Transorgan Short-Chain Fatty Acid Fluxes in the Fasted and Postprandial State in the Pig

The short-chain fatty acids (SCFAs) acetate, propionate, butyrate, isovalerate, and valerate are end products of intestinal bacterial fermentation and important mediators in the interplay between the intestine and peripheral organs. To unravel the transorgan fluxes and mass balance comparisons of SCFAs, we measured their net fluxes across several organs in a translational pig model. In multi-catheterized conscious pigs (n=12, 25.6 (95% CI [24.2, 26.9]) kg, 8-12 weeks old), SCFA fluxes across portal drained viscera (PDV), liver, kidneys, and hindquarter (muscle compartment) were measured after an overnight fast and in the postprandial state, 4 h after administration of a fiber-free, mixed meal. PDV was the main releasing compartment of acetate, propionate, butyrate, isovalerate, and valerate during fasting and in the postprandial state (all P=0.001). Splanchnic acetate release was high due to the absence of hepatic clearance. All other SCFAs were extensively taken up by the liver (all P<0.05). Even though only 7% [4, 10] (propionate), 42% [23, 60] (butyrate), 26% [12, 39] (isovalerate), and 3% [0.4, 5] (valerate) of PDV release were excreted from the splanchnic area in the fasted state, splanchnic release of all SCFAs was significant (all P≤0.01). Splanchnic propionate, butyrate, isovalerate and valerate release remained low but significant in the postprandial state (all P<0.01). We identified muscle and kidneys as main peripheral SCFA metabolizing organs, taking up the majority of all splanchnically released SCFAs in the fasted state and in the postprandial state. We conclude that the PDV is the main SCFA releasing and the liver the main SCFA metabolizing organ. Splanchnically released SCFAs appear to be important energy substrates to peripheral organs not only in the fasted but also in the postprandial state.

Density and size-dependent bioturbation effects of the infaunal polychaete Nephtys incisa on sediment biogeochemistry and solute exchange

The impact of bioturbation on the geochemistry of aquatic sediments is known to depend on the benthic infauna species that are present. However, burrowing and activity patterns of each species may also change during the different stages of a life cycle. In this study, we examined the effects of four size classes of the polychaete Nephtys incisa on burrow networks and sediment biogeochemistry. In our experimental aquaria, the total biovolume (~ biomass) of Nephtys was kept constant, but different age classes were introduced, so the size and abundance varied between treatments. Despite differences in the geometry of burrow networks (due to varying density and size of burrows as revealed by X-radiography), the transport of nonreactive solutes (Br–) showed little difference between treatments. In contrast, the depth distribution of reactive solutes (Fe2+, Mn2+, TPO3– 4, TCO2, O2, pH) depended on oxidized sediment volumes and on spatial micro-heterogeneity related to burrowing patterns. Net fluxes of O2, TCO2, and NO– 3 fluxes were strongly affected by age-dependent burrowing patterns. Carbonate dissolution and remineralization rates (reflected by TCO 2fluxes) were enhanced as the size of individuals increased. NO– 3fluxes showed progressive change from dominance of nitrification (release) to denitrification (uptake) as burrow densities decreased with larger individuals. We conclude that different age-size classes of a single species at identical biovolume affect biogeo- chemical cycling differently, due to changes in burrow sizes and burrow densities. Because of redox reaction coupling associated with burrow geometries (Fe2+, Mn2+ oxidation patterns), similar magnitudes of nonlocal transport may be a misleading indicator of biogenic impacts. Our observations demonstrate that biogeochemical impacts must be evaluated in the context of size (age-) specific traits and population densities rather than biomass or biovolume alone.

Physiological Characteristics and Transcriptomic Dissection in Two Root Segments with Contrasting Net Fluxes of Ammonium and Nitrate of Poplar Under Low Nitrogen Availability

To investigate physiological and transcriptomic regulation mechanisms underlying the distinct net fluxes of NH4+ and NO3- in different root segments of Populus species under low nitrogen (N) conditions, we used saplings of P. × canescens supplied with either 500 (normal N) or 50 (low N) μM NH4NO3. The net fluxes of NH4+ and NO3-, and the concentrations of NH4+, amino acids, organic acids and the enzymatic activities of nitrite reductase (NiR) and glutamine synthetase (GS) in root segment II (SII, 35-70 mm to the apex) were lower than those in root segment I (SI, 0-35 mm to the apex). The net NH4+ influxes and the concentrations of organic acids were elevated, whereas the concentrations of NH4+ and NO3-, and the activities of NiR and GS were reduced in SI and SII in response to low N. A number of genes were significantly differentially expressed in SII vs SI and in both segments grown under low vs normal N conditions, and these genes were mainly involved in transport of NH4+ and NO3-, N metabolism, and adenosine triphosphate (ATP) synthesis. Moreover, the hub gene coexpression networks were dissected and correlated with N physiological processes in SI and SII under normal and low N conditions. These results suggest that the hub gene coexpression networks play pivotal roles in regulating N uptake and assimilation, amino acid metabolism as well as the levels of organic acids from TCA cycle in the two root segments of poplars in acclimation to low N availability.

Diverging responses of high-latitude CO₂ and CH₄ emissions in idealized climate change scenarios

The present study investigates the response of the high-latitude carbon cycle to changes in atmospheric greenhouse gas (GHG) concentrations in idealized climate change scenarios. To this end we use an adapted version of JSBACH – the land surface component of the Max Planck Institute for Meteorology Earth System Model (MPI-ESM) – that accounts for the organic matter stored in the permafrost-affected soils of the high northern latitudes. The model is run under different climate scenarios that assume an increase in GHG concentrations, based on the Shared Socioeconomic Pathway 5 and the Representative Concentration Pathway 8.5, which peaks in the years 2025, 2050, 2075 or 2100, respectively. The peaks are followed by a decrease in atmospheric GHGs that returns the concentrations to the levels at the beginning of the 21st century, reversing the imposed climate change. We show that the soil CO2 emissions exhibit an almost linear dependence on the global mean surface temperatures that are simulated for the different climate scenarios. Here, each degree of warming increases the fluxes by, very roughly, 50 % of their initial value, while each degree of cooling decreases them correspondingly. However, the linear dependence does not mean that the processes governing the soil CO2 emissions are fully reversible on short timescales but rather that two strongly hysteretic factors offset each other – namely the net primary productivity and the availability of formerly frozen soil organic matter. In contrast, the soil methane emissions show a less pronounced increase with rising temperatures, and they are consistently lower after the peak in the GHG concentrations than prior to it. Here, the net fluxes could even become negative, and we find that methane emissions will play only a minor role in the northern high-latitude contribution to global warming, even when considering the high global warming potential of the gas. Finally, we find that at a global mean temperature of roughly 1.75 K (±0.5 K) above pre-industrial levels the high-latitude ecosystem turns from a CO2 sink into a source of atmospheric carbon, with the net fluxes into the atmosphere increasing substantially with rising atmospheric GHG concentrations. This is very different from scenario simulations with the standard version of the MPI-ESM, in which the region continues to take up atmospheric CO2 throughout the entire 21st century, confirming that the omission of permafrost-related processes and the organic matter stored in the frozen soils leads to a fundamental misrepresentation of the carbon dynamics in the Arctic.

Metabolic flux analysis of Branched-chain amino and keto acids (BCAA, BCKA) and β-Hydroxy β-methylbutyric acid (HMB) across multiple organs in the pig.

Objective: Branched-chain amino acids (BCAA) and their metabolites the branched-chain keto acids (BCKA) and β-Hydroxy β-methylbutyric acid (HMB) are involved in the regulation of key signaling pathways in the anabolic response to a meal. However, their (inter)organ kinetics remain unclear. Therefore, BCAA (leucine (LEU), valine (VAL), isoleucine (ILE)), BCKA (α-ketoisocaproic acid (KIC), 3-methyl-2-oxovaleric acid (KMV), 2-oxoisovalerate (KIV)) and HMB across organ net fluxes were measured. Methods: In multi-catheterized pigs (n=12, ±25 kg), net fluxes across liver, portal drained viscera (PDV), kidney and hindquarter (HQ, muscle compartment) were measured before and 4h after bolus feeding of a complete meal (30% daily intake) in conscious state. Arterial and venous plasma were collected and concentrations were measured by LC- or GC-MS/MS. Data are expressed as mean[95%CI] and significance (p<0.05) from zero by Wilcoxon Signed Rank Test. Results: In the postabsorptive state (in nmol/kg bw/min), the kidney takes up HMB (3.2[1.3,5.0] ). BCKA is taken up by PDV (144[13,216]) but no release by other organs. In the postprandial state, the total net fluxes over 4h (in µmol/kg bw/4h) showed a release of all BCKA by HQ (46.2[34.2,58.2]), KIC by the PDV(12.3[7.0,17.6]) and KIV by the kidney(10.0[2.3,178]). HMB was released by the liver (0.76[0.49,1.0]). All BCKA were taken up by the liver (200[133,268]). Conclusions: Substantial differences are present in (inter)organ metabolism and transport among the BCAA and its metabolites BCKA and HMB. The presented data in a translation animal model are relevant for the future development of optimized clinical nutrition.

Transports and Net Fluxes of Surface Wave Energy and Momentum inside Tropical Cyclones: Spectrum Computation and Modeling

Transports and net fluxes of surface wave energy and momentum inside tropical cyclones (TCs) are analyzed with wave spectra acquired by hurricane hunters. Previous analyses of dominant wave properties show a primary feature of sinusoidal azimuthal variation. Transports calculated from directional wave spectra are also primarily sinusoidal, which is modeled as a harmonic series. The result reveals that forward transport peaks are in the right-front quarter relative to the TC heading, and somewhat weaker valleys of backward transports are in the left-back quarter. Rightward transport peaks are in the right-back quarter and stronger leftward transport valleys are in the left-front quarter. Net fluxes are derived analytically from the gradients of transports. Their azimuthal variations are primarily biharmonic with forward trend confined in a slightly left-tilted parallel channel about a width two to three radius of maximum wind (RMW) on each side of the TC center. Leftward net fluxes are in a parallel channel of similar size and normal to that of the forward net fluxes. In vectors, the right-back quarter is a region of net influxes of energy and momentum. The TC central region has strong local fluxes that lead to bifurcation of the flux lines into leftward and forward paths. This may play a role in stabilizing the TC propagation. The net fluxes are a small fraction of the expected energy and momentum inputs from local wind except near the eye region. Within about 30 km from the TC center the local wind speed may exceed 30 m s−1 and the net fluxes can exceed 50% of the expected local wind input.

Superior growth, N uptake and NH4+ tolerance in the giant bamboo Phyllostachys edulis over the broad-leaved tree Castanopsis fargesii at elevated NH4+ may underlie community succession and favor the expansion of bamboo

The unbridled expansion of bamboo has imposed serious threats on ecosystem processes and functions. Considerable evidence indicates that bamboo invasions can alter plant-available soil nitrogen (N) pools and rates of N cycling, but the consequences of altered N availability for plant growth and community structure have thus far been poorly characterized. The primary soil-accessible N forms for most plants are ammonium (NH4+) and nitrate (NO3−), but plants differ in their ability to use the different N forms, and these differences can be related to their ecological characteristics and drive community structure. In this context, we evaluated the growth response, N uptake and interspecific competition in two subtropical species, Phyllostachys edulis (Carrière) J. Houzeau (Synonym Phyllostachys heterocycla Carrière) and Castanopsis fargesii Franch., dominant species of bamboo and secondary evergreen broad-leaved forests, respectively, under changing N availability in seedlings supplied with different N concentrations and NH4+/NO3− proportions, in vermiculite culture, in a controlled environment. The results show that (i) both species display an NH4+ preference at elevated N concentrations. The growth of P. edulis seedlings was strongly enhanced at increased ratios of NH4+ to NO3− especially at higher N concentrations, but to a much lesser extent in C. fargesii. (ii) NH4+ preference at the level of N uptake in both species was confirmed by the Non-invasive Micro-test Technology and by examining 15N signatures. Phyllostachys edulis had higher NH4+ net fluxes and N concentration under NH4+ treatments than C. fargesii. (iii) NH4+ at higher concentrations caused toxicity in both species as it inhibited root growth and even caused seedling death, but P. edulis had a higher NH4+-tolerance threshold (24 mM) than C. fargesii (16 mM). (iv) When mixed-species cultures were examined in an NH4+-rich medium, the growth of C. fargesii, but not P. edulis, was significantly inhibited compared with growth in monoculture. Therefore, P. edulis exhibited stronger plasticity and adaptation to changing N availability, whereas C. fargesii had low responsiveness and capacity to acclimate to soil N changes. Phyllostachys edulis displayed a significant competitive growth advantage compared with C. fargesii on NH4+-dominated substrates.

Remobilization and fate of sulphur in mustard

Background and Aims Sulphur (S) is an essential macronutrient involved in numerous metabolic pathways required for plant growth. Crops of the plant family Brassicaceae require more S compared with other crops for optimum growth and yield, with most S ultimately sequestered in the mature seeds as the storage proteins cruciferin and napin, along with the unique S-rich secondary metabolite glucosinolate (GSL). It is well established that S assimilation primarily takes place in the shoots rather than roots, and that sulphate is the major form in which S is transported and stored in plants. We carried out a developmental S audit to establish the net fluxes of S in two lines of Brassica juncea mustard where seed GSL content differed but resulted in no yield penalty. Methods We quantified S pools (sulphate, GSL and total S) in different organs at multiple growth stages until maturity, which also allowed us to test the hypothesis that leaf S, accumulated as a primary S sink, becomes remobilized as a secondary source to meet the requirements of GSL as the dominant seed S sink. Key Results Maximum plant sulphate accumulation had occurred by floral initiation in both lines, at which time most of the sulphate was found in the leaves, confirming its role as the primary S sink. Up to 52 % of total sulphate accumulated by the low-GSL plants was lost through senesced leaves. In contrast, S from senescing leaves of the high-GSL line was remobilized to other tissues, with GSL accumulating in the seed from commencement of silique filling until maturity. Conclusion We have established that leaf S compounds that accumulated as primary S sinks at early developmental stages in condiment type B. juncea become remobilized as a secondary S source to meet the demand for GSL as the dominant seed S sink at maturity.