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1.
In a multidisciplinary study, highly significant interactional effects were found among land use, livestock component, soil
properties and rainfall. On an average, 16.2 to 82.2 tonnes of sediment yield km−2 and more than 90% of rainwater was retained in-situ in new land use systems as against 3621.3 tonnes of sediment and 66.3% rainwater retention in shifting cultivation, because
of poor land cover. Good vegetation cover reduced the runoff load, resulting in significant reduction in the soil and nutrient
erosion. The average sediment yield was only 0.44%, 2.68%, 1.47%, 0.31%, 0.73% and 2.27% in livestock based, forestry, agro-forestry,
agriculture, agri-horti-silvi-pastoral and horticulture land use systems of that of shifting cultivation. Highest average
sediment yield was 704.3 t km−2 when the annual rainfall was 2770 mm and minimum 405.4 t km−2 when the annual rainfall was 1992 mm. More in-situ retention of rainwater helped in the availability of adequate moisture
from the soil to the succeeding crops when the rainy season receded. The sediment yield varied according to the rainfall received
during a particular year and the nature of vegetation in a particular land use. There was sufficient fertility build-up in
the watersheds where animals were kept and after ten years of start of the study, no need of inorganic sources of nutrients
was required. The organic carbon, humus, exchangeable calcium, magnesium, potassium and available phosphorus increased significantly
in the new land use systems compared to shifting cultivation, however, the DTPA (Diethylene triamine penta acetic acid) extractable
zinc, copper, iron and exchangeable aluminium decreased over the initial soil status. It showed that the vegetation in the
new land uses had a smothering effect on the soil and increase in the elements had a favourable impact on the crop productivity. 相似文献
2.
Zhao Liang Xu Shixiao Li Yingnian Tang Yanhong Zhao Xinquan Gu Song Du Mingyuan Yu Guirui 《Frontiers of Biology in China》2007,2(3):324-332
Carbon dioxide fluxes of Kobresia humilis and Potentilla fruticosa shrub meadows, two typical ecosystems in the Qinghai-Tibet Plateau, were measured by eddy covariance technology and the data
collected in August 2003 were employed to analyze the relations between carbon dioxide fluxes and environmental factors of
the ecosystems. August is the time when the two ecosystems reach their peak leaf area indexes and stay stable, and also the
period when the net carbon absorptions of Kobresia humilis and Potentilla fruticosa shrub meadows reach 56.2 g C·m−2 and 32.6 g C·m−2, with their highest daily carbon dioxide absorptions standing at 12.7 μmol·m−2·s−1 and 9.3 μmol·m−2·s−1, and their highest carbon discharges at 5.1 μmol·m−2·s−1 and 5.7 μmol·m−2·s−1, respectively. At the same photosynthetic photo flux densities (PPFD), the carbon dioxide-uptake rate of the Kobresia humilis meadow is higher than that of the Potentilla fruticosa shrub meadow; where the PPFD are higher than 1,200 μmol·m−2·s−1. The carbon dioxide uptake rates of the two ecosystems declined as air temperature increased, but the carbon dioxide uptake
rate of the Kobresia humilis meadow decreased more quickly (−0.086) than that of the Potentilla fruticosa shrub meadow (−0.016). Soil moistures exert influence on the soil respirations and this varies with the vegetation type.
The daily carbon dioxide absorptions of the ecosystems increase with increased diurnal temperature differences and higher
diurnal temperature differences result in higher carbon dioxide exchanges. There exists a negative correlation between the
vegetation albedos and the carbon dioxide fluxes.
Translated from Acta Bot Boreal—Occident Sin, 2006, 26(1): 133–142 [译自: 西北植物学报] 相似文献
3.
We used the natural abundance of 15N in soils in forests, pastures and cultivated lands in the Menagesha and Wendo-Genet areas of Ethiopia to make inferences
about the N cycles in these ecosystems. Since we have described the history of these sites based on variations in 13C natural abundance, patterns of δ15N and δ13C values were compared to determine if shifts of 15N correlate with shifts of vegetation. At Menagesha, a > 500-yr-old planted forest, we found δ15N values from −8.8 to +3.5‰ in litter, from −3.5 to +4.5‰ in 0–10 cm soil layer, and from −1.5 to +6.8‰ at >20 cm soil depth.
The low δ15N in litter and surface mineral soils suggests that a closed N cycle has operated for a long time. At this site, the low δ13C of the surface horizon and the high δ13C of the lower soil horizons is clear evidence of a long phase of C4 grass dominance or cultivation of C4 crops before the establishment of the forest >500 years ago. In contrast, at Wendo-Genet, high δ13C of soils reveals that most of the land has been uncovered by forests until recently. Soil δ15N was high throughout (3.4–9.8‰), and there were no major differences between forested, cultivated and pasture soils in δ15N values of surface mineral soils. The high δ15N values suggest that open N cycles operate in the Wendo-Genet area. From the points of view of soil fertility management,
it is interesting that tall forest ecosystems with relatively closed N cycling could be established on the fairly steep slopes
at Menagesha after a long period of grass vegetation cover or cultivation.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
4.
Pristine peatlands are a significant source of atmospheric methane (CH4). Large spatio–temporal variation has been observed in flux rates within and between peatlands. Variation is commonly associated
with water level, vegetation structure, soil chemistry and climatic variability. We measured spatial and temporal variation
in CH4 fluxes in a blanket bog during the period 2003–2005. The surface of the bog was composed of different vegetation communities
(hummocks, lawns and hollows) along a water level gradient. CH4 fluxes were measured in each community using a chamber method. Regression modelling was used to relate the fluxes with environmental
variables and to integrate fluxes over the study period. Water level was the strongest controller of spatial variation; the
average flux rate was lowest in hummocks and highest in hollows, ranging from 3 to 53 mg CH4 m−2 day−1. In vegetation communities with a permanently high water level, the amount and species composition of vegetation was also
a good indicator of flux rate. We observed a clear seasonal variation in flux that was chiefly controlled by temperature.
The annual average flux (6.2 g CH4 m−2 year−1) was similar to previous estimates from blanket bogs and continental raised bogs. No interannual variation was observed. 相似文献
5.
Plumbing the Global Carbon Cycle: Integrating Inland Waters into the Terrestrial Carbon Budget 总被引:33,自引:1,他引:33
J. J. Cole Y. T. Prairie N. F. Caraco W. H. McDowell L. J. Tranvik R. G. Striegl C. M. Duarte P. Kortelainen J. A. Downing J. J. Middelburg J. Melack 《Ecosystems》2007,10(1):172-185
ABSTRACT
Because freshwater covers such a small fraction of the Earth’s surface area, inland freshwater ecosystems (particularly lakes,
rivers, and reservoirs) have rarely been considered as potentially important quantitative components of the carbon cycle at
either global or regional scales. By taking published estimates of gas exchange, sediment accumulation, and carbon transport
for a variety of aquatic systems, we have constructed a budget for the role of inland water ecosystems in the global carbon
cycle. Our analysis conservatively estimates that inland waters annually receive, from a combination of background and anthropogenically
altered sources, on the order of 1.9 Pg C y−1 from the terrestrial landscape, of which about 0.2 is buried in aquatic sediments, at least 0.8 (possibly much more) is returned
to the atmosphere as gas exchange while the remaining 0.9 Pg y−1 is delivered to the oceans, roughly equally as inorganic and organic carbon. Thus, roughly twice as much C enters inland
aquatic systems from land as is exported from land to the sea. Over prolonged time net carbon fluxes in aquatic systems tend
to be greater per unit area than in much of the surrounding land. Although their area is small, these freshwater aquatic systems
can affect regional C balances. Further, the inclusion of inland, freshwater ecosystems provides useful insight about the
storage, oxidation and transport of terrestrial C, and may warrant a revision of how the modern net C sink on land is described. 相似文献
6.
It is generally known that the water quality of shallow lakes can be influenced significantly by marginal wetlands. In order
to study the efficacy of constructed littoral wetlands in the IJsselmeer area (The Netherlands) for water quality improvement,
a field survey was carried out in 2003. Vegetation, soil, pore water and surface water characteristics were measured in spring
and summer in two types of littoral zones: natural and constructed for 8–16 years. The study showed that constructed wetlands
perform well and are suitable to enlarge the vegetated littoral zone in the IJsselmeer area. In both natural and constructed
sites vegetation biomass varied between 2,200 g m−2 for helophyte vegetation and 1,300 g m−2 for low herbaceous vegetation. Nutrient concentrations in the pore water of constructed sites tended to be higher than in
natural sites.
and concentrations in pore water were much lower when vegetation was present, probably as a result of plant uptake. The N and
P accumulation rate in the soil of constructed wetlands was 20 g N m−2 y−1 and 3 g P m−2 y−1 in vegetated plots; without vegetation the rate was much lower (8 g N m−2 y−1 and 1.8 g P m−2 y−1). We conclude that concerning their effect on water quality, constructed sites may replace natural sites, at least after
8–16 years. Principal component analysis showed a relationship between vegetation biomass and flooding, and nutrient concentrations
in soil and pore water. Biomass was negatively correlated with extractable nutrients and positively with soil total N and
P content. Flooding duration was negatively related to pore water salinity and positively to pore water nutrients. Due to
their high biomass, helophyte stands retained significantly more nutrients than low pioneer vegetation and are therefore more
suitable for improving water quality.
Handling editor: S. Declerck 相似文献
7.
Michael L. Scott Pamela L. Nagler Edward P. Glenn Carlos Valdes-Casillas Joseph A. Erker Elizabeth W. Reynolds Patrick B. Shafroth Euduardo Gomez-Limon Cory L. Jones 《Biodiversity and Conservation》2009,18(2):247-269
Conservation of forested riparian ecosystems is of international concern. Relatively little is known of the structure, composition,
diversity, and extent of riparian ecosystems in Mexico. We used high- and low-resolution satellite imagery from 2000 to 2006,
and ground-based sampling in 2006, to assess the spatial pattern, extent, and woody plant composition of riparian forests
across a range of spatial scales for the state of Sonora, Mexico. For all 3rd and higher order streams, river bottomlands
with riparian forests occupied a total area of 2,301 km2. Where forested bottomlands remained, on average, 34% of the area had been converted to agriculture while 39% remained forested.
We estimated that the total area of riparian forest along the principal streams was 897 km2. Including fencerow trees, the total forested riparian area was 944 km2, or 0.5% of the total land area of Sonora. Ground-based sampling of woody riparian vegetation consisted of 92, 50 m radius
circular plots. About 79 woody plant species were noted. The most important tree species, based on cover and frequency, were
willow species Salix spp. (primarily S. goodingii and S. bonplandiana), mesquite species Prosopis spp. (primarily P. velutina), and Fremont cottonwood Populus fremontii. Woody riparian taxa at the reach scale showed a trend of increasing diversity from north to south within Sonora. Species
richness was greatest in the willow-bald cypress Taxodium distichum var. mexicanum—Mexican cottonwood P. mexicana subsp. dimorphia ecosystem. The non-native tamarisk Tamarix spp. was rare, occurring at just three study reaches. Relatively natural stream flow patterns and fluvial disturbance regimes
likely limit its establishment and spread. 相似文献
8.
Eeva-Stiina Tuittila Veli-Matti Komulainen Harri Vasander Jukka Laine 《Oecologia》1999,120(4):563-574
In a field study, we examined the relationship between vegetation, abiotic factors and the CO2 exchange dynamics of a cut-away peatland 20 years after production had ended. The main objective was to determine the effect
of rewetting on the CO2 exchange dynamics, measured separately in Eriophorum vaginatum tussocks and intertussocks (almost non-vegetated surfaces) using closed-chamber techniques, one growing season before and
three growing seasons after the rewetting treatment. Rewetting lowered total respiration (R
TOT) and increased gross photosynthesis (P
G), which resulted in a higher incorporation of CO2 into the system. The seasonal CO2 balance for the almost continuously submerged section of the rewetted site became positive 2 years after rewetting (9.1 g CO2-C m−2), and it was still higher in the 3rd year (64.5 g CO2-C m−2), i.e. the system accumulated carbon. In the driest section of the rewetted site the seasonal balance increased strongly,
but the balance was still negative during the 3 years following rewetting with losses from the system of 44.1, 26.1, 38.3 g CO2-C m−2 in 1995, 1996 and 1997 respectively. At the control site seasonal balance during 1995–1997 varied between ecosystem C losses
of 41.8 and 95.3 in an area with high Eriophorum cover and between 52.1 and 109.9 g CO2-C m−2 with lower cover. Simulation of a cut-away peatland with dense Eriophorum vegetation (Eriophorum cover 70%) showed that if the water level (WT) is low, the seasonal CO2 balance of the ecosystem can reach the compensation point of no net C change (P
G = R
TOT) only if weather conditions are favourable, but with a high WT the seasonal CO2 balance would be positive even under varying weather conditions. It can be concluded that with dense Eriophorum vegetation a restored cut-away peatland acts as a functional mire and becomes a sink for atmospheric CO2.
Received: 21 September 1998 / Accepted: 18 May 1999 相似文献
9.
Highly productive papyrus (Cyperus papyrus L.) wetlands dominate many permanently flooded areas of tropical East Africa; however, the cycling of carbon and water within
these ecosystems is poorly understood. The objective of this study was to utilise Eddy Covariance (EC) techniques to measure
the fluxes of carbon dioxide and water vapour between papyrus vegetation and the atmosphere in a wetland located near Jinja,
Uganda on the Northern shore of Lake Victoria. Peak, midday rates of photosynthetic CO2 net assimilation were approximately 40 μmol CO2 m−2 s−1, while night time losses through respiration ranged between 10 and 20 μmol CO2 m−2 s−1. Numerical integration of the flux data suggests that papyrus wetlands have the potential to sequester approximately 0.48 kg C m−2 y−1. The average daily water vapour flux from the papyrus vegetation through canopy evapotranspiration was approximately 4.75 kg
H2O m−2 d−1, which is approximately 25% higher than water loss through evaporation from open water. 相似文献
10.
Moro D Bradshaw SD 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1999,169(8):538-548
A laboratory study investigated the metabolic physiology, and response to variable periods of water and sodium supply, of
two arid-zone rodents, the house mouse (Mus domesticus) and the Lakeland Downs short-tailed mouse (Leggadina lakedownensis) under controlled conditions. Fractional water fluxes for M. domesticus (24 ± 0.8%) were significantly higher than those of L. lakedownensis (17 ± 0.7%) when provided with food ad libitum. In addition, the amount of water produced by M. domesticus and by L. lakedownensis from metabolic processes (1.3 ± 0.4 ml · day−1 and 1.2 ± 0.4 ml · day−1, respectively) was insufficient to provide them with their minimum water requirement (1.4 ± 0.2 ml · day−1 and 2.0 ± 0.3 ml · day−1, respectively). For both species of rodent, evaporative water loss was lowest at 25 °C, but remained significantly higher
in M. domesticus (1.1 ± 0.1 mg H2O · g−0.122 · h−1) than in L. lakedownensis (0.6 ± 0.1 mg H2O · g−0.122 · h−1). When deprived of drinking water, mice of both species initially lost body mass, but regained it within 18 days following
an increase in the amount of seed consumed. Both species were capable of drinking water of variable saline concentrations
up to 1 mol · l−1, and compensated for the increased sodium in the water by excreting more urine to remove the sodium. Basal metabolic rate
was significantly higher in M. domesticus (3.3 ± 0.2 mg O2 · g−0.75 · h−1) than in L. lakedownensis (2.5 ± 0.1 mg O2 · g−0.75 · h−1). The study provides good evidence that water flux differences between M. domesticus and L. lakedownensis in the field are due to a requirement for more water in M. domesticus to meet their physiological and metabolic demands. Sodium fluxes were lower than those observed in free-ranging mice, whose
relatively high sodium fluxes may reflect sodium associated with available food.
Accepted: 16 August 1999 相似文献
11.
京津冀地区城市化对植被覆盖度及景观格局的影响 总被引:8,自引:0,他引:8
定量研究了2000—2010年,京津冀地区植被覆盖度及其景观格局的动态变化,揭示了城市化进程对植被景观的干扰过程及生态质量的影响。结果表明:(1)2000—2010年,城市化进程显著是京津冀城市群土地变化的一大特点,人工表面面积从2000年的1.79×10~4km~2增加至2.16×10~4km~2,增幅高达21.16%;(2)京津冀平均植被覆盖度呈增加趋势但不显著(P=0.46),存在明显的时空动态差异。在覆盖度结构上形成了以中低和中植被覆盖度为主导的格局;(3)从景观空间格局变化来看,中低、高覆盖度区域植被景观更加破碎,而低、中等覆盖度区域的植被面积增加,景观破碎度减小;尤其是低植被覆盖度为主的城市区域,景观格局变化幅度大,表现为绿地面积有所增加,景观破碎化程度降低,生态质量有所改善;(4)在整个研究区范围,城市化对区域植被覆盖度存在负面影响,表现为城市化程度与区域平均植被覆盖度存在负相关(P=0.08);但是在低植被覆盖度的区域(主要为城市区域),城市化程度与植被覆盖面积呈显著正相关(P0.001),表明城市区域在城市化进程中植被覆盖面积有所提高,生态质量有所改善,与城市化过程中,日益重视城市绿地的建设有关。 相似文献
12.
中国陆地生态系统分类识别及其近20年的时空变化 总被引:3,自引:0,他引:3
生态系统分类制图是理解生态系统时空格局和支撑生态系统分类管理的基础。研究以反映生态系统主导服务功能和人类干预强度为主线,构建了包括9个一级和25个二级类的生态系统分类体系,集成土地利用、气候、地形、植被、土壤、居民点分布等多源数据,开展了2000和2020年中国陆地生态系统的分类制图,并对其类型、结构、格局及时空变化特征进行了分析。结果表明:近20年,我国城镇生态系统扩张1.1倍,64.51%来自耕种生态系统。耕种生态系统缩减0.88万km2,其中水田和旱田分别减少0.60万km2和2.09万km2,但绿洲扩张1.81万km2。受退耕还林还草影响,农牧和农林混合生态系统分别减少2.88万km2和0.92万km2,林地生态系统增加1.61万km2。水域湿地生态系统增加0.31万km2,70%源自沼泽生态系统的扩张,尤其是青藏高原水域湿地,受气候变暖影响扩张明显。气候暖湿化促使部分干旱荒漠和冰冻寒漠生态系统的盖度增加,使牧草地生态系统增加9.97万km2,而干旱荒漠和冰冻寒漠生态系统分别减少14.98万km2和0.92万km2。我国生态系统变化导致整体景观的连接性下降、破碎度增加、类型多样性增加,斑块间生态过程的阻碍增强。我国生态状况明显改善,92.06%的区域NDVI增加,平均NDVI增幅为0.74%/a,其中农牧和农林混合生态系统NDVI增幅最显著,分别为1.26%/a和0.85%/a。该分类方案与制图结果突出了生态系统结构、生态环境风险和生产力的差异,可为宏观尺度的生态系统管理提供科学支撑。 相似文献
13.
Baker TR Honorio Coronado EN Phillips OL Martin J van der Heijden GM Garcia M Silva Espejo J 《Oecologia》2007,152(3):495-504
The stocks and dynamics of coarse woody debris (CWD) are significant components of the carbon cycle within tropical forests.
However, to date, there have been no reports of CWD stocks and fluxes from the approximately 1.3 million km2 of lowland western Amazonian forests. Here, we present estimates of CWD stocks and annual CWD inputs from forests in southern
Peru. Total stocks were low compared to other tropical forest sites, whether estimated by line-intercept sampling (24.4 ± 5.3 Mg ha−1) or by complete inventories within 11 permanent plots (17.7 ± 2.4 Mg ha−1). However, annual inputs, estimated from long-term data on tree mortality rates in the same plots, were similar to other
studies (3.8 ± 0.2 or 2.9 ± 0.2 Mg ha−1 year−1, depending on the equation used to estimate biomass). Assuming the CWD pool is at steady state, the turnover time of coarse
woody debris is low (4.7 ± 2.6 or 6.1 ± 2.6 years). These results indicate that these sites have not experienced a recent,
large-scale disturbance event and emphasise the distinctive, rapid nature of carbon cycling in these western Amazonian forests. 相似文献
14.
Tim R. Moore Allison De Young Jill L. Bubier Elyn R. Humphreys Peter M. Lafleur Nigel T. Roulet 《Ecosystems》2011,14(4):646-657
The Mer Bleue peatland is a large ombrotrophic bog with hummock-lawn microtopography, poor fen sections and beaver ponds at
the margin. Average growing-season (May–October) fluxes of methane (CH4) measured in 2002–2003 across the bog ranged from less than 5 mg m−2 d−1 in hummocks, to greater than 100 mg m−2 d−1 in lawns and ponds. The average position of the water table explained about half of the variation in the season average CH4 fluxes, similar to that observed in many other peatlands in Canada and elsewhere. The flux varied most when the water table
position ranged between −15 and −40 cm. To better establish the factors that influence this variability, we measured CH4 flux at approximately weekly intervals from May to November for 5 years (2004–2008) at 12 collars representing the water
table and vegetation variations typical of the peatland. Over the snow-free season, peat temperature is the dominant correlate
and the difference among the collars’ seasonal average CH4 flux is partially dependent on water table position. A third important correlate on CH4 flux is vegetation, particularly the presence of Eriophorum vaginatum, which increases CH4 flux, as well as differences in the potential of the peat profile to produce and consume CH4 under anaerobic and aerobic conditions. The combination of peat temperature and water table position with vegetation cover
was able to explain approximately 44% of the variation in daily CH4 flux, based on 1097 individual measurements. There was considerable inter-annual variation in fluxes, associated with varying
peat thermal and water table regimes in response to variations in weather, but also by variations in the water level in peripheral
ponds, associated with beaver dam activity. Raised water level in the beaver ponds led to higher water tables and increased
CH4 emission in the peatland. 相似文献
15.
Phosphorus (P) is one of main pollution elements of eutrophication. P emissions from different pathways and sources are a
key issue in the protection of water quality and sustainable watershed management practices. We have estimated net anthropogenic
P accumulation (NAPA), as an index of P pollution potential in the Beijing metropolitan region, China. The NAPA estimation
is based on an inventory of P fertilizer use, consumption of human food and animal feed, non-food P, and riverine P net flux.
The overall average NAPA for 1991, 1997, 2003, and 2007 are 777, 943, 1218, and 1084 kg P km−2 y−1, about two times that reported in developed countries. The Urban unit has the largest NAPA (5526 kg P km−2 y−1), whereas Mentougou P was negative, outputting 34 kg P km−2 y−1. P input of fertilizer is the largest source of NAPA, accounting for 40.7% (455 kg P km−2 y−1) of the total P input, followed by non-food P and P in human food and animal feed. NAPA is closely related to land use, on
average 5433 kg P km−2 y−1 in densely populated developed land, 503 kg P km−2 y−1 in agricultural land and 84 kg P km−2 y−1 in forest land. Human population density is the best single predictor of NAPA. Our results provide a basis for understanding
the potential impact of anthropogenic P inputs on environmental problems, such as nation-wide water quality degradation under
the current rapid urban expansion in modern China. 相似文献
16.
In temporary freshwater systems, the type of vegetation within a system can influence community structure. Vegetation not
only provides physical structure, but can also contribute to changes in abundance and quality of food and in water quality
through decomposition. An experiment was undertaken using natural and artificial vegetation in small mesocosms to examine
the influence of the physical structure of vegetation on invertebrate community structure in terms of water quality, food
abundance, and physical structure. It was predicted that invertebrate community structure would be identical in natural and
artificial treatments if the effect of vegetative decomposition was negligible. Furthermore, invertebrate community structure
in bare ground treatments would be identical to those with vegetation if the physical structure of vegetation has no significant
effect. Five treatments were used: a bare ground control, artificial vegetation (×2), and natural vegetation treatments (grass,
eucalypt leaf litter). Water quality, food abundance, and invertebrate abundance were examined after six weeks of inundation.
All treatments had high water temperatures (34–40°C), and natural vegetation treatments had slightly higher conductivity (208–316 mS cm−1) and lower turbidity (40–231 NTU) than other treatments (47–156 mS cm−1 and 55–400 NTU, respectively). The physical structure of artificial vegetation did not significantly influence invertebrate
community structure compared to the bare ground treatment, whereas treatments with decomposing natural vegetation had relatively
low abundances of microcrustaceans (0–96 individuals/mesocosm) and relatively high abundances of chironomids (192–1576 individuals/mesocosm)
compared to other treatments (>100 microcrustaceans/mesocosm if present, and <370 chironomids/mesocosm, respectively). This
suggests that food availability had greater importance than physical structure in determining community structure in these
small aquatic ecosystems.
Handling editor: S. M. Thomaz 相似文献
17.
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
18.
Stream water exports of nutrients and pollutants to water bodies integrate internal and external watershed processes that
vary in both space and time. In this paper, we explore nitrate (NO3) fluxes for the 326 km2 mixed-land use Fall Creek watershed in central New York for 1972–2005, and consider internal factors such as changes in land
use/land cover, dynamics in agricultural production and fertilizer use, and external factors such as atmospheric deposition.
Segmented regression analysis was applied independently to dormant and growing seasons for three portions of the period of
record, which indicated that stream water NO3 concentrations increased in both dormant and growing seasons from the 1970s to the early 1990s at all volumes of streamflow
discharge. Dormant season NO3 concentrations then decreased at all flow conditions between the periods 1987–1993 and 1994–2005. Results from a regression-based
stream water loading model (LOADEST) normalized to mean annual concentrations showed annual modeled NO3 concentration in stream water increased by 34% during the 1970s and 1980s (from 1.15 to 1.54 mg l−1), peaked in about 1989, and then decreased by 29% through 2005 (to 1.09 mg l−1). Annual precipitation had the strongest correlation with stream water NO3 concentrations (r = −0.62, P = 0.01). Among land use factors, corn production for grain was the variable most highly correlated to stream water NO3 concentrations (r = 0.53, P = 0.01). The strongest associative trend determined using Chi-squared Automatic Interaction Detection (CHAID) was found between
stream water NO3 concentrations and N-equivalence of dairy production (Bonferroni adjusted P value = 0.0003). Large increases in dairy production were coincident with declining nitrate concentrations over the past
decade, which suggest that dairy management practices may have improved in the watershed. However, because dairy production
in the Fall Creek watershed has been fueled by large increases in feed imports, the environmental costs of feed production
have likely been externalized to other watersheds. 相似文献
19.
Rainfall partitioning into throughfall and stemflow was studied in a diverse and in a mono specific stand of secondary vegetation
in Eastern Amazonia. The nutrient concentrations in the water were analysed in order to quantify the related hydrochemical
fluxes. Secondary vegetation forms the fallow in the local shifting cultivation system and is usually dominated by shrubs
and trees. Phenakospermum guyannense (Strelitziaceae), a banana-like herb, is one of the predominant non-woody species. The study was conducted during an 18-month
period in a 2.5-year-old relatively species-rich stand and a 10-year-old stand dominated by P. guyannense. In a year with 1956 mm of rainfall 65% (1281 mm) of this quantity reached the soil as throughfall in the diverse stand and
38% (743 mm) in the mono specific stand. Stemflow was estimated to be 23% and 41% respectively. P. guyannense and Banara guianensis (Flacourtiaceae), a tree species, were causing these high funnelling effects. In the young diverse stand B. guianensis had a stemflow of more than 200 l year−1 and P. guyannense had a median flux of 77 l year−1 per pseudostem. In the older stand the taller plants of P.␣guyannense collected 644 l year−1 per pseudostem on the median. The reason for these high values could be the banana-like growth form of P. guyannense and the crown morphology of B. guianensis, which has inclined branches. The low proportion of throughfall and the high stemflow values differ from all previous studies
in Amazonian primary forests. The proximity to the Atlantic Ocean strongly influenced the nutrient fluxes via rainfall at
our study site. This becomes obvious from the high Na and Cl fluxes with rainfall (19.7 kg Na ha−1 year−1, 37.2 kg Cl ha−1 year−1) which were approximately equal to the Na and Cl fluxes with the sum of throughfall and stemflow for both stands. K fluxes
in throughfall and stemflow in both stands were higher than in rainfall by a factor of 8. The high K enrichment during the
crown passage is assumed to be caused by a␣high K concentration in the leaf tissue resulting in enhanced leaching from the
leaves. In months with low␣rainfall the concentrations of Ca, Mg, S and Cl in throughfall of the diverse stand were significantly
higher than in months with high rainfall. This was mainly due to vegetation burns in the dry period, which resulted in ash
deposition on the canopy and subsequent wash-off and solution of ash particles.
Received: 11 May 1997 / Accepted: 2 November 1997 相似文献
20.
The surface of bogs is commonly patterned and composed of different vegetation communities, defined by water level. Carbon
dioxide (CO2) dynamics vary spatially between the vegetation communities. An understanding of the controls on the spatial variation of
CO2 dynamics is required to assess the role of bogs in the global carbon cycle. The water level gradient in a blanket bog was
described and the CO2 exchange along the gradient investigated using chamber based measurements in combination with regression modelling. The aim
was to investigate the controls on gross photosynthesis (PG), ecosystem respiration (RE) and net ecosystem CO2 exchange (NEE) as well as the spatial and temporal variation in these fluxes. Vegetation structure was strongly controlled
by water level. The species with distinctive water level optima were separated into the opposite ends of the gradient in canonical
correspondence analysis. The number of species and leaf area were highest in the intermediate water level range and these
communities had the highest PG. Photosynthesis was highest when the water level was 11 cm below the surface. Ecosystem respiration, which includes decomposition,
was less dependent on vegetation structure and followed the water level gradient more directly. The annual NEE varied from
−115 to 768 g CO2 m−2, being lowest in wet and highest in dry vegetation communities. The temporal variation was most pronounced in PG, which decreased substantially during winter, when photosynthetic photon flux density and leaf area were lowest. Ecosystem
respiration, which is dependent on temperature, was less variable and wintertime RE fluxes constituted approximately 24% of the annual flux. 相似文献