共查询到20条相似文献,搜索用时 31 毫秒
1.
Nitrogen budget and riverine nitrogen output in a rice paddy dominated agricultural watershed in eastern China 总被引:5,自引:0,他引:5
Xiaoyuan Yan Zucong Cai Rong Yang Chaopu Ti Yongqiu Xia Feiyue Li Jianqun Wang Aijun Ma 《Biogeochemistry》2011,106(3):489-501
The nitrogen (N) budget calculation approach is a useful means of evaluating the impact of human activity on the N cycle. Field scale N budget calculations may ignore the interactions between landscapes, and regional scale calculations rely on statistical data and indirect parameters. Watershed scale budget calculations allow for a more direct quantification of N inputs and outputs. We conducted N budget calculations for a rice paddy-dominated agricultural watershed in eastern China for 2007?C2009, based on intensive monitoring of stream N dynamics, atmospheric deposition, ammonia (NH3) volatilization and household interviews about N-related agricultural activities. The results showed that although total N input to the watershed was up to 280 kg N ha?1 year?1, riverine discharge was only 4.2 kg N ha?1 year?1, accounting for 1.5% of the total N input, and was further reduced to 2.0 kg N ha?1 year?1 after reservoir storage and/or denitrification removal. The low riverine N output was because of the characteristics of the rice paddy-dominated landscape, which intercepts run-off and enhances soil denitrification. The watershed actually purified the N in rainwater, as N concentrations in river discharge were much lower than those in rain water. Major N outputs included food/feed export, NH3 volatilization from chemical fertilizer and manure, and emissions from crop residue burning. Net reactive gaseous emissions (emissions minus deposition) accounted for 5.5% of the total N input, much higher than riverine discharge. Therefore, the agricultural N cycle in such paddy-dominated watersheds impacts the environment mainly through gas exchange rather than water discharge. 相似文献
2.
Mark S. Castro Keith N. Eshleman Louis F. Pitelka Geoff Frech Molly Ramsey William S. Currie Karen Kuers Jeffrey A. Simmons Bob R. Pohlad Carolyn L. Thomas David M. Johnson 《Biogeochemistry》2007,84(3):333-348
The objective of this study was to evaluate the nitrogen (N) biogeochemistry of an 18–22 year old forested watershed in western
Maryland. We hypothesized that this watershed should not exhibit symptoms of N saturation. This watershed was a strong source
of nitrate (NO3
−) to the stream in all years, with a mean annual export of 9.5 kg N ha−1 year−1 and a range of 4.4–18.4 kg N ha−1 year−1. During the 2001 and 2002 water years, wet deposition of inorganic N was 9.0 kg N ha−1 year−1 and 6.3 kg N ha−1 year−1, respectively. Watershed N export rates in 2001 and 2002 water years were 4.2 kg N ha−1 year−1 and 5.3 kg N ha−1 year−1, respectively. During the wetter water years of 2003 and 2004, the watershed exported 15.0 kg N ha−1 year−1 and 18.4 kg N ha−1 year−1, rates that exceeded annual wet deposition of N by a factor of two (7.5 kg N ha−1 year−1 in 2003) and three (5.5 kg N ha−1 year−1 in 2004). Consistent with the high rates of N export, were high concentrations (2.1–3.3%) of N in foliage, wood (0.3%) and
fine roots, low C:N ratios in the forest floor (17–24) and mineral soil (14), high percentages (83–96%) of the amount of mineralized
N that was nitrified and elevated N concentrations (up to 3 mg N l−1) in soil solution. Although this watershed contained a young aggrading forest, it exhibited several symptoms of N saturation
commonly observed in more mature forests. 相似文献
3.
Kyung Won Seo Su Jin Heo Yowhan Son Nam Jin Noh Sue Kyoung Lee Chun Gyeong Yoon 《Landscape and Ecological Engineering》2011,7(1):93-99
This study was conducted to examine the influences of soil-moisture conditions on soil nitrogen (N) dynamics, including in
situ soil N mineralization, N availability, and denitrification in a pure Alnus japonica forest located in Seoul, central Korea. The soil N mineralization, N availability, and denitrification were determined using
the buried bag incubation method, ion exchange resin bag method, and acetylene block method, respectively. The annual net
N mineralization rate (kg N ha−1 year−1) and annual N availability (mg N bag−1) were 40.26 and 80.65 in the relatively dry site, −5.43 and 45.39 in the moist site, and 7.09 and 39.17 in the wet site,
respectively. The annual net N mineralization rate and annual N availability in the dry site were significantly higher than
those in the moist and wet sites, whereas there was no significant difference between the moist and wet sites. The annual
mean denitrification rate (kg N ha−1 year−1) in the dry, moist, and wet sites was 2.37, 2.76, and 1.59, respectively. However, there was no significant difference among
sites due to the high spatial and temporal variations. Our results indicate that soil-moisture condition influenced the in
situ N mineralization and resin bag N availability in an A. japonica forest, and treatments of proper drainage for poorly drained sites would increase soil N mineralization and N availability
and consequently be useful to conserve and manage the A. japonica forest. 相似文献
4.
Jorge R. Ortiz-Zayas Elvira Cuevas Olga L. Mayol-Bracero Loreto Donoso Ivonne Trebs Debora Figueroa-Nieves William H. McDowell 《Biogeochemistry》2006,79(1-2):109-133
Anthropogenic actions are altering fluxes of nitrogen (N) in the biosphere at unprecedented rates. Efforts to study these impacts have concentrated in the Northern hemisphere, where experimental data are available. In tropical developing countries, however, experimental studies are lacking. This paper summarizes available data and assesses the impacts of human activities on N fluxes in Puerto Rico, a densely populated Caribbean island that has experienced drastic landscape transformations over the last century associated with rapid socioeconomic changes. N yield calculations conducted in several watersheds of different anthropogenic influences revealed that disturbed watersheds export more N per unit area than undisturbed forested watersheds. Export of N from urban watersheds ranged from 4.8 kg ha?1 year?1 in the Río Bayamón watershed to 32.9 kg ha?1 year?1 in the highly urbanized Río Piedras watershed and 33.3 kg ha?1 year?1 in the rural-agricultural Río Grande de Añasco watershed. Along with land use, mean annual runoff explained most of the variance in fluvial N yield. Wastewater generated in the San Juan Metropolitan Area receives primary treatment before it is discharged into the Atlantic Ocean. These discharges are N-rich and export large amounts of N to the ocean at a rate of about 140 kg ha?1 year?1. Data on wet deposition of inorganic N ( $\hbox{NH}_{4}^{+}+\hbox{NO}_{3}^{-}Anthropogenic actions are altering fluxes of nitrogen (N) in the biosphere at unprecedented rates. Efforts to study these impacts have concentrated in the Northern hemisphere, where experimental data are available. In tropical developing countries, however, experimental studies are lacking. This paper summarizes available data and assesses the impacts of human activities on N fluxes in Puerto Rico, a densely populated Caribbean island that has experienced drastic landscape transformations over the last century associated with rapid socioeconomic changes. N yield calculations conducted in several watersheds of different anthropogenic influences revealed that disturbed watersheds export more N per unit area than undisturbed forested watersheds. Export of N from urban watersheds ranged from 4.8 kg ha−1 year−1 in the Río Bayamón watershed to 32.9 kg ha−1 year−1 in the highly urbanized Río Piedras watershed and 33.3 kg ha−1 year−1 in the rural-agricultural Río Grande de A?asco watershed. Along with land use, mean annual runoff explained most of the variance in fluvial N yield. Wastewater generated in the San Juan Metropolitan Area receives primary treatment before it is discharged into the Atlantic Ocean. These discharges are N-rich and export large amounts of N to the ocean at a rate of about 140 kg ha−1 year−1. Data on wet deposition of inorganic N () suggest that rates of atmospheric N deposition are increasing in the pristine forests of Puerto Rico. Stationary and mobile sources of NO
x
(NO+NO2) and N2O generated in the large urban centers may be responsible for this trend. Comprehensive measurements are required in Puerto Rico to quantitatively characterize the local N cycle. More research is required to assess rates of atmospheric N deposition, N fixation in natural and human-dominated landscapes, N-balance associated with food and feed trade, and denitrification. 相似文献
5.
Although agricultural systems in tropical monsoon Asia play a central role in the global nitrogen (N) cycle, details of the
N cycle in this region on a watershed scale remain unclear. This study quantified the N budget in a tropical watershed of
221 km2 on Java Island, where paddy fields cover 28% of the land, by conducting field surveys. The amount of net biochemical gaseous
N loss to the atmosphere (X
GB
), which is generally difficult to determine, was calculated as the residual of the N balance. Assuming that NH3 volatilization balances deposition, and hence subtracting NH4–N from the N import with atmospheric deposition, the average total import and export of N per year was found to be 46.5 kg ha−1 year−1 over the watershed. Of this, 71% was imported as fertilizer (M
F
) and 29% with atmospheric deposition (M
AD
). On the export side, 42% was lost as X
GB
, 37% with incineration of rice residues and wood fuel (X
GI
), 13% with river discharge (X
D
) and 9% with rice surplus export (X
R
). A large portion of X
GB
, and consequently, a small portion of X
D
could be explained by the high rate of denitrification resulting from the high temperature and humid climate, and are thought
to be common features of tropical watersheds where paddy fields are found. 相似文献
6.
Sources of Nitrogen to the Riparian Zone of a Desert Stream: Implications for Riparian Vegetation and Nitrogen Retention 总被引:5,自引:1,他引:4
John D. Schade Eugenia Marti Jill R. Welter Stuart G. Fisher Nancy B. Grimm 《Ecosystems》2002,5(1):68-79
Riparian zones effectively remove nitrogen (N) from water flowing through riparian soils, particularly in agricultural watersheds.
The mechanism of N removal is still unclear, especially the role of vegetation. Uptake and denitrification are the two most
commonly studied mechanisms. Retention of groundwater N by plant uptake is often inferred from measurements of N in net incremental
biomass. However, this assumes other sources of N are not contributing to the N demand of plants. The purpose of this work
was to investigate the relative importance of three sources of available N to riparian trees in a desert stream—input in stream
water during floods, input during baseflow, and mineralization of N from soil organic matter. Two approaches were used; a
mass balance approach in which the mass of available N from each source was estimated, and a correlational approach in which
indexes of each source were compared to leaf N for individual willow trees. Total N from all sources was 396 kg ha−1 y−1, with 172 kg ha−1 y−1 from mineralization, 214 kg ha−1 y−1 from the stream during baseflow, and 9.6 kg ha−1 y−1 from floods. Leaf N was significantly related to N mineralization rates and flood inputs; it was not related to baseflow
inputs. We conclude that mineralization is a major source of available N for willow trees, subsidized by input of N from floods.
Baseflow inputs are most likely removed by rapid denitrification at the stream–riparian edge, while higher rates of flood
supply exceed the capacity of this “filter.”
Received 18 January 2001; accepted 15 June 2001. 相似文献
7.
Alexandra Maltas Marc Corbeels Eric Scopel Robert Oliver Jean-Marie Douzet Fernando Antonio Macena da Silva Jacques Wery 《Plant and Soil》2007,298(1-2):161-173
In the Cerrado region of Brazil conventional soybean monoculture is since the 1980s being replaced by direct seeding mulch-based
cropping (DMC) with two crops per year and absence of tillage practices. The objective of this study was to assess the long-term
impact of DMC on soil organic matter accumulation and nitrogen (N) mineralization. Measurements of soil organic carbon (C)
content, soil total N content and soil N mineralization, both under laboratory conditions using disturbed soil samples and
under field conditions using intact soil cores were conducted on a chronosequence of 2-, 6-, 9- and 14-year-old DMC fields
(DMC-2, DMC-6, DMC-9 and DMC-14, respectively). The average increase of organic C in the 0–30 cm topsoil layer under DMC was
1.91 Mg C ha−1 year−1. Soil total N increased with 103 kg N ha−1 year−1 (0–30 cm). The potential N mineralization rate under laboratory conditions (28°C, 75% of soil moisture at field capacity)
was 0.27, 0.28, 0.39 and 0.36 mg N kg soil−1 day−1 for, respectively, the DMC-2, DMC-6, DMC-9 and DMC-14 soils. The corresponding specific N mineralization rates were 0.16,
0.15, 0.22 and 0.17 mg N g N−1 day−1. There was no obvious explanation for the higher specific N mineralization rate of soils under DMC-9, given the similar soil
conditions and land-use history before DMC was introduced. Results from the in situ N incubation experiments were in good
agreement with those from the laboratory incubations. We estimated that soil N mineralization increases with about 2.0 kg
N ha−1 year−1 under DMC. The increase was mainly attributed to the larger soil total N content. These results indicate that even in the
medium term (10 years), continuous DMC cropping has limited implications for N fertilization recommendations, since the extra
soil N supply represents less than 20% of the common N fertilization dose for maize in the region. 相似文献
8.
Werner Härdtle Goddert von Oheimb Marion Niemeyer Thomas Niemeyer Thorsten Assmann Hartmut Meyer 《Biogeochemistry》2007,86(2):201-215
Atmospheric nutrient deposition has contributed to widespread changes in sensitive seminatural ecosystems throughout Europe.
For an understanding of underlying processes it is important to quantify input–output flows in relation to ongoing atmospheric
inputs and current management strategies. In this study we quantified losses of N, P, Ca, Mg, and K via leaching in heathland
ecosystems (Lüneburger Heide, NW Germany) as a function of current deposition rates and different management measures (mowing,
prescribed burning, choppering, sod-cutting) which aim to prevent shrub and tree encroachment. Leaching was only moderately
related to atmospheric input rates, indicating that leaching was mostly affected by internal turnover processes. Leaching
significantly increased for most of the nutrients after the application of management measures, particularly in the choppered
and sod-cut plots. However, atmospheric nutrient inputs exceeded leaching outputs for most of the nutrients, even in the plots
subjected to management. Despite high deposition rates (20–25 kg N ha−1 year−1), retention of atmospheric N input ranged between 74% and 92% in the control plots. In the treated plots, N retention decreased
to 59–80%. However, in the study area mean N leaching in the controls has almost doubled since 1980 and currently amounts
to 3.7 kg ha−1 year−1, indicating an early stage of N saturation. Our study provides evidence that leaching did not compensate for atmospheric
nutrient deposition, particularly as regards N. Management, thus, will be an indispensable tool for the maintenance of the
low-nutrient status as a prerequisite for the long-term preservation of heathland ecosystems. 相似文献
9.
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
10.
A Phosphorus Budget for the Lake Mendota Watershed 总被引:6,自引:0,他引:6
Elena M. Bennett Tara Reed-Andersen Jeffrey N. Houser John R. Gabriel Stephen R. Carpenter 《Ecosystems》1999,2(1):69-75
A phosphorus (P) budget was calculated for the agriculture-dominated Lake Mendota watershed located in Dane and Columbia
Counties, Wisconsin, USA. P inputs included fertilizer for agricultural crops and lawns, dietary supplements for dairy cattle,
and natural inputs such as dry and wet deposition. Outputs included agricultural crops, livestock and livestock products,
and hydrologic export to Lake Mendota. The total P input to the watershed (1,307,000 kg year−
1) and total output (732,000 kg year−
1) are large relative to the average of 34,000 kg P washing into the lake each year, indicating that the P flux that eutrophies
Lake Mendota is a veryminor component of the total watershed P budget. Using the formula inputs
−
outputs = change in storage, we found that 575,000 kg P accumulated in the watershed in 1995. This estimate was corroborated by long-term soil P concentration
data, which showed an average annual increase in soil P of over 450,000 kg year−
1. Future management programs designed to reduce P inputs to Lake Mendota will be compelled to cope with the large amount of
P being stored in the watershed.
Received 31 August 1998; accepted 21 October 1998. 相似文献
11.
Estimates of biomass and primary productivity in a high-altitude maple forest of the west central Himalayas 总被引:4,自引:0,他引:4
S. C. Garkoti 《Ecological Research》2008,23(1):41-49
The paper describes the biomass and productivity of maple (Acer cappadocicum) forest occurring at an altitude of 2,750 m in the west central Himalayas. Total vegetation biomass was 308.3 t ha−1, of which the tree layer contributed the most, followed by herbs and shrubs. The seasonal forest-floor litter mass varied
between 5.4 t ha−1 (in rainy season) and 6.6 t ha−1 (in winter season). The annual litter fall was 6.2 t ha−1, of which leaf litter contributed the largest part (59% of the total litter fall). Net primary productivity of total vegetation
was 19.5 t ha−1 year−1. The production efficiency of leaves (net primary productivity/leaf mass) was markedly higher (2.9 g g−1 foliage mass year−1) than those of the low-altitude forests of the region. 相似文献
12.
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
13.
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
14.
Differences in Englemann Spruce Forest Biogeochemistry East and West of the Continental Divide in Colorado, USA 总被引:3,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
15.
Woody encroachment into herbaceous ecosystems is emerging as an important ecological response to global change. A primary
concern is alterations in C and N cycling and associated variations across a variety of ecosystems. We quantified seasonal
variation in litterfall and litter N concentration in Morella cerifera shrub thickets to assess changes in litterfall and associated N input after shrub expansion on an Atlantic coast barrier
island. We also used the natural abundance of 15N to estimate the proportion of litterfall N originating from symbiotic N fixation. Litterfall for shrub thickets ranged from
8,991 ± 247 to 3,810 ± 399 kg ha−1 year−1 and generally declined with increasing thicket age. Litterfall in three of the four thickets exceeded previous estimates
of aboveground annual net primary production in adjacent grasslands by 300–400%. Leaf N concentration was also higher after
shrub expansion and, coupled with low N resorption efficiency and high litterfall, resulted in a return of as much as 169 kg N ha−1 year−1 to the soil. We estimated that ∼70% of N returned to the soil was from symbiotic N fixation resulting in an ecosystem input
of between 37 and 118 kg ha−1 year−1 of atmospheric N depending on site. Considering the extensive cover of shrub thickets on Virginia barrier islands, N fixation
by shrubs is likely the largest single source of N to the system. The shift from grassland to shrub thicket on barrier islands
results in a substantial increase in litterfall and foliar N concentration that will likely have a major impact on the size
and cycling of ecosystem C and N pools. Increasing C and N availability in these nutrient-poor soils is likely to permanently
reduce cover of native grasses and alter community structure by favoring species with greater N requirements. 相似文献
16.
Denitrification in a semi-arid grazing ecosystem 总被引:3,自引:0,他引:3
The effect of large herbivores on gaseous N loss from grasslands, particularly via denitrification, is poorly understood.
In this study, we examined the influence of native migratory ungulates on denitrification in grasslands of Yellowstone National
Park in two ways, by (1) examining the effect of artificial urine application on denitrification, and (2) comparing rates
inside and outside long-term exclosures at topographically diverse locations. Artificial urine did not influence denitrification
3 and 12 days after application at hilltop, mid-slope, and slope-bottom sites. Likewise, grazers had no effect on community-level
denitrification at dry exclosure sites, where rates were low. At mesic sites, however, ungulates enhanced denitrification
by as much as 4 kg N ha−1 year−1, which was double atmospheric N inputs to this ecosystem. Denitrification enzyme activity (DEA, a measure of denitrification
potential) was positively associated with soil moisture at exclosure sites, and herbivores stimulated DEA when accounting
for the soil moisture effect. Glucose additons to soils increased denitrification and nitrate additions had no influence,
suggesting that denitrification was limited by the amount of labile soil carbon, which previously has been shown to be enhanced
by ungulates in Yellowstone. These results indicate that denitrification can be an ecologically important flux in portions
of semi-arid landscapes, and that there is a previously unsuspected regulation of this process by herbivores.
Received: 6 March 1998 / Accepted: 28 August 1998 相似文献
17.
Net anthropogenic phosphorus inputs: spatial and temporal variability in the Chesapeake Bay region 总被引:4,自引:0,他引:4
Marc J. Russell Donald E. Weller Thomas E. Jordan Kevin J. Sigwart Kathryn J. Sullivan 《Biogeochemistry》2008,88(3):285-304
We estimated net anthropogenic phosphorus inputs (NAPI) in the Chesapeake Bay region. NAPI is an index of phosphorus pollution
potential. NAPI was estimated by quantifying all phosphorus inputs and outputs for each county. Inputs include fertilizer
applications and non-food phosphorus uses, while trade of food and feed can be an input or an output. The average of 1987,
1992, 1997, and 2002 NAPI for individual counties ranged from 0.02 to 78.46 kg P ha−1 year−1. The overall area-weighted average NAPI for 266 counties in the region was 4.52 kg P ha−1 year−1, indicating a positive net phosphorus input that can accumulate in the landscape or can pollute the water. Large positive
NAPI values were associated with agricultural and developed land cover. County area-weighted NAPI increased from 4.43 to 4.94 kg P ha−1 year−1 between 1987 and 1997 but decreased slightly to 4.86 kg P ha−1 year−1 by 2002. Human population density, livestock unit density, and percent row crop land combined to explain 83% of the variability
in NAPI among counties. Around 10% of total NAPI entering the Chesapeake Bay watershed is discharged into Chesapeake Bay.
The developed land component of NAPI had a strong direct correlation with measured phosphorus discharges from major rivers
draining to the Bay (R
2 = 0.81), however, the correlation with the simple percentage of developed land was equally strong. Our results help identify
the sources of P in the landscape and evaluate the utility of NAPI as a predictor of water quality. 相似文献
18.
The deposition and cycling of carbon and nitrogen in carbonate sediments located between coral reefs on the northern and central
sections of the Great Barrier Reef were examined. Rates of mass sediment accumulation ranged from 1.9 kg m−2 year−1 (inshore reefs) to 2.1–4.9 kg m−2 year−1 (between mid-shelf reefs); sedimentation was minimal off outer-shelf reefs. Rates of total organic carbon decomposition ranged
from 1.7 to 11.4 mol C m−2 year−1 and total nitrogen mineralization ranged from 77 to 438 mmol N m−2 year−1, declining significantly with distance from land. Sediment organic matter was highly reactive, with mineralization efficiencies
ranging from 81 to 99% for organic carbon and 64–100% for nitrogen, with little C and N burial. There was no evidence of carbonate
dissolution/precipitation in short-term incubation experiments. Rates of sulfate reduction (range 0–3.4 mmol S m−2 day−1) and methane release (range 0–12.8 μmol CH4 m−2 day−1) were minor or modest pathways of carbon decomposition. Aerobic respiration, estimated by difference between total O2 consumption and the sum of the other pathways, accounted for 55–98% of total carbon mineralization. Rates of ammonification
ranged from 150 to 1,725 μmol NH4 m−2 day−1, sufficient to support high rates of denitrification (range 30–2,235 μmol N2 m−2 day−1). N2O release was not detected and rates of NH4
+ and NO2
− + NO3
− efflux were low, indicating that most mineralized N was denitrified. The percentage of total N input removed via denitrification
averaged ≈75% (range 28–100%) with little regenerated N available for primary producers. Inter-reef environments are therefore
significant sites of energy and nutrient flow, especially in spatially complex reef matrices such as the Great Barrier Reef. 相似文献
19.
Yuji Isagi 《Ecological Research》1994,9(1):47-55
Gross production and carbon cycling in aPhyllostachys bambusoides stand in Kyoto Prefecture, central Japan, were determined, and then a compartment model showing the carbon stock and cycling
within the ecosystem was developed. Aboveground carbon stock was 52.3 tC ha−1, increasing at a rate of 3.6 tC ha−1 year−1. Belowground carbon stock was 20.8 tC ha−1 in the root system and 92.0 tC ha−1 in the soil. Aboveground net production was 11.2 tC ha−1 year−1. Belowground net production was crudely estimated at 4.5 tC ha−1 year−1. The gross production was estimated at 41.8 tC ha−1 year−1 by summing the amount of outflow to the environment and the increment in biomass. Leaves consumed 13.7 tC ha−1 year−1 by respiration; the rest (41.8−13.7=28.1 tC ha−1 year−1) was surplus production of the leaves and flowed into the other compartments. The amounts of construction and maintenance
respiration of the aboveground compartments were 3.4 and 18.5 tC ha−1 year−1, respectively. The annual amount of soil respiration was 11.2 tC ha−1 year−1. Soil respiration levels of 4.3 and 3.1 tC ha−1 year−1 were estimated for the flow of root respiration and root detritus. The proportion of net to gross production was 37%, which
fell within the range of young and mature forests. A shorter life span of culms, compared to tree trunks, resulted in smaller
biomass accumulation ratio (biomass/net production) in the ecosystem, of 4.66. 相似文献
20.
The theoretical basis of fine root turnover estimation in forest soils is discussed, in relation to appropriate experimental
techniques of measurement. After sequential coring, the correct expression is the sum of significant positive increments of
live and dead roots of the various diameter categories, to which the transfer of dead roots to organic matter derived from
roots, OMDR, has to be added. This should not be confounded with dead root mineralization. The transfer rates should first
be estimated in root dimensions and not in weight of dry matter.
The measurements were carried out in a 120 year old beech (Fagus sylvatica L.) stand and a 35 year old Norway spruce (Picea abies Karst) stand, in the Eastern Ardennes, Belgium.
The turnover rate of fine roots (diam. <5 mm) was 4393 kg ha−1 year−1 (root dry weight), including 711.2 kg ha−1 year−1 for dead root transfer to OMDR, for beech.
For spruce, turnover rate was 7011 kg ha−1 year−1 (root dry weight), including 1498 kg ha−1 year−1 for dead root transfer to OMDR.
Under beech, there was a slight root density increase in spring. No seasonal fluctuations were observed under spruce, but
a strong irreversible drop in live root growth was found in the later season 1980–1981, corresponding to a decrease of tree
height growth and trunk radius increment.
Turnover rates were further expressed in dry weight and in amounts of elements (kg ha−1 year−1) (Ca, Mg, K, Na, Al, N, P, S).
Correlative relations between root dimensions and dry weight and element concentrations show that the derived values, and
in particular root specific density (dry weight volume−1) vary according to species, root category, and seasonal sampling.
Various schemes of seasonal variations of root growth, described in Europe, show that the major dependance on general climate
is obscured by environmental factors (soil, exposure, species). It is suggested that root density fluctuation approach the
steady state on an annual basis under mild Atlantic conditions. 相似文献