, i.e. lipid-extracted samples are not suitable for δ15 N analysis. C:N and δ13 C were significantly affected by lipid extraction, proportional to initial tissue lipid content. For both variables, rates of change with lipid content (ΔC:N and Δδ13 C) were species specific. All tested lipid normalization and correction models produced biased estimates of fish tissue δ13 C, probably due to a non-representative database and incorrect assumptions and generalizations the models were based on. Improved models need a priori more extensive and detailed studies of the relationships between lipid content, C:N and δ13 C, as well as of the underlying biochemical processes. 相似文献
5.
Interactive effects of elevated atmospheric CO2 and arbuscular mycorrhizal (AM) fungi on biomass production and N2 fixation were investigated using black locust ( Robinia pseudoacacia ). Seedlings were grown in growth chambers maintained at either 350 μmol mol−1 or 710 μmol mol−1 CO2 . Seedlings were inoculated with Rhizobium spp. and were grown with or without AM fungi. The 15 N isotope dilution method was used to determine N source partitioning between N2 fixation and inorganic fertilizer uptake. Elevated atmospheric CO2 significantly increased the percentage of fine roots that were colonized by AM fungi. Mycorrhizal seedlings grown under elevated CO2 had the greatest overall plant biomass production, nodulation, N and P content, and root N absorption. Additionally, elevated CO2 levels enhanced nodule and root mass production, as well as N2 fixation rates, of non- mycorrhizal seedlings. However, the relative response of biomass production to CO2 enrichment was greater in non-mycorrhizal seedlings than in mycorrhizal seedlings. This study provides strong evidence that arbuscular mycorrhizal fungi play an important role in the extent to which plant nutrition of symbiotic N2 -fixing tree species is affected by enriched atmospheric CO2 . 相似文献
6.
Symbiotic N2 fixation in a high Alpine grassland: effects of four growing seasons of elevated CO2 总被引:1,自引:0,他引:1
J. A. Arnone Iii 《Functional ecology》1999,13(3):383-387
1. Increasing carbon dioxide concentration (E: 680 μl CO2 litre–1 vs ambient, A: 355 μl CO2 litre–1 ) around late-successional Alpine sedge communities of the Swiss Central Alps (2450 m) for four growing seasons (1992–1995) had no detectable effect on symbiotic N2 fixation in Trifolium alpinum —the sole N2 -fixing plant species in these communities (74 ± 30 mg N m–2 year–1 , A and E plots pooled).
2. This result is based on data collected in the fourth growing season showing that elevated CO2 had no effect on Trifolium above-ground biomass (4·4 ± 1·7 g m–2 , A and E plots pooled, n = 24) or N content per unit land area (124 ± 51 mg N m–2 , A and E pooled), or on the percentage of N Trifolium derived from the atmosphere through symbiotic N2 fixation (%Ndfa: 61·0 ± 4·1 across A and E plots) estimated using the 15 N dilution method.
3. Thus, it appears that N inputs to this ecosystem via symbiotic N2 fixation will not be dramatically affected in the foreseeable future even as atmospheric CO2 continues to rise. 相似文献
2. This result is based on data collected in the fourth growing season showing that elevated CO
3. Thus, it appears that N inputs to this ecosystem via symbiotic N
7.
J. PEARSON D. M. WELLS K. J. SELLER A. BENNETT A. SOARES J. WOODALL & M. J. INGROUILLE 《The New phytologist》2000,147(2):317-326
Mosses have been used as biomonitors of atmospheric pollution for some years, but few studies have been carried out on the effect of NOx emissions from traffic on moss tissue N. Eight species of moss (102 samples) growing on walls or roofs next to roads exposed to different traffic densities were collected from urban and rural sites in the UK. The shoots were sampled for total N, their stable isotope 15 N/14 N content (δ15 N) and heavy metal content (Pb, Zn). There was a lack of correlation between tissue total N and traffic exposure, but a very good correlation between traffic exposure and tissue δ15 N. Plants collected near motorways or busy urban roads had δ15 N values ranging between +6 and −1‰, while in rural areas with hardly any traffic these ranged from −2 to −12‰. In a separate survey of mosses, the average δ15 N of shoots from busy roadsides in London was +3.66‰, whereas from samples collected from farm buildings near poultry or cattle pens it was −7.8‰. This indicates that the two main atmospheric N sources, NOx and NHx , have different δ15 N signatures, the former tending to be positive and the latter negative. Tissue concentrations of both Pb and Zn show a strong positive correlation with traffic exposure, with Zn in particular being greater than Pb. The results are discussed with regard to the use of moss tissue Zn as a means for monitoring or mapping pollution from vehicles, and of δ15 N as an aid to distinguish between urban (NOx ) and rural (NHx ) forms of N pollution. 相似文献
8.
Leif Skøt 《Physiologia plantarum》1983,59(4):581-584
The quantitative relationship between C2 H2 reduction, H2 evolution and 15 N2 fixation was investigated in excised root nodules from pea plants ( Pisum sativum L. cv. Bodil) grown under controlled conditions. The C2 H2 /N2 conversion factor varied from 3.31 to 5.12 between the 32nd and the 67th day after planting. After correction for H2 evolution in air, the factor (C2 H2 -H2 )/N2 decreased to values near the theoretical value 3, or in one case to a value significantly ( P < 0.05) below 3. The proportion of the total electron flow through nitrogenase, which is not wasted in H2 production but used for N2 reduction, is often stated as the relative efficiency (1-H2 /C2 H2 ). This factor varied significantly ( P < 0.05) during the growth period. The actual allocation of electrons to H2 and N2 , expressed as the H2 /N2 ratio, was independent of plant age, however. This discrepancy and the observation that the (C2 H2 -H2 )/N2 conversion factor tended to be lower than 3, suggests that the C2 H2 reduction assay underestimates the total electron flow through nitrogenase. 相似文献
9.
We report a novel use of the 15 N dilution technique to detail the translocation of amino compounds in the legume Sesbania rostrata . The conventional 15 N dilution technique follows the dilution of 15 N within a labelled plant, as 14 N2 is fixed by symbiotic bacteria. In our experiments, stem-nodulated Sesbania rostrata were enriched by feeding with 15 N ammonium nitrate for 2 weeks, followed by a 1 week period where the only N available to the plants was via nitrogen fixation of atmospheric N2 . We measured the composition, concentration and 15 N enrichment of amino compounds in various plant tissues, both above and below the stem nodules, using GC-MS and isotopic abundance mass spectrometry techniques. Approximately 28% of the total N in the stem nodules was derived from internal plant sources. The ureides allantoic acid and allantoin were not abundant in xylem, leaf or nodule tissues. The amides asparagine and glutamine were the major export products from stem nodules although a wide range of other amino compounds are also synthesized. Amino acids within the nodules had a low level of enrichment, demonstrating that a small fraction (≈ 11%) was derived from outside the nodules, and significant cycling of N (28% of xylem N) through the root system was revealed by measurements of 15 N distribution and amino acid concentrations. 相似文献
10.
11.
Ecosystem CO2 and N2 O exchanges between soils and the atmosphere play an important role in climate warming and global carbon and nitrogen cycling; however, it is still not clear whether the fluxes of these two greenhouse gases are correlated at the ecosystem scale. We collected 143 pairs of ecosystem CO2 and N2 O exchanges between soils and the atmosphere measured simultaneously in eight ecosystems around the world and developed relationships between soil CO2 and N2 O fluxes. Significant linear regressions of soil CO2 and N2 O fluxes were found for all eight ecosystems; the highest slope occurred in rice paddies and the lowest in temperate grasslands. We also found the dominant role of growing season on the relationship of annual CO2 and N2 O fluxes. No significant relationship between soil CO2 and N2 O fluxes was found across all eight ecosystem types. The estimated annual global N2 O emission based on our findings is 13.31 Tg N yr−1 with a range of 8.19–18.43 Tg N yr−1 for 1980–2000, of which cropland contributes nearly 30%. Our findings demonstrated that stoichiometric relationships may work on ecological functions at the ecosystem level. The relationship of soil N2 O and CO2 fluxes developed here could be helpful in biogeochemical modeling and large-scale estimations of soil CO2 and N2 O fluxes. 相似文献
12.
Abstract A denitrifying Cytophaga was isolated from soil enriched by anaerobic incubation with glucose, sulfide (S2− ), nitrous oxide (N2 O), and acetylene (C2 H2 ). Such soil enrichments and pure cultures of the isolated Cytophaga reduced N2 O rapidly even in the presence of a normally inhibitory concentration of C2 H2 (4 kPa) providing S2− was present (8 μmol/g soil or 0.4 μmol/ml culture). Since C2 H2 inhibition of the reduction of N2 O is used as a tool in the assay of denitrification, the presence in large numbers of such a Cytophaga may influence the effectiveness of this assay especially in sulfidic environments. 相似文献
13.
LYDIE CHAPUIS-LARDY NICOLE WRAGE† AURÉLIE METAY‡ JEAN-LUC CHOTTE§ MARTIAL BERNOUX§ 《Global Change Biology》2007,13(1):1-17
Soils are the main sources of the greenhouse gas nitrous oxide (N2 O). The N2 O emission at the soil surface is the result of production and consumption processes. So far, research has concentrated on net N2 O production. However, in the literature, there are numerous reports of net negative fluxes of N2 O, (i.e. fluxes from the atmosphere to the soil). Such fluxes are frequent and substantial and cannot simply be dismissed as experimental noise.
Net N2 O consumption has been measured under various conditions from the tropics to temperate areas, in natural and agricultural systems. Low mineral N and large moisture contents have sometimes been found to favour N2 O consumption. This fits in with denitrification as the responsible process, reducing N2 O to N2 . However, it has also been reported that nitrifiers consume N2 O in nitrifier denitrification. A contribution of various processes could explain the wide range of conditions found to allow N2 O consumption, ranging from low to high temperatures, wet to dry soils, and fertilized to unfertilized plots. Generally, conditions interfering with N2 O diffusion in the soil seem to enhance N2 O consumption. However, the factors regulating N2 O consumption are not yet well understood and merit further study.
Frequent literature reports of net N2 O consumption suggest that a soil sink could help account for the current imbalance in estimated global budgets of N2 O. Therefore, a systematic investigation into N2 O consumption is necessary. This should concentrate on the organisms, reactions, and environmental factors involved. 相似文献
Net N
Frequent literature reports of net N
14.
Abstract: Over 60 Salsola species of Chenopodiaceae from South Africa were studied for their photosynthesis type, using δ13 C analysis and light microscopy of leaf anatomy. These species cover about 70 % of the total list of Southern African Salsola species and grow naturally in South and Southwest African desert regions. All species are shrubby forms and belong to the single subsection Caroxylon. Only C4 photosynthesis was found in the Salsola species determined with 13 C/12 C carbon isotope discrimination values that ranged from - 11.04 to - 14.03 % (PDB), plus the presence of a Kranz type assimilation tissue anatomy. The apparent absence of C3 in Salsola in South and Southwest Africa and the known presence of C3 and C3 - C4 intermediate photosynthesis in Caroxylon, Salsola species in Asia strongly indicate that the genus Salsola originated in Asia and later migrated to South Africa. 相似文献
15.
A. KOHZU T. YOSHIOKA T. ANDO M. TAKAHASHI K. KOBA & E. WADA 《The New phytologist》1999,144(2):323-330
The natural abundance of 13 C and 15 N was measured in basidiocarps of at least 115 species in 88 genera of ectomycorrhizal, wood-decomposing and litter-decomposing fungi from Japan and Malaysia. The natural abundance of 13 C and 15 N was also measured in leaves, litter, soil and wood from three different sites. 15 N and 13 C were enriched in ectomycorrhizal and wood-decomposing fungi, respectively, relative to their substrates. Ectomycorrhizal and wood-decomposing fungi could be distinguished on the basis of their δ13 C and δ15 N signatures. Although there was high variability in the isotopic composition of fungi, the following isotope- enrichment factors (ε, mean±SD) of the fungi relative to substrates were observed:
εectomycorrhizal fungi/litter = 6.1±0.4‰15 N
εectomycorrhizal fungi/wood = 1.4±0.8‰13 C
εwood-decomposing fungi/wood = −0.6±0.7‰15 N
εwood-decomposing fungi/wood = 3.5±0.9‰13 C
The basis of isotope fractionation in C metabolism from wood to wood-decomposing fungus is discussed. 相似文献
ε
ε
ε
ε
The basis of isotope fractionation in C metabolism from wood to wood-decomposing fungus is discussed. 相似文献
16.
《The New phytologist》1998,139(3):595-595
The following citations were erroneously omitted from the 'References':
Groffman PM, Zak DR, Christensen S, Mosier A, Tiedje JM. 1993. Early spring nitrogen dynamics in a temperate forest landscape. Ecology 74 : 1579–1585.
Handley LL, Brendel O, Scrimgeour CM, Schmidt S, Raven JA, Turnbull MH, Stewart GR. 1996. The15 N natural abundance patterns of field-collected fungi from three kinds of ecosystems. Rapid Communications in Mass Spectrometry 10 : 974–978.
Handley LL, Daft MJ, Wilson J, Scrimgeour CM, Ingleby K, Sattar, MA. 1993. Effects of the ecto- and VA-mycorrhizal fungi Hydnagium carneum and Glomus clarum on the δ15 N and δ13 C values of Eucalyptus globulus and Ricinus communis. Plant, Cell and Environment 16 : 375–382.
Handley LL, Odee D, Scrimgeour CM. 1994. δ15 N and δ13 C patterns in savanna vegetation: dependence on water availability and disturbance. Functional Ecology 8 : 306–314.
Handley LL, Raven JH. 1992. The use of natural abundance of nitrogen isotopes in plant physiology and ecology: commissioned review. Plant, Cell and Environment 15 : 965–985.
Handley LL, Scrimgeour CM. 1997. Terrestrial plant ecology and15 N natural abundance: the present limits to interpretation for uncultivated systems with original data from a Scottish old field. Advances in Ecological Research 27 : 133–212.
Hansen AP, Pate JS. 1987. Evaluation of the15 N natural abundance method and xylem sap analysis for assessing N2 fixation of understorey legumes in jarrah ( Eucalyptus marginata Donn ex Sm.) forest in S.W. Australia. Journal of Experimental Botany 38 : 1446–1458.
New Phytologist apologizes unreservedly to all authors of the above papers for this error. 相似文献
Groffman PM, Zak DR, Christensen S, Mosier A, Tiedje JM. 1993. Early spring nitrogen dynamics in a temperate forest landscape. Ecology 74 : 1579–1585.
Handley LL, Brendel O, Scrimgeour CM, Schmidt S, Raven JA, Turnbull MH, Stewart GR. 1996. The
Handley LL, Daft MJ, Wilson J, Scrimgeour CM, Ingleby K, Sattar, MA. 1993. Effects of the ecto- and VA-mycorrhizal fungi Hydnagium carneum and Glomus clarum on the δ
Handley LL, Odee D, Scrimgeour CM. 1994. δ
Handley LL, Raven JH. 1992. The use of natural abundance of nitrogen isotopes in plant physiology and ecology: commissioned review. Plant, Cell and Environment 15 : 965–985.
Handley LL, Scrimgeour CM. 1997. Terrestrial plant ecology and
Hansen AP, Pate JS. 1987. Evaluation of the
New Phytologist apologizes unreservedly to all authors of the above papers for this error. 相似文献
17.
DARYL CODRON JAMES S. BRINK LLOYD ROSSOUW MARCUS CLAUSS JACQUI CODRON JULIA A. LEE-THORP MATT SPONHEIMER 《Biological journal of the Linnean Society. Linnean Society of London》2008,94(4):755-764
We assess whether interspecific differences in craniodental morphology within a single ruminant feeding guild, the grazers, represent anatomical adaptations to subtle differences in diet. Differences in craniodental anatomy follow a distinct taxonomic pattern that is paralleled by dietary niche differentiation recorded in species' stable carbon (δ13 C) and nitrogen isotope (δ15 N) compositions, strongly supporting a hypothesis for functional divergence within the grazers. We propose that the evolutionary origin of grazers were multifold; at least two and up to four different types of grazing can be discerned within the 11 taxa studied here alone. However, correspondence between craniodental adaptations and isotopic differences across species are not found when only δ13 C data are considered (i.e. morphological differences do not reflect varying proportions of C3 browse to C4 grass consumed). This implies that alternate anatomical adaptations to grazing are not related to differences between variable (part-time browsing) and obligate grazers, as previously predicted. Rather, anatomical differences correlate strongly with changes in δ15 N, which we infer to reflect functional responses to changes in diet quality associated with the degree of feeding selectivity and short-, medium-, or tall-grass grazing. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 94 , 755–764. 相似文献
18.
Joseph M. Craine rew J. Elmore Marcos P. M. Aidar Mercedes Bustamante Todd E. Dawson Erik A. Hobbie Ansgar Kahmen Michelle C. Mack Kendra K. McLauchlan ers Michelsen Gabriela B. Nardoto Linda H. Pardo Josep Peñuelas Peter B. Reich Edward A. G. Schuur William D. Stock Pamela H. Templer Ross A. Virginia Jeffrey M. Welker Ian J. Wright 《The New phytologist》2009,183(4):980-992
Ratios of nitrogen (N) isotopes in leaves could elucidate underlying patterns of N cycling across ecological gradients. To better understand global-scale patterns of N cycling, we compiled data on foliar N isotope ratios (δ15 N), foliar N concentrations, mycorrhizal type and climate for over 11 000 plants worldwide. Arbuscular mycorrhizal, ectomycorrhizal, and ericoid mycorrhizal plants were depleted in foliar δ15 N by 2‰, 3.2‰, 5.9‰, respectively, relative to nonmycorrhizal plants. Foliar δ15 N increased with decreasing mean annual precipitation and with increasing mean annual temperature (MAT) across sites with MAT ≥ −0.5°C, but was invariant with MAT across sites with MAT < −0.5°C. In independent landscape-level to regional-level studies, foliar δ15 N increased with increasing N availability; at the global scale, foliar δ15 N increased with increasing foliar N concentrations and decreasing foliar phosphorus (P) concentrations. Together, these results suggest that warm, dry ecosystems have the highest N availability, while plants with high N concentrations, on average, occupy sites with higher N availability than plants with low N concentrations. Global-scale comparisons of other components of the N cycle are still required for better mechanistic understanding of the determinants of variation in foliar δ15 N and ultimately global patterns in N cycling. 相似文献
19.
Mycorrhizal and saprotrophic (SAP) fungi are essential to terrestrial element cycling due to their uptake of mineral nutrients and decomposition of detritus. Linking these ecological roles to specific fungi is necessary to improve our understanding of global nutrient cycling, fungal ecophysiology, and forest ecology. Using discriminant analyses of nitrogen (δ15 N) and carbon (δ13 C) isotope values from 813 fungi across 23 sites, we verified collector-based categorizations as either ectomycorrhizal (ECM) or SAP in > 91% of the fungi, and provided probabilistic assignments for an additional 27 fungi of unknown ecological role. As sites ranged from boreal tundra to tropical rainforest, we were able to show that fungal δ13 C (26 sites) and δ15 N (32 sites) values could be predicted by climate or latitude as previously shown in plant and soil analyses. Fungal δ13 C values are likely reflecting differences in C-source between ECM and SAP fungi, whereas 15 N enrichment of ECM fungi relative to SAP fungi suggests that ECM fungi are consistently delivering 15 N depleted N to host trees across a range of ecosystem types. 相似文献
20.
We evaluated diurnal and seasonal patterns of carbon isotope composition of leaf dark-respired CO2 ( δ 13 Cl ) in the C3 perennial shrub velvet mesquite ( Prosopis velutina ) across flood plain and upland savanna ecosystems in the south-western USA. δ 13 Cl of darkened leaves increased to maximum values late during daytime periods and declined gradually over night-time periods to minimum values at pre-dawn. The magnitude of the diurnal shift in δ 13 Cl was strongly influenced by seasonal and habitat-related differences in soil water availability and leaf surface vapour pressure deficit. δ 13 Cl and the cumulative flux-weighted δ 13 C value of photosynthates were positively correlated, suggesting that progressive 13 C enrichment of the CO2 evolved by darkened leaves during the daytime mainly resulted from short-term changes in photosynthetic 13 C discrimination and associated shifts in the δ 13 C signature of primary respiratory substrates. The 13 C enrichment of dark-respired CO2 relative to photosynthates across habitats and seasons was 4 to 6‰ at the end of the daytime period (1800 h), but progressively declined to 0‰ by pre-dawn (0300 h). The origin of night-time and daytime variations in δ 13 Cl is discussed in terms of the carbon source(s) feeding respiration and the drought-induced changes in carbon metabolism. 相似文献