Total Efflux Research Articles

Interacting microbe and litter quality controls on litter decomposition: a modeling analysis.

The decomposition of plant litter in soil is a dynamic process during which substrate chemistry and microbial controls interact. We more clearly quantify these controls with a revised version of the Guild-based Decomposition Model (GDM) in which we used a reverse Michaelis-Menten approach to simulate short-term (112 days) decomposition of roots from four genotypes of Zea mays that differed primarily in lignin chemistry. A co-metabolic relationship between the degradation of lignin and holocellulose (cellulose+hemicellulose) fractions of litter showed that the reduction in decay rate with increasing lignin concentration (LCI) was related to the level of arabinan substitutions in arabinoxylan chains (i.e., arabinan to xylan or A∶X ratio) and the extent to which hemicellulose chains are cross-linked with lignin in plant cell walls. This pattern was consistent between genotypes and during progressive decomposition within each genotype. Moreover, decay rates were controlled by these cross-linkages from the start of decomposition. We also discovered it necessary to divide the Van Soest soluble (labile) fraction of litter C into two pools: one that rapidly decomposed and a second that was more persistent. Simulated microbial production was consistent with recent studies suggesting that more rapidly decomposing materials can generate greater amounts of potentially recalcitrant microbial products despite the rapid loss of litter mass. Sensitivity analyses failed to identify any model parameter that consistently explained a large proportion of model variation, suggesting that feedback controls between litter quality and microbial activity in the reverse Michaelis-Menten approach resulted in stable model behavior. Model extrapolations to an independent set of data, derived from the decomposition of 12 different genotypes of maize roots, averaged within <3% of observed respiration rates and total CO2 efflux over 112 days.

Minimising methodological biases to improve the accuracy of partitioning soil respiration using natural abundance 13C

Microbial degradation of soil organic matter (heterotrophic respiration) is a key determinant of net ecosystem exchange of carbon, but it is difficult to measure because the CO2 efflux from the soil surface is derived not only from heterotrophic respiration, but also from plant root and rhizosphere respiration (autotrophic). Partitioning total CO2 efflux can be achieved using the different natural abundance stable isotope ratios (δ(13)C) of root and soil CO2. Successful partitioning requires very accurate measurements of total soil efflux δ(13)CO2 and the δ(13)CO2 of the autotrophic and heterotrophic sources, which typically differ by just 2-8‰. In Scottish moorland and grass mesocosm studies we systematically tested some of the most commonly used techniques in order to identify and minimise methodological errors. Typical partitioning methods are to sample the total soil-surface CO2 efflux using a chamber, then to sample CO2 from incubated soil-free roots and root-free soil. We investigated the effect of collar depth on chamber measurements of surface efflux δ(13)CO2 and the effect of incubation time on estimates of end-member δ(13)CO2. (1) a 5 cm increase in collar depth affects the measurement of surface efflux δ(13)CO2 by -1.5‰ and there are fundamental inconsistencies between modelled and measured biases; (2) the heterotrophic δ(13)CO2 changes by up to -4‰ within minutes of sampling; we recommend using regression to estimate the in situ δ(13)CO2 values; (3) autotrophic δ(13)CO2 measurements are reliable if root CO2 is sampled within an hour of excavation; (4) correction factors should be used to account for instrument drift of up to 3‰ and concentration-dependent non-linearity of CRDS (cavity ringdown spectroscopy) analysis. Methodological biases can lead to large inaccuracies in partitioning estimates. The utility of stable isotope partitioning of soil CO2 efflux will be enhanced by consensus on the optimum measurement protocols and by minimising disturbance, particularly during chamber measurements.

Gestational diabetes mellitus modulates neonatal high-density lipoprotein composition and its functional heterogeneity

Gestational diabetes mellitus (GDM) is related to neonatal macrosomia and an increased risk of vascular events. We hypothesized that GDM exerts qualitative effects on neonatal high-density lipoprotein (HDL). HDL was isolated from control (n=11) and GDM maternal/neonatal donors (n=9) and subjected to shotgun proteomics. Differences in HDL mobility were assessed by FPLC and native gel-electrophoresis. Paraoxonase (PON1) activity, cholesterol ester-transfer protein (CETP) mass and activity, phospholipid, triglyceride and cholesterol concentrations were quantified with commercial kits. Total anti-oxidative capacity and cholesterol efflux capability of HDLs were measured. Four proteins involved in lipid metabolism, inflammation and innate immunity were differentially expressed between controls and GDM neonates. ApoM (decreased, p<0.05) and SAA1 (increased, p<0.05) showed the same differences on both, maternal and neonatal GDM HDL. Lower PON1 protein expression was corroborated by lower activity (p<0.05) which in turn was associated with attenuated anti-oxidant capacity of GDM HDL. Protein changes were accompanied by increased levels of triglycerides and decreased levels of cholesterol esters, respectively. The observed differences in GDM HDL lipid moiety may be related to CETP mass and activity alterations. The rate of cholesterol efflux from term trophoblasts to maternal and from placental endothelial cells to neonatal GDM HDL was impaired (p<0.05). In conclusion, GDM causes changes in HDL composition and is intimately associated with impaired cholesterol efflux capability as well as diminished anti-oxidative particle properties. Remodeling of neonatal GDM HDL in utero supports the hypothesis that maternal conditions in pregnancy impact neonatal lipoprotein metabolism.

Biochar from sugarcane filtercake reduces soil CO2 emissions relative to raw residue and improves water retention and nutrient availability in a highly-weathered tropical soil.

In Brazil, the degradation of nutrient-poor Ferralsols limits productivity and drives agricultural expansion into pristine areas. However, returning agricultural residues to the soil in a stabilized form may offer opportunities for maintaining or improving soil quality, even under conditions that typically promote carbon loss. We examined the use of biochar made from filtercake (a byproduct of sugarcane processing) on the physicochemical properties of a cultivated tropical soil. Filtercake was pyrolyzed at 575°C for 3 h yielding a biochar with increased surface area and porosity compared to the raw filtercake. Filtercake biochar was primarily composed of aromatic carbon, with some residual cellulose and hemicellulose. In a three-week laboratory incubation, CO2 effluxes from a highly weathered Ferralsol soil amended with 5% biochar (dry weight, d.w.) were roughly four-fold higher than the soil-only control, but 23-fold lower than CO2 effluxes from soil amended with 5% (d.w.) raw filtercake. We also applied vinasse, a carbon-rich liquid waste from bioethanol production typically utilized as a fertilizer on sugarcane soils, to filtercake- and biochar-amended soils. Total CO2 efflux from the biochar-amended soil in response to vinasse application was only 5% of the efflux when vinasse was applied to soil amended with raw filtercake. Furthermore, mixtures of 5 or 10% biochar (d.w.) in this highly weathered tropical soil significantly increased water retention within the plant-available range and also improved nutrient availability. Accordingly, application of sugarcane filtercake as biochar, with or without vinasse application, may better satisfy soil management objectives than filtercake applied to soils in its raw form, and may help to build soil carbon stocks in sugarcane-cultivating regions.

Sustainable biochar effects for low carbon crop production: A 5-crop season field experiment on a low fertility soil from Central China

Biochar’s effects on improving soil fertility, enhancing crop productivity and reducing greenhouse gases (GHGs) emission from croplands had been well addressed in numerous short-term experiments with biochar soil amendment (BSA) mostly in a single crop season/cropping year. However, the persistence of these effects, after a single biochar application, has not yet been well known due to limited long-term field studies so far. Large scale BSA in agriculture is often commented on the high cost due to large amount of biochar in a single application. Here, we try to show the persistence of biochar effects on soil fertility and crop productivity improvement as well as GHGs emission reduction, using data from a field experiment with BSA for 5-crop seasons in central North China. A single amendment of biochar was performed at rates of 0 (C0), 20 (C20) and 40tha−1 (C40) before sowing of the first crop season. Emissions of CO2, CH4 and N2O were monitored with static closed chamber method throughout the crop growing season for the 1st, 2nd and 5th cropping. Crop yield was measured and topsoil samples were collected at harvest of each crop season. BSA altered most of the soil physico-chemical properties with a significant increase over control in soil organic carbon (SOC) and available potassium (K) content. The increase in SOC and available K was consistent over the 5-crop seasons after BSA. Despite a significant yield increase in the first maize season, enhancement of crop yield was not consistent over crop seasons without corresponding to the changes in soil nutrient availability. BSA did not change seasonal total CO2 efflux but greatly reduced N2O emissions throughout the five seasons. This supported a stable nature of biochar carbon in soil, which played a consistent role in reducing N2O emission, which showed inter-annual variation with changes in temperature and soil moisture conditions. The biochar effect was much more consistent under C40 than under C20 and with GHGs emission than with soil property and crop yield. Thus, our study suggested that biochar amended in dry land could sustain a low carbon production both of maize and wheat in terms of its efficient carbon sequestration, lower GHGs emission intensity and soil improvement over 5-crop seasons after a single amendment.

A novel ApoA-I truncation (ApoA-IMytilene) associated with decreased ApoA-I production

ObjectiveWe report a novel apolipoprotein (apo) A-I truncation (apoA-IMytilene) due to a heterozygous nonsense mutation (c.718C > T, p.Gln216*) in a 68-year-old male proband with premature coronary heart disease (CHD), corneal arcus, and very low plasma concentrations of HDL cholesterol (HDL-C) and apoA-I. Two family members also had the same mutation. Our objectives were to characterize the kindred and to examine the kinetics of apoA-I, as well as cellular cholesterol efflux capacity in the proband. MethodsWe carried out the kinetic studies using a primed constant infusion of [5,5,5-D3]L-leucine and isotopic enrichment was determined by gas chromatography mass spectrometry in the proband and seven controls with low HDL-C. To assess cellular cholesterol efflux capacity, we used a validated ex vivo system that involved incubation of J774 macrophages with apoB-depleted serum from the proband, five controls with normal HDL-C, and two controls with low HDL-C. ResultsStable isotope kinetic studies indicated that the proband had an apoA-I production rate (PR) that was 41% lower than the mean PR observed in low HDL-C controls (n = 7). The cellular cholesterol efflux capacity assessment showed normalized cholesterol efflux capacity in the proband was decreased by 36% compared to the mean normalized cholesterol efflux capacity of normal controls (n = 5). ConclusionsOur data indicate that this novel heterozygous apoA-I truncation is associated with markedly decreased levels of HDL-C, plasma apoA-I, and apoA-I in large α-1 HDL particles, as well as decreased total cellular cholesterol efflux and decreased apoA-I production.

Vertical variations in wood CO2 efflux for live emergent trees in a Bornean tropical rainforest.

Difficult access to 40-m-tall emergent trees in tropical rainforests has resulted in a lack of data related to vertical variations in wood CO2 efflux, even though significant variations in wood CO2 efflux are an important source of errors when estimating whole-tree total wood CO2 efflux. This study aimed to clarify vertical variations in wood CO2 efflux for emergent trees and to document the impact of the variations on the whole-tree estimates of stem and branch CO2 efflux. First, we measured wood CO2 efflux and factors related to tree morphology and environment for seven live emergent trees of two dipterocarp species at four to seven heights of up to ∼ 40 m for each tree using ladders and a crane. No systematic tendencies in vertical variations were observed for all the trees. Wood CO2 efflux was not affected by stem and air temperature, stem diameter, stem height or stem growth. The ratios of wood CO2 efflux at the treetop to that at breast height were larger in emergent trees with relatively smaller diameters at breast height. Second, we compared whole-tree stem CO2 efflux estimates using vertical measurements with those based on solely breast height measurements. We found similar whole-tree stem CO2 efflux estimates regardless of the patterns of vertical variations in CO2 efflux because the surface area in the canopy, where wood CO2 efflux often differed from that at breast height, was very small compared with that at low stem heights, resulting in little effect of the vertical variations on the estimate. Additionally, whole-tree branch CO2 efflux estimates using measured wood CO2 efflux in the canopy were considerably different from those measured using only breast height measurements. Uncertainties in wood CO2 efflux in the canopy did not cause any bias in stem CO2 efflux scaling, but affected branch CO2 efflux.

The effect of cholesteryl ester transfer protein inhibition on lipids, lipoproteins, and markers of HDL function after an acute coronary syndrome: the dal-ACUTE randomized trial

The effects of cholesteryl ester transfer protein (CETP) inhibition on lipids, inflammation, and markers of high-density lipoprotein (HDL) function, following an acute coronary syndrome (ACS), are unknown. The dal-ACUTE study randomized 300 patients (1 : 1) to dalcetrapib 600 mg/day or placebo within 1 week of an ACS. The primary endpoint was per cent change in HDL-cholesterol (HDL-C) after 4 weeks. Secondary endpoints included apolipoprotein levels, markers of HDL function, and inflammation. Dalcetrapib treatment increased HDL-C and apolipoprotein A1 by 33.7 and 11.8%, respectively (both P < 0.001) and total cholesterol efflux by 9.5% (P = 0.003) after 4 weeks, principally via an increase in non-ATP-binding cassette transporter (ABC) A1-mediated efflux, without statistically significant changes in pre-β1-HDL levels. The increase in total efflux with dalcetrapib correlated most strongly with increases in apolipoprotein A1 and HDL-C (r = 0.46 and 0.43, respectively) rather than the increase in pre-β1-HDL (r = 0.32). Baseline and on-treatment ABCA1-mediated efflux correlated most strongly with pre-β1-HDL levels; in contrast, non-ABCA1-mediated efflux correlated better with apolipoprotein A1 and HDL-C levels. High-density lipoprotein raised through CETP inhibition with dalcetrapib improves cholesterol efflux, principally via a non-ABCA1-mediated pathway. While HDL-C was increased by one-third, apolipoprotein A1 and total efflux were increased only by one-tenth, supporting the concept of dissociation between improvements in HDL function and HDL-C levels, which may be of relevance to ongoing trials and the development of therapeutic interventions targeting HDL.

Evidence for the presence of lipid-free monomolecular apolipoprotein A-1 in plasma

The first step in reverse cholesterol transport is a process by which lipid-free or lipid-poor apoA-1 removes cholesterol from cells through the action of ATP binding cassette transporter A1 at the plasma membrane. However the structure and composition of lipid-free or -poor apoA-1 in plasma remains obscure. We previously obtained a monoclonal antibody (MAb) that specifically recognizes apoA-1 in preβ1-HDL, the smallest apoA-1-containing particle in plasma, which we used to establish a preβ1-HDL ELISA. Here, we purified preβ1-HDL from fresh normal plasma using said antibody, and analyzed the composition and structure. ApoA-1 was detected, but neither phospholipid nor cholesterol were detected in the purified preβ1-HDL. Only globular, not discoidal, particles were observed by electron microscopy. In nondenaturing PAGE, no difference in the mobility was observed between the purified preβ1-HDL and original plasma preβ1-HDL, or between the preβ1-HDL and lipid-free apoA-1 prepared by delipidating HDL. In sandwich ELISA using two anti-preβ1-HDL MAbs, reactivity with intact plasma preβ1-HDL was observed in ELISA using two MAbs with distinct epitopes but no reactivity was observed in ELISA using a single MAb, and the same phenomenon was observed with monomolecular lipid-free apoA-1. These results suggest that plasma preβ1-HDL is lipid-free monomolecular apoA-1.

Controls of soil respiration in a salinity-affected ephemeral wetland

The total efflux of CO2 derived from metabolic processes in soil (Rsoil) exerts a large control on the terrestrial carbon balance. In landscapes that have been radically transformed by humans, the natural carbon balance may be altered by shifts in Rsoil. After accounting for temperature, we sought to determine the main factors that govern Rsoil at Toolibin Lake, an ephemeral wetland threatened by salinization as a result of land clearing. We found strong statistical support for a positive effect of soil gravimetric water content (θ) on Rsoil and weaker support for a negative effect of salinity (measured as the electrical conductivity of a soil extract (ECe)) on Rsoil. We also detected weak support for a positive interaction between θ and ECe, such that θ had a greater positive effect on Rsoil at elevated soil salinities. These results confirm not only that soil moisture is an important driver of Rsoil under native conditions, but also that elevated soil salinities have the potential to accentuate the link between Rsoil and moisture content.

Abstract 18589: Safety and Tolerability of CSL112 in Subjects With Stable Atherothrombotic Disease: Results From a Phase 2a, Multicenter, Randomized, Double-Blind, Placebo-Controlled, Ascending-Dose Study

Purpose: CSL112 is a novel formulation of apoA-I purified from human plasma and reconstituted to form HDL particles. Based on the ability of infused apoA-I to rapidly remove cholesterol from atherosclerotic plaque, CSL112 is being developed to reduce CV events following ACS. This phase 2a trial assessed the safety profile and pharmacokinetics (PK)/pharmacodynamics (PD) of CSL112 after a single IV infusion and is the first study of CSL112 in pts with stable atherothrombotic disease. Methods: 45 subjects were randomized to either CSL112 (1.7, 3.4, 6.8 g) or matching placebo in a 3:1 ratio. The primary safety profile was assessed by the frequency of elevations in alanine aminotransferase (ALT) or aspartate aminotransferase (AST) (&gt;3x ULN) and study-drug-related adverse events (AEs). PK/PD assessments included apoA-I plasma concentration and serum cholesterol efflux capacity. Results: Of the 45 subjects randomized, 33 received CSL112 and 11 received placebo; 1 patient (6.8 g group) did not receive study drug and was excluded from the safety analyses. Elevations (&gt;3x ULN) in AST or ALT were not observed in any treatment group. AEs occurring within 72 h of infusion or considered drug-related by investigators were nonserious and mild except for one case of atrial fibrillation in the placebo group. AEs were reported in 5 of 7 (71.4%), 5 of 12 (41.7%), and 6 of 14 (42.9%) subjects in the CSL112 1.7, 3.4, and 6.8 g groups, respectively, compared with 3 of 11 (27.3%) subjects in the placebo group. The numeric imbalance in AEs for CSL112 groups was attributable to vessel puncture site/infusion site bruising and headache. Evaluations of mean levels and absolute change of serum creatinine over time were similar across CSL112 and placebo groups. Robust and immediate dose-related increases in baseline-corrected apoA-I AUC and Cmax were observed, resulting in similar dose-related increases in baseline-corrected total cholesterol efflux capacity. Conclusion: CSL112 was well tolerated and did not adversely impact hepatic or renal function in subjects with stable atherothrombotic disease. CSL112 represents a novel investigational approach to raise apoA-I levels and to reduce cholesterol content in atherosclerotic plaque. Additional clinical studies of CSL112 are warranted.

Oyster-mediated benthic-pelagic coupling modifies nitrogen pools and processes

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 493:23-30 (2013) - DOI: https://doi.org/10.3354/meps10516 Oyster-mediated benthic-pelagic coupling modifies nitrogen pools and processes Ashley R. Smyth1,2,*, Nathan R. Geraldi1, Michael F. Piehler1 1The University of North Carolina at Chapel Hill, Institute of Marine Sciences, 3431 Arendell St. Morehead City, North Carolina 28557, USA 2Department of Biological Sciences, Virginia Institute of Marine Science, College of William and Mary, Gloucester Point, Virginia 23062, USA *Email: arsmyth@vims.edu ABSTRACT: Removal of nitrogen through enhanced denitrification has been identified as an ecosystem service provided by oysters. In this study, we assessed the effects of an individual oyster (Crassostrea virginica) on nitrogen dynamics. Fluxes of N2, O2, nitrate/nitrite (NOx) and ammonium (NH4+) were measured from continuous-flow microcosms that contained a live oyster, sediment, or a live oyster + sediment. Net N2 fluxes were indicative of nitrogen fixation in the sediment treatment and denitrification in the oyster and oyster + sediment treatments. Organic matter deposition and ammonium production associated with oyster biodeposits and excretion likely decreased N limitation, and thus the demand for fixation of new nitrogen, while increasing nitrification and subsequent denitrification. Oyster-mediated denitrification accounted for 48% of the total inorganic nitrogen efflux in the oyster microcosms and 35% in the oyster + sediment microcosms. Despite high rates of ammonium production, inclusion of the eastern oyster did not increase the pool of bioavailable nitrogen but shifted the microcosms from a nitrogen source to a nitrogen sink. KEY WORDS: Crassostrea virginica · Denitrification · Nitrogen · Nitrogen fixation Full text in pdf format PreviousNextCite this article as: Smyth AR, Geraldi NR, Piehler MF (2013) Oyster-mediated benthic-pelagic coupling modifies nitrogen pools and processes. Mar Ecol Prog Ser 493:23-30. https://doi.org/10.3354/meps10516 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 493. Online publication date: November 20, 2013 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2013 Inter-Research.

Contrasting genotypes, soil amendments, and their interactive effects on short-term total soil CO2 efflux in a 3-year-old Pinus taeda L. plantation

Intensively managed pine forests in the southeastern United States are considered an important C sink and may play a critical role in offsetting increased global CO2 emissions. The combination of improved silvicultural methods and the use of superior genotypes are estimated to result in future volume gains of up to 60 percent. However to date, no work has looked at whether selection of elite genotypes could influence soil C dynamics, which could decrease the time necessary for the stand to function as a C sink. We evaluated the effects of contrasting loblolly pine genotypes on total soil surface CO2 efflux (FS) and heterotrophic respiration (RH) under two soil amendment treatments: 1.) fertilization and 2.) logging residue (LR) incorporation. We found an immediate and sustained difference in FS (p = 0.05) and RH (p < 0.01) among our two genotypes throughout the first two years of stand development. Our soil amendment treatments did not significantly change FS, but did influence RH. LR increased (p = 0.05) RH while N and P fertilization induced a slight (p = 0.06) decrease throughout the study. Our genotypes differed (p = 0.05) in their temperature response of FS, which resulted in an 11% difference in total cumulative C loss from the soil over the duration of the study. We hypothesize that observed treatment effects in FS and RH are largely due to differences in belowground C allocation among genotypes, which is supported by others that have looked at fine-root standing crop and turnover on these same genotypes. This work underscores the importance of accounting for differences among genotypes when developing stand-level C estimates.

Chironomus plumosus larvae increase fluxes of denitrification products and diversity of nitrate-reducing bacteria in freshwater sediment

Benthic invertebrates affect microbial processes and communities in freshwater sediment by enhancing sediment-water solute fluxes and by grazing on bacteria. Using microcosms, the effects of larvae of the widespread midge Chironomus plumosus on the efflux of denitrification products (N2O and N2+N2O) and the diversity and abundance of nitrate- and nitrous-oxide-reducing bacteria were investigated. Additionally, the diversity of actively nitrate- and nitrous-oxide-reducing bacteria was analyzed in the larval gut. The presence of larvae increased the total effluxes of N2O and N2+N2O up to 8.6- and 4.2-fold, respectively, which was mostly due to stimulation of sedimentary denitrification; incomplete denitrification in the guts accounted for up to 20% of the N2O efflux. Phylotype richness of the nitrate reductase gene narG was significantly higher in sediment with than without larvae. In the gut, 47 narG phylotypes were found expressed, which may contribute to higher phylotype richness in colonized sediment. In contrast, phylotype richness of the nitrous oxide reductase gene nosZ was unaffected by the presence of larvae and very few nosZ phylotypes were expressed in the gut. Gene abundance of neither narG, nor nosZ was different in sediments with and without larvae. Hence, C. plumosus increases activity and diversity, but not overall abundance of nitrate-reducing bacteria, probably by providing additional ecological niches in its burrow and gut.

Origin, concentration, availability and fate of dissolved organic carbon in coastal lagoons of the Rio de Janeiro State

The coastal lagoons in the northern Rio de Janeiro State (Brazil) present a wide gradient of dissolved organic carbon (DOC) and water color, with the highest DOC concentrations reported in the literature for aquatic ecosystems. Thus, they represent a peculiar set of ecosystems for the study of the origin, processing and fate of DOC in inland waters. We reviewed data from 2 decades of studies on the carbon cycle in these coastal lagoons and discussed the fluctuations in the concentration and quality of DOC, factors affecting DOC microbial and photochemical degradation, CO2 emission, as well as the role of humic and non-humic carbon to the energy flow through the trophic chains. We show that DOC quality, not its quantity, determines the rates of photochemical and microbial degradation both seasonally (within system) and spatially (among systems), with the exception of DOC photo-oxidation among lagoons, which is partially explained by DOC concentration at regional scale. In humic lagoons, there is a fairly predictable pattern of seasonal variation in DOC concentration associated to rainfall-induced inputs of allochthonous C. However, little is known about the exact timing of these allochthonous inputs and how they relate to the seasonal variation of DOC chemical properties (i.e. its quality). Depth-integrated photo-oxidation rates were less representative in highly humic lagoons, due to strong light attenuation in the water column. Nevertheless, the potential contribution of photo-oxidation and bacterial respiration to total CO2 efflux (~11%) did not differ significantly when all lagoons were pooled together. Contrary to prevailing paradigms for humic waters, microalgae seem to be the main C source in humic lagoons, sustaining pelagic food webs through zooplankton, in spite of some contribution of allochthonous C. Thus, the predominant role of the microbial loop in the DOC recovery to food webs in such systems is to be questioned.

Effect of environmental variables and stand structure on ecosystem respiration components in a Mediterranean beech forest

The temporal variability of ecosystem respiration (RECO) has been reported to have important effects on the temporal variability of net ecosystem exchange, the net amount of carbon exchanged between an ecosystem and the atmosphere. However, our understanding of ecosystem respiration is rather limited compared with photosynthesis or gross primary productivity, particularly in Mediterranean montane ecosystems. In order to investigate how environmental variables and forest structure (tree classes) affect different respiration components and RECO in a Mediterranean beech forest, we measured soil, stem and leaf CO2 efflux rates with dynamic chambers and RECO by the eddy-covariance technique over 1 year (2007-2008). Ecosystem respiration showed marked seasonal variation, with the highest rates in spring and autumn and the lowest in summer. We found that the soil respiration (SR) was mainly controlled by soil water content below a threshold value of 0.2 m(3) m(-3), above which the soil temperature explained temporal variation in SR. Stem CO2 effluxes were influenced by air temperature and difference between tree classes with higher rates measured in dominant trees than in co-dominant ones. Leaf respiration (LR) varied significantly between the two canopy layers considered. Non-structural carbohydrates were a very good predictor of LR variability. We used these measurements to scale up respiration components to ecosystem respiration for the whole canopy and obtained cumulative amounts of carbon losses over the year. Based on the up-scaled chamber measurements, the relative contributions of soil, stem and leaves to the total annual CO2 efflux were: 56, 8 and 36%, respectively. These results confirm that SR is the main contributor of ecosystem respiration and provided an insight on the driving factors of respiration in Mediterranean montane beech forests.

Temporal Variations in Soil CO2 Efflux Under Different Land Use Types in the Black Soil Zone of Northeast China

The quantification of soil CO2 efflux is crucial for better understanding the interactions between driving variables and C losses from black soils in Northeast China and for assessing the function of black soil as a net source or sink of atmospheric CO2 depending upon land use. This study investigated responses of soil CO2 efflux variability to soil temperature interactions with different soil moisture levels under various land use types including grassland, bare land, and arable (maize, soybean, and wheat) land in the black soil zone of Northeast China. The soil CO2 effluxes with and without live roots, defined as the total CO2 efflux (FtS) and the root-free CO2 efflux (FrfS), respectively, were measured from April 2009 to May 2010 using a static closed chamber technique with gas chromatography. The seasonal soil CO2 fluxes tended to increase from the beginning of the measurements until they peaked in summer and then declined afterwards. The mean seasonal FtS ranged from 20.3±7.8 to 58.1±21.3 mg CO2-C m−2 h−1 for all land use types and decreased in the order of soybean land > grassland > maize land > wheat land > bare land, while the corresponding values of FrfS were relatively lower, ranging from 20.3±7.8 to 42.3±21.3 mg CO2-C m−2 h−1. The annual cumulative FtS was in the range of 107–315 g CO2-C m−2 across all land uses types. The seasonal CO2 effluxes were significantly (P < 0.001) sensitive to soil temperature at 10 cm depth and were responsible for up to 62% of the CO2 efflux variability. Correspondingly, the temperature coefficient Q10 values varied from 2.1 to 4.5 for the seasonal FtS and 2.2 to 3.9 for the FrfS during the growing season. Soil temperature interacting with soil moisture accounted for a significant fraction of the CO2 flux variability for FtS (up to 61%) and FrfS (up to 67%) via a well-defined multiple regression model, indicating that temperature sensitivity of CO2 flux can be mediated by water availability, especially under water stress.

Temporal patterns of soil CO2 efflux in a temperate Korean Larch (Larix olgensis Herry.) plantation, Northeast China

There is little information available regarding seasonal and annual variations in soil CO2 efflux from Korean Larch plantations, which are an important component of forests’ carbon balance in temperate China. In this study, the soil respiration rate (R s), soil temperature (T 10) and soil moisture (SM10) at 10 cm depth were observed in a Korean Larch (Larix olgensis Herry.) plantation in Northeast China from 2008 to 2012. Mean R s in growing season (GS) varied greatly, ranged from 2.32 ± 0.08 to 3.88 ± 0.09 μmol CO2 m−2 s−1 (mean ± SE) over the period of 2008–2012. In comparison with T-model, the increase of explained variability by applying both T 10 and SM10 to the T-M model is very small. It is indicated that R s was controlled largely by T 10 in the present study. By accounting for 22.2 and 17.7 % of the total soil CO2 emissions in 2010/2011 and 2011/2012, respectively, the soil CO2 efflux in dormant season (DS) was an essential component of the total soil CO2 efflux. The Q 10 value in the study period was always smaller for GS than DS, suggesting that soil carbon cycling may be more sensitive to the temperature changes at low than at high temperature range. These results indicated that climate changes may have great potential impacts on temperate Larch plantations in Northeast China, owing to soil carbon emissions of Larch plantation during the long period of DS being more sensitive to T 10 than in GS, and played a significant role in the annual forest ecosystems carbon budget.

Carbon input manipulation affects soil respiration and microbial community composition in a subtropical coniferous forest

We determined the effects of aboveground and belowground C inputs on soil CO2 efflux and microbial community composition by phospholipid fatty acids using aboveground litter addition or removal and root trenching in a subtropical forest in Southern China. From January 2011 to December 2011, soil respiration varied with the seasonal changes in soil temperature and water content, but its pattern was not altered by C input manipulation. The effects of C input manipulation on the temperature sensitivity of soil respiration was season-dependent, which were greater in the dormant season than in the growing season. Litter addition increased the soil respiration by 33% compared with the control, whereas litter removal decreased it by 22.6%. Root trenching decreased soil respiration by 20.4%. Aboveground litter decomposition, root and rhizosphere respiration, and mineral soil respiration contributed to 22.3%, 20.1%, and 57.6% of total soil CO2 efflux, respectively. We also found that increase in soil CO2 efflux induced by litter addition was 10.4% greater than decrease by litter removal. Litter removal increased 21.6% of the concentration of Gram-positive bacteria and decreased 32.8% of the bacteria to fungi ratio, compared with the control. Root trenching increased the concentrations of bacteria, fungi, and actinomycetes by 28.8%, 161.2% and 32.5%, respectively, but decreased the Gram-negative to Gram-positive bacteria and the bacteria to fungi ratios by 57.4% and 107.9%. C input treatment did not increase the Gram-positive bacteria but nor decreased the Gram-negative to Gram-positive bacteria ratio. The concentration of the 16:0 PLFA and the Gram-negative to Gram-positive bacteria ratio were significantly correlated with soil respiration. These results suggest that root C input has greater influence on soil microbial community composition than the aboveground litter C input.

Abstract 387: HDL Structure and Function in Individuals with Extreme High HDL-C Who Have Coronary Artery Disease Compared with Those Without CAD

Plasma levels of high-density lipoprotein cholesterol (HDL-C) are strongly inversely associated with coronary artery disease (CAD) in epidemiologic studies, and high HDL-C is generally associated with apparent ‘protection’ from CAD. We have been recruiting individuals with high HDL-C for about 15 years, and while most have no CAD, a minority has premature CAD, a paradoxical phenotype. We hypothesize that such individuals may have HDL with altered structure and/ or function, and are systematically comparing these individuals (cases) to older individuals with extreme high HDL-C without CAD (controls) and a healthy control group with normal HDL-C levels. We identified 60 subjects with HDL-C above the 90th percentile, premature CAD, and no other major risk factors for coronary disease. We selected 2 controls per case, each matched for age, race, gender, and HDL level. Demographic information and lipid profile (mean ± SD) of the study groups are shown below. Controls are well matched to the cases. Studies are well underway to assess HDL size distribution by NMR, HDL composition, total and ABCA1-specific cholesterol efflux capacity, lecithin-cholesterol acyltransferase (LCAT) activity, and cholesteryl ester transfer protein (CETP) activity in cases and controls. We will also compare to a group of healthy controls with normal HDL-C levels. We expect that the findings from this study will provide insight into the etiology of CAD in this paradoxical phenotype.