排序方式: 共有63条查询结果,搜索用时 31 毫秒
11.
Global synthesis of the temperature sensitivity of leaf litter breakdown in streams and rivers
下载免费PDF全文
![点击此处可从《Global Change Biology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Jennifer J. Follstad Shah John S. Kominoski Marcelo Ardón Walter K. Dodds Mark O. Gessner Natalie A. Griffiths Charles P. Hawkins Sherri L. Johnson Antoine Lecerf Carri J. LeRoy David W. P. Manning Amy D. Rosemond Robert L. Sinsabaugh Christopher M. Swan Jackson R. Webster Lydia H. Zeglin 《Global Change Biology》2017,23(8):3064-3075
Streams and rivers are important conduits of terrestrially derived carbon (C) to atmospheric and marine reservoirs. Leaf litter breakdown rates are expected to increase as water temperatures rise in response to climate change. The magnitude of increase in breakdown rates is uncertain, given differences in litter quality and microbial and detritivore community responses to temperature, factors that can influence the apparent temperature sensitivity of breakdown and the relative proportion of C lost to the atmosphere vs. stored or transported downstream. Here, we synthesized 1025 records of litter breakdown in streams and rivers to quantify its temperature sensitivity, as measured by the activation energy (Ea, in eV). Temperature sensitivity of litter breakdown varied among twelve plant genera for which Ea could be calculated. Higher values of Ea were correlated with lower‐quality litter, but these correlations were influenced by a single, N‐fixing genus (Alnus). Ea values converged when genera were classified into three breakdown rate categories, potentially due to continual water availability in streams and rivers modulating the influence of leaf chemistry on breakdown. Across all data representing 85 plant genera, the Ea was 0.34 ± 0.04 eV, or approximately half the value (0.65 eV) predicted by metabolic theory. Our results indicate that average breakdown rates may increase by 5–21% with a 1–4 °C rise in water temperature, rather than a 10–45% increase expected, according to metabolic theory. Differential warming of tropical and temperate biomes could result in a similar proportional increase in breakdown rates, despite variation in Ea values for these regions (0.75 ± 0.13 eV and 0.27 ± 0.05 eV, respectively). The relative proportions of gaseous C loss and organic matter transport downstream should not change with rising temperature given that Ea values for breakdown mediated by microbes alone and microbes plus detritivores were similar at the global scale. 相似文献
12.
Maeda-Martínez Alejandro M. Belk Denton Obregón-Barboza Hortencia Dumont Henri J. 《Hydrobiologia》1997,366(1-3):45-62
Cu, Cd, Zn and Pb concentrations in both dissolved andparticulate phase were assessed during 1995. DataQuality Assurance was
an integral part of this studyand involved all major steps of the analysis proceduresuch as sampling, sample handling, preconcentrationand
determination.
Desorption and redox processes clearly control thedissolved Cu and Cd profiles. Mobilisation ofdissolved Zn is small and essentially
restricted tothe low salinity area and the late spring survey.Dissolved Pb shows the clearest dilution pattern. Theparameters
representative of these processes(dissolved oxygen and salinity) also correlate verywell with the particulate metal profiles.
In addition, the plankton activity (expressed by thechlorophyll-a levels) may influence the dissolved andparticulate metal
profiles. In combination withdesorption and redox processes, seasonal variationswere induced.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
13.
Hortencia Silva‐Jiménez Álvaro Ortega Cristina García‐Fontana Juan Luis Ramos Tino Krell 《Microbial biotechnology》2015,8(1):103-115
The reason for the existence of complex sensor kinases is little understood but thought to lie in the capacity to respond to multiple signals. The complex, seven‐domain sensor kinase TodS controls in concert with the TodT response regulator the expression of the toluene dioxygenase pathway in Pseudomonas putida F1 and DOT‐T1E. We have previously shown that some aromatic hydrocarbons stimulate TodS activity whereas others behave as antagonists. We show here that TodS responds in addition to the oxidative agent menadione. Menadione but no other oxidative agent tested inhibited TodS activity in vitro and reduced PtodX expression in vivo. The menadione signal is incorporated by a cysteine‐dependent mechanism. The mutation of the sole conserved cysteine of TodS (C320) rendered the protein insensitive to menadione. We evaluated the mutual opposing effects of toluene and menadione on TodS autophosphorylation. In the presence of toluene, menadione reduced TodS activity whereas toluene did not stimulate activity in the presence of menadione. It was shown by others that menadione increases expression of glucose metabolism genes. The opposing effects of menadione on glucose and toluene metabolism may be partially responsible for the interwoven regulation of both catabolic pathways. This work provides mechanistic detail on how complex sensor kinases integrate different types of signal molecules. 相似文献
14.
15.
Chaya Pooput Erica Rosemond Joel Karpiak Francesca Deflorian Santiago Vilar Stefano Costanzi Jürgen Wess Kenneth L. Kirk 《Bioorganic & medicinal chemistry》2009,17(23):7987-7992
The important and diverse biological functions of adrenergic receptors, a subclass of G protein-coupled receptors (GPCRs), have made the search for compounds that selectively stimulate or inhibit the activity of different adrenergic receptor subtypes an important area of medicinal chemistry. We previously synthesized 2-, 5-, and 6-fluoronorepinehprine (FNE) and 2-, 5-, and 6-fluoroepinephrine (FEPI) and found that 2FNE and 2FEPI were selective β-adrenergic agonists and that 6FNE and 6FEPI were selective α-adrenergic agonists, while 5FNE and 5FEPI were unselective. Agonist potencies correlated well with receptor binding affinities. Here, through a combination of molecular modeling and site-directed mutagenesis, we have identified N293 in the β2-adrenergic receptor as a crucial residue for the selectivity of the receptor for catecholamines fluorinated at different positions. 相似文献
16.
Rosemond MJ St John-Williams L Yamaguchi T Fujishita T Walsh JS 《Chemico-biological interactions》2004,147(2):129-139
S-1360, a 1,3-diketone derivative, was the first HIV integrase inhibitor to enter human trials. Clinical data suggested involvement of non-cytochrome P450 clearance pathways, including reduction and glucuronidation. Reduction of S-1360 generates a key metabolite in humans, designated HP1, and constitutes a major clearance pathway. For characterization of subcellular location and cofactor dependence of HP1 formation, [(14)C]-S-1360 was incubated with commercially available pooled human liver fractions, including microsomes, cytosol, and mitochondria, followed by HPLC analysis with radiochemical detection. Incubations were performed in the presence and absence of the cofactors NADH or NADPH. Results showed that the enzyme system responsible for generation of HP1 in vitro is cytosolic and NADPH-dependent, implicating aldo-keto reductases (AKRs) and/or short-chain dehydrogenases/reductases (SDRs). A validated LC/MS/MS method was developed for investigating the reduction of S-1360 in detail. The reduction reaction exhibited sigmoidal kinetics with a K(m,app) of 2 microM and a Hill coefficient of 2. The ratio of V(max)/K(m) was approximately 1 ml/(min mg cytosolic protein). The S-1360 kinetic data were consistent with positive cooperativity and a single enzyme system. The relative contributions of AKRs and SDRs were examined through the use of chemical inhibitors. For these experiments, non-radiolabeled S-1360 was incubated with pooled human liver cytosol and NADPH in the presence of inhibitors, followed by quantitation of HP1 by LC/MS/MS. Quercetin and menadione produced approximately 30% inhibition at a concentration of 100 microM. Enzymes sensitive to these inhibitors include the carbonyl reductases (CRs), a subset of the SDR enzyme family predominantly located in the cytosol. Flufenamic acid and phenolphthalein were the most potent inhibitors, with > 67% inhibition at a concentration of 20 microM, implicating the AKR enzyme family. The cofactor dependence, subcellular location, and chemical inhibitor results implicated the aldo-keto reductase family of enzymes as the most likely pathway for generation of the major metabolite HP1 from S-1360. 相似文献
17.
Interactions among irradiance,nutrients, and herbivores constrain a stream algal community 总被引:10,自引:0,他引:10
A. D. Rosemond 《Oecologia》1993,94(4):585-594
Using stream-side, flow-through channels, I tested for the effects of nutrients (NU) (nitrogen plus phosphorus), irradiance
(L), and snail grazing (G) on a benthic algal community in a small, forested stream. Grazed communities were-dominated by
a chlorophyte (basal cells ofStigeoclonium) and a cyanophyte (Chamaesiphon investiens), whereas ungrazed communities were comprised almost entirely of diatoms, regardless of nutrient and light levels. Snails
maintained low algal biomass in all grazed treatments, presumably by consuming increased algal production in treatments to
which L and NU were increased. When nutrients were increased, cellular nutrient content increased under ambient conditions
(shaded, grazed) and biomass and productivity increased when snails were removed and light was increased. Together, nutrients
and light had positive effects and grazing had negative effects on biomass (chlorophylla, AFDM, algal biovolume) and chlorophyll-and areal-specific productivity in ANOVAs. However, in most cases, only means from
treatments in which all three factors were manipulated (ungrazed, +NU&L treatments) were significantly different from controls;
effects of single factors were generally undetectable. These results indicate that all three factors simultaneously limited
algal biomass and productivity in this stream during the summer months. Additionally, the effects of these factors in combination
were in some cases different from the effects of single factors. For example, light had slight negative effects on some biomass
parameters when added at ambient snail densities and nutrient concentrations, but had strong positive effects in conjunction
with nutrient addition and snail removal. This study demonstrates that algal biomass and productivity can be under multiple
constraints by irradiance, nutrients, and herbivores and indicates the need to employ multifactor experiments to test for
such interactive effects. 相似文献
18.
Amy D. Rosemond 《Journal of phycology》2000,36(3):621-622
19.
20.