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221.
GRANT R. SINGLETON† COLIN R. TANN§ CHARLES J. KREBS†‡ 《Journal of Applied Ecology》2007,44(3):644-652
222.
Bryan J. Culbertson Jaymie Krone Erastus Gatebe Norbert C. Furumo Steven L. Daniel 《World journal of microbiology & biotechnology》2007,23(10):1357-1362
The impact of various supplemental carbon sources (oxalate, glyoxylate, glycolate, pyruvate, formate, malate, acetate, and
succinate) on growth and oxalate formation (i.e., oxalogenesis) by Sclerotinia sclerotiorum was studied. With isolates D-E7, 105, W-B10, and Arg-L of S. sclerotiorum, growth in an undefined broth medium (0.1% soytone; pH 5) with 25 mM glucose and 25 mM supplemental carbon source was increased
by the addition of malate and succinate. Oxalate accumulation occurred in the presence of glucose and a supplemental carbon
source, with malate, acetate, and succinate supporting the most oxalate synthesis. With S. sclerotiorum Arg-L, oxalate-to-biomass ratios, an indicator of oxalogenic potential, were dissimilar when the organism was grown in the
presence of different carbon sources. The highest oxalate-to-biomass ratios were observed with pyruvate, formate, malate,
acetate, and succinate. Time-course studies with acetate-supplemented cultures revealed that acetate and glucose consumption
by S. sclerotiorum D-E7 coincided with oxalogenesis and culture acidification. By day 5 of incubation, oxalogenesis was halted when cultures
reached a pH of 3 and were devoid of acetate. In succinate-supplemented cultures, oxalogenesis essentially paralleled glucose
and succinate utilization over the 9-day incubation period; during this time period, culture pH declined but never fell below
4. Overall, these results indicate that carbon sources can regulate the accumulation of oxalate, a key pathogenicity determinant
for S. sclerotiorum. 相似文献
223.
224.
This paper investigates the greenhouse gas emissions from a Swedish wetland, constructed to decrease nutrient content in sewage
treatment water. To evaluate the effect of the construction in terms of greenhouse gas emissions we carried out ecosystem-atmosphere
flux measurements of CO2, CH4 and N2O using a closed chamber technique. To evaluate the importance of vascular plant species composition to gas emissions we distributed
the measurement plots over the three dominating plant species at the field site, i.e., Typha latifolia, Phragmites australis and Juncus effusus. The fluxes of CO2 (total respiration), CH4 and N2O from vegetated plots ranged from 1.39 to 77.5 (g m−2 day−1), −377 to 1387 and −13.9 to 31.5 (mg m−2 day−1) for CO2, CH4 and N2O, respectively. Presence of vascular plants lead as expected to significantly higher total respiration rates compared with
un-vegetated control plots. Furthermore, we found that the emission rates of N2O and CH4 was affected by presence of vascular plants and tended to be species-specific. We assessed the integrated greenhouse warming
effect of the emissions using a Global Warming Potential over a 100-year horizon (GWP100) and it corresponded to 431 kg CO2 equivalents m−2 day−1. Assuming a 7-month season with conditions similar to the study period this is equal to 90 tonnes of CO2 equivalents annually. N2O emissions were responsible for one third of the estimated total greenhouse forcing. Furthermore, we estimated that the emission
from the forested bog that was the precursor land to Magle constructed wetland amounted to 18.6 tonnes of CO2 equivalents annually. Hence, the constructed wetland has increased annual greenhouse gas emissions by 71.4 tonnes of CO2 equivalents for the whole area. Our findings indicate that management processes in relation to wetland construction projects
must consider the primary function of the wetland in decreasing eutrophication, in relation to other positive aspects on for
instance plant and animal life and recreation as well as possible negative climatic aspects of increased emissions of CH4 and N2O. 相似文献
225.
R.J. Harper A.C. Beck P. Ritson M.J. Hill C.D. Mitchell D.J. Barrett K.R.J. Smettem S.S. Mann 《Ecological Engineering》2007,29(4):329-341
The current agricultural systems of broad areas of Australia are unsustainable, with large projected increases in salinization, decreases in water quality, wind erosion, and losses of biodiversity. It is well known that these problems can be partially resolved by farmland reforestation; however, a major issue is financing the scale of activity required. The international response to global warming, the United Nations Framework Convention on Climate Change and its Kyoto Protocol, includes provisions that enable greenhouse sinks (sequestration of carbon in soils and vegetation) to be used by parties to fulfil their obligations. The Kyoto Protocol also allows for trading in emission reductions, and this opens the possibility that investment in carbon sinks may help underwrite broader natural resource management objectives. This paper examines the possibilities for improved land management in Western Australia arising from the development of carbon sinks by considering: (a) the likelihood of a carbon market developing and the likely depth of that market as a result of current national and international policies, (b) the data available to provide estimates on different types of sinks, and (c) the likely benefits of wide-scale sink investment.It was estimated that the total amount of carbon that could be sequestered by reforesting 16.8 Mha of cleared farmland is 2200 Mt CO2-e, and between 290 and 1170 Mt CO2-e by destocking 94.8 Mha of rangelands. There were insufficient data to produce estimates of sequestration following changes in tillage practice in cropping systems or the revegetation of already salinized land. We conclude that carbon sinks are only likely to become profitable as a broad-scale stand-alone enterprise when carbon prices reach AUD$15/t CO2-e, with this threshold value varying with carbon yield and project costs. Below this price, their value can be significant as an adjunct to reforestation schemes that are aimed at providing other products (wood, pulp, bioenergy) and land and water conservation benefits. Irrespective of this, carbon sinks provide an opportunity to both sequester carbon in a least-cost fashion and improve soil and watershed management. 相似文献
226.
Decelerating growth in tropical forest trees 总被引:1,自引:0,他引:1
The impacts of global change on tropical forests remain poorly understood. We examined changes in tree growth rates over the past two decades for all species occurring in large (50-ha) forest dynamics plots in Panama and Malaysia. Stem growth rates declined significantly at both forests regardless of initial size or organizational level (species, community or stand). Decreasing growth rates were widespread, occurring in 24–71% of species at Barro Colorado Island, Panama (BCI) and in 58–95% of species at Pasoh, Malaysia (depending on the sizes of stems included). Changes in growth were not consistently associated with initial growth rate, adult stature, or wood density. Changes in growth were significantly associated with regional climate changes: at both sites growth was negatively correlated with annual mean daily minimum temperatures, and at BCI growth was positively correlated with annual precipitation and number of rainfree days (a measure of relative insolation). While the underlying cause(s) of decelerating growth is still unresolved, these patterns strongly contradict the hypothesized pantropical increase in tree growth rates caused by carbon fertilization. Decelerating tree growth will have important economic and environmental implications. 相似文献
227.
Populations are at risk of extinction when unsuitable or when sink habitat exceeds a threshold frequency in the environment. Sinks that present cues associated with high-quality habitats, termed ecological traps, have especially detrimental effects on net population growth at metapopulation scales. Ecological traps for viruses arise naturally, or can be engineered, via the expression of viral-binding sites on cells that preclude viral reproduction. We present a model for virus population growth in a heterogeneous host community, parameterized with data from populations of the RNA bacteriophage Φ6 presented with mixtures of suitable host bacteria and either neutral or trap cells. We demonstrate that viruses can sustain high rates of population growth in the presence of neutral non-hosts as long as some host cells are present, whereas trap cells dramatically reduce viral fitness. In addition, we demonstrate that the efficacy of traps for viral elimination is frequency dependent in spatially structured environments such that population viability is a nonlinear function of habitat loss in dispersal-limited virus populations. We conclude that the ecological concepts applied to species conservation in altered landscapes can also contribute to the development of trap cell therapies for infectious human viruses. 相似文献
228.
Tree growth,mortality, and above-ground biomass accumulation in a holm oak forest under a five-year experimental field drought 总被引:2,自引:0,他引:2
A holm oak forest was exposed to an experimental drought during 5 years to elucidate the growth responses of the dominant
species Quercus ilex, Arbutus unedo and Phillyrea latifolia. Soil water availability was partially reduced, about 15% as predicted for this area for the next decades by GCM and ecophysiological
models, by plastic strips intercepting rainfall and by ditch exclusion of water runoff. The stem diameter increment was highly
correlated with annual rainfall in all species, and drought treatment strongly reduced the diameter increment of Q. ilex (41%) and specially of A. unedo (63%), the species showing higher growth rates. Stem mortality rates were highly correlated with previous stem density, but
drought treatment increased mortality rates in all species. Q. ilex showed the highest mortality rates (9% and 18% in control and drought plots, respectively), and P. latifolia experienced the lowest mortality rates (1% and 3% in control and drought plots, respectively). Drought strongly reduced the
increment of live aboveground biomass during these 5 years (83%). A. unedo and Q. ilex experienced a high reduction in biomass increment by drought, whereas P. latifolia biomass increment was insensitive to drought. The different sensitivity to drought of the dominant species of the holm oak
forest may be very important determining their future development and distribution in a drier environment as expected in Mediterranean
areas for the next decades. These drier conditions could thus have strong effects on structure (species composition) and functioning
(carbon uptake and biomass accumulation) of these Mediterranean forests. 相似文献
229.
为了研究四氯化碳(CCL4)联合二乙基亚硝胺(DEN)对小鼠(Mus musculus domesticus)精巢的毒性作用。将昆明小鼠随机分为对照组与实验组,各12只个体。实验组每周2次腹腔注射含有15%CCl4的花生油溶液,同时自由饮用0.07‰的DEN溶液,连续诱导8周。对照组每周2次注射花生油,饮用蒸馏水。分别于第3、6、8周处死实验组及对照组小鼠各4只,对其精巢组织进行常规固定、包埋、切片、H.E染色,观察精巢的形态及精子数量的变化。与实验组比较,对照组小鼠体重明显增加,且实验组与对照组差异显著;与对照组相比,实验组睾丸系数以及精子存活率均显著减少。对照组小鼠精巢都具有正常的生精小管结构,管腔中存在大量精子;第3周,实验组小鼠的精巢与对照组类似,生精小管较为完整,生精细胞稍有散乱;第6周,实验组生精小管变形,生精细胞排列疏松,精子数目减少且畸形;第8周,实验组生精小管残缺不全,生精细胞和精子散乱排列,精子数量大大减少且变形更为严重。实验说明,CCl4联合DEN能够造成小鼠精巢组织的损害以及精子数目的减少和畸变。 相似文献
230.
Commonly used anesthetics induce widespread neuronal degeneration in the developing mammalian brain via the oxidative-stress-associated mitochondrial apoptosis pathway. Dysregulation of cytochrome oxidase (CcOX), the terminal oxidase of the electron transport chain, can result in reactive oxygen species (ROS) formation. Isoflurane has previously been shown to activate this enzyme. Carbon monoxide (CO), as a modulator of CcOX, is of interest because infants and children are routinely exposed to CO during low-flow anesthesia. We have recently demonstrated that low concentrations of CO limit and prevent isoflurane-induced neurotoxicity in the forebrains of newborn mice in a dose-dependent manner. However, the effect of CO on CcOX in the context of anesthetic-induced oxidative stress is unknown. Seven-day-old male CD-1 mice underwent 1 h exposure to 0 (air), 5, or 100 ppm CO in air with or without isoflurane. Exposure to isoflurane or CO independently increased CcOX kinetic activity and increased ROS within forebrain mitochondria. However, exposure to CO combined with isoflurane paradoxically limited CcOX activation and oxidative stress. There were no changes seen in steady-state levels of CcOX I protein, indicating post-translational modification of CcOX as an etiology for changes in enzyme activity. CO exposure led to differential effects on CcOX subunit I tyrosine phosphorylation depending on concentration, while combined exposure to isoflurane with CO markedly increased the enzyme phosphorylation state. Phosphorylation of tyrosine 304 of CcOX subunit I has been shown to result in strong enzyme inhibition, and the relative reduction in CcOX kinetics following exposure to CO combined with isoflurane may have been due, in part, to such phosphorylation. Taken together, the data suggest that CO modulates CcOX in the developing brain during isoflurane exposure, thereby limiting oxidative stress. These CO-mediated effects could have implications for the development of low-flow anesthesia in infants and children to prevent anesthesia-induced oxidative stress. 相似文献