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1.
Greenhouse Gas Budget of a Cool-Temperate Deciduous Broad-Leaved Forest in Japan Estimated Using a Process-Based Model 总被引:1,自引:0,他引:1
A terrestrial ecosystem model, called the Vegetation Integrative Simulator for Trace gases model (VISIT), which fully integrates
biogeochemical carbon and nitrogen cycles, was developed to simulate atmosphere–ecosystem exchanges of greenhouse gases (CO2, CH4, and N2O), and to determine the global warming potential (GWP) taking into account the radiative forcing effect of each gas. The
model was then applied to a cool-temperate deciduous broad-leaved forest in Takayama, central Japan (36°08′N, 137°25′E, 1420 m
above sea level). Simulations were conducted at a daily time step from 1948 to 2008, using time-series meteorological and
nitrogen deposition data. VISIT accurately captured the carbon and nitrogen cycles of this typical Japanese forest, as validated
by tower and chamber flux measurements. During the last 10 years of the simulation, the model estimated that the forest was
a net greenhouse gas sink, having a GWP equivalent of 1025.7 g CO2 m−2 y−1, most of which (1016.9 g CO2 m−2 y−1) was accounted for by net CO2 sequestration into forest biomass regrowth. CH4 oxidation by the forest soil made a small contribution to the net sink (11.9 g CO2-eq. m−2 y−1), whereas N2O emissions were a very small source (3.2 g CO2-eq. m−2 y−1), as expected for a volcanic soil in a humid climate. Analysis of the sensitivity of GWP to changes in temperature, precipitation,
and nitrogen deposition indicated that warming temperatures would decrease the size of the sink, mainly as a result of increased
CO2 release due to increased ecosystem respiration. 相似文献
2.
Carbon Dioxide Variation in a Hardwood Forest Stream: An Integrative Measure of Whole Catchment Soil Respiration 总被引:8,自引:3,他引:5
The concentration of CO2 in stream water is a product of not only instream metabolism but also upland, riparian, and groundwater processes and as
such can provide an integrative measure of whole catchment soil respiration. Using a 5-year dataset of pH, alkalinity, Ca2+, and Mg2+ in surface water of the West Fork of Walker Branch in eastern Tennessee in conjunction with a hydrological flowpath chemistry
model, we investigated how CO2 concentrations and respiration rates in stream, bedrock, and soil environments vary seasonally and interannually. Dissolved
inorganic carbon concentration was highest in summer and autumn (P < 0.05) although the proportion as free CO2 (pCO2) did not vary seasonally (P > 0.05). Over the 5 years, pCO2 was always supersaturated with respect to the atmosphere ranging from 374 to 3626 ppmv (1.0- to 10.1-fold greater than atmospheric
equilibrium), and CO2 evasion from the stream to the atmosphere ranged from 146 to 353 mmol m−2 d−1. Whereas pCO2 in surface water exhibited little intra-annual or interannual variation, distinct seasonal patterns in soil and bedrock pCO2 were revealed by the catchment CO2 model. Seasonally, soil pCO2 increased from a winter low of 8167 ppmv to a summer high of 27,068 ppmv. Driven by the seasonal variation in gas levels,
evasion of CO2 from soils to the atmosphere ranged from 83 mmol m−2 d−1 in winter to 287 mmol m−2 d−1 in summer. The seasonal variation in soil CO2 tracked soil temperature (r
2= 0.46, P < 0.001) and model-derived estimates of CO2 evasion rate from soils agreed with previously reported fluxes measured using chambers (Pearson correlation coefficient =
0.62, P < 0.05) supporting the model assumptions. Although rates of CO2 evasion were similar between the stream and soils, the overall rate of evasion from the channel was only 0.4% of the 70,752
mol/d that evaded from soils due to the vastly different areas of the two subsystems. Our model provides a means to assess
whole catchment CO2 dynamics from easily collected and measured stream-water samples and an approach to study catchment scale variation in soil
ecosystem respiration.
Received 24 July 1997; accepted 14 November 1997. 相似文献
3.
Atmospheric Deposition to the Turkey Lakes Watershed: Temporal Variations and Characteristics 总被引:3,自引:0,他引:3
We investigated the atmospheric concentrations and deposition fluxes of major ions to the Turkey Lakes Watershed (TLW) between
1980 and 1996. During that time, daily SO4
2− concentrations in precipitation decreased markedly, while NO3
−, NH4
+, and H+ concentrations remained roughly constant. It appears that precipitation acidity did not decrease in spite of declining SO4
2− concentrations due to a concurrent and counterbalancing decrease in the concentrations of Ca2+, Mg2+, and K+ in precipitation. The reasons for the decline in base cations are unknown, but this decline is probably related to decreasing
emissions of soil-derived particles from agricultural, industrial, and road sources. A similar situation was seen during the
same period in other parts of Canada, the eastern United States, and Europe. Wet, dry, and total (wet + dry) deposition fluxes
of sulphur (S) and nitrogen (N) were estimated annually for the years 1980–96. The 17-year mean annual total (wet + dry) deposition
of S to the watershed was estimated at 38.5 mmol m−2 y−1 (range 24.3–50.3). Total S deposition decreased by 35% from the early 1980s (1982–84) to the mid-1990s (1994–96), a decline
consistent with the 23% decline in annual SO2 emissions in eastern North America during the same period. In contrast, the annual total (wet + dry) deposition of oxidized
N ranged from 39.8 to 60.4 mmol m−2 y−1, with a 15-year mean of 50.1 mmol m−2 y−1 and a net increase of 10% between the early 1980s (1983–85) and the mid-1990s (1994–96). This is in keeping with a 10% increase
in NOx emissions in eastern North America during the same period. For both S and N (oxidized), wet deposition dominated over dry
deposition as the major mechanism for atmospheric input to the watershed. Annually, wet deposition accounted for approximately
two-thirds of the total atmospheric deposition of both S and N. Dry S deposition was due more to gaseous SO2 deposition (two-thirds of dry S deposition) than to particulate SO4
2− deposition (one-third of dry S deposition). Dry deposition of oxidized N, however, was dominated (95%) by gaseous HNO3 deposition, with minimal input from particulate NO3
− deposition. Compared to several selected watershed/forest sites in Canada, the United States, and Europe, the estimated total
deposition of S and N at the TLW was relatively high during the measurement period.
Received 5 October 1999; accepted 1 March 2001. 相似文献
4.
Juxiu Liu Zhihong Xu Deqiang Zhang Guoyi Zhou Qi Deng Honglang Duan Liang Zhao Chunlin Wang 《Ecosystems》2011,14(5):683-697
Soil mineral weathering may serve as a sink for atmospheric carbon dioxide (CO2). Increased weathering of soil minerals induced by elevated CO2 concentration has been reported previously in temperate areas. However, this has not been well documented for the tropics
and subtropics. We used model forest ecosystems in open-top chambers to study the effects of CO2 enrichment alone and together with nitrogen (N) addition on inorganic carbon (C) losses in the leachates. Three years of
exposure to an atmospheric CO2 concentration of 700 ppm resulted in increased annual inorganic C export through leaching below the 70 cm soil profile. Compared
to the control without any CO2 and N treatments, net biocarbonate C (HCO3
−-C) loss increased by 42%, 74%, and 81% in the high CO2 concentration treatment in 2006, 2007, and 2008, respectively. Increased inorganic C export following the exposure to the
elevated CO2 was related to both increased inorganic C concentrations in the leaching water and the greater amount of leaching water.
Net annual inorganic C (HCO3
−-C and carbonate C: CO3
2−-C) loss via the leaching water in the high CO2 concentration chambers reached 48.0, 49.5, and 114.0 kg ha−1 y−1 in 2006, 2007, and 2008, respectively, compared with 33.8, 28.4, and 62.8 kg ha−1 y−1 in the control chambers in the corresponding years. The N addition showed a negative effect on the mineral weathering. The
decreased inorganic C concentration in the leaching water and the decreased leaching water amount induced by the high N treatment
were the results of the adverse effect. Our results suggest that tropical forest soil systems may be able to compensate for
a small part of the atmospheric CO2 increase through the accelerated processing of CO2 into HCO3
−-C during soil mineral weathering, which might be transported in part into ground water or oceans on geological timescales. 相似文献
5.
Ecosystem-level experiments on the effects of atmospheric CO2 enrichment and N deposition on forest trees are urgently needed. Here we present data for nine model ecosystems of spruce
(Picea abies) on natural nutrient-poor montane forest soil (0.7 m2 of ground and 350 kg weight). Each system was composed of six 7-year-old (at harvest) trees each representing a different
genotype, and a herbaceous understory layer (three species). The model ecosystems were exposed to three different CO2 concentrations (280, 420, 560 μl l−1) and three different rates of wet N deposition (0, 30, 90 kg ha−1 year−1) in a simulated annual course of Swiss montane climate for 3 years. The total ecosystem biomass was not affected by CO2 concentration, but increased with increasing N deposition. However, biomass allocation to roots increased with increasing
CO2 leading to significantly lower leaf mass ratios (LMRs) and leaf area ratios (LARs) in trees grown at elevated CO2. In contrast to CO2 enrichment, N deposition increased biomass allocation to the aboveground plant parts, and thus LMR and LAR were higher with
increasing N deposition. We observed no CO2 × N interactions on growth, biomass production, or allocation, and there were also no genotype × treatment interactions.
The final leaf area index (LAI) of the spruce canopies was 19% smaller at 420 and 27% smaller at 560 than that measured at
280 μl CO2 l−1, but was not significantly altered by increasing N deposition. Lower LAIs at elevated CO2 largely resulted from shorter branches (less needles per individual tree) and partially from increased needle litterfall.
Independently of N deposition, total aboveground N content in the spruce communities declined with increasing CO2 (−18% at 420 and −31% at 560 compared to 280 μl CO2 l−1). N deposition had the opposite effect on total above ground N content (+18% at 30 and +52% at 90 compared to 0 kg N ha−1 year−1). Our results suggest that under competitive conditions on natural forest soil, atmospheric CO2 enrichment may not lead to higher ecosystem biomass production, but N deposition is likely to do so. The reduction in LAI
under elevated CO2 suggests allometric down-regulation of photosynthetic carbon uptake at the canopy level. The strong decline in the tree nitrogen
mass per unit ground area in response to elevated CO2 may indicate CO2-induced reductions of soil N availability.
Received: 11 May 1997 / Accepted: 4 August 1997 相似文献
6.
The flux of CO2 and CH4 from lakes and rivers in arctic Alaska 总被引:5,自引:2,他引:3
Partial pressures of CO2 and CH4 were measured directly or calculated from pH and alkalinity or DIC measurements for 25 lakes and 4 rivers on the North Slope
of Alaska. Nearly all waters were super-saturated with respect to atmospheric pressures of CO2 and CH4. Gas fluxes to the atmosphere ranged from −6.5 to 59.8 mmol m−2 d−1 for CO2 and from 0.08 to 1.02 mmol m−2 d−1 for CH4, and were uncorrelated with latitude or lake morphology. Seasonal trends include a buildup of CO2 and CH4 under ice during winter, and often an increased CO2 flux rate in August due to partial lake turnover. Nutrient fertilization experiments resulted in decreased CO2 release from a lake due to photosynthetic uptake, but no change in CO2 release from a river due to the much faster water renewal time. In lakes and rivers the groundwater input of dissolved CO2 and CH4 is supplemented by in-lake respiration of dissolved and particulate carbon washed in from land. The release of carbon from
aquatic systems to the atmosphere averaged 24 g C m−2 y−1, and in coastal areas where up to 50% of the surface area is water, this loss equals frac 1/5 to 1/2 of the net carbon accumulation
rates estimated for tundra. 相似文献
7.
8.
Richard D. Bowden Mark S. Castro Jerry M. Melillo Paul A. Steudler John D. Aber 《Biogeochemistry》1993,21(2):61-71
Fluxes of nitrous oxide (N2O), carbon dioxide (CO2), and methane (CH4) between soils and the atmosphere were measured monthly for one year in a 77-year-old temperate hardwood forest following
a simulated hurricane blowdown. Emissions of CO2 and uptake of CH4 for the control plot were 4.92 MT C ha−1 y−1 and 3.87 kg C ha−1 y−1, respectively, and were not significantly different from the blowdown plot. Annual N2O emissions in the control plot (0.23 kg N ha−1 y−1) were low and were reduced 78% by the blowdown. Net N mineralization was not affected by the blowdown. Net nitrification
was greater in the blowdown than in the control, however, the absolute rate of net nitrification, as well as the proportion
of mineralized N that was nitrified, remained low. Fluxes of CO2 and CH4 were correlated positively to soil temperature, and CH, uptake showed a negative relationship to soil moisture. Substantial
resprouting and leafing out of downed or damaged trees, and increased growth of understory vegetation following the blowdown,
were probably responsible for the relatively small differences in soil temperature, moisture, N availability, and net N mineralization
and net nitrification between the control and blowdown plots, thus resulting in no change in CO2 or CH4 fluxes, and no increase in N2O emissions. 相似文献
9.
In two mountain ecosystems at the Alptal research site in central Switzerland, pulses of 15NO3 and 15NH4 were separately applied to trace deposited inorganic N. One forested and one litter meadow catchment, each approximately
1600 m2, were delimited by trenches in the Gleysols. K15NO3 was applied weekly or fortnightly over one year with a backpack sprayer, thus labelling the atmospheric nitrate deposition.
After the sampling and a one-year break, 15NH4Cl was applied as a second one-year pulse, followed by a second sampling campaign. Trees (needles, branches and bole wood),
ground vegetation, litter layer and soil (LF, A and B horizon) were sampled at the end of each labelling period. Extractable
inorganic N, microbial N, and immobilised soil N were analysed in the LF and A horizons. During the whole labelling period,
the runoff water was sampled as well. Most of the added tracer remained in both ecosystems. More NO3− than NH4+ tracer was retained, especially in the forest. The highest recovery was in the soil, mainly in the organic horizon, and in
the ground vegetation, especially in the mosses. Event-based runoff analyses showed an immediate response of 15NO3− in runoff, with sharp 15N peaks corresponding to discharge peaks. NO3− leaching showed a clear seasonal pattern, being highest in spring during snowmelt. The high capacity of N retention in these
ecosystems leads to the assumption that deposited N accumulates in the soil organic matter, causing a progressive decline
of its C:N ratio. 相似文献
10.
Dolly N. Kothawala Shaun A. Watmough Martyn N. Futter Leiming Zhang Peter J. Dillon 《Ecosystems》2011,14(2):274-286
Ecosystem acidification and eutrophication resulting from increased deposition of dissolved inorganic nitrogen (DIN) are issues
of increasing global concern. Consequently, costly policy decisions are being implemented to decrease nitrogen oxide (NO
x
) emissions. Although declining DIN deposition along with rapid declines of DIN in surface waters have been reported in parts
of Europe, the same observation is just emerging in North America. Here we find a significant decline in bulk deposition NO3
− during the later part of a 28-year record in southcentral Ontario, Canada. Despite high N retention and substantial inter-annual
variability in the long-term record due to periods of drought, we find significant declines in annual NO3
− concentrations and export at six out of 11 streams that drain upland-dominated catchments. In contrast, five streams draining
primarily wetland-dominated catchments with lower levels of NO3
− show no decreasing trend in NO3
− concentration or export. The rapid response in stream NO3
− to declining atmospheric inputs was observed at sites with historically moderate inputs of DIN (~870 mg m−2 y−1) in bulk deposition. Topographic features such as slope, and related catchment features including wetland cover, appear to
influence which catchments will respond positively to declining DIN deposition. These findings force us to revise our original
conceptualization of the N saturation status of these catchments. 相似文献
11.
N and P budgets quantify inputs and outputs of nutrients at the catchment scale to allow evaluation of inputs and outputs
as well as inferences about transport and processing based on unaccounted-for nutrients. N and P budgets were constructed
for two catchments in southeastern Michigan with markedly different numbers of impoundments, over two years, to evaluate the
influence of impoundments on nutrient fluxes from each catchment. The Huron, with 88 impoundments >10 ha, stored 156 kg P km−2 y−1, while the Raisin (with 14 impoundments) had a net export of 102 kg P km−2 y−1. The Huron catchment also stored and denitrified more N than the Raisin catchment – 2,418 kg N km−2 y−1 compared to 1,538 kg N km−2 y−1. Riverine export of N and P also varied markedly between the catchments, with the Huron River exporting 288 kg N and 7 kg P km−2 y−1 and the Raisin River exporting 1,268 kg N and 34 kg P km−2 y−1. We then re-calculated budget results from previous studies using the approach of the present study, altering input and outputs
fluxes as well as system boundaries to obtain comparable budgets. For these comparable budgets, annual P outputs on average
accounted for 77% of inputs whereas N outputs accounted for only 39% of N inputs. Across catchments, the percent of inputs
exported by the river averaged 16% for N and 5% for P, indicating more effective retention of P than N. 相似文献
12.
Stream export of nitrogen (N) as nitrate (NO3−; the most mobile form of N) from forest ecosystems is thought to be controlled largely by plant uptake of inorganic N, such
that reduced demand for plant N during the non-growing season and following disturbances results in increased stream NO3− export. The roles of microbes and soils in ecosystem N retention are less clear, but are the dominant controls on N export
when plant uptake is low. We used a mass balance approach to investigate soil N retention during winter (December through
March) at the Hubbard Brook Experimental Forest by comparing NO3− inputs (atmospheric deposition), internal production (soil microbial nitrification), and stream output. We focused on months
when plant N uptake is nearly zero and the potential for N export is high. Although winter months accounted for only 10–15%
of annual net nitrification, soil NO3− production (0.8–1.0 g N m−2 winter−1) was much greater than stream export (0.03–0.19 N m−2 winter−1). Soil NO3− retention in two consecutive winters was high (96% of combined NO3− deposition and soil production; year 1) even following severe plant disturbance caused by an ice-storm (84%; year 2) We show
that soil NO3− retention is surprisingly high even when N demand by plants is low. Our study highlights the need to better understand mechanisms
of N retention during the non-growing season to predict how ecosystems will respond to high inputs of atmospheric N, disturbance,
and climate change. 相似文献
13.
Response of soil respiration to simulated N deposition in a disturbed and a rehabilitated tropical forest in southern China 总被引:3,自引:1,他引:2
Jiangming Mo Wei Zhang Weixing Zhu Yunting Fang Dejun Li Ping Zhao 《Plant and Soil》2007,296(1-2):125-135
Responses of soil respiration (CO2 emission) to simulated N deposition were studied in a disturbed (reforested forest with previous understory and litter harvesting)
and a rehabilitated (reforested forest with no understory and litter harvesting) tropical forest in southern China from October
2005 to September 2006. The objectives of the study were to test the following hypotheses: (1) soil respiration is higher
in rehabilitated forest than in disturbed forest; (2) soil respiration in both rehabilitated and disturbed tropical forests
is stimulated by N additions; and (3) soil respiration is more sensitive to N addition in disturbed forest than in rehabilitated
forest due to relatively low soil nutrient status in the former, resulting from different previous human disturbance. Static
chamber and gas chromatography techniques were employed to quantify the soil respiration, following different N treatments
(Control, no N addition; Low-N, 5 g N m−2 year−1; Medium-N, 10 g N m−2 year−1), which had been applied continuously for 26 months before the respiration measurement. Results showed that soil respiration
exhibited a strong seasonal pattern, with the highest rates observed in the hot and wet growing season (April–September) and
the lowest rates in winter (December–February) in both rehabilitated and disturbed forests. Soil respiration rates exhibited
significant positive exponential relationship with soil temperature and significant positive linear relationship with soil
moisture. Soil respiration was also significantly higher in the rehabilitated forest than in the disturbed forest. Annual
mean soil respiration rate in the rehabilitated forest was 20% lower in low-N plots (71 ± 4 mg CO2-C m−2 h−1) and 10% lower in medium-N plots (80 ± 4 mg CO2-C m−2 h−1) than in the control plots (89 ± 5 mg CO2-C m−2 h−1), and the differences between the control and low-N or medium-N treatments were statistically significant. In disturbed forest,
annual mean soil respiration rate was 5% lower in low-N plots (63 ± 3 mg CO2-C m−2 h−1) and 8% lower in medium-N plots (61 ± 3 mg CO2-C m−2 h−1) than in the control plots (66 ± 4 mg CO2-C m−2 h−1), but the differences among treatments were not significant. The depressed effects of experimental N deposition occurred
mostly in the hot and wet growing season. Our results suggest that response of soil respiration to elevated N deposition in
the reforested tropical forests may vary depending on the status of human disturbance.
Responsible Editor: Hans Lambers. 相似文献
14.
The Impact of Nitrogen Placement and Tillage on NO, N2O, CH4 and CO2 Fluxes from a Clay Loam Soil 总被引:4,自引:0,他引:4
Xuejun J. Liu Arvin R. Mosier Ardell D. Halvorson Fusuo S. Zhang 《Plant and Soil》2006,280(1-2):177-188
To evaluate the impact of N placement depth and no-till (NT) practice on the emissions of NO, N2O, CH4 and CO2 from soils, we conducted two N placement experiments in a long-term tillage experiment site in northeastern Colorado in 2004.
Trace gas flux measurements were made 2–3 times per week, in zero-N fertilizer plots that were cropped continuously to corn
(Zea mays L.) under conventional-till (CT) and NT. Three N placement depths, replicated four times (5, 10 and 15 cm in Exp. 1 and 0,
5 and 10 cm in Exp. 2, respectively) were used. Liquid urea–ammonium nitrate (UAN, 224 kg N ha−1) was injected to the desired depth in the CT- or NT-soils in each experiment. Mean flux rates of NO, N2O, CH4 and CO2 ranged from 3.9 to 5.2 μg N m−2 h−1, 60.5 to 92.4 μg N m−2 h−1, −0.8 to 0.5 μg C m−2 h−1, and 42.1 to 81.7 mg C m−2 h−1 in both experiments, respectively. Deep N placement (10 and 15 cm) resulted in lower NO and N2O emissions compared with shallow N placement (0 and 5 cm) while CH4 and CO2 emissions were not affected by N placement in either experiment. Compared with N placement at 5 cm, for instance, averaged
N2O emissions from N placement at 10 cm were reduced by more than 50% in both experiments. Generally, NT decreased NO emission
and CH4 oxidation but increased N2O emissions compared with CT irrespective of N placement depths. Total net global warming potential (GWP) for N2O, CH4 and CO2 was reduced by deep N placement only in Exp. 1 but was increased by NT in both experiments. The study results suggest that
deep N placement (e.g., 10 cm) will be an effective option for reducing N oxide emissions and GWP from both fertilized CT-
and NT-soils. 相似文献
15.
Response of Litter Decomposition to Simulated N Deposition in Disturbed, Rehabilitated and Mature Forests in Subtropical China 总被引:16,自引:1,他引:15
The response of decomposition of litter for the dominant tree species in disturbed (pine), rehabilitated (pine and broadleaf
mixed) and mature (monsoon evergreen broadleaf) forests in subtropical China to simulated N deposition was studied to address
the following hypothesis: (1) litter decomposition is faster in mature forest (high soil N availability) than in rehabilitated/disturbed
forests (low soil N availability); (2) litter decomposition is stimulated by N addition in rehabilitated and disturbed forests
due to their low soil N availability; (3) N addition has little effect on litter decomposition in mature forest due to its
high soil N availability. The litterbag method (a total of 2880 litterbags) and N treatments: Control-no N addition, Low-N:
−5 g N m−2 y−1, Medium-N: −10 g N m−2 y−1, and High-N: −15 g N m−2 y−1, were employed to evaluate decomposition. Results indicated that mature forest, which has likely been N saturated due to both long-term high N deposition in the region
and the age of the ecosystem, had the highest litter decomposition rate, and exhibited no significant positive and even some
negative response to nitrogen additions. However, both disturbed and rehabilitated forests, which are still N limited due
to previous land use history, exhibited slower litter decomposition rates with significant positive effects from nitrogen
additions. These results suggest that litter decomposition and its responses to N addition in subtropical forests of China
vary depending on the nitrogen status of the ecosystem. 相似文献
16.
We studied the effect of water exchange on the depletion (or accumulation) of bacterioplankton, dissolved organic matter and inorganic nutrients in small open framework cavities (50–70 l) at 15 m depth on the coral reef along Curaçao, Netherlands Antilles. The bacterioplankton removal rate in cavities increased with increasing water exchange rates up to a threshold of 0.0045 s−1, reaching values of 50–100 mg C m−2 total interior cavity surface area (CSA) per day. Beyond the threshold, bacterioplankton removal dropped. The cryptic community is apparently adapted to the average water exchange in these cavities (0.0041 s−1). Dissolved inorganic nitrogen (DIN), nitrate + nitrite (NO
x
) in particular, accumulated in cavity water and the accumulation decreased with increasing water exchange. Net NO
x
effluxes exceeded net DIN effluxes from cavities (average efflux rate of 1.9 mmol NO
x
vs. 0.8 mmol DIN m−2 interior CSA per day). The difference is ascribed to net ammonium losses (NH4) in cavities at reef concentrations >0.025 μM NH4, possibly due to enhanced nitrification. Dissolved inorganic phosphate accumulated in cavities, but was not related to water exchange. The cryptic biota in cavities depend on water exchange for optimization of consumption of bacterioplankton and removal of inorganic nitrogen. Coral cavities are an evident sink of bacterioplankton and a source of NO
x and PO
4
3−
. 相似文献
17.
Short-term soil inorganic N pulse after experimental fire alters invasive and native annual plant production in a Mojave Desert shrubland 总被引:1,自引:0,他引:1
Todd C. Esque Jason P. Kaye Sara E. Eckert Lesley A. DeFalco C. Richard Tracy 《Oecologia》2010,164(1):253-263
Post-fire changes in desert vegetation patterns are known, but the mechanisms are poorly understood. Theory suggests that
pulse dynamics of resource availability confer advantages to invasive annual species, and that pulse timing can influence
survival and competition among species. Precipitation patterns in the American Southwest are predicted to shift toward a drier
climate, potentially altering post-fire resource availability and consequent vegetation dynamics. We quantified post-fire
inorganic N dynamics and determined how annual plants respond to soil inorganic nitrogen variability following experimental
fires in a Mojave Desert shrub community. Soil inorganic N, soil net N mineralization, and production of annual plants were
measured beneath shrubs and in interspaces during 6 months following fire. Soil inorganic N pools in burned plots were up
to 1 g m−2 greater than unburned plots for several weeks and increased under shrubs (0.5–1.0 g m−2) more than interspaces (0.1–0.2 g m−2). Soil NO3
−−N (nitrate−N) increased more and persisted longer than soil NH4
+−N (ammonium−N). Laboratory incubations simulating low soil moisture conditions, and consistent with field moisture during
the study, suggest that soil net ammonification and net nitrification were low and mostly unaffected by shrub canopy or burning.
After late season rains, and where soil inorganic N pools were elevated after fire, productivity of the predominant invasive
Schismus spp. increased and native annuals declined. Results suggest that increased N availability following wildfire can favor invasive
annuals over natives. Whether the short-term success of invasive species following fire will direct long-term species composition
changes remains to be seen, yet predicted changes in precipitation variability will likely interact with N cycling to affect
invasive annual plant dominance following wildfire. 相似文献
18.
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
19.
Responses of Vegetation and Ecosystem CO2 Exchange to 9 Years of Nutrient Addition at Mer Bleue Bog 总被引:1,自引:0,他引:1
Anthropogenic nitrogen (N) loading has the potential to affect plant community structure and function, and the carbon dioxide
(CO2) sink of peatlands. Our aim is to study how vegetation changes, induced by nutrient input, affect the CO2 exchange of a nutrient-limited bog. We conducted 9- and 4-year fertilization experiments at Mer Bleue bog, where we applied
N addition levels of 1.6, 3.2, and 6.4 g N m−2 a−1, upon a background deposition of about 0.8 g N m−2 a−1, with or without phosphorus and potassium (PK). Only the treatments 3.2 and 6.4 g N m−2 a−1 with PK significantly affected CO2 fluxes. These treatments shifted the Sphagnum moss and dwarf shrub community to taller dwarf shrub thickets without moss, and the CO2 responses depended on the phase of vegetation transition. Overall, compared to the large observed changes in the vegetation,
the changes in CO2 fluxes were small. Following Sphagnum loss after 5 years, maximum ecosystem photosynthesis (Pgmax) and net CO2 exchange (NEEmax) were lowered (−19 and −46%, respectively) in the highest NPK treatment. In the following years, while shrub height increased,
the vascular foliar biomass did not fully compensate for the loss of moss biomass; yet, by year 8 there were no significant
differences in Pgmax and NEEmax between the nutrient and the control treatments. At the same time, an increase (24–32%) in ecosystem respiration (ER) became
evident. Trends in the N-only experiment resembled those in the older NPK experiment by the fourth year. The increasing ER
with increasing vascular plant and decreasing Sphagnum moss biomass across the experimental plots suggest that high N deposition may lessen the CO2 sink of a bog. 相似文献
20.
CO2 exchange of the endolithic lichen Verrucaria baldensis was measured in the laboratory under different conditions of water content, temperature, light, and CO2 concentration. The species had low CO2 exchange rates (maximum net photosynthesis: c. 0.45 μmol CO2 m−2 s−1; maximum dark respiration: c. 0.3 μmol CO2 m−2 s−1) and a very low light compensation point (7 μmol photons m−2 s−1 at 8°C). The net photosynthesis/respiration quotient reached a maximum at 9–15°C. Photosynthetic activity was affected only
after very severe desiccation, when high resaturation respiratory rates were measured. Microclimatic data were recorded under
different weather conditions in an abyss of the Trieste Karst (northeast Italy), where the species was particularly abundant.
Low photosynthetically active radiation (normally below 40 μmol photons m−2 s−1), very high humidities (over 80%), and low, constant temperatures were measured. Thallus water contents sufficient for CO2 assimilation were often measured in the absence of condensation phenomena.
Received: 22 September 1996 / Accepted: 26 April 1997 相似文献