Total Hydrolysable Amino Acids Research Articles

Variation and Reactivity of Organic Matter in the Surface Sediments of the Changjiang Estuary and Its Adjacent East China Sea

AbstractThe Changjiang Estuary and its adjacent sea make up a highly dynamic ecosystem where the processes influencing the sources and degradation of organic matter (OM) in sediments are still not well understood. In this study, we analyzed the total organic carbon (TOC), total nitrogen (TN), stable carbon isotope (δ13C), and total hydrolysable amino acids (THAA) to investigate the distribution and degradation of sedimentary organic matter (SOM). TOC and TN contents ranged from 0.13% to 0.93% and 0.03% to 0.15%, respectively, with elevated values occurring in the muddy areas near the estuary. The δ13C of SOM became increasingly enriched from inshore (−23.5‰) to offshore (−20.5‰), and the TOC/TN molar ratios (C/N ratios) decreased from 8.16 to 5.84, indicating increasing contributions of marine OM. As the labile fraction of bulk OM, THAA concentrations ranged from 1.36 to 11.76 μmol/g and the distribution of THAA was influenced by terrestrial inputs along with the complex hydrography. The δ13C values and C/N ratios indicated that the SOM in the study area was mainly from marine and terrestrial origins (soil derived). The relatively low degradation index (DI) of SOM (mean: −0.57 ± 0.36) indicated that the OM had already undergone extensive degradation. Consistent with previous findings, our results indicated that the degraded OM was adsorbed by fine‐grained particles and selectively transported southward along the coast. The fresh SOM in the sandy area was mainly from in situ production. Additionally, diatoms appeared to be the primary source of the fresh OM buried in the sediments of the study area.

Organic Matter Composition at Ocean Station Papa Affects Its Bioavailability, Bacterioplankton Growth Efficiency and the Responding Taxa.

The bioavailability of organic matter (OM) to marine heterotrophic bacterioplankton is determined by both the chemical composition of OM and the microbial community composition. In the current study, changes in OM bioavailability were identified at Ocean Station Papa as part of the 2018 Export Processes in the Ocean from Remote Sensing (EXPORTS) field study. Removal rates of carbon (C) in controlled experiments were significantly correlated with the initial composition of total hydrolyzable amino acids, and C removal rates were high when the amino acid degradation index suggested a more labile composition. Carbon remineralization rates averaged 0.19 ± 0.08 μmol C L−1 d−1 over 6–10 days while bacterial growth efficiencies averaged 31 ± 7%. Amino acid composition and tandem mass spectrometry analysis of compound classes also revealed transformations to a more degraded OM composition during experiments. There was a log2-fold increase in the relative abundances of 16S rDNA-resolved bacterioplankton taxa in most experiments by members of the Methylophilaceae family (OM43 genus) and KI89A order. Additionally, when OM was more bioavailable, relative abundances increased by at least threefold for the classes Bacteroidetes (Flavobacteriaceae NS2b genus), Alphaproteobacteria (Rhodobacteraceae Sulfitobacter genus), and Gammaproteobacteria (Alteromonadales and Ectothiorhodospiraceae orders). Our data suggest that a diverse group of bacterioplankton was responsible for removing organic carbon and altering the OM composition to a more degraded state. Elevated community diversity, as inferred from the Shannon-Wiener H index, may have contributed to relatively high growth efficiencies by the bacterioplankton. The data presented here shed light on the interconnections between OM bioavailability and key bacterioplankton taxa for the degradation of marine OM.

First sequencing of ancient coral skeletal proteins

Here we report the first recovery, sequencing, and identification of fossil biomineral proteins from a Pleistocene fossil invertebrate, the stony coral Orbicella annularis. This fossil retains total hydrolysable amino acids of a roughly similar composition to extracts from modern O. annularis skeletons, with the amino acid data rich in Asx (Asp + Asn) and Glx (Glu + Gln) typical of invertebrate skeletal proteins. It also retains several proteins, including a highly acidic protein, also known from modern coral skeletal proteomes that we sequenced by LC–MS/MS over multiple trials in the best-preserved fossil coral specimen. A combination of degradation or amino acid racemization inhibition of trypsin digestion appears to limit greater recovery. Nevertheless, our workflow determines optimal samples for effective sequencing of fossil coral proteins, allowing comparison of modern and fossil invertebrate protein sequences, and will likely lead to further improvements of the methods. Sequencing of endogenous organic molecules in fossil invertebrate biominerals provides an ancient record of composition, potentially clarifying evolutionary changes and biotic responses to paleoenvironments.

Fractions and mineralization potential of the sediment organic nitrogen in Daya Bay, South China Sea: Anthropogenic influence and ecological implications

Nitrogen mineralization is a critical biogeochemical process that transfers organic nitrogen into inorganic forms using heterotrophic microorganisms. However, few studies have focused on this potential nutrient supplier. In this study, the composition of sediment organic nitrogen (SON) was studied, and nitrogen mineralization flux entering the water column was quantified. The results indicate that acid-hydrolyzable nitrogen (AHN) accounts for more than 40% of the SON, especially in the riverine input and marine aquaculture areas, which had significantly higher concentrations than the bay mouth area. Similar results were found for the ammonium nitrogen (AN), amino-sugar nitrogen (ASN), the total hydrolyzable amino acid (THAA), and unidentified hydrolyzable nitrogen (HUN). The mineralization rate in the marine aquaculture area was as high as 9.03 ± 1.33 mg·kg−1·d−1, while those of the riverine input (4.77 ± 1.55 mg·kg−1·d−1) and bay mouth (5.12 ± 1.42 mg·kg−1·d−1) areas were lower. The SON fractions, including the AHN, AN, ASN, and AAN, could obviously affect the mineralization of the SON. However, the extracellular enzymes, including proteinase and urease, are the predominant factors controlling the SON mineralization process. Anthropogenic activities, including riverine input and marine aquaculture, exert significant influences on the fractions and mineralization of the SON, and thus, they may increase the amount of dissolved inorganic nitrogen in the bottom of the water column in Daya Bay.

The Lability and Source of Particulate Organic Matter in the Northern Gulf of Mexico Hypoxic Zone

AbstractDecomposition of particulate organic matter (POM) plays a key role in the formation of hypoxia in subsurface waters of coastal ocean, yet little is known about the lability and transformation of POM in the hypoxic zone. Suspended particles were collected from surface waters to overlying waters (~30 cm above the sediment‐water interface) along the shelf of northern Gulf of Mexico (nGOM) in late spring/early summer of 2010–2013. Total hydrolyzable amino acids (THAA) and pigments were measured in these particulate samples to trace organic matter lability. The degradation indices, derived from the THAA and chloropigments, were positively correlated with dissolved oxygen (DO) concentrations in the shelf region, suggesting that decomposition of POM contributed greatly to DO utilization. Bacterial degradation appears to be the major pathway for POM decomposition on both inner and mid shelves, while zooplankton grazing played a minor role. POM samples in the overlying water on the inner shelf were the most degraded from the THAA and pigment results, and they also had high C/N ratios (9–14) and depleted δ 13C values (−29‰ to −24‰), pointing to a source of terrestrial C3 plant material. This distinct terrestrial signal of POM in the overlying water suggests strong selective degradation of marine‐sourced organic matter, but how the terrestrial organic matter is settled to this layer and its ultimate fate remain unclear. Taken together, these data offer new angles looking into the lability and degradation pathways of POM, and mechanisms of hypoxia formation in coastal waters.

Evolution of physiological characteristics and nutritional quality in fresh goji berry ( Lycium barbarum ) stored under different temperatures

Freshly harvested goji berry was stored at 4°C or −4°C for up to 21 days to track the evolution of physiological characteristics and nutritional quality after picking. During the 4°C- and −4°C-storage, respiration rates peaked at 205.06 and 131.33 mg (CO2)·kg−1·h−1, respectively, on Day 4, while ethylene production rates peaked at 83.38 and 45.41 µg (C2H4)·kg−1·h−1, respectively, on Day 2. For the −4°C-stored fruit, respiration and C2H4 production rates were significantly downregulated, fruit firmness and marketable fruit rate were well maintained, and accumulations of total soluble solids, polysaccharides, total free amino acids, and total hydrolyzed amino acids were promoted. In contrast, for the 4°C-stored fruit, accumulation of total flavonoids was enhanced, degradation of essential amino acids was delayed, and significantly higher content of zeaxanthin dipalmitate was maintained for most of the storage time. Practical applications As fresh goji is highly perishable, goji is usually marketed and consumed as dried fruit. As a result, there is a lack of information about its postharvest behavior. Our results suggested that fresh goji berry could be stored at 4°C or −4°C for up to 21 days and the fruit could be considered as a climacteric fruit. The presented study provides new insights into the evolution of physiological characteristics and nutritional quality of harvested goji berry stored at different temperatures, and will facilitate the preservation and circulation of fresh goji berry in the supply chain.

Composition and lability of riverine dissolved organic matter: Insights from thermal slicing ramped pyrolysis GC–MS, amino acid, and stable isotope analyses

Dissolved organic matter (DOM) is one of the key carbon substrates transported by rivers from land to sea, yet only a small fraction of it has been characterized at the molecular level. Here we characterize high molecular weight DOM (HMW-DOM, >1 kDa) isolated by ultrafiltration from nine North American rivers using thermal slicing ramped pyrolysis gas chromatography mass spectrometry (TSRP-GC–MS), carbon and nitrogen stable isotopes, elemental composition and total hydrolyzable amino acids (THAA). Samples from the more anthropogenically altered watersheds carried more enriched δ15N-HMW-DOM signatures than observed in samples from the more pristine watersheds. The TSRP-GC–MS results, coupled with THAA data, constrained DOM degradation process. Specifically, the diversity of pyrolyzates of HMW-DOM samples correlated well with the degradation index derived from the THAA data, with more degraded samples being more thermally stable and less molecularly diverse. The relationship between degradation index and pyrolyzate diversity observed in the HMW-DOM samples from across such a broad spatial scale suggests that degradative processes reduce riverine DOM complexity through the loss of more reactive moieties. Overall, TSRP-GC–MS, in combination with specific compound or isotope analyses, illuminates processes controlling DOM composition in different North American river systems with varying degrees of bio-lability and anthropogenic influence.

Impact of Water-Sediment Regulation on Variations of Amino Acids in the Middle-Lower Yellow River, China

In order to examine the impacts of water-sediment regulation on regional carbon cycling, we collected water, particulate and sediment samples from the middle-lower Yellow River in late June and early July, 2015 and analyzed their specific amino acids (AA), DOC, POC, and bacteria abundance. Summarized by 14 specific AA, the total hydrolysable AA (THAA), particulate AA (PAA), and sediment AA (SAA) varied in ranges of 2.29–9.05 µmol L−1, 5.22–22.96 µmol L−1, and 81.7–137.19 µg g−1 dry weight. After the regulation, dissolved free AA (DFAA) decreased by 29% while DCAA increased by 72%. These variations suggested that DFAA were further degraded, while DCAA molecules were further activated. Meanwhile, PAA increased almost 4 times as many as those before regulation, and SAA increased as well. After regulation, the amounts of bioactive amino acids (Asp, Glu and Gly) increased in THAA but decreased in PAA, with little changes in SAA. The ratios of Asp/Gly in different phases increased after regulation, indicating the AA contributions were promoted by calcareous organisms rather than by siliceous organisms. Multiple correlation analysis showed that PAA was primary representatives of AA and organic carbon, followed by DCAA and POC. Moreover, bacterial reproduction played a key role in shaping the AA compositions and properties, followed by the redox condition and acid-base balance. The results of this study provided a clear evidence for the effects of water-sediment regulation on regional biogeochemistry of organic carbon in the middle-lower Yellow River.

Effect of Bellamya purificata on organic matter degradation in surface sediment as revealed by amino acids

The accumulation of organic matter (OM) in the sediment of aquaculture ponds is a potential threat for aquaculture ecosystems and the surrounding environment. The snailBellamya purificatais a potential bioremediation species which may solve this problem. To investigate the effects ofB. purificataon OM degradation in surface sediment, an 84 d experiment was carried out. The experimental setup entailed 6 glass tanks which were divided intoB. purificatatreatment (BPT) and control (CON). At the end of the experiment, a significantly lower degradation index (DI), reactivity index (RI), and carbon-normalized yield of amino acids were observed in BPT compared to CON, with mean ± SD values of -0.47 ± 0.43, 1.24 ± 0.01, and 6.24 ± 0.44, respectively. BPT showed higher oxidation-reduction potential and bacterial 16S rRNA gene copies than CON. Total organic carbon, total nitrogen, and total hydrolysable amino acid concentrations in the BPT treatment were 1.83 ± 0.10%, 0.07 ± 0.01%, and 22.38 ± 0.53 µmol g-1, respectively, all of which were significantly lower than in CON. A clustered heat-map of different indexes related to OM degradation in sediments showed the final BPT as one separate category, which was different from the initial samples and the final CON. Overall,B. purificatacould effectively facilitate OM degradation by promoting oxidation-reduction potential and bacterial populations, and ultimately by inhibiting the OM accumulation in sediment. Our results therefore provide support for the application ofB. purificatato reduce the risk of endogenous pollution caused by OM accumulation in aquaculture ponds.

Identification of reworked foraminifera in temperate carbonate sediments – A pilot study from the Coorong Coastal Plain, southern Australia

The extent of aspartic acid and valine racemization (total hydrolysable amino acids) in single tests of the benthic foraminifer Lamellodiscorbis dimidiatus is examined as a potential method for identifying remanié fossils within temperate, bioclastic carbonate sediments. The foraminifer Lamellodiscorbis dimidiatus is a physically robust species capable of withstanding reworking from weathered calcarenites, and has the potential to experience multiple sedimentary cycles of deposition and erosion with subsequent inclusion in younger sedimentary units. The extent of racemization measured in single tests of Lamellodiscorbis sp., reveals that the skeletal carbonate sand sampled from the modern foreshore at Long Beach, Guichen Bay, southern Australia, contains foraminifera ranging in age, from modern individuals, to specimens of late Holocene and Late Pleistocene age. The age of individual foraminifer, however, cannot easily be distinguished based on their taphonomic appearances. The AAR data for Lamellodiscorbis sp., imply that a significant proportion of the skeletal carbonate constituents within the calcarenites of the Coorong Coastal Plain represent reworked bioclasts. The reworked sedimentary constituents within younger sediments, has resulted from the erosion of older calcarenites during glacial cycles.

Amino acids in surface sediments of the Zannone Island shelf (Western Mediterranean Sea): Possible bioindicators of submarine hydrothermal activity

This study shows results from amino acid analysis of seafloor sediment sampled between ~80 and ~130 m depth, within an active hydrothermal field located off Zannone Island (Tyrrhenian Sea). The total hydrolysable amino acid (THAA) content was determined at eight stations, three located within the main hydrothermal depression (i.e. the Zannone Giant Pockmark, ZGP) and five located in the surrounding seafloor. THAA concentration ranged between ~2 and ~11 nmol mg−1 dw and the lowest THAA concentrations were found at stations located within the ZGP. Amino acids resistant to degradation or originating from bacteria (β-alanine, histidine, leucine, arginine and lysine) had higher relative abundances inside the ZGP, whereas amino acids susceptible to degradation or originating from cellular plasma (proline, phenylalanine and tyrosine) showed higher relative abundances outside the ZGP. Degradation and reactivity indices were calculated, and the sedimentary organic matter in the three outside ZGP stations B07, B08 and B09 was found to be the most labile and reactive. Together with THAA concentrations, sediment grain size and carbon percentages were measured at 12 stations, five located within the ZGP and seven located outside the ZGP. At all stations, the percentage of sand was ~75% or higher. Carbon percentages were lower in samples located inside the ZGP than in the surrounding stations. The southern outside ZGP station B12 was found to be similar in terms of amino acids composition to the three inside ZGP stations, suggesting the influence of the hydrothermal fluids at this station.

Sources and preservation dynamics of organic matter in surface sediments of Narmada River, India – Illustrated by amino acids

Abstract The preservation process of organic matter (OM) in estuarine environments determines the recycling and sinking of nutrients. This process requires the identification of sources, degradation states and the main processes affecting OM transformations. Unfortunately, our understandingof the sources, degradation and factors affecting OM distribution in tropical rivers experiencing strong seasonality and monsoonal influence is still limited. This study examined the sources, degradation and factors affecting OM distribution along the Narmada River and its estuary during different seasons. Surface waters and sediments were analyzed seasonally for selected physico-chemical parameters and bulk compositions of sediments, together with amino acids (AA, including the bacterial biomarker, D-AA). The sources of OM were soils containing detrital terrestrial plant material, with C4 and C3 plants dominating the estuarine and riverine stations, respectively. The other sources of OM were in-situ production, together with bacteria and their remnants. Strong seasonality and monsoonal conditions control the sources and distribution of OM in the river. Higher concentrations of total hydrolysable amino acids (THAA) were observed in riverine stations, suggesting the presence of relatively fresher OM. The lower OC:SA ratios recorded in the estuarine sediments indicated a limited OM preservation in the studied river. Positive degradation index (DI) values were obtained during the pre-monsoon season, suggesting seasonal changes in OM diagenesis. Physical (strong tidal currents, rainfall, reduced water flow due to seasonal variations and shallow water depth within the estuary) and geochemical (mineral surface adsorption processes) factors control the distribution and transport of OM. Taken together, the sources, preservation and diagenesis of terrestrial OM along the Narmada River was controlled differentially by the strong seasonal variability of the region. Thus, under variable temporal conditions, tropical estuaries and rivers form important realms for examining, determining, evaluating and assessing OM in order to better interpret nutrient budgets of the seas and oceans.

Factors regulating the compositions and distributions of dissolved organic matter in the estuaries of Jiaozhou Bay in North China

Summary Water samples collected from the Jiaozhou Bay every two months between April 2016 and February 2017 were analyzed for dissolved organic carbon (DOC), particulate organic carbon (POC), total dissolved carbohydrates (TCHO), total hydrolyzed amino acids (THAA), and chromophoric dissolved organic matter (CDOM) to explore the biogeochemical processes of dissolved organic matter (DOM) in anthropogenic estuarine and coastal environments. In addition, nutrients, chlorophyll a and COD (chemical oxygen demand) in these samples were also analyzed. All parameters exhibited temporal and spatial variations: POC 0.13–22.40 mg/L (average 1.75 mg/L), DOC 0.98–32.75 mg/L (average 5.04 mg/L), COD 0.23–7.58 mg/L (average 1.67 mg/L), TCHO 0.34–14.09 µM (average 3.18 µM), THAA 0.89–8.30 µM (average 4.04 µM), and the absorption coefficient a(355) of CDOM 0.23–16.35 m − 1 (average 3.09 m−1). The temporal and spatial variations in the concentrations of TCHO, THAA, and DOC implied that the DOM in the study areas had a relatively higher biochemical activity. The canonical correspondence analysis (CCA) and maximal information coefficient (MIC) revealed that seasonal variations in temperature and the phosphate concentration were the dominant factors regulating the DOM distributions in Jiaozhou Bay, while riverine inputs and in situ reproduction mainly controlled the DOM compositions.

Distribution, degradation and bioavailability of dissolved organic matter in the East China Sea

Water samples were collected from the East China Sea (ECS) in October 2015 to investigate the distribution, degradation and bioavailability of organic matter. Concentrations of dissolved organic carbon (DOC), total hydrolyzable amino acids (THAAs, including dissolved free, DFAA and combined fraction, DCAA), particulate amino acids (PAAs), and total dissolved carbohydrates (TDCHO, including monosaccharides, MCHO and polysaccharides, PCHO) were measured. DOC and TCHO concentrations exhibited similar distribution patterns with high values occurring at nearshore stations, revealing the effects of terrestrial input and similar source and removal pathways of DOC and TCHO. The distributions of THAA, DCAA, and PAA displayed declining trends from the north to south of the ECS. Elevated THAA values simultaneously occurred in the center of the transect. The onboard incubation experiments with surface seawater from one station showed that the values of degradation index based on amino acids decreased with the increase of dissolved inorganic nitrogen (DIN) concentrations, indicating the mineralization of THAA to DIN during degradation process. TCHO-C% and THAA-C% are defined as the percentages of carbohydrates and amino acids in DOC, respectively. There were 21 stations suffering P limitation, implying that PO 4 3− -P content was the key factor limiting the growth of phytoplankton. High TCHO-C% values were found at P-limited stations, indicating that phytoplankton preferentially produced carbohydrates when experiencing nutrient limitation. The difference of dissolved organic matter bioavailability between surface and bottom water were probably due to water stratification. Overall, the present study may have implications for the source, removal and bioavailability of organic mater in the ECS.

Source and Biogeochemical Distribution of Organic Matter in Surface Sediment in the Deep Oligotrophic Lake Fuxian, China

The source, quantity and quality of sedimentary organic matter (SOM) were investigated in the surface sediments of Lake Fuxian, a deep oligotrophic lacustrine system in China. Granulometry, biochemical organic composition, bulk organic proxies and their stable isotopes were determined in the surface sediments (0–4 cm). The values of δ13C, δ15N and atomic ratio of total organic carbon to total nitrogen (TOC/TN) indicated that the sediments in the large partial lake were influenced by autochthonous organic matter. The concentrations of TOC, protein (PRT) and total hydrolysable amino acids may be mainly modulated by phytodetritus sinking from euphotic zones since they correlated significantly with chlorins. Otherwise, the lack of correlation between chlorins concentrations and carbohydrate (CHO) and lipid (LIP) indicated that the latter may have an additional terrestrial source. The highest sediment quantity was found in the deepest station NC owing to its fine sediment. Stations near northwestern shore accumulated more SOM than other littoral stations, which was in accordance with sewage discharge strength. Degradation quality indices, such as chlorin index, degradation index, PRT/CHO, and LIP/CHO, were in general agreement in showing the degraded status of SOM in Lake Fuxian. No clear spatial patterns were found in sediment degradation quality, which may be influenced by bottom oxygen concentration in the deep stations.

Amino acids as indicators to elucidate organic matter degradation profile in the Cochin estuarine sediments, Southwest coast of India

Surface sediments from three zones (fresh water, estuarine, and riverine/industrial zones) of the Cochin estuary, Southwest coast of India, were seasonally analyzed to understand the nature and degradation status of organic matter. Amino acid-based indices such as total hydrolyzable amino acids (THAAs), percentage contributions of amino acid carbon to total organic carbon (THAA-C%) and those of amino acid nitrogen to total nitrogen (THAA-N%), and degradation index (DI) were calculated. Elevated levels of amino acids in the sediments of the estuary were attributed to river runoff, autochthonous production, allochthonous inputs, and industrial and domestic effluent discharges. Higher levels of THAA-C%, THAA-N%, THAA, and positive DI found in most of the stations suggest the fresh deposition of organic matter. Multivariate statistical analyses revealed that the dispersal pattern of amino acids depends on the sediment texture, organic matter, redox state, and microbial processes in the study region.

Diagenesis of amino compounds in water column and sediment of Lake Baikal

The diagenesis of amino compounds in Lake Baikal was studied in sediment trap material (18 different water depths between 50–1350m) and underlying sediment (0–40 cm). Total hydrolysable amino acids (THAA), the amino acid (AA) composition including d- and l-enantiomers and amino sugars were analyzed. The study provides information on early diagenesis (<1 year) of settling material as well as on longer-term diagenesis (up to 600 years) occurring in the sediment. AA based diagenetic indicators were successfully applied to reveal changes at the different diagenetic stages. With increasing water and sediment depth, consistent decreases were found in: (1) the contributions of AA to total organic carbon (%TAAC, from 20 to 7%) and total nitrogen (%TAAN, from 54 to 20%); (2) the ratios of protein AA and their respective non-protein degradation products (aspartic acid:β-alanine, from 15 to 2; glutamic acid:γ-aminobutyric acid, from 28 to 2; arginine:ornithine, from 19 to 2); and (3) the AA based degradation index (from 0.7 to −1.1). There was multiple evidence that diagenesis went along with a progressive transformation of phytoplankton and zooplankton into bacterial organic material. Glycine, which is enriched in bacterial peptidoglycan, increased in relative abundance and bacteria-derived d-AA preferentially accumulated over proteinaceous l-AA. Molar ratios of glucosamine and galactosamine decreased towards a ratio of 1.0 ± 0.1 in the sediment, similar to ratios previously reported for detrital marine organic material. The general pattern of amino compound diagenesis in Lake Baikal resembles the pattern observed in marine systems, indicating a universal character of the processes controlling diagenesis in aquatic environments.

The origin of soil organic matter controls its composition and bioreactivity across a mesic boreal forest latitudinal gradient.

Warmer climates have been associated with reduced bioreactivity of soil organic matter (SOM) typically attributed to increased diagenesis; the combined biological and physiochemical transformation of SOM. In addition, cross-site studies have indicated that ecosystem regime shifts, associated with long-term climate warming, can affect SOM properties through changes in vegetation and plant litter production thereby altering the composition of soil inputs. The relative importance of these two controls, diagenesis and inputs, on SOM properties as ecosystems experience climate warming, however, remains poorly understood. To address this issue we characterized the elemental, chemical (nuclear magnetic resonance spectroscopy and total hydrolysable amino acids analysis), and isotopic composition of plant litter and SOM across a well-constrained mesic boreal forest latitudinal transect in Atlantic Canada. Results across forest sites within each of three climate regions indicated that (1) climate history and diagenesis affect distinct parameters of SOM chemistry, (2) increases in SOM bioreactivity with latitude were associated with elevated proportions of carbohydrates relative to plant waxes and lignin, and (3) despite the common forest type across regions, differences in SOM chemistry by climate region were associated with chemically distinct litter inputs and not different degrees of diagenesis. The observed climate effects on vascular plant litter chemistry, however, explained only part of the regional differences in SOM chemistry, most notably the higher protein content of SOM from warmer regions. Greater proportions of lignin and aliphatic compounds and smaller proportions of carbohydrates in warmer sites' soils were explained by the higher proportion of vascular plant relative to moss litter in the warmer relative to cooler forests. These results indicate that climate change induced decreases in the proportion of moss inputs not only impacts SOM chemistry but also increases the resistance of SOM to decomposition, thus significantly altering SOM cycling in these boreal forest soils.

Sources and transformation of dissolved and particulate organic nitrogen in the North Pacific Subtropical Gyre indicated by compound-specific δ15N analysis of amino acids

This study explores the use of compound-specific nitrogen isotopes of amino acids (δ15NAA) of coupled dissolved and particulate organic nitrogen (DON, PON) samples as a new approach to examine relative sources, transformation processes, and the potential coupling of these two major forms of Ncycle in the ocean water column. We measured δ15NAA distributions in high-molecular-weight dissolved organic nitrogen (HMW DON) and suspended PON in the North Pacific Subtropical Gyre (NPSG) from surface to mesopelagic depths. A new analytical approach achieved far greater δ15NAA measurement precision for DON than earlier work, allowing us to resolve previously obscured differences in δ15NAA signatures, both with depth and between ON pools. We propose that δ15N values of total hydrolysable amino acids (THAA) represents a proxy for proteinaceous ON δ15N values in DON and PON. Together with bulk δ15N values, this allows δ15N values and changes in bulk, proteinaceous, and “other-N” to be directly evaluated.These novel measurements suggest three main conclusions. First, the δ15NAA signatures of both surface and mesopelagic HMW DON suggest mainly heterotrophic bacterial sources, with mesopelagic HMW DON bearing signatures of far more degraded material compared to surface material. These results contrast with a previous proposal that HMW DON δ15NAA patterns are essentially “pre-formed” by cyanobacteria in the surface ocean, undergo little change with depth. Second, different δ15NAA values and patterns of HMW DON vs. suspended PON in the surface NPSG suggest that sources and cycling of these two N reservoirs are surpisingly decoupled. Based on molecular δ15N signatures, we propose a new hypothesis that production of surface HMW DON is ultimately derived from subsurface nitrate, while PON in the mixed layer is strongly linked to N2 fixation and N recycling. In contrast, the comparative δ15NAA signatures of HMW DON vs. suspended PON in the mesopelagic also suggest a possible PON source for some HMW DON in the mid-water column. Together, these results suggest that conversion of relatively labile ON to less labile DON by heterotrophic bacteria (a “microbial nitrogen pump”) may be the key pathway for production and alteration of DON in both the surface and the mesopelagic oligotrophic ocean. Finally, in contrast to THAA, δ15N values of the other-N were substantially less affected by heterotrophic alteration, which may be consistent with a larger than expected contribution of amino sugars, or other less labile nitrogenous organic molecules.

Photochemical behavior of dissolved and colloidal organic matter in estuarine and oceanic waters

Chromophoric dissolved organic matter (CDOM), carbohydrates, and amino acids were analyzed to investigate the photochemistry of total dissolved (<0.22μm) organic matter (DOM), high-molecular-weight (HMW, 1kDa–0.22μm) DOM and low-molecular-weight (LMW, <1kDa) DOM at stations in the Yangtze River and its coastal area, and in the Western Pacific Ocean. Results revealed that the humic-like and tryptophan-like CDOM fluorescent components in riverine, coastal, and oceanic surface waters were photodegraded during irradiation. However, the photochemical behavior of tyrosine-like component was obscured by the excessive fluorescence intensities of humic- and tryptophan-like fluorescent components. Light sensitivity varied depending on the source material; terrestrially derived DOM was more susceptible to irradiation than autochthonous DOM. In contrast to the expected photodegradation of CDOM, photo-induced synthetic reaction transformed the LMW matters to polysaccharides (PCHO) and degradation reaction decomposed the HMW DOM to Monosaccharides. Colloidal DOM preferentially underwent photodegradation, whereas permeate DOM mainly photosynthesized PCHO. The total hydrolysable amino acid (THAA) pool changed because of the additional input by the photodegradation of DOM or THAA itself. The compositions of THAA changed during the irradiation experiments, indicating that the different photochemical behavior of individual amino acids were related to their different original photoreactivities; the relatively stable amino acids (e.g., Ser and Gly) significantly accumulated during irradiation, whereas photo-active aromatic amino acids (e.g. Tyr and His) were prone to photodegradation. The data presented here demonstrated that irradiation significantly influence the conversion between dissolved and colloid organic matter. These results can promote the understanding of irradiation effect on the carbon and nitrogen cycle in riverine, estuarine and oceanic ecosystems.