Albutensin A, an ileum-contracting peptide derived from serum albumin, acts through both receptors for complements C3a and C5a

Albutensin A is an ileum-contracting peptide derived from serum albumin. The sequences of bovine, human and porcine albutensin A are ALKAWSVAR, AFKAWAVAR, and AFKAWSLAR, respectively. These albutensin A homologs all exhibited biphasic ileal contractions in the longitudinal strips of guinea pig ileum. The order of potency in the contraction was porcine > bovine > human homologs. The ileal contraction profiles were similar to those of oryzatensin and casoxin C, agonist peptides for complement C3a receptors derived from rice albumin and bovine -casein, respectively. All three homologs of albutensin A have homology with the COOH-terminal sequences of complements C3a and C5a, which are essential for their activities; porcine albutensin A showed the highest homology. Indeed, porcine albutensin A was confirmed to act through both C3a and C5a receptors by a radioreceptor assay and cross-desensitization in the ileal contraction. In addition, bovine and human homologs also showed affinity for both receptors. This study suggests that a bioactive peptide acting through both C3a and C5a receptors is released by the proteolytic cleavage of serum proteins other than complement components.     

Albutensin A,an ileum-contracting peptide derived from serum albumin,acts through both receptors for complements C3a and C5a

Summary Albutensin A is an ileum-contracting peptide derived from serum albumin. The sequences of bovine, human and porcine albutensin A are ALKAWSVAR, AFKAWAVAR, and AFKAWSLAR, respectively. These albutensin A homologs all exhibited biphasic ileal contractions in the longitudinal strips of guinea pig ileum. The order of potency in the contraction was porcine>bovine>human homologs. The ileal contraction profiles were similar to those of oryzatensin and casoxin C, agonist peptides for complement C3a receptors derived from rice albumin and bovine κ-casein, respectively. All three homologs of albutensin A have homology with the COOH-terminal sequences of complements C3a and C5a, which are essential for their activities; porcine albutensin A showed the highest homology. Indeed, porcine albutensin A was confirmed to act through both C3a and C5a receptors by a radioreceptor assay and cross-desensitization in the ileal contraction. In addition, bovine and human homologs also showed affinity for both receptors. This study suggests that a bioactive peptide acting through both C3a and C5a receptors is released by the proteolytic cleavage of serum proteins other than complement components.     

Design and analysis of structure-activity relationship of novel antimicrobial peptides derived from the conserved sequence of cecropin.

We have de novo designed four antimicrobial peptides AMP-A/B/C/D, the 51-residues peptides, which are based on the conserved sequence of cecropin. In the present study, the four peptides were chemically synthesized and their activities assayed. Their secondary structure, amphipathic property, electric field distribution and transmembrane domain were subsequently predicted by bioinformatics tools. Finally, the structure-activity relationship was analyzed from the results of activity experiments and prediction. The results of activity experiments indicated that AMP-B/C/D clearly possessed excellent broad-spectrum activity against bacteria, whereas AMP-A was almost inactive against most of the bacterial strains tested. AMP-B/C/D showed more potent activity against Gram-positive bacteria than against Gram-negative bacteria. By utilizing bioinformatics analysis tools, we found that the secondary structure of the four cation peptides was mainly alpha-helix, and the result of CD spectrum also displayed that all the peptides had considerable alpha-helix in the presence of either 50% TFE or SDS micelles. AMP-C showed much better activity than other peptides against most of the bacteria tested, owing to its remarkable cation property and the amphipathic character of its N-terminal. The study of structure-activity relationship of the designed peptides confirmed that amphipathic structure and high net positive charge were prerequisites for maintaining their activities.     

Internal motional amplitudes and correlated bond rotations in an alpha-helical peptide derived from 13C and 15N NMR relaxation

Peptide GFSKAELAKARAAKRGGY folds in an alpha-helical conformation that is stabilized by formation of a hydrophobic staple motif and an N-terminal capping box (Munoz V. Blanco FJ, Serrano L, 1995, Struct Biol 2:380-385). To investigate backbone and side-chain internal motions within the helix and hydrophobic staple, residues F2, A5, L7, A8, and A10 were selectively 13C- and 15N-enriched and NMR relaxation experiments were performed in water and in water/trifluoroethanol (TFE) solution at four Larmor frequencies (62.5, 125, 150, and 200 MHz for 13C). Relaxation data were analyzed using the model free approach and an anisotropic diffusion model. In water, angular variances of motional vectors range from 10 to 20 degrees and backbone phi,psi bond rotations for helix residues A5, L7, A8, and A10 are correlated indicating the presence of Calpha-H, Calpha-Cbeta, and N-H rocking-type motions along the helix dipole axis. L7 side-chain CbetaH2 and CgammaH motions are also correlated and as motionally restricted as backbone CalphaH, suggesting considerable steric hindrance with neighboring groups. In TFE which stabilizes the fold, internal motional amplitudes are attenuated and rotational correlations are increased. For the side chain of hydrophobic staple residue F2, wobbling-in-a-cone type motions dominate in water, whereas in TFE, the Cbeta-Cgamma bond and phenyl ring fluctuate more simply about the Calpha-Cbeta bond. These data support the Daragan-Mayo model of correlated bond rotations (Daragan VA, Mayo KH, 1996, J Phys Chem 100:8378-8388) and contribute to a general understanding of internal motions in peptides and proteins.     

Synthesis and physicochemical studies of amyloidogenic hexapeptides derived from human cystatin C

Human cystatin C (hCC) is a low molecular mass protein that belongs to the cystatin superfamily. It is an inhibitor of extracellular cysteine proteinases, present in all human body fluids. At physiological conditions, hCC is a monomer, but it has a tendency to dimerization. Naturally occurring hCC mutant, with leucine in position 68 substituted by glutamine (L68Q), is directly involved in the formation of amyloid deposits, independently of other proteins. This process is the primary cause of hereditary cerebral amyloid angiopathy, observed mainly in the Icelandic population. Oligomerization and fibrillization processes of hCC are not explained equally well, but it is proposed that domain swapping is involved in both of them. Research carried out on the fibrillization process led to new hypothesis about the existence of a steric zipper motif in amyloidogenic proteins. In the hCC sequence, there are 2 fragments which may play the role of a steric zipper: the loop L1 region and the C‐terminal fragment. In this work, we focused on the first of these. Nine hexapeptides covering studied hCC fragment were synthesized, and their fibrillogenic potential was assessed using an array of biophysical methods. The obtained results showed that the studied hCC fragment has strong profibrillogenic propensities because it contains 2 fragments fulfilling the requirements for an effective steric zipper located next to each other, forming 1 super‐steric zipper motif. This hCC fragment might therefore be responsible for the enhanced amyloidogenic properties of dimeric or partially unfolded hCC.     

MAP1 structural organization in Drosophila: in vivo analysis of FUTSCH reveals heavy- and light-chain subunits generated by proteolytic processing at a conserved cleavage site

The MAP1 (microtubule-associated protein 1) family is a class of microtubule-binding proteins represented by mammalian MAP1A, MAP1B and the recently identified MAP1S. MAP1A and MAP1B are expressed in the nervous system and thought to mediate interactions of the microtubule-based cytoskeleton in neural development and function. The characteristic structural organization of mammalian MAP1s, which are composed of heavy- and light-chain subunits, requires proteolytic cleavage of a precursor polypeptide encoded by the corresponding map1 gene. MAP1 function in Drosophila appears to be fulfilled by a single gene, futsch. Although the futsch gene product is known to share several important functional properties with mammalian MAP1s, whether it adopts the same basic structural organization has not been addressed. Here, we report the identification of a Drosophila MAP1 light chain, LC(f), produced by proteolytic cleavage of a futsch-encoded precursor polypeptide, and confirm co-localization and co-assembly of the heavy chain and LC(f) cleavage products. Furthermore, the in vivo properties of MAP1 proteins were further defined through precise MS identification of a conserved proteolytic cleavage site within the futsch-encoded MAP1 precursor and demonstration of light-chain diversity represented by multiple LC(f) variants. Taken together, these findings establish conservation of proteolytic processing and structural organization among mammalian and Drosophila MAP1 proteins and are expected to enhance genetic analysis of conserved MAP1 functions within the neuronal cytoskeleton.     

施肥措施对不同母质发育的稻田生态系统土壤微生物量碳、氮的影响

以湖南省稻田土壤肥力监测点为基础,研究了稻田生态系统土壤微生物量碳、氮的特性.结果表明,不同施肥措施对不同地域和母质发育的稻田生态系统土壤微生物量碳、氮的影响程度不同.经过18年的不同施肥处理,不同母质发育的稻田生态系统土壤微生物量碳、氮的变化趋势基本一致,变化顺序为湖积物发育的水稻土>河流冲积物和第四纪红土发育的水稻土>石灰岩发育的水稻土>板页岩发育的水稻土.土壤微生物量碳为259.5～864.4 mg·kg^-1,土壤微生物量氮为8.7～70.7 mg·kg^-1.施肥可以明显提高稻田生态系统土壤微生物量碳、氮含量;有机肥是改善土壤微生物量碳、氮的主要基础物质,但以有机无机配合施用效果最好.与对照相比,施化肥和有机无机配施处理土壤微生物量碳、氮最大增量分别为407.6和59.2 mg·kg^-1,最大增长率分别为102.8%和514.8%.     

Maize C4 and non-C4 NADP-dependent malic enzymes are encoded by distinct genes derived from a plastid-localized ancestor

NADP-dependent malic enzymes (NADP-ME; EC1.1.1.40) have been implicated in a wide range of metabolic pathways in the plastids and cytosol of plant cells. In maize, an NADP-ME type C4 plant, the most abundant NADP-ME form is the chloroplastic leaf isoform that delivers CO₂ intracellularly to ribulose bisphosphate carboxylase (RuBPCase). A second NADP-ME isoform predominates in maize roots and exhibits distinct C3-like enzymatic characteristics. We show that the C3-like isoform is encoded by a pair of nearly identical genes that encode precursor proteins with functional chloroplast transit peptides. Using RT-PCR, we also show that the messages encoding the C4 and C3-like NADP-ME isoforms are differentially regulated with respect to the developmental stage of the leaf, light conditions, and tissue type. Based on these characteristics and on sequence comparison of ME families in other species, we propose a scheme for the origin of the C4-specific NADP-ME gene.     

Specific immune response to a synthetic peptide derived from outer surface protein C of Borrelia burgdorferi predicts protective borreliacidal antibodies

In a previous study, we described the development of a new specific serodiagnostic test for Lyme disease involving enzyme-linked immunosorbent assay and a synthetic peptide, OspC-I. The OspC-I peptide is derived from part of the outer surface protein C (OspC) amino acid sequence of Borrelia burgdorferi and is located in the region conserved among B. burgdorferi sensu stricto or sensu lato isolates. In this study, we demonstrate that sera containing antibodies against OspC-I from patients with early Lyme disease had borreliacidal activity against isolates of three genospecies of Lyme disease spirochete, B. burgdoreferi B31, B. garinii HPI and B. afzelii HT61. However, the borreliacidal activity against B. burgdorferi, which has not been isolated in Japan, was weaker than that against the other species. Vaccination of mice with OspC-I induced the production of anti-OspC-I antibodies in serum with borreliacidal activity. The immune mouse serum had significantly higher levels of borreliacidal activity against HP1 and HT61, than against B31. Neutralization of borreliacidal activity with anti-IgM antibodies showed that the borreliacidal activity of anti-OspC-I antibodies in serum was due to IgM. Furthermore. mice vaccinated with OspC-I were protected against challenge with HPI and HT61. but not fully protected against infection with B31. These results suggest that OspC-I is not only a specific antigen for use in serodiagnostic tests for Lyme disease, but is also a potential candidate for a Lyme disease vaccine in Japan.     

Design and synthesis of a peptide derived from positions 195–244 of human cdc25C phosphatase

We have designed, synthesized and purified a 51 amino acid peptide derived from an essential domain of human cdc25C phosphatase. In vivo, differential phosphorylation of this domain regulates either the induction of mitotic processes, or the checkpoint arrest of eukaryotic cells in response to DNA damage. Peptide synthesis was achieved using the stepwise Fmoc strategy and resulted in an important yield of highly pure peptide. The final peptide was identified by amino acid analysis, electrospray mass spectrometry and nuclear magnetic resonance, which revealed that one of the two methionines within the peptide was oxidized into its sulphoxide derivative We investigated whether this 51 amino acid peptide folded into secondary structures in solution by circular dichroism and observed the formation of alpha helices in TFE. Finally, we verified that this peptide could bind to its biologically relevant 14‐3‐3 partner in vitro by fluorescence spectroscopy. Copyright © 1999 European Peptide Society and John Wiley & Sons, Ltd.     

Coordinate increase of isopenicillin N synthetase, isopenicillin N epimerase and deacetoxycephalosporin C synthetase in a high cephalosporin-producing mutant of Acremonium chrysogenum and simultaneous loss of the three enzymes in a non-producing mutant

Abstract An early blocked mutant in cephalosporin biosynthesis ( Acremonium chrysogenum N₂) had simultaneously lost 3 enzymes of the cephalosporin biosynthetic pathway (isopenicillin N synthetase, isopenicillin N epimerase and deacetoxycephalosporin C synthetase) and accumulated the tripeptide α-aminoadipyl-cysteinyl-valine. An overproducing mutant ( A. chrysogenum C-10) showed a 2-fold increase in the same 3 enzymes throughout fermentation, with respect to the low-producing strain A. chrysogenum CW-19. These results suggest that expression of the genes coding for cephalosporin biosynthetic enzymes is altered in a coordinate form in these mutants.     

Combined insertion of basic and non-basic amino acids at hemagglutinin cleavage site of highly pathogenic H7N9 virus promotes replication and pathogenicity in chickens and mice

Since mid-2016, the low pathogenic H7N9 influenza virus has evolved into a highly pathogenic (HP) phenotype in China, raising many concerns about public health and poultry industry. The insertion of a “KRTA” motif at hemagglutinin cleavage site (HACS) occurred in the early stage of HP H7N9 variants. During the co-circulation, the HACS of HP-H7N9 variants were more polymorphic in birds and humans. Although HP-H7N9 variants, unlike the H5 subtype virus, exhibited the insertions of basic and non-basic amino acids, the underlying function of those insertions and substitutions remains unclear. The results of bioinformatics analysis indicated that the PEVPKRKRTAR/G motif of HACS had become the dominant motif in China. Then, we generated six H7N9 viruses bearing the PEIPKGR/G, PEVPKGR/G, PEVPKRKRTAR/G, PEVPKGKRTAR/G, PEVPKGKRIAR/G, and PEVPKRKRR/G motifs. Interestingly, after the deletion of threonine and alanine (TA) at HACS, the H7N9 viruses manifested decreased thermostability and virulence in mice, and the PEVPKRKRTAR/G-motif virus is prevalent in birds and humans probably due to its increased transmissibility and moderate virulence. By contrast, the insertion of non-basic amino acid isoleucine and alanine (IA) decreased the transmissibility in chickens and virulence in mice. Remarkably, the I335V substitution of H7N9 virus enhanced infectivity and transmission in chickens, suggesting that the combination of mutations and insertions of amino acids at the HACS promoted replication and pathogenicity in chickens and mice. The ongoing evolution of H7N9 increasingly threatens public health and poultry industry, so, its comprehensive surveillance and prevention of H7N9 viruses should be pursued.     

C、N、P对杜氏盐藻突变藻株Zea1生长和积累玉米黄素的影响

通过UV辐照和NTG诱变处理杜氏盐藻野生型藻株得到一株杜氏盐藻高产玉米黄素突变株Zea1,以此突变藻株为实验材料,系统研究了光照强度、盐浓度、碳源、氮源、磷源等对Zea1生长和玉米黄素积累合成的影响。葡萄糖在10mmol/L时既适合Zea1生长,又有利于其玉米黄素的积累。KNO3浓度为1mmol/L时最适合突变株藻细胞生长,而(NH4)2SO4浓度为1mmol/L最有利于藻细胞内玉米黄素的积累。综合来看,1mmol/L(NH4)2SO4为最优氮源。KH2PO4浓度为0.1mmol/L时Zea1藻细胞积累玉米黄素含量最高,同时在此浓度下也最适宜藻细胞的生长。讨论了此结果的机理和意义,为利用杜氏盐藻大规模生产玉米黄素提供了理论依据。     

Structural and functional characterization of peptides derived from the carboxy‐terminal region of a defensin from the tick Ornithodoros savignyi

Tick defensins may serve as templates for the development of multifunctional peptides. The purpose of this study was to evaluate shorter peptides derived from tick defensin isoform 2 (OsDef2) in terms of their antibacterial, antioxidant, and cytotoxic activities. We compared the structural and functional properties of a synthetic peptide derived from the carboxy‐terminal of the parent peptide (Os) to that of an analogue in which the three cysteine residues were omitted (Os–C). Here, we report that both peptides were bactericidal (MBC values ranging from 0.94–15 µg/ml) to both Gram‐positive and Gram‐negative bacteria, whereas the parent peptide only exhibited Gram‐positive antibacterial activity. The Os peptide was found to be two‐fold more active than Os–C against three of the four tested bacteria but equally active against Staphylococcus aureus. Os showed rapid killing kinetics against both Escherichia coli and Bacillus subtilis, whereas Os–C took longer, suggesting different modes of action. Scanning electron microscopy showed that in contrast to melittin for which blebbing of bacterial surfaces was observed, cells exposed to either peptide appeared flattened and empty. Circular dichroism data indicated that in a membrane‐mimicking environment, the cysteine‐containing peptide has a higher α‐helical content. Both peptides were found to be non‐toxic to mammalian cells. Moreover, the peptides displayed potent antioxidant activity and were 12 times more active than melittin. Multifunctional peptides hold potential for a wide range of clinical applications and further investigation into their mode of antibacterial and antioxidant properties is therefore warranted. Copyright © 2013 European Peptide Society and John Wiley & Sons, Ltd.     

Design of bacteria-agglutinating peptides derived from parotid secretory protein, a member of the bactericidal/permeability increasing-like protein family

Parotid secretory protein (PSP) (SPLUNC2), a potential host-defense protein related to bactericidal/permeability-increasing protein (BPI), was used as a template to design antibacterial peptides. Based on the structure of BPI, new PSP peptides were designed and tested for antibacterial activity. The peptides did not exhibit significant bactericidal activity or inhibit growth but the peptide GL-13 induced bacterial matting, suggesting passive agglutination of bacteria. GL-13 was shown to agglutinate the Gram negative bacteria Pseudomonas aeruginosa and Aggregatibacter (Actinobacillus) actinomycetemcomitans, Gram positive Streptococcus gordonii and uncoated sheep erythrocytes. Bacterial agglutination was time and dose-dependent and involved hydrophobic interactions. Variant forms of GL-13 revealed that agglutination also depended on the number of amine groups on the peptide. GL-13 inhibited the adhesion of bacteria to plastic surfaces and the peptide prevented the spread of P. aeruginosa infection in a lettuce leaf model, suggesting that GL-13 is active in vivo. Moreover, GL-13-induced agglutination enhanced the phagocytosis of P. aeruginosa by RAW 264.7 macrophage cells. These results suggest that GL-13 represents a class of antimicrobial peptides, which do not directly kill bacteria but instead reduce bacterial adhesion and promote agglutination, leading to increased clearance by host phagocytic cells. Such peptides may cause less bacterial resistance than traditional antibiotic peptides.     

Synthetic peptides derived from an N‐terminal domain of the E2 protein of GB virus C in the study of GBV‐C/HIV‐1 co‐infection

Synthetic peptides derived from GB virus C (GBV‐C) have previously been studied in our group for the development of new systems capable of diagnosing diseases caused by this humanotropic virus. We also recently described specific peptide domains of the E2 envelop protein of GBV‐C that have the capacity to interfere with the HIV‐1 fusion peptide, produce a notable decrease in cellular membrane fusion, and perturb HIV‐1 infectivity in a dose‐dependent manner. The present work discloses the design and synthesis of both linear and cyclic branched peptides based on a previously reported N‐terminal sequence of the GBV‐C E2 protein. Immunoassays and cell–cell fusion assays were performed to evaluate their diagnostic value to detect anti‐GBV‐C antibodies in HIV‐1 patients, as well as their putative anti‐HIV‐1 activity as entry inhibitors. Our results showed that chemical modifications of the selected E2(7–26) linear peptide to afford cyclic architecture do not result in an enhanced inhibition of gp41 HIV‐1‐mediated cell–cell fusion nor improved sensitivity in the detection of GBV‐C antibodies in HIV‐1 co‐infected patients. Thus, the ELISA data reinforce the potential utility of linear versions of the E2(7–26) region for the development of new peptide‐based immunosensor devices for the detection of anti‐GBV‐C antibodies in HIV‐1 co‐infected patients. Copyright © 2012 European Peptide Society and John Wiley & Sons, Ltd.     

东北次生杨桦林土壤碳氮动态特征

土壤分级组分是研究其碳氮动态的基础,次生杨桦林作为东北地区主要的天然林类型,目前相关数据的欠缺状态要求对此进行深入研究。为此,采集0—10cm、10—20cm、20—30cm长白山次生杨桦林土壤,通过土壤颗粒组分物理化学分级方法,将土壤分成5种组分:沙和稳定团聚体土壤组分(SA)、酸不溶土壤组分(AI)、易氧化土壤组分(EO)、颗粒态土壤组分(P)和可溶性土壤组分(S),进而分析了不同组分的质量分数、碳氮含量、碳氮分配比例及红外光谱5类官能团相对含量,旨在探讨次生杨桦林土壤固碳、氮供应机制。结果显示,接近90%的土壤质量集中在稳定组分AI(66.21%)和SA(22.11%)上,导致稳定组分中碳截获量最大(占土壤总碳量的2/3),而且其C/N比活跃组分(P和EO)大2—9倍;与碳不同,由于活跃组分中N含量比稳定组分大4—80倍,致使活跃组分P和EO氮的分配比例最大,分别占土壤总氮的33.1%和26.0%;除了占土壤质量很少的P和S外,组分间以及组分内的碳氮间多具有显著相关关系。这种土壤碳、氮在不同组分间贮存方式的差异使得土壤碳储存稳定性更高、而N肥力供应更快速。伴随不同组分碳氮储存的变化,不同组分间红外官能团存在显著差异,AI组分中绝大多数官能团相对含量均最低,而P和S组分中绝大多数官能团相对含量均较高,绝大多数官能团相对含量与碳含量、氮含量呈现显著的正相关关系,反映了官能团具有维持土壤碳氮的功能。同时,官能团与土壤C/N具有显著相关关系,反映出组分官能团相对含量的高低具有指示组分化学活性高低的作用。研究发现对于林分土壤的碳截获与氮供应的机制阐明具有重要的科学意义,这为深入了解东北次生杨桦林碳氮动态及对未来气候的响应提供基础数据。     

Solid-phase synthesis and purification of a set of uniformly 13C, 15N labelled de novo designed membrane fusogenic peptides.

The transmembrane segments of soluble N-ethylmaleimide-sensitive factor (SNARE) proteins or viral envelope proteins drive membrane fusion, which suggests that simple synthetic biology constructs for fusion exist and can be evaluated. We describe the high-yield synthesis of a set of de novo designed fusogenic peptides for use in functional investigations, which are highly enriched in 13C and 15N using three equivalents of labelled amino acids and optimized reaction conditions minimizing aggregation. The biomimetic peptides have a high purity >90% and show reproducible and fusogenic activity that correlates well with the intended functional design characteristics, from strongly fusogenic to almost non-fusogenic.     

Comparative studies of the endogenous phospholipids and their in vitro hydrolysis by endogenous phospholipases of various tissues from 7-day-old chicks: a thin layer chromatographic and densitometric analysis

The phospholipid profiles of heart, kidney, and pectoral muscle of 7-day-old chicks and their in vitro response to the endogenous lipolytic enzymes (mainly in the phospholipase group) at pH 7.4 and 38 degrees C for 60 min were analysed by TLC technology and densitometry. The noticeable preferential deacylation of cardiolipin (CL) as detected by the formation of monolysocardiolipin (MLCL) and concurrent reduction of CL level were the most prevalent lipolytic events of chick cardiac muscle, but the least prevalent in chick pectoral muscle. Deacylation of ethanolamine plasmalogen (PE) as revealed by the formation of the corresponding lyso alkenyl derivative was also prominent in cardiac muscle, but much less so in kidney and none at all was detected in pectoral muscle. The level of sphingomyelin (SM) was much higher in kidney than heart and pectoral muscle. Following in vitro incubation, the reduction in the level of SM and the high level of ceramide (Cer) production were most conspicuous in kidney, less in cardiac muscle and least in pectoral muscle. The hydrolysis of PE and SM confirm the action of endogenous PLA(2) and endogenous sphingomyelinase on PE and SM respectively. These data clearly illustrate the differential response of the endogenous substrates (phospholipids) to the endogenous phospholipases of the tissues studied and are probably related to their physiological activities in vivo.     

亚热带典型流域C、N沉降季节变化特征及其耦合输出过程

大气湿沉降是流域生态系统水体中碳氮的重要来源,对生态系统的健康及稳定性有很大的影响。通过对江西千烟洲典型亚热带流域降雨过程的碳、氮湿沉降和径流过程的季节性动态特征进行监测分析,探讨流域沉降、径流输出的C、N耦合及平衡关系。结果表明:千烟洲香溪流域降雨径流中碳氮浓度明显低于雨水,流域大气降水中DOC浓度和TN浓度呈极显著正相关关系。香溪河流域常规水体C∶N均值为2.81,远低于根据Redfield比率得出的适宜浮游生物生长的C∶N(6.6左右),说明外源性N输入导致该流域水体环境处于N过量的状态,长期输出会提高下游鄱阳湖水系的营养化程度。降雨过程对流域碳输入输出平衡影响较小,对氮输入输出平衡的影响较大。流域湿沉降DOC年输入量为69.41 kg hm~(-2)a~(-1),TN湿沉降通量为77.23 kg hm~(-2)a~(-1),碳氮沉降水平受区域降雨量及空气污染情况控制。香溪流域生态系统截留的沉降TN占当地氮肥年均使用量的33.13%,大气降水对亚热带流域生态系统的大量营养物质输入不容忽视。