共查询到20条相似文献,搜索用时 31 毫秒
1.
Landscape Controls on Organic and Inorganic Nitrogen Leaching across an Alpine/Subalpine Ecotone,Green Lakes Valley,Colorado Front Range 总被引:5,自引:0,他引:5
Here we report measurements of organic and inorganic nitrogen (N) fluxes from the high-elevation Green Lakes Valley catchment
in the Colorado Front Range for two snowmelt seasons (1998 and 1999). Surface water and soil samples were collected along
an elevational gradient extending from the lightly vegetated alpine to the forested subalpine to assess how changes in land
cover and basin area affect yields and concentrations of ammonium-N (NH4-N), nitrate-N (NO3-N), dissolved organic N (DON), and particulate organic N (PON). Streamwater yields of NO3-N decreased downstream from 4.3 kg ha−1 in the alpine to 0.75 kg ha−1 at treeline, while yields of DON were much less variable (0.40–0.34 kg ha−1). Yields of NH4-N and PON were low and showed little variation with basin area. NO3-N accounted for 40%–90% of total N along the sample transect and was the dominant form of N at all but the lowest elevation
site. Concentrations of DON ranged from approximately 10% of total N in the alpine to 45% in the subalpine. For all sites,
volume-weighted mean concentrations of total dissolved nitrogen (TDN) were significantly related to the DIN:DON ratio (R
2 = 0.81, P < 0.001) Concentrations of NO3-N were significantly higher at forested sites that received streamflow from the lightly vegetated alpine reaches of the catchment
than in a control catchment that was entirely subalpine forest, suggesting that the alpine may subsidize downstream forested
systems with inorganic N. KCl-extractable inorganic N and microbial biomass N showed no relationship to changes in soil properties
and vegetative cover moving downstream in catchment. In contrast, soil carbon–nitrogen (C:N) ratios increased with increasing
vegetative cover in catchment and were significantly higher in the subalpine compared to the alpine (P < 0.0001) Soil C:N ratios along the sample transect explained 78% of the variation in dissolved organic carbon (DOC) concentrations
and 70% of the variation in DON concentrations. These findings suggest that DON is an important vector for N loss in high-elevation
ecosystems and that streamwater losses of DON are at least partially dependent on catchment soil organic matter stoichiometry.
Received 26 July 2001; accepted 6 May 2002. 相似文献
2.
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
3.
Winter and summer nitrous oxide and nitrogen oxides fluxes from a seasonally snow-covered subalpine meadow at Niwot Ridge,Colorado 总被引:4,自引:3,他引:1
Gianluca Filippa Michele Freppaz Mark W. Williams Detlev Helmig Daniel Liptzin Brian Seok Brad Hall Kurt Chowanski 《Biogeochemistry》2009,95(1):131-149
The soil emission rates (fluxes) of nitrous oxide (N2O) and nitrogen oxides (NO + NO2 = NO
x
) through a seasonal snowpack were determined by a flux gradient method from near-continuous 2-year measurements using an
automated system for sampling interstitial air at various heights within the snowpack from a subalpine site at Niwot Ridge,
Colorado. The winter seasonal-averaged N2O fluxes of 0.047–0.069 nmol m−2 s−1 were ~15 times higher than observed NO
x
fluxes of 0.0030–0.0067 nmol m−2 s−1. During spring N2O emissions first peaked and then dropped sharply as the soil water content increased from the release of snowpack meltwater,
while other gases, including NO
x
and CO2 did not show this behavior. To compare and contrast the winter fluxes with snow-free conditions, N2O fluxes were also measured at the same site in the summers of 2006 and 2007 using a closed soil chamber method. Summer N2O fluxes followed a decreasing trend during the dry-out period after snowmelt, interrupted by higher values related to precipitation
events. These peaks were up to 2–3 times higher than the background summer levels. The integrated N2O-N loss over the summer period was calculated to be 1.1–2.4 kg N ha−1, compared to ~0.24–0.34 kg N ha−1 for the winter season. These wintertime N2O fluxes from subniveal soil are generally higher than the few previously published data. These results are of the same order
of magnitude as data from more productive ecosystems such as fertilized grasslands and high-N-cycling forests, most likely
because of a combination of the relatively well-developed soils and the fact that subnivean biogeochemical processes are promoted
by the deep, insulating snowpack. Hence, microbially mediated oxidized nitrogen emissions occurring during the winter can
be a significant part of the N-cycle in seasonally snow-covered subalpine ecosystems. 相似文献
4.
Soil carbon storage, litterfall and CO2 efflux in fertilized and unfertilized larch (Larix leptolepis) plantations 总被引:1,自引:0,他引:1
Choonsig Kim 《Ecological Research》2008,23(4):757-763
This study evaluated the effects of forest fertilization on the forest carbon (C) dynamics in a 36-year-old larch (Larix leptolepis) plantation in Korea. Above- and below-ground C storage, litterfall, root decomposition and soil CO2 efflux rates after fertilization were measured for 2 years. Fertilizers were applied to the forest floor at rates of 112 kg
N ha−1 year−1, 75 kg P ha−1 year−1 and 37 kg K ha−1 year−1 for 2 years (May 2002, 2003). There was no significant difference in the above-ground C storage between fertilized (41.20 Mg C
ha−1) and unfertilized (42.25 Mg C ha−1) plots, and the C increment was similar between the fertilized (1.65 Mg C ha−1 year−1) and unfertilized (1.52 Mg C ha−1 year−1) plots. There was no significant difference in the soil C storage between the fertilized and unfertilized plots at each soil
depth (0–15, 15–30 and 30–50 cm). The organic C inputs due to litterfall ranged from 1.57 Mg C ha−1 year−1 for fertilized to 1.68 Mg C ha−1 year−1 for unfertilized plots. There was no significant difference in the needle litter decomposition rates between the fertilized
and unfertilized plots, while the decomposition of roots with 1–2 mm diameters increased significantly with the fertilization
relative to the unfertilized plots. The mean annual soil CO2 efflux rates for the 2 years were similar between the fertilized (0.38 g CO2 m−2 h−1) and unfertilized (0.40 g CO2 m−2 h−1) plots, which corresponded with the similar fluctuation in the organic carbon (litterfall, needle and root decomposition)
and soil environmental parameters (soil temperature and soil water content). These results indicate that little effect on
the C dynamics of the larch plantation could be attributed to the 2-year short-term fertilization trials and/or the soil fertility
in the mature coniferous plantation used in this study. 相似文献
5.
A regional data set on water chemistry from 1995 was used to set critical values for the survival of brown trout in Norwegian
lakes (n = 790) in relation to pH, inorganic Al and acid neutralizing capacity (ANC). ANC was estimated both traditionally (ANCtrad) and modified by treating one-third of the dissolved organic matter as part of the strong acid anions (ANCmod). The threshold value to avoid fish damage (ANClimit) was compared with that found in a similar study from 1986. Brown trout populations were categorized as unaffected, damaged
or extinct on the basis of questionnaires. In 1995, threshold values to avoid fish damage on the basis of ANCtrad and ANCmod were 67 and 48 μeq l−1, respectively, compared with 20 and 8 μeq l−1, respectively, in 1986. The higher ANClimit found for the data from 1995 is probably caused by a lower pH and a higher inorganic Al concentration at a given ANC value
in 1995 than in the 1980s. ANClimit was highly related to organic carbon concentrations in the study lakes, being estimated at 33, 73 and >100 μeq l−1 for three different TOC categories (<2 mg C l−1, 2–5 mg C l−1 and >5 mg C l−1). These differences in ANClimit are due to lower pH and higher concentrations of inorganic Al in humic lakes than in clear water lakes at the same level
of ANC. It is suggested that the change in ANClimit for fish in acidified lakes is linked to increased concentrations of TOC in recent years. 相似文献
6.
Adam Gibbon Miles R. Silman Yadvinder Malhi Joshua B. Fisher Patrick Meir Michael Zimmermann Greta C. Dargie William R. Farfan Karina C. Garcia 《Ecosystems》2010,13(7):1097-1111
Improved management of carbon storage by terrestrial biomes has significant value for mitigating climate change. The carbon
value of such management has the potential to provide additional income to rural communities and provide biodiversity and
climate adaptation co-benefits. Here, we quantify the carbon stores in a 49,300-ha landscape centered on the cloud forest–grassland
transition of the high Andes in Manu National Park, Peru. Aboveground carbon densities were measured across the landscape
by field sampling of 70 sites above and below the treeline. The forest near the treeline contained 63.4 ± 5.2 Mg C ha−1 aboveground, with an additional 13.9 ± 2.8 Mg C ha−1 estimated to be stored in the coarse roots, using a root to shoot ratio of 0.26. Puna grasslands near the treeline were found
to store 7.5 ± 0.7 Mg C ha−1 in aboveground biomass. Comparing our result to soil data gathered by Zimmermann and others (Ecosystems 13:62–74, 2010), we found the ratio of belowground:aboveground carbon decreased from 15.8 on the puna to 8.6 in the transition zone and
2.1 in the forest. No significant relationships were found between carbon densities and slope, altitude or fire disturbance
history, though grazing (for puna) was found to reduce aboveground carbon densities significantly. We scaled our study sites
to the study region with remote sensing observations from Landsat. The carbon sequestration potential of improved grazing
management and assisted upslope treeline migration was also estimated. Afforestation of puna at the treeline could generate
revenues of US $1,374 per ha over the project lifetime via commercialization of the carbon credits from gains in aboveground
carbon stocks. Uncertainties in the fate of the large soil carbon stocks under an afforestation scenario exist. 相似文献
7.
Rose C. Kaggwa Anne A. van Dam John S. Balirwa Frank Kansiime Patrick Denny 《Wetlands Ecology and Management》2009,17(3):257-277
The processes driving primary productivity and its impacts on fish production were investigated in field trials in eight seasonal
earthen wetland ponds ‘Fingerponds’ (192 m2) in Uganda between 2003 and 2005. The ponds were stocked by the seasonal flood with predominantly Oreochromis spp. at densities ranging from 0.1 to 0.5 fish m−2. Chicken manure (521, 833 or 1,563 kg ha−1) was applied fortnightly. Results showed that primary productivity was enhanced with maximum average net primary productivity
(±Standard Error) of 11.7 (±2.5) g O2 m−2 day−1 at the Gaba site and 8.3 (±1.5) g O2 m−2 day−1 at the Walukuba site. Net fish yields were higher in manured ponds with up to 2,670 kg ha−1 yield for a 310 day growth period compared to less than 700 kg ha−1 in unmanured ponds. Fish production was limited mainly by high recruitment, falling water levels, light limitation from high
suspended solids and turbidity, and low zooplankton biomass. It was concluded that Fingerponds have a high potential for sustainable
fish production and can contribute to the alleviation of protein shortages amongst the riparian communities around Lake Victoria.
Production can be enhanced further with improved stock management. 相似文献
8.
The effects on growth, quality and N uptake by turfgrass (Cynodon dactylon L.) during sod production of four fertiliser types applied at three application rates (100, 200 or 300 kg N ha−1 per ‘crop’) under two irrigation treatments (70% and 140% daily replacement of pan evaporation) were investigated. The fertiliser
types were: water-soluble (predominately NH4NO3), control-release, pelletised poultry manure, and pelletised biosolids; and the experiment was conducted on a sandy soil
in a Mediterranean-type climate. Plots were established from rhizomes, with the turfgrass harvested as sod every 16–28 weeks
depending upon the time of the year. Four crops were produced during the study. Applying water-soluble and control-release
fertilisers doubled shoot growth and improved turfgrass greenness by up to 10% in comparison with plots receiving pelletised
poultry manure and pelletised biosolids. Nitrogen uptake into the shoots after four crops (averaged across irrigation treatments
and N rates) was 497 kg N ha−1 for the water-soluble fertiliser, 402 kg N ha−1 for the control-release, 188 kg N ha−1 for the pelletised poultry manure and 237 kg N ha−1 for the pelletised biosolids. Consequently, the agronomic nitrogen-use efficiency (NAE, kg DM kg−1 N applied) of the inorganic fertilisers was approximately twice that of the organic fertilisers. Increasing irrigation from
70% to 140% replacement of pan evaporation was detrimental to turfgrass growth and N uptake for the first crop when supplied
with the water-soluble fertiliser. Under the low irrigation treatment, inorganic N fertilisers applied at 200–300 kg N ha−1 were adequate for production of turfgrass sod.
Section Editor: P. J. Randall 相似文献
9.
Carbon storage in post-mining forest soil,the role of tree biomass and soil bioturbation 总被引:3,自引:0,他引:3
Carbon storage in aboveground tree biomass and soil organic matter (in depth of A layer development i.e., up to 20 cm) was
studied in 22–32 year-old post-mining sites in the northwest of the Czech Republic. Four replicated sites afforested with
different tree species (spruce, pine, larch, oak, lime or alder) were compared with sites left to natural regeneration which
were dominated by aspen, birch and willow. No topsoil was applied at the sites; hence carbon accumulation resulted from in
situ soil development on alkaline tertiary clays that were dumped on the heaps. In aboveground tree biomass, carbon storage
ranged from 17.0 ± 5.9 (mean ± SEM) to 67.6 ± 5.9 t ha−1 and the rate of C accumulation increased from 0.60 ± 0.09 to 2.31 ± 0.23 t ha−1 year−1 (natural regeneration < pine < spruce < oak < lime < alder < larch). Carbon storage in soil organic matter varied from 4.5 ± 3.7
to 38.0 ± 7.1 t ha−1 and the rate of C accumulation in soil organic matter increased from 0.15 ± 0.05 to 1.28 ± 0.34 t ha−1 year−1 at sites in the order: natural regeneration < spruce < pine, oak < larch < alder < lime. Carbon storage in the soil was positively
correlated with aboveground tree biomass. Soil carbon was equivalent to 98.1% of the carbon found in aboveground tree biomass
at lime dominated sites, but only 21.8% at sites with natural regeneration. No significant correlation was found between C
storage in soil and aboveground litter input. Total soil carbon storage was correlated positively and significantly with earthworm
density, and occurrence of earthworm cast in topsoil, which indicated that bioturbation could play an important role in soil
carbon storage. Hence, not only restoring of wood production, but also restoring of soil community is critical for C storage
in soil and whole ecosystem. 相似文献
10.
Altitudinal changes in carbon storage of temperate forests on Mt Changbai, Northeast China 总被引:8,自引:0,他引:8
Biao Zhu Xiangping Wang Jingyun Fang Shilong Piao Haihua Shen Shuqing Zhao Changhui Peng 《Journal of plant research》2010,123(4):439-452
A number of studies have investigated regional and continental scale patterns of carbon (C) stocks in forest ecosystems; however,
the altitudinal changes in C storage in different components (vegetation, detritus, and soil) of forest ecosystems remain
poorly understood. In this study, we measured C stocks of vegetation, detritus, and soil of 22 forest plots along an altitudinal
gradient of 700–2,000 m to quantify altitudinal changes in carbon storage of major forest ecosystems (Pinus koraiensis and broadleaf mixed forest, 700–1,100 m; Picea and Abies forest, 1,100–1,800 m; and Betula ermanii forest, 1,800–2,000 m) on Mt Changbai, Northeast China. Total ecosystem C density (carbon stock per hectare) averaged 237 t C ha−1 (ranging from 112 to 338 t C ha−1) across all the forest stands, of which 153 t C ha−1 (52–245 t C ha−1) was stored in vegetation biomass, 14 t C ha−1 (2.2–48 t C ha−1) in forest detritus (including standing dead trees, fallen trees, and floor material), and 70 t C ha−1 (35–113 t C ha−1) in soil organic matter (1-m depth). Among all the forest types, the lowest vegetation and total C density but the highest
soil organic carbon (SOC) density occurred in Betula ermanii forest, whereas the highest detritus C density was observed in Picea and Abies forest. The C density of the three ecosystem components showed distinct altitudinal patterns: with increasing altitude, vegetation
C density decreased significantly, detritus C density first increased and then decreased, and SOC density exhibited increasing
but insignificant trends. The allocation of total ecosystem C to each component exhibited similar but more significant trends
along the altitudinal gradient. Our results suggest that carbon storage and partitioning among different components in temperate
forests on Mt Changbai vary greatly with forest type and altitude. 相似文献
11.
Soil Inorganic N Leaching in Edges of Different Forest Types Subject to High N Deposition Loads 总被引:2,自引:0,他引:2
Karen Wuyts An De Schrijver Jeroen Staelens Lotte Van Nevel Sandy Adriaenssens Kris Verheyen 《Ecosystems》2011,14(5):818-834
We report on soil leaching of dissolved inorganic nitrogen (DIN) along transects across exposed edges of four coniferous and
four deciduous forest stands. In a 64-m edge zone, DIN leaching below the main rooting zone was enhanced relative to the interior
(at 128 m from the edge) by 21 and 14 kg N ha−1 y−1 in the coniferous and deciduous forest stands, respectively. However, the patterns of DIN leaching did not univocally reflect
those of DIN throughfall deposition. DIN leaching in the first 20 m of the edges was lower than at 32–64 m from the edge (17
vs. 36 kg N ha−1 y−1 and 15 vs. 24 kg N ha−1 y−1 in the coniferous and deciduous forests, respectively). Nitrogen stocks in the mineral topsoil (0–30 cm) were, on average,
943 kg N ha−1 higher at the outer edges than in the interior, indicating that N retention in the soil is probably one of the processes
involved in the relatively low DIN leaching in the outer edges. We suggest that a complex of edge effects on biogeochemical
processes occurs at the forest edges as a result of the interaction between microclimate, tree dynamics (growth and litterfall),
and atmospheric deposition of N and base cations. 相似文献
12.
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
13.
A. Bryce Cooper 《Plant and Soil》1986,93(3):383-394
Summary Nitrate-N losses to stream waters and soil inorganic N pools, nitrifying potentials and NO3-N production rates were measured in 2 adjacent watersheds, one used as pasture and the other planted in exotic conifer forest
(Pinus radiata D. Don). Estimated NO3-N loss to stream waters draining the pine and pasture watersheds were 0.6kg ha−1 y−1 and 7.6 kg ha−1 y−1 respectively. Ammonium-N pool sizes were not significantly different between soils in the two watersheds but NO3−N pools and nitrifying potentials were always lower in the pine watershed soil samples. Laboratory incubation experiments
indicated that suppression of NO3−N formation in pine watershed soils required the presence of live tree roots and was not due to the direct action of allelopathic
chemicals on nitrifiers. 相似文献
14.
Culm recruitment, standing crop biomass, net production and carbon flux were estimated in mature (5 years after last harvest)
and recently harvested bamboo (Dendrocalamus strictus (Roxb.) Nees) savanna sites in the dry tropics. During the 2 study years bamboo shoot recruitment was 1711–3182 and 1432–1510
shoots ha−1 in harvested and mature sites, respectively. Corresponding shoot mortality was 66–93% and 62–69%, respectively. Total biomass
was 34.9 t ha−1 at the harvested site and 47.4 t ha−1 at the mature site. Harvesting increased the relative contribution of belowground bamboo biomass. Annual litter input to
soil was 2.7 and 5.9 t ha−1 year−1 at the harvested and mature sites, respectively. The bulk of the annual litterfall (78–88%) occurred in the cool dry season
(November to February). The mean litter mass on the savanna floor ranged from 3.1 to 3.3 t ha−1; at the harvested site wood litter contributed 70% of the litter mass and at the mature site leaves formed 77% of the litter
mass. The mean total net production (TNP) for the two annual cycles was 15.8 t ha−1 year−1 at the harvested site and 19.3 t ha−1 year−1 at the mature site. Nearly half (46–57%) of the TNP was allocated to the belowground parts. Short lived components (leaves
and fine roots) contributed about four-fifths of the net production of bamboo. Total carbon storage in the system was 64.4
t ha−1 at the harvested site and 75.4 t ha−1 at the mature site, of which 23–28% was distributed in vegetation, 2% in litter and 70–75% in soil. Annual net carbon deposition
was 6.3 and 8.7 t ha−1 year−1 at harvested and mature sites, respectively. 相似文献
15.
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
16.
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
17.
Cloudwater Inputs of Nitrogen to Forest Ecosystems in Southern Chile: Forms, Fluxes, and Sources 总被引:6,自引:0,他引:6
Nitrogen (N) has been considered a limiting nutrient to many aquatic and terrestrial ecosystems. However, human activity has
resulted in increased atmospheric N deposition worldwide such that N pollution is now altering ecosystem function in many
locations. Research on atmospheric deposition has focused primarily on inorganic nitrogen (DIN; NH4
+-N + NO3
−-N) via rainwater and dry deposition as the main N input to ecosystems. Recently, organic N (ON) has been shown to be an important
constituent in rainwater or dry deposition. Here we show that ON dominated (66%) total N in cloudwater from a remote site
in southern Chile. Cloudwater from more human-impacted sites in northeastern USA had lower ON concentrations and DIN was dominant.
We estimate that cloudwater delivers up to 2 kg ha−1 DIN and 9 kg ha−1 ON annually, compared to less than 1 kg ha−1 of DIN deposition via rainwater, thus it may contribute substantially to the N-economy of Chilean coastal forests. We also
suggest that the adjacent ocean, where biologic productivity is high, may be a major source of N in Chilean cloudwater. This
proposed marine-terrestrial flux via cloud deposition has not previously been identified and may be an example of the ocean
feeding the forest. We suggest that this type of cross boundary flux may be common in other upwelling zones, such as along
the west coasts of Africa, North and South America and east India, and warrants further substantiation and investigation.
Received 30 June 2000; accepted 18 October 2000 相似文献
18.
The sensitivity of surface waters to acidic deposition is governed by the interaction of catchment geology, soils, topography,
land use, climate and atmospheric deposition. Accordingly at the landscape scale, catchment attributes may be used to predict
lake chemistry (for example, acid neutralising capacity (ANC), pH, calcium (Ca2+) and dissolved organic carbon (DOC)). Empirical (multiple linear regression) models based on average measured chemistry (2000–2006)
for 204 lakes in Nova Scotia (NS) Canada, and their catchment attributes, were used to predict chemistry for all lakes in
NS (n = 6104). Damage to aquatic biota, such as loss of species and/or reduced biodiversity has been widely evaluated using critical
chemical thresholds commonly based on pH, ANC and Ca2+. The proportion of sensitive lakes in NS (that is, the stock at risk) was estimated as lakes with ANC less than 20 μeq l−1, pH below 6, and Ca2+ less than 75 μeq l−1 (13, 73 and 74%, respectively). Many lakes in NS are characterized by high DOC (>7 mg l−1); in these lakes organic acids contribute to total acidity, making anthropogenic influences difficult to discern. To account
for the potential contribution of organic acidity, all lakes with pH below 6 (and DOC < 7 mg l−1) and lakes below a threshold for ANC adjusted for organic acids were quantified; 63% of the lakes fell below either of these
thresholds. Despite substantial reductions in sulphur emissions in North America since the 1980s, many lakes in NS remain
at risk to acidic deposition. 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.
Prunings of Calliandra calothyrsus, Grevillea robusta, Leucaena diversifolia and farm yard manure were applied each cropping season at 3 and 6 t dry matter ha−1 to an Oxisol in Burundi. The field plots also received basal applications of nitrogen (N), phosphorus (P) and potassium (K).
Application of the tree prunings or farm yard manure decreased the concentration of monomeric inorganic aluminium (Al) in
soil solution from 2.92 mg Al dm−3 in the control plots to 0.75 mg Al dm−3 in the plots receiving 6 t ha−1
Calliandra prunings. The other organic materials also decreased the concentration of monomeric inorganic aluminium in the soil solution.
The lowered Al concentration led to a corresponding decrease in the percentage Al saturation of the 0–10 cm soil layer from
80% to 68%. Grain yields of maize and beans were strongly inversely related to the percentage Al saturation of the soil. This
confirms that soil acidity was the main constraint to maize and beans production. The yield improvement was mainly attributed
to the ameliorating effects of the organic matter application on Al toxicity. The nutrient content had less effect presumably
because of fertilizer use. In the best treatments, the yield of maize increased from 0.9 to 2.2 t ha−1 and the corresponding beans yield increased from 0.2 to 1.2 t ha−1. A C Borstlap Section editor 相似文献