共查询到20条相似文献,搜索用时 218 毫秒
1.
Winter and summer nitrous oxide and nitrogen oxides fluxes from a seasonally snow-covered subalpine meadow at Niwot Ridge,Colorado 总被引:4,自引:3,他引:1
Gianluca Filippa Michele Freppaz Mark W. Williams Detlev Helmig Daniel Liptzin Brian Seok Brad Hall Kurt Chowanski 《Biogeochemistry》2009,95(1):131-149
The soil emission rates (fluxes) of nitrous oxide (N2O) and nitrogen oxides (NO + NO2 = NO
x
) through a seasonal snowpack were determined by a flux gradient method from near-continuous 2-year measurements using an
automated system for sampling interstitial air at various heights within the snowpack from a subalpine site at Niwot Ridge,
Colorado. The winter seasonal-averaged N2O fluxes of 0.047–0.069 nmol m−2 s−1 were ~15 times higher than observed NO
x
fluxes of 0.0030–0.0067 nmol m−2 s−1. During spring N2O emissions first peaked and then dropped sharply as the soil water content increased from the release of snowpack meltwater,
while other gases, including NO
x
and CO2 did not show this behavior. To compare and contrast the winter fluxes with snow-free conditions, N2O fluxes were also measured at the same site in the summers of 2006 and 2007 using a closed soil chamber method. Summer N2O fluxes followed a decreasing trend during the dry-out period after snowmelt, interrupted by higher values related to precipitation
events. These peaks were up to 2–3 times higher than the background summer levels. The integrated N2O-N loss over the summer period was calculated to be 1.1–2.4 kg N ha−1, compared to ~0.24–0.34 kg N ha−1 for the winter season. These wintertime N2O fluxes from subniveal soil are generally higher than the few previously published data. These results are of the same order
of magnitude as data from more productive ecosystems such as fertilized grasslands and high-N-cycling forests, most likely
because of a combination of the relatively well-developed soils and the fact that subnivean biogeochemical processes are promoted
by the deep, insulating snowpack. Hence, microbially mediated oxidized nitrogen emissions occurring during the winter can
be a significant part of the N-cycle in seasonally snow-covered subalpine ecosystems. 相似文献
2.
Process-level controls on CO<Subscript>2</Subscript> fluxes from a seasonally snow-covered subalpine meadow soil,Niwot Ridge,Colorado 总被引:4,自引:4,他引:0
Daniel Liptzin Mark W. Williams Detlev Helmig Brian Seok Gianluca Filippa Kurt Chowanski Jacques Hueber 《Biogeochemistry》2009,95(1):151-166
Fluxes of CO2 during the snow-covered season contribute to annual carbon budgets, but our understanding of the mechanisms controlling the
seasonal pattern and magnitude of carbon emissions in seasonally snow-covered areas is still developing. In a subalpine meadow
on Niwot Ridge, Colorado, soil CO2 fluxes were quantified with the gradient method through the snowpack in winter 2006 and 2007 and with chamber measurements
during summer 2007. The CO2 fluxes of 0.71 μmol m−2 s−1 in 2006 and 0.86 μmol m−2 s−1 in 2007 are among the highest reported for snow-covered ecosystems in the literature. These fluxes resulted in 156 and 189 g C m−2 emitted over the winter, ~30% of the annual soil CO2 efflux at this site. In general, the CO2 flux increased during the winter as soil moisture increased. A conceptual model was developed with distinct snow cover zones
to describe this as well as the three other reported temporal patterns in CO2 flux from seasonally snow-covered soils. As snow depth and duration increase, the factor controlling the CO2 flux shifts from freeze–thaw cycles (zone I) to soil temperature (zone II) to soil moisture (zone III) to carbon availability
(zone IV). The temporal pattern in CO2 flux in each zone changes from periodic pulses of CO2 during thaw events (zone I), to CO2 fluxes reaching a minimum when soil temperatures are lowest in mid-winter (zone II), to CO2 fluxes increasing gradually as soil moisture increases (zone III), to CO2 fluxes decreasing as available carbon is consumed. This model predicts that interannual variability in snow cover or directional
shifts in climate may result in dramatically different seasonal patterns of CO2 flux from seasonally snow-covered soils. 相似文献
3.
Emission and plant uptake of atmospheric nitrogen oxides (NO + NO2) significantly influence regional climate change by regulating the oxidative chemistry of the lower atmosphere, species composition
and the recycling of carbon and nutrients, etc. Plant uptake of nitrogen dioxide (NO2) is concentration-dependent and species-specific, and covaries with environmental factors. An important factor determining
NO2 influx into leaves is the replenishment of the substomatal cavity. The apoplastic chemistry of the substomatal cavity plays
crucial roles in NO2 deposition rates and the tolerance to NO2, involving the reactions between NO2 and apoplastic antioxidants, NO2-responsive germin-like proteins, apoplastic acidification, and nitrite-dependent NO synthesis, etc. Moreover, leaf apoplast
is a favorable site for the colonization by microbes, which disturbs nitrogen metabolism of host plants. For most plant species,
NO2 assimilation in a leaf primarily depends on the nitrate (NO3
−) assimilation pathway. NO2–N assimilation is coupled with carbon and sulfur (sulfate and SO2) assimilation as indicated by the mutual needs for metabolic intermediates (or metabolites) and the NO2-caused changes of key metabolic enzymes such as phosphoenolpyruvate carboxylase (PEPc) and adenosine 5′-phosphosulfate sulfotransferase,
organic acids, and photorespiration. Moreover, arbuscular mycorrhizal (AM) colonization improves the tolerance of host plants
to NO2 by enhancing the efficiency of nutrient absorption and translocation and influencing foliar chemistry. Further progress is
proposed to gain a better understanding of the coordination between NO2–N, S and C assimilation, especially the investigation of metabolic checkpoints, and the effects of photorespiratory nitrogen
cycle, diverse PEPc and the metabolites such as cysteine, O-acetylserine (OAS) and glutathione. 相似文献
4.
Detlev Helmig Eric Apel Donald Blake Laurens Ganzeveld Barry L. Lefer Simone Meinardi Aaron L. Swanson 《Biogeochemistry》2009,95(1):167-183
Whole air drawn from four heights within the high elevation (3,340 m asl), deep, winter snowpack at Niwot Ridge, Colorado,
were sampled into stainless steel canisters, and subsequently analyzed by gas chromatography for 51 volatile inorganic and
organic gases. Two adjacent plots with similar snow cover were sampled, one over bare soil and a second one from within a
snow-filled chamber where Tedlar/Teflon-film covered the ground and isolated it from the soil. This comparison allowed for
studying effects from processes in the snowpack itself versus soil influences on the gas concentrations and fluxes within
and through the snowpack. Samples were also collected from ambient air above the snow surface for comparison with the snowpack
air. Analyzed gas species were found to exhibit three different kinds of behavior: (1) One group of gases, i.e., carbon dioxide
(CO2), chloroform (CHCl3), dimethylsulfide (CH3)2S, carbondisulfide (CS2), and dichlorobromomethane (CHBrCl2), displayed higher concentrations inside the snow, indicating a formation of these species and release into the atmosphere.
(2) A second group of compounds, including carbon monoxide (CO), carbonyl sulfide (COS), the hydrocarbons methane, ethane,
ethyne, benzene, and the halogenated compounds methylchloride (CH3Cl), methylbromide (CH3Br), dibromomethane (CH2Br2), bromoform (CHBr3), tetrachloromethane (CCl4), CFC-11, CFC-12, HCFC-22, CFC-113, 1,2-dichloroethane, methylchloroform, HCFC-141b, and HCFC-142b, were found at lower concentrations
in the snow, indicating that the snow and/or soil constitute a sink for these gases. (3) For 21 other gases absolute concentrations,
respectively concentration gradients, were too low to unequivocally identify their uptake or release behavior. For gases listed
in the first two groups, concentration gradients were incorporated into a snowpack gas diffusion model to derive preliminary
estimates of fluxes at the snow-atmosphere interface. The snowpack gradient flux technique was found to offer a highly sensitive
method for the study of these surface gas exchanges. Microbial activities below this deep, winter snowpack appear to be the
driving mechanism behind these gas sources and sinks. Flux results were applied to a simple box model to assess the potential
contribution of the snowpack uptake rates to atmospheric lifetimes of these species. 相似文献
5.
Storage and release of solutes from a subalpine seasonal snowpack: soil and stream water response, Niwot Ridge, Colorado 总被引:2,自引:2,他引:0
Much of the research on the chemistry of snow and surface waters of the western US, Europe, and Asia has been conducted in
high-elevation catchments above treeline. Here we provide information on the solute content of the seasonal snowpack at the
Soddie site on Niwot Ridge, Colorado, a subalpine site near treeline. We focus on the storage and release of both inorganic
and organic solutes to the soils underneath the snowpack, and subsequent effects on the chemical and nutrient content of the
underlying soil solution and the adjacent headwater stream. The concentration of inorganic nitrogen (N) stored in the seasonal
snowpack at the Soddie site of about 11 μeq L−1 was on the upper end of values reported for the northern hemisphere when compared to most areas of the Alps, Himalayas, and
Tien Shan mountain ranges, but consistent with other reports of snowpacks in the Rocky Mountains. The storage of inorganic
N in the snowpack at maximum accumulation averaged about 17 meq m−2, or 170 eq ha−1 (on the order of 2 kg-N ha−1). Solutes were released from storage in the form of an ionic pulse, with a maximum concentration factor of about four. In
contrast to the seasonal snowpack, the dominant form of N in the soil solution was dissolved organic N. Thus, soils underlying
the seasonal snowpack appear to assimilate inorganic N released from storage in the snowpack and convert it to organic N.
A two component mixing model suggests that the majority of streamflow was this year’s snowmelt that had infiltrated the subsurface
and undergone subsequent biological and geochemical reactions. The inorganic N in surface waters at the headwaters of Como
creek were always near or below detection limits, suggesting that this area at treeline is still N-limited. 相似文献
6.
Winter production of CO2 and N2O from alpine tundra: environmental controls and relationship to inter-system C and N fluxes 总被引:15,自引:0,他引:15
Fluxes of CO2 and N2O were measured from both natural and experimentally augmented snowpacks during the winters of 1993 and 1994 on Niwot Ridge
in the Colorado Front Range. Consistent snow cover insulated the soil surface from extreme air temperatures and allowed heterotrophic
activity to continue through much of the winter. In contrast, soil remained frozen at sites with inconsistent snow cover and
production did not begin until snowmelt. Fluxes were measured when soil temperatures under the snow ranged from –5°C to 0°C,
but there was no significant relationship between flux for either gas and temperature within this range. While early developing
snowpacks resulted in warmer minimum soil temperatures allowing production to continue for most of the winter, the highest
CO2 fluxes were recorded at sites which experienced a hard freeze before a consistent snowpack developed. Consequently, the seasonal
flux of CO2
–C from snow covered soils was related both to the severity of freeze and the duration of snow cover. Over-winter CO2
–C loss ranged from 0.3 g C m−2 season−1 at sites characterized by inconsistent snow cover to 25.7 g C m−2 season−1 at sites that experienced a hard freeze followed by an extended period of snow cover. In contrast to the pattern observed
with C loss, a hard freeze early in the winter did not result in greater N2O–N loss. Both mean daily N2O fluxes and the total over-winter N2O–N loss were related to the length of time soils were covered by a consistent snowpack. Over-winter N2O–N loss ranged from less 0.23 mg N m−2 from the latest developing, short duration snowpacks to 16.90 mg N m−2 from sites with early snow cover. These data suggest that over-winter heterotrophic activity in snow-covered soil has the
potential to mineralize from less than 1% to greater than 25% of the carbon fixed in ANPP, while over-winter N2O fluxes range from less than half to an order of magnitude higher than growing season fluxes. The variability in these fluxes
suggests that small changes in climate which affect the timing of seasonal snow cover may have a large effect on C and N cycling
in these environments.
Received: 5 April 1996 / Accepted: 25 November 1996 相似文献
7.
Since 1987 we have studied weekly change in winter (December–April) precipitation, snowpack, snowmelt, soil water, and stream
water solute flux in a small (176-ha) Northern Michigan watershed vegetated by 65–85 year-old northern hardwoods. Our primary
study objective was to quantify the effect of change in winter temperature and precipitation on watershed hydrology and solute
flux. During the study winter runoff was correlated with precipitation, and forest soils beneath the snowpack remained unfrozen.
Winter air temperature and soil temperature beneath the snowpack increased while precipitation and snowmelt declined. Atmospheric
inputs declined for H+, NO3−, NH4+, dissolved inorganic nitrogen (DIN), and SO42−. Replicated plot-level results, which could not be directly extrapolated to the watershed scale, showed 90% of atmospheric
DIN input was retained in surface shallow (<15 cm deep) soils while SO42− flux increased 70% and dissolved organic carbon (DOC) 30-fold. Most stream water base cation (CB), HCO3−, and Cl− concentrations declined with increased stream water discharge, K+, NO3−, and SO42− remained unchanged, and DOC and dissolved organic nitrogen (DON) increased. Winter stream water solute outputs declined or
were unchanged with time except for NO3− and DOC which increased. DOC and DIN outputs were correlated with the percentage of winter runoff and stream discharge that
occurred when subsurface flow at the plot-level was shallow (<25 cm beneath Oi). Study results suggest that the percentage
of annual runoff occurring as shallow lateral subsurface flow may be a major factor regulating solute outputs and concentrations
in snowmelt-dominated ecosystems. 相似文献
8.
Process improvement in amino acid N-carboxyanhydride synthesis by N-carbamoyl amino acid nitrosation
Amino acid N-carboxyanhydrides (NCA), convenient monomer for polypeptide synthesis, are easily prepared in high purity as the result of
N-carbamoyl amino acids (CAA) nitrosation by gaseous NOx (4:1 NO + O2 mixture, or NOCl) in toluene. Removal of polar side products is then efficiently carried out during subsequent work-up and
crystallisation so that the resulting NCA obtained in good yield is suitable for controlled, primary amine-initiated polymerisation. 相似文献
9.
Brian Seok Detlev Helmig Mark W. Williams Daniel Liptzin Kurt Chowanski Jacques Hueber 《Biogeochemistry》2009,95(1):95-113
An experimental system for sampling trace gas fluxes through seasonal snowpack was deployed at a subalpine site near treeline
at Niwot Ridge, Colorado. The sampling manifold was in place throughout the entire snow-covered season for continuous air
sampling with minimal disturbance to the snowpack. A series of gases (carbon dioxide, water vapor, nitrous oxide, nitric oxide,
ozone, volatile organic compounds) was determined in interstitial air withdrawn at eight heights in and above the snowpack
at ~hourly intervals. In this paper, carbon dioxide data from 2007 were used for evaluation of this technique. Ancillary data
recorded inlcuded snow physical properties, i.e., temperature, pressure, and density. Various vertical concentration gradients
were determined from the multiple height measurements, which allowed calculation of vertical gas fluxes through the snowpack
using Fick’s 1st law of diffusion. Comparison of flux results obtained from different height inlet combinations show that
under most conditions fluxes derived from individual gradient intervals agree with the overall median of all data within a
factor of 1.5. Winds were found to significantly influence gas concentration and gradients in the snowpack. Under the highest
observed wind conditions, concentration gradients and calculated fluxes dropped to as low as 13% of non-wind conditions. Measured
differential pressure amplitude exhibited a linear relationship with wind speed. This suggests that wind speed is a sound
proxy for assessing advection transport in the snow. Neglecting the wind-pumping effect resulted in considerable underestimation
of gas fluxes. An analysis of dependency of fluxes on wind speeds during a 3-week period in mid-winter determined that over
this period actual gas fluxes were most likely 57% higher than fluxes calculated by the diffusion method, which omits the
wind pumping dependency.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
10.
D. R. Bowling W. J. Massman S. M. Schaeffer S. P. Burns R. K. Monson M. W. Williams 《Biogeochemistry》2009,95(1):37-59
Considerable research has recently been devoted to understanding biogeochemical processes under winter snow cover, leading
to enhanced appreciation of the importance of many winter ecological processes. In this study, a comprehensive investigation
of the stable carbon isotope composition (δ13C) of CO2 within a high-elevation subalpine forest snowpack was conducted. Our goals were to study the δ13C of biological soil respiration under snow in winter, and to assess the relative importance of diffusion and advection (ventilation
by wind) for gas transport within snow. In agreement with other studies, we found evidence of an active microbial community
under a roughly 1-m deep snowpack during winter and into spring as it melted. Under-snow CO2 mole fractions were observed up to 3,500 μmol mol−1, and δ13C of CO2 varied from ~−22 to ~−8‰. The δ13C of soil respiration calculated from mixing relationships was −26 to −24‰, and although it varied in time, it was generally
close to that of the bulk organic horizon (−26.0‰). Subnivean CO2 and δ13C were quite dynamic in response to changes in soil temperature, liquid water availability, and wind events. No clear biologically-induced
isotopic changes were observed during periods when microbial activity and root/rhizosphere activity were expected to vary,
although such changes cannot be eliminated. There was clear evidence of isotopic enrichment associated with diffusive transport
as predicted by theory, but simple diffusive enrichment (4.4‰) was not observed. Instead, ventilation of the snowpack by sustained
wind events in the forest canopy led to changes in the diffusively-enriched gas profile. The isotopic influence of diffusion
on gases in the snowpack and litter was greatest at greater depths, due to the decreased relative contribution of advection
at depth. There were highly significant correlations between the apparent isotopic content of respiration from the soil with
wind speed and pressure. In summary, physical factors influencing gas transport substantially modified and potentially obscured
biological factors in their effects on δ13C of CO2 within this subalpine forest snowpack. 相似文献
11.
J. Keelan M. P. Brand T. E. Bates J. M. Land J. B. Clark S. J. R. Heales 《Neurochemical research》1996,21(8):923-927
Nitric oxide (NO) has been implicated in the process of cerebral ischemia/reperfusion injury. We have examined the production
of NO, as reflected by nitrite (NO2
−)+nitrate (NO3
−) accumulation, from synaptosomes isolated from neonatal or adult rat brain and subjected to a period of glucose and oxygen
deprivation. There was a significant increase in the amount of NO2
−+NO3
− production from adult synaptosomes under these conditions, whereas there was no difference compared to control in the production
of NO2
−+NO3
− from the neonatal synaptosomes. The total antioxidant status of the synaptosomes at these different stages of brain development
was found to be the same. These data suggest that the vulnerability of the adult brain to ischemia/reperfusion injury may
be associated with the production of NO from nerve terminals. The ratios of antioxidant capacity to NO production under such
conditions have been shown here to be different between the neonatal and adult nerve terminals. Thus the well documented resistance
of neonatal brain to ischemia/reperfusion injury may involve the neonatal nerve terminal being under less oxidative stress
than the adult. 相似文献
12.
Microbial activity under alpine snowpacks, Niwot Ridge, Colorado 总被引:19,自引:9,他引:10
Experiments were conducted during 1993 at Niwot Ridge in the Colorado Front Range to determine if the insulating effect of winter snow cover allows soil microbial activity to significantly affect nitrogen inputs and outputs in alpine systems. Soil surface temperatures under seasonal snowpacks warmed from –14 °C in January to 0 °C by May 4th. Snowmelt began in mid-May and the sites were snow free by mid June. Heterotrophic microbial activity in snow-covered soils, measured as C02 production, was first identified on March 4, 1993. Net C02 flux increased from 55 mg CO2-C m–2 day–1 in early March to greater than 824 mg CO2-C m-2 day–1 by the middle of May. Carbon dioxide production decreased in late May as soils became saturated during snowmelt. Soil inorganic N concentrations increased before snowmelt, peaking between 101 and 276 mg kg–1 soil in May, and then decreasing as soils became saturated with melt water. Net N mineralization for the period of March 3 to May 4 ranged from 2.23 to 6.63 g N m–2, and were approximately two orders of magnitude greater than snowmelt inputs of 50.4 mg N m–2 for NH4
+ and 97.2 mg N m–2 for NO3
–. Both NO3
– and NH4
+ concentrations remained at or below detection limits in surface water during snowmelt, indicating the only export of inorganic N from the system was through gaseous losses. Nitrous oxide production under snow was first observed in early April. Production increased as soils warned, peaking at 75 g N2O-N m–2 day–1 in soils saturated with melt water one week before the sites were snow free. These data suggest that microbial activity in snow-covered soils may play a key role in alpine N cycling before plants become active. 相似文献
13.
Sheila F. Christopher Hideaki Shibata Megumi Ozawa Yasunori Nakagawa Myron J. Mitchell 《Biogeochemistry》2008,88(1):15-30
Climate change models predict that the snowpacks of temperate forests will develop later and be shallower resulting in a higher
propensity for soil freezing. In the northern most island of Japan, Hokkaido, snowpack depth decreases from west to east.
This snowpack depth gradient provided a unique opportunity to test the effects of variable snowpack and soil freezing on N
biogeochemistry. The Shibecha Northern Catchment in Shibecha Experimental Forest, eastern Hokkaido had deciduous trees and
a mean annual snowpack of 0.7 m while the M3 catchment in Uryu Experimental Forest, western Hokkaido had mixed deciduous and
coniferous tree species and a mean annual snowpack of 2.0 m. We conducted a field study (October 2004–April 2005) to determine
if differences in Shibecha and Uryu soil extractable N, N mineralization, and nitrification were controlled by the variability
in soil freezing during winter or tree species composition that affected the quality of the forest floor. The mixed deciduous
and coniferous trees forming the Uryu forest floor had a higher C:N ratio (25.0 vs. 22.4 at Shibecha), higher lignin:N ratio
(15 vs. 8.8), and higher lignin concentrations (0.28 vs. 0.18 g lignin g−1). These differences in forest floor quality contributed to higher net N mineralization and nitrification in Shibecha compared
to Uryu. In Shibecha, soil remained frozen for the entire study. For Uryu, except for an early period with cold temperatures
and no snow, the soil generally remained unfrozen. As a result of the early winter cold period and soil freezing, extractable
soil NH4+ did not change but NO3− increased. Reciprocal 0–5 cm mineral soil transplants made between Shibecha and Uryu and incubated during winter at 0, 5,
and 30 cm suggested that soil freezing resulted in greater net N mineralization yet lower nitrification regardless of the
soil origin. The effect of soil freezing should be considered when evaluating differences in N dynamics between temperate
ecosystems having a propensity for soil freezing. 相似文献
14.
R. Thomas James Wayne S. Gardner Mark J. McCarthy Stephen A. Carini 《Hydrobiologia》2011,669(1):199-212
Total nitrogen (TN) in Lake Okeechobee, a large, shallow, turbid lake in south Florida, has averaged between 90 and 150 μM
on an annual basis since 1983. No TN trends are evident, despite major storm events, droughts, and nutrient management changes
in the watershed. To understand the relative stability of TN, this study evaluates nitrogen (N) dynamics at three temporal/spatial
levels: (1) annual whole lake N budgets, (2) monthly in-lake water quality measurements in offshore and nearshore areas, and
(3) isotope addition experiments lasting 3 days and using 15N-ammonium (15NH4
+) and 15N-nitrate (15NO3
−) at two offshore locations. Budgets indicate that the lake is a net sink for N. TN concentrations were less variable than
net N loads, suggesting that in-lake processes moderate these net loads. Monthly NO3
− concentrations were higher in the offshore area and higher in winter for both offshore and nearshore areas. Negative relationships
between the percentage of samples classified as algal blooms (defined as chlorophyll a > 40 μg l−1) and inorganic N concentrations suggest N-limitation. Continuous-flow experiments over intact sediment cores measured net
fluxes (μmol N m−2 h−1) between 0 and 25 released from sediments for NH4
+, 0–60 removed by sediments for NO3
−, and 63–68 transformed by denitrification. Uptake rates in the water column (μmol N m−2 h−1) determined by isotope dilution experiments and normalized for water depth were 1,090–1,970 for NH4
+ and 59–119 for NO3
−. These fluxes are similar to previously reported results. Our work suggests that external N inputs are balanced in Lake Okeechobee
by denitrification. 相似文献
15.
Henglong Xu Yong Jiang Khaled A. S. Al-Rasheid Weibo Song Alan Warren 《Hydrobiologia》2011,665(1):67-78
Taxonomic distinctness of ciliated protozoan communities at genus-level resolution was studied over a 12-month period (June
2007–May 2008) in Jiaozhou Bay, northern China. Samples were collected biweekly from three different depths at each of five
sites. A range of physico-chemical parameters were also measured in order to determine water quality. Multivariate and univariate
analyses showed that (1) spatial patterns of ciliated protozoan communities were significantly different among the five sampling
sites (P < 0.05); (2) there were no significant differences among the three depths at each site (P > 0.05); (3) the taxonomic patterns of ciliate communities at genus-level resolution were significantly correlated with the
spatial variation of environmental variables, in particular nitrate nitrogen (NO3-N), sum of NO3-N and nitrite nitrogen (NO
n
-N), and soluble reactive phosphate (SRP); (4) the Margalef’s index did not show a significant correlation with chemical parameters
although it was higher for the less eutrophic than the more eutrophic sites (P > 0.05); (5) the average taxonomic distinctness (Δ+) and variation in taxonomic distinctness (Λ+) of the ciliate communities at genus-level resolution were significantly negatively correlated with the combination of NO
n
-N and SRP; (6) the paired taxonomic biodiversity indices (Δ+ and Λ+) showed a clear decreasing trend of departure from the expected taxonomic breadth in response to water quality. These results
suggest that spatial patterns and taxonomic distinctness (especially the paired Δ+ and Λ+) of ciliated protozoan communities at genus-level resolution can be used as potential indicators for assessing marine water
quality while minimizing costs in terms of the time and resources needed for sample analysis. 相似文献
16.
White on green: under-snow microbial processes and trace gas fluxes through snow,Niwot Ridge,Colorado Front Range 总被引:1,自引:1,他引:0
The importance of snow and related cryospheric processes as an ecological factor has been recognized since at least the beginning
of the twentieth century. Even today, however, many observations remain anecdotal. The research to date on cold-lands ecosystems
results in scientists being unable to evaluate to what extent changes in the cryosphere will be characterized by abrupt changes
in local and global biogeochemical cycles, and how these changes in seasonality may affect the rates and timing of key ecological
processes. Studies of gas exchanges through snow have revealed that snow plays an important role in modulating wintertime
soil biogeochemical processes, and that these can be the driving processes for gas exchange at the snow surface. Previous
research has primarily focused on carbon dioxide, and resulted from episodic experiments at a number of snow-covered sites.
Here we report new insights from several field sites on Niwot Ridge in the Colorado Rocky Mountains, including a dedicated
snow gas flux research facility established at the 3340 m Soddie site. A novel in situ experimental system was developed at
this site to continuously sample trace gases from above and within the snowpack for the duration of seasonal snow cover. The
suite of chemical species investigated includes carbon dioxide, nitrous oxide, nitrogen oxides, ozone, and volatile inorganic
and organic gases. Wintertime measurements have been supplemented by soil chamber experiments and eddy covariance measurements
to allow assessment of the contribution of wintertime fluxes to annual biogeochemical budgets. This research has resulted
in a plethora of new insight into the physics of gas transport through the snowpack, and the magnitude and the chemical and
biogeochemical processes that control fluxes at the soil-snowpack and the snow-atmosphere interface. This article provides
an overview of the history and evolution of this research, and highlights the findings from the ten articles that constitute
this special issue. 相似文献
17.
Michael A. Nicodemus K. Francis Salifu Douglass F. Jacobs 《Trees - Structure and Function》2008,22(5):685-695
Nitrogen (N) limits plant productivity and its uptake and assimilation may be regulated by N source, N availability, and nitrate
reductase activity (NRA). Knowledge of how these factors interact to affect N uptake and assimilation processes in woody angiosperms
is limited. We fertilized 1-year-old, half-sib black walnut (Juglans nigra L.) seedlings with ammonium (NH4
+) [as (NH4)2SO4], nitrate (NO3
−) (as NaNO3), or a mixed N source (NH4NO3) at 0, 800, or 1,600 mg N plant−1 season−1. Two months following final fertilization, growth, in vivo NRA, plant N status, and xylem exudate N composition were assessed.
Specific leaf NRA was higher in NO3
−-fed and NH4NO3-fed plants compared to observed responses in NH4
+-fed seedlings. Regardless of N source, N addition increased the proportion of amino acids (AA) in xylem exudate, inferring
greater NRA in roots, which suggests higher energy cost to plants. Root total NRA was 37% higher in NO3
−-fed than in NH4
+-fed plants. Exogenous NO3
− was assimilated in roots or stored, so no difference was observed in NO3
− levels transported in xylem. Black walnut seedling growth and physiology were generally favored by the mixed N source over
NO3
− or NH4
+ alone, suggesting NH4NO3 is required to maximize productivity in black walnut. Our findings indicate that black walnut seedling responses to N source
and level contrast markedly with results noted for woody gymnosperms or herbaceous angiosperms. 相似文献
18.
The effects of nitric oxide (NO) on caulogenesis, shoot organogenesis and rhizogenesis from hypocotyl explants of Linum usitatissimum were investigated. Exogenously supplied NO donors, 5 μM sodium nitroprusside (SNP), 2 μM S-nitroso-N-acetylpenicillamine (SNAP) and 2 μM 3-morpholinosydnonimine (SIN-1), significantly promoted shoot differentiation from the
hypocotyl explants of L. usitatissimum excised from its in vitro raised seedlings. Potassium ferrocyanide, a structural analogue of SNP, lacking NO group, did not
promote shoot organogenesis. Likewise, products of NO,
\textNO2 - {\text{NO}}_{2}^{ - } and
\textNO3 - {\text{NO}}_{3}^{ - } supplied as 5 μM NaNO2 and 5 μM NaNO3 did not enhance shoot differentiation. Another source of NO, a mixture of sodium nitrite (SN) provided along with ascorbic
acid (AsA), also caused significant promotion in the average number of shoots per responding explant. SNP also augmented the
rhizogenic response of the microshoots in terms of percentage of responding explants, number of roots per responding explant
and average root length. The NO scavengers, 2-(4-carboxy-phenyl)-4, 4, 5, 5-tetramethylimideazoline-1-oxyl-3-oxide (cPTIO)
or methylene blue (MB), provided along with SNP, SNAP, SIN-1 or SN + AsA, at concentrations equimolar to the optimum concentration
of the donors, reversed the promotory influence, thereby, confirming the role of NO in promotion of in vitro morphogenesis.
However, NO scavengers individually did not affect the observed morphogenic processes. Morphological and histological studies
of hypocotyl segments cultured on BM or BM + SNP for 4, 8 and 12 days demonstrated that SNP enhanced shoot differentiation
by inducing a higher number of shoot primordia, each of which develops into a single shoot. 相似文献
19.
Poornananda Madhava Naik Shirugumbi Hanamanthagouda Manohar Hosakatte Niranjana Murthy 《Acta Physiologiae Plantarum》2011,33(4):1553-1557
The present work deals with optimization of adventitious shoot culture of Bacopa monnieri for the production of biomass and bacoside A and has investigated the effects of macro elements (NH4NO3, KNO3, CaCl2, MgSO4 and KH2PO4) and nitrogen source [NH4
+/NO3
−] of Murashige and Skoog (Physiol Plant 15:473–497, 1962) medium (MS) on accumulation of biomass and bacoside A content. Optimum number of adventitious shoots (99.33 shoots explant−1), fresh weight (1.841 g) and dry weight (0.150 g) were obtained in the medium with 2.0× strength of NH4NO3. The highest production of bacoside A content was also recorded in the medium of 2.0× NH4NO3, which produced 17.935 mg g−1 DW. The number of adventitious shoot biomass and bacoside A content were optimum when the NO3
− concentration was higher than that of NH4
+. Maximum number of shoots (70.00 shoots explant−1), biomass (fresh weight 1.137 g and dry weight 0.080 g) and also bacoside A content (27.106 mg g−1 DW) were obtained at NH4
+/NO3
− ratio of 14.38/37.60 mM. Overall, MS medium supplemented with 2.0× NH4NO3 is recommended for most efficient bacoside A production. 相似文献
20.
D.W. Johnson R.B. Susfalk R.A. Dahlgren T.G. Caldwell W.W. Miller 《Biogeochemistry》2001,55(3):219-246
We tested five hypotheses regarding the potential effects of precipitation change on spatial and temporal patterns of water flux, ion flux, and ion concentration in a semiarid, snowmelt-dominated forest in Little Valley, Nevada. Variations in data collected from 1995 to 1999 were used to examine the potential effects of snowpack amount and duration on ion concentrations and fluxes. Soil solution NO3
–, NH4
+, and ortho-phosphate concentrations and fluxes were uniformly low, and the variations in concentration bore no relationship to snowmelt water flux inputs of these ions. Weathering and cation exchange largely controlled the concentrations and fluxes of base cations from soils in these systems; however, soil solution base cation concentrations were affected by cation concentrations during snowmelt episodes. Soil solution Cl– and SO4
2– concentrations closely followed the patterns in snowmelt water, suggesting minimal buffering of either ion by soils. In contrast to other studies, the highest concentration and the majority of ion flux from the snowpack in Little Valley occurred in the later phases of snowmelt. Possible reasons for this include sublimation of the snowpack and dry deposition of organic matter during the later stages of snowmelt. Our comparison of interannual and spatial patterns revealed that variation in ion concentration rather than water flux is the most important driver of variation in ion flux. Thus, it is not safe to assume that changes in total precipitation amount will cause concomitant changes in ion inputs to this system. 相似文献