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1.
Harry Olde Venterink Ignacy Kardel Wiktor Kotowski Wilma Peeters Martin J. Wassen 《Biogeochemistry》2009,93(3):235-252
To provide a reference for wetlands elsewhere we analysed soil nutrients and the vegetation of floodplains and fens in the
relatively undisturbed Biebrza-valley, Poland. Additionally, by studying sites along a water-table gradient, and by comparing
pairs of mown and unmown sites, we aimed with exploring long-term effects of drainage and annual hay-removal on nutrient availabilities
and vegetation response. In undrained fens and floodplains, N mineralization went slowly (0–30 kg N ha−1 year−1) but it increased strongly with decreasing water table (up to 120 kg N ha−1 year−1). Soil N, P and K pools were small in the undisturbed mires. Drainage had caused a shift from fen to meadow species and the
disappearance of bryophytes. Biomass of vascular plants increased with increasing N mineralization and soil P. Annual hay-removal
tended to have reduced N mineralization and soil K pools, but it had increased soil P. Moreover, N concentrations in vascular
plants were not affected, but P and K concentrations and therefore N:P and N:K ratios tended to be changed. Annual hay-removal
had induced a shift from P to K limitation in the severely drained fen, and from P to N limitation in the floodplain. The
low nutrient availabilities and productivity of the undisturbed Biebrza mires illustrate the vulnerability of such mires to
eutrophication in Poland and elsewhere. In nutrient-enriched areas, hay removal may prevent productivity increase of the vegetation,
but also may severely alter N:P:K stoichiometry, induce K-limitation at drained sites, and alter vegetation structure and
composition. 相似文献
2.
Short-term soil inorganic N pulse after experimental fire alters invasive and native annual plant production in a Mojave Desert shrubland 总被引:1,自引:0,他引:1
Todd C. Esque Jason P. Kaye Sara E. Eckert Lesley A. DeFalco C. Richard Tracy 《Oecologia》2010,164(1):253-263
Post-fire changes in desert vegetation patterns are known, but the mechanisms are poorly understood. Theory suggests that
pulse dynamics of resource availability confer advantages to invasive annual species, and that pulse timing can influence
survival and competition among species. Precipitation patterns in the American Southwest are predicted to shift toward a drier
climate, potentially altering post-fire resource availability and consequent vegetation dynamics. We quantified post-fire
inorganic N dynamics and determined how annual plants respond to soil inorganic nitrogen variability following experimental
fires in a Mojave Desert shrub community. Soil inorganic N, soil net N mineralization, and production of annual plants were
measured beneath shrubs and in interspaces during 6 months following fire. Soil inorganic N pools in burned plots were up
to 1 g m−2 greater than unburned plots for several weeks and increased under shrubs (0.5–1.0 g m−2) more than interspaces (0.1–0.2 g m−2). Soil NO3
−−N (nitrate−N) increased more and persisted longer than soil NH4
+−N (ammonium−N). Laboratory incubations simulating low soil moisture conditions, and consistent with field moisture during
the study, suggest that soil net ammonification and net nitrification were low and mostly unaffected by shrub canopy or burning.
After late season rains, and where soil inorganic N pools were elevated after fire, productivity of the predominant invasive
Schismus spp. increased and native annuals declined. Results suggest that increased N availability following wildfire can favor invasive
annuals over natives. Whether the short-term success of invasive species following fire will direct long-term species composition
changes remains to be seen, yet predicted changes in precipitation variability will likely interact with N cycling to affect
invasive annual plant dominance following wildfire. 相似文献
3.
Erica A. H. Smithwick Daniel M. Kashian Michael G. Ryan Monica G. Turner 《Ecosystems》2009,12(5):792-806
Long-term, landscape patterns in inorganic nitrogen (N) availability and N stocks following infrequent, stand-replacing fire
are unknown but are important for interpreting the effect of disturbances on ecosystem function. Here, we present results
from a replicated chronosequence study in the Greater Yellowstone Ecosystem (Wyoming, USA) directed at measuring inorganic
N availability (ion-exchange resin bags) and ecosystem N pools among 77 lodgepole pine stands that varied in age and density.
Inorganic N availability ranged from 0.07 to 3.20 μN bag−1 d−1 and nitrate (NO3−) was, on average, 65% of total resin-sorbed N. Total ecosystem N stocks (live + detrital + soil) averaged 109.9 ± 3.0 g N m−2 (range = 63.7–185.8 g N m−2). Live N was 14%, detrital N was 29%, and soil N was 57% of total stocks. Soil NO3−, total ecosystem N, live N, and detrital N generally increased with stand age, but soil N stocks decreased. Models (AICc) to predict soil N availability and N stocks included soil P, soil Ca, bulk density, and pH in addition to age (adj R
2 ranged from 0.18 to 0.53) and density was included only for live N stocks. Patterns of N stocks and N availability with density
were strongest for young stands (<20 years) regenerating from extensive fire in 1988; for example, litterfall N stocks increased
with density (adj R
2 = 0.86, P < 0.001) but inorganic N availability declined (adj R
2 = 0.47, P < 0.003). Across the complex Yellowstone landscape, we conclude that N stocks and N availability are best predicted by a
combination of local soil characteristics in addition to factors that vary at landscape scales (stand density and age). Overall,
total ecosystem N stocks were recovered quickly following stand-replacing fire, suggesting that moderate increases in fire
frequency will not affect long-term landscape N storage in Greater Yellowstone.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.
Author contributions EAHS, MGT, and MGR conceived the study; DMK performed field research; EAHS and DMK oversaw laboratory analyses and analyzed
data; EAHS wrote the paper. 相似文献
4.
Nitrogen Transformations in Flowpaths Leading from Soils to Streams in Amazon Forest and Pasture 总被引:1,自引:0,他引:1
Joaquín Chaves Christopher Neill Sonja Germer Sergio Gouveia Neto Alex V. Krusche Adriana Castellanos Bonilla Helmut Elsenbeer 《Ecosystems》2009,12(6):961-972
The modification of large areas of tropical forest to agricultural uses has consequences for the movement of inorganic nitrogen
(N) from land to water. Various biogeochemical pathways in soils and riparian zones can influence the movement and retention
of N within watersheds and affect the quantity exported in streams. We used the concentrations of NO3
− and NH4
+ in different hydrological flowpaths leading from upland soils to streams to investigate inorganic N transformations in adjacent
watersheds containing tropical forest and established cattle pasture in the southwestern Brazilian Amazon Basin. High NO3
− concentrations in forest soil solution relative to groundwater indicated a large removal of N mostly as NO3
− in flowpaths leading from soil to groundwater. Forest groundwater NO3
− concentrations were lower than in other Amazon sites where riparian zones have been implicated as important N sinks. Based
on water budgets for these watersheds, we estimated that 7.3–10.3 kg N ha−1 y−1 was removed from flowpaths between 20 and 100 cm, and 7.1–10.2 kg N ha−1 y−1 was removed below 100 cm and the top of the groundwater. N removal from vertical flowpaths in forest exceeded previously
measured N2O emissions of 3.0 kg N ha−1 y−1 and estimated emissions of NO of 1.4 kg N ha−1 y−1. Potential fates for this large amount of nitrate removal in forest soils include plant uptake, denitrification, and abiotic
N retention. Conversion to pasture shifted the system from dominance by processes producing and consuming NO3
− to one dominated by NH4
+, presumably the product of lower rates of net N mineralization and net nitrification in pasture compared with forest. In
pasture, no hydrological flowpaths contained substantial amounts of NO3
− and estimated N removal from soil vertical flowpaths was 0.2 kg N ha−1 y−1 below the depth of 100 cm. This contrasts with the extent to which agricultural sources dominate N inputs to groundwater
and stream water in many temperate regions. This could change, however, if pasture agriculture in the tropics shifts toward
intensive crop cultivation. 相似文献
5.
Shannon KE Saleh-Lakha S Burton DL Zebarth BJ Goyer C Trevors JT 《Antonie van Leeuwenhoek》2011,100(2):183-195
The effect of glucose addition (0 and 500 μg C g−1 soil) and nitrate (NO3) addition (0, 10, 50 and 500 μg NO3–N g−1 soil) on nitric oxide reductase (cnorB) gene abundance and mRNA levels, and cumulative denitrification were quantified over 48 h in anoxic soils inoculated with
Pseudomonas mandelii. Addition of glucose-C significantly increased cnorB
p
(P. mandelii and related species) mRNA levels and abundance compared with soil with no glucose added, averaged over time and NO3 addition treatments. Without glucose addition, cnorB
p
mRNA levels were higher when 500 μg NO3–N g−1 soil was added compared with other NO3 additions. In treatments with glucose added, addition of 50 μg NO3–N g−1 soil resulted in higher cnorB
p
mRNA levels than soil without NO3 but was not different from the 10 and 500 μg NO3–N g−1 treatments. cnorB
p
abundance in soils without glucose addition was significantly higher in soils with 500 μg NO3–N g−1 soil compared to lower N-treated soils. Conversely, addition of 500 μg NO3–N g−1 soil resulted in lower cnorB
p
abundance compared with soil without N-addition. Over 48 h, cumulative denitrification in soils with 500 μg glucose-C g−1 soil, and 50 or 500 μg NO3–N g−1 was higher than all other treatments. There was a positive correlation between cnorB
p
abundance and cumulative denitrification, but only in soils without glucose addition. Glucose-treated soils generally had
higher cnorB
p
abundance and mRNA levels than soils without glucose added, however response of cnorB
p
abundance and mRNA levels to NO3 supply depended on carbon availability. 相似文献
6.
Kristell Hergoualc’h Ute Skiba Jean-Michel Harmand Catherine Hénault 《Biogeochemistry》2008,89(3):329-345
The objective of this study was to evaluate the effect of N fertilization and the presence of N2 fixing leguminous trees on soil fluxes of greenhouse gases. For a one year period, we measured soil fluxes of nitrous oxide
(N2O), carbon dioxide (CO2) and methane (CH4), related soil parameters (temperature, water-filled pore space, mineral nitrogen content, N mineralization potential) and
litterfall in two highly fertilized (250 kg N ha−1 year−1) coffee cultivation: a monoculture (CM) and a culture shaded by the N2 fixing legume species Inga densiflora (CIn). Nitrogen fertilizer addition significantly influenced N2O emissions with 84% of the annual N2O emitted during the post fertilization periods, and temporarily increased soil respiration and decreased CH4 uptakes. The higher annual N2O emissions from the shaded plantation (5.8 ± 0.3 kg N ha−1 year−1) when compared to that from the monoculture (4.3 ± 0.1 kg N ha−1 year−1) was related to the higher N input through litterfall (246 ± 16 kg N ha−1 year−1) and higher potential soil N mineralization rate (3.7 ± 0.2 mg N kg−1 d.w. d−1) in the shaded cultivation when compared to the monoculture (153 ± 6.8 kg N ha−1 year−1 and 2.2 ± 0.2 mg N kg−1 d.w. d−1). This confirms that the presence of N2 fixing shade trees can increase N2O emissions. Annual CO2 and CH4 fluxes of both systems were similar (8.4 ± 2.6 and 7.5 ± 2.3 t C-CO2 ha−1 year−1, −1.1 ± 1.5 and 3.3 ± 1.1 kg C-CH4 ha−1 year−1, respectively in the CIn and CM plantations) but, unexpectedly increased during the dry season. 相似文献
7.
Impact of long-term nitrogen addition on carbon stocks in trees and soils in northern Europe 总被引:4,自引:2,他引:2
The aim of this study was to quantify the effects of fertiliser N on C stocks in trees (stems, stumps, branches, needles,
and coarse roots) and soils (organic layer +0–10 cm mineral soil) by analysing data from 15 long-term (14–30 years) experiments
in Picea abies and Pinus sylvestris stands in Sweden and Finland. Low application rates (30–50 kg N ha−1 year−1) were always more efficient per unit of N than high application rates (50–200 kg N ha−1 year−1). Addition of a cumulative amount of N of 600–1800 kg N ha−1 resulted in a mean increase in tree and soil C stock of 25 and 11 kg (C sequestered) kg−1 (N added) (“N-use efficiency”), respectively. The corresponding estimates for NPK addition were 38 and 11 kg (C) kg−1 (N). N-use efficiency for C sequestration in trees strongly depended on soil N status and increased from close to zero at
C/N 25 in the humus layer up to 40 kg (C) kg−1 (N) at C/N 35 and decreased again to about 20 kg (C) kg−1 (N) at C/N 50 when N only was added. In contrast, addition of NPK resulted in high (40–50 kg (C) kg−1 (N)) N-use efficiency also at N-rich (C/N 25) sites. The great difference in N-use efficiency between addition of NPK and
N at N-rich sites reflects a limitation of P and K for tree growth at these sites. N-use efficiency for soil organic carbon
(SOC) sequestration was, on average, 3–4 times lower than for tree C sequestration. However, SOC sequestration was about twice
as high at P. abies as at P. sylvestris sites and averaged 13 and 7 kg (C) kg−1 (N), respectively. The strong relation between N-use efficiency and humus C/N ratio was used to evaluate the impact of N
deposition on C sequestration. The data imply that the 10 kg N ha−1 year−1 higher deposition in southern Sweden than in northern Sweden for a whole century should have resulted in 2.0 ± 1.0 (95% confidence
interval) kg m−2 more tree C and 1.3 ± 0.5 kg m−2 more SOC at P. abies sites in the south than in the north for a 100-year period. These estimates are consistent with differences between south
and north in tree C and SOC found by other studies, and 70–80% of the difference in SOC can be explained by different N deposition. 相似文献
8.
Macrophyte presence is an indicator of enhanced denitrification and nitrification in sediments of a temperate restored agricultural stream 总被引:1,自引:0,他引:1
Stream macrophytes are often removed with their sediments to deepen stream channels, stabilize channel banks, or provide habitat
for target species. These sediments may support enhanced nitrogen processing. To evaluate sediment nitrogen processing, identify
seasonal patterns, and assess sediment processes relative to stream load, we measured denitrification and nitrification rates
in a restored third- to fourth-order agricultural stream, Black Earth Creek, Wisconsin, and estimated processing over a 10 km
reach. Our results show that sediments with submerged and emergent macrophytes (e.g., Potomageton spp. and Phalaris arudinacea) support greater denitrification rates than bare sediments (1.12 μmol N g−1 h−1 vs. 0.29). Sediments with macrophytes were not carbon limited and organic matter fraction was weakly correlated to denitrification.
The highest denitrification potential occurred in macrophyte beds (5.19 μmol N g−1 h−1). Nitrification rates were greater in emergent beds than bare sediments (1.07 μg N ml−1day−1 vs. 0.35) with the greatest nitrification rates during the summer. Total denitrification removal in sediments with macrophytes
was equivalent to 43% of the nitrate stream load (463.7 kg N day−1) during spring and nitrification in sediments with macrophytes was equivalent to 247% of summer ammonium load (3.5 kg N day−1). Although the in-channel connectivity to nitrogen rich water was limited, actual stream nitrogen loads could increase with
removal of macrophytes. Macrophyte beds and supporting fringing wetted areas are important if nitrogen management is a concern
for riparian stream restoration efforts. 相似文献
9.
We used a previously described precipitation gradient in a tropical montane ecosystem of Hawai’i to evaluate how changes in
mean annual precipitation (MAP) affect the processes resulting in the loss of N via trace gases. We evaluated three Hawaiian
forests ranging from 2200 to 4050 mm year−1 MAP with constant temperature, parent material, ecosystem age, and vegetation. In situ fluxes of N2O and NO, soil inorganic nitrogen pools (NH4+ and NO3−), net nitrification, and net mineralization were quantified four times over 2 years. In addition, we performed 15N-labeling experiments to partition sources of N2O between nitrification and denitrification, along with assays of nitrification potential and denitrification enzyme activity
(DEA). Mean NO and N2O emissions were highest at the mesic end of the gradient (8.7±4.6 and 1.1±0.3 ng N cm−2 h−1, respectively) and total oxidized N emitted decreased with increased MAP. At the wettest site, mean trace gas fluxes were
at or below detection limit (≤0.2 ng N cm−2 h−1). Isotopic labeling showed that with increasing MAP, the source of N2O changed from predominately nitrification to predominately denitrification. There was an increase in extractible NH4+ and decline in NO3−, while mean net mineralization and nitrification did not change from the mesic to intermediate sites but decreased dramatically
at the wettest site. Nitrification potential and DEA were highest at the mesic site and lowest at the wet site. MAP exerts
strong control N cycling processes and the magnitude and source of N trace gas flux from soil through soil redox conditions
and the supply of electron donors and acceptors. 相似文献
10.
Understanding mulching influences on nitrogen (N) availability is important for developing N management strategies in plantations
at the upland sites of the southwestern China. Dynamics of biomass loss and nutrient release of mulching material, N availability
in the soil and N mineralization in situ were evaluated for the treatments with different mulch quantity in degraded agricultural
soil. The time taken for 95% decomposition of the initial biomass of Cogon grass (Imperata cylindrical L. Beauv. var. major) was 17 months with a half-life (t
1/2) of about 4.8 months. During the first 4 months about 55.2% of N was released, and after 1-year decomposition about 71.6%
of N was released from the mulch material. The fresh grass mulch increased the available N in the soil as they decomposed.
Compared to no mulch treatment, mulch treatments with 2.5, 5.0 and 7.5 kg m−2 mulching grass increased available N by about 13.1, 40.8 and 56.4% in the top soil (0–5 cm), and about 23.6, 78.0 and 139.3%
in the middle layer (5–20 cm), respectively. The mean annual net N mineralization in the mulched plots had 9.0–40.9% higher
cumulative rate than that in no-mulch plots, and the majority of the accumulated N in the incubated soils existed as NO3–N. There was a positive relationship between the rate of N mineralization and the available N in both the top soil and the
middle layer. Mulch improves soil nutrients and this improvement increased with increasing mulching quantity. The increment
of net N mineralization was approximately 69, 161 and 322 kg N ha−1 year−1 in the soil of 0–20 cm depth for the 2.5, 5.0 and 7.5 kg m−2 grass mulch treatments, respectively. The results from this study will provide a basis to optimize mulching techniques for
poplar plantations in degraded agricultural soils of southwestern China. 相似文献
11.
Christian Brümmer Nicolas Brüggemann Klaus Butterbach-Bahl Ulrike Falk Jörg Szarzynski Konrad Vielhauer Reiner Wassmann Hans Papen 《Ecosystems》2008,11(4):582-600
In a combined field and laboratory study in the southwest of Burkina Faso, we quantified soil-atmosphere N2O and NO exchange. N2O emissions were measured during two field campaigns throughout the growing seasons 2005 and 2006 at five different experimental
sites, that is, a natural savanna site and four agricultural sites planted with sorghum (n = 2), cotton and peanut. The agricultural fields were not irrigated and not fertilized. Although N2O exchange mostly fluctuated between −2 and 8 μg N2O–N m−2 h−1, peak N2O emissions of 10–35 μg N2O–N m−2 h−1 during the second half of June 2005, and up to 150 μg N2O–N m−2 h−1 at the onset of the rainy season 2006, were observed at the native savanna site, whereas the effect of the first rain event
on N2O emissions at the crop sites was low or even not detectable. Additionally, a fertilizer experiment was conducted at a sorghum
field that was divided into three plots receiving different amounts of N fertilizer (plot A: 140 kg N ha−1; plot B: 52.5 kg N ha−1; plot C: control). During the first 3 weeks after fertilization, only a minor increase in N2O emissions at the two fertilized plots was detected. After 24 days, however, N2O emission rates increased exponentially at plot A up to a mean of 80 μg N2O–N m−2 h−1, whereas daily mean values at plot B reached only 19 μg N2O–N m−2 h−1, whereas N2O flux rates at plot C remained unchanged. The calculated annual N2O emission of the nature reserve site amounted to 0.52 kg N2O–N ha−1 a−1 in 2005 and to 0.67 kg N2O–N ha−1 a−1 in 2006, whereas the calculated average annual N2O release of the crop sites was only 0.19 kg N2O–N ha−1 a−1 and 0.20 kg N2O–N ha−1 a−1 in 2005 and 2006, respectively. In a laboratory study, potential N2O and NO formation under different soil moisture regimes were determined. Single wetting of dry soil to medium soil water
content with subsequent drying caused the highest increase in N2O and NO emissions with maximum fluxes occurring 1 day after wetting. The stimulating effect lasted for 3–4 days. A weaker
stimulation of N2O and NO fluxes was detected during daily wetting of soil to medium water content, whereas no significant stimulating effect
of single or daily wetting to high soil water content (>67% WHCmax) was observed. This study demonstrates that the impact of land-use change in West African savanna on N trace gas emissions
is smaller—with the caveat that there could have been potentially higher N2O and NO emissions during the initial conversion—than the effect of timing and distribution of rainfall and of the likely
increase in nitrogen fertilization in the future. 相似文献
12.
Nitrogen Oxide Fluxes and Nitrogen Cycling during Postagricultural Succession and Forest Fertilization in the Humid Tropics 总被引:2,自引:0,他引:2
The effects of changes in tropical land use on soil emissions of nitrous oxide (N2O) and nitric oxide (NO) are not well understood. We examined emissions of N2O and NO and their relationships to land use and forest composition, litterfall, soil nitrogen (N) pools and turnover, soil
moisture, and patterns of carbon (C) cycling in a lower montane, subtropical wet region of Puerto Rico. Fluxes of N2O and NO were measured monthly for over 1 year in old (more than 60 years old) pastures, early- and mid-successional forests
previously in pasture, and late-successional forests not known to have been in pasture within the tabonuco (Dacryodes excelsa) forest zone. Additional, though less frequent, measures were also made in an experimentally fertilized tabonuco forest.
N2O fluxes exceeded NO fluxes at all sites, reflecting the consistently wet environment. The fertilized forest had the highest
N oxide emissions (22.0 kg N · ha−1· y−1). Among the unfertilized sites, the expected pattern of increasing emissions with stand age did not occur in all cases. The
mid-successional forest most dominated by leguminous trees had the highest emissions (9.0 kg N · ha−1· y−1), whereas the mid-successional forest lacking legumes had the lowest emissions (0.09 kg N · ha−1· y−1). N oxide fluxes from late-successional forests were higher than fluxes from pastures. Annual N oxide fluxes correlated positively
to leaf litter N, net nitrification, potential nitrification, soil nitrate, and net N mineralization and negatively to leaf
litter C:N ratio. Soil ammonium was not related to N oxide emissions. Forests with lower fluxes of N oxides had higher rates
of C mineralization than sites with higher N oxide emissions. We conclude that (a) N oxide fluxes were substantial where the
availability of inorganic N exceeded the requirements of competing biota; (b) species composition resulting from historical
land use or varying successional dynamics played an important role in determining N availability; and (c) the established
ecosystem models that predict N oxide loss from positive relationships with soil ammonium may need to be modified.
Received 22 February 2000; accepted 6 September 2000. 相似文献
13.
To clarify the relationship between denitrification activity and dry–wet levels in the littoral wetland sediments of Lake
Biwa, Japan, denitrification rates and their regulating parameters (degree of dryness, redox potential, nitrate concentration)
were measured on different moisture sediments. Redox potential in sediments was higher in the exposed region in contact with
atmosphere than the flooded region covered with water. The nitrate concentration in interstitial waters was undetectable in
the flooded region. On the other hand, concentration in the exposed region increased with increase in the degree of sediment
dryness. The denitrification rate ranged from <0.001 to 0.88 μg N cm−3 h−1 in the exposed region and increased with the increase in the degree of dryness. In the flooded region, on the other hand,
no detectable rate (<0.001 μg N cm−3 h−1) was observed. This indicates that the rates in the exposed region were mainly influenced by nitrate concentration in the
interstitial waters accumulated by desiccation of sediments, whereas rates in the flooded region were strongly limited by
no accumulation of nitrate in the anaerobic conditions. The potential denitrification rate, under the application condition
of nitrate, ranged from 0.13 to 0.26 μg N cm−3 h−1 in the flooded region and from 0.77 to 1.5 μg N cm−3 h−1 in the exposed region. The potential rates in the flooded region had a tendency to be lower than those in the exposed region,
implying that the number of denitrifying bacteria in the flooded region was low due to inactivation of aerobic respiration
and denitrification in the denitrifying bacteria community. Kinetic parameters, maximum rate (V
max) and half-saturation constant (K
s) for denitrification were calculated on the experimental procedures of the wetting–drying cycles of sediments. Both parameters
decreased by the wetting treatment and increased by the drying treatment. The fluctuation of V
max values with wetting–drying cycles indicated that the number of denitrifying bacteria was influenced by aerobic respiration
and denitrification in the denitrifying bacteria community similar to the potential rates, and denitrifying enzyme was induced
by the nitrate supplied by nitrification accelerated through the drying process. On the other hand, the fluctuation of K
s values implied that members of denitrifying bacteria were shifted to members of high nitrate affinity by wetting treatment
and of low nitrate affinity by drying treatment. 相似文献
14.
R. Thomas James Wayne S. Gardner Mark J. McCarthy Stephen A. Carini 《Hydrobiologia》2011,669(1):199-212
Total nitrogen (TN) in Lake Okeechobee, a large, shallow, turbid lake in south Florida, has averaged between 90 and 150 μM
on an annual basis since 1983. No TN trends are evident, despite major storm events, droughts, and nutrient management changes
in the watershed. To understand the relative stability of TN, this study evaluates nitrogen (N) dynamics at three temporal/spatial
levels: (1) annual whole lake N budgets, (2) monthly in-lake water quality measurements in offshore and nearshore areas, and
(3) isotope addition experiments lasting 3 days and using 15N-ammonium (15NH4
+) and 15N-nitrate (15NO3
−) at two offshore locations. Budgets indicate that the lake is a net sink for N. TN concentrations were less variable than
net N loads, suggesting that in-lake processes moderate these net loads. Monthly NO3
− concentrations were higher in the offshore area and higher in winter for both offshore and nearshore areas. Negative relationships
between the percentage of samples classified as algal blooms (defined as chlorophyll a > 40 μg l−1) and inorganic N concentrations suggest N-limitation. Continuous-flow experiments over intact sediment cores measured net
fluxes (μmol N m−2 h−1) between 0 and 25 released from sediments for NH4
+, 0–60 removed by sediments for NO3
−, and 63–68 transformed by denitrification. Uptake rates in the water column (μmol N m−2 h−1) determined by isotope dilution experiments and normalized for water depth were 1,090–1,970 for NH4
+ and 59–119 for NO3
−. These fluxes are similar to previously reported results. Our work suggests that external N inputs are balanced in Lake Okeechobee
by denitrification. 相似文献
15.
We examined soil nitrogen (N) mineralization and nitrification rates, and soil and forest floor properties in one native forest:
evergreen broad-leaved forest (EBLF), one secondary shrubs (SS), and three adjacent plantation forests: Chinese fir plantation
(CFP), bamboo plantation (BP) and waxberry groves (WG) in Tiantong National Forest Park, Eastern China. All forests showed
seasonal dynamics of N mineralization and nitrification rates. Soil N mineralization rate was highest in EBLF (1.6 ± 0.3 mg-N kg−1 yr−1) and lowest in CFP (0.4 ± 0.1 mg-N kg−1 yr−1). Soil nitrification rate was also highest in EBLF (0.6 ± 0.1 mg-N kg−1 yr−1), but lowest in SS (0.02 ± 0.01 mg-N kg−1 yr−1). During forest conversion of EBLF to SS, CFP, BP and WG, soil N mineralization rate (10.7%, 73%, 40.3% and 69.8%, respectively),
soil nitrification rate (94.9%, 32.2%, 33.9% and 39%, respectively), and soil N concentration (50%, 65.4%, 78.9% and 51.9%,
respectively) declined significantly. Annual soil N mineralization was positively correlated with total C and N concentrations
of surface soil and total N concentration of forest floor, and negatively correlated with soil bulk density, soil pH and C:N
ratio of forest floor across the five forests. Annual soil nitrification was positively correlated with total C concentration
of surface soil and N concentration of forest floor, and negatively correlated with soil bulk density and forest floor mass.
In contrast, annual soil nitrification was not correlated to pH value, total N concentration, C:N ratio of surface soil and
total C concentration and C:N ratio of forest floor. 相似文献
16.
Ungulate stimulation of nitrogen cycling and retention in Yellowstone Park grasslands 总被引:4,自引:0,他引:4
We studied how ungulates and a large variation in site conditions influenced grassland nitrogen (N) dynamics in Yellowstone
National Park. In contrast to most grassland N studies that have examined one or two soil N processes, we investigated four
rates, net N mineralization, nitrification, denitrification, and inorganic N leaching, at seven paired sites inside and outside
long-term (33+ year) exclosures. Our focus was how N fluxes were related to one another among highly variable grasslands and
how grazers influenced those relationships. In addition, we examined variation in soil δ15N among grasslands and the relationships between soil 15N abundance and N processes. Previously, ungulates were reported to facilitate net N mineralization across variable Yellowstone
grasslands and denitrification at mesic sites. In this study, we found that herbivores also promoted nitrification among diverse
grasslands. Furthermore, net N mineralization, nitrification, and denitrification (kg N ha–1 year–1, each variable) were postively and linearly related to one another among all grasslands (grazed and fenced), and grazers
reduced the nitrification/net N mineralization and denitrification/net N mineralization ratios, indicating that ungulates
inhibited the proportion of available NH4
+ that was nitrified and denitrified. There was no relationship between net N mineralization or nitrification with leaching
(indexed by inorganic N adsorbed to resin buried at the bottom of rooting zones) and leaching was unaffected by grazers. Soil
δ15N was positively and linearly related to in situ net N mineralization and nitrification in ungrazed grasslands; however, there
was no relationship between isotopic composition of N and those rates among grazed grasslands. The results suggested that
grazers simultaneously increased N availability (stimulated net N mineralization and nitrification per unit area) and N conservation
(reduced N loss from the soil per unit net N mineralization) in Yellowstone grasslands. Grazers promoted N retention by stimulating
microbial productivity, probably caused by herbivores promoting labile soil C. Process-level evidence for N retention by grazers
was supported by soil δ15N data. Grazed grassland with high rates of N cycling had substantially lower soil δ15N relative to values expected for ungrazed grassland with comparable net N mineralization and nitrification rates. These soil
15N results suggest that ungulates inhibited N loss at those sites. Such documented evidence for consumer control of N availability
to plants, microbial productivity, and N retention in Yellowstone Park is further testimony for the widespread regulation
of grassland processes by large herbivores.
Received: 5 May 1999 / Accepted: 1 November 1999 相似文献
17.
Compared to upland forests, riparian forest soils have greater potential to remove nitrate (NO3) from agricultural runoff through denitrification. It is unclear, however, whether prolonged exposure of riparian soils to nitrogen (N) loading will affect the rate of denitrification and its end products. This research assesses the rate of denitrification and nitrous oxide (N2O) emissions from riparian forest soils exposed to prolonged nutrient runoff from plant nurseries and compares these to similar forest soils not exposed to nutrient runoff. Nursery runoff also contains high levels of phosphate (PO4). Since there are conflicting reports on the impact of PO4 on the activity of denitrifying microbes, the impact of PO4 on such activity was also investigated. Bulk and intact soil cores were collected from N-exposed and non-exposed forests to determine denitrification and N2O emission rates, whereas denitrification potential was determined using soil slurries. Compared to the non-amended treatment, denitrification rate increased 2.7- and 3.4-fold when soil cores collected from both N-exposed and non-exposed sites were amended with 30 and 60 μg NO3-N g−1 soil, respectively. Net N2O emissions were 1.5 and 1.7 times higher from the N-exposed sites compared to the non-exposed sites at 30 and 60 μg NO3-N g−1 soil amendment rates, respectively. Similarly, denitrification potential increased 17 times in response to addition of 15 μg NO3-N g−1 in soil slurries. The addition of PO4 (5 μg PO4-P g−1) to soil slurries and intact cores did not affect denitrification rates. These observations suggest that prolonged N loading did not affect the denitrification potential of the riparian forest soils; however, it did result in higher N2O emissions compared to emission rates from non-exposed forest soils. 相似文献
18.
Impact of drying and re-wetting on N,P and K dynamics in a wetland soil 总被引:11,自引:0,他引:11
As increased nutrient availability due to drainage is considered a major cause of eutrophication in wetlands rewetting of drained wetlands is recommended as a restoration measure. The effect of soil drying and rewetting on the contribution of various nutrient release or transformation processes to changed nutrient availability for plants is however weakly understood. We measured effects of soil drying and re-wetting on N mineralization, and denitrification, as well as on release of dissolved organic nitrogen (DON), phosphorus, and potassium in incubated soil cores from a wet meadow in southern Sweden. Additionally, the impact of re-wetting with sulphate-enriched water was studied. Soil drying stimulated N mineralization (3 times higher) and reduced denitrification (5 times lower) compared to continuously wet soil. In the wet cores, denitrification increased to 20 mg N m–2 d–1, which was much higher than denitrification measured in the field. In the field, increased inorganic-N availability for plants due to drainage seemed primarily to be caused by increased N mineralization, and less by decreased denitrification. Soil drying also stimulated the release of DON and K, but P release was not affected. Re-wetting of dried soil cores strongly stimulated denitrification (up to 160 mg N m–2 d–1), but N mineralization was not significantly decreased, neither were DON or K release. In contrast, the extractable P pool increased upon soil wetting. Re-wetting with sulphate-enriched water had no effect on any of the nutrient release or transformation rates. We conclude that caution is required in re-wetting of drained wetlands, because it may unintendently cause internal eutrophication through an increased P availability for plants. 相似文献
19.
Nitrogen export by surface runoff from a small agricultural watershed in southeast China: seasonal pattern and primary mechanism 总被引:1,自引:0,他引:1
The seasonal pattern and primary mechanism of nitrogen (N) export by surface runoff from the Wuchuan subwatershed (WCW), an
agricultural upper watershed (1.88 km2) located in southeast China, were investigated based on extensive streamwater measurements in 2004–2005 under subtropical
climatic conditions. The results disclosed a highly variable but strong linkage between hydrological and anthropogenic controls
and N export. N export via surface runoff presented a significant seasonal pattern caused by changes in rainfall and watershed
N input. Approximately 75% of the annual N export (67 kg ha−1) was flushed by those storm runoff mainly occurred during the wet season (March through September). The WCW dataset of N
concentrations and loads during both baseflow and stormflow implied an interactive effects of anthropogenetic N input and
hydrology conditions: N export was flush-driven in late spring, summer and autumn (wet season), but highly related with soil
N in winter and early spring. Compared to undisturbed watersheds under similar rainfall conditions, WCW exported a considerable
amount of N due to intensive fertilizer application (a mean of 690 kg N ha−1 year−1, commonly as surface applications). This work provides a first characterization of a small agricultural Chinese catchment
under subtropical climates and its associated N export behavior. 相似文献
20.
Differential Controls of Water Input on Litter Decomposition and Nitrogen Dynamics in the Patagonian Steppe 总被引:3,自引:0,他引:3
Studies of the effects of precipitation on litter decomposition and nitrogen mineralization in arid and semiarid environments
have demonstrated contradictory results. We conducted a manipulative experiment with rainout shelters in the semiarid Patagonian
steppe, aimed at assessing the direct effects of water availability on litter decomposition and net nitrogen mineralization
while isolating the indirect effects. We created four levels of precipitation input: control and three levels (30, 55 and
80%) of precipitation interception and we examined litter decomposition and nutrient release of a dominant grass species,
Stipa speciosa, inorganic soil nitrogen, and in situ net nitrogen mineralization over two consecutive years. Litter decomposition rates
(k, year−1) varied significantly (P < 0.001) among precipitation interception treatments and were positively correlated with incoming annual precipitation (APPT,
mm/year) (k = 0.0007 × APPT + 0.137). In contrast, net N mineralization was not correlated with incoming precipitation. Soil NO3− significantly decreased with increasing precipitation input, whereas soil NH4+ concentration did not differ among precipitation interception treatments. Controls of water input on litter decomposition
appear to be different from controls on N mineralization in the semiarid Patagonian steppe. We suggest that although water
availability affects both the mineralization of C and N, it differentially affects the movement and fate of the inorganic
products. A consequence of the accumulation of inorganic N during dry episodes is that periods of maximum water and soil nutrient
availability may occur at different times. This asynchrony in the availability of N and water in the soil may explain the
observed lags in the response of primary production to increases in water availability. 相似文献