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1.
Eutrophication of moderately deep Dutch lakes during the past century: flaws in the expectations of water management? 总被引:1,自引:0,他引:1
We studied the trophic development of the past 30–100 years in eight moderately deep Dutch lakes based on their sedimentary
fossil diatom assemblages. The dominant diatoms indicating meso- to eutrophic conditions were Aulacoseira subarctica, Cyclotella ocellata, C. cyclopuncta, C. meneghiniana, Puncticulata bodanica, Aulacoseira granulata, Cyclostephanos dubius, C. invisitatus, Stephanodiscus hantzschii, S. medius, and S. parvus. Ordination of diatom data separated the lakes into four groups according to their total phosphorus concentrations (TP),
water supply, water management, and origin. The first group consists of dike-breach lakes, which were in stable eutrophic
to hypertrophic conditions throughout the past century with diatom-inferred TP (DI-TP) concentrations of between 70 and 300 μg l−1. The main factors influencing these dike-breach lakes are river management, ground water supply of riverine origin, and local
land use. The second group are artificial lakes of fluctuating oligo- to mesotrophic conditions and DI-TP concentrations of
10–30 μg l−1. Only one of the artificial lakes showed a DI-TP increase due to changes in catchment agricultural practice. A third group
includes an artificial moat and an inland dike-breach lake with DI-TP concentrations of 50–100 μg l−1. The fourth group contains an individual dike-breach lake with stable mesotrophic conditions of 50 μg l−1 throughout the past century. Rather than showing a regional pattern, the studied lakes behave very individualistically with
regard to their trophic history, reflecting changes in the local hydrology and in their nutrient sources. 相似文献
2.
Impact of long-term nitrogen addition on carbon stocks in trees and soils in northern Europe 总被引:4,自引:2,他引:2
The aim of this study was to quantify the effects of fertiliser N on C stocks in trees (stems, stumps, branches, needles,
and coarse roots) and soils (organic layer +0–10 cm mineral soil) by analysing data from 15 long-term (14–30 years) experiments
in Picea abies and Pinus sylvestris stands in Sweden and Finland. Low application rates (30–50 kg N ha−1 year−1) were always more efficient per unit of N than high application rates (50–200 kg N ha−1 year−1). Addition of a cumulative amount of N of 600–1800 kg N ha−1 resulted in a mean increase in tree and soil C stock of 25 and 11 kg (C sequestered) kg−1 (N added) (“N-use efficiency”), respectively. The corresponding estimates for NPK addition were 38 and 11 kg (C) kg−1 (N). N-use efficiency for C sequestration in trees strongly depended on soil N status and increased from close to zero at
C/N 25 in the humus layer up to 40 kg (C) kg−1 (N) at C/N 35 and decreased again to about 20 kg (C) kg−1 (N) at C/N 50 when N only was added. In contrast, addition of NPK resulted in high (40–50 kg (C) kg−1 (N)) N-use efficiency also at N-rich (C/N 25) sites. The great difference in N-use efficiency between addition of NPK and
N at N-rich sites reflects a limitation of P and K for tree growth at these sites. N-use efficiency for soil organic carbon
(SOC) sequestration was, on average, 3–4 times lower than for tree C sequestration. However, SOC sequestration was about twice
as high at P. abies as at P. sylvestris sites and averaged 13 and 7 kg (C) kg−1 (N), respectively. The strong relation between N-use efficiency and humus C/N ratio was used to evaluate the impact of N
deposition on C sequestration. The data imply that the 10 kg N ha−1 year−1 higher deposition in southern Sweden than in northern Sweden for a whole century should have resulted in 2.0 ± 1.0 (95% confidence
interval) kg m−2 more tree C and 1.3 ± 0.5 kg m−2 more SOC at P. abies sites in the south than in the north for a 100-year period. These estimates are consistent with differences between south
and north in tree C and SOC found by other studies, and 70–80% of the difference in SOC can be explained by different N deposition. 相似文献
3.
Studies on the role of endogenous metabolites such as bilirubin and their interactions with biomolecules have attracted considerable
attention over the past several years. In this work, the interaction of bilirubin (BR) with purified goat liver cystatin (LC)
was studied using fluorescence and ultraviolet (UV) spectroscopy. The fluorescence data proved that the fluorescence quenching
of liver cystatin by BR was the result of BR–cystatin complex formation. Stern–Volmer analysis of fluorescence quenching data
showed the binding constant to be 9.27 × 104 M−1 and the number of binding sites to be close to unity. The conformation of the BR–cystatin complex was found to change upon
varying the pH of the complex. The BR–cystatin complex was found to have reduced papain inhibitory activity. Photo-illumination
of BR–cystatin complex causes perturbation in the micro-environment of goat liver cystatin as indicated by red-shift. This
report summarizes our research efforts to reveal the mechanism of interaction of bilirubin with liver cystatin. 相似文献
4.
Salmon sperm DNA platination has been conducted under strictly pseudo-first-order conditions with cisplatin (1) and rac-{(1S,2S,4S)-exo-2-(aminomethyl)-2-amino-7-bicyclo[2.2.1]heptane}dichloroplatinum(II) (2). An aquation step first occurs for both complexes, with the rate constants k
1 = 1.12(0.02)×10–4 s–1 and 1.47(0.02)×10–4 s–1 respectively for 1 and 2 at 37 °C, values in agreement with those previously reported. It is followed by the actual platination step whose second-order
rate constant has been determined for the first time by physicochemical techniques. The values for 1 and 2 respectively are: k
2 = 2.08(0.07) M–1 s–1 and 3.9(0.4) M–1 s–1. These kinetic data are discussed in the context of a comparison of several biological properties of the two complexes.
Received: 15 May 1998 / Accepted: 26 June 1998 相似文献
5.
This paper presents seasonal in situ monitoring data on benthic coverage and coral–algae interactions in high-latitude fringing reefs of the Northern Red Sea over a period of 19 months. More than 30% of all
hermatypic corals were involved in interaction with benthic reef algae during winter compared to 17% during summer, but significant
correlation between the occurrence of coral–algae interactions and monitored environmental factors such as temperature and inorganic nutrient availability was not detected.
Between 5 and 10-m water depth, the macroalgae Caulerpa serrulata,
Peyssonnelia capensis and filamentous turf algae represented almost 100% of the benthic algae involved in interaction with corals. Turf algae were
most frequently (between 77 and 90% of all interactions) involved in interactions with hermatypic corals and caused most tissue
damage to them. Maximum coral tissue loss of 0.75% day−1 was observed for Acropora-turf algae interaction during fall, while an equilibrium between both groups of organisms appeared during summer. Slow-growing
massive corals were more resistant against negative algal influence than fast-growing branching corals. Branching corals of
the genus Acropora partly exhibited a newly observed phenotypic plasticity mechanism, by development of a bulge towards the competing organism,
when in interaction with algae. These findings may contribute to understand the dynamics of phase shifts in coral reefs by
providing seasonally resolved in situ monitoring data on the abundance and the competitive dynamic of coral–algae interactions. 相似文献
6.
Density functional theory (DFT) was used to investigate the Rh(I)-catalyzed intermolecular hydroacylation of vinylsilane with
benzaldehyde. All intermediates and transition states were optimized completely at the B3LYP/6-31G(d,p) level (LANL2DZ(f)
for Rh). Calculations indicated that Rh(I)-catalyzed intermolecular hydroacylation is exergonic, and the total free energy
released is −110 kJ mol−1. Rh(I)-catalyzed intermolecular hydroacylation mainly involves the active catalyst CA2, rhodium–alkene–benzaldehyde complex M1, rhodium–alkene–hydrogen–acyl complex M2, rhodium–alkyl–acyl complex M3, rhodium–alkyl–carbonyl–phenyl complex M4, rhodium–acyl–phenyl complex M5, and rhodium–ketone complex M6. The reaction pathway CA2 + R2 → M1b → T1b → M2b → T2b1 → M3b1 → T4b → M4b → T5b → M5b → T6b → M6b → P2 is the most favorable among all reaction channels of Rh(I)-catalyzed intermolecular hydroacylation. The reductive elimination
reaction is the rate-determining step for this pathway, and the dominant product predicted theoretically is the linear ketone,
which is consistent with Brookhart’s experiments. Solvation has a significant effect, and it greatly decreases the free energies
of all species. The use of the ligand Cp′ (Cp′ = C5Me4CF3) decreased the free energies in general, and in this case the rate-determining step was again the reductive elimination reaction. 相似文献
7.
Reversibility of Soil Productivity Decline with Organic Matter of Differing Quality Along a Degradation Gradient 总被引:8,自引:0,他引:8
Joseph M. Kimetu Johannes Lehmann Solomon O. Ngoze Daniel N. Mugendi James M. Kinyangi Susan Riha Lou Verchot John W. Recha Alice N. Pell 《Ecosystems》2008,11(5):726-739
In the highlands of Western Kenya, we investigated the reversibility of soil productivity decline with increasing length of
continuous maize cultivation over 100 years (corresponding to decreasing soil organic carbon (SOC) and nutrient contents)
using organic matter additions of differing quality and stability as a function of soil texture and inorganic nitrogen (N)
additions. The ability of additions of labile organic matter (green and animal manure) to improve productivity primarily by
enhanced nutrient availability was contrasted with the ability of stable organic matter (biochar and sawdust) to improve productivity
by enhancing SOC. Maize productivity declined by 66% during the first 35 years of continuous cropping after forest clearing.
Productivity remained at a low level of 3.0 t grain ha-1 across the chronosequence stretching up to 105 years of continuous cultivation despite full N–phosphorus (P)–potassium (K)
fertilization (120–100–100 kg ha−1). Application of organic resources reversed the productivity decline by increasing yields by 57–167%, whereby responses to
nutrient-rich green manure were 110% greater than those from nutrient-poor sawdust. Productivity at the most degraded sites
(80–105 years since forest clearing) increased in response to green manure to a greater extent than the yields at the least
degraded sites (5 years since forest clearing), both with full N–P–K fertilization. Biochar additions at the most degraded
sites doubled maize yield (equaling responses to green manure additions in some instances) that were not fully explained by
nutrient availability, suggesting improvement of factors other than plant nutrition. There was no detectable influence of
texture (soils with either 11–14 or 45–49% clay) when low quality organic matter was applied (sawdust, biochar), whereas productivity
was 8, 15, and 39% greater (P < 0.05) on sandier than heavier textured soils with high quality organic matter (green and animal manure) or only inorganic
nutrient additions, respectively. Across the entire degradation range, organic matter additions decreased the need for additional
inorganic fertilizer N irrespective of the quality of the organic matter. For low quality organic resources (biochar and sawdust),
crop yields were increasingly responsive to inorganic N fertilization with increasing soil degradation. On the other hand,
fertilizer N additions did not improve soil productivity when high quality organic inputs were applied. Even with the tested
full N–P–K fertilization, adding organic matter to soil was required for restoring soil productivity and most effective in
the most degraded sites through both nutrient delivery (with green manure) and improvement of SOC (with biochar). 相似文献
8.
Marieke L. Overeijnder Wilfred R. Hagen Peter-Leon Hagedoorn 《Journal of biological inorganic chemistry》2009,14(5):703-710
Pyrococcus furiosus hybrid cluster protein (HCP) was expressed in Escherichia coli, purified, and characterized. This is the first archaeal and thermostable HCP to be isolated. Compared with the protein sequences
of previously characterized HCPs from mesophiles, the protein sequence of P. furiosus HCP exhibits a deletion of approximately 13 kDa as a single amino acid stretch just after the N-terminal cysteine motif,
characteristic for class-III HCPs from (hyper)thermophilic archaea and bacteria. The protein was expressed as a thermostable,
soluble homodimeric protein. Hydroxylamine reductase activity of P. furiosus HCP showed a K
m value of 0.40 mM and a k
cat value of 3.8 s−1 at 70 °C and pH 9.0. Electron paramagnetic resonance spectroscopy showed evidence for the presence of a spin-admixed, S = 3/2 [4Fe–4S]+ cubane cluster and of the hybrid cluster. The cubane cluster of P. furiosus HCP is presumably coordinated by a CXXC–X7–C–X5–C motif close to the N-terminus, which is similar to the CXXC–X8–C–X5–C motif of the Desulfovibrio desulfuricans and Desulfovibrio vulgaris HCPs. Amino acid sequence alignment and homology modeling of P. furiosus HCP reveal that the deletion results in a loss of one of the two three-helix bundles of domain 1. Clearly the loss of one
of the three-helix bundles of domain 1 does not diminish the hydroxylamine reduction activity and the incorporation of the
iron–sulfur clusters. 相似文献
9.
The aim of this research was to formulate Marsupsin–phospholipid complex (M–P Complex) in attempt to increase the bioavailability
of marsupsin and to characterize this new formulation along with its evaluation. Marsupsin–phospholipid complex was formulated
by mechanical dispersion method. In this new formulation, complex formation was confirmed by carrying out transmission electron
microscopy (TEM), IR, 1H-NMR and RP-HPLC analysis. TEM showed M–P Complex diameter range of 0.05–0.5 μm. The entrapment efficiency of M–P Complex
was found to be 44%. In vitro release study revealed its first order release profile. Mean blood serum concentration vs time curve of marsupsin was of first order after oral administration of M–P Complex in albino rabbits which clearly showed
remarkably increased bioavailability of M–P Complex than standardized marsupsin. The average value of C
max and T
max of M–P Complex were found to be 3.02 mg/ml and 10.2 h, respectively. Hence the findings demonstrate that complexing marsupsin
with phospholipids results in better oral bioavailability and improved biological response than free form of standardized
marsupsin. 相似文献
10.
The amenability of Caenorhabditis elegans against pathogen provides a valuable tool for studying host–pathogen interactions. Physiological experiments revealed that
the P. aeruginosa was able to kill C. elegans efficiently. The effects of P. aeruginosa PA14, PAO1 and their isolated lipopolysaccharide (LPS) on the host system were analyzed. The LPS at higher concentrations
(≥2 mg/ml) was toxic to the host animals. Kinetic studies using qPCR revealed the regulation of host-specific candidate antimicrobial
genes during pathogen-mediated infections. In addition, the pathogen-specific virulent gene, exoT expression, was anlyzed and found to be varied during the interactions with the host system. Ability of the pathogens to
modify their internal machinery in the presence of the host was analyzed by XRD, FTIR and PCA. LPS isolated from pathogens
upon exposure to C. elegans showed modifications at their functional regions. LPS from PAO1 showed difference in d-spacing angle (Å) and °2Th position.
FTIR spectra revealed alterations in polysaccharide (1,200–900 cm−1) and fatty acid (3,000–2,800 cm−1) regions of LPS from P. aeruginosa PAO1 exposed to the host system. These data provide additional insights on how the pathogens subvert its own and host machinery
during interactions. 相似文献
11.
Carter BZ Mak DH Morris SJ Borthakur G Estey E Byrd AL Konopleva M Kantarjian H Andreeff M 《Apoptosis : an international journal on programmed cell death》2011,16(1):67-74
XIAP, a potent caspase inhibitor, is highly expressed in acute myeloid leukemia (AML) cells and contributes to chemoresistance.
A multi-center phase 1/2 trial of XIAP antisense oligonucleotide AEG35156 in combination with idarubicin/cytarabine was conducted
in 56 patients with relapsed/refractory AML. Herein we report the pharmacodynamic studies of the patients enrolled at M. D.
Anderson Cancer Center. A total of 13 patients were enrolled in our institution: five in phase 1 (12–350 mg/m2 AEG35156) and eight in phase 2 (350 mg/m2 AEG35156) of the protocol. AEG35156 was administered on 3 consecutive days and then weekly up to a maximum of 35 days. Blood
samples were collected from patients on days 1 through 5 and on day 28–35 post-chemotherapy for detection of XIAP levels and
apoptosis. AEG35156 treatment led to dose-dependent decreases of XIAP mRNA levels (42–100% reduction in phase 2 patients).
XIAP protein levels were reduced in all five samples measured. Apoptosis induction was detected in 1/4 phase 1 and 4/5 phase
2 patients. Importantly, apoptosis was most pronounced in CD34
+
38
−
AML stem cells and all phase 2 patients showing apoptosis induction in CD34
+
38
−
cells achieved response. We conclude that at 350 mg/m2, AEG35156 is effective in knocking down XIAP in circulating blasts accompanied by the preferential induction of apoptosis
in CD34
+
38
−
AML stem cells. 相似文献
12.
Edward Castañeda-Moya Robert R. Twilley Victor H. Rivera-Monroy Brian D. Marx Carlos Coronado-Molina Sharon M. L. Ewe 《Ecosystems》2011,14(7):1178-1195
Patterns of mangrove vegetation in two distinct basins of Florida Coastal Everglades (FCE), Shark River estuary and Taylor
River Slough, represent unique opportunities to test hypotheses that root dynamics respond to gradients of resources, regulators,
and hydroperiod. We propose that soil total phosphorus (P) gradients in these two coastal basins of FCE cause specific patterns
in belowground biomass allocation and net primary productivity that facilitate nutrient acquisition, but also minimize stress
from regulators and hydroperiod in flooded soil conditions. Shark River basin has higher P and tidal hydrology with riverine
mangroves, in contrast to scrub mangroves of Taylor basin with more permanent flooding and lower P across the coastal landscape.
Belowground biomass (0–90 cm) of mangrove sites in Shark River and Taylor River basins ranged from 2317 to 4673 g m−2, with the highest contribution (62–85%) of roots in the shallow root zone (0–45 cm) compared to the deeper root zone (45–90 cm).
Total root productivity did not vary significantly among sites and ranged from 407 to 643 g m−2 y−1. Root production in the shallow root zone accounted for 57–78% of total production. Root turnover rates ranged from 0.04
to 0.60 y−1 and consistently decreased as the root size class distribution increased from fine to coarse roots, indicating differences
in root longevity. Fine root biomass was negatively correlated with soil P density and frequency of inundation, whereas fine
root turnover decreased with increasing soil N:P ratios. Lower P availability in Taylor River basin relative to Shark River
basin, along with higher regulator and hydroperiod stress, confirms our hypothesis that interactions of stress from resource
limitation and long duration of hydroperiod account for higher fine root biomass along with lower fine root production and
turnover. Because fine root production and organic matter accumulation are the primary processes controlling soil formation
and accretion in scrub mangrove forests, root dynamics in the P-limited carbonate ecosystem of south Florida have a major
controlling role as to how mangroves respond to future impacts of sea-level rise. 相似文献
13.
The zooxanthellate octocoral Sinularia flexibilis is a producer of potential pharmaceutically important metabolites such as antimicrobial and cytotoxic substances. Controlled
rearing of the coral, as an alternative for commercial exploitation of these compounds, requires the study of species-specific
growth requirements. In this study, phototrophic vs. heterotrophic daily energy demands of S. flexibilis was investigated through light and Artemia feeding trials in the laboratory. Rate of photosynthetic oxygen by zooxanthellae in light (≈200 μmol quanta m−2 s−1) was measured for the coral colonies with and without feeding on Artemia nauplii. Respiratory oxygen was measured in the dark, again with and without Artemia nauplii. Photosynthesis–irradiance curve at light intensities of 0, 50, 100, 200, and 400 μmol quanta m−2 s−1 showed an increase in photosynthetic oxygen production up to a light intensity between 100 and 200 μmol quanta m−2 s−1. The photosynthesis to respiration ratio (P/R > 1) confirmed phototrophy of S. flexibilis. Both fed and non-fed colonies in the light showed high carbon contribution by zooxanthellae to animal (host) respiration
values of 111–127%. Carbon energy equivalents allocated to the coral growth averaged 6–12% of total photosynthesis energy
(mg C g
−
1 buoyant weight day
−
1) and about 0.02% of the total daily radiant energy. “Light utilization efficiency (ε)” estimated an average ε value of 75%
12 h
−
1 for coral practical energetics. This study shows that besides a fundamental role of phototrophy vs. heterotrophy in daily
energy budget of S. flexibilis, an efficient fraction of irradiance is converted to useable energy. 相似文献
14.
Li Y Efferson CL Ramesh R Peoples GE Hwu P Ioannides CG 《Cancer immunology, immunotherapy : CII》2011,60(4):515-524
Bacterial cell wall polysaccharides, such as PGN, bind and activate TLR-2, NOD2 and PGRP on monocytes/macrophages and activate
inflammation. We found that the peptides containing basic amino acids (cations) at N
-terminus and tyrosine at C-terminus interfered with activating ability of PGN. This finding is significant because the ECD
of TLR-2 in vivo encounters a large number of proteins or peptides. Some should bind ECD and “pre-form” TLR-2 to respond or
not to its activators, although they cannot activate TLR-2 alone. TLR-2 is receptor for a large number of ligands, including
lipopeptides and bacterial cell wall glycoproteins. A binding site for lipopeptides has been identified; however, a binding
site for soluble or multimeric PGN has not been proposed. To identify the candidate binding sites of peptides and PGN on TLR-2,
we modeled docking of peptides and of the PGN monomer (PGN-S-monomer) to extracellular domain (ECD-TLR-2) of the unbound TLR-2.
Quantification, in silico, of free energy of binding (DG) identified 2 close sites for peptides and PGN. The PGN-S-monomer
binding site is between amino acids TLR-2, 404–430 or more closely TLR-2, 417–428. The peptide-binding site is between amino
acids TLR-2, 434–455. Molecular models show PGN-S-monomer inserts its N
-acetyl-glucosamine (NAG) deep in the TLR-2 coil, while its terminal lysine interacts with inside (Glu403) and outside pocket (Tyr378). Peptides insert their two N
-terminal arginines or their C-terminal tyrosines in the TLR-2 coil. PGN did not bind the lipopeptide-binding site in the TLR-2.
It can bind the C-terminus, 572–586 (DG = 0.026 kcal), of “lipopeptide-bound” TLR-2. An additional, low-affinity PGN-binding
site is TLR-2 (227–237). MTP, MDP, and lysine-less PGN bind to TLR-2, 87–113. This is the first report identifying candidate
binding sites of monomer PGN and peptides on TLR-2. Experimental verification of our findings is needed to create synthetic
adjuvant for vaccines. Such synthetic PGN can direct both adjuvant and cancer antigen to TLR-2. 相似文献
15.
Two 60-day experiments were conducted to study the influence of photon flux density (PFD) and temperature on the attachment
and development of Gloiopeltis tenax and Gloiopeltis furcata tetraspores. In the first experiment, tetraspores of the two Gloiopeltis species were incubated at five temperature ranges (8°C, 12°C, 16°C, 20°C, 24°C) under a constant PFD of 80 μmol photons m−2 s−1 with a photoperiod of 12:12. In a second experiment, tetraspores were incubated under five PFD gradients (30, 55, 80, 105,
130 μmol photons m−2 s−1) at a constant temperature of 16°C with a photoperiod of 12:12. Maximum density of attached tetraspores was observed at 16°C
for both species. Maximum per cent of spore germinating into disc was recorded at 12–16°C for G. tenax and 8–12°C for G. furcata. Maximum per cent of discs producing erect axes for G. tenax and G. furcata were recorded at 24°C and 20°C, respectively. Light had no significant effect on tetraspore attachment and developing into
disc, but it affected the growth, sprouting and survival of its discs. Under 30–55 μmol photons m−2 s−1, the discs of the two species of Gloiopeltis did not form thallus until the end of the experiment. Optimum PFD range for G. tenax discs was 80–105 μmol photons m−2 s−1, whilst it was 80–130 μmol photons m−2 s−1 for G. furcata. Results presented in this study are expected to assist the progress of artificial seeding of Gloiopeltis. 相似文献
16.
We quantified cover, population densities, size distribution and biomass of zebra mussels along 7 transects in eutrophic Lake
Ekoln (Sweden). We also analyzed the elemental (C, N, P) composition of zebra mussel soft tissue and computed their retention
rates of N and P their quantitative role in the lake’s nutrient budget. We hypothesized that zebra mussels play an important
role in the nutrient budget of the lake and speculate that the successive harvesting of cultured mussels could contribute
to the lake’s rate of recovery from cultural eutrophication. At depths exceeding 5 m, mussels covered consistently less than
5% or were absent. Similarly, mean densities were 3,158 ± 2,143 ind m−2 between 2 and 4 m, but rapidly declined at larger depths. Calculated clearance rates averaged 19.4 ± 2.3 km3 y−1, implying the entire lake is filtered every 8–10 days. Concentrations of N and P in mussel soft tissue averaged 100.9 ± 1.5 mg N g−1 DW and 9.3 ± 0.2 mg P g−1 DW. The lake population was estimated to 22.2 ± 2.6 × 1010 mussels, corresponding to a standing stock biomass of 362 ± 42 ton DW, or conservative estimates of 36.6 ± 4.3 ton N and
3.4 ± 0.4 ton P. Assuming a life span of 2–3 years gives a retention estimate of 1.2–1.8 ton P y−1 by mussels, corresponding to 50–77% of the annual P influx from Uppsala sewage treatment plant to the lake. Similarly, annual
N-retention by zebra mussels makes up 13–20 ton N y−1, largely equaling the annual N-deposition from atmospheric sources on the lake’s surface. These retention rates correspond
to only a few percent of the annual P-load from agricultural sources, but we argue that the quantitative role of zebra mussels
in nutrient budgets is much larger if these budgets are adjusted for the bias introduced by coarse estimates of N and P pools
that include a large share of refractory P. 相似文献
17.
We examined the hydrologic controls on nitrogen biogeochemistry in the hyporheic zone of the Tanana River, a glacially-fed
river, in interior Alaska. We measured hyporheic solute concentrations, gas partial pressures, water table height, and flow
rates along subsurface flowpaths on two islands for three summers. Denitrification was quantified using an in situ 15NO3− push–pull technique. Hyporheic water level responded rapidly to change in river stage, with the sites flooding periodically
in mid−July to early−August. Nitrate concentration was nearly 3-fold greater in river (ca. 100 μg NO3−–N l−1) than hyporheic water (ca. 38 μg NO3−–N l−1), but approximately 60–80% of river nitrate was removed during the first 50 m of hyporheic flowpath. Denitrification during
high river stage ranged from 1.9 to 29.4 mg N kg sediment−1 day−1. Hotspots of methane partial pressure, averaging 50,000 ppmv, occurred in densely vegetated sites in conjunction with mean
oxygen concentration below 0.5 mgO2 l−1. Hyporheic flow was an important mechanism of nitrogen supply to microbes and plant roots, transporting on average 0.41 gNO3−–N m−2 day−1, 0.22 g NH4+–N m−2 day−1, and 3.6 g DON m−2 day−1 through surface sediment (top 2 m). Our results suggest that denitrification can be a major sink for river nitrate in boreal
forest floodplain soils, particularly at the river-sediment interface. The stability of the river hydrograph and the resulting
duration of soil saturation are key factors regulating the redox environment and anaerobic metabolism in the hyporheic zone. 相似文献
18.
P. W. Inglett E. M. D’Angelo K. R. Reddy P. V. McCormick S. E. Hagerthey 《Wetlands Ecology and Management》2009,17(2):131-144
The use of periphyton nitrogenase activity (biological N2 fixation) as an indicator of wetland P impact was assessed using patterns of nutrient content (C, N, P, Ca, Mg, K, Fe, and
Mn) and acetylene reduction (AR) in floating cyanobacterial periphyton mat (metaphyton) communities of a P-enriched portion
of the Florida Everglades, USA (Water Conservation Area-2A, WCA-2A). Spatial patterns of nutrients indicate the enrichment
of floating mat periphyton N, P, Fe, and K, and the reduction of Mn and TN:TP in enriched marsh areas. In highly enriched
areas, floating mat periphyton AR was approximately threefold greater than that in less enriched, interior marsh zones. Multiple
regression models indicated AR dependence on P in eutrophic WCA-2A areas while the AR of more interior marsh periphyton mats
was more closely related to tissue levels of Ca and Fe. Nitrogenase activity of floating mat periphyton from P-loaded mesocosms
revealed a significant enhancement of N2 fixation in samples receiving approximately 2–3 mg P m−2 of cumulative P dosing or with biomass TP content of 100–300 mg kg−1. At P contents above the optimum, mat periphyton AR was suppressed possibly as a result of changes in species composition
or increased levels of NH4+. After 3 years of dosing, consistently high AR occurred only at low rates of P enrichment (0.4–0.8 g P m−2 yr−1), and the patterns appeared to be seasonal. These findings agree with the hypothesis that P availability is a key determinant
of nitrogenase activity in aquatic systems, and thus, may support the use of periphyton nitrogenase to indicate P impacts
in P-limited systems. These results also demonstrate the potential existence of a P threshhold for biogeochemical alteration
of periphyton mat function in the Everglades, and that cumulative loading of limiting nutrients (i.e., P), rather than instantaneous
concentrations, should be considered when evaluating nutrient criteria. 相似文献
19.
Theoretical studies of an unsymmetrical calix[4]-crown-5-N-azacrown-5 (1) in a fixed 1,3-alternate conformation and the complexes 1·K+(a), 1·K+(b), 1·K+(c) and 1·K+K+ were performed using density functional theory (DFT) at the B3LYP/6-31G* level. The fully optimized geometric structures
of the free macroligand and its 1:1 and 1:2 complexes, as obtained from DFT calculations, were used to perform natural bond
orbital (NBO) analysis. The two main types of driving force metal–ligand and cation–π interactions were investigated. NBO
analysis indicated that the stabilization interaction energies (E
2) for O…K+ and N…K+ are larger than the other intermolecular interactions in each complex. The significant increase in electron density in the
RY* or LP* orbitals of K+ results in strong host–guest interactions. In addition, the intermolecular interaction thermal energies (ΔE, ΔH, ΔG) were calculated by frequency analysis at the B3LYP/6-31G* level. For all structures, the most pronounced changes in the
geometric parameters upon interaction are observed in the calix[4]arene molecule. The results indicate that both the intermolecular
electrostatic interactions and the cation–π interactions between the metal ion and π orbitals of the two pairs that face the
inverted benzene rings play a significant role. 相似文献
20.
Characterization of phosphorus fractions in the sediments of a tropical intertidal mangrove ecosystem 总被引:2,自引:0,他引:2
Solid phases of phosphorus fractions in the surface and core sediments were studied to understand the biogeochemical cycling
and bioavailability of phosphorus in the Pichavaram intertidal mangrove sediments of India. Total P in surface and core sediments
ranged between 451–552 and 459–736 μg g−1 respectively and Fe bound P was the dominant fraction. Low levels of Fe bound P in the mangrove zone than the two estuarine
zones may be because of high salinity inhibition of phosphate adsorption onto the Fe-oxides/hydroxides. Post-depositional
reorganization of P was observed in surface sediments, converting organic P and Fe bound P into the authigenic P. High levels
of organic P in the mangrove zone is primarily due to intensive cycling and degradation of organic matter and adsorption of
phosphate on the organic molecules. The burial rates and regeneration efficiency of P in the intertidal mangrove ecosystem
ranged from 5.41 to 7.27 μmol P cm−2 year−1 and 0.122 to 0.233 μmol P cm−2 year−1, respectively. High burial efficiency (≈99%) of P proves the earlier observation of limiting nature of P for the biological
productivity. Further, bioavailable P (exchangeable P + Fe bound P + organic P) constituted a considerable proportion of sedimentary
P pool of which an average accounted for 55 and 50% in surface and core sediments respectively. The results indicate that
significant amount of P is locked in sediments in the form of authigenic P and detrital P which makes P as a limiting nutrient
for the biological productivity. 相似文献