Search

Five distinct transient warming (hyperthermal) events (Paleocene-Eocene Thermal Maximum [PETM], H1/ETM2/ELMO, H2, I1, and I2), marked by negative carbon isotope excursions (CIEs) occurred between Late Paleocene and Early Eocene (similar to 56 to 52 Ma) interval. However, not many records of either the PETM or definitive Early Eocene Hyperthermals (EEHs) are yet available from terrestrial realm in the tropics except two neo-tropical sections of Colombia and Venezuela (Jaramillo et al., 2010). Therefore, response of the tropical biosphere to these warming events is not very well known. Here we report high resolution carbon isotope (delta C-13) chemostratigraphy, biomarker, calcareous nannofossils, and pollen data from the Cambay shale Formation of Western India (paleolatitude similar to 5 degrees S), which show complete preservation of all the above CIE events including the PETM, hitherto unknown from tropical terrestrial record. Comparatively larger magnitudes of CIEs for all the hyperthermal events (the PETM and EEHs) point towards a possible intensification of precipitation during the PETM and all the early Eocene hyperthermal/CIE events. This inference is supported by data of lignin phenols and presence of tropical rain forest elements spanning the entire time period similar to 56-52 Ma and suggest that higher organic burial and soil erosion favored deposition of thick lignitic seams as a consequence of high tropical precipitation. (C) 2013 Elsevier B.V. All rights reserved.

Brown rot fungi are theorized to use both free radicals and enzymes to degrade wood. If these incompatible agents are employed in sequence (enzymatic after oxidative) in order to avoid interaction, this should be resolvable spatially in rotting wood. To assess this, we used thin spruce wafers as substrates, with the largest face the transverse plane. Propped wafers were colonized from the bottom (tangential to grain) by Postia placenta, using wood cell orientation and gravity to slow fungal egress and accentuate spatial gradients. After brief colonization, wafers were cut into 1-mm strips progressing up the wafer, and subsectioned for complementary analyses. Analyses included fungal growth, pH, cellulase activity, and wood modifications attributable to non-enzymatic mechanisms. Hyphae were imaged using confocal microscopy of fluorophore-tagged chitin. Dilute alkali solubility and lignin demethylation were measured as proxies (consequences) of carbohydrate depolymerization and lignin oxidation, respectively. Because P. placenta lacks genes for cellobiohydrolases, endoglucanase (EG) activity was measured. In composites of reassembled sections, hyphal fronts and apparent depolymerization preceded EG and lignin demethylation fronts by more than 6 mm. Although detection limits are a caveat when implicating novel fungal metabolites, results encourage and provide methodology for targeting this interesting leading edge of cellulolysis.

The chemistry and physical association of soil organic matter in the patchwork of successional forest stands in the eastern US is strongly controlled by past land use. Invasive earthworm activity in these same systems, however, may impart a chemical and physical disturbance exceeding that of land use legacy. We established eight plots within forests of the Smithsonian Environmental Research Center (SERC) (Edgewater, MD), to compare sites with no record of significant agricultural disturbance or earthworm activity and successional mixed hardwood forests recovering from past agriculture (60–132 yr) that contained both native and non-native earthworms. Soils (0–15 cm) were separated into physical fractions by size (microaggregates) and density (light and heavy particulate organic matter) and investigated for organic carbon (C) and nitrogen (N) partitioning. In addition, molecular composition was analyzed using FTIR spectroscopy and lignin phenol and substituted fatty acid (SFA) extraction. Even after 132 yr of recovery, the successional forests were nearly devoid of O a+e horizons; a condition we attribute to high activity of invasive earthworms. Additionally, soil organic carbon (SOC) concentration profiles, and 14 C derived mean residence times indicated mixing of the surface soils and fresh input of carbon to 10 cm, distinct from the undisturbed, mature sites. The proportion of microaggregated particulate organic matter (iPOM) and silt + clay (iSC) was significantly higher in successional than undisturbed forests, which we attribute to the combined influence of past agricultural land use and high earthworm activity. Among the successional sites, older forests exhibited a significant decrease in the proportion of C and N in iSC but an increase in their proportion in iPOM, suggesting selective incorporation of iPOM with earthworm activity over great periods of time. In addition, continual consumption and mixing activities of the earthworm population could also be a primary control of the higher concentration and less oxidized lignin phenols as well as a higher proportion of lignin phenols to SFA in all soil fractions in the successional sites. Using partial least squares (PLS) regression of FTIR spectra, we also demonstrated a strong correlation between soil C physical distribution (microaggregated vs. non-microaggregated) and chemical aspects of specific FTIR regions which confirmed our findings from the lignin and SFA and showed distinct chemical dominance among the different sites. Our results indicated that while past agricultural practice may have been the primary initial influence on C and N stock and soil physical distribution in the successional sites, the prolonged legacy and trajectory of recovery from the past land disturbance can be controlled by the nature of the invasive and native earthworm activity during afforestation.

The environmental fate of functionalized carbon nanomaterials (CNM) remains poorly understood. Using

While carbon stabilization had been increasingly concerned as ecosystem properties, the link between carbon stabilization and soil biological activity had been yet poorly assessed in soil dynamics of carbon and aggregation. In this study, topsoil samples were collected from rice soils derived from salt marsh under different lengths of rice cultivation up to 700 years from a coastal area of China. Particle size fractions (PSF) of soil aggregates were separated using a low energy dispersion protocol. Carbon fractions in the PSFs were analyzed with either FTIR spectros copy or chemical fractionation. Soil microbial community of bacterial, fungal and archaeal were analyzed with molecular fingerprinting using specific gene primers. Soil respiration and carbon gain from maize straw amendment as well as enzyme activities were respectively measured, using lab incubation protocols. While the PSFs were dominated by fine sand (200–20 μm) and silt (20–2 μm) fractions, the mass proportion both of sand (2000–200 μm) and clay (< 2 μm) fraction increased with prolonged rice cultivation. Soil organic carbon was enriched mostly in coarse sand fraction (40–60 g/kg), followed by the clay fraction (20–25 g/kg), but depleted in the silt fraction (~ 10 g/kg). Contents of recalcitrant C pool were higher (33–40 % of total SOC) in both coarse sand and clay fractions than in fine sand and silt fractions (20–29 % of total SOC). However, the ratio of LOC/SOC showed a weak decreasing trend with decreasing size of the PSFs. Total soil DNA content in the size fractions followed a similar trend to that of SOC. Bacterial and archaeal gene abundance were concentrated in both sand and clay fractions but that of fungi in sand fraction only, but increased with prolonged rice cultivation in both sand and clay fractions. Change in community diversity with sizes of the PSFs was found of fungi and weakly of bacterial but not of archaeal. Soil respiration quotient (Respired CO2-C to SOC) was highest in silt fraction, follo wed by the fine sand fraction but lowest in sand and clay fractions in the rice soils cultivated over 100 years. Whereas, scaled by total DNA concentration, respiration was higher in silt fraction than in other fractions for these rice soils. For the size fractions other th an clay fraction, soil DNA concentration, archaeal gene abundance, normalized enzyme activity and carbon sequestration was seen increased but SOC- and DNA-content scaled soil respiration decreased, more or less with prolonged rice cultivation. Carbon chemical stability and respiration were in a similar between sand and clay fractions but correlations of total DNA contents and bacterial gene abundance as well as normalized enzyme activity to SOC and labile OC content were only observed in sand fraction only. Our findings suggested that carbon accumulation and stabilization was prevalent in both sand and clay fraction, only the coarse sand fraction was found responsible for bioactivity dynamics in the rice soils.

East African climate change since the Late Miocene consisted of persistent shorter-term, orbital-scale wet–dry cycles superimposed upon a long-term trend towards more open, grassy landscapes. Either or both of these modes of palaeoclimate variability may have influenced East African mammalian evolution, yet the interrelationship between these secular and orbital palaeoclimate signals remains poorly understood. Here, we explore whether the long-term secular climate change was also accompanied by significant changes at the orbital-scale. We develop northeast African hydroclimate and vegetation proxy data for two 100 kyr-duration windows near 3.05 and 1.75 Ma at ODP Site 967 in the eastern Mediterranean basin, where sedimentation is dominated by eastern Sahara dust input and Nile River run-off. These two windows were selected because they have comparable orbital configurations and bracket an important increase in East African C 4 grasslands. We conducted high-resolution (2.5 kyr sampling) multiproxy biomarker, H- and C-isotopic analyses of plant waxes and lignin phenols to document orbital-scale changes in hydrology, vegetation and woody cover for these two intervals. Both intervals are dominated by large-amplitude, precession-scale (approx. 20 kyr) changes in northeast African vegetation and rainfall/run-off. The δ 13 C wax values and lignin phenol composition record a variable but consistently C 4 grass-dominated ecosystem for both intervals (50–80% C 4 ). Precessional δD wax cycles were approximately 20–30‰ in peak-to-peak amplitude, comparable with other δD wax records of the Early Holocene African Humid Period. There were no significant differences in the means or variances of the δD wax or δ 13 C wax data for the 3.05 and 1.75 Ma intervals studied, suggesting that the palaeohydrology and palaeovegetation responses to precessional forcing were similar for these two periods. Data for these two windows suggest that the eastern Sahara did not experience the significant increase in C 4 vegetation that has been observed in East Africa over this time period. This observation would be consistent with a proposed mechanism whereby East African precipitation is reduced, and drier conditions established, in response to the emergence of modern zonal sea surface temperature gradients in the tropical oceans between 3 and 2 Ma. This article is part of the themed issue ‘Major transitions in human evolution’.

The factors regulating soil animal communities are poorly understood. Current theory favors niche complementarity and facilitation over competition as the primary forms of non-trophic interspecific interaction in soil fauna; however, competition has frequently been suggested as an important community-structuring factor in earthworms, ecosystem engineers that influence belowground processes. To date, direct evidence of competition in earthworms is lacking due to the difficulty inherent in identifying a limiting resource for saprophagous animals. In the present study, we offer the first direct evidence of interspecific competition for food in this dominant soil detritivore group by combining field observations with laboratory mesocosm experiments using 13C and 15N double-enriched leaf litter to track consumption patterns. In our experiments, the Asian invasive species Amynthas hilgendorfi was a dominant competitor for leaf litter against two European species currently invading the temperate deciduous forests in North America. This competitive advantage may account for recent invasion success of A. hilgendorfi in forests with established populations of European species, and we hypothesize that specific phenological differences play an important role in determining the outcome of the belowground competition. In contrast, Eisenoides lonnbergi, a common native species in the Eastern United States, occupied a unique trophic position with limited interactions with other species, which may contribute to its persistence in habitats dominated by invasive species. Furthermore, our results supported neither the hypothesis that facilitation occurs between species of different functional groups nor the hypothesis that species in the same group exhibit functional equivalency in C and N translocation in the soil. We propose that species identity is a more powerful approach to understand earthworm invasion and its impacts on belowground processes.

Future rates of atmospheric N deposition have the potential to slow litter decay and increase the accumulation of soil organic matter by repressing the activity of lignolytic soil microorganisms. We investigated the relationship between soil biochemical characteristics and enzymatic responses in a series of sugar maple (Acer saccharum)-dominated forests that have been subjected to 16 yrs of chronic N deposition (ambient + 3 g NO3−–N m−2 yr−1), in which litter decay has slowed and soil organic matter has accumulated in sandy spodosols. Cupric-oxide-extractable lignin-derived phenols were quantified to determine the presence, source, and relative oxidation state of lignin-like compounds under ambient and experimental N deposition. Pools of respired C and mineralized N, along with rate constants for these processes, were used to quantify biochemically labile substrate pools during a 16-week laboratory incubation. Extracellular enzymes mediating cellulose and lignin metabolism also were measured under ambient and experimental N deposition, and these values were compared with proxies for the relative oxidation of lignin in forest floor and surface mineral soil. Chronic N deposition had no influence on the pools or rate constants for respired C and mineralized N. Moreover, neither the total amount of extractable lignin (forest floor, P = 0.260; mineral soil, P = 0.479), nor the relative degree of lignin oxidation in the forest floor or mineral soil (forest floor P = 0.680; mineral soil P = 0.934) was influenced by experimental N deposition. Given their biochemical attributes, lignin-derived molecules in forest floor and mineral soil appear to originate from fine roots, rather than leaf litter. Under none of the studied circumstances was the presence or relative oxidation of lignin correlated with the activity of cellulolytic and lignolytic extracellular enzymes. Although chronic atmospheric N deposition has slowed litter decay and increased organic matter in our experiment, it had little effect on biochemical composition of lignin-derived molecules in forest floor and surface mineral soil suggesting organic matter has accumulated by other means. Moreover, the specific dynamics of lignin phenol decay is decoupled from short-term organic matter accumulation under chronic N deposition in this ecosystem.

Up to 50% of organic C and 80% of organic N within soil can exist as amino acids, amino sugars and carbohydrates. To determine how potential microbial accessibility and turnover of these compounds is impacted by encroachment of woody plants into grasslands, we investigated changes in evolved CO2 during thermal analysis and in carbohydrate and amino compound chemistry after long term laboratory incubation of sandy loam grassland woodland soils from southern Texas, USA. Thermal analysis showed that incubation increased the amount of soil organic matter (SOM) released at higher temperatures and that evolved CO2 profiles correlated with increases in amino C. During incubation, total carbohydrate C decreased slightly faster than bulk soil C, with preferential loss of plant-derived carbohydrates and/or production of microbial carbohydrates most strongly expressed in grassland and younger woodland soils. Total N content did not change during incubation, so the reduction in extractable amino N in older woodland soils suggested that N became more resistant to extraction during incubation. These data, along with previous measurements of respired CO2, indicate that changes in carbohydrate C and amino C did not predict mineralized CO2 yields and that amino compounds and microbial carbohydrate C were not selectively lost during incubation. The differing response in SOM loss (or enrichment) during incubation of the older woodland soils revealed a system with altered SOM dynamics due to woody encroachment, confirming that the short term ‘lability’ or ‘recalcitrance’ of SOM components is dependent on a number of interacting variables.

Encroachment of nitrogen-fixing trees and shrubs into grasslands and savannas is a well-documented land cover change that occurs worldwide. In the Rio Grande Plains region of southern Texas, previous studies have shown woody encroachment by leguminous Prosopis glandulosa (mesquite) trees increases soil C and N, decreases microbial biomass N relative to soil N, and accelerates N mineralization and nitrification. We examined responses of the dominant organic N components in soil (amino acids and amino sugars) and two soil-bound protein-N acquiring enzymes (arylamidase and β-N-acetylglucosaminidase) along a grassland-to-woodland successional chronosequence to determine changes to soil N chemistry and extractability. The proportion of total N held within amino compounds was significantly lower in the woodlands (47 %) relative to the grassland soils (62 %). This increase in non-hydrolysable N was accompanied by increases in plant cell wall derived amino acids (e.g. hydroxyproline, serine) and losses of microbial amino sugars, indicating the woodland organic N pool was altered in composition and potentially in quality, either because it was more structurally protected or difficult to degrade due to polymerization/condensation reactions. Soil carbon-normalized activities of both soil-bound N-acquiring enzymes were significantly higher in woodland soils, consistent with changes in the biochemical composition of organic N. Although soil total N increases following woody encroachment, this additional organic N appears to be less extractable by chemical hydrolysis and thus potentially in more refractory forms, which may limit microbial N accessibility, slow the cycling of soil organic carbon, and contribute to observed soil C and N accrual in these systems.

A B S T R A C T Tillage practices affect soil microorganisms, which in turn influence many processes essential to the function and sustainability of soil. In this study, the changes in soil microbial biomass and community composition in response to conventional tillage (CT, moldboard plowing and post-harvest residue removal) and no-tillage (NT) practices were examined during a maize (Zea mays L.) growing season in a clay loam soil (Typic Hapludoll) in northeastern China. Soil samples were taken in May, June, July, August, and September of 2008 at 0–5, 5–10, and 10–20 cm depths. Microbial communities were characterized by phospholipid fatty acid (PLFA) analysis. While microbial biomass increased at the beginning then decreased toward the end of the growing season in CT soils, it showed the opposite trend in NT soils. Microbial community structure showed better distinction among sampling months than between tillage practices. These results suggest that seasonal variations in soil microbial communities could be greater than changes associated with tillage treatments. However, microbial biomass accumulation was tillage dependent. On average, NT treatment resulted in 21% higher microbial biomass in 0–5 cm depth than CT treatment (P < 0.05). Higher fungi to bacteria ratio was also observed under NT than CT treatment at both the 0–5 and 5–10 cm sampling depths. These data demonstrate that examining the effect of management practices on soil quality based on soil microbial communities should consider seasonal changes in the environmental properties. It is strongly recommended that NT practice should be adopted as an effective component of an overall strategy to improve soil quality and sustainability in northeastern China.

Brown rot fungi Gloeophyllum trabeum and Postia placenta were used to degrade aspen, spruce, or corn stover over 16 weeks. Decayed residues were saccharified using commercial cellulases or brown rot fungal extracts, loaded at equal but low endoglucanase titers. Saccharification was then repeated for high-yield samples using full strength commercial cellulases. Overall, brown rot pretreatments enhanced yields up to threefold when using either cellulase preparation. In the best case, aspen degraded 2 weeks by G. trabeum yielded 72% glucose-from-cellulose, a 51% yield relative to original glucan. A follow-up trial with more frequent harvests showed similar patterns and demonstrated interplay between tissue modifications and saccharification. Hemicellulose and vanillic acid (G6) or vanillin (G4) lignin residues were good predictors of saccharification potential, the latter notable given lignin's potential active role in brown rot. Results show basic relationships over a brown rot time course and lend targets for controlling an applied bioconversion process.

On-line thermally assisted hydrolysis and methylation (THM) in the presence of both unlabelled and 13C-labelled tetramethylammonium hydroxide (TMAH) was used to assess the relative contributions of phenolics (lignin, demethylated lignin and non-lignin phenolics) in a peaty gley soil profile beneath an unimproved grassland (LL), from a study site located at Harwood (Northumberland, northeast England, UK). This site also includes an unforested moorland (ML) and a second rotation Sitka spruce stand (SS). The common lignin proxies have been corrected for contributions of non-lignin phenols and demethylated lignin in the LL ecosystem and then compared with those from the ML and SS ecosystems. The phenolic compositions from the contributory vegetation inputs (i.e. grasses, heather and Sitka spruce) to all three soils (LL, ML and SS) were also analysed. By using 13C-labelled TMAH it was possible to show that the chemical composition of soil organic matter (SOM) reflected the different vegetation inputs in each of the L/F layers but these characteristics were lost from the deeper organic and mineral layers. Similar changes in the yield of lignin monomers (Λ) with increasing soil depth were displayed in the LL soil profile as reported previously in the ML soil in that no maxima were observed in these amount-depth profiles. The tannin input to the LL soil is low and as a consequence, unlike the ML and SS soils, there is no progressive decrease in the amounts of these non-lignin phenolics with increasing depth. Finally the methylated carbohydrate derivatives (MC) become more abundant relative to the phenolics with increasing soil depth in all three ecosystems (LL, ML and SS).

In many mid-Atlantic forests where both native and non-native earthworms exist, it is the non-native species that are the dominant component of the soil macrofauna. Few earthworm ecology studies, however, focus attention on these forest systems in order to determine the relative ecological roles and potential interactions of the native and non-native earthworms. In a series of field samplings and experimental manipulations we collected data on the effects of earthworms on below-and aboveground ecosystem processes. Earthworm abundance and the ecological processes measured were dynamic in space and time across the range of study sites. Leaf litter decay rates doubled at sites that had abundant non-native earthworms. Earthworms also altered the abundance of soil fungi, the activity of extracellular enzymes, soil respiration, and the growth of tree seedlings but the effects varied among sites depending on differences in land-use history and forest age. Red oak seedling growth was less at sites that had abundant earthworms but tulip poplar and red maple seedlings grew equally well with and without abundant earthworms. These preliminary results suggest that non-native earthworms have significant ecosystem effects, even in forests where native earthworms still occur. Land use history, however, plays an important role in determining what those effects will be, and these effects are likely to be dynamic, depending on the abundance of non-native earthworms.

Soil carbon turnover models generally divide soil carbon into pools with varying intrinsic decomposition rates. Although these decomposition rates are modified by factors such as temperature, texture, and moisture, they are rationalized by assuming chemical structure is a primary controller of decomposition. In the current work, we use near edge X-ray absorption fine structure (NEXAFS) spectroscopy in combination with differential scanning calorimetry (DSC) and alkaline cupric oxide (CuO) oxidation to explore this assumption. Specifically, we examined material from the 2.3–2.6 kg L � 1 density fraction of three soils of different type (Oxisol, Alfisol, Inceptisol). The density fraction with the youngest 14 C age (Oxisol, 107 years) showed the highest relative abundance of aromatic groups and the lowest O-alkyl C/aromatic C ratio as determined by NEXAFS. Conversely, the fraction with the oldest C (Inceptisol, 680 years) had the lowest relative abundance of aromatic groups and highest O-alkyl C/aromatic C ratio. This sample also had the highest proportion of thermally labile materials as measured by DSC, and the highest ratio of substituted fatty acids to lignin phenols as indicated by CuO oxidation. Therefore, the organic matter of the Inceptisol sample, with a 14 C age associated with ‘passive’ pools of carbon (680 years), had the largest proportion of easily metabolizable organic molecules with low thermodynamic stability, whereas the organic matter of the much younger Oxisol sample (107 years) had the highest proportion of supposedly stable organic structures considered more difficult to metabolize. Our results demonstrate that C age is not necessarily related to molecular structure or thermodynamic stability, and we suggest that soil carbon models would benefit from viewing turnover rate as codetermined by the interaction between substrates, microbial actors, and abiotic driving variables. Furthermore, assuming that old carbon is composed of complex or ‘recalcitrant’ compounds will erroneously attribute a greater temperature sensitivity to those materials than they may actually possess.

We studied the degradation of lignin in leaf and needle litter of ash, beech, maple, pine and spruce using 13C-labelled tetramethylammonium hydroxide (13C TMAH) thermochemolysis. Samples were allowed to decompose for 27 months in litter bags at a German spruce forest site, resulting in a range of mass loss from 26% (beech) to 58% (ash). In contrast to conventional unlabelled TMAH thermochemolysis, 13C-labelling allows thermochemolysis products from lignin, demethylated lignin and other polyphenolic litter compounds (e.g. tannins) to be distinguished. Proxies for lignin degradation (phenol yield; acid/aldehyde ratio of products) changed considerably upon correction for the contribution of non-lignin sources to the thermochemolysis products. Using the corrected values, we found increasing acid/aldehyde values as well as decreasing or constant yield of lignin derived phenols normalised to litter carbon, suggesting pronounced lignin degradation by wood-rotting fungi. No indication for build up of demethylated lignin through the action of brown rot fungi on ring methoxyls was found. The results were compared with those of other analytical techniques applied in previous studies. Like 13C-TMAH thermochemolysis, CuO oxidation showed increasing lignin oxidation (acid/aldehyde ratio) and no/little enrichment of lignin derived phenols in the litter. Molecular lignin degradation patterns did not match those from analysis of total acid unhydrolysable residues (AURs). In particular, the long assumed selective preservation of lignin during the first months of litter decomposition, based on AUR analysis, was not supported by results from the CuO and 13C TMAH methods.

High sedimentation rates along river-dominated margins make these systems important repositories for organic carbon derived from both allochthonous and autochthonous sources. Using elemental carbon/nitrogen ratios, molecular biomarker (lignin phenol), and stable carbon isotopic (bulk and compound-specific) analyses, this study examined the sources of organic carbon to the Louisiana shelf within one of the primary dispersive pathways of the Mississippi River. Surface sediment samples were collected from stations across the inner, mid, and outer Louisiana shelf, within the Mississippi River plume region, during two cruises in the spring and fall of 2000. Lignin biomarker data showed spatial patterns in terrestrial source plant materials within the river plume, such that sediments near the mouth of the Mississippi River were comparatively less degraded and richer in C4 plant carbon than those found at mid-depth regions of the shelf. A molecular and stable isotope-based mixing model defining riverine, marsh, and marine organic carbon suggested that the highest organic carbon inputs to the shelf in spring were from marine sources (55–61% marine organic carbon), while riverine organic carbon was the highest (63%) in fall, likely due to lower inputs of marine organic carbon at this time compared with the spring season. This model also indicated that marsh inputs, ranging from 19 to 34% and 3–15% of the organic carbon in spring and fall, respectively, were significantly more important sources of organic carbon on the inner Louisiana shelf than previously suggested. Finally, we propose that the decomposition of terrestrial-derived organic carbon (from the river and local wetlands sources) in mobile muds may serve as a largely unexplored additional source of oxygen-consuming organic carbon in hypoxic bottom waters of the Louisiana shelf.

Tree taxa and pyrolysis temperature are the major controllers of the physicochemical properties of the resultant pyrogenic organic matter (PyOM) produced in fire-prone forests. However, we know little about how these controls determine the residence time of PyOM once introduced to soil. In this study, we tracked the fate of 13C-enriched red maple (RM) or jack pine (JP) wood and PyOM, produced over a range of temperatures (200, 300, 450, or 600 &deg, C) added to soil from a northern temperate forest in Michigan, USA. Pyrolysis temperature was the main controller of PyOM-C mineralization rates, with mean residence times (MRT) ranging from ~4 to 450 years for both taxa. The PyOM-C mineralization rates for both taxa and the pyrolysis temperature correlated positively with PyOMw (leachable C content), however, the potential PyOMw contribution to net PyOM-C mineralization was lower for JP (14&ndash, 65%) than RM (24&ndash, 84%). The correlation between PyOMw and mineralization rate was strongest where carbonization and the thermochemical conversion of carbohydrates and non-lignin phenols was most pronounced during pyrolysis for each taxa (300 &deg, C for JP and 450 &deg, C for RM). Contrary to expectations, the addition of a labile C source, sucrose, to the soil did not enhance the decomposition of PyOM, indicating that soil microbes were not energy limited in the soil-PyOM system studied (regardless of pyrolysis temperature). Our results showed that while the first-order control on PyOM decomposition in this soil is pyrolysis temperature, wood taxa did affect PyOM-C MRT, likely in part due to differences in the amount of reactive water-soluble C present in PyOM.

The brown rot fungus Wolfiporia cocos and the selective white rot fungus Perenniporia medulla-panis produce peptides and phenolate-derivative compounds as low molecular weight Fe 3? -reductants. Phenolates were the major compounds with Fe 3? -reducing activity in both fungi and displayed Fe 3? -reducing activity at pH 2.0 and 4.5 in the absence and presence of oxalic acid. The chemical structures of these compounds were identified. Together with Fe 3? and H2O2 (mediated Fenton reaction) they pro- duced oxygen radicals that oxidized lignocellulosic poly- saccharides and lignin extensively in vitro under conditions similar to those found in vivo. These results indicate that, in addition to the extensively studied Gloeophyllum trabeum— a model brown rot fungus—other brown rot fungi as well as selective white rot fungi, possess the means to promote Fenton chemistry to degrade cellulose and hemicellulose, and to modify lignin. Moreover, new information is pro- vided, particularly regarding how lignin is attacked, and either repolymerized or solubilized depending on the type of fungal attack, and suggests a new pathway for selective white rot degradation of wood. The importance of Fenton reactions mediated by phenolates operating separately or synergistically with carbohydrate-degrading enzymes in brown rot fungi, and lignin-modifying enzymes in white rot fungi is discussed. This research improves our understand- ing of natural processes in carbon cycling in the environ- ment, which may enable the exploration of novel methods for bioconversion of lignocellulose in the production of biofuels or polymers, in addition to the development of new and better ways to protect wood from degradation by microorganisms.

Sequential density fractionation separated soil particles into “light” predominantly mineral-free organic matter vs. increasingly “heavy” organo-mineral particles in four soils of widely differing mineralogy. With increasing particle density C concentration decreased, implying that the soil organic matter (OM) accumulations were thinner. With thinner accumulations we saw evidence for both an increase in 14C-based mean residence time (MRT) of the OM and a shift from plant to microbial origin.Evidence for the latter included: (1) a decrease in C/N, (2) a decrease in lignin phenols and an increase in their oxidation state, and (3) an increase in δ13C and δ15N. Although bulk-soil OM levels varied substantially across the four soils, trends in OM composition and MRT across the density fractions were similar. In the intermediate density fractions (~1.8–2.6 g cm−3), most of the reactive sites available for interaction with organic molecules were provided by aluminosilicate clays, and OM characteristics were consistent with a layered mode of OM accumulation. With increasing density (lower OM loading) within this range, OM showed evidence of an increasingly microbial origin. We hypothesize that this microbially derived OM was young at the time of attachment to the mineral surfaces but that it persisted due to both binding with mineral surfaces and protection beneath layers of younger, less microbially processed C. As a result of these processes, the OM increased in MRT, oxidation state, and degree of microbial processing in the sequentially denser intermediate fractions. Thus mineral surface chemistry is assumed to play little role in determining OM composition in these intermediate fractions. As the separation density was increased beyond ~2.6 g cm−3, mineralogy shifted markedly: aluminosilicate clays gave way first to light primary minerals including quartz, then at even higher densities to various Fe-bearing primary minerals. Correspondingly, we observed a marked drop in δ15N, a weaker decrease in extent of microbial processing of lignin phenols, and some evidence of a rise in C/N ratio. At the same time, however, 14C-based MRT time continued its increase. The increase in MRT, despite decreases in degree of microbial alteration, suggests that mineral surface composition (especially Fe concentration) plays a strong role in determining OM composition across these two densest fractions.

Alterations in forest productivity and changes in the relative proportion of above- and belowground biomass may have nonlinear effects on soil organic matter (SOM) storage. To study the influence of plant litter inputs on SOM accumulation, the Detritus Input Removal and Transfer (DIRT) Experiment continuously alters above- and belowground plant inputs to soil by a combination of trenching, screening, and litter addition. Here, we used biogeochemical indicators [i.e., cupric oxide extractable lignin-derived phenols and suberin/cutin-derived substituted fatty acids (SFA)] to identify the dominant sources of plant biopolymers in SOM and various measures [i.e., soil density fractionation, laboratory incubation, and radiocarbon-based mean residence time (MRT)] to assess the stability of SOM in two contrasting forests within the DIRT Experiment: an aggrading deciduous forest and an old-growth coniferous forest. In the deciduous forest, removal of both above- and belowground inputs increased the total amount of SFA over threefold compared with the control, and shifted the SFA signature towards a root-dominated source. Concurrently, light fraction MRT increased by 101 years and C mineralization during incubation decreased compared with the control. Together, these data suggest that root-derived aliphatic compounds are a source of SOM with greater relative stability than leaf inputs at this site. In the coniferous forest, roots were an important source of soil lignin-derived phenols but needle-derived, rather than root-derived, aliphatic compounds were preferentially preserved in soil. Fresh wood additions elevated the amount of soil C recovered as light fraction material but also elevated mineralization during incubation compared with other DIRT treatments, suggesting that not all of the added soil C is directly stabilized. Aboveground needle litter additions, which are more N-rich than wood debris, resulted in accelerated mineralization of previously stored soil carbon. In summary, our work demonstrates that the dominant plant sources of SOM differed substantially between forest types. Furthermore, inputs to and losses from soil C pools likely will not be altered uniformly by changes in litter input rates.

In this work, pyrolysis-molecular beam mass spectrometry analysis coupled with principal components analysis and (13)C-labeled tetramethylammonium hydroxide thermochemolysis were used to study lignin oxidation, depolymerization, and demethylation of spruce wood treated by biomimetic oxidative systems. Neat Fenton and chelator-mediated Fenton reaction (CMFR) systems as well as cellulosic enzyme treatments were used to mimic the nonenzymatic process involved in wood brown-rot biodegradation. The results suggest that compared with enzymatic processes, Fenton-based treatment more readily opens the structure of the lignocellulosic matrix, freeing cellulose fibrils from the matrix. The results demonstrate that, under the current treatment conditions, Fenton and CMFR treatment cause limited demethoxylation of lignin in the insoluble wood residue. However, analysis of a water-extractable fraction revealed considerable soluble lignin residue structures that had undergone side chain oxidation as well as demethoxylation upon CMFR treatment. This research has implications for our understanding of nonenzymatic degradation of wood and the diffusion of CMFR agents in the wood cell wall during fungal degradation processes.

Soil C stocks in the Grand Prairie region of eastern Arkansas have declined under the prevalent 2-yr rotation of rice (Orzya sativa L.)-soybean [Glycine max (L.) Merr.]. Continuous rice cropping could promote soil C sequestration, but in previous work continuous rice averaged 19% less grain yield than rice following soybean, apparently due to N deficiency. To further study N cycling, microplots were imbedded during the rice phase of a crop rotation field study in 2002 and 2004. Urea labeled with 15 N was applied preflood, when all N fertilizer is conventionally applied. Crop biomass was often smaller with continuous rice than with rice following soybean (sampled both years) and rice following corn (Zea mays L.) (sampled only in 2004), although the difference varied by growth stage. Crop uptake of native 14 N, presumably mineralized from soil organic matter, was inhibited with continuous rice in both years. This trend was clearest at harvest (P = 0.02), when continuous rice averaged 40 kg 14 N ha -1 less uptake than rice in the two rotations. Fertilizer 15 N averaged only 30% of total crop N and its uptake differed among cropping treatments only in 2002. At harvest, soil C with continuous rice cropping was enriched by 42% with syringyl phenols and by 83% with cinnamic phenols compared with the rotations. These enrichments appear unrelated to estimated input rates of lignin-derived phenols. Results support the hypothesis that continuous rice cropping promotes the binding of soil N by lignin-derived phenols, thereby inhibiting N mineralization and late-season crop growth. Similar observations were reported for tropical rice production, suggesting that the responsible soil processes might be common in continuous rice cropping.

Accurate reconstructions of past hydrological variability are essential for understanding the climate history of the tropics. In tropical Africa, the relative proportion of vegetation utilizing the C3 vs. C4 photosynthetic pathway is mainly controlled by precipitation and thus past hydrological changes can be inferred from the vegetation record. In this study, biomarkers of terrestrial plants (lignin phenols and plant leaf wax carbon isotopes) are examined from a well-dated sedimentary record from Lake Malawi to provide a vegetation (aridity) record of the past 23 cal ka from southeast Africa. We suggest that the ratio of cinammyl to vanillyl (C/V) lignin phenols in Lake Malawi sediments mainly reflects inputs of C3 trees (woody tissue) vs. C4 grasses (non-woody tissue) and find that changes in the C/V ratio generally support variability noted in the n-alkane carbon isotope record. Together, these records provide evidence for increased C4 vegetation (grasses) surrounding Lake Malawi during Last Glacial Maximum (LGM), the Younger Dryas, in the early Holocene, and from ~ 2 cal ka to the present, suggesting drier conditions at these times. Elevated inputs of C3 vegetation are noted in the intervals from ~ 17–13.6 cal ka and ~ 7.7–2 cal ka, indicating wet conditions in southeast Africa. A relationship is noted between the n-alkane average chain length (ACL) and temperature, with longer ACLs associated with higher temperatures. Higher n-alkane carbon preference index (CPI) values correlate with higher mass accumulation rates of biogenic silica and may result from periodic increased northerly winds over Lake Malawi, which enhance upwelling and diatom productivity while simultaneously increasing erosion and transport of plant leaf waxes to the lake. The molecular data produced in this study suggest that the carbon isotopic signature of bulk sediment (δ13CTOC) in Lake Malawi is primarily a reflection of terrestrial inputs (C3 vs. C4 vegetation) and may not mainly reflect changes in algal productivity, as previously thought.

In Britain substantial areas of both deep and shallow peatland have been afforested with conifers since the 1950s. However, information about the effects of afforestation on the properties of soil organic carbon (SOC) is lacking. Investigating the geochemical changes that take place when lignin- and tannin-derived phenols are degraded and incorporated into SOC will provide us with an insight into soil carbon dynamics at the molecular level. Here we compare the phenolic distributions in two different peaty gley soil profiles using on-line thermally assisted hydrolysis and methylation (THM) in the presence of both unlabelled and 13 C-labelled tetramethylammonium hydroxide (TMAH). The two soil profiles were beneath respectively an unforested moorland (ML) and a second rotation Sitka spruce ( Picea sitchensis ) afforested moorland (SS), from Harwood (Northumberland, northeast England, UK). THM of these soils in the presence of 13 C-labelled TMAH enabled us to assess the relative contributions of lignin, demethylated lignin, and non-lignin phenolics. The lignin phenolic distributions differed in both soil profiles reflecting changing source and decay dynamics within and between the sites. A progressive degradation of syringyl (S) and guaiacyl (G) phenolics was observed in the ML soil, compared with an increase of such components in the organic/mineral horizons of the SS soil. A significant tannin input was observed, particularly in the upper horizons of the SS soil. The S/G ratio gradually decreased with increasing burial in the ML soil, whilst a change in vegetation input and land preparation was recorded by this ratio in the SS soil. Overall, this suggests that afforestation influences the phenolic compositional profiles in these peaty gley soils as a result of one or more of the following processes: changing vegetation input, horizon inversion prior to planting, root input or leaching. This highlights the potential of using lignin and tannins as molecular indicators to assess the effects of afforestation on SOC.

Industrially produced carbon-based nanomaterials (CNM), including fullerenes and nanotubes, will be introduced into the environment in increasing amounts in the next decades. One likely environmental chemical transformation of C60 is oxidation to C60 fullerol through both abiotic- and biotic-mediated means. Unfortunately, knowledge of the environmental fate of oxidized CNM is lacking. This study used bulk and compound-specific 13C stable isotope ratio mass spectrometry techniques and spectroradiometry analysis to examine the ability of two white rot basidiomycete fungi (Phlebia tremellosa and Trametes versicolor) to metabolize and degrade an oxygenated CNM, C60 fullerol. After 32 weeks of decay, both fungi were able to bleach and oxidize fullerol to CO2. Additionally, the fungi incorporated minor amounts of the fullerol carbon into lipid biomass. These findings are significant in that they represent the first report of direct biodegradation and utilization of any fullerene derivative and provide valuable information about the possible environmental fates of other CNM.

Non-permineralized or mummified ancient wood found within proglacial soil near the ad Astra Ice Cap (81°N, 76°W), Ellesmere Island, Canada was investigated to ascertain the identification of the trees, current morphological and chemical characteristics of the woods and the fungi within them. These woods, identified as Betula, Larix, Picea and Pinus, were found with varying states of physical and chemical degradation. Modern microbial decomposition caused by soft rot fungi was evident and rDNA sequencing of fungi obtained from the samples revealed several species including Cadophora sp., Exophiala sp., Phialocephala sp., as well as others. Analytical 13C-labeled tetramethylammonium hydroxide thermochemolysis showed the lignin from the ancient wood was in a high degree of preservation with minor side chain alteration and little to no demethylation or ring hydroxylation. The exposure of these ancient woods to the young soils, where woody debris is not usually prevalent, provides carbon and nutrients into the polar environment that are captured and utilized by unique decay fungi at this Arctic site.

The landscapes colonized by invasive earthworms in the eastern U.S. are often patchworks of forest stands in various stages of successional development. We established six field sites in tulip poplar dominated forests in the Smithsonian Environmental Research Center in Edgewater, MD, that span mid (50–70 years-three plots) and late (120–150 years-three plots) successional stages where younger sites had greater earthworm density and biomass than older sites and were dominated by non-native lumbricid species. In particular Lumbricus rubellus, a litter-feeding species, was abundant in mid successional forests. Here, we separated particulate organic matter (POM) from the bulk soil by a combination of size and density fractionation and found that patterns in soil POM chemistry were similar to those found previously during litter decay: in younger forests with high abundance of earthworms, organic carbon normalized cutin- and suberin-derived substituted fatty acid (SFA) concentration was lower and lignin-derived phenols greater than in older forests where earthworms were less abundant. The chemistry of the dominant litter from mid versus late successional tree species did not fully explain the differences in POM chemistry between age classes. Instead, the differences in leaf body versus petiole and leaf versus root chemistry were the dominant drivers of POM chemistry in mid versus late successional stands, although aspects of stand age and tree species also impacted POM chemistry. Our results indicate that preferential ingestion of leaf body tissue by earthworms and the subsequent shifts in sources of plant biopolymers in soil influenced POM chemistry in mid successional forests. These results indicate that invasive earthworm activity in North American forests contributes to a shift in the aromatic and aliphatic composition of POM and thus potentially influences carbon stabilization in soil.

Tannin, condensed and hydrolysable, and lignin are two of the most abundant natural biopolymers in the environment. Yet it is still not possible using one analytical technique to simultaneously track each of their dynamics in litter and soils. Thermally assisted hydrolysis and methylation (THM) using tetramethylammonium hydroxide (TMAH) has been employed to investigate the cycling of tannin and lignin forms in one analysis, but sometimes with equivocal results as many of the products released may originate from both biopolymers. In this study we applied 13 C-labeled TMAH in the analysis of soil organic matter in a soil profile under Corsican pine, an input lacking in hydrolysable tannins, to show the potential of this tool in tracking complex phenol chemistry. This method successfully allowed for a qualitative distinction among tannin and lignin input as well as permitting the inference of ring specific decay of condensed tannins.

A comparison was made between tetramethylammonium hydroxide (TMAH) thermochemolysis and CuO oxidation methods for lignin characterization as a means of assessing terrestrial input to marine sediments. Surface marine sediments from the Louisiana shelf just outside the outflow of the Mississippi River were analyzed. The overall lignin yields and the compound ratios used as plant source proxies were found to be considerably different depending on the method used. The CuO technique afforded higher amounts of lignin phenols and in a simpler compound distribution. Additionally, comparison of the molecular source indicators using the liberated syringyl, cinnamyl and vanillyl phenols showed that the two techniques suggest different plant types contributing to the sediments; however, both techniques exhibited similar trends in oxidation state proxies. This source discrepancy is a function of the different chemical mechanisms of lignin chemolysis, with extractable tannins, polyphenols and cinnamyl-based products being emphasized by the TMAH method. Also, source comparison is hampered by a poorly developed database of plant source-to-lignin chemistry relationship for the TMAH method. One important benefit of the CuO technique is that it allows analysis of up to 5 times the sediment mass compared to the TMAH method, which is an important consideration for sediments with low terrestrial organic carbon content where lignin yield may be near detection limits. In general, the CuO technique proved more suited for lignin-based plant source assessment than the conventional (i.e., not 13C-labeled) TMAH thermochemolysis method for those marine sediments containing low plant input.

The aromatic polymer lignin protects plants from most forms of microbial attack. Despite the fact that a significant fraction of all lignocellulose degraded passes through arthropod guts, the fate of lignin in these systems is not known. Using tetramethylammonium hydroxide thermochemolysis, we show lignin degradation by two insect species, the Asian longhorned beetle ( Anoplophora glabripennis ) and the Pacific dampwood termite ( Zootermopsis angusticollis ). In both the beetle and termite, significant levels of propyl side-chain oxidation (depolymerization) and demethylation of ring methoxyl groups is detected; for the termite, ring hydroxylation is also observed. In addition, culture-independent fungal gut community analysis of A. glabripennis identified a single species of fungus in the Fusarium solani / Nectria haematococca species complex. This is a soft-rot fungus that may be contributing to wood degradation. These results transform our understanding of lignin degradation by wood-feeding insects.

Tillage events have an important influence on residue incorporation into soil profiles and soil aggregate disruption, and ultimately influence the net C gain or loss in soils. Thus, our objective was to evaluate tillage-induced influences on aggregate structure, residue-derived C stabilization, and the subsequent efficiency of C stabilization in aggregates of no-till (NT) and tillage management (TM) practices at different depth increments of the soil profile. Uniformly 13 C-labeled wheat residues were added to incubation cores representing soils under NT and TM during a year-long in situ incubation at a dryland agriculture experiment site. Residue was added directly onto the surface of NT cores, while residues were incorporated into the 0- to 5-, 5- to 15-, and 15- to 30-cm depth increments of the TM cores. We found that residue additions did not have a significant effect (P > 0.05) on aggregate dynamics in either NT or TM, but NT management did result in the greatest stabilization of residue-derived C (11.2 ± 2.4 g residue C kg -1 soil kg -1 residue C added, P 250-μm) fraction of the 0- to 15-cm increment. Residue-derived C stabilization was significantly greater (P < 0.05) in the 0- to 30-cm increment than in the 0- to 15-cm increment of the TM management cores. Overall, our results indicate that, within a plow depth of 15 cm, limiting the tillage-induced disruption of aggregates has a stronger influence on the efficiency of C stabilization than residue incorporation into the profile via tillage. When residues are distributed to a 30-cm depth, however, the negative impact of aggregate disruption through tillage appears counterbalanced, with similar efficiencies of C stabilization between the NT and TM practices, possibly due to slower decomposition of residues deeper in the profile.

Because of the bioaccumulation of penta- and tetrapolybrominated diphenyl ether (PBDE) flame retardants in biota,the environmental biotransformation of decabromodiphenyl ether (BDE-209) is of interest. BDE-209 accounts for more than 80% by mass of PBDE production and is the dominant PBDE in sediments. Most sediments are anaerobic and reports of microbial reductive dehalogenation of hydrophobic persistent organohalogen pollutants are numerous. Reductive debromination of BDE-209 in the environment could provide a significant source of lesser-brominated PBDEs to biota. Moreover, a recent study showed that BDE-209 debrominates in sewage sludge, and another demonstrated that some halorespiring bacteria will debrominate BDE-209. To determine whether reductive debromination of BDE-209 occurs in sediments, parallel experiments were conducted using anaerobic sediment microcosms and a cosolvent-enhanced biomimetic system. In the biomimetic system, reductive debromination occurred at rates corresponding to bromine substitution levels with a BDE-209 half-life of only 18 s compared with a halflife of almost 60 days for 2,2',4,4'-tetrabromodiphenyl ether. In sediment, the measured debromination half-life of BDE-209 was well over a decade and was in good agreement with the predicted value obtained from the biomimetic experiment. Product congeners were predominantly double para-substituted. BDE-209 debrominated in sediment with a corresponding increase in nona-, octa-, hepta-, and hexa-PBDEs. Nine new PBDE congeners appeared in sediment from reductive debromination. Given the very large BDE-209 burden already in sediments globally, it is important to determine whether this transformation is a significant source of lesser-brominated PBDEs to the environment.

In this study, we examined the temporal changes of terrestrially-derived particulate organic carbon (POC) in the lower Mississippi River (MR) and in a very limited account, the upper tributaries (Upper MR, Ohio River, and Missouri River). We used for the first time a combination of lignin-phenols, bulk stable carbon isotopes, and compound-specific isotope analyses (CSIA) to examine POC in the lower MR and upper tributaries. A lack of correlation between POC and lignin phenol abundances (Λ8) was likely due to dilution effects from autochthonous production in the river, which has been shown to be considerably higher than previously expected. The range of δ13C values for p-hydroxycinnamic and ferulic acids in POC in the lower river do support that POM in the lower river does have a significant component of C4 in addition to C3 source materials. A strong correlation between δ13C values of p-hydroxycinnamic, ferulic, and vanillyl phenols suggests a consistent input of C3 and C4 carbon to POC lignin while a lack of correlation between these same phenols and POC bulk δ13C further indicates the considerable role of autochthonous carbon in the lower MR POC budget. Our estimates indicate an annual flux of POC of 9.3 × 108 kg y−1 to the Gulf of Mexico. Total lignin fluxes, based on Λ8 values of POC, were estimated to be 1.2 × 105 kg y−1. If we include the total dissolved organic carbon (DOC) flux (3.1 × 109 kg y−1) reported by [Bianchi T. S., Filley T., Dria K. and Hatcher, P. (2004) Temporal variability in sources of dissolved organic carbon in the lower Mississippi River. Geochim. Cosmochim. Acta 68, 959–967.], we get a total organic carbon flux of 4.0 × 109 kg y−1. This represents 0.82% of the annual total organic carbon supplied to the oceans by rivers (4.9 × 1011 kg).

Defining the control that hydrology exerts on organic carbon (OC) export at the watershed scale is important for understanding how the source and quantity of OC in streams and rivers is influenced by climate change or by landscape drainage. To this end, molecular (lignin phenol), stable carbon isotope, and dissolved organic carbon (DOC) data were collected over a range of flow conditions to examine the influence of hydrology on annual OC export from an 850 km2 Midwestern United States agricultural watershed located in west central Indiana. In years 2002 and 2003, modeled annual DOC loads were 19.5 and 14.1 kg ha−1yr−1, while 71% and 85%, respectively, of the total annual OC was exported in flow events occurring during less than 20% of that time. These results highlight the importance of short-duration, high-discharge events (common in smaller watersheds) in controlling annual OC export. Based on reported increases in annual stream discharge coupled with current estimates of DOC export, annual DOC loads in this watershed may have increased by up to 40% over the past 50 years. Molecular (lignin phenol) characterization of quantity and relative degradation state of terrestrial OC shows as much temporal variability of lignin parameters (in high molecular weight dissolved organic carbon) in this one watershed as that demonstrated in previously published studies of dissolved organic matter in the Mississippi and Amazon Rivers. These results suggest that hydrologic variability is at least as important in determining the nature and extent of OC export as geographic variability. Moreover, molecular and bulk stable carbon isotope data from high molecular weight dissolved organic carbon and colloidal organic carbon showed that increased stream flow from the study watershed was responsible for increased export of agriculturally derived OC. When considered in the context of results from other studies that show the importance of flood events and in-stream processing of terrestrial organic carbon, our results show how hydrologic variability in smaller watersheds can reflect landscape-scale carbon dynamics in ways that cannot necessarily be measured at the outlets of large rivers due to multiple source signals and attenuated hydrology.

Recent studies indicate that while unfunctionalized carbon nanomaterials (CNMs) exhibit very low decomposition rates in soils, even minor surface functionalization (e.g., as a result of photochemical weathering) may accelerate microbial decay. We present results from a C60 fullerene-soil incubation study designed to investigate the potential links between photochemical and microbial degradation of photo-irradiated C60. Irradiating aqueous (13)C-labeled C60 with solar-wavelength light resulted in a complex mixture of intermediate products with decreased aromaticity. Although addition of irradiated C60 to soil microcosms had little effect on net soil respiration, excess (13)C in the respired CO2 demonstrates that photo-irradiating C60 enhanced its degradation in soil, with ∼ 0.78% of 60 day photo-irradiated C60 mineralized. Community analysis by DGGE found that soil microbial community structure was altered and depended on the photo-treatment duration. These findings demonstrate how abiotic and biotic transformation processes can couple to influence degradation of CNMs in the natural environment.

Decabromodiphenyl ether (BDE-209) is a major component of a commercial flame retardant formulation; however, there is limited information on the fate of BDE-209 in the environment, including metal oxide mediated degradation. Laboratory experiments were conducted to investigate the birnessite (delta-MnO(2))-promoted debromination of BDE-209 in tetrahydrofuran (THF)-water systems as well as catechol solutions. Up to 100% (0.1044 micromol initial charge) of BDE-209 disappeared upon reaction with birnessite in THF/H(2)O (4:6-9:1). The formation of aqueous Br(-) from BDE-209 reduction was determined and up to 16 mole% of initial bromine was released over the course of the reaction indicating approximately 1.7 Br-C bonds were reduced per BDE-209 molecule. The distribution of debrominated congeners, however, indicated a much greater extent of debromination for some products than what was inferred from an average bromine mass balance. The produced congeners varied from tetra- to nona-bromodiphenyl ether, including BDE-47 and -99, during the 24 h reaction. Experiments with deuterated water indicated that water was not the major hydrogen donor in the reduction but rather THF provided the reducing power. This conclusion was supported by the presence of succinic acid, which was produced from oxidation of THF. The reactions with aqueous catechol, rather than THF-water mixtures, were performed to assess the possible role that compounds found in natural environments, such a tannin-like phenols, might have on the chemistry. These experiments indicated that birnessite mediated debromination of BDE-209 might occur in natural settings.

A problem inherent in analytical procedures where thermochemolyis or pyrolysis is coupled with in situ methylation by tetramethylammonium hydroxide is the inability to determine if an observed aromatic methoxyl group was originally present as a hydroxyl or a methoxyl functionality. This analytical insensitivity makes it impossible to ascertain relative inputs of fresh lignin, demethylated lignin and polyphenols (hydrolysable) into natural organic matter pools. 13C-TMAH thermochemolysis, however, methylates using a 13C-labeled methyl group permitting the differentiation of original and analytically-added methyl groups and therefore the potential source of many 'lignin' phenols. Common oak root, senescent leaf, wood, and bark as well as brown rot decayed oak wood are compared herein to test if the 13C-TMAH modification can be used to differentiate sources of phenols. Oak was chosen as it exhibits extremely high contents of hydrolysable tannins which interfere with the study of wood decomposition but also confound any comparative studies of the fate of lignin and tannin in soil profiles, dissolved organic matter, and sediments when using the unlabeled TMAH thermochemolysis technique. The average % monohydroxyl (i.e. 3,5-dimethoxyl, 4-hydroxyl in source) content of syringyl compounds for each sample varies as leaves (70%) < root (75%) < bark (77%) < brown rot wood (85.9%) < wood (89%). Some compounds such as permethylated syringic acid were almost 90% 3,4,5-trihydroxyl benzoic acid in origin as was determined for oak leaf, or, put another way, S6 was derived almost exclusively from gallic acid. Similarly, what was assumed to be permethylated ferulic acid in roots turned out to be predominantly caffeic acid with a 3,4-dihydroxyl substitution rather than the 3-methoxy, 4-hydroxy substitution. When individual compound concentrations are corrected for the polyhydroxyl content to better reflect 'true' lignin, or at least lignin predominantly bound via a ß-O-4 configuration as is released by this chemolysis procedure, the values for lignin proxies changed substantially. As such, it must be considered that many unlabeled TMAH methylated compounds released from natural systems and ascribed to a 'lignin' source may in fact be from tannins or other fresh or degraded phenolics.

A suite of nickel, cobalt, iron, copper, and zinc containing sulfides are assayed for the promotion of a model carbon fixation reaction with relevance to local reducing environments of the early Earth. The assay tests the promotion of hydrocarboxylation (the Koch reaction) wherein a carboxylic acid is synthesized via carbonyl insertion at a metal-sulfide-bound alkyl group. The experimental conditions are chosen for optimal assay, i.e., high reactant concentrations and pressures (200 MPa) to enhance chemisorption, and high temperature (250°C) to enhance reaction kinetics. All of the metal sulfides studied, with the exception CuS, promote hydrocarboxylation. Two other significant reactions involve the catalytic reduction of CO to form a surface-bound methyl group, detected after nucleophilic attack by nonane thiol to form methyl nonyl sulfide, and the formation of dinonyl sulfide via a similar reaction. Estimation of the catalytic turnover frequencies for each of the metal sulfides with respect to each of the primary reactions reveals that NiS, Ni3S2, and CoS perform comparably to commonly employed industrial catalysts. A positive correlation between the yield of primary product to NiS and Ni3S2 surface areas provides strong evidence that the reactions are surface catalytic in these cases. The sulfides FeS and Fe(1−x)S are unique in that they exhibit evidence of extensive dissolution, thus, complicating interpretation regarding heterogeneous vs. homogeneous catalysis. With the exception of CuS, each of the metal sulfides promotes reactions that mimic key intermediate steps manifest in the mechanistic details of an important autotrophic enzyme, acetyl-CoA synthase. The relatively high temperatures chosen for assaying purposes, however, are incompatible with the accumulation of thioesters. The results of this study support the hypothesis that transition metal sulfides may have provided useful catalytic functionality for geochemical carbon fixation in a prebiotic world (at least intially) devoid of peptide-based enzymes.

Here we report on the temporal changes in the composition of dissolved organic carbon (DOC) collected in the tidal freshwater region of the lower Mississippi River. Lignin-phenols, bulk stable carbon isotopes, compound-specific isotope analyses (CSIA) and 13C nuclear magnetic resonance (NMR) spectrometry were used to examine the composition of high molecular weight dissolved organic matter (HMW DOM) at one station in the lower river over 6 different flow regimes in 1998 and 1999. It was estimated that the annual input of DOC delivered to the Gulf of Mexico from the Mississippi River was of 3.1 × 10−3 Pg, which represents 1.2% of the total global input of DOC from rivers to the ocean. Average DOC and HMW DOC were 489 ±163 and 115 ± 47 μM, respectively. 13C-NMR spectra revealed considerably more aliphatic structures than aromatic carbons in HMW DOC. Lignin phenols were significantly 13C-depleted with respect to bulk HMW DOM indicating that C4 grass inputs to the HMW DOM were not significant. It is speculated that C4 organic matter in the river is not being converted (via microbial decay) to HMW DOM as readily as C3 organic matter is, because of the association of C4 organic matter with finer sediments. The predominantly aliphatic 13C NMR signature of HMW DOM suggests that autochthonous production in the river may be more important as a source of DOC than previously thought. Increases in nutrient loading and decreases in the suspended load (because of dams) in the Mississippi River, as well as other large rivers around the world, has resulted in significant changes in the sources and overall cycling of riverine DOC.

The organic residues produced in the brown-rot (BR) of wood by many basidiomycetes fungi are ubiquitous on most coniferous forest floors. This degraded wood tissue is characterized by low levels of polysaccharides and a high proportion of demethylated lignin with minor glycerol side chain oxidation. Because of the selective enrichment in an aromatic dihydroxy-rich lignin residue, the chemical and biological reactivity of BR degraded wood will be distinctly different from white rot, the other primary class of fungal wood decay, which typically produces oxidized, lignin-depleted residues. The biochemical mechanism by which BR fungi perform this distinctive degradative chemistry is only starting to become known, and molecular studies which examine the chemical changes imparted to lignin over the long-term decay process are lacking. Using 13C-labeled tetramethylammonium hydroxide thermochemolysis (13C-TMAH) and solid state 13C NMR, we investigated the relationship between lignin oxidation/demethylation and polysaccharide metabolism in a 32-week time series study of spruce sapwood inoculated with either of two BR fungi (Postia placenta and Gloeophyllum trabeum). Our findings demonstrate a close relationship between lignin demethylation and polysaccharide loss and suggest demethylation may play a mechanistic role in polysaccharide loss, possibly by assisting in Fenton reactions where catechol/quinone oxidation and cycling aids in iron reduction. The residue remaining after 16 weeks of decay is devoid of polysaccharides, in contrast to the 68% polysaccharide carbon present in the initial spruce, and exhibits an increased aromatic dihydroxy content (resulting from demethylation of the 3-methoxyl carbon) of up to 22% of the lignin, as determined by 13C-TMAH thermochemolysis. In a typical soil or porewater environment these chemical changes would make BR residues highly reactive toward redox sensitive polyvalent metals (e.g. ferric iron) and likely to adsorb to metal hydroxide surfaces.

Archaeological wood in ancient tombs is found usually with extensive degradation, limiting what can be learned about the diet, environment, health, and cultural practices of the tomb builders and occupants. Within Tumulus Midas Mound at Gordion, Turkey, thought to be the tomb of the Phrygian King Midas of the 8th century B.C., we applied a stable nitrogen isotope test to infer the paleodiet of the king and determine the nitrogen sources for the fungal community that decomposed the wooden tomb, cultural objects, and human remains. Here we show through analysis of the coffin, furniture, and wooden tomb structure that the principal degrader, a soft-rot fungus, mobilized the king's highly 15 N-enriched nutrients, values indicative of a diet rich in meat, to decay wood throughout the tomb. It is also evident from the δ 15 N values of the degraded wood that the nitrogen needed for the decay of many of the artifacts in the tomb came from multiple sources, mobilized at potentially different episodes of decay. The redistribution of nutrients by the fungus was restricted by constraints imposed by the cellular structure of the different wood materials that apparently were used intentionally in the construction to minimize decay.

A molecular and isotopic study of sediment cores from a sinkhole lake, Mud Lake, Florida, USA, was performed in order to relate documented changes in the regional terrestrial vegetation and water table over the last ∼5500 years to molecular and isotopic proxies for biological sources of organic matter to the lake sediments. Temporal shifts in the source of organic matter to the sediment, as determined by the stable carbon-isotope composition of bulk organic matter and biomarkers, correspond with previously defined regional scale transitions in forest ecosystems ( Quercus to Pinus at ∼5500 14 C yr BP and Taxodium expansion at 2500 14 C yr BP) and coincident increases in the Floridan water table. The δ 13 C values for total sedimentary organic carbon showed a shift from terrestrial and aquatic macrophyte sources (−27.8‰, in sediments dated at ∼5400 14 C yr BP) within the basal peat, to a cyanobacterial-dominated sapropel (−18.1‰) at the surface. A comparison of the δ 13 C values of bulk sediment and biomarkers representative of cyanobacterial and algal input (e.g. 7- and 8-methylheptadecane and the n -alkane C 17 ) indicates that the present shallow lake was fully developed by ∼2400 14 C yr BP. Differences among the δ 13 C values of specific biomarkers derived from vascular plants (C 29 and C 31 n -alkanes and CuO lignin oxidation products) and from cyanobacteria and algae are nearly equivalent in magnitude to the shift recorded in δ 13 C of TOC, indicating their effective use as source proxies in this system.

The emergence of biochemical homochirality was a key step in the origin of life, yet prebiotic mechanisms for chiral separation are not well constrained. Here we demonstrate a geochemically plausible scenario for chiral separation of amino acids by adsorption on mineral surfaces. Crystals of the common rock-forming mineral calcite (CaCO 3 ), when immersed in a racemic aspartic acid solution, display significant adsorption and chiral selectivity of d - and l -enantiomers on pairs of mirror-related crystal-growth surfaces. This selective adsorption is greater on crystals with terraced surface textures, which indicates that d - and l -aspartic acid concentrate along step-like linear growth features. Thus, selective adsorption of linear arrays of d - and l -amino acids on calcite, with subsequent condensation polymerization, represents a plausible geochemical mechanism for the production of homochiral polypeptides on the prebiotic Earth.

This paper presents the results from an assessment of the application of a new molecular analytical procedure, 13 CTMAH thermochemolysis, to study the chemical modification of lignin by white-rot and brown-rot fungi. This technique diAers from other molecular chemolysis procedures (e.g. TMAH thermochemolysis and CuO alkaline oxidation) as it enables one to determine the amount of hydroxylated aromatic components in degraded lignin residues through a selective lignin depolymerization and 13 C-labeled methylation reaction. Major diAerences were observed in the chemical composition and yield of lignin monomers released from a limited sample set of field and laboratory inoculation brown-rot and white-rot degraded residues when analyzed by 13 C-TMAH thermochemolysis. The brown-rot residues were characterized by high yields of 3,4-dihydroxy phenyl compounds, presumably due to fungal demethylation of methoxyl groups on guaiacyl lignin, and relatively low yields of aromatic acids that result from microbial side chain oxidation. The white-rot residues were characterized by low yields of demethylated lignin monomers but relatively high yields of monomers exhibiting side chain oxidation. If generally applicable, this distinct chemical functionality has important implications for the chemical reactivity and solubility of degraded wood residues and consequently the cycling of terrestrial carbon in the geosphere. The 13 C-TMAH thermochemolysis procedure provides a rapid and sensitive tool for tracking microbial modifications of lignin in terrestrial environments including coastal sediments, forest soils and waters receiving terrestrial organic matter. # 2000 Elsevier Science Ltd. All rights reserved.

The mechanism by which heated tetramethylammonium hydroxide (TMAH) degrades the lignin biopolymer was investigated by the novel application of 13C-labeled TMAH (13C-TMAH) in the thermochemolysis of a synthetic model guaiacyl lignin dimer. GC-MS analysis of the products showed labeling patterns consistent with a base-catalyzed intramolecular displacement of the β-phenoxy group and the formation of two intermediate guaiacyl propane epoxides, a γ-hydroxy-α,β-epoxide and an α-hydroxy-β,γ-epoxide. Methoxide then functions as a nucleophile to open the epoxide ring. These results substantiate the base-catalyzed reactions previously postulated by Gierer (1970) to explain alkali wood pulping and also explain the facile formation and distribution of lignin derivatives obtained in the TMAH thermochemolysis of natural samples. The absence of substantial numbers of bonds involving propyl-aryl ether linkages with adjacent hydroxyl groups is the limiting factor in the complete decomposition of lignin by TMAH thermochemolysis, as propyl-aryl ether linkages without adjacent hydroxyl groups cannot react via this mechanism. This helps to explain why materials such as highly degraded lignin residues, with significant side chain alteration and type III kerogens above the rank of lignite, where aliphatic-aryl ether linkages are thought to be insignificant, are reported to give low yields of TMAH thermochemolysis products.

This study presents the first combined application of 13 C labeling and isotope-ratio-monitoring gas chromatography-mass spectrometry (irmGCMS) to analyze the thermochemical transformations of specific organic compounds within a complex heavy oil. Specifically, this technique was used to monitor the hydrocarbons produced during the carbonization of a fluid catalytic cracking decant oil (FCCDO). Structural GC/MS analysis of these products has previously shown that 4-methyldibenzothiophene, 13 C-labeled at the methyl position (4- 13 MDBT), undergoes methylation to form a number of polymethyldibenzothiophenes and cleavage of its aryl-methyl bond to give dibenzothiophene (Energy Fuels 1997, 11,623, 631). The irmGCMS analysis of these products shows that the 4- 13 MDBT is a source of 13 C-enriched methyl that reacts with polyaromatic hydrocarbons (PAH) to produce a number of methylated PAHs. Precise measurement of 13 C enrichment and concentration of specific compounds enables tracking of the labeled carbon within a complex mixture as a function of reaction time. There are large differences in apparent reactivities of mono- and dimethyl-substituted naphthalenes, phenanthrenes, and pyrenes. The differences in observed reactivities of methylnaphthalene, methylphenanthrene, and methylpyrene isomers are consistent with calculated free valence indices at specific positions. There is no significant 13 C enrichment in unsubstituted PAH compounds, indicating that the labeled methyl group is not involved in producing GC-amenable unsubstituted PAH during early carbonization. This combined use of 13 C-labeled reactants and irmGCMS analysis will have broad applications in oil processing and geochemical fields associated with the study of thermochemical transformations of organic compounds within complex mixtures.

Elevated atmospheric CO2 concentrations can change chemistry and input rate of plant tissue to soil, potentially influencing above- and below-ground biogeochemical cycles. Given the important role played by leaf and root litter chemistry in controlling ecosystem function and vulnerability to environmental stresses, we investigated the hydrolyzable amino acid distribution and concentration in leaf and fine root litter among control and elevated CO2 treatments at the Rhinelander free air CO2 enrichment (FACE) experiment (WI, USA). We extracted hydrolyzable amino acids from leaf litter and fine (< 2 mm) roots at three depths for both control and elevated CO2 plots. We found that elevated CO2 decreased the proportion of total leaf amino acid carbon (C), but had no effect on total leaf amino acid nitrogen (N). There was no treatment effect for total root amino acid N or amino acid C for any depth. The decrease in leaf amino acids is probably a result of the shift of protein compounds to more structural compounds. Despite the decrease in leaf amino acid C concentrations, the overall increase in annual plant production under elevated CO2 would result in an increase in plant amino acids to the soil.