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1.
María Fernanda Adame Ruth Reef Jorge A. Herrera-Silveira Catherine E. Lovelock 《Hydrobiologia》2012,691(1):239-253
Poor water quality affects the biogeochemistry functions and the biological community structure of coastal ecosystems. In this study we investigated the effect of water quality on: (a) The exchange of dissolved organic carbon (DOC) between floodwater and mangrove forests, (b) the abundance of sediment bacteria, (c) the microbial community composition, and (d) the microbial catabolic activity. We selected six mangrove forests that were flooded by creeks with differing water qualities to test for thresholds of nutrient concentrations associated with changes in DOC dynamics and the microbial community. Our results show that in sites flooded by water high in soluble reactive phosphorus (SRP) (>20 μg l−1) and NH4 + (>30 μg l−1) the DOC concentrations in the floodwater were higher than in ebb water, suggesting DOC import by the mangroves. In contrast, in sites flooded by water low in SRP (<20 μg l−1) and NH4 + (<30 μg l−1), DOC concentrations in the floodwater were lower than in the ebb water, suggesting DOC export by the mangroves. Bacterial abundance was higher in sediments with low bulk density, high organic carbon and when flooded by water with low N:P (1–2), but the microbial composition and total catabolic activity assessed using Biolog Ecoplates™ did not differ among sites. The relationship between water quality, microbial communities and DOC exchange suggests that, at least during some periods of the year, poor water quality increases bacterial abundance and modifies DOC exchange of mangrove forests with floodwater and thus, their role in supporting near-shore productivity. 相似文献
2.
Dissolved organic carbon (DOC) plays an important role in surface water chemistry and ecology and trends in DOC concentration
have been also associated with shifts in terrestrial carbon pools. Numerous studies have reported long-term trends in DOC
concentration; however, some studies consider changes in average measured DOC whereas other compute discharge weighted concentrations.
Because of differences in reporting methods and variable record lengths it is difficult to compare results among studies and
make regional generalizations. Furthermore, changes in stream discharge may impact long-term trends in DOC concentration and
the potentially subtle effect of shifts in stream flow may be missed if only measured DOC concentrations are considered. In
this study we compare trends in volume-weighted vs. average measured DOC concentration between 1980 and 2001 at seven headwater
streams in south-central Ontario, Canada that vary in wetland coverage and DOC (22-year mean vol. wt.) from 3.4 to 10.6 mg l−1. On average, annual measured DOC concentrations were 13–34% higher than volume-weighted values, but differences of up to
290% occurred in certain years. Estimates of DOC flux were correspondingly higher using measured concentration values. Both
measured and volume-weighted DOC concentrations increased significantly between 1980 and 2001, but slopes were larger in measured
data (0.04–0.35 mg l−1 year−1 compared with 0.05–0.15 mg l−1 year−1) and proportional increases at the most wetland-influenced sites ranged from 32 to 43% in volume-weighted DOC and from 52
to 75% in measured DOC. In contrast, DOC flux did not change with time when estimated using either method, because of the
predominant influence of stream flow on DOC export. Our results indicate that changes in stream flow have an important impact
on trends in DOC concentration, and extrapolation of trend results from one region to another should be made cautiously and
consider methodological and reporting differences among sites. 相似文献
3.
Dissolved Nitrogen, Phosphorus, and Sulfur forms in the Ecosystem Fluxes of a Montane Forest in Ecuador 总被引:1,自引:0,他引:1
Rainer Goller Wolfgang Wilcke Katrin Fleischbein Carlos Valarezo Wolfgang Zech 《Biogeochemistry》2006,77(1):57-89
The N, P, and S cycles in pristine forests are assumed to differ from those of anthropogenically impacted areas, but there
are only a few studies to support this. Our objective was therefore to assess the controls of N, P, and S release, immobilization,
and transport in a remote tropical montane forest. The study forest is located on steep slopes of the northern Andes in Ecuador.
We determined the concentrations of NO3-N, NH4-N, dissolved organic N (DON), PO4-P, dissolved organic P (DOP), SO4-S, dissolved organic S (DOS), and dissolved organic C (DOC) in rainfall, throughfall, stemflow, lateral flow (in the organic
layer), litter leachate, mineral soil solution, and stream water of three 8–13 ha catchments (1900–2200 m a.s.l.). The organic
forms of N, P, and S contributed, on average, 55, 66, and 63% to the total N, P, and S concentrations in all ecosystem fluxes,
respectively. The organic layer was the largest source of all N, P, and S species except for inorganic P and S. Most PO4 was released in the canopy by leaching and most SO4 in the mineral soil by weathering. The mineral soil was a sink for all studied compounds except for SO4. Consequently, concentrations of dissolved inorganic and organic N and P were as low in stream water (TDN: 0.34–0.39 mg N l−1, P not detectable) as in rainfall (TDN: 0.39–0.48 mg N l−1, P not detectable), whereas total S concentrations were elevated (stream water: 0.04–0.15, rainfall: 0.01–0.07 mg S l−1). Dissolved N, P, and S forms were positively correlated with pH at the scale of soil peda except inorganic S. Soil drying
and rewetting promoted the release of dissolved inorganic N. High discharge levels following heavy rainstorms were associated
with increased DOC, DON, NO3-N and partly also NH4-N concentrations in stream water. Nitrate-N concentrations in the stream water were positively correlated with stream discharge
during the wetter period of the year. Our results demonstrate that the sources and sinks of N, P, and S were element-specific.
More than half of the cycling N, P, and S was organic. Soil pH and moisture were important controls of N, P, and S solubility
at the scale of individual soil peda whereas the flow regime influenced the export with stream water. 相似文献
4.
To determine the chemical and physicochemical characteristics of dissolved organic carbon in the Ado River and the Yasu River,
the main rivers flowing into Lake Biwa, the adsorption behavior onto hydrous iron oxide (HIO) and the reactivity to KMnO4 oxidant were investigated in parallel with measurement of the distribution profiles of dissolved organic carbon (DOC) along
the rivers. In one year of observation at the mouths of the two rivers, DOC concentrations were found to vary in the Ado over
the range 0.28–1.21 mg C l−1 and in the Yasu over the range 1.01–2.68 mg C l−1. Act-DOC, one of the fractions separated from the total DOC by its adsorption-active character onto HIO at pH 4, was thought
primarily to control the variation of total DOC, as in Lake Biwa. The int-DOC, another fraction separated by its adsorption-inert
or -inactive character onto HIO, remained at almost a steady value around 0.18 ± 0.07 mg C l−1 in the Ado, which was lower than that (0.35 ± 0.05 mg C l−1) in Lake Biwa. The act-DOC in river waters was reactive to KMnO4 oxidant, showing a linear relation with the amount of permanganate consumed for the reaction (chemical oxygen demand: COD).
In river waters, the relation can be approximated by a straight line expressed as COD (mg O2 l−1) = 0.64 × act-DOC (mg C l−1) − 0.02. In contrast, in the lake water the relation was COD (mg O2 l−1) = 0.97 × act-DOC (mg C l−1) − 0.50.
Received: March 3, 1999 / Accepted: December 2, 1999 相似文献
5.
It has long been assumed that the peat underlying tropical peat swamp forests accumulates because the extreme conditions (water
logged, nutrient poor, anaerobic and acidic—pH 2.9–3.5) impede microbial activity. Litterbag studies in a tropical Malaysian
peat swamp (North Selangor peat swamp forest) showed that although the sclerophyllous, toxic leaves of endemic peat forest
plants (Macaranga pruinosa, Campnosperma coriaceum, Pandanus atrocarpus, Stenochlaena palustris) were barely decomposed by bacteria and fungi (decay rates of only 0.0006–0.0016 k day−1), leaves of M. tanarius, a secondary forest species were almost completely decomposed (decay rates of 0.0047–0.005 k day−1) after 1 year. Thus it is intrinsic properties of the leaves (that are adaptations to deter herbivory in the nutrient poor
environment) that impede microbial breakdown. The water of the peat swamp was very high in dissolved organic carbon (70–84 mg l−1 DOC). Laboratory studies revealed initial rapid leaching of DOC from leaves (up to 1,720 mg l−1 from 4 g of leaves in 7 days), but the DOC levels then fell rapidly. The leaching of DOC resulted in weight loss but the
physical structure of the leaves remained intact. It is suggested that the DOC is used as a substrate for microbial growth
hence lowering the concentration of DOC in the water and transferring energy from the leaves to other trophic levels. This
would explain how nutrient poor tropical peatswamps support diverse, abundant flora and fauna despite low nutrient levels
and lack of rapid litter cycling such as occurs in other types of tropical rainforests. 相似文献
6.
Samir C. Debnath Kenneth B. McRae 《In vitro cellular & developmental biology. Plant》2001,37(2):243-249
Summary Cultures of two eranberry (Vaccinium macrocarpon Ait.) cultivars, ‘Ben Lear’ and ‘Pilgrim’, and three eranberry clones from natural stands in Newfoundland were established
in a nutrient medium containing N6[2-isopentenyl]adenine (2iP) from nodal and/or shoot-tip explants obtained under aseptic conditions. The cultivars differed
in shoot regeneration in terms of shoot number per explant with various concentrations of 2iP over two culture periods. Best
total shoot production was obtained when nodal segments were cultured in the medium supplemented with 2.5–5.0 mg 2iP l−1 (12.3–24.6 μM). With higher 2iP levels, shoots did not expand and had a high mortality rate. Nodal explants of the three clones cultured
in the same nutrient medium supplemented with 2.5 mg 2iP l−1 (12.3 μM) produced three to five healthy axillary shoots per explant. In another experiment, nodal explants were more productive than
shoot tips. In all experiments with subculture, there was an increase in shoot multiplication rate for all genotypes. Shoots
were rooted in vitro in the same media used for shoot proliferation, but without any growth regulators. After their transfer to potting medium,
almost all of the rooted plants survived. Cranberry genotypes can be efficiently propagated and maintained through nodal culture
in a nutrient medium without auxin that contains 2.5–5 mg 2iP l−1 (12–25 μM). 相似文献
7.
We examined patterns of dissolved organic carbon (DOC) and total dissolved nitrogen (TDN) loading to a small urban stream
during baseflow and stormflow. We hypothesized that lower DOC and TDN contributions from impervious surfaces would dilute
natural hydrologic flowpath (i.e., riparian) contributions during storm events in an urban watershed, resulting in lower concentrations
of DOC and TDN during storms. We tested these hypotheses in a small urban watershed in Portland, Oregon, over a 3-month period
during the spring of 2003. We compared baseflow and stormflow chemistry using Mann–Whitney tests (significant at p<0.05). We also applied a mass balance to the stream to compare the relative significance of impervious surface contributions
versus riparian contributions of DOC and TDN. Results showed a significant increase in stream DOC concentrations during stormflows
(median baseflow DOC = 2.00 mg l−1 vs. median stormflow DOC = 3.46 mg l−1). TDN streamwater concentrations, however, significantly decreased with stormflow (median baseflow TDN = 0.75 mg l−1 vs. median stormflow TDN = 0.56 mg l−1). During storms, remnant riparian areas contributed 70–74% of DOC export and 38–35% of TDN export to the stream. The observed
pattern of increased DOC concentrations during stormflows in this urban watershed was similar to patterns found in previous
studies of forested watersheds. Results for TDN indicated that there were relatively high baseflow nitrogen concentrations
in the lower watershed that may have partially masked the remnant riparian signal during stormflows. Remnant riparian areas
were a major source of DOC and TDN to the stream during storms. These results suggest the importance of preserving near-stream
riparian areas in cities to maintain ambient carbon and nitrogen source contributions to urban streams. 相似文献
8.
Post treatment of effluents from heterotrophic groundwater denitrification fluidized bed reactors (FBR) designed to achieve
drinking water quality has been investigated. The denitrification process adds to the dissolved organic compounds, biomass
and bacteria in the effluent. They are also lacking dissolved oxygen. Effluents from the process were treated in combined
post treatment processes based on either a trickling filter and sedimentation unit (‘TF combination’) or contact flocculation
(‘CF combination’). Both processes were followed by sand filtration, granular activated carbon (GAC) and chlorination. Results
regarding total suspended solids (TSS) and turbidity removal showed an advantage to the ‘CF combination’, and the target turbidity
(NTU <1) was always achieved when the alum dose was 10 or 20 mg l−1. Backwash of the sand filter and GAC column was required after 27 h of operation (average value). An average total reduction
in dissolved organic carbon (DOC) of 40% was observed with a final DOC of 3.5–4 mg L−1. Most of the removal of the DOC occurred in the sand filter (28%), while the GAC contribution was smaller (18%). No regrowth
potential was observed using the Werner method when a pure culture of Pseudomonas fluorescens P17 was used as inoculum in samples of chlorinated effluent (post chlorination). When a mixed culture of indigenous bacteria
was used as inoculum, a high regrowth potential was observed. Installing an additional chlorination unit before the sand filter
column (pre and post chlorination) resulted in effluent with no regrowth potential for both Pseudomonas fluorescens P17 and indigenous bacteria.
Received 17 October 1997/ Accepted in revised form 29 May 1998 相似文献
9.
Céline Guéguen Laodong Guo Deli Wang Noriyuki Tanaka Chin-Chang Hung 《Biogeochemistry》2006,77(2):139-155
Monthly (or bi-weekly) water samples were collected from the Yukon River, one of the largest rivers in North America, at a
station near the US Geological Survey Stevens Village hydrological station, Alaska from May to September 2002, to examine
the quantity and quality of dissolved organic matter (DOM) and its seasonal variations. DOM was further size fractionated
into high molecular weight (HMW or colloidal, 1 kDa–0.45 μm) and low molecular weight (LMW, <1 kDa) fractions. Dissolved organic
carbon (DOC), colored dissolved organic matter (C-DOM) and total dissolved carbohydrate (TCHO) species were measured in the
size fractionated DOM samples. Concentrations of DOC were as high as 2830 μmol-C l−1 during the spring breakup in May and decreased significantly to 508–558 μmol-C l−1 during open-water season (June–September). Within the DOC pool, up to 85% was in the colloidal fraction (1 kDa–0.45 μm) in
early May. As DOC concentration decreased, this colloidal portion remained high (70–85% of the bulk DOC) throughout the sampling
season. Concentrations of TCHO, including monosaccharides (MCHO) and polysaccharides (PCHO), varied from 722 μmol-C l−1 in May to 129 μmol-C l−1 in September, which comprised a fairly constant portion of bulk DOC (24±2%). Within the TCHO pool, the MCHO/TCHO ratio consistently
increased from May to September. The C-DOM/DOM ratio and the size fractionated DOM increased from May to September, indicating
that DOM draining into the Yukon River contained increased amounts of humified materials, likely related to a greater soil
leaching efficiency in summer. The average composition of DOM was 76% pedogenic humic matter and 24% aquagenic CHO. Characteristics
of soil-derived humic substances and low chlorophyll-a concentrations support a dominance of terrestrial DOM in Yukon River waters. 相似文献
10.
J. Y. Choi H. J. Kim C. H. Lee J. M. Bae Y. S. Chung J. S. Shin N. I. Hyung 《In vitro cellular & developmental biology. Plant》2001,37(2):274-279
Summary An efficient and simple plant regeneration system via organogenesis from leaf segments of persimmon (Diospyros kaki Thunb.) cultivars ‘Fuyu’ and ‘Nishimurawase’ has been developed. The regeneration capacity was influenced by the culture
vessels, gelling agents, plant growth regulators, and light conditions. Leaf explants taken from in vitro shoots were cultured on a modified Murashige and Skoog medium (MS1/2N), for 16 wk without transfer to fresh medium. Adventious
shoots appeared after 4 and 8 wk in culture of ‘Nishimurawase’ and ‘Fuyu’ tissues, respectively. The culture of leaf explants
in Erlenmeyer flasks with medium containing 4 g l−1 agar enhanced shoot formation in comparison to media with increased agar concentrations. Optimal shoot regeneration was obtained
with 5 mg l−1 (22.8 μM) zeatin and 0.1 mg l−1 (0.05 μM) indole-3-butyric acid (IBA) for ‘Nishimurawase’, and 10 mg l−1 (45.6 μM) zeatin and 0.1 mg l−1 (0.05 μM) IBA for ‘Fuyn’. Shoot regeneration frequencies in both cultivars were 100%, and shoot numbers per explant reached up to
9.2 for ‘Nishimurawase’ and 2.2 for ‘Fuyu’. Dark incubation during the first 4–5 wk was the most effective condition to successfully
influence shoot regeneration in both cultivars. While dark incubation was essential for adventitious shoot formation by ‘Fuyu’,
it was only slightly beneficial to ‘Nishimurawase’. More than 80% of the regenerated shoots rooted within 4 wk on hormone-free
MS1/2N demium after having been dipped for 30 s in 250 mg l−1 (1.1. mM) IBA solution. 相似文献
11.
Concentrations of plankton, suspended particles 0.74–87 μm equivalent spherical diameter and dissolved organic carbon (DOC)
were measured from May to February at an Antarctic coastal site. Bacteria-sized particles 0.74–1 μm diameter, and bacterial
cells and heterotrophic protists all exhibited a seasonal minimum during winter and maxima in summer. Bacteria composed <10%
of the bacteria-sized particles. Release of autotrophic protists from the ice caused water column biomass of autotrophs to
reach maximum concentrations in October and November, but maximum cell concentration in the water column was reached in January.
Microheterotroph biomass weakly reflected the release of the ice algal community but reached maximum concentration during
the water column bloom in January. Total DOC concentrations varied from 0.36 mg C l−1 in July to 3.10 mg C l−1 in October, with a yearly average of 1.51 mg C l−1. Ultrafiltration of DOC revealed that the molecular weight composition of the DOC differed greatly through the year. DOC
<5 kDa molecular weight reached a maximum of 1.25 mg C l−1 in October and accounted for up to 60% of total DOC in July. Concentrations of high molecular weight DOC (>100 kDa) were
highest in July and November, with the DOC (100 kDa–0.5 μm) fraction reaching a maximum of 1.22 mg C l−1 in November and composing 82% of the total DOC in January. Wet chemical oxidation and high-temperature catalytic oxidation
organic carbon analyses were compared. Good correlation was observed between methods during summer but no significant correlation
existed in winter, indicating that winter DOC may be refractory.
Accepted: 21 March 2000 相似文献
12.
Theophilus M. Mutui Vallantino E. Emongor Margaret J. Hutchinson 《Plant Growth Regulation》2006,48(3):207-214
Leaf yellowing is a major problem in Alstroemeria and absence of leaf senescence symptoms is an important quality attribute. Two Alstroemeria cultivars ‘Yellow King’ and ‘Marina’ were sourced from a commercial farm and harvested when sepals began to reflex. Stems
were re-cut under water and kept in vase solutions of gibberellin A4+7 (0, 2.5, 5.0, 7.5, 10.0, 12.5 or 15.0 mg l−1 [Provider]). Treatments and cultivars were combined in a factorial fashion and arranged in a completely randomised design. Application
of GA4+7 in the holding solution at 2.5–10.0 mg l−1 significantly delayed the onset of leaf senescence by around 7 days and significantly increased days to 50% petal fall by
ca. 2 days. Additionally, these GA4+7 concentrations resulted in higher retention of leaf nitrogen, leaf chlorophyll and also increased leaf water content, while
reducing leaf dry weight, all relative to untreated controls. Cultivar ‘Yellow King’ had significantly longer vase life and
a better retention of leaf quality than ‘Marina’. Our results suggest that a concentration of 10 mg l−1 GA4+7 can be used to prolong vase life, delay leaf senescence and enhance post-harvest quality of Alstroemeria cut flowers during their transport to market. 相似文献
13.
Plant regeneration from callus culture of a Paphiopedilum hybrid 总被引:4,自引:0,他引:4
Totipotent calli of a Paphiopedilum hybrid (Paphiopedilum callosum ‘Oakhi’ × Paph. lawrenceanum ‘Tradition’) were induced from seed-derived protocorms on a 1/2 strength Murashige–Skoog medium plus 1–10 mg l−1 2,4-dichlorophenoxyacetic acid (2,4-D) and 0.1–1 mg l−1 1-phenyl-3-(1.2.3-thiadiazol-5-yl)urea (TDZ). These calli grew well when subcultured on the same medium, but proliferated
more on 1/2 MS medium plus 5 mg l−1 2,4-D and 1 mg l−1 TDZ. Calli developed further along a route of production of protocorm-like bodies and eventually formed plantlets that could
be transplanted to pots and grew well.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
14.
Mark S. Johnson Johannes Lehmann Eduardo Guimarães Couto João Paulo Novães Filho Susan J. Riha 《Biogeochemistry》2006,81(1):45-57
Organic and inorganic carbon (C) fluxes transported by water were evaluated for dominant hydrologic flowpaths on two adjacent headwater catchments in the Brazilian Amazon with distinct soils and hydrologic responses from September 2003 through April 2005. The Ultisol-dominated catchment produced 30% greater volume of storm-related quickflow (overland flow and shallow subsurface flow) compared to the Oxisol-dominated catchment. Quickflow fluxes were equivalent to 3.2 ± 0.2% of event precipitation for the Ultisol catchment, compared to 2.5 ± 0.3% for the Oxisol-dominated watershed (mean response ±1 SE, n = 27 storms for each watershed). Hydrologic responses were also faster on the Ultisol watershed, with time to peak flow occurring 10 min earlier on average as compared to the runoff response on the Oxisol watershed. These different hydrologic responses are attributed primarily to large differences in saturated hydraulic conductivity (K
s). Overland flow was found to be an important feature on both watersheds. This was evidenced by the response rates of overland flow detectors (OFDs) during the rainy season, with overland flow intercepted by 54 ± 0.5% and 65 ± 0.5% of OFDs for the Oxisol and Ultisol watersheds respectively during biweekly periods. Small volumes of quickflow correspond to large fluxes of dissolved organic C (DOC); DOC concentrations of the hydrologic flowpaths that comprise quickflow are an order of magnitude higher than groundwater flowpaths fueling base flow (19.6 ± 1.7 mg l−1 DOC for overland flow and 8.8 ± 0.7 mg l−1 DOC for shallow subsurface flow versus 0.50 ± 0.04,mg l−1 DOC in emergent groundwater). Concentrations of dissolved inorganic C (DIC, as dissolved CO2–C plus HCO3−–C) in groundwater were found to be an order of magnitude greater than quickflow DIC concentrations (21.5 mg l−1 DIC in emergent groundwater versus 1.1 mg l−1 DIC in overland flow). The importance of deeper flowpaths in the transport of inorganic C to streams is indicated by the 40:1 ratio of DIC:DOC for emergent groundwater. Dissolved CO2–C represented 92% of DIC in emergent groundwater. Results from this study illustrate a highly dynamic and tightly coupled linkage between the C cycle and the hydrologic cycle for both Ultisol and Oxisol landscapes: organic C fluxes strongly tied to flowpaths associated with quickflow, and inorganic C (particularly dissolved CO2) transported via deeper flowpaths. 相似文献
15.
Modeled Effects of Dissolved Organic Carbon and Solar Spectra on Photobleaching in Lake Ecosystems 总被引:1,自引:0,他引:1
Dissolved organic matter (DOM) contains molecules that absorb light at various wavelengths. This chromophoric DOM (CDOM) influences
the transmission of both visible and ultraviolet energy through water. The absorption of light by CDOM often causes structural
changes that reduce its capacity to further absorb light, a process termed ‘photobleaching‘. A model was designed to assess
photobleaching through the entire water column of lake ecosystems. The model uses lake morphometry and dissolved organic carbon
(DOC) concentration in conjunction with a defined solar spectrum and experimentally measured photobleaching rates to compute
the total water columm photobleaching. The model was initially applied to a theoretical ‘average‘ lake using solar spectra
for both the north (N) and south (S) temperate western hemispheres and variable DOC from 0.3 to 30 mg L−1. The consequences of varying waveband-specific photobleaching coefficients and lake morphometry were explored in a second
set of simulations. Finally, the model was also applied to four temperate northern lakes for which we had prior measurements
of CDOM photobleaching rates. The model demonstrates that all three wavebands of solar radiation (UVB, UVA, and PAR) contribute
significantly to total water column photobleaching, with UVA being most important. The relative contributions of the three
wavebands were invariant for DOC more than 3 mg L−1. Total water column photobleaching at 440 nm was three to five times faster under the UV-enriched solar spectrum of the southern
hemisphere. Increasing the lake’s mean depth (from 0.37 to 9.39 m) resulted in five- or 15-fold slower rates of total water
column photobleaching for DOC concentrations of 1 or 10 mg L−1, respectively. Varying the waveband-specific photobleaching coefficients by 10-fold resulted in a similar change in total
water column photobleaching rates. Applying the model to four specific lakes revealed that photobleaching for the entire water
column would reduce CDOM light absorption by 50% in 18–44 days under summer conditions.
Received 17 November 1998; accepted 27 June 2000. 相似文献
16.
Leaching losses of inorganic N and DOC following repeated drying and wetting of a spruce forest soil
Forest soils are frequently subjected to dry–wet cycles, but little is known about the effects of repeated drying and wetting
and wetting intensity on fluxes of , and DOC. Here, undisturbed soil columns consisting of organic horizons (O columns) and organic horizons plus mineral soil
(O + M columns) from a mature Norway spruce stand at the Fichtelgebirge; Germany, were repeatedly desiccated and subsequently
wetted by applying different amounts of water (8, 20 and 50 mm day−1) during the initial wetting phase. The constantly moist controls were not desiccated and received 4 mm day−1 during the entire wetting periods. Cumulative inorganic N fluxes of the control were 12.4 g N m−2 (O columns) and 11.4 g N m−2 (O + M columns) over 225 days. Repeated drying and wetting reduced cumulative and fluxes of the O columns by 47–60 and 76–85%, respectively. Increasing (0.6–1.1 g N m−2) and decreasing fluxes (7.6–9.6 g N m−2) indicate a reduction in net nitrification in the O + M columns. The negative effect of dry–wet cycles was attributed to
reduced net N mineralisation during both the desiccation and wetting periods. The soils subjected to dry–wet cycles were considerably
drier at the final wetting period, suggesting that hydrophobicity of soil organic matter may persist for weeks or even months.
Based on results from this study and from the literature we hypothesise that N mineralisation is mostly constrained by hydrophobicity
in spruce forests during the growing season. Wetting intensity did mostly not alter N and DOC concentrations and fluxes. Mean
DOC concentrations increased by the treatment from 45 mg l−1 to 61–77 mg l−1 in the O tlsbba columns and from 12 mg l−1 to 21–25 mg l−1 in the O + M columns. Spectroscopic properties of DOC from the O columns markedly differed within each wetting period, pointing
to enhanced release of rather easily decomposable substrates in the initial wetting phases and the release of more hardly
decomposable substrates in the final wetting phases. Our results suggest a small additional DOC input from organic horizons
to the mineral soil owing to drying and wetting. 相似文献
17.
O. Boussadia K. Steppe H. Zgallai S. Ben El Hadj M. Braham R. Lemeur M. C. Van Labeke 《Photosynthetica》2011,49(1):149-153
For Tunisian olive tree orchards, nitrogen deficiency is an important nutritional problem, in addition to the availability
of water. Establishment of relationships between nutrients such as nitrogen and ecophysiological parameters is a promising
method to manage fertilisation at orchard level. Therefore, a nitrogen stress experiment with one-year-old olive trees (Olea europaea L. ‘Koroneiki’ and ‘Meski’) was conducted with trees respectively subjected to four nitrogen supply regimes (23.96 meq l−1, 9.58 meq l−1, 4.79 meq l−1 and 0 meq l−1 NO3
−1). 相似文献
18.
Effects of exogenous B supply on growth, B accumulation and distribution of two navel orange cultivars 总被引:3,自引:0,他引:3
Ou Sheng Shang W. Song Yun J. Chen Shu A. Peng Xiu X. Deng 《Trees - Structure and Function》2009,23(1):59-68
To investigate the effects of boron (B) on growth, B concentration and distribution of two navel orange cultivars, ‘Newhall’
(Citrus sinensis Osbeck) and ‘Skagg’s Bonanza’ (Citrus sinensis Osbeck) grafted on the rootstock trifoliate orange [Poncirus trifoliata (L.) Raf.], B at five levels was exogenously supplied to 1-year-old grafted plants of both cultivars under greenhouse conditions.
Plants were grown in sand:perlite (1:1, v/v) medium and were irrigated every 2 days with half-strength Hoagland’s No. 2 nutrient
solutions containing different B, 0.01, 0.05, 0.10, 0.25 and 2.50 mg l−1 (0.25 and 2.50 mg l−1 were considered as control and excess B treatment, respectively, and the other three B levels were considered as low B treatments).
After treatments for 183 days, leaves (from basal, middle, upper parts of the shoots), stem of scion, stem of rootstock and
root were separately sampled. Our results showed that plant growth (plant height, root volume and dry weights of various parts)
was inhibited in response to low or excess B supplies in both cultivars. It was found that B concentrations in the upper leaves
of both cultivars were substantially higher than those in the basal leaves when low concentrations (≤0.05 mg l−1) of exogenous B were applied, suggesting that B was preferentially translocated to the upper-younger leaves to support their
growth. Analysis of B distribution in different parts indicated that translocation of B from the root to the scion’s shoots
(stems and leaves of scion) may be restricted upon exposure to low B conditions. When B was inadequately supplied, growth
of ‘Skagg’s Bonanza’ was better than ‘Newhall’, implying that the former cultivar was more tolerant to low B status, which
may be due to the higher efficiency of B translocation from the root to the scion’s shoots. However, when the plants were
treated with excess B (2.50 mg l−1), both cultivars showed a similar degree of B toxicity. The probability of scion–rootstock interactions in relation to the
differential responses of growth and different efficiency of B translocation involved in the two orange cultivars following
the long-term low B stress were discussed. 相似文献
19.
The effects of nutrient enrichment on the release of dissolved organic carbon and nitrogen (DOC and DON, respectively) from
the coral Montipora digitata were investigated in the laboratory. Nitrate (NO3
−) and phosphate (PO4
3−) were supplied to the aquarium to get the final concentrations of 10 and 0.5 μmol l−1, respectively, and the corals were incubated for 8 days. The release rate of DON per unit coral surface area significantly
decreased after the nutrient enrichment, while the release rate of DOC was constant. Because the chlorophyll a (chl a) content of zooxanthellae per unit surface area increased, the release rate of DOC significantly decreased when normalized
to unit chl a. These results suggested that the incorporation of NO3
− and PO4
3− stimulated the synthesis of new cellular components in the coral colonies and consequently, reduced extracellular release
of DOC and DON. Actually, significant increase in N and P contents relative to C content was observed in the coral’s tissue
after the nutrient enrichment. The present study has concluded that inorganic nutrient enrichment not only affects coral-algal
metabolism inside the colony but also affects a microbial community around the coral because the organic matter released from
corals functions as energy carrier in the coral reef ecosystem. 相似文献
20.
Algesten G Sobek S Bergström AK Jonsson A Tranvik LJ Jansson M 《Microbial ecology》2005,50(4):529-535
We measured sediment production of carbon dioxide (CO2) and methane (CH4) and the net flux of CO2 across the surfaces of 15 boreal and subarctic lakes of different humic contents. Sediment respiration measurements were
made in situ under ambient light conditions. The flux of CO2 between sediment and water varied between an uptake of 53 and an efflux of 182 mg C m−2 day−1 from the sediments. The mean respiration rate for sediments in contact with the upper mixed layer (SedR) was positively correlated
to dissolved organic carbon (DOC) concentration in the water (r2 = 0.61). The net flux of CO2 across the lake surface [net ecosystem exchange (NEE)] was also closely correlated to DOC concentration in the upper mixed
layer (r2 = 0.73). The respiration in the water column was generally 10-fold higher per unit lake area compared to sediment respiration.
Lakes with DOC concentrations <5.6 mg L−1 had net consumption of CO2 in the sediments, which we ascribe to benthic primary production. Only lakes with very low DOC concentrations were net autotrophic
(<2.6 mg L−1) due to the dominance of dissolved allochthonous organic carbon in the water as an energy source for aquatic organisms. In
addition to previous findings of allochthonous organic matter as an important driver of heterotrophic metabolism in the water
column of lakes, this study suggests that sediment metabolism is also highly dependent on allochthonous carbon sources. 相似文献