Soil microbial respiration in arctic soil does not acclimate to temperature

Warming-induced release of CO2 from the large carbon (C) stores in arctic soils could accelerate climate change. However, declines in the response of soil respiration to warming in long-term experiments suggest that microbial activity acclimates to temperature, greatly reducing the potential for enhanced C losses. As reduced respiration rates with time could be equally caused by substrate depletion, evidence for thermal acclimation remains controversial. To overcome this problem, we carried out a cooling experiment with soils from arctic Sweden. If acclimation causes the reduction in soil respiration observed after experimental warming, then it should subsequently lead to an increase in respiration rates after cooling. We demonstrate that thermal acclimation did not occur following cooling. Rather, during the 90 days after cooling, a further reduction in the soil respiration rate was observed, which was only reversed by extended re-exposure to warmer temperatures. We conclude that over the time scale of a few weeks to months, warming-induced changes in the microbial community in arctic soils will amplify the instantaneous increase in the rates of CO2 production and thus enhance C losses potentially accelerating the rate of 21st century climate change.     

Predawn plant water potential does not necessarily equilibrate with soil water potential under well-watered conditions

Predawn leaf water potential (O_w) and xylem pressure potential (O_p) are expected to be in equilibrium with the soil water potential (soil O_w) around roots of well-watered plants. We surveyed 21 plant species (desert, chaparral, and coastal salt marsh species, as well as two temperate tree and two crop species) for departures from this expectation and for two potential mechanisms explaining the departures. We measured soil O_w, leaf O_w, and xylem O_p in the glasshouse under well-watered conditions that eliminated soil moisture heterogeneity and ensured good soil-root hydraulic continuity. Most species failed to equilibrate fully with soil O_w, depending on whether leaf O_w or xylem O_p was used as the measure of predawn plant water potential. The contribution of nighttime transpiration to predawn disequilibrium was assessed by comparing plants with bagged canopies (enclosed overnight in plastic bags to eliminate transpiration) to plants with unbagged canopies. Nighttime transpiration significantly reduced predawn xylem O_p for 16 of 21 species and the magnitude of this contribution to predawn disequilibrium was large (0.50-0.87 MPa) in four woody species: Atriplex confertifolia, Batis maritima, Larrea tridentata, and Sarcobatus vermiculatus. The contribution of nighttime transpiration to predawn disequilibrium was not more prevalent in mesic compared with xeric or desert phreatophytic compared with non-phreatophytic species. Even with bagging that eliminated nighttime transpiration, plants did not necessarily equilibrate with soil O_w. Plant xylem O_p or leaf O_w were significantly more negative than soil O_w for 15 of 15 species where soil O_w was measured. Predawn disequilibrium based on leaf O_w was of large magnitude (0.50-2.34 MPa) for seven of those 15 species, predominately halophytes and Larrea tridentata. A portion of the discrepancy between leaf and soil O_w is consistent with the putative mechanism of high concentrations of leaf apoplastic solutes as previously modeled for a halophyte, but an additional portion remains unexplained. Predawn leaf O_w and xylem O_p may not reflect soil O_w, particularly for woody plants and halophytes, even under well-watered conditions.     

Cocoa procyanidin chain length does not determine ability to protect LDL from oxidation when monomer units are controlled

Cocoa flavan-3-ols (catechin, epicatechin and oligomeric procyanidins) were tested for their ability to decrease LDL oxidative susceptibility and spare alpha-tocopherol (alpha-toc) in vitro. Physiologic concentration (0.10-0.50 &mgr;M) of flavanols were used. The flavanols increased LDL conjugated diene lag times dose-dependently from 23-207% and 15-143% in response to copper and AAPH oxidation, respectively, and delayed alpha-toc consumption. Sparing of LDL alpha-toc represents a possible mechanism for flavanols to enhance the resistance of plasma and LDL to oxidative stress. Procyanidins decreased LDL oxidative susceptibility with increasing chain length. However, when based on equivalent amounts of monomeric units, they inhibited LDL oxidation to a similar extent. This suggests that antioxidant activity of procyanidins with biologic substrates is not attributable to chain length or charge delocalization through polymeric linkages, but primarily to ring structures and catechol groups. Additionally, human plasma was analyzed for the presence of oligomeric procyanidins following consumption of a flavanol-rich cocoa product. Procyanidin dimers were detected in plasma concordant with the appearance of monomeric flavanols, with a peak of 0.08 +/- 0.01 &mgr;mol/L (n = 6) at two hours after consumption. Thus, this paper confirms the occurrence of procyanidins in human plasma, and extends previous structure-function observations regarding flavanoid protection of LDL.     

Induction of autophagy does not affect human rhinovirus type 2 production

Induction of autophagy has been shown to be beneficial for the replication of poliovirus, a phenomenon that might also apply for other picornaviruses. We demonstrate that de novo synthesis of human rhinovirus type 2 (HRV2), an HRV of the minor receptor group, is unaffected by tamoxifen, rapamycin, and 3-methyladenine (3-MA), drugs either stimulating (tamoxifen and rapamycin) or inhibiting (3-MA) autophagic processes. Furthermore, LC3-positive vesicles (i.e., autophagosomes) are not induced upon infection. Therefore, multiplication of this particular picornavirus is not dependent on autophagy.     

Intrinsic post‐ejaculation sperm ageing does not affect offspring fitness in Atlantic salmon

Post‐meiotic sperm ageing, both before ejaculation and after ejaculation, has been shown to negatively affect offspring fitness by lowering the rate of embryonic development, reducing embryonic viability and decreasing offspring condition. These negative effects are thought to be caused by intrinsic factors such as oxidative stress and ATP depletion or extrinsic factors such as temperature and osmosis. Effects of post‐ejaculation sperm ageing on offspring fitness have so far almost exclusively been tested in internal fertilizers. Here, we tested whether intrinsic post‐ejaculation sperm ageing affects offspring performance in an external fertilizer, the Atlantic salmon Salmo salar. We performed in vitro fertilizations with a split‐clutch design where sperm were subjected to four post‐ejaculation ageing treatments. We varied the duration between sperm activation and fertilization while minimizing extrinsic stress factors and tested how this affected offspring fitness. We found no evidence for an effect of our treatments on embryo survival, hatching time, larval standard length, early larval survival or larval growth rate, indicating that intrinsic post‐ejaculation sperm ageing may not occur in Atlantic salmon. One reason may be the short life span of salmon sperm after ejaculation. Whether our findings are true in other external fertilizers with extended sperm activity remains to be tested.     

Soil water potential and temperature sum during reproductive growth control seed dormancy in Alopecurus myosuroides Huds.

The sustainable management of unwanted vegetation in agricultural fields through integrated weed control strategies requires detailed knowledge about the maternal formation of primary seed dormancy, to support the prediction of seedling emergence dynamics. This knowledge is decisive for the timing of crop sowing and nonchemical weed control measures. Studies in controlled environments have already demonstrated that thermal conditions and, to some extent, water availability during seed set and maturation has an impact on the level of dormancy. However, it is still unclear if this applies also under field conditions, where environmental stressors and their timing are more variable. We address this question for Alopecurus myosuroides in south‐western Sweden. We quantified the effects of cumulated temperature and precipitation as well as soil water potential during the reproductive growth phase of A myosuroides on primary seed dormancy under field conditions. Empirical models differing in focal time intervals and, in case of soil water potential, focal soil depths were compared regarding their predictive power. The highest predictive power for the level of primary dormancy of A. myosuroides seeds was found for a two‐factorial linear model containing air temperature sum between 0 and 7 days before peak seed shedding as well as the number of days with soil water potential below field capacity between 7 and 35 days before peak seed shedding. For soil water potential, it was found that only the top 10 cm soil layer is of relevance, which is in line with the shallow root architecture of A. myosuroides. We conclude that for this species the level of dormancy depends on the magnitude and timing of temperature and water availability during the reproductive growth phase. Water availability appears to be more important during maternal environmental perception and temperature during zygotic environmental perception.     

血管紧张素II2型受体基因缺失不影响肾素—血管紧张素系统

基于目前对血管紧张素Ⅱ２型受体（ＡＴ２）功能的认识,认为血管紧张素Ⅱ１型受体（ＡＴ１）和ＡＴ２受体有相互拮抗作用。依据上述论点,本研究利用ＡＴ２受体基因敲出小鼠,观察了ＡＴ２受体缺失后是否造成肾素－血管紧张素系统其它成分代偿性紊乱。结果发现,ＡＴ２受体基因缺失小鼠血浆和肾组织中血管紧张素Ⅱ的浓度以及肾组织中肾素、ＡＴ１Ａ受体的基因表达均未发生明显改变,表明ＡＴ２受体缺失未对肾素－血管紧张素系统产生     

Caterpillar biomass depends on temperature and precipitation,but does not affect bird reproduction

Complex changes in phenological events appear as temperatures are increasing: In deciduous forests bud burst, hatching of herbivorous caterpillars, egg laying and nestling time of birds when feeding chicks on caterpillars, may differentially shift into early season and alter synchronization. If timing of bird reproduction has to match with short periods of food availability, phenological mismatch could negatively affect reproductive success. Using a unique empirical approach along an altitudinal temperature gradient, we firstly asked whether besides temperature, also precipitation and leaf phenology interplay and affect caterpillar biomass, since impacts of rainfall on caterpillars have been largely neglected so far. Secondly, we asked whether abundance of caterpillars and thereby body mass of great tit nestlings, which are mainly fed with caterpillars, vary along the altitudinal temperature gradient. We demonstrated that next to temperature also precipitation and leaf phenology affected caterpillar biomass. In our beech forest, even along altitudes, caterpillars were available throughout the great tit breeding season but in highly variable amounts. Our findings revealed that although timing of leaf phenology and great tit breeding season were delayed with decreasing temperature, caterpillars occurred synchronously and were not delayed according to altitude. However, altitude negatively affected caterpillar biomass, but body mass of fledglings at high altitude sites was not affected by lower amounts of caterpillar biomass. This might be partially outweighed by larger territory sizes in great tits.     

High seed Mn content does not affect germination of in vitro produced Centaurium pulchellum seeds

The effect of high Mn²⁺ content on Centaurium pulchellum seed germination has been investigated. Seeds containing extremely high Mn²⁺ content were produced by culturing single-node flowering explants for 2 months in the MS-media, supplemented with Mn in concentrations ranging from 1 to 10,000 μM. Although the seeds displayed the capacity to accumulate high amount of Mn, their germination was undisturbed. EPR spectroscopy was used to measure the ratio of free (aqueous) Mn to bound Mn and it was found that over 97% of total Mn was in the bound form. With elevating the external Mn supply, seed Mn concentration also increased, but the proportion of free Mn²⁺ fraction decreased from 3% in the control (1 μM Mn) to 0.35% and 0.15% in high Mn supply (1000 μM and 10,000 μM, respectively). These results suggest that an elevation of internal Mn concentration in seeds is associated with increased Mn binding pools, hence Mn remains bound during germination. Consequently, the action of potentially harmful Mn²⁺ ions, which may generate ROS and affect seed viability, is alleviated.     

Soil respiration does not acclimatize to warmer temperatures when modeled over seasonal timescales

Soil warming studies have generally demonstrated an ephemeral response of soil respiration to warming suggesting acclimatization to increased temperatures. Many of these studies depict acclimatization as an empirical temperature-respiration model with data collected from late spring through early autumn. We examined the apparent temperature sensitivity of soil respiration in chronically warmed soils over three different timescales: annually, during the growing season, and seasonally during winter, spring, summer, and fall. Temperature sensitivity was evaluated by fitting exponential and flexible temperature functions as mixed effects models. From model coefficients, we estimated annual, growing season, and season-specific Q ₁₀ values, and assessed the ability of model coefficients to predict daily soil respiration rates over a two-year period. We found that respiration in warmed soils can exhibit characteristics of acclimatized temperature sensitivity depending on the timeframe and the function (exponential or flexible) used. Models using growing season data suggested acclimatization while models using data collected in winter or spring indicated enhanced temperature sensitivity with 5 °C of warming. Differences in temperature sensitivity affected predicted daily soil respiration rates, particularly in winter and spring. Models constructed over longer timescales overestimated daily respiration rates by as much 10–40 % whereas season-specific predictions were generally within 2 % of actual values. Failure to use season-specific models to depict changes in temperature dependence may over- or under-estimate carbon losses due to climate warming, especially during the colder months of the year.     

Soil moisture level and substrate type determine long-term seed lifespan in a soil seed bank

Plant and Soil - Seeds are usually classified as short- or long-term persistent. It is still hardly understood how environmental conditions influence seed persistence. The study aimed to monitor...     

Indomethacin does not affect endogenous glucose production in type 2 diabetes mellitus.

In healthy subjects, basal endogenous glucose production is partly regulated by paracrine intrahepatic factors. It is currently unknown whether paracrine intrahepatic factors also influence the increased basal endogenous glucose production in patients with type 2 diabetes mellitus. Administration of indomethacin to patients with type 2 diabetes mellitus stimulates endogenous glucose production and inhibits insulin secretion. Our aim was to evaluate whether this stimulatory effect on glucose production is solely attributable to inhibition of insulin secretion. In order to do this, we administered indomethacin to 5 patients with type 2 diabetes during continuous infusion of somatostatin to block endogenous insulin and glucagon secretion and infusion of basal concentrations of insulin and glucagon in a placebo-controlled study. Endogenous glucose production was measured 3 hours after the start of the somatostatin, insulin and glucagon infusion, for 4 hours after administration of placebo/indomethacin, by primed, continuous infusion of [6,6-(2)H(2)] glucose. At the time of administration of placebo or indomethacin, there were no significant differences in plasma glucose concentrations and endogenous glucose production rates between the two experiments (16.4 +/- 2.09 mmol/l vs. 16.6 +/- 1.34 mmol/l and 17.7 +/- 1.05 micromol/kg/min and 17.0 +/- 1.06 micromol/kg/min), control vs. indomethacin). Plasma glucose concentration did not change significantly in the four hours after indomethacin or placebo administration. Endogenous glucose production in both experiments was similar after both placebo and indomethacin. Mean plasma C-peptide concentrations were all below the detection limit of the assay, reflecting adequate suppression of endogenous insulin secretion by somatostatin. There were no differences in plasma concentrations of insulin (76 +/- 5 vs. 74 +/- 4 pmol/l) and glucagon (69 +/- 8 vs. 71 +/- 6 ng/l) between the studies with levels remaining unchanged in both experiments. Plasma concentrations of cortisol, epinephrine, and norepinephrine were similar in the two studies and did not change significantly. We conclude that indomethacin stimulates endogenous glucose production in patients with type 2 diabetes mellitus by inhibition of insulin secretion.     

Litter decay controlled by temperature,not soil properties,affecting future soil carbon

Widespread global changes, including rising atmospheric CO₂ concentrations, climate warming and loss of biodiversity, are predicted for this century; all of these will affect terrestrial ecosystem processes like plant litter decomposition. Conversely, increased plant litter decomposition can have potential carbon‐cycle feedbacks on atmospheric CO₂ levels, climate warming and biodiversity. But predicting litter decomposition is difficult because of many interacting factors related to the chemical, physical and biological properties of soil, as well as to climate and agricultural management practices. We applied ¹³C‐labelled plant litter to soil at ten sites spanning a 3500‐km transect across the agricultural regions of Canada and measured its decomposition over five years. Despite large differences in soil type and climatic conditions, we found that the kinetics of litter decomposition were similar once the effect of temperature had been removed, indicating no measurable effect of soil properties. A two‐pool exponential decay model expressing undecomposed carbon simply as a function of thermal time accurately described kinetics of decomposition. (R² = 0.94; RMSE = 0.0508). Soil properties such as texture, cation exchange capacity, pH and moisture, although very different among sites, had minimal discernible influence on decomposition kinetics. Using this kinetic model under different climate change scenarios, we projected that the time required to decompose 50% of the litter (i.e. the labile fractions) would be reduced by 1–4 months, whereas time required to decompose 90% of the litter (including recalcitrant fractions) would be reduced by 1 year in cooler sites to as much as 2 years in warmer sites. These findings confirm quantitatively the sensitivity of litter decomposition to temperature increases and demonstrate how climate change may constrain future soil carbon storage, an effect apparently not influenced by soil properties.     

Tree identity and diversity directly affect soil moisture and temperature but not soil carbon ten years after planting

1. Soil C is the largest C pool in forest ecosystems that contributes to C sequestration and mitigates climate change. Tree diversity enhances forest productivity, so diversifying the tree species composition, notably in managed forests, could increase the quantity of organic matter being transferred to soils and alter other soil properties relevant to the C cycle.
2. A ten‐year‐old tree diversity experiment was used to study the effects of tree identity and diversity (functional and taxonomic) on soils. Surface (0–10 cm) mineral soil was repeatedly measured for soil C concentration, C:N ratio, pH, moisture, and temperature in twenty‐four tree species mixtures and twelve corresponding monocultures (replicated in four blocks).
3. Soil pH, moisture, and temperature responded to tree diversity and identity. Greater productivity in above‐ and below‐ground tree components did not increase soil C concentration. Soil pH increased and soil moisture decreased with functional diversity, more specifically, when species had different growth strategies and shade tolerances. Functional identity affected soil moisture and temperature, such that tree communities with more slow‐growing and shade‐tolerant species had greater soil moisture and temperature. Higher temperature was measured in communities with broadleaf‐deciduous species compared to communities with coniferous‐evergreen species.
4. We conclude that long‐term soil C cycling in forest plantations will likely respond to changes in soil pH, moisture, and temperature that is mediated by tree species composition, since tree species affect these soil properties through their litter quality, water uptake, and physical control of soil microclimates.

     

Reducing endogenous estrogen during prepuberal life does not affect boar libido or sperm fertilizing potential

Increasing sperm production per breeding male has economic significance with increasing use of artificial insemination. Manipulations to increase sperm production in livestock will only be useful if libido and sperm fertilizing capacity are not adversely affected. Reducing endogenous estrogens in the postnatal interval increases the number of Sertoli cells and hence testicular sperm production capacity. These experiments were designed to evaluate the effects of reducing endogenous estrogens on libido and sperm fertilizing capacity. Boars were treated with an aromatase inhibitor, letrozole, to reduce testicular estrogen production between 1 and 6 weeks of age or between 11 and 16 weeks of age, and the littermates to these boars were treated with the canola oil vehicle. Letrozole treatment did not affect time to first mount at 22 weeks of age, regardless of whether the treatment occurred from 1 to 6 weeks of age (118 seconds vs. 233 seconds, SEM = 161 for letrozole-treated and vehicle-treated boars, respectively) or from 11 to 16 weeks of age (107 seconds vs. 67 seconds, SEM = 63 for letrozole-treated and vehicle-treated boars, respectively). Similarly, sperm fertilizing ability and in vivo fertility were equivalent in letrozole-treated boars and their vehicle-treated littermates. Surprisingly, the increase in Sertoli cell numbers observed in the letrozole-treated boars at 20 weeks of age (5.8 vs. 4.3 billion, SEM = 0.5; P < 0.05) was not maintained to 40 weeks of age in their letrozole-treated littermates. Reducing endogenous estrogen production neonatally or prepuberally had no detectable adverse effect on libido or sperm fertilizing capacity.     

Root exclusion through trenching does not affect the isotopic composition of soil CO2 efflux

Disentangling the autotrophic and heterotrophic components of soil CO₂ efflux is critical to understanding the role of soil system in terrestrial carbon (C) cycling. In this study, we combined a stable C-isotope natural abundance approach with the trenched plot method to determine if root exclusion significantly affected the isotopic composition (δ¹³C) of soil CO₂ efflux (R_S). This study was performed in different forest ecosystems: a tropical rainforest and two temperate broadleaved forests, where trenched plots had previously been installed. At each site, R_S and its δ¹³C (δ¹³C_Rs) tended to be lower in trenched plots than in control plots. Contrary to R_S, δ¹³C_Rs differences were not significant. This observation is consistent with the small differences in δ¹³C measured on organic matter from root, litter and soil. The lack of an effect on δ¹³C_Rs by root exclusion could be from the small difference in δ¹³C between autotrophic and heterotrophic soil respirations, but further investigations are needed because of potential artefacts associated with the root exclusion technique.     

How universal are human mate choices? Size does not matter when Hadza foragers are choosing a mate

It has been argued that size matters on the human mate market: both stated preferences and mate choices have been found to be non-random with respect to height and weight. But how universal are these patterns? Most of the literature on human mating patterns is based on post-industrial societies. Much less is known about mating behaviour in more traditional societies. Here we investigate mate choice by analysing whether there is any evidence for non-random mating with respect to size and strength in a forager community, the Hadza of Tanzania. We test whether couples assort for height, weight, body mass index (BMI), per cent fat and grip strength. We test whether there is a male-taller norm. Finally, we test for an association between anthropometric variables and number of marriages. Our results show no evidence for assortative mating for height, weight, BMI or per cent fat; no evidence for a male-taller norm and no evidence that number of marriages is associated with our size variables. Hadza couples may assort positively for grip strength, but grip strength does not affect the number of marriages. Overall we conclude that, in contrast to post-industrial societies, mating appears to be random with respect to size in the Hadza.     

Computerized equipment to control soil water matric potential and soil temperature in inoculum potential assays of soil-borne pathogens

Computerized equipment to control soil temperature and soil water matric potential, at high soil hydric conditions was developed and evaluated. A series of experiments demonstrated the accuracy and reproducibility of the equipment's performance and its adequacy for the assessment of the inoculum potential of soil-borne pathogens in soils with different characteristics. Control of soil water potential is achieved by variation in the height of the water table in a medium with high water conductivity supporting the soil. The equipment consists of double-walled tanks, permitting the adjustment of soil temperature. It is provided with sensors, control software and valves for automatic operation. in a growth chamber at 24°C. with RH 70% and irradiation of 90 W.m^–2, was maintained in dynamic equilibrium for pF values ranging from 1 (–1 kPa) to 2 (–10 kPa) in various arable soil samples during the four to five weeks period of the bioassays. During the fourth week of pea or iris growth at pF=2, the system controlled within an amplitude of 0.4 pF-units. Between replications, variance was approximately 0.1 at F=2, decreasing with increasing. Soil temperature in the system could be maintained at a constant level with a variance below 0.1, within an amplitude of 0.3°C.