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1.
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
2.
During 1999–2001 the chemical composition and fluxes were measured in rainfall, throughfall, soil solution and stream water
in a remote forested site in the Italian Alps. The analysis of temporal patterns revealed the differential behaviour of nitrogen
and sulphur and suggested that different mechanisms controlled their flux. No important changes in sulphate concentration
and fluxes emerged as the solution passed through the various components of the forest ecosystem, and temporal variations
of SO4 in the soil solution and stream were likely driven by the physical process of dilution. The availability of nitrate and ammonia,
by contrast, was drastically reduced as throughfall water entered the soil and passed through the mineral layers, irrespective
of season. The calculated hydrochemical budget based on throughfall and soil solution N fluxes revealed that ~80% N retention
in the forest soil, corresponding to 12 kg ha−1 yr−1, despite a relatively high N deposition loading (15 kg ha−1 yr−1). Most of the leached nitrogen (90%) was in the organic form. Indicators of the N status of this ecosystem, such as C/N ratio
in solid and solution phase of the soil and N foliage content as well as land use history were examined. Despite the strong
N retention in the forested part of the catchment, the stream water N–NO3 levels were consistently above 10 μg l−1 suggesting that the Val Masino catchment as a whole was less efficient in processing atmospheric N inputs. This contrasting
N behaviour illustrates the role of landscape features, such as the soil cover and vegetation type, that is characteristic
of an alpine catchment. 相似文献
3.
Response of dissolved organic matter in the forest floor to long-term manipulation of litter and throughfall inputs 总被引:1,自引:0,他引:1
Dissolved organic matter (DOM) contributes to organic carbon either stored in mineral soil horizons or exported to the hydrosphere.
However, the main controls of DOM dynamics are still under debate. We studied fresh leaf litter and more decomposed organic
material as the main sources of DOM exported from the forest floor of a mixed beech/oak forest in Germany. In the field we
doubled and excluded aboveground litter input and doubled the input of throughfall. From 1999 to 2005 we measured concentrations
and fluxes of dissolved organic C and N (DOC, DON) beneath the Oi and Oe/Oa horizon. DOM composition was traced by UV and
fluorescence spectroscopy. In selected DOM samples we analyzed the concentrations of phenols, pentoses and hexoses, and lignin-derived
phenols by CuO oxidation. DOC and DON concentrations and fluxes almost doubled instantaneously in both horizons of the forest
floor by doubling the litter input and DOC concentrations averaged 82 mg C l−1 in the Oe/Oa horizon. Properties of DOM did not suggest a change of the main DOM source towards fresh litter. In turn, increasing
ratios of hexoses to pentoses and a larger content of lignin-derived phenols in the Oe/Oa horizon of the Double litter plots in comparison to the Control plots indicated a priming effect: Addition of fresh litter stimulated microbial activity resulting in increased microbial
production of DOM from organic material already stored in Oe/Oa horizons. Exclusion of litter input resulted in an immediate
decrease in DOC concentrations and fluxes in the thin Oi horizon. In the Oe/Oa horizon DOC concentrations started to decline
in the third year and were significantly smaller than those in the Control after 5 years. Properties of DOM indicated an increased proportion of microbially and throughfall derived compounds after
exclusion of litter inputs. Dissolved organic N did not decrease upon litter exclusion. We assume a microbial transformation
of mineral N from throughfall and N mineralization to DON. Increased amounts of throughfall resulted in almost equivalently
increased DOC fluxes in the Oe/Oa horizon. However, long-term additional throughfall inputs resulted in significantly declining
DOC concentrations over time. We conclude that DOM leaving the forest floor derives mainly from decomposed organic material
stored in Oe/Oa horizons. Leaching of organic matter from fresh litter is of less importance. Observed effects of litter manipulations
strongly depend on time and the stocks of organic matter in forest floor horizons. Long-term experiments are particularly
necessary in soils/horizons with large stocks of organic matter and in studies focusing on effects of declined substrate availability.
The expected increased primary production upon climate change with subsequently enhanced litter input may result in an increased
production of DOM from organic soil horizons. 相似文献
4.
Matthias Peichl Tim R. Moore M. Altaf Arain Mike Dalva David Brodkey Joshua McLaren 《Biogeochemistry》2007,86(1):1-17
We determined concentrations and fluxes of dissolved organic carbon (DOC) in precipitation, throughfall, forest floor and
mineral soil leachates from June 2004 to May 2006 across an age-sequence (2-, 15-, 30-, and 65-year-old) of white pine (Pinus strobus L.) forests in southern Ontario, Canada. Mean DOC concentration in precipitation, throughfall, leachates of forest floor,
Ah-horizon, and of mineral soil at 1 m depth ranged from ∼2 to 7, 9 to 18, 32 to 88, 20 to 66, and 2 to 3 mg DOC L−1, respectively, for all four stands from April (after snowmelt) through December. DOC concentration in forest floor leachates
was highest in early summer and positively correlated to stand age, aboveground biomass and forest floor carbon pools. DOC
fluxes via precipitation, throughfall, and leaching through forest floor and Ah-horizon between were in the range of ∼1 to
2, 2 to 4, 0.5 to 3.5, and 0.1 to 2 g DOC m−2, respectively. DOC export from the forest ecosystem during that period through infiltration and groundwater discharge was
estimated as ∼7, 4, 3, and 2 g DOC m−2 for the 2-, 15-, 30-, and 65-year-old sites, respectively, indicating a decrease with increasing stand age. Laboratory DOC
sorption studies showed that the null-point DOC concentration fell from values of 15 to 60 mg DOC L−1 at 0 to 5 cm to <15 mg DOC L−1 at 50 cm. Specific ultraviolet light absorption at 254 nm (SUVA254) increased from precipitation and throughfall to a maximum in forest floor and decreased with mineral soil depth. No age-related
pattern was observed for SUVA254 values. DOC concentration in forest floor soil solutions showed a positive exponential relationship with soil temperature,
and a negative exponential relationship with soil moisture at all four sites. Understanding the changes and controls of DOC
concentrations, chemistry, and fluxes at various stages of forest stand development is necessary to estimate and predict DOC
dynamics on a regional landscape level and to evaluate the effect of land-use change. 相似文献
5.
Concentration and Fluxes of Dissolved Organic Carbon (DOC) in Three Norway Spruce Stands along a Climatic Gradient in Sweden 总被引:6,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
6.
Detrital Controls on Soil Solution N and Dissolved Organic Matter in Soils: A Field Experiment 总被引:1,自引:1,他引:0
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
7.
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
8.
Coarse woody debris (CWD) may play a role in nutrient cycling in temperate forests through the leaching of solutes, including dissolved organic carbon (DOC) and dissolved organic nitrogen (DON), to the underlying soil. These fluxes need to be considered in element budget calculations, and have the potential to influence microbial activity, soil development, and other processes in the underlying soil, but studies on leaching from CWD are rare. In this study, we collected throughfall, litter leachate, and CWD leachate in situ at a young mixed lowland forest in NY State, USA over one year. We measured the concentrations of DOC, DON, NH4+, NO3−, dissolved organic sulfur, SO42−, Cl−, Al, Ca, K, Mg, Na, and P, estimated the flux of these solutes in throughfall, and measured the cover of CWD to gain some insight into possible fluxes from CWD. Concentrations of DOC were much higher in CWD leachate than in throughfall or litter leachate (15 vs. 0.7 and 1.6 mM, respectively), and greater than reported values for other leachates from within forested ecosystems. Other solutes showed a similar pattern, with inorganic N being an exception. Our results suggest that microsite scale fluxes of DOC from CWD may be An high relative to throughfall and litter leaching fluxes, but since CWD covered a relatively small fraction (2%) of the forest floor in our study, ecosystem scale fluxes from CWD may be negligible for this site. Soil directly beneath CWD may be influenced by CWD leaching, in terms of soil organic matter, microbial activity, and N availability. Concentrations of some metals showed correlations to DOC concentrations, highlighting the possibility of complexation by DOM. Several solute concentrations in throughfall, including DOC, showed positive correlations to mean air temperature, and fewer showed positive correlations in litter leachate, while negative correlations were observed to precipitation, suggesting both biological and hydrologic control of solute concentrations. 相似文献
9.
Pools and fluxes of carbon in three Norway spruce ecosystems along a climatic gradient in Sweden 总被引:1,自引:0,他引:1
Dan Berggren Kleja Magnus Svensson Hooshang Majdi Per-Erik Jansson Ola Langvall Bo Bergkvist Maj-Britt Johansson Per Weslien Laimi Truus Anders Lindroth Göran I. Ågren 《Biogeochemistry》2008,89(1):7-25
This paper presents an integrated analysis of organic carbon (C) pools in soils and vegetation, within-ecosystem fluxes and
net ecosystem exchange (NEE) in three 40-year old Norway spruce stands along a north-south climatic gradient in Sweden, measured
2001–2004. A process-orientated ecosystem model (CoupModel), previously parameterised on a regional dataset, was used for
the analysis. Pools of soil organic carbon (SOC) and tree growth rates were highest at the southernmost site (1.6 and 2.0-fold,
respectively). Tree litter production (litterfall and root litter) was also highest in the south, with about half coming from
fine roots (<1 mm) at all sites. However, when the litter input from the forest floor vegetation was included, the difference
in total litter input rate between the sites almost disappeared (190–233 g C m−2 year−1). We propose that a higher N deposition and N availability in the south result in a slower turnover of soil organic matter
than in the north. This effect seems to overshadow the effect of temperature. At the southern site, 19% of the total litter
input to the O horizon was leached to the mineral soil as dissolved organic carbon, while at the two northern sites the corresponding
figure was approx. 9%. The CoupModel accurately described general C cycling behaviour in these ecosystems, reproducing the
differences between north and south. The simulated changes in SOC pools during the measurement period were small, ranging
from −8 g C m−2 year−1 in the north to +9 g C m−2 year−1 in the south. In contrast, NEE and tree growth measurements at the northernmost site suggest that the soil lost about 90 g C m−2 year−1.
An erratum to this article can be found at 相似文献
10.
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
11.
The Ferrous Wheel Hypothesis (Davidson et al. 2003) postulates the abiotic formation of dissolved organic N (DON) in forest floors, by the fast reaction of NO2
− with dissolved organic C (DOC). We investigated the abiotic reaction of NO2
− with dissolved organic matter extracted from six different forest floors under oxic conditions. Solutions differed in DOC
concentrations (15–60 mg L−1), NO2
− concentrations (0, 2, 20 mg NO2
−-N L−1) and DOC/DON ratio (13.4–25.4). Concentrations of added NO2
− never decreased within 60 min, therefore, no DON formation from added NO2
− took place in any of the samples. Our results suggest that the reaction of NO2
− with natural DOC in forest floors is rather unlikely. 相似文献
12.
Metal pollution, in combination with other environmental stressors such as acid deposition and climate change, may disturb
metal biogeochemical cycles. To investigate the influence of dissolved organic carbon, acidity and seasonality on metal geochemistry,
this study has described concentrations of 19 metals as they pass through an acidified forested catchment on the Precambrian
Shield in south-central Ontario, Canada. Metal, dissolved organic carbon (DOC) and sulphate (SO4
2−) concentrations fluctuate throughout the catchment compartments as the water passes through and interacts with vegetation,
soils and bedrock. Relationships among metals, DOC and SO4
2− are most pronounced in compartments where DOC and SO4
2− exhibit high variability, namely in the throughfall, organic horizon soil water, and wetland-draining stream. Metal, DOC
and SO4
2− concentrations varied seasonally in the streams, and temporal coherence occurred among metal, DOC and SO4
2− concentrations in the organic horizon soil water and the wetland-draining stream (PC1). In the wetland-draining stream, the
highest DOC, Cr, Cu, Fe, Pb, and V concentrations occur in the summer, whereas concentrations of SO4
2− and most other metals peak in the fall after a period of drought. Despite the rural location, provincial water quality objectives
for surface water were exceeded for many metals when the peak fall values occurred. 相似文献
13.
The dissolved oxygen concentration (DO) was sampled during a diurnal cycle in three water holes heavily used by wildlife and
with distinctive biological features along the Seronera River. The DO fluctuated widely (by up to 11.5 mg l−1) as a function of time, mechanical stirring and aeration by animals, and the presence of fringing wetlands. The DO cycle
was successfully modeled (within 0.3 mg l−1) by assuming that the four dominant processes were photosynthesis and respiration by algae near the surface, trapping by
wetlands, decomposition of dead organic matter on the bottom, and stirring/aeration by hippos. The rate of DO decline from
the decay of dead organic matter was equal to the rate of DO removal by algal respiration at night. 相似文献
14.
Although dissolved organic matter (DOM) released from the forest floor plays a crucial role in transporting carbon and major nutrients through the soil profile, its formation and responses to changing litter inputs are only partially understood. To gain insights into the controlling mechanisms of DOM release from the forest floor, we investigated responses of the concentrations and fluxes of dissolved organic carbon (DOC) and nitrogen (DON) in forest floor leachates to manipulations of throughfall (TF) flow and aboveground litter inputs (litter removal, litter addition, and glucose addition) at a hardwood stand in Bavaria, Germany. Over the two-year study period, litter manipulations resulted in significant changes in C and N stocks of the uppermost organic horizon (Oi). DOC and DON losses via forest floor leaching represented 8 and 11% of annual litterfall C and N inputs at the control, respectively. The exclusion of aboveground litter inputs caused a slight decrease in DOC release from the Oi horizon but no change in the overall leaching losses of DOC and DON in forest floor leachates. In contrast, the addition of litter or glucose increased the release of DOC and DON either from the Oi or from the lower horizons (Oe + Oa). Net releases of DOC from the Oe + Oa horizons over the entire manipulation period were not related to changes in microbial activity (measured as rates of basal and substrate-induced respiration) but to the original forest floor depths prior to manipulation, pointing to the flux control by the size of source pools rather than a straightforward relationship between microbial activity and DOM production. In response to doubled TF fluxes, net increases in DOM fluxes occurred in the lower forest floor, indicating the presence of substantial pools of potentially soluble organic matter in the Oe + Oa horizons. In contrast to the general assumption of DOM as a leaching product from recent litter, our results suggest that DOM in forest floor leachates is derived from both newly added litter and older organic horizons through complex interactions between microbial production and consumption and hydrologic transport. 相似文献
15.
Boreal forests are increasing in age partly due to reduced logging and efficient wildfire control. As a result, they also
stock more carbon. Whether increased forest C stock causes greater production of dissolved organic carbon (DOC) is uncertain.
DOC in bulk precipitation, throughfall and soil water was studied in 10-, 30-, 60- and 120-year-old stands of Norway spruce
(Picea abies (L.) Karst.) DOC concentrations in throughfall and O horizon soil water followed the order 10 < 30 < 60 = 120 and 10 = 30 < 120 < 60,
respectively. DOC fluxes followed the order 10 = 30 < 60 = 120 in throughfall, while no significant difference between stands
was found for O horizon soil water. Above-ground tree litter varied according to 10 < 30 < 60 = 120, a pattern identical to
that for DOC concentrations in throughfall and resembling but not identical to that for DOC concentrations in O horizon soil
water. This indicates additional sources for DOC in soil water. Seasonality in DOC concentrations was observed at the base
of the O horizon, and seasonality in DOC fluxes in both throughfall and O horizon soil water. Our results suggest differences
in the polarity of DOC between the 10-year stand and the others, which we interpret as reflecting the lack of grown trees
and possibly the different vegetation on the 10-year stand. 相似文献
16.
Old growth forest soils are large C reservoirs, but the impacts of tree-fall gaps on soil C in these forests are not well
understood. The effects of forest gaps on soil C dynamics in old growth northern hardwood–hemlock forests in the upper Great
Lakes region, USA, were assessed from measurements of litter and soil C stocks, surface C efflux, and soil microbial indices
over two consecutive growing seasons. Forest floor C was significantly less in gaps (19.0 Mg C ha−1) compared to gap-edges (39.5 Mg C ha−1) and the closed forest (38.0 Mg C ha−1). Labile soil C (coarse particulate organic matter, cPOM) was significantly less in gaps and edges (11.1 and 11.2 Mg C ha−1) compared to forest plots (15.3 Mg C ha−1). In situ surface C efflux was significantly greater in gaps (12.0 Mg C ha−1 y−1) compared to edges and the closed forest (9.2 and 8.9 Mg C ha−1 y−1). Microbial biomass N (MBN) was significantly greater in edges (0.14 Mg N ha−1) than in the contiguous forest (0.09 Mg N ha−1). The metabolic quotient (qCO2) was significantly greater in the forest (0.0031 mg CO2 h−1 g−1/mg MBC g−1) relative to gaps or edges (0.0014 mg CO2 h−1 g−1/mg MBC g−1). A case is made for gaps as alleviators of old growth forest soil C saturation. Relative to the undisturbed closed forest,
gaps have significantly less labile C, significantly greater in situ surface C efflux, and significantly lower decreased qCO2 values. 相似文献
17.
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
18.
Understanding how the concentration and chemical quality of dissolved organic matter (DOM) varies in soils is critical because
DOM influences an array of biological, chemical, and physical processes. We used PARAFAC modeling of excitation–emission fluorescence
spectroscopy, specific UV absorbance (SUVA254) and biodegradable dissolved organic carbon (BDOC) incubations to investigate the chemical quality of DOM in soil water collected
from 25 cm piezometers in four different wetland and forest soils: bog, forested wetland, fen and upland forest. There were
significant differences in soil solution concentrations of dissolved organic C, N, and P, DOC:DON ratios, SUVA254 and BDOC among the four soil types. Throughout the sampling period, average DOC concentrations in the four soil types ranged
from 9–32 mg C l−1 and between 23–42% of the DOC was biodegradable. Seasonal patterns in dissolved nutrient concentrations and BDOC were observed
in the three wetland types suggesting strong biotic controls over DOM concentrations in wetland soils. PARAFAC modeling of
excitation–emission fluorescence spectroscopy showed that protein-like fluorescence was positively correlated (r
2 = 0.82; P < 0.001) with BDOC for all soil types taken together. This finding indicates that PARAFAC modeling may substantially improve
the ability to predict BDOC in natural environments. Coincident measurements of DOM concentrations, BDOC and PARAFAC modeling
confirmed that the four soil types contain DOM with distinct chemical properties and have unique fluorescent fingerprints.
DOM inputs to streams from the four soil types therefore have the potential to alter stream biogeochemical processes differently
by influencing temporal patterns in stream heterotrophic productivity. 相似文献
19.
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
20.
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