短花针茅叶片水分利用效率对放牧强度的响应及其影响因素

为明确植物的用水策略及适应性机制,以内蒙古四子王旗短花针茅荒漠草原为研究对象,设置对照(CK)、轻度放牧(LG)、中度放牧(MG)和重度放牧(HG)4个放牧梯度,其载畜率分别为每1 hm^(2)每年0、0.93、1.82和2.71个羊单位的放牧强度,调查建群种短花针茅的高度、盖度、密度、地上生物量以及土壤的理化性状,并且采用稳定碳同位素法和红外光合仪法对短花针茅水分利用效率进行了测定,旨在阐明短花针茅水分利用效率在不同放牧强度下的响应规律及其影响因素。结果显示:(1)放牧对短花针茅盖度、密度以及地上生物量的影响显著;随着载畜率的增大,有利于短花针茅的扩散使其分布面积增加,且在中度放牧条件下尤为明显。(2)随着放牧强度的增加,土壤水分含量较对照显著提高,土壤全氮含量呈先增加后减少的变化趋势,土壤速效钾呈现降低的变化趋势,而对土壤全碳含量和pH无显著影响,说明适度放牧能够提高土壤水分含量、促进土壤氮含量的积累,但放牧会导致土壤速效钾减少。(3)随着放牧强度的增大,短花针茅长期水分利用效率(WUE l)呈现“V”形变化趋势,而瞬时水分利用效率(WUE t)与内在水分利用效率(WUE i)总体呈降低的变化趋势。(4)相关分析显示,放牧强度与短花针茅密度、地上生物量呈显著正相关关系,土壤全氮含量与有机碳、pH、WUE i呈显著正相关关系,WUE t与WUE i呈显著正相关关系;短花针茅内在水分利用效率与土壤有机碳含量密切相关。研究表明,重度放牧导致短花针茅株丛破碎化,增加了种群的扩散面积,是短花针茅长期水分利用效率提高的直接原因;短花针茅瞬时水分利用效率随放牧强度的增加而降低可能是由其内在水分利用效率降低引起的。     

Hydrogen and oxygen trapping at the H-cluster of [FeFe]-hydrogenase revealed by site-selective spectroscopy and QM/MM calculations

[FeFe]-hydrogenases are superior hydrogen conversion catalysts. They bind a cofactor (H-cluster) comprising a four-iron and a diiron unit with three carbon monoxide (CO) and two cyanide (CN^?) ligands. Hydrogen (H₂) and oxygen (O₂) binding at the H-cluster was studied in the C169A variant of [FeFe]-hydrogenase HYDA1, in comparison to the active oxidized (Hox) and CO-inhibited (Hox-CO) species in wildtype enzyme. ⁵⁷Fe labeling of the diiron site was achieved by in vitro maturation with a synthetic cofactor analogue. Site-selective X-ray absorption, emission, and nuclear inelastic/forward scattering methods and infrared spectroscopy were combined with quantum chemical calculations to determine the molecular and electronic structure and vibrational dynamics of detected cofactor species. Hox reveals an apical vacancy at Fe_d in a [4Fe4S-2Fe]^3 ? complex with the net spin on Fe_d whereas Hox-CO shows an apical CN^? at Fe_d in a [4Fe4S-2Fe(CO)]^3 ? complex with net spin sharing among Fe_p and Fe_d (proximal or distal iron ions in [2Fe]). At ambient O₂ pressure, a novel H-cluster species (Hox-O₂) accumulated in C169A, assigned to a [4Fe4S-2Fe(O₂)]^3 ? complex with an apical superoxide (O₂^?) carrying the net spin bound at Fe_d. H₂ exposure populated the two-electron reduced Hhyd species in C169A, assigned as a [(H)4Fe4S-2Fe(H)]^3 ? complex with the net spin on the reduced cubane, an apical hydride at Fe_d, and a proton at a cysteine ligand. Hox-O₂ and Hhyd are stabilized by impaired O₂^– protonation or proton release after H₂ cleavage due to interruption of the proton path towards and out of the active site.     

High Polarity Poly(vinylidene difluoride) Thin Coating for Dendrite‐Free and High‐Performance Lithium Metal Anodes

The high‐polarity β‐phase poly(vinylidene difluoride) (β‐PVDF), which has all trans conformation with F and H atoms located on the opposite sides of the polymer backbone, is demonstrated to be a promising artificial solid‐electrolyte interphase coating on both Cu and Li metal anodes for dendrite‐free Li deposition/stripping and enhanced cycling performance. A thin (≈4 µm) β‐PVDF coating on Cu enables uniform Li deposition/stripping at high current densities up to 5 mA cm^?2, Li‐plating capacity loadings of up to 4 mAh cm^?2, and excellent cycling stability over hundreds of cycles under practical conditions (1 mA cm^?2 with 2 mAh cm^?2). Full cells containing an LiFePO₄ cathode and an anode of either β‐PVDF coated Cu or Li also exhibit excellent cycling stability. The profound effects of the high‐polarity PVDF coating on dendrite suppression are attributed to the electronegative F‐rich interface that favors layer‐by‐layer Li deposition. This study offers a new strategy for the development of dendrite‐free metal anode technology.     

The population ecology of Rattus exulans on Tiritiri Matangi Island,and a model of comparative population dynamics in New Zealand

Abstract

On Tiritiri, a small predator-free island in northern New Zealand, kiore (Rattus exulans) were live and snap trapped in grassland and forest. In both habitats, kiore abundance peaked in late summer/autumn. The increase followed a 3 month breeding season during which females produced two to three litters, each averaging 7 young. During the population decline in autumn and winter, animals lost weight. Few bred in the breeding season of their birth and none lived to breed in a second breeding season, so the population consisted of distinct age cohorts. These patterns may relate to a highly seasonal food supply.

Kiore elsewhere in New Zealand show seasonal breeding, but the length of breeding, sexual maturation, and litter size vary. Other studies of kiore in the Pacific show less marked seasonal fluctuations, longer breeding seasons, and smaller litters. We propose a model to explain the variation in rodent demography in New Zealand. The model is based on the seasonal availability of food, along with the modifying influences of predation and dispersal.     

Predictive markers of safety and immunogenicity of adjuvanted vaccines

Vaccination represents one of the greatest public health triumphs; in part due to the effect of adjuvants that have been included in vaccine preparations to boost the immune responses through different mechanisms. Although a variety of novel adjuvants have been under development, only a limited number have been approved by regulatory authorities for human vaccines. This report reflects the conclusions of a group of scientists from academia, regulatory agencies and industry who attended a conference on the current state of the art in the adjuvant field. Held at the U.S. Pharmacopeial Convention (USP) in Rockville, Maryland, USA, from 18 to 19 April 2013 and organized by the International Association for Biologicals (IABS), the conference focused particularly on the future development of effective adjuvants and adjuvanted vaccines and on overcoming major hurdles, such as safety and immunogenicity assessment, as well as regulatory scrutiny. More information on the conference output can be found on the IABS website, http://www.iabs.org/.     

A bioenergetic assessment of the influence of stocking practices on rainbow trout (Oncorhynchus mykiss) growth and consumption in a New Zealand lake

Summary

• 1 To investigate the carrying capacity and factors affecting growth of rainbow trout in Lake Rotoiti, we employed a bioenergetics model to assess the influence of stocking rates, timing of releases and prey abundance on growth and prey consumption. We hypothesised that stocking rates and prey abundance would affect growth and prey consumption by influencing per‐capita prey availability, and that the environmental conditions encountered by fish at the time of stocking would affect growth and consumption.
• 2 Prey consumption of stocked rainbow trout was calculated with the Wisconsin bioenergetics model. We calculated growth trajectories of released trout based on data from stocked trout that were released in spring and autumn from 1993 to 2009 and then re‐captured by anglers. Diet, prey energy density, body mass lost during spawning and lake temperature were measured locally.
• 3 Stocking timing had no effect on return rates to anglers or length or weight of caught fish. Although trout released in autumn were smaller than those released in spring, autumn‐released trout grew at a faster rate and had similar lengths and weights to spring cohorts after 2 years of growth in the lake. Modelled consumption parameters were negatively correlated with trout population size, suggesting that stocking rates (347–809 fish ha^?1 year^?1) caused density‐dependent effects on growth. Although common smelt (Retropinna retropinna) accounted for 85% of total prey consumption, no significant relationship was found between prey consumption by individual trout and adult smelt abundance, possibly because trout are targeting smaller smelt that our abundance estimate did not account for.
• 4 Releasing trout in autumn appears to be advantageous for growth, possibly because (i) temperature is more suitable for growth in autumn–winter than in spring–summer and (ii) prey for small trout is abundant in autumn. Mild winter conditions appear to enhance overwinter survival and growth of rainbow trout in warm‐temperate lakes compared to higher latitudes. This implies that moderately productive warm‐temperate lake ecosystems are highly suitable for trout growth in winter, but less so in summer, when lake stratification and high nutrient levels may create conditions suitable for algal blooms and hypolimnetic deoxygenation. High growth rates of trout in warm‐temperate lakes can therefore be supported by timing releases to coincide with favourable winter conditions.

     

Very long diapause and extreme resistance to population disturbance in a galling insect

1. Some insects have a prolonged diapause – a dormancy that extends over more than 1 year. In most species prolonged diapause involves one or a few extra years, but in extreme cases diapause may surpass 10 years. Few cases of very long diapause have been described, and very little is known about the population consequences of the temporal refuge formed by the diapausing individuals. 2. The gall midge Contarinia vincetoxici Kieffer galls the flowers of a long‐lived herb Vincetoxicum hirundinaria Med. After completing development, larvae leave the galls for the ground where they enter diapause. Extending an earlier published inoculation experiment, we show that the diapause may last up to at least 13 years, with a median duration of at least 6 years. 3. The gall midge is attacked by two parasitoid species. Dissections of gall midge larvae for presence of parasitoids revealed that Omphale salicis Haliday had a maximum 2 year diapause and Synopeas acuminatus Kieffer a maximum 4 years. The very long diapause of the gall midge may thus provide a temporal refuge from these enemies. 4. In a 15‐year field experiment all galls were removed every year from six isolated habitat patches. Density changes in experimental populations were not statistically different from control populations for over a decade. After 14–15 years a modest decline could be observed. This slow response illustrates that prolonged diapause in C. vincetoxici provides a very strong population buffer against mortality during the galling stage.     

Effects of group size and group density on trade-offs in resource selection by a group-territorial central-place foraging woodpecker

Trade-offs in resource selection by central-place foragers are driven by the need to balance the benefits of selecting resources against the costs of travel from the central place. For group-territorial central-place foraging birds, trade-offs in resource selection are likely to be complicated by a competitive advantage for larger groups at high group density that may limit accessibility of high-quality distant resources to small groups. We used the group-territorial, central-place foraging Red-cockaded Woodpecker Leuconotopicus borealis (RCW) as a case study to test predictions that increases in group density lead to differences in foraging distances and resource selection for groups of different sizes. We used GPS tracking and LiDAR-derived habitat data to model effects of group size on foraging distances and selection for high-quality pines (≥ 35.6 cm diameter at breast height (dbh)) and lower quality pines (25.4–35.6 cm dbh) by RCW groups across low (n = 14), moderate (n = 10) and high group density (n = 10) conditions. At low and moderate group density, all RCW groups selected distant high-quality pines in addition to those near the central place because competition for resources was low. In contrast, at high group density, larger groups travelled further to select high-quality pines, whereas smaller groups selected high-quality pines only when they were close to the central place and, conversely, were more likely to select lower quality pines at greater distances from the central place. Selection for high-quality pines only when close to the cavity tree cluster at high group density is important to long-term fitness of small RCW groups because it allows them to maximize benefits from both territorial defence and selecting high-quality resources while minimizing costs of competition. These relationships suggest that intraspecific competition at high group density entails substantive costs to smaller groups of territorial central-place foragers by limiting accessibility of distant high-quality foraging resources.     

Nutrient uptake relationship to root characteristics of rice

Data on root parameters and distribution are important for an improved understanding of the factors influencing nutrient uptake by a crop. Therefore, a study was conducted on a Crowley silt loam at the Rice Research and Extension Center near Stuttgart, Arkansas to measure root growth and N, P and K uptake by three rice (Oryza sativa L.) cultivars at active tillering (36 days after emergence (DAE)), maximum tillering (41 DAE), 1.25 cm internode elongation (55 DAE), booting (77 DAE) and heading (88 DAE). Soil-root core samples were taken to a depth of 40 cm after plant samples were removed, sectioned into 5 cm intervals, roots were washed from soil and root lengths, dry weights and radii were measured. Root parameters were significantly affected by the soil depth × growth stage interaction. In addition, only root radius was affected by cultivar. At the 0- to 5-cm soil depth, root length density ranged from 38 to 93 cm cm^-3 throughout the growing season and decreased with depth to about 2 cm cm^-3 in the 35- to 40-cm depth increment. The increase in root length measured with each succeeding growth stage in each soil horizon also resulted in increased root surface area, hence providing more exposed area for nutrient uptake. About 90% of the total root length was found in the 0- to 20-cm soil depth throughout the season. Average root radius measured in the 0- to 5-cm and 35- to 40-cm depth increments ranged from 0.012 to 0.013 cm and 0.004 to 0.005 cm, respectively throughout the season. Total nutrient uptake by rice differed among cultivars only during vegetative growth. Differences in total nutrient uptake among the cultivars in the field appear to be related to absorption kinetics of the cultivars measured in a growth chamber study. Published with permission of the Arkansas Agricultural Experiment Station.     

Effect of differential gastric evacuation and multispecies prey items on estimates of daily energy intake in juvenile chinook salmon

Synopsis The caloric density of stomach contents in juvenile chinook salmon,Oncorhynchus tshawytscha, was not affected by gastric evacuation, suggesting a constant caloric density of stomach contents during evacuation. Differences in the caloric density of prey consumed did affect caloric density of stomach contents over a 24-h period. Consumption of the amphipodCorophium sp. was associated with reduced caloric densities of stomach contents. During periods whenCorophium contributed more than 4% of the stomach contents, average caloric density declined from 5.56 to 5.33 kcal g^–1. Despite this difference, estimates of daily energy intake of juvenile chinook salmon were only 3%, greater when developed from the mean caloric density of stomach contents excludingCorophium.