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1.
The above-ground accumulation of N,N uptake and litter quality resulting from improved or deteriorated availability of water
and nutrients in a 25 year old Norway spruce stand in SW Sweden (as part of the Skogaby project) is presented. Treatment include
irrigation; artificial drought; ammonium sulphate addition; N-free-fertilisation and irrigation with liquid fertilisers including
a complete set of nutrients according to the Ingested principle (fertigation).
At start of the experiment the stand contained 86.5 t dry mass and 352 kg N ha−1. The following three years the annual N uptake in untreated trees was 32 kg N ha−1 to be compared with the annual N throughfall of 17 kg ha−1. Simultaneously, the treatment with ammonium sulphate and liquid fertilisation resulted in 48 and 56 kg ha−1 y−1, respectively, in treatment specific N-uptake following an application of 100 kg N ha−1 y−1. Addition of a N-free fertiliser resulted in improved N-uptake by 19 kg N ha−1 y−1 and irrigation by 10 kg N ha−1 y−1, compared to control. A linear relation between total above-ground dry mass production and N-uptake was found for trees growing
with similar water availability. Dry mass production increased with increased water availability given the same N-uptake.
It is concluded that the studied stand this far is not N saturated', as N fertilisation resulted in both increased N uptake
and increased growth. Addition of a N-free-fertiliser resulted in increased uptake of N compared to the control, indicating
an increased mineralisation rate or uptake capacity of the root system. The linear relation between N uptake and biomass production
shows that at this study site N is a highly limiting factor for growth. 相似文献
2.
Akinori Yamada Tetsushi Inoue Decha Wiwatwitaya Moriya Ohkuma Toshiaki Kudo Atsuko Sugimoto 《Ecosystems》2006,9(1):75-83
Nitrogen (N) fixed by termites was evaluated as a N input to decomposition processes in two tropical forests, a dry deciduous
forest (DDF) and the neighboring dry evergreen forest (DEF), Thailand. A diverse group of termite species were assayed by
acetylene reduction method and only the wood/litter-feeding termites were found to fix N. More intensive samplings of two
abundant species, Microcerotermes crassus and Globitermes sulphureus, were done across several seasons, suggesting N fixation rates of 0.21 and 0.28 kg ha−1 y−1 by termites in the DDF and DEF, respectively. Also, estimates of asymbiotic N fixation rates were 0.75 and 3.95 kg ha−1 y−1. N fixed by termites and by asymbiotic fixers is directly supplied to decomposers breaking down dead plant material and could
be a major source of their N. N fixed by termites was 7–22% of that fixed by termites and asymbiotic fixers. Although N fixed
by termites is a small input compared to other inputs, this N is likely important for decomposition processes. 相似文献
3.
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
4.
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
5.
Differences in Englemann Spruce Forest Biogeochemistry East and West of the Continental Divide in Colorado, USA 总被引:5,自引:2,他引:3
We compared Englemann spruce biogeochemical processes in forest stands east and west of the Continental Divide in the Colorado
Front Range. The divide forms a natural barrier for air pollutants such that nitrogen (N) emissions from the agricultural
and urban areas of the South Platte River Basin are transported via upslope winds to high elevations on the east side but
rarely cross over to the west side. Because there are far fewer emissions sources to the west, atmospheric N deposition is
1–2 kg N ha−1 y−1 on the west side, as compared with 3–5 kg N ha−1 y−1 on the east side. Species composition, elevation, aspect, parent material, site history, and climate were matched as closely
as possible across six east and six west side old-growth forest stands. Higher N deposition sites had significantly lower
organic horizon C:N and lignin:N ratios, lower foliar C:N ratios, as well as greater %N, higher N:Ca, N:Mg, and N:P ratios,
and higher potential net mineralization rates. When C:N ratios dropped below 29, as they did in east-side organic horizon
soils, mineralization rates increased linearly. Our results are comparable to those from studies of the northeastern United
States and Europe that have found changes in forest biogeochemistry in response to N deposition inputs between 3 and 60 kg
ha−1 y−1. Though they are low by comparison with more densely populated and agricultural regions, current levels of N deposition,
have caused measurable changes in Englemann spruce forest biogeochemistry east of the Continental Divide in Colorado.
Received 22 January 2001; accepted 11 June 2001. 相似文献
6.
Nitrogen Removal by Riparian Buffers along a European Climatic Gradient: Patterns and Factors of Variation 总被引:9,自引:1,他引:8
Sergi Sabater Andrea Butturini Jean-Christophe Clement Tim Burt David Dowrick Mariet Hefting Véronique Matre Gilles Pinay Carmen Postolache Marek Rzepecki Francesc Sabater 《Ecosystems》2003,6(1):0020-0030
We evaluated nitrogen (N) removal efficiency by riparian buffers at 14 sites scattered throughout seven European countries
subject to a wide range of climatic conditions. The sites also had a wide range of nitrate inputs, soil characteristics, and
vegetation types. Dissolved forms of N in groundwater and associated hydrological parameters were measured at all sites; these
data were used to calculate nitrate removal by the riparian buffers. Nitrate removal rates (expressed as the difference between
the input and output nitrate concentration in relation to the width of the riparian zone) were mainly positive, ranging from
5% m−1 to 30% m−1, except for a few sites where the values were close to zero. Average N removal rates were similar for herbaceous (4.43% m−1) and forested (4.21% m−1) sites. Nitrogen removal efficiency was not affected by climatic variation between sites, and no significant seasonal pattern
was detected. When nitrate inputs were low, a very large range of nitrate removal efficiencies was found both in the forested
and in the nonforested sites. However, sites receiving nitrate inputs above 5 mg N L−1 showed an exponential negative decay of nitrate removal efficiency (nitrate removal efficiency = 33.6 e−0.11 NO3input, r
2
= 0.33, P < 0.001). Hydraulic gradient was also negatively related to nitrate removal (r = −0.27, P < 0.05) at these sites. On the basis of this intersite comparison, we conclude that the removal of nitrate by biological mechanisms
(for example, denitrification, plant uptake) in the riparian areas is related more closely to nitrate load and hydraulic gradient
than to climatic parameters.
Received 15 August 2001; accepted 2 May 2002. 相似文献
7.
N and P budgets quantify inputs and outputs of nutrients at the catchment scale to allow evaluation of inputs and outputs
as well as inferences about transport and processing based on unaccounted-for nutrients. N and P budgets were constructed
for two catchments in southeastern Michigan with markedly different numbers of impoundments, over two years, to evaluate the
influence of impoundments on nutrient fluxes from each catchment. The Huron, with 88 impoundments >10 ha, stored 156 kg P km−2 y−1, while the Raisin (with 14 impoundments) had a net export of 102 kg P km−2 y−1. The Huron catchment also stored and denitrified more N than the Raisin catchment – 2,418 kg N km−2 y−1 compared to 1,538 kg N km−2 y−1. Riverine export of N and P also varied markedly between the catchments, with the Huron River exporting 288 kg N and 7 kg P km−2 y−1 and the Raisin River exporting 1,268 kg N and 34 kg P km−2 y−1. We then re-calculated budget results from previous studies using the approach of the present study, altering input and outputs
fluxes as well as system boundaries to obtain comparable budgets. For these comparable budgets, annual P outputs on average
accounted for 77% of inputs whereas N outputs accounted for only 39% of N inputs. Across catchments, the percent of inputs
exported by the river averaged 16% for N and 5% for P, indicating more effective retention of P than N. 相似文献
8.
The nitrogen (N) budget was developed for Jiulong River Watershed (JRW), an agricultural watershed in a warm and humid area
of southeast China. Water quality monitoring, field surveys, modelling and GIS techniques were applied to estimate N flux
of atmospheric deposition, mineralization, runoff, denitrification, and ammonia volatilization. Over the whole watershed,
fertilizers, import of animal feeds, biotic fixation, mineralization and atmospheric deposition contributed 67.1%, 16.5%,
2.1%, 4.9% and 9.5%, respectively, of total N input (129.3 kg N ha−1 year−1). Runoff, sale of production, denitrification, and ammonia volatilization contributed 7.3%, 24.4%, 10.5% and 57.8% of total
N output (72.9 kg N ha−1 year−1), respectively. The N budget for the JRW suggested that more than 50% of the N input was lost to the environment, and about
14% was discharged as riverine N, which indicated that agricultural and human activities in the watershed substantially impacted
the estuary and coastal water quality, and so altered the N biogeochemistry process. 相似文献
9.
The Long-term Effects of Disturbance on Organic and Inorganic Nitrogen Export in the White Mountains, New Hampshire 总被引:22,自引:8,他引:14
Traditional biogeochemical theories suggest that ecosystem nitrogen retention is controlled by biotic N limitation, that stream
N losses should increase with successional age, and that increasing N deposition will accelerate this process. These theories
ignore the role of dissolved organic nitrogen (DON) as a mechanism of N loss. We examined patterns of organic and inorganic
N export from sets of old-growth and historically (80–110 years ago) logged and burned watersheds in the northeastern US,
a region of moderate, elevated N deposition. Stream nitrate concentrations were strongly seasonal, and mean (± SD) nitrate
export from old-growth watersheds (1.4 ± 0.6 kg N ha−1 y−1) was four times greater than from disturbed watersheds (0.3 ± 0.3 kg N ha−1 y−1), suggesting that biotic control over nitrate loss can persist for a century. DON loss averaged 0.7 (± 0.2) kg N ha−1 y−1 and accounted for 28–87% of total dissolved N (TDN) export. DON concentrations did not vary seasonally or with successional
status, but correlated with dissolved organic carbon (DOC), which varied inversely with hardwood forest cover. The patterns
of DON loss did not follow expected differences in biotic N demand but instead were consistent with expected differences in
DOC production and sorption. Despite decades of moderate N deposition, TDN export was low, and even old-growth forests retained
at least 65% of N inputs. The reasons for this high N retention are unclear: if due to a large capacity for N storage or biological
removal, N saturation may require several decades to occur; if due to interannual climate variability, large losses of nitrate
may occur much sooner.
Received 27 April 1999; accepted 30 May 2000. 相似文献
10.
Richard D. Bowden Mark S. Castro Jerry M. Melillo Paul A. Steudler John D. Aber 《Biogeochemistry》1993,21(2):61-71
Fluxes of nitrous oxide (N2O), carbon dioxide (CO2), and methane (CH4) between soils and the atmosphere were measured monthly for one year in a 77-year-old temperate hardwood forest following
a simulated hurricane blowdown. Emissions of CO2 and uptake of CH4 for the control plot were 4.92 MT C ha−1 y−1 and 3.87 kg C ha−1 y−1, respectively, and were not significantly different from the blowdown plot. Annual N2O emissions in the control plot (0.23 kg N ha−1 y−1) were low and were reduced 78% by the blowdown. Net N mineralization was not affected by the blowdown. Net nitrification
was greater in the blowdown than in the control, however, the absolute rate of net nitrification, as well as the proportion
of mineralized N that was nitrified, remained low. Fluxes of CO2 and CH4 were correlated positively to soil temperature, and CH, uptake showed a negative relationship to soil moisture. Substantial
resprouting and leafing out of downed or damaged trees, and increased growth of understory vegetation following the blowdown,
were probably responsible for the relatively small differences in soil temperature, moisture, N availability, and net N mineralization
and net nitrification between the control and blowdown plots, thus resulting in no change in CO2 or CH4 fluxes, and no increase in N2O emissions. 相似文献
11.
Fumikazu Akamatsu Koichi Ide Koji Shimano Hideshige Toda 《Landscape and Ecological Engineering》2011,7(1):109-115
Fixation of river flow passages and riverbed degradation may facilitate the development of higher floodplains with the establishment
of exotic species such as black locust (Robinia pseudoacacia L.). We quantitatively evaluated the relationship between nitrogen (N) levels in black locust trees and in sediments under
different flood disturbance regimes in a riparian area of the Chikuma River. In this study, allometric equations were developed
for relating leaf N content to diameter at breast height of black locust. The amount of leaf N in black locust increased with
distance from the river, reaching 159 kg N ha−1 at 180 m from the river. There was a small difference in N content between green and fallen leaves (0.2%), and so the leaf
N was almost equivalent to N input to riparian sediments. Fine sediments accumulated on the riparian area, where the amount
of sediments N increased with distance from the river, ranging from 1091 ± 767 to 4953 ± 2953 kg N ha−1. The N accumulation rates also increased with distance from the river, corresponding with the amount of leaf N in black locust
per unit area, but the former exceeded the latter. The sediment N accumulation might be accelerated by sediment trapping effect
due to riparian vegetation itself. A large input of N provided by invaded black locust might alter nutrient dynamics and native
plant community structure in the riparian area. 相似文献
12.
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
13.
E. Bornemisza 《Plant and Soil》1982,67(1-3):241-246
Nitrogen inputs to the coffee ecosystem are dominated by additions of fertilizer-N (100–300 kg N ha?1 yr?1). Small nitrogen inputs from rains and variable from inputs fixation by the leguminous shade trees can amount to 1–40 kg N ha?1 yr?1. Organic matter mineralization can be an important nitrogen source also. Nitrogen losses from the system include removal of N in the harvest (15–90 kg N ha?1 yr?1), the removal of coffee and shade tree prunings for firewood, losses from erosion, leaching losses and gaseous losses. Unfortunately, very little information exists for leaching and gaseous losses and for the factors that regulate these processes. The overall nitrogen cycle in shaded coffee plantings includes three interrelated subsystems. These are the coffee, shade and weeds subcycles. 相似文献
14.
Soil nitrogen cycling and nitrous oxide flux in a Rocky Mountain Douglas-fir forest: effects of fertilization,irrigation and carbon addition 总被引:6,自引:4,他引:2
Pamela A. Matson Stith Thoma Gower Carol Volkmann Christine Billow Charles C. Grier 《Biogeochemistry》1992,18(2):101-117
Nitrous oxide fluxes and soil nitrogen transformations were measured in experimentally-treated high elevation Douglas-fir
forests in northwestern New Mexico, USA. On an annual basis, forests that were fertilized with 200 kg N/ha emitted an average
of 0.66 kg/ha of N2O-N, with highest fluxes occurring in July and August when soils were both warm and wet. Control, irrigated, and woodchip
treated plots were not different from each other, and annual average fluxes ranged from 0.03 to 0.23 kg/ha. Annual net nitrogen
mineralization and nitrate production were estimated in soil and forest floor usingin situ incubations; fertilized soil mineralized 277 kg ha−1 y−1 in contrast to 18 kg ha−1 y−1 in control plots. Relative recovery of15NH4-N applied to soil in laboratory incubations was principally in the form of NO3-N in the fertilized soils, while recovery was mostly in microbial biomass-N in the other treatments. Fertilization apparently
added nitrogen that exceeded the heterotrophic microbial demand, resulting in higher rates of nitrate production and higher
nitrous oxide fluxes. Despite the elevated nitrous oxide emission resulting from fertilization, we estimate that global inputs
of nitrogen into forests are not currently contributing significantly to the increasing concentrations of nitrous oxide in
the atmosphere. 相似文献
15.
Jean-Michel Harmand Hector Ávila Etienne Dambrine Ute Skiba Sergio de Miguel Reina Vanessa Renderos Robert Oliver Francisco Jiménez John Beer 《Biogeochemistry》2007,85(2):125-139
Nitrogen fertilization is a key factor for coffee production but creates a risk of water contamination through nitrate (NO3−) leaching in heavily fertilized plantations under high rainfall. The inclusion of fast growing timber trees in these coffee
plantations may increase total biomass and reduce nutrient leaching. Potential controls of N loss were measured in an unshaded
coffee (Coffea arabica L.) plot and in an adjacent coffee plot shaded with the timber species Eucalyptus deglupta Blume (110 trees ha−1), established on an Acrisol that received 180 kg N ha−1 as ammonium-nitrate and 2,700 mm yr−1 rainfall. Results of the one year study showed that these trees had little effect on the N budget although some N fluxes
were modified. Soil N mineralization and nitrification rates in the 0–20 cm soil layer were similar in both systems (≈280 kg N ha−1 yr−1). N export in coffee harvest (2002) was 34 and 25 kg N ha−1 yr−1 in unshaded and shaded coffee, and N accumulation in permanent biomass and litter was 25 and 45 kg N ha−1 yr−1, respectively. The losses in surface runoff (≈0.8 kg mineral N ha−1 yr−1) and N2O emissions (1.9 kg N ha−1 yr−1) were low in both cases. Lysimeters located at 60, 120, and 200 cm depths in shaded coffee, detected average concentrations
of 12.9, 6.1 and 1.2 mg NO3−-N l−1, respectively. Drainage was slightly reduced in the coffee-timber plantation. NO3− leaching at 200 cm depth was about 27 ± 10 and 16 ± 7 kg N ha−1 yr−1 in unshaded and shaded coffee, respectively. In both plots, very low NO3− concentrations in soil solution at 200 cm depth (and in groundwater) were apparently due to NO3− adsorption in the subsoil but the duration of this process is not presently known. In these conventional coffee plantations,
fertilization and agroforestry practices must be refined to match plant needs and limit potential NO3− contamination of subsoil and shallow soil water. 相似文献
16.
17.
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
18.
Nitrogen mineralization in high elevation forests of the Appalachians. I. Regional patterns in southern spruce-fir forests 总被引:4,自引:0,他引:4
Annual and seasonal rates of net nitrogen mineralization were determined for 19 sites in the spruce-fir forests of the Southern
Appalachian Mountains. These sites included high and low elevation stands of red spruce (Picea rubens Sarg.) and Fraser fir (Abies fraseri (Pursh.) Poir.) on east and west exposures on Whitetop Mountain, Virginia; Mt. Mitchell, North Carolina; and Clingman's Dome
in the Great Smoky Mountains National Park. Mineralization rates were determined using in situ soil incubations in PVC tubes
with ion exchange resin bags placed in the bottom of the tubes to collect leachate. Throughfall was collected in resin bags
placed in the top of the tubes. Average initial NH4-N + NO3-N ranged from 0.6 to 4.8 kg N/ha across all plots, and average mineralization rates ranged from 26 to 180 kg-N ha−1 yr−1. Throughfall ranged from 18 to 32 kg-N ha−1 yr−1 with NH4-N accounting for about two-thirds of the throughfall N across all sites. Throughfall and mineralization rates were not related
to elevation or exposure. The high rates of N mineralization and relatively high nitrate concentrations indicate that leaching
losses of nitrogen and associated cations could be substantial.
Requests for offprints 相似文献
19.
Toshiyuki Ohtsuka Wenhong Mo Takami Satomura Motoko Inatomi Hiroshi Koizumi 《Ecosystems》2007,10(2):324-334
Biometric based carbon flux measurements were conducted over 5 years (1999–2003) in a temperate deciduous broad-leaved forest
of the AsiaFlux network to estimate net ecosystem production (NEP). Biometric based NEP, as measured by the balance between
net primary production (including NPP of canopy trees and of forest floor dwarf bamboo) and heterotrophic respiration (RH),
clarified the contribution of various biological processes to the ecosystem carbon budget, and also showed where and how the
forest is storing C. The mean NPP of the trees was 5.4 ± 1.07 t C ha−1 y−1, including biomass increment (0.3 ± 0.82 t C ha−1 y−1), tree mortality (1.0 ± 0.61 t C ha−1 y−1), aboveground detritus production (2.3 ± 0.39 t C ha−1 y−1) and belowground fine root production (1.8 ± 0.31 t C ha−1 y−1). Annual biomass increment was rather small because of high tree mortality during the 5 years. Total NPP at the site was
6.5 ± 1.07 t C ha−1 y−1, including the NPP of the forest floor community (1.1 ± 0.06 t C ha−1 y−1). The soil surface CO2 efflux (RS) was averaged across the 5 years of record using open-flow chambers. The mean estimated annual RS amounted to
7.1 ± 0.44 t C ha−1, and the decomposition of soil organic matter (SOM) was estimated at 3.9 ± 0.24 t C ha−1. RH was estimated at 4.4 ± 0.32 t C ha−1 y−1, which included decomposition of coarse woody debris. Biometric NEP in the forest was estimated at 2.1 ± 1.15 t C ha−1 y−1, which agreed well with the eddy-covariance based net ecosystem exchange (NEE). The contribution of woody increment (Δbiomass + mortality)
of the canopy trees to NEP was rather small, and thus the SOM pool played an important role in carbon storage in the temperate
forest. These results suggested that the dense forest floor of dwarf bamboo might have a critical role in soil carbon sequestration
in temperate East Asian deciduous forests. 相似文献
20.
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