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1.
Absorption of solar ultraviolet radiation (UVR) in aquatic ecosystems is primarily controlled by dissolved organic carbon
(DOC). The role of iron (Fe) has also been suggested to contribute to UVR attenuation either directly or by interactions with
DOC. Here we present findings from three laboratory manipulations of Fe and DOC on changes to the dissolved UVR absorption
(ad,320) in a mid-latitude, dimictic, humic lake. In a laboratory simulation of lake turnover where anoxic, hypolimnetic water was
oxygenated ad,320 significantly increased from 23.3 to 81.7 m−1 (p<0.0001). In a second laboratory experiment, addition of ferrous Fe to deoxygenated lake water increased ad,320 upon reoxygenation up to a concentration of 1.0 mg l−1 Fe, where a solubility saturation threshold may have been reached. In situ lake experiments were designed to simulate release of UV absorbing substances from anoxic sediments by placing 20-l carboys
(open at the bottom, sealed at the top) onto the lake bottom. UV absorption at 320 nm increased over time for samples from
within the experimental carboys. Finally, samples from several lake profiles and sediment experiments were analyzed for ad,320, total Fe, and DOC. UV absorption of dissolved substances at 320 nm and total Fe concentration both increased with depth,
however DOC remained relatively constant over depth. Furthermore, total Fe and spectral slope showed tight coupling up to
1 mg l−1 total Fe in our survey analysis. Our results provide evidence for the importance of anoxic sediments as a source of ferrous
iron and UV absorbing substances and suggest a role for ferric iron in increasing UVR and PAR absorption in lake water. We
suggest that as this ferrous Fe oxidizes, its absorptive properties increase, and it may bind with dissolved organic matter,
enabling it to remain in solution and thus increasing the dissolved absorption of lake water for extended periods of time. 相似文献
2.
Seasonal Variations of Dissolved Nitrogen and DOC:DON Ratios in an Intermittent Mediterranean Stream
Seasonal variations of dissolved inorganic nitrogen (DIN) (NO3–N and NH4–N) and dissolved organic nitrogen (DON) were determined in Fuirosos, an intermittent stream draining an unpolluted Mediterranean
forested catchment (10.5 km2) in Catalonia (Spain). The influence of flow on streamwater concentrations and seasonal differences in quality and origin
of dissolved organic matter, inferred from dissolved organic carbon to nitrogen ratios (DOC:DON ratios), were examined. During
baseflow conditions, nitrate and ammonium had opposite behaviour, probably controlled by biological processes such as vegetation
uptake and mineralization activity. DON concentrations did not have a seasonal trend. During storms, nitrate and DON increased
by several times but discharge was not a good predictor of nutrient concentrations. DOC:DON ratios in streamwater were around
26, except during the months following drought when DOC:DON ratios ranged between 42 and 20 during baseflow and stormflow
conditions, respectively. Annual N export during 2000–2001 was 70 kg km−1 year−1, of which 75% was delivered during stormflow. The relative contribution of nitrogen forms to the total annual export was
57, 35 and 8% as NO3–N, DON and NH4–N, respectively. 相似文献
3.
We established a long-term field study in an old growth coniferous forest at the H.J. Andrews Experimental Forest, OR, USA,
to address how detrital quality and quantity control soil organic matter accumulation and stabilization. The Detritus Input
and Removal Treatments (DIRT) plots consist of treatments that double leaf litter, double woody debris inputs, exclude litter
inputs, or remove root inputs via trenching. We measured changes in soil solution chemistry with depth, and conducted long-term
incubations of bulk soils from different treatments in order to elucidate effects of detrital inputs on the relative amounts
and lability of different soil C pools. In the field, the addition of woody debris increased dissolved organic carbon (DOC)
concentrations in O-horizon leachate and at 30 cm, but not at 100 cm, compared to control plots, suggesting increased rates
of DOC retention with added woody debris. DOC concentrations decreased through the soil profile in all plots to a greater
degree than did dissolved organic nitrogen (DON), most likely due to preferential sorption of high C:N hydrophobic dissolved
organic matter (DOM) in upper horizons; percent hydrophobic DOM decreased significantly with depth, and hydrophilic DOM had
a much lower and less variable C:N ratio. Although laboratory extracts of different litter types showed differences in DOM
chemistry, percent hydrophobic DOM did not differ among soil solutions from different detrital treatments in the field, suggesting
that microbial processing of DOM leachate in the field consumed easily degradable components, thus equalizing leachate chemistry
among treatments. Total dissolved N leaching from plots with intact roots was very low (0.17 g m−2 year−1), slightly less than measured deposition to this very unpolluted forest (~s 0.2 g m−2 year−1). Total dissolved N losses showed significant increases in the two treatments without roots whereas concentrations of DOC
decreased. In these plots, N losses were less than half of estimated plant uptake, suggesting that other mechanisms, such
as increased microbial immobilization of N, accounted for retention of N in deep soils. In long-term laboratory incubations,
soils from plots that had both above- and below-ground litter inputs excluded for 5 years showed a trend towards lower DOC
loss rates, but not lower respiration rates. Soils from plots with added wood had similar respiration and DOC loss rates as
control soils, suggesting that the additional DOC sorption observed in the field in these soils was stabilized in the soil
and not readily lost upon incubation. 相似文献
4.
The Role of Dissolved Organic Carbon, Dissolved Organic Nitrogen, and Dissolved Inorganic Nitrogen in a Tropical Wet Forest Ecosystem 总被引:3,自引:0,他引:3
Although tropical wet forests play an important role in the global carbon (C) and nitrogen (N) cycles, little is known about the origin, composition, and fate of dissolved organic C (DOC) and N (DON) in these ecosystems. We quantified and characterized fluxes of DOC, DON, and dissolved inorganic N (DIN) in throughfall, litter leachate, and soil solution of an old-growth tropical wet forest to assess their contribution to C stabilization (DOC) and to N export (DON and DIN) from this ecosystem. We found that the forest canopy was a major source of DOC (232 kg C ha–1 y–1). Dissolved organic C fluxes decreased with soil depth from 277 kg C ha–1 y–1 below the litter layer to around 50 kg C kg C ha–1 y–1 between 0.75 and 3.5m depth. Laboratory experiments to quantify biodegradable DOC and DON and to estimate the DOC sorption capacity of the soil, combined with chemical analyses of DOC, revealed that sorption was the dominant process controlling the observed DOC profiles in the soil. This sorption of DOC by the soil matrix has probably led to large soil organic C stores, especially below the rooting zone. Dissolved N fluxes in all strata were dominated by mineral N (mainly NO3−). The dominance of NO3– relative to the total amount nitrate of N leaching from the soil shows that NO3– is dominant not only in forest ecosystems receiving large anthropogenic nitrogen inputs but also in this old-growth forest ecosystem, which is not N-limited. 相似文献
5.
Large Loss of Dissolved Organic Nitrogen from Nitrogen-Saturated Forests in Subtropical China 总被引:5,自引:0,他引:5
Yunting Fang Weixing Zhu Per Gundersen Jiangming Mo Guoyi Zhou Muneoki Yoh 《Ecosystems》2009,12(1):33-45
Dissolved organic nitrogen (DON) has recently been recognized as an important component of terrestrial N cycling, especially
under N-limited conditions; however, the effect of increased atmospheric N deposition on DON production and loss from forest
soils remains controversial. Here we report DON and dissolved organic carbon (DOC) losses from forest soils receiving very
high long-term ambient atmospheric N deposition with or without additional experimental N inputs, to investigate DON biogeochemistry
under N-saturated conditions. We studied an old-growth forest, a young pine forest, and a young mixed pine/broadleaf forest
in subtropical southern China. All three forests have previously been shown to have high nitrate (NO3−) leaching losses, with the highest loss found in the old-growth forest. We hypothesized that DON leaching loss would be forest
specific and that the strongest response to experimental N input would be in the N-saturated old-growth forest. Our results
showed that under ambient deposition (35–50 kg N ha−1 y−1 as throughfall input), DON leaching below the major rooting zone in all three forests was high (6.5–16.9 kg N ha−1 y−1). DON leaching increased 35–162% following 2.5 years of experimental input of 50–150 kg N ha−1 y−1. The fertilizer-driven increase of DON leaching comprised 4–17% of the added N. A concurrent increase in DOC loss was observed
only in the pine forest, even though DOC:DON ratios declined in all three forests. Our data showed that DON accounted for
23–38% of total dissolved N in leaching, highlighting that DON could be a significant pathway of N loss from forests moving
toward N saturation. The most pronounced N treatment effect on DON fluxes was not found in the old-growth forest that had
the highest DON loss under ambient conditions. DON leaching was highly correlated with NO3− leaching in all three forests. We hypothesize that abiotic incorporation of excess NO3− (through chemically reactive NO2−) into soil organic matter and the consequent production of N-enriched dissolved organic matter is a major mechanism for the
consistent and large DON loss in the N-saturated subtropical forests of southern China.
Dr. YT Fang performed research, analyzed data, and wrote the paper; Prof. WX Zhu participated in the initial experimental
design, analyzed data, and took part in writing the paper; Prof. P Gundersen conceived the study and took part in writing;
Prof. JM Mo and Prof. GY Zhou conceived study; Prof. M Yoh analyzed part of the data and contributed to the development of
DON model. 相似文献
6.
Chemistry and Dynamics of Dissolved Organic Matter in a Temperate Coniferous Forest on Andic Soils: Effects of Litter Quality 总被引:4,自引:0,他引:4
Dissolved organic matter (DOM) plays an important role in transporting carbon and nitrogen from forest floor to mineral soils in temperate forest ecosystems. Thus, the retention of DOM via sorption or microbial assimilation is one of the critical steps for soil organic matter formation in mineral soils. The chemical properties of DOM are assumed to control these processes, yet we lack fundamental information that links litter quality, DOM chemistry, and DOM retention. Here, we studied whether differences in litter quality affect solution chemistry and whether changes in litter inputs affect DOM quality and removal in the field. The effects of litter quality on solution chemistry were evaluated using chemical fractionation methods for laboratory extracts and for soil water collected from a temperate coniferous forest where litter inputs had been altered. In a laboratory extraction, litter type (needle, wood, root) and the degree of decomposition strongly influenced solution chemistry. Root litter produced more than 10 times more water-extractable dissolved organic N (DON) than any other litter type, suggesting that root litter may be most responsible for DON production in this forest ecosystem. The chemical composition of the O-horizon leachate was similar under all field treatments (doubled needle, doubled wood, and normal litter inputs). O-horizon leachate most resembled laboratory extracts of well-decomposed litter (that is, a high proportion of hydrophobic acids), in spite of the significant amount of litter C added to the forest floor and a tendency toward higher mean DOM under doubled-Litter treatments. A lag in DOM production from added litter or microbial modification might have obscured chemical differences in DOM under the different treatments. Net DOM removal in this forest soil was strong; DOM concentration in the water deep in the mineral soil was always low regardless of concentrations in water that entered the mineral soil and of litter input manipulation. High net removal of DOM from O-horizon leachate, in spite of extremely low initial hydrophilic neutral content (labile DOM), coupled with the lack of influence by season or soil depth, suggests that DOM retention in the soil was mostly by abiotic sorption. 相似文献
7.
Production of Total Potentially Soluble Organic C, N, and P Across an Ecosystem Chronosequence: Root versus Leaf Litter 总被引:2,自引:0,他引:2
Dissolved organic matter (DOM) plays several important roles in forest ecosystem development, undergoing chemical, physical
and/or biological reactions that affect ecosystem nutrient retention. Very few studies have focused on gross rates of DOM
production, and we know of no study that has directly measured DOM production from root litter. Our objectives were to quantify
major sources of total potentially water-soluble organic matter (DOMtps) production, with an emphasis on production from root litter, to quantify and compare total potentially soluble organic C,
N, and P (DOCtps, DONtps, and DOPtps) production, and to quantify changes in their production during forest primary succession and ecosystem development at the
Mt. Shasta Mudflows ecosystem chronosequence. To do so, we exhaustively extracted freshly senesced root and leaf and other
aboveground litter for DOCtps, DONtps, and DOPtps by vegetation category, and we calculated DOMtps production (g m−2 y−1) at the ecosystem level using data for annual production of fine root and aboveground litter. DOM production from throughfall
was calculated by measuring throughfall volume and concentration over 2 years. Results showed that DOMtps production from root litter was a very important source of DOMtps in the Mount Shasta mudflow ecosystems, in some cases comparable to production from leaf litter for DONtps and larger than production from leaf litter for DOPtps. Total DOCtps and DONtps production from all sources increased early in succession from the 77- to the 255-year-old ecosystem. However, total DOPtps production across the ecosystem chronosequence showed a unique pattern. Generally, the relative importance of root litter
for total fine detrital DOCtps and DONtps production increased significantly during ecosystem development. Furthermore, DOCtps and DONtps production were predominantly driven by changes in biomass production during ecosystem development, whereas changes in litter
solubility due to changes in species composition had a smaller effect. We suggest that DOMtps production from root litter may be an important source of organic matter for the accumulation of SOM during forest ecosystem
development.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.
Shauna M. Uselman, Robert G. Qualls, and Juliane Lilienfein conceived of or designed the study and performed research. SMU
analyzed data and wrote the article. SMU and RGQ contributed new methods or models. 相似文献
8.
森林生态系统DOM的来源、特性及流动 总被引:17,自引:1,他引:17
可溶性有机物质(Dissolved Organic Matter)是森林生态系统主要的可移动碳库及重要的养分库。系统综述了森林生态系统DOM的来源,组成,性质,季节动态;DOM释放与存留机制及影响因素,森林生态系统DOM的流动及干扰对DOM动态影响等,已有研究表明DOM的森林生态系统C、N、P循环,成土作用,污染物迁移等方面起着重要作用。今后森林生态系统DOM的研究应集中于以几方面:(1)确定森林生态系统中DOM源和汇;(2)评价森林水文条件对DOM释放与存留的调节作用;(3)探讨全球气候变化对森林生态系统DOM的影响;(4)可溶性有机氮(Dissolved Organic Nitrogen),可溶性有机磷(Dissolved Organic Phosphorus)动态与可溶性有碳(Dissolved Organic Carbon)动态的差别。 相似文献
9.
杉木人工林土壤可溶性有机质及其与土壤养分的关系 总被引:23,自引:5,他引:23
通过在福建省来舟林场对不同栽植代数杉木人工林土壤可溶性有机碳(DOC)和氮(DON)及土壤养分的研究,其结果表明,随着杉木栽植代数的增加林地土壤DOC和DON含量逐渐下降,在0~10cm土层内第3代杉木林土壤DOC和DON含量分别是第1代杉木林的83.9%和87.1%、第2代杉木林的90.6%和96.9%,在10~20cm土层内第3代杉木林土壤DOC和DON含量分别是第1代杉木林的80.2%和81.5%、第2代杉木林的81.8%和90.0%。在不同林地和土层内土壤DOC含量之间的差异性达到了显著或极显著水平,而DON含量之间的差异性不显著。不同栽植代数杉木林土壤养分的变化趋势与DOM一致,随着杉木连栽,土壤养分含量呈下降趋势。在0~10cm土层内第3代杉木林土壤全氮、全钾、铵态氮和速效钾含量分别是第1代杉木林的83.1%、60.4%、68.1%和44.3%,是第2代杉木林的84.6%、68.5%、74.4%和58.7%;在10~20cm土层内第3代杉木林土壤全氮、全钾、铵态氮和速效钾含量分别是第1代杉木林的74.0%、53.4%、57.6%和54.6%,是第2代杉木林的94.8%、59.5%、74.3%和65.5%。经相关性分析,在各土层内土壤DOC和DON含量与土壤全氮、全钾、铵态氮和速效钾等土壤养分含量存在着不同程度的相关性。 相似文献
10.
三种湿地植物的生长及根系溶解性有机碳分泌物研究 总被引:1,自引:0,他引:1
研究了美人蕉(Canna indica Linn.)、风车草(Cyperus flabelliformis Rottb.)和水鬼蕉(Hymenocallis littoralis (Jack) Salisb.)3种湿地植物在人工气候室水培条件下的根系溶解性有机碳分泌物分泌量及其与生长的关系.结果表明,风车草和美人蕉的植... 相似文献
11.
Leaf Litter as a Source of Dissolved Organic Carbon in Streams 总被引:4,自引:1,他引:4
Dissolved organic carbon (DOC) is an abundant form of organic matter in stream ecosystems. Most research has focused on the
watershed as the source of DOC in streams, but DOC also comes from leaching of organic matter stored in the stream channel.
We used a whole-ecosystem experimental approach to assess the significance of leaching of organic matter in the channel as
a source of DOC in a headwater stream. Inputs of leaf litter were excluded from a forested Appalachian headwater stream for
3 years. Stream-water concentration, export, and instream generation of DOC were reduced in the litter-excluded stream as
compared with a nearby untreated reference stream. The proportion of high molecular weight (HMW) DOC (more than 10,000 daltons)
in stream water was not altered by litter exclusion. Mean DOC concentration in stream water was directly related to benthic
leaf-litter standing stock. Instream generation of DOC from leaf litter stored in the stream channel contributes approximately
30% of daily DOC exports in this forested headwater stream. This source of DOC is greatest during autumn and winter and least
during spring and summer. It is higher during increasing discharge than during base flow. We conclude that elimination of
litter inputs from a forested headwater stream has altered the biogeochemistry of DOC in this ecosystem.
Received 2 September 1997; accepted 27 January 1998. 相似文献
12.
Marianne Holmer Henning Skovgaard Jensen Kasper Kjellberg Christensen Cathleen Wigand Frede Østergård Andersen 《Aquatic Botany》1998,60(4):307-324
Sulfur cycling was examined in sediments inhabited with the isoetids Littorella uniflora and Isoetes lacustris in the oligotrophic soft-water Lake Kalgaard, Denmark. Based on short-term tracer incubations sulfate reduction was measured along a transect from the shore (0.6 m) to profundal sediments (4.6 m). The sulfate reduction rates were low (0.008–0.8 mmol m−2 d−1) in the sandy shallow sediments with low organic content (<1.3 mmol C g−1 sed DW) and high redox potentials (>100 mV), whereas sulfate reduction was higher at the deeper sites (2.7–4.6 mmol m−2 d−1) with high organic content (max. 11.5 mmol C g−1 sed DW) and lower redox potentials (<100 mV). High concentrations of dissolved organic carbon (DOC) were found in the low particulate organic sediments (up to 18.4 mM), and most of the DOC pool consisted of acetate (40–77%). Reoxidation of sulfides due to root oxygen release was probably important at all sites and a positive efflux of sulfate across the sediment–water interface was measured, attaining rates (up to 4.8 mmol m−2 d−1) similar to the sulfate reduction rates. Reoxidation of sulfides was also manifested by high fraction (>80%) of reduced sulfides being accumulated as elemental sulfur or pyrite (chromium reducible sulfur, CRS). The largest pools of CRS were found in high organic sediment with vertical distributions resembling those of the sulfate reduction rates. The overall effect of isoetid growth on sulfur cycling in the rhizosphere is a suppression of sulfate reduction in low organic sediments and the governing of sulfide reoxidation in sediments with higher organic content. 相似文献
13.
Abstract
The stream–riparian interface, characterized by a dynamic and complex hydrology, is an important control point for nutrient
fluxes and processing between terrestrial and aquatic systems. Predicted alterations in the discharge regime in Mediterranean
climate regions make it necessary to understand the effects of abrupt hydrological transition between dry and wet conditions
on the transport and fate of dissolved organic carbon (DOC) across the stream–riparian interface. In this study, the concentrations
and fate of total DOC (TDOC) and a subset of four molecular weight fractions (<1 kDa, 1–10 kDa, 10–100 kDa, >100 kDa) were
investigated in stream water and riparian groundwater during autumn of 2003 and 2004. The two study periods were characterized
by contrasting antecedent hydrological conditions: the streamflow was interrupted in summer 2003 but was permanent in summer
2004. Comparison of the two study periods indicates that an abrupt dry–wet hydrological transition amplifies the water exchange
across the stream–riparian interface and favors retention of up to 57% of the TDOC that flows across the interface. Furthermore,
the efficiency of DOC retention across the stream-riparian interface also varies greatly depending on DOC molecular size.
More than 70% of DOC fractions higher than 10 kDa were retained, whereas the smaller fraction (less than 1 kDa) was nearly
conserved. Consequently, our study helps to clarify the effects of extreme hydrological events on DOC transport in running
waters in Mediterranean regions. 相似文献
14.
Composition,Dynamics, and Fate of Leached Dissolved Organic Matter in Terrestrial Ecosystems: Results from a Decomposition Experiment 总被引:8,自引:0,他引:8
Fluxes of dissolved organic matter (DOM) are an important vector for the movement of carbon (C) and nutrients both within and between ecosystems. However, although DOM fluxes from throughfall and through litterfall can be large, little is known about the fate of DOM leached from plant canopies, or from the litter layer into the soil horizon. In this study, our objectives were to determine the importance of plant-litter leachate as a vehicle for DOM movement, and to track DOM decomposition [including dissolve organic carbon (DOC) and dissolved organic nitrogen (DON) fractions], as well as DOM chemical and isotopic dynamics, during a long-term laboratory incubation experiment using fresh leaves and litter from several ecosystem types. The water-extractable fraction of organic C was high for all five plant species, as was the biodegradable fraction; in most cases, more than 70% of the initial DOM was decomposed in the first 10 days of the experiment. The chemical composition of the DOM changed as decomposition proceeded, with humic (hydrophobic) fractions becoming relatively more abundant than nonhumic (hydrophilic) fractions over time. However, in spite of proportional changes in humic and nonhumic fractions over time, our data suggest that both fractions are readily decomposed in the absence of physicochemical reactions with soil surfaces. Our data also showed no changes in the 13C signature of DOM during decomposition, suggesting that isotopic fractionation during DOM uptake is not a significant process. These results suggest that soil microorganisms preferentially decompose more labile organic molecules in the DOM pool, which also tend to be isotopically heavier than more recalcitrant DOM fractions. We believe that the interaction between DOM decomposition dynamics and soil sorption processes contribute
to the 13C enrichment of soil organic matter commonly observed with depth in soil profiles.
published online 2004 相似文献
15.
We examined the influence of watershed land use and morphology on dissolved organic carbon (DOC) concentration in 32 south-central
Ontario streams having varying agricultural land-use intensities in their catchments. For streams in this region, both univariate
and multivariate regression models identify the proportion of the watershed with poorly drained soils (r
2 up to 0.67) as a better predictor of stream DOC concentrations than any other landscape characteristic, including the proportion
of the watershed as wetland. Agricultural land use did not strongly influence DOC concentrations in our study area; however,
we do show that land-use changes could significantly alter the delivery of DOC to streams in the region. We also identify
how landscape–DOC relationships change over a 2-year time period, as related to season, regional climatic conditions, soil
moisture, and hydrology. Our results indicate that the relationships between landscape predictors and stream DOC concentrations
are temporally dynamic. Strong temporal trends are shown seasonally and in association with climate, through its control of
modelled soil moisture conditions. During periods of positive and negative deviation from normal soil moisture conditions,
the relationships of DOC concentrations with landscape characteristics become less predictable. We show that these dominant
patterns are likely a function of varying flow paths and that anthropogenic changes that affect soil moisture conditions or
flow path will in turn strongly influence DOC dynamics.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
16.
研究以‘丹红’杨(美洲黑杨)和‘通辽1号’杨(小叶杨)为材料,在田间进行施氮肥和不施氮肥处理,分析2个杨树品种的生长性状、碳氮相关代谢物和发育木质部转录组的变化特征,探讨不同杨树品种氮肥利用的生理机制,为杨树的氮高效利用遗传育种奠定基础。结果表明:(1)‘丹红’杨和‘通辽1号’杨的总生物量在施氮处理后分别比不施氮处理提高了1.69倍和1.10倍;‘丹红’杨的总生物量在施氮肥和不施氮肥条件下分别是‘通辽1号’杨的13倍和10倍。(2)施氮处理显著抑制‘丹红’杨和‘通辽1号’杨树皮和木质部中总氮和多种水解氨基酸的含量,但是没有明显影响木质部的总碳、纤维素、半纤维素和木质素含量。(3)施氮处理显著影响了2个杨树品种发育木质部碳固定、糖代谢、氨基酸合成等碳氮代谢途径的基因的高表达,从而促进了植株生物量的积累。研究发现,施氮处理可以显著促进杨树发育木质部碳氮代谢途径相关基因的高表达,从而促进了杨树生物量的积累和生长;‘丹红’杨的木材产量在不同的氮素环境下都远远高于‘通辽1号’杨,更加适合人工林的大面积推广和种植。 相似文献
17.
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
18.
Concentration and Fluxes of Dissolved Organic Carbon (DOC) in Three Norway Spruce Stands along a Climatic Gradient in Sweden 总被引:3,自引:3,他引:3
Leaching of dissolved organic carbon (DOC) from the forest floor and transport in soil solution into the mineral soil are
important for carbon cycling in boreal forest ecosystems. We examined DOC concentrations in bulk deposition, throughfall and
in soil solutions collected under the O and B horizons in three Norway spruce stands along a climatic gradient in Sweden.
Mean annual temperature for the three sites was 5.5, 3.4 and 1.2 °C. At each site we also examined the effect of soil moisture
on DOC dynamics along a moisture gradient (dry, mesic and moist plots). To obtain information about the fate of DOC leached
from the O horizon into the mineral soil, 14C measurements were made on bulk organic matter and DOC. The concentration and fluxes of DOC in O horizon leachates were highest
at the southern site and lowest at the northern. Average DOC concentrations at the southern, central and northern sites were
49, 39 and 30 mg l−1, respectively. We suggest that DOC leaching rates from O horizons were related to the net primary production of the ecosystem.
Soil temperature probably governed the within-year variation in DOC concentration in O horizon leachates, but the peak in
DOC was delayed relative to that of temperature, probably due to sorption processes. Neither soil moisture regime (dry, mesic
or moist plots) nor seasonal variation in soil moisture seemed to be of any significance for the concentration of DOC leached
from the O horizon. The 14C measurements showed that DOC in soil solution collected below the B horizon was derived mainly from the B horizon itself,
rather than from the O horizon, indicating a substantial exchange (sorption–desorption reactions) between incoming DOC and
soil organic carbon in the mineral soil. 相似文献
19.
A stormflow/baseflow comparison of dissolved organic matter concentrations and bioavailability in an Appalachian stream 总被引:2,自引:4,他引:2
Patterns of dissolved organic carbon (DOC) and nitrogen (DON) delivery were compared between times of stormflow and baseflow in Paine Run, an Appalachian stream draining a 12.4 km2 forested catchment in the Shenandoah National Park (SNP), Virginia. The potential in-stream ecological impact of altered concentrations and/or chemical composition of DOM during storms also was examined, using standardized bacterial bioassays. DOC and DON concentrations in Paine Run were consistently low during baseflow and did not show a seasonal pattern. During storms however, mean DOC and DON concentrations approximately doubled, with maximum concentrations occurring on the rising limb of storm hydrographs. The rapid response of DOM concentration to changes in flow suggests a near-stream or in-stream source of DOM during storms. Stormflow (4% of the time, 36% of the annual discharge) contributed >50% of DOC, DON and NO3
– flux in Paine Run during 1997. In laboratory bacterial bioassays, growth rate constants were higher on Paine Run stormflow water than on baseflow water, but the fraction of total DOM which was bioavailable was not significantly different. The fraction of the total stream DOC pool taken up by water column bacteria was estimated to increase from 0.03 ± 0.02% h–1 during baseflow, to 0.15 ± 0.04% h–1 during storms. This uptake rate would have a minimal effect on bulk DOM concentrations in Paine Run, but storms may still have considerable impact on the bacterial stream communities by mobilizing them into the water column and by supplying a pulse of DOM. 相似文献
20.
Response of Oxidative Enzyme Activities to Nitrogen Deposition Affects Soil Concentrations of Dissolved Organic Carbon 总被引:10,自引:0,他引:10
Recent evidence suggests that atmospheric nitrate (NO
3
−
) deposition can alter soil carbon (C) storage by directly affecting the activity of lignin-degrading soil fungi. In a laboratory
experiment, we studied the direct influence of increasing soil NO
3
−
concentration on microbial C cycling in three different ecosystems: black oak–white oak (BOWO), sugar maple–red oak (SMRO),
and sugar maple–basswood (SMBW). These ecosystems span a broad range of litter biochemistry and recalcitrance; the BOWO ecosystem
contains the highest litter lignin content, SMRO had intermediate lignin content, and SMBW leaf litter has the lowest lignin
content. We hypothesized that increasing soil solution NO
3
−
would reduce lignolytic activity in the BOWO ecosystem, due to a high abundance of white-rot fungi and lignin-rich leaf litter.
Due to the low lignin content of litter in the SMBW, we further reasoned that the NO
3
−
repression of lignolytic activity would be less dramatic due to a lower relative abundance of white-rot basidiomycetes; the
response in the SMRO ecosystem should be intermediate. We increased soil solution NO
3
−
concentrations in a 73-day laboratory incubation and measured microbial respiration and soil solution dissolved organic carbon
(DOC) and phenolics concentrations. At the end of the incubation, we measured the activity of β-glucosidase, N-acetyl-glucosaminidase,
phenol oxidase, and peroxidase, which are extracellular enzymes involved with cellulose and lignin degradation. We quantified
the fungal biomass, and we also used fungal ribosomal intergenic spacer analysis (RISA) to gain insight into fungal community
composition. In the BOWO ecosystem, increasing NO
3
−
significantly decreased oxidative enzyme activities (−30% to −54%) and increased DOC (+32% upper limit) and phenolic (+77%
upper limit) concentrations. In the SMRO ecosystem, we observed a significant decrease in phenol oxidase activity (−73% lower
limit) and an increase in soluble phenolic concentrations (+57% upper limit) in response to increasing NO
3
−
in soil solution, but there was no significant change in DOC concentration. In contrast to these patterns, increasing soil
solution NO
3
−
in the SMBW soil resulted in significantly greater phenol oxidase activity (+700% upper limit) and a trend toward lower DOC
production (−52% lower limit). Nitrate concentration had no effect on microbial respiration or β-glucosidase or N-acetyl-glucosaminidase
activities. Fungal abundance and basidiomycete diversity tended to be highest in the BOWO soil and lowest in the SMBW, but
neither displayed a consistent response to NO
3
−
additions. Taken together, our results demonstrate that oxidative enzyme production by microbial communities responds directly
to NO
3
−
deposition, controlling extracellular enzyme activity and DOC flux. The regulation of oxidative enzymes by different microbial
communities in response to NO
3
−
deposition highlights the fact that the composition and function of soil microbial communities directly control ecosystem-level
responses to environmental change. 相似文献