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1.
It is cost-effective protocol to identify a functional species pool for marine bioassessment by removing redundant species from a raw dataset. The feasibility of functional species pool for discriminating water quality status was studied based on a dataset of 120 samples of ciliated protozoa. From the full 60-species dataset of the whole ciliate communities, a 35-species subset was identified as a functional species pool, the species number, abundance and biodiversity indices of which were significantly correlated with those of the full species dataset. The spatial pattern of the subset was significantly related to the changes in nutrients soluble reactive phosphates (SRP), nitrate/nitrite nitrogen (NO 3-N/NO 2-N) and ammonium nitrogen (NH 4-N). Four indices of the taxonomic diversity ( Δ), taxonomic distinctness ( Δ*), average in taxonomic distinctness ( Δ+) and the variation in taxonomic distinctness ( Λ+) based on this small species pool were significantly correlated with the changes of nutrients NO 3-N and/or (NH 4-N). The paired indices Δ+ and Λ+ showed a clear decreasing trend of departure from the expected taxonomic pattern. These findings suggest that the 35-species functional species subset may be used as a feasible functional surrogate of ciliated protozoan assemblages for community-based bioassessment in marine ecosystems. 相似文献
2.
Taxonomic distinctness indices measure the taxonomic relatedness among species and have been used for environmental assessment to detect disturbed habitats. This is the first application of the Average Taxonomic Distinctness (Δ+) and Variance in Taxonomic Distinctness (Λ+) indices to the presence/absence data of rotifer communities to examine their sensitiveness in discriminating perturbed environments. The 26 Greek lakes studied spanned a wide range of morphological and physical–chemical characteristics. Δ+ was significantly correlated (P < 0.05) with maximum depth, salinity and trophic state, while Λ+ was correlated only with salinity. The index Δ+ identified lakes characterized by periods of increased salinity. Communities in these lakes were less diverse, consisting of more closely related species as seen by the reduced number of families than other lakes with similar species richness. Lakes identified by Λ+ had a higher community distinctness than expected due to the overrepresentation of the family Brachionidae; they were also characterized by periods of water-level fluctuations. Both indices were unaffected by sampling effort in terms of number of species and sampling visits; whereas Shannon diversity index (H′) was correlated to species number. Also, based on the randomization test, the taxonomic distinctness indices differentiated lakes anthropogenically disturbed based on the expected patterns of diversity of the area. 相似文献
3.
In this study, a bioassessment was conducted to determine the effectiveness of best management practices (BMPs) implemented
in farms in the Upper Delaware River watershed, NY (USA). Diatom and macroinvertebrate communities were analyzed across 17
low-order streams, designated as reference, BMP, or non-BMP. Streams lacking improvements (non-BMP) had significantly greater
specific conductance, pH, TDP, NH 4
+-N, and NO 3
−-N than did reference streams. Diatom model affinity (DMA) values were significantly greater in reference and BMP streams
than in non-BMP streams; non-BMP streams bordered on a “severely impacted” rating. The Trophic Diatom Index (TDI) varied two-fold
among stream classes, with non-BMP > BMP > reference. TDI and DMA values were highly correlated, and both varied significantly
with conductance, TDP, NH 4
+-N, and NO 3
−-N. Macroinvertebrate taxa, EPT richness, and Simpson’s diversity did not differ significantly among stream classes. Macroinvertebrate
metrics (HBI, Bioassessment Profile, Percent Model Affinity) varied by stream class, but none indicated greater water quality
in BMP sites. Nonetheless, each correlated significantly with conductance and TDP in the directions predicted by each model.
Our data suggest that diatoms are more sensitive to moderate increases in nutrients, conductivity, and pH in high-gradient
agricultural streams, and may be more useful in assessing stream management practices. 相似文献
4.
The aim of this research was to test whether NH 4
+ and NO 3
− affect the growth, P demand, cell composition and N 2 fixation of Cylindrospermopsis raciborskii under P limitation. Experiments were carried out in P-limited (200 μg l −1 PO 4-P) chemostat cultures of C. raciborskii using an inflowing medium containing either 4,000 μg l −1 NH 4-N, 4,000 μg l −1 NO 3-N or no combined N. The results showed the cellular N:P and C:P ratios of C. raciborskii decreased towards the Redfield ratio with increasing dilution rate ( D) due to the alleviation of P limitation. The cellular C:N and carotenoids:chlorophyll- a ratios also decreased with D, predominantly as a result of an increase in the chlorophyll- a and N content. The NH 4
+ and NO 3
− supply reduced the P maintenance cell quota of C. raciborskii. Consequently, the biomass yield of the N 2-grown culture was significantly lower. The maximum specific growth rate of N 2-grown culture was also the lowest observed. It is suggested that these differences in growth parameters were caused by the
P and energy requirement for heterocyte formation, nitrogenase synthesis and N 2 fixation. N 2 fixation was partially inhibited by NO 3
− and completely inhibited by NH 4
+. It was probably repressed through the high N content of cells at high dissolved N concentrations. These results indicate
that C. raciborskii is able to grow faster and maintain a higher biomass under P limitation where a sufficient supply of NH 4
+ or NO 3
− is maintained. Information gained about the species-specific nutrient and pigment stoichiometry of C. raciborskii could help to access the degree of nutrient limitation in water bodies.
Handling editor: Luigi Naselli-Flores 相似文献
5.
Mediterranean climates predispose aquatic systems to both flood and drought periods, therefore, stream sediments may be exposed
to desiccation periods. Changes in oxygen concentrations and sediment water content influence the biotic processes implicated
in nitrogen dynamics. The objectives of this study were to identify (1) the changes of inorganic nitrogen in stream sediments
during the transition from wet to dry conditions, and (2) the underlying processes in N dynamics and its regulation. Extractable
sediment NO 3
−-N and NH 4
+-N, organic matter and extractable organic carbon content were assessed during natural desiccation in microcosms with sediments
from an intermittent Mediterranean stream. In agreement with our initial hypothesis, our results showed how the NO 3
−-N content of the sediment was enhanced during the first 10 days of sediment drying, whereas NH 4
+-N was lost by 14 days post-drying. During the first 10 days, sediment desiccation seemed to stimulate the net N-mineralization
and net nitrification from sediments. Afterwards, the extractable NO 3
−-N concentration sharply dropped, which may be attributed to lower ammonium-oxidation rates as ammonium and organic matter
are depleted, and to an increase in NO 3
−-N consumption by microbial populations. Denitrification was inhibited, with a significant decrease as % water-filled pore
space lowered. We hypothesize that the sediment inorganic N content enhanced during sediment desiccation could be released
as part of the N pulse observed after sediment rewetting. However, the stream N availability after rewetting dried sediments
would differ depending on desiccation period duration. 相似文献
6.
We investigated the effects of removing near-stream Rhododendron and of the natural blowdown of canopy trees on nutrient export to streams in the southern Appalachians. Transects were instrumented
on adjacent hillslopes in a first-order watershed at the Coweeta Hydrologic Laboratory (35°03′N, 83°25′W). Dissolved organic
carbon (DOC), K +, Na +, Ca 2+, Mg 2+, NO 3
−-N, NH 4
+-N, PO 4
3−-P, and SO 4
2− were measured for 2 years prior to disturbance. In August 1995, riparian Rhododendron on one hillslope was cut, removing 30% of total woody biomass. In October 1995, Hurricane Opal uprooted nine canopy trees
on the other hillslope, downing 81% of the total woody biomass. Over the 3 years following the disturbance, soilwater concentrations
of NO 3
−-N tripled on the cut hillslope. There were also small changes in soilwater DOC, SO 4
2−, Ca 2+, and Mg 2+. However, no significant changes occurred in groundwater nutrient concentrations following Rhododendron removal. In contrast, soilwater NO 3
−-N on the storm-affected hillslope showed persistent 500-fold increases, groundwater NO 3
−-N increased four fold, and streamwater NO 3
−-N doubled. Significant changes also occurred in soilwater pH, DOC, SO 4
2−, Ca 2+, and Mg 2+. There were no significant changes in microbial immobilization of soil nutrients or water outflow on the storm-affected hillslope.
Our results suggest that Rhododendron thickets play a relatively minor role in controlling nutrient export to headwater streams. They further suggest that nutrient
uptake by canopy trees is a key control on NO 3
−-N export in upland riparian zones, and that disruption of the root–soil connection in canopy trees via uprooting promotes
significant nutrient loss to streams.
Received 30 January 2001; accepted 25 July 2002. 相似文献
7.
Two novel denitrifying bacteria were successfully isolated from industrial wastewater and soil samples. Using morphological,
biochemical/biophysical and 16S rRNA gene analyses, these two bacteria were identified as Stenotrophomonas sp. ZZ15 and Oceanimonas sp. YC13, respectively. Both of these two bacteria showed efficient NO 3
−-N removing abilities under a semi-anaerobic condition without obvious accumulation of NO 2
−-N, N 2O-N and NH 4
+-N. NO 3
−-N removal from paper mill wastewater was also successful by treatments with either a denitrifier or an immobilization method.
Therefore, this study provides valuable denitrifying bacteria in biotreatment of industrial wastewater and other environmental
pollution caused by NO 3
−/NO 2
−. 相似文献
8.
Humans have increased the availability of nutrients including nitrogen and phosphorus worldwide; therefore, understanding
how microbes process nutrients is critical for environmental conservation. We examined nutrient limitation of biofilms colonizing
inorganic (fritted glass) and organic (cellulose sponge) substrata in spring, summer, and autumn in three streams in Michigan,
USA. Biofilms were enriched with nitrate (NO 3
−), phosphate (PO 4
3−), ammonium (NH 4
+), NO 3
− + PO 4
3−, NH 4
+ + PO 4
3−, or none (control). We quantified biofilm structure and function as chlorophyll a (i.e., primary producer biomass) and community respiration on all substrata. In one stream, we characterized bacterial and
fungal communities on cellulose in autumn using clone library sequencing and denaturing gradient gel electrophoresis to determine
if community structure was linked to nutrient limitation status. Despite oligotrophic conditions, primary producer biomass
was infrequently nutrient limited. In contrast, respiration on organic substrata was frequently limited by N + P combinations.
We found no difference between biofilm response to NH 4
+ versus NO 3
− enrichment, although the response to both N-species was positively related to water column PO 4
3− concentrations and temperature. Molecular analysis for fungal community composition suggested no relationship to nutrient
limitation, but the dominant members of the bacterial community on cellulose were different on NO 3
−, PO 43, and NO 3
− + PO 4
3− treatments relative to control, NH 4
+, and NH 4
+ + PO 4
3− treatments, which matched patterns for biofilm respiration rates from each treatment. Our results show discrete patterns
of nutrient limitation dependent upon substratum type and season, and imply changes in bacterial community structure and function
may be linked following nutrient enrichment in streams. 相似文献
9.
The impacts of various nitrogen sources, i.e. NO −
3, NH 4
+ or NH 4NO 3 in combination with gaseous NH 3, on nitrogen-, carbon- and water-use efficiency and 13C discrimination (δ 13C) by plants of the C 3 species Triticum aestivum L. (wheat) and the C 4 species Zea mays L. (maize) were studied. Triticum aestivum and Z. mays were hydroponically grown with 2 mol · m −3 of N supplied as NO −
3, NH 4
+ or NH 4NO 3 for 21 and 18 d, respectively, and thereafter exposed to gaseous NH 3 at 320 μg · m −3 or to ambient air for 7 d. In T. aestivum and Z. mays over a 7-d growth period, nitrogen-use efficiency (NUE) values were influenced by N-sources in the decreasing order NH 4NO 3-N > NO −
3-N > NH 4
+-N and NO −
3-N > NH 4NO 3-N > NH 4
+-N, respectively. Fumigation with NH 3 decreased the NUE values of plants grown with any of the N-forms. During 28- and 7-d growth periods, N-sources affected water-use
efficiency (WUE) values in the decreasing order of NH 4
+-N > NO −
3-N≈NH 4NO 3-N in non-fumigated T. aestivum, while fumigation with NH 3 increased the WUE of NO −
3-grown plants. There were insignificant effects of N-sources on WUE values of Z. mays over 25- and 7-d growth periods. Furthermore, δ 13C values in plant tissues (leaves, stubble and roots) were higher (less negative) in NH 4
+-grown plants of T. aestivum and Z. mays than in those supplied with NH 4NO 3 or NO −
3. Regardless of the N-form supplied to the roots of the plant species, exposure to NH 3 caused more-positive δ 13C values in the plant tissues. These results indicate that the variations in N-source were associated with small but significant
variations in δ 13C values in plants of T. aestivum and Z. mays. These differences in δ 13C values are in the direction expected from differences in WUE values over long or short growth periods and with differences
in the extent of non-Rubisco (ribulose-1,5-bisphosphate carboxylase-oxygenase, EC 4.1.1.39) carboxylate contribution to net
C acquisition, as a function of N-source.
Received: 12 September 1997 / Accepted: 13 January 1998 相似文献
10.
森林群落在净化空气、截留沉降污染物、改善地表水质等方面具有重要作用。本研究以北亚热带地区3种典型森林群落(毛竹林、杉木林、青冈阔叶林)为研究对象,通过分析沉降污染物(NH 4+-N、NO 3--N、NO 2--N、TP和SO 42-)在大气降水、林内穿透雨、树干茎流、枯透水和地表径流中的浓度和通量变化特征,探讨不同森林群落对氮、磷、硫的截留净化作用和分配特征。结果表明,该区域大气降水中NH 4+-N、NO 3--N、NO 2--N、TP和SO 42-年均浓度分别为1.06、0.61、0.04、0.07、1.84 mg/L,其年均pH为5.88;各森林群落林冠层能够调升降雨的pH且全年稳定,对TP和NH 4+-N均有吸附作用,截留率分别为79.09%-84.68%和30.88%-69.36%;而枯落物层则是林下氮、磷、硫的主要释放源,对NH 4+-N、NO 3--N、TP和SO 42-均具有淋溶作用;此外,由地表径流(输出)与大气降水(输入)的对比分析可知,各林地对沉降污染物中氮、磷、硫的截留率均超过98%;3种森林群落对沉降污染物中氮、磷、硫的截留能力依次为:青冈阔叶林 > 毛竹林 > 杉木林,阔叶林对沉降污染物的净化能力要高于毛竹林及针叶的杉木林。 相似文献
11.
通过对九龙江河口区陆基养虾塘水样和沉积物样品采集分析及结合室内模拟实验,探讨了虾塘在不同养殖阶段沉积物-水界面营养盐通量时间变化特征及其主要影响因素。虾塘沉积物向上覆水体释放NO_x~--N(NO_2~--N和NO_3~--N)、NH_4~+-N和PO_4~(3-)-P能力均呈现随养殖时间推移而降低的特征。沉积物在养殖中期和后期分别呈现对上覆水体NO_x~--N和PO_4~(3-)-P的吸收现象,但总体表现为释放(平均通量分别为(1.87±1.15)、(1.58±0.52)mg m~(-2)h~(-1)和(1.22±0.62)mg m~(-2)h~(-1))。沉积物-水界面溶解无机氮交换以NH_4~+-N为主(沉积物平均释放通量为(46.18±13.82)mg m~(-2)h~(-1))。沉积物间隙水与上覆水间的营养盐浓度差(梯度)及温度对上述交换通量的时间动态特征具有重要调控作用。研究结果表明养殖初期或中期沉积物较高的无机氮(尤其是NO_2~--N和NH_4~+-N)释放是养殖塘水质恶化的一个极具潜力的污染内源,可能会对虾的健康生长产生负面效应,控制沉积物无机氮释放是养虾塘养殖初期和中期重要的日常管理活动之一。 相似文献
12.
Using vegetative propagules (ramuli) of the iota carrageenan producing red seaweed Solieria chordalis, a maximum growth rate of 6.8% d −1 was achieved when cultured at 20 °C and 100 μmol photon m −2 s −1 in seawater supplemented with 20 μM NO 3-N or 10 μM NO 3-N plus 10 μM NH 4-N. Ramuli grew less well when nitrogen was supplied solely as NH
4
+
. Maximum carrageenan content was observed at the same temperature, irradiance and salinity as growth, but at lower nitrogen
concentrations. These findings are discussed in relation to results obtained from studies on other iota-carrageenan producing
carrageenophytes. 相似文献
13.
Heterotrophic carbon utilizing microbes were acclimatized in the laboratory by inoculating sludge collected from the waste
discharge pond of a small-scale rural abattoir in India in a nutrient solution intermittently fed with glucose and ammonium
chloride. Cultures of 10 well-developed isolates were selected and grown in a basal medium containing glucose and ammonium
chloride. Culture supernatants were periodically analyzed for ammonium nitrogen (NH 4
+-N) and chemical oxygen demand (COD). Polyphasic taxonomic study of the most active nitrifier (S18) was done. Half saturation
concentration ( K
s), maximum rate of substrate utilization ( k), yield coefficient ( Y) and decay coefficient ( K
d) were determined from the Lineweaver–Burk plot using the modified Monod equation. S18 was able to remove 97 ± 2% of (NH 4
+-N) and 88 ± 3% of COD. Molecular phylogenetic study supported by physiological and biochemical characteristics assigned S18
as Achromobacter xylosoxidans. Nitrification activity of A. xylosoxidans was demonstrated for the first time, while interestingly, the distinctive anaerobic denitrification property was preserved
in S18. K
s values were determined as 232.13 ± 1.5 mg/l for COD reduction and 2.131 ± 1.9 mg/l for NH 4
+-N utilization. Yield coefficients obtained were 0.4423 ± 0.1134 mg of MLVSS/mg of COD and 0.2461 ± 0.0793 mg of MLVSS/mg
of NH 4
+-N while the decay coefficients were 0.0627 ± 0.0013 per day and 0.0514 ± 0.0008 per day, respectively . After a contact period of 24 h, 650 ± 5 mg/l solids were produced when the initial concentration of COD and NH 4
+-N were 1820 ± 10 mg/l and 120 ± 5.5 mg/l, respectively. This is the first report on the kinetic coefficients for carbon oxidation
and nitrification by a single bacterium isolated from slaughterhouse wastewater. 相似文献
14.
In the pH 6.6 Na 2HPO 4–NaH 2PO 4 buffer solutions and in the presence of urease catalyst, urea can be decomposed to form NH 4
+. The NH 4
+ reacted with sodium tetraphenyl boron (NaTPB) to form the association particles that exhibited a resonance scattering (RS)
peak at 474 nm. When the urea concentration increased, NH 4
+ increased, and RS intensity at 474 nm enhanced linearly. Under the chosen conditions, the increased RS intensity (Δ I
474 nm) had a linear response to the urea concentration in the range of 0.125–15 μM, with a detection limit of 0.058 μM urea, and
a regression equation of Δ I
474 nm = 31.6 C + 2.1, a correlation coefficient of 0.9986. This catalytic RS method was applied for the detection of urea in human serum
sample, with good selectivity and sensitivity, and the results were consistent with the reference method. 相似文献
15.
Withania somnifera is an important medicinal plant that contains withanolides and withaferins, both bioactive compounds. We have tested the
effects of macroelements and nitrogen source in W. somnifera cell suspension cultures with the aim of optimizing the production of biomass and withanolide A. The effects of the macroelements
NH 4NO 3, KNO 3, CaCl 2, MgSO 4 and KH 2PO 4 at concentrations of 0.0, 0.5, 1.0, 1.5 and 2.0× strength and of the nitrogen source [NH 4
+/NO 3
− (mM/mM) ratio of: 0.00/18.80, 7.19/18.80, 14.38/18.80, 21.57/18.80, 28.75/18.80, 14.38/0.00, 14.38/9.40, 14.38/18.80, 14.38/28.20,
and 14.38/37.60 (mM)] in Murashige and Skoog medium were tested for biomass and withanolide A production. The highest accumulation
of biomass [147.81 g l −1 fresh weight (FW) and 14.02 g l −1 (dry weight (DW)] was recorded in the medium containing a 0.5× concentration of NH 4NO 3, and the highest production of withanolide A content was recorded in the medium with 2.0× KNO 3 (4.36 mg g −1 DW). The NH 4
+/NO 3
− ratio also influenced cell growth and withanolide A production, with both parameters being larger when the NO 3
− concentration was higher than that of NH 4
+. Maximum biomass growth (110.45 g l −1 FW and 9.29 g l −1 DW) was achieved at an NH 4
+/NO 3
− ratio of 7.19/18.80, while withanolide A production was greatest (3.96 mg g −1 DW) when the NH 4
+/NO 3
− ratio was 14.38/37.60 mM. 相似文献
16.
We test the hypothesis that the biodiversity of the death assemblage of shelled molluscs (gastropods and bivalves) on a single sandflat is representative of the biodiversity of the regional living fauna from the complete spectrum of habitat types, and can therefore be used as a surrogate for the purposes of rapid biodiversity assessment. Two biodiversity indices considered appropriate for such an assessment are average taxonomic distinctness ( +) and the variation in taxonomic distinctness ( +), which are, respectively, measures of the degree to which the species are taxonomically related to each other (i.e. the average taxonomic spread), and the degree to which taxa are over or under represented (i.e. the evenness of the distribution across the taxonomic tree). In each case, measured values were compared with the regional living species pool using a randomisation test. Collections and identifications of shells were made by both a non-expert in mollusc taxonomy and by taxonomic experts, the latter using microscopic examination of sediment samples as well as simple surface searches for macro-species. In all studies, + for the gastropods in the death assemblage was fully representative of the regional living fauna, but for bivalves it was significantly lower. This is because most of the bivalves were characteristic of the sandflat habitat, which introduced a bias, whereas post-mortem transport of gastropods, characterising exotic habitats, is more random. For gastropods, in all studies but one, + was significantly higher than expected from a random sample of the regional species pool, and for bivalves this was the case for all studies, suggesting the over-representation of some taxa and the under-representation of others. For the total shelled molluscan fauna (gastropods + bivalves) all + values were below, and all + values above, expectation. Results obtained by experts and a non-expert in mollusc taxonomy did not differ. In general, death assemblages at a single location are only likely to be representative of a wider region if there is randomisation as a result of post-mortem transport processes. 相似文献
17.
Elevation of the external potassium concentration induced a two-phase inward current in freshly isolated pyramidal hippocampal
neurons. This current was voltage-dependent and demonstrated strong inward rectification. The current consisted of a leakage
current and a time-dependent current (τ=40–50 msec at 21°C); the latter was designated as I
ΔK. As was shown earlier, K + is a major charge carrier in the development of slow potassium-activated current. The pharmacological properties of I
ΔK were studied using a patch-clamp technique. I
ΔK was completely blocked by external 10 mM TEA or 5 mM Ba 2+ (IC 50=480±90 mM) and exhibited low sensitivity to extracellular Cs + (2 mM). This current was not affected by 1 mM 4-aminopyridine and was insensitive to a muscarinic agonist, carbachol (50
μM), and to 1 mM extracellular Cd 2+. Elevation of external Ca 2+ from 2.5 mM to 10 mM did not change I
ΔK. Our data indicate that the pharmacological properties of I
ΔK differ from those of other voltage-gated potassium currents, but more specific blockers must be used to make this evidence
conclusive. 相似文献
18.
Nitrogen relations of natural and disturbed tropical plant communities in northern Australia (Kakadu National Park) were
studied. Plant and soil N characteristics suggested that differences in N source utilisation occur at community and species
level. Leaf and xylem sap N concentrations of plants in different communities were correlated with the availability of inorganic
soil N (NH +
4 and NO −
3). In general, rates of leaf NO −
3 assimilation were low. Even in communities with a higher N status, including deciduous monsoon forest, disturbed wetland,
and a revegetated mine waste rock dump, levels of leaf nitrate reductase, xylem and leaf NO −
3 levels were considerably lower than those that have been reported for eutrophic communities. Although NO −
3 assimilation in escarpment and eucalypt woodlands, and wetland, was generally low, within these communities there was a suite
of species that exhibited a greater capacity for NO −
3 assimilation. These “high- NO −
3 species” were mainly annuals, resprouting herbs or deciduous trees that had leaves with high N contents. Ficus, a high-NO −
3 species, was associated with soil exhibiting higher rates of net mineralisation and net nitrification. “Low-NO −
3 species” were evergreen perennials with low leaf N concentrations. A third group of plants, which assimilated NO −
3 (albeit at lower rates than the high-NO −
3 species), and had high-N leaves, were leguminous species. Acacia species, common in woodlands, had the highest leaf N contents of all woody species. Acacia species appeared to have the greatest potential to utilise the entire spectrum of available N sources. This versatility in
N source utilisation may be important in relation to their high tissue N status and comparatively short life cycle. Differences
in N utilisation are discussed in the context of species life strategies and mycorrhizal associations.
Received: 5 July 1997 / Accepted: 13 July 1998 相似文献
19.
The current expansion of Phragmites australis into the high marsh shortgrass ( Spartina patens, Distichlis spicata) communities of eastern U.S. salt marshes provided an opportunity to identify the influence of vegetation types on pools
and fluxes of dissolved inorganic nitrogen (DIN). Two brackish tidal marshes of the National Estuarine Research Reserve system
were examined, Piermont Marsh of the Hudson River NERR in New York and Hog Island in the Jacques Coustaeu NERR of New Jersey.
Pools of DIN in porewater and rates of DIN surface flux were compared in replicated pairs of recently-expanded P. australis and neighboring S. patens-dominated patches on the high marsh surface. Both marshes generally imported nitrate (NO 3−) and exported ammonium (NH 4+), such that overall DIN was exported. No differences in surface exchange of NO 3− or NH 4+ were observed between vegetation types. Depth-averaged porewater NH 4+ concentrations over the entire growing season were 56% lower under P. australis than under S. patens (average 1.4 vs. 3.2 mg NH 4+ L −1) with the most profound differences in November. Porewater profiles showed an accumulation of NH 4+ at depth in S. patens and constant low concentrations in P. australis from the soil surface to 50 cm depth, with no significant differences in porewater salinity. Despite these profound differences
in porewater, NH 4+ diffusion from soils of P. australis and S. patens were not measurably different, were similar to other published rates, and were well below estimated rates based on passive
diffusion alone. Rapid adsorption and uptake by litter and microbes in surface soils of both communities may buffer NH 4+ loss to flooding tides in both communities, thereby reducing the impact of P. australis invasion on NH 4+ flux to flooding waters. 相似文献
20.
城乡交错带土壤氮素是城乡生态系统中最重要的氮源与氮汇,但是城市化下的土壤氮素分布及其影响机制还不清楚,基于3S平台研究了土壤氮素在成都西郊城乡交错带的空间分布特征及城市化对土壤氮素的影响。结果表明,研究区内土壤全氮(STN)、硝态氮(NO_3~--N)和铵态氮(NH_4~+-N)含量均值分别为(1.46±0.06)g/kg、(50.04±3.59)mg/kg和(6.72±0.53)mg/kg。区内土壤氮素含量从近郊向远郊逐渐增高,STN和NO_3~--N含量为中部高于南北部,NH_4~+-N含量则由西北部和东南部向中部递增。方差分析表明,区内不同土地利用方式下STN、NO_3~--N和NH_4~+-N含量差异显著(P0.05)。回归分析显示STN含量与建筑密度(BD)、道路密度(RD)均呈现显著线性负相关(P0.05),NO_3~--N含量与道路密度呈极显著线性负相关(P=0.001),与建筑密度关系不明显(P=0.217)。土壤NH_4~+-N与建筑密度呈显著负线性相关(P=0.001),与道路密度呈显著指数相关关系(P=0.021)。研究结果显示城市发展使得城乡交错带土壤氮素含量降低,这种影响伴随着建筑面积的增加,道路长度的增加而加强。 相似文献
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