Hydrolysable Amino Acids Research Articles

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.

Kinetic study of the effect of kiwi fruit actinidin on various proteins of chicken meat

Abstract In this research, the effect of kiwi protein on the physicochemical properties of chicken meat was investigated (Ross breed). Chicken thighs have been marinated in the form of cubes with dimensions of 2 cm in 20 mL of kiwi protein with activity of 0.9 u/mL for 2, 4, 6, 8, 24, 48, 72, and 96 hr, and kept in a refrigerator at 4 ± 1 °C. Then, the enzyme actinidin was inactivated at 60 °C for 10 min, and the samples were evaluated. The results showed that the kiwi protein had a significant effect on the punch force, springiness, and chewiness of the chicken meat samples, and the reduced hardness was due to the activity of photolytic enzymes on myofibrillar proteins, and breaking the connective tissues. Muscle hydrolysis and release of amino acids significantly reduced pH in the treated samples compared to control. The affecting time of the enzyme had a significant effect on the degradation of meat proteins; it increased the solubility and hydrolysis degree, and reduced the average peptide chain length. The marination of chicken in kiwi increased lightness significantly (p < 0.05).

Effect of Pepsin–Trypsin In Vitro Gastro-Intestinal Digestion on the Antioxidant Capacities of Ultra-Filtrated Rice Bran Protein Hydrolysates (Molecular Weight &gt; 10 kDa; 3–10 kDa, and &lt; 3 kDa)

The antioxidant capacities of rice bran protein hydrolysates (RBPH) obtained by in vitro gastro-intestinal (GI) digestion by pepsin–trypsin (P–T) system were investigated. The hydrolysates were separated by ultrafiltration into three fractions (FI: molecular weight (MW) > 10 kDa, FII: MW 3–10 kDa, and FIII: MW < 3 kDa). Furthermore, the protein content and free amino acids of hydrolysates were studied. The results showed that fraction FII with MW 3–10 kDa had the highest antioxidant activity: DPPH of 28.34 ± 0.16%, ABTS of 30.66 ± 0.29%, and metal chelating activity of 61.04 ± 0.38%, and was further purified by RP-HPLC. Four sub-peptide fractions (F1, F2, F3, and F4) were collected and their antioxidant activities were assessed. The results displayed that F2 sub-peptide fraction owned a higher metal chelating activity (72.09 ± 0.32%) than other sub-peptide fractions. The amino acids composition of the purified peptide (F2) was evaluated, which could play an essential role in its antioxidant activity. The results indicated that rice bran proteins are rich in antioxidant peptides which can be employed as a potential source of natural bioactive compounds. The peptides produced can resist physiological digestion in the GI tract.

A rational design for improving the pepsin resistance of cellulase E4 isolated from T. fusca based on the evaluation of the transition complex and molecular structure

When feeding enzymes are consumed by livestock and poultry, the stomach is the first organ to come in contact with feeding enzymes. They will face major hazards: acidolysis and enzymatic hydrolysis. Therefore, it is very important to improve the tolerance of feed enzymes to the gastric juice such as pepsin. However, the hydrolysis of amino acids by pepsin is not specific, so improving the resistance of enzymes to pepsin is a great challenge. In this paper, we have selected cellulase E4 isolated from Thermonospora fusca as our study object, which exhibits unique properties because of its endo- and exocellulase characteristics, good synergistic property, and has great potential application value as feed addictive. So we propose a strategy to improve pepsin resistance of cellulose E4, including the following steps: 1) predicting amino acids that affect the formation of transitional complexes between pepsin and E4; 2) selection of candidate mutation sites; 3) prediction of optimal mutants. The mutant of E4L691H/L800H was predicted the best, and then we expressed and tested the characteristics of E4L691H/L800H, the results showed that the E4L691H/L800H had 25% more protein residual than the wild-type after 1-hour digestion, and the enzymatic properties were consistent with those of the wild-type. This study provides a useful molecular improvement strategy for protein pepsin resistance.

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.

Nutritional characterization of sake cake (sake-kasu) after heat-drying and freeze-drying.

Sake cake contains rice-derived components, as well as cell components and metabolites of Aspergillus oryzae and Saccharomyces cerevisiae. In this study, the effect of food processing on sake cake (sake-kasu) ingredients was investigated. Sake cake, obtained through brewing liquefied rice, was heat-dried (HD) or freeze-dried (FD) and analyzed. There were no differences in the amounts of proteins, lipids, carbohydrates, vitamin B6, choline, betaine, nicotinic acid, β-glucan and resistant proteins in HD and FD. There was also no difference in the amount of hydrolyzed amino acids in HD and FD, but many free amino acids were observed in HD. S-adenosyl methionine (SAM) was found to be abundant in FD. Meanwhile, nucleic acid-related components were found to be increased in HD, which seems to be due to the degradation of microbial metabolites. When considering the health benefits of sake cake, it is necessary to pay attention to the effects of processing method. Abbreviations CE-TOFMS: capillary electrophoresis time-of-flight mass spectrometry.

Biotechnological processing procedures of collagen-containing raw materials for creation of functional foods

The article presents the results of research into the biotechnological processing of collagencontaining raw materials (bovine rumina) to create functional foods. The patterns of biotransformation of collagen-containing raw materials by activated cultures of probiotic microorganisms (Bifidobacterium longum B379 M, Propionibacterium shermanii KM 186 and Lactobacillus helveticus Н17-18) have been studied and theoretically substantiated. It is noted that bovine rumina, following preliminary heat treatment, comprise a good nutrient medium for the development of probiotic cultures. It was revealed that low-molecular compounds formed during the heat treatment of rumina possess prebiotic properties that stimulate the growth of microorganisms. It was established that after 5–8 hours of cultivation, the number of viable cells of the studied cultures in the collagen substrate increases to 10 9 –10 10 CFU / g. It is noted that the biomodification of rumina improves their organoleptic properties and consistency, causing it to become succulent, soft and ductile. Biotransformation of collagen-containing raw materials by probiotic microorganisms leads to a significant increase in amino acids in hydrolysates in comparison with the control sample. The greatest increase in amino acids is observed during the fermentation of collagen Lactobacillus helveticus H17-18, which indicates a higher proteolytic activity of this culture. It was shown that the rumen microstructure undergoes changes under the action of probiotic microorganisms in comparison with the initial state (the muscle carcass becomes thinner and looser, as well as undergoing change in terms of the structure of its morphological elements). As a result of the research, a fundamentally new scheme of biotechnological processing of collagen-containing raw materials was developed. The obtained results open up broad prospects for the creation of BAA-synbiotics and food products intended for functional nutrition.

The hypertrehalosaemic neuropeptide conformational twins of cicadas consist of only L-amino acids: are they cis-trans isomers?

It is known for almost 25years that the corpora cardiaca (neurosecretory glands) of cicadas synthesize two isobaric peptides with hypertrehalosaemic activity denominated Placa-HrTH-I and II. Both decapeptides have the same amino acid sequence (pGlu-Val-Asn-Phe-Ser-Pro-Ser-Trp-Gly-Asn amide) and mass, but differ in their chromatographic retention time. The slightly more hydrophobic peptide, Placa-HrTH-II, co-elutes with the synthetic peptide of the same sequence and is less active in biological assays than Placa-HrTH-I. Ion mobility separation in conjunction with high-resolution mass spectrometry detected the differing structural feature between both peptides in the region Pro6-Ser7-Trp8. Here, it was shown that Placa-HrTH-I co-eluted with a synthetic peptide containing D-Pro in position 6, while dextrorotatory amino acid residues in positions 7 and 8 could be excluded in this way. Amino acid hydrolysis followed by chiral analysis using a relative of Marfey's reagent was then used to validate the presence of D-Pro in Placa-HrTH-I. Interestingly, this experiment unambiguously proved both the absence of D-Pro and the presence of L-Pro in Placa-HrTH-I. Racemization as a reason for the structural differences of the twin adipokinetic hormones was hence ruled out and cis-trans isomerism as the likely alternative came into focus. It remains to be investigated if Pro6 in cis-conformation is indeed present and responsible for the increased bioactivity of Placa-HrTH-I.

Glycine transformation induces repartition of cadmium and lead in soil constituents

Heavy metal stress in soil accelerates the plant root exudation of organic ligands. The degradation of exudate ligands can be fundamental to controlling the complexation of heavy metals. However, this process remains poorly understood. Here, we investigated the relationship between the transformation of glycine, a representative amino acid exudate, and cadmium/lead mobility in soils. Two 48-h incubation experiments were conducted after glycine addition to the soils. Parameters related to glycine distribution and degradation, Cd/Pb mobility, and the formation of glycine-Cd complex were analyzed. Glycine addition gradually decreased the Cd and Pb mobility throughout the 48-h incubation. By the end of the experiment, the CaCl2-extracted Cd and Pb concentrations decreased by 63.5% and 43.6%, respectively. The glycine mineralization was strong in the first 6 h, as indicated by a sharp decrease in CO2 efflux rates from 10.04 ± 0.62 to 3.51 ± 0.07 mg C–CO2 kg−1 soil h−1. The mineralization rates notably decreased after 6 h. The comparisons of dissolved organic carbon and hydrolyzable amino acid contents indicated that glycine mineralization in solution (95.6%) was much stronger than that in soil solids (49.3%). At the end of incubation, 0.22 mmol kg−1 glycine remained in soil solids. The remaining glycine provided sufficient sorption sites for Cd2+ and Pb2+, resulting in enhanced metal fixation via complexation. Comparisons of zeta potentials supported the formation of the glycine-Cd complex. The Cd and Pb immobilization processes could be attributed to metal-glycine complex formation, sorption re-equilibrium, and glycine degradation. These findings emphasize that the biogeochemical processes of glycine, derived from root exudates or protein degradation products, increased the sorption of heavy metals to soils and thus reduced their toxicity to plants.

Dissolved hydrolyzed amino acids in precipitation in suburban Guiyang, southwestern China: Seasonal variations and potential atmospheric processes

Proteinaceous compounds are particularly interesting because of their ubiquity and importance in many atmospheric processes. We investigated hydrolyzed amino acid (HAA), dissolved organic nitrogen (DON), nitrate (NO3−) and ammonium (NH4+) concentrations in precipitation samples collected in a suburban site in Guiyang over a 12 month period. Annually averaged total HAA, DON, NO3− and NH4+ concentrations were 3.7 μmol L−1, 151.1 μmol L−1, 68.9 μmol L−1 and 117.3 μmol L−1, respectively. Regarding the HAAs in precipitation, glutamic acid, glycine and proline were present in relatively high concentrations, followed by aspartic acid and alanine. The concentrations of total HAAs in precipitation showed a clear seasonal cycle, with a minimum level in winter and a maximum level in spring. Based on seasonal variations of total HAAs together with back-trajectory analysis, the air mass origins did not significantly impact the precipitation HAA levels. The NO3− concentrations recorded a better positive correlation (P < 0.01) with both the DON and total HAA concentrations than the NH4+ concentrations, possibly revealing that the sources for precipitation amino acids in suburban Guiyang were more linked with NO3− sources (from biomass burning, microbial activities and agricultural activities) than with NH4+ sources (from biomass burning and agricultural activities). In particular, in some specific periods, such as spring, abundant pollen releases may have been responsible for the relatively high precipitation amino acid concentrations. The average air temperature and the highest air temperature showed a positive correlation with the total HAA levels in precipitation. Clearly, the increase in precipitation total HAAs with higher air temperatures may indicate the enhanced temperature-induced degradation of high molecular weight atmospheric proteinaceous matter. Moreover, the volume-weighted precipitation glycine and total HAA levels were positively correlated with the product of atmospheric ozone and nitrogen dioxide, indicating that atmospheric proteinaceous matter may be inextricably bound up with both ozone- and nitrogen dioxide-related atmospheric processes. In conclusion, this study improves current knowledge on the origins and atmospheric processes of atmospheric proteinaceous compounds.

Nutritional impact on the biomass yield of Hirsutella citriformis and sporulation on inorganic substrates

ABSTRACTThe Mexican INIFAP-Hir-2 Hirsutella citriformis strain was cultured in six liquid media at different C:N ratios. Glucose and hydrolysed amino acids were used as C and N sources, respectively. During fermentation, low-cost nitrogen sources were used to obtain an improved biomass production, and these cultures were then air-dried, vacuum packed, and evaluated for germination. Cultures containing mycelia were inoculated on different clays to observe spore formation. The highest biomass yield (19.47 g/L) was obtained from the medium supplemented with 36 g/L glucose and hydrolysed casamino acids added at a C:N ratio of 10:1. Furthermore, upon the use of low-cost nitrogen source, the highest dry biomass weights were obtained when cottonseed flour (51.30 g/L) and soybean meal (48.40 g/L) were used. This showed a significant difference with respect to the media supplemented with casamino acids, yeast extract or corn steep powder. Synnemata production on clays was observed only for those cultures grown on soybean meal. Germination and conidia production were evaluated on 8 different clays and diatomaceous earth (Hyflo®). Here, hydrous aluminosilicate (HAS) and montmorillonite (MONT) clay showed a higher percentage of germination, whereas Attapulgite (GA) granulometry −325 y Verge montmorillonite S-140 showed lower germination percentages. Twelve days post inoculation of liquid cultures on various clays, Attapulgite 16/30, HAS 24/48 and Hyflo® showed a higher production of conidia where values reached more than 1 × 107 conidia/g.

Validation of microwave-assisted sample extraction-high performance liquid chromatography (HPLC) method for quantitative analysis of hydrolysed amino acids in aquatic biological samples

A sensitive and widely applicable High-Performance Liquid Chromatography (HPLC) with fluorescence detector (FLD) method for determination hydrolysed amino acids in fish and aquatic products was developed and validated through study. The method involved a microwave-assisted sample extraction and protein hydrolysed with the hydrochloric acid and propionic acid. The separation was performed by Shim-pack HR-ODS column with a gradient mobile phase. The total separation time was 25 min per run. The method showed satisfactory linearity, repeatability, accuracy, and limit of detection for 21 amino acids with the 1-100 mg/L calibration range based on 10 µL injection. The fish, fish feed, canned fish and seaweeds samples were analysed successfully by using this developed method.

Characterization of a seafood-flavoring enzymatic hydrolysate from brown alga Laminaria japonica

A seafood-flavoring enzymatic hydrolysate was prepared from brown alga Laminaria japonica. Response surface method was utilized to optimize the degree of hydrolysis and yield of the preparation process. The results indicated that the optimal conditions for the seafood flavoring production were as follows: temperature 50 °C, pH 7.5, solid–liquid ration 1:7 (g/mL), enzyme concentration 9.34%, and reaction time 21.3 h. Under this condition, the yield achieved was 29.90 ± 0.07%, and the degree of hydrolysis was 8.91 ± 0.24%. Amino acids and volatile aromatic substances of the enzymatic hydrolysate were subsequently determined by high performance liquid chromatography (HPLC) and gas chromatography-mass spectrometry, respectively. Electronic tongue and electronic nose were used to assess the taste and flavor of the hydrolysate, respectively. Hexanal (43.31 ± 0.57%), (E)-2-octenal (10.42 ± 0.34%), nonanal (6.91 ± 0.65%), pentanal (6.41 ± 0.97%), heptanal (4.64 ± 0.26) and 4-ethylcyclohexanol (4.52 ± 0.21%) were the most abundant flavor compounds in the enzymatic hydrolysate with % peak areas in GC–MS. The contents of aspartic acid (11.27 ± 1.12%) and glutamic acid (13.79 ± 0.21%) were higher than other free amino acids in the enzymatic hydrolysate. Electronic tongue revealed a taste profile characterized by high scores on umami and saltiness, consistent with the HPLC results.

Simultaneous RP-HPLC-DAD determination of dansyl amino acids in chemically treated human hair

A simple, rapid and reliable RP-HPLC-DAD method for the analysis of 19 amino acids in the protein hydrolysate of chemically treated hair is developed. The pre-column dansylation and RP-HPLC separation were optimized and peak resolution was improved as compared to previously published HPLC methods. The developed method showed excellent linearity for all tested amino acids in the concentration range 0.05-0.5 mmol/l. The obtained results show that the concentration of all amino acids detected in bleached hair decreases with increasing the concentration of hydrogen peroxide, this is most significant for cystine, compared to virgin hair. Higher amounts of the typical amino acids for keratin have been measured after exposure of hair to protein treatments. The method has been shown as very useful for amino acids analysis in a protein hydrolisate and it can be also used for establishing the amino acid profiles of other protein samples using this optimized procedure.

Drought differently affects growth properties, leaf ultrastructure, nitrogen absorption and metabolism of two dominant species of Hippophae in Tibet Plateau

Hippophae has been exploited as food, medicine as well as pioneer species for fixing nitrogen (N) and preventing desertification in Tibetan Plateau. In the paper, the eco-physiological responses and adaptive abilities of Hippophae rhamnoides and Hippophae thibetana seedlings under two levels of drought (50% and 30% field capacity) were investigated. The results indicated that two drought treatments differently affected biomass partition, water use efficiency, ammonia (NH4-N) and nitrate nitrogen (NO3-N) absorption, contents of hydrolysable amino acids (AA) and leaf ultrastructure of the two species of Hippophae. The two species had better resistance to moderate drought, while extreme drought showed more negative effects on biomass and ultrastructure of H. rhamnoides. Two drought treatments significantly increased water use efficiency of the two species. In H. rhamnoides, the two levels of drought stresses decreased the absorption of ammonia and nitrate nitrogen, whereas only inhibited NO3-N absorption of H. thibetana. The H. thibetana seedlings had more root nodules and higher R/S ratio than H. rhamnoides, while H. rhamnoides seedlings increased most individual and total AA in leaf and root organs under two drought treatments. The different growth, N-related absorption as well as metabolism responses of the two dominant species of Hippophae to drought stress may affect seedling colonization, the ecological function of N fixation and preventing desertification in Tibet Plateau in the future.

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.

Biochemical and structural controls on the decomposition dynamics of boreal upland forest moss tissues

Abstract. Mosses contribute an average of 20 % of boreal upland forest net primary productivity and are frequently observed to degrade slowly compared to vascular plants. If this is caused primarily by the chemical complexity of their tissues, moss decomposition could exhibit high temperature sensitivity (measured as Q10) due to high activation energy, which would imply that soil organic carbon (SOC) stocks derived from moss remains are especially vulnerable to decomposition with warming. Alternatively, the physical structure of the moss cell-wall biochemical matrix could inhibit decomposition, resulting in low decay rates and low temperature sensitivity. We tested these hypotheses by incubating mosses collected from two boreal forests in Newfoundland, Canada, for 959 days at 5 ∘C and 18 ∘C, while monitoring changes in the moss tissue composition using total hydrolyzable amino acid (THAA) analysis and 13C nuclear magnetic resonance (NMR) spectroscopy. Less than 40 % of C was respired in all incubations, revealing a large pool of apparently recalcitrant C. The decay rate of the labile fraction increased in the warmer treatment, but the total amount of C loss increased only slightly, resulting in low Q10 values (1.23–1.33) compared to L horizon soils collected from the same forests. NMR spectra were dominated by O-alkyl C throughout the experiment, indicating the persistence of potentially labile C. The accumulation of hydroxyproline (derived primarily from plant cell-wall proteins) and aromatic C indicates the selective preservation of biochemicals associated with the moss cell wall. This was supported by scanning electron microscope (SEM) images of the moss tissues, which revealed few changes in the physical structure of the cell wall after incubation. This suggests that the moss cell-wall matrix protected labile C from microbial decomposition, accounting for the low temperature sensitivity of moss decomposition despite low decay rates. Climate drivers of moss biomass and productivity, therefore, represent a potentially important regulator of boreal forest SOC responses to climate change that needs to be assessed to improve our understanding of carbon–climate feedbacks.