Contribution to lignocellulose degradation and DOC formation from a salt marsh macrophyte by the ascomycete Phaeosphaeria spartinicola

Abstract Specifically radiolabeled [¹⁴C-lignin] lignocellulose and uniformly [U-¹⁴C] lignocellulose from the salt marsh grass Spartina alterniflora were incubated with the ascomycete Phaesphaeria s spartinicola . This fungus is the predominant one found on decaying standing dead S. alterniflora leaves in the salt marsh ecosystem. After 45 days of incubation at 20°C, 3.3% of the lignin moiety was mineralized to ¹⁴CO₂ and 2.7% solubilized to DO¹⁴C. Mineralization of the polysaccharides was seven times faster than that of the lignin. About 22% of the radioactivity was evolved as ¹⁴CO₂ but merely 4% was solubilized to DO¹⁴C within the incubation time. Experiments monitoring the ergosterol content of the mycelium incubated with S. alterniflora plant material were done to elucidate the carbon conversion efficiency of the fungus as well as the influence of the cinnamyl phenols p -coumaric and ferulic acid on lignocellulose degration. After 21 days of incubation, P. spartinicola showed a growth yield of 0.45 and 0.38 with and without the additional cinnamyl phenols, respectively. Grown on unextracted S. alterniflora the fungus caused a loss of organic plant material of about 50% with a corresponding growth yield of 0.38 during the incubation period. Investigation of cupric oxide oxidation products of sound and degraded lignocellulose revealed a preferential utilization of the syrinyl and cinnamly phenols compared with vanilly phenols.     

Correlations Between Foliar Stable Carbon Isotope Composition and Environmental Factors in Desert Plant Reaumuria soongorica （Pall.） Maxim.

Leaves of 407 individuals of Reaumuria soongorica （Pall.） Maxim. collected from the major distribution areas were measured to investigate the distribution characteristics of the stable carbon isotope in this desert plant, as well as correlations between δ^13C values and environmental factors. Results showed that δ^13C values in R. soongorica ranged from -22.77‰ to -29.85‰ and that the mean δ^13C value （-26.52‰） was higher than a previously reported δ^13C value for a different desert ecosystem. This indicates that R. soongorica belongs to the C3 photosynthetic pathway and has higher water use efficiency than other species. The correlations between δ^13C values and environmental factors demonstrated that the foliar δ^13C values in R. soongorica increased significantly with decreasing mean annual precipitation and mean relative humidity, and decreased with decreasing duration of sunshine and evaporation. The spatial distribution trend of δ^13C values in R. soongorica was not obvious and there was no significant correlation between the δ^13C values and mean annual temperature. We conclude that different distribution trends in δ^13C values for R. soongorica were likely caused by stomatal limitation rather than by nutrient-related changes in photosynthetic efficiency and that precipitation played an important role in the wide distribution range of R. soongorica. This pattern of δ^13C values for R. soongorica reinforced that it is a super-xerophil in terms of its adaptive strategies to a desert environment.     

Stable isotope profiles of partially migratory salmonid populations in Atlantic rivers of Patagonia

In the present study, profiles of stable isotope composition were characterized for two species with partially migratory populations in rivers along the latitudinal gradient of Patagonia, brown trout Salmo trutta and rainbow trout Oncorhynchus mykiss . The effects of factors ( e.g. ontogeny of fishes, location, species and fasting) that may influence the stable isotope analysis (SIA) were evaluated, as was SIA evaluated as a tool to assign individual fish to their corresponding ecotype. Anadromous fishes exhibited enriched δ¹⁵N (15·2 ± 1·0‰; mean ± s . d .) and δ¹³C (−19·2 ± 1·3‰) relative to resident fishes'δ¹⁵N (8·8 ± 1·1‰) and δ¹³C (−23·2 ± 2·5‰). For both species, the difference in δ¹⁵N was larger between resident (range 6·8–10·7‰) and anadromous (range 14·3–17·8‰) fishes than that in δ¹³C. Values of δ¹³C, while not as dramatically contrasting in rainbow trout, provided a powerful anadromy marker for brown trout in the region. Increases were found in both δ¹⁵N and δ¹³C during the spawning migration of anadromous rainbow trout, most likely due to fasting. Differences in stable isotopes between location, size and species were found, suggesting different stable isotopes base levels in freshwater environments and different trophic levels and feeding location of anadromous populations. The SIA was demonstrated as a powerful tool for ecotype discrimination in Patagonian Rivers, overriding any effect of sampling location, size or species.     

Seasonal and annual changes in leaf δ13C in two co-occurring Mediterranean oaks: relations to leaf growth and drought progression

1. Changes of δ¹³C and its relation to leaf development, biochemical content and water stress were monitored over a 2 year period in two co-occurring Mediterranean oak species: the deciduous Quercus pubescens and the evergreen Quercus ilex .
2. The time course of leaf δ¹³C showed different patterns in the two species. Young Q. pubescens leaves had a high δ¹³C and a marked decrease occurred during leaf growth. In contrast, leaves at budburst and maturity did not differ significantly in the case of Q. ilex . We suggest that the difference between δ¹³C of young leaves was linked to differential use of reserves of carbon compounds in the two species.
3. δ¹³C values of mature leaves were negatively correlated with minimum seasonal values of predawn water potential, suggesting that a functional adjustment to water resources occurred.
4. There was a significant correlation between individual δ¹³C values for two successive years. This interannual dependence showed that δ¹³C rankings between trees were constant through time.     

Correlations between net primary productivity and foliar carbon isotope ratio across a Tibetan ecosystem transect

Warming climate could affect leaf-level carbon isotope composition (δ¹³C) through variations in photosynthetic gas exchange. However, it is still unclear to what extent variations in foliar δ¹³C can be used to detect changes in net primary productivity (NPP) because leaf physiology is only one of many determinants of stand productivity. We aim to examine how well site-mean foliar δ¹³C and stand NPP co-vary across large resource gradients using data obtained from the Tibetan Alpine Vegetation Transects (1900–4900 m, TAVT). The TAVT data indicated a robust negative correlation between foliar δ¹³C and NPP across ecosystems (NPP=−2.7224δ¹³C-67.738, r²=0.60, p<0.001). The mean foliar δ¹³C decreased with increasing annual precipitation and its covariation with mean temperature and soil organic carbon and nitrogen contents. The results were further confirmed by global literature data. Pooled δ¹³C data from global literature and this study explained 60% of variations in annual NPP both from TAVT-measures and MODIS-estimates across 67 sites. Our results appear to support a conceptual model relating foliar δ¹³C and nitrogen concentration (N_mass) to NPP, suggesting that: 1) there is a general (negative) relationship between δ¹³C and NPP across different water availability conditions; 2) in water-limited conditions, water availability has greater effects on NPP than N_mass; 3) when water is not limiting, NPP increases with increasing N_mass.     

Weather and climate controls over the seasonal carbon isotope dynamics of sugars from subalpine forest trees

We examined the environmental variables that influence the δ ¹³C value of needle and phloem sugars in trees in a subalpine forest. We collected sugars from Pinus contorta , Picea engelmannii and Abies lasiocarpa from 2006 to 2008. Phloem and needle sugars were enriched in ¹³C during the autumn, winter and early spring, but depleted during the growing season. We hypothesized that the late-winter and early-spring ¹³C enrichment was due to the mobilization of carbon assimilated the previous autumn; however, needle starch concentrations were completely exhausted by autumn, and we observed evidence of new starch production during episodic warm weather events during the winter and early-spring. Instead, we found that ¹³C enrichment was best explained by the occurrence of cold night-time temperatures. We also observed seasonal decoupling in the ¹³C/¹²C ratios of needle and phloem sugars. We hypothesized that this was due to seasonally-changing source-sink patterns, which drove carbon translocation from the needles towards the roots early in the season, before bud break, but from the roots towards the needles later in the season, after bud break. Overall, our results demonstrate that the ¹³C/¹²C ratio of recently-assimilated sugars can provide a sensitive record of the short-term coupling between climate and tree physiology.     

Starvation and low feeding levels result in an enrichment of 13C in lipids and 15N in protein of Nile tilapia Oreochromis niloticus L.

The influence of different feeding levels below and slightly above maintenance on whole body δ¹³C and δ¹⁵N values of Nile tilapia Oreochromis niloticus was examined. The energy budget of each fish was determined by indirect calorimetry. The δ¹³C values of the lipid-free material of Nile tilapia fed below and slightly above maintenance level did not differ between the feeding groups, but the δ¹³C values in the lipids and the δ¹⁵N values of the lipid-free material showed small but significant differences. Those fish with a negative lipid retention had significantly higher δ¹³C values in the lipid fraction compared to fish that synthesized fatty acids. There was a significant negative correlation between the amount of energy metabolized by the fish and both the δ¹³C values in the lipids and the δ¹⁵N values of the lipid-free material. Fasting and feeding below the maintenance level may influence the isotopic composition of animals and should therefore be considered in ecological and nutritional studies.     

Continuous variation in the pattern of marine v. freshwater foraging in brown trout Salmo trutta L. from Loch Lomond, Scotland

Carbon stable-isotope analysis showed that individual brown trout Salmo trutta in Loch Lomond adopted strategies intermediate to that of freshwater residency or anadromy, suggesting either repeated movement between freshwater and marine environments, or estuarine residency. Carbon stable-isotope (δ¹³C) values from Loch Lomond brown trout muscle tissue ranged from those indicative of assimilation of purely freshwater-derived carbon to those reflecting significant utilization of marine-derived carbon. A single isotope, two-source mixing model indicated that, on average, marine C made a 33% contribution to the muscle tissue C of Loch Lomond brown trout. Nitrogen stable isotope, δ¹⁵N, but not δ¹³C was correlated with fork length suggesting that larger fish were feeding at a higher trophic level but that marine feeding was not indicated by larger body size. These results are discussed with reference to migration patterns in other species.     

δ13C variability of benthic algae: effects of water colour via modulation by stream current

1. Increased water motion is expected to reduce boundary layer diffusion resistance of autotrophs, thereby enabling greater isotopic discrimination against ¹³C such that lower δ¹³C values (ratio of ¹³C : ¹²C) should ensue. A field test of this hypothesis was undertaken by sampling benthic algae in streams of differing current speed.
2. Contrary to the expected negative relationship between δ¹³C and water motion, filamentous benthic algae were found to exhibit higher δ¹³C values in rapid water.
3. Under conditions of low current in the streams studied, concentrations of dissolved organic carbon as measured by water colour are elevated through the microbial decomposition of largely terrestrial organic matter. Photoassimilation of this respired carbon by benthic filamentous algae generates ¹³C‐depletion and lower δ¹³C values, and appears to be substantial enough in the streams used in the present study to override the competing influence of water motion on boundary layer thickness.     

Lignin-modifying enzymes from selected white-rot fungi: production and role from in lignin degradation

Abstract: White-rot fungi produce extracellular lignin-modifying enzymes, the best characterized of which are laccase (EC 1.10.3.2), lignin peroxidases (EC 1.11.1.7) and manganese peroxidases (EC 1.11.1.7). Lignin biodegradation studies have been carried out mostly using the white-rot fungus Phanerochaete chrysosporium which produces multiple isoenzymes of lignin peroxidase and manganese peroxidase but does not produce laccase. Many other white-rot fungi produce laccase in addition to lignin and manganese peroxidases and in varying combinations. Based on the enzyme production patterns of an array of white-rot fungi, three categories of fungi are suggested: (i) lignin-manganese peroxidase group (e.g. P. chrysosporium and Phlebia radiata ), (ii) manganese peroxidase-laccase group (e.g. Dichomitus squalens and Rigidoporus lignosus ), and (iii) lignin peroxidase-laccase group (e.g. Phlebia ochraceofulva and Junghuhnia separabilima ). The most efficient lignin degraders, estimated by ¹⁴CO₂ evolution from ¹⁴C-[Ring]-labelled synthetic lignin (DHP), belong to the first group, whereas many of the most selective lignin-degrading fungi belong to the second, although only moderate to good [¹⁴C]DHP mineralization is obtained using fungi from this group. The lignin peroxidase-laccase fungi only poorly degrade [¹⁴C]DHP.     

δ 13C of CO2 respired in the dark in relation to δ13C of leaf carbohydrates in Phaseolus vulgaris L. under progressive drought

The variations in δ ¹³C in both leaf carbohydrates (starch and sucrose) and CO₂ respired in the dark from the cotyledonary leaves of Phaseolus vulgaris L. were investigated during a progressive drought. As expected, sucrose and starch became heavier (enriched in ¹³C) with decreasing stomatal conductance and decreasing p _i/ p _a during the first half (15 d) of the dehydration cycle. Thereafter, when stomata remained closed and leaf net photosynthesis was near zero, the tendency was reversed: the carbohydrates became lighter (depleted in ¹³C). This may be explained by increased p _i/ p _a but other possible explanations are also discussed. Interestingly, the variations in δ ¹³C of CO₂ respired in the dark were correlated with those of sucrose for both well-watered and dehydrated plants. A linear relationship was obtained between δ ¹³C of CO₂ respired in the dark and sucrose, respired CO₂ always being enriched in ¹³C compared with sucrose by ≈ 6‰. The whole leaf organic matter was depleted in ¹³C compared with leaf carbohydrates by at least 1‰. These results suggest that: (i) a discrimination by ≈ 6‰ occurs during dark respiration processes releasing ¹³C-enriched CO₂; and that (ii) this leads to ¹³C depletion in the remaining leaf material.     

Trophic structure of a boreal forest arthropod community revealed by stable isotope (δ13C, δ15N) analyses

Terrestrial arthropods are important components of boreal ecosystems but relatively little is known about their trophic structure within communities. We measured δ¹³C and δ¹⁵N values in a broad range of arthropod taxa (Coleoptera, Diptera, Ephemeroptera, Homoptera, Hymenoptera, Lepidoptera, Odonata, Orthoptera, Araneae) from boreal forest in Prince Albert National Park, Saskatchewan, Canada. Isotopic measurements supported previous conventional investigations on foraging niches based on stomach content analysis and direct feeding observations but additional, new information was also obtained using the stable isotope approach. Significant differences were observed in both δ¹⁵N and δ¹³C values between various orders and families or superfamilies within orders. Higher variance in stable isotope values for scavengers (e.g. carrion beetles; Coleoptera, Silphidae) and generalists (e.g. ground beetles; Coleoptera, Carabidae) was found compared to specialists (e.g. grasshoppers; Orthoptera). Consistent isotopic differences between terrestrial and aquatic species were not found. However, aquatic insect δ¹³C values tended to be lower than those of their terrestrial counterparts. We discuss the potential for using stable isotope methods to reconstruct trophic linkages and interaction involving arthropods.     

13C/12C isotope fractionation of aromatic hydrocarbons during microbial degradation

The influence of microbial degradation on the ¹³C/¹²C isotope composition of aromatic hydrocarbons is presented using toluene as a model compound. Four different toluene-degrading bacterial strains grown in batch culture with oxygen, nitrate, ferric iron or sulphate as electron acceptors were studied as representatives of different environmental redox conditions potentially prevailing in contaminated aquifers. The biological degradation induced isotope shifts in the residual, non-degraded toluene fraction and the kinetic isotope fractionation factors αC for toluene degradation by Pseudomonas putida (1.0026 ± 0.00017), Thauera aromatica (1.0017 ± 0.00015), Geobacter metallireducens (1.0018 ± 0.00029) and the sulphate-reducing strain TRM1 (1.0017 ± 0.00016) were in the same range for all four species, although they use at least two different degradation pathways. A similar ¹³C/¹²C isotope fractionation factor (αC = 1.0015 ± 0.00015) was observed in situ in a non-sterile soil column in which toluene was degraded under sulphate-reducing conditions. No carbon isotope shifts resulting from soil–hydrocarbon interactions were observed in a non-degrading soil column control with aquifer material under the same conditions. The results imply that microbial degradation of toluene can produce a ¹³C/¹²C isotope fractionation in the residual hydrocarbon fraction under different environmental conditions.     

Links between methanotroph community composition and CH4 oxidation in a pine forest soil

The main gap in our knowledge about what determines the rate of CH₄ oxidation in forest soils is the biology of the microorganisms involved, the identity of which remains unclear. In this study, we used stable-isotope probing (SIP) following ¹³CH₄ incorporation into phospholipid fatty acids (PLFAs) and DNA/RNA, and sequencing of methane mono-oxygenase ( pmoA ) genes, to identify the influence of variation in community composition on CH₄ oxidation rates. The rates of ¹³C incorporation into PLFAs differed between horizons, with low ¹³C incorporation in the organic soil and relatively high ¹³C incorporation into the two mineral horizons. The microbial community composition of the methanotrophs incorporating the ¹³C label also differed between horizons, and statistical analyses suggested that the methanotroph community composition was a major cause of variation in CH₄ oxidation rates. Both PLFA and pmoA -based data indicated that CH₄ oxidizers in this soil belong to the uncultivated 'upland soil cluster α'. CH₄ oxidation potential exhibited the opposite pattern to ¹³C incorporation, suggesting that CH₄ oxidation potential assays may correlate poorly with in situ oxidation rates. The DNA/RNA-SIP assay was not successful, most likely due to insufficient ¹³C-incorporation into DNA/RNA. The limitations of the technique are briefly discussed.     

Diurnal and seasonal variation in the carbon isotope composition of leaf dark-respired CO2 in velvet mesquite (Prosopis velutina)

We evaluated diurnal and seasonal patterns of carbon isotope composition of leaf dark-respired CO₂ ( δ ¹³C_l) in the C₃ perennial shrub velvet mesquite ( Prosopis velutina ) across flood plain and upland savanna ecosystems in the south-western USA. δ ¹³C_l 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 ¹³C_l was strongly influenced by seasonal and habitat-related differences in soil water availability and leaf surface vapour pressure deficit. δ ¹³C_l and the cumulative flux-weighted δ ¹³C value of photosynthates were positively correlated, suggesting that progressive ¹³C enrichment of the CO₂ evolved by darkened leaves during the daytime mainly resulted from short-term changes in photosynthetic ¹³C discrimination and associated shifts in the δ ¹³C signature of primary respiratory substrates. The ¹³C 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 ¹³C_l is discussed in terms of the carbon source(s) feeding respiration and the drought-induced changes in carbon metabolism.     

Leaf δ13C reflects ecosystem patterns and responses of alpine plants to the environments on the Tibetan Plateau

Leaf δ¹³C is an indicator of water-use efficiency and provides useful information on the carbon and water balance of plants over longer periods. Variation in leaf δ¹³C between or within species is determined by plant physiological characteristics and environmental factors. We hypothesized that variation in leaf δ¹³C values among dominant species reflected ecosystem patterns controlled by large-scale environmental gradients, and that within-species variation indicates plant adaptability to environmental conditions. To test these hypotheses, we collected leaves of dominant species from six ecosystems across a horizontal vegetation transect on the Tibetan Plateau, as well as leaves of Kobresia pygmaea (herbaceous) throughout its distribution and leaves of two coniferous tree species ( Picea crassifolia, Abies fabri ) along an elevation gradient throughout their distribution in the Qilian Mountains and Gongga Mountains, respectively. Leaf δ¹³C of dominant species in the six ecosystems differed significantly, with values for evergreen coniferous13C values of the dominant species and of K. pygmaea were negatively correlated with annual precipitation along a water gradient, but leaf δ¹³C of A. fabri was not significantly correlated with precipitation in habitats without water-stress. This confirms that variation of δ¹³C between or within species reflects plant responses to environmental conditions. Leaf δ¹³C of the dominant species also reflected water patterns on the Tibetan Plateau, providing evidence that precipitation plays a primary role in controlling ecosystem changes from southeast to northwest on the Tibetan Plateau.     

Enrichment and characterization of a sulfate-reducing toluene-degrading microbial consortium by combining in situ microcosms and stable isotope probing techniques

A toluene-degrading microbial consortium was enriched directly in a BTEX-contaminated aquifer under sulfate-reducing conditions using in situ microcosms consisting of toluene-loaded activated carbon pellets. Degradation of toluene and concomitant sulfide production by the consortium was subsequently demonstrated in laboratory microcosms. The consortium was physiologically and phylogenetically characterized by isotope tracer experiments using nonlabeled toluene, [¹³C]-α-toluene or [¹³C₇]-toluene as growth substrates. Cells incubated with [¹³C]-α-toluene or [¹³C₇]-toluene incorporated 8–15 at.%¹³C and 51–57 at.%¹³C into total lipid fatty acids, respectively, indicating a lower specific incorporation of ¹³C from [¹³C₇]-toluene. In order to identify the toluene-assimilating bacteria, the incorporation of carbon from both [¹³C]-α-toluene and [¹³C₇]-toluene into rRNA was analyzed by stable isotope probing. Time and buoyant density-resolved 16S rRNA gene-based terminal restriction fragment length polymorphism profiles, combined with cloning and sequencing, revealed that an uncultured bacterium (99% sequence similarity) related to the genus Desulfocapsa was the main toluene-degrading organism in the consortium. The ratio of the respective terminal restriction fragments changed over time, indicating trophic interactions within this consortium.     

THE USE OF STABLE CARBON ISOTOPE ANALYSIS FOR DETERMINING THE DIETARY HABITS OF THE FLORIDA MANATEE, TRICHECHUS MANATUS LATIROSTRIS

The sloughed skin from three captive manatees at Lowry Park Zoological Garden (Tampa, Florida) was examined over a period of one year to determine its stable carbon isotopic composition (δ¹³C). The food consumed by these manatees in a controlled diet was also sampled and its δ¹³C values determined. The sloughed skin δ¹³C values from the captive manatees were enriched by an average of +4.1%0 relative to lettuce (generally >98% of the diet) the animals consumed. δ¹³C values of the skin were shown to be related to changes in δ¹³C values of the lettuce.
The stable carbon isotopic composition of internal tissues (liver, kidney, and blubber) and skin from dead, stranded manatees was also determined. These values were compared to values of vegetation that manatees are known to eat in the wild. The δ¹³C values of the internal tissues and skin of wild manatees were consistent with the range of δ¹³C values of their expected diet.     

Using stable isotopes to determine soil carbon input differences under ambient and elevated atmospheric CO2 conditions

Quantitative estimates of soil C input under ambient (35 Pa) and elevated (60 Pa) CO₂-partial pressure (pCO₂) were determined in a Free-Air Carbon dioxide Enrichment (FACE) experiment. To facilitate ¹³C-tracing, Trifolium repens L. was grown in a soil with an initial δ¹³C distinct by at least 5‰ from the δ¹³C of T. repens grown under ambient or elevated pCO₂. A shift in δ¹³C of the soil organic C was detected after one growing season. Calculated new soil C inputs in soil under ambient and elevated pCO₂ were 2 and 3 t ha^–1, respectively. Our findings suggest that under elevated CO₂ conditions, soil C sequestration may be altered by changes in plant biomass production and quality.     

Relationships of grain δ13C and δ18O with wheat phenology and yield under water-limited conditions

Stable carbon isotope composition (δ¹³C) of dry matter has been widely investigated as a selection tool in cereal breeding programmes. However, reports on the possibilities of using stable oxygen isotope composition (δ¹⁸O) as a yield predictor are very scarce and only in the absence of water stress. Indeed, it remains to be tested whether changes in phenology and stomatal conductance in response to water stress overrule the use of either δ¹³C or δ¹⁸O when water is limited. To answer this question, a set of 24 genotypes of bread wheat ( Triticum aestivum ) were assayed in two trials with different levels of deficit irrigation and a third trial under rainfed conditions in a Mediterranean climate (northwest Syria). Grain yield (GY) and phenology (duration from planting to anthesis and from anthesis to maturity) were recorded, and the δ¹³C and δ¹⁸O of grains were analysed to assess their suitability as GY predictors. Both δ¹³C and δ¹⁸O showed higher broad-sense heritabilities ( H ²) than GY. Genotype means of GY across trials were negatively correlated with δ¹³C, as previously reported, but not with δ¹⁸O. Both isotopes were correlated with grain filling duration, whereas δ¹⁸O was also strongly affected by crop duration from planting to anthesis. We concluded that δ¹⁸O of grains is not a proper physiological trait to breed for suboptimal water conditions, as its variability is almost entirely determined by crop phenology. In contrast, δ¹³C of grains, despite being also affected by phenology, still provides complementary information associated with GY.