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1.
Soil-mixing effects on inorganic nitrogen production
and consumption in forest and shrubland soils 总被引:1,自引:0,他引:1
Soils that are physically disturbed are often reported to show net nitrification and NO3− loss. To investigate the response of soil N cycling rates to soil mixing, we assayed gross rates of mineralization, nitrification, NH4+ consumption, and NO3− consumption in a suite of soils from eleven woody plant communities in Oregon, New Mexico, and Utah. Results suggest that the common response of net NO3− flux from disturbed soils is not a straightforward response of increased gross nitrification, but instead may be due to the balance of several factors. While mineralization and NH4+ assimilation were higher in mixed than intact cores, NO3− consumption declined. Mean net nitrification was 0.12 mg N kg−1 d−1 in disturbed cores, which was significantly higher than in intact cores (−0.19 mg N kg−1 d−1). However, higher net nitrification rates in disturbed soils were due to the suppression of NO3− consumption, rather than an increase in nitrification. Our results suggest that at least in the short term, disturbance may significantly increase NO3− flux at the ecosystem level, and that N cycling rates measured in core studies employing mixed soils may not be representative of rates in undisturbed soils. 相似文献
2.
Nitrification and nitrogen mineralization in a lowland rainforest succession in Costa Rica,Central America 总被引:9,自引:0,他引:9
G. Philip Robertson 《Oecologia》1984,61(1):99-104
Summary Nitrogen availability is a critical component of productivity in successional lowland rainforests, and nitrogen losses from a given system may largely depend on rates of nitrification in soils of the system. Two hypotheses were tested in a study of a 6-point secondary rainforest sere in the coastal lowlands of Costa Rica: that nitrification and N mineralization change in a directed fashion in lowland rainforest successions, and that nitrification is regulated by ammonium availability at all points along the sere. Nitrate and mineral N production were measured in short-term laboratory incubations of soils from different stages of secondary succession corresponding to 0, 3, 8, 16, 31 and 60 + years following disturbance. Results indicate that nitrification increases through the first 4 successional stages and then declines somewhat before leveling off. In soil from all sites, most of the N mineralized was nitrified, and added NH4Cl strikingly stimulated net nitrate production. Added NaH2PO4, CaCO3, and CaSO4 did not stimulate net nitrate production or did not result in a greater proportion of nitrate than in controls. These results suggest that nitrification and N mineralization may tend to increase through secondary rainforest succession and that ammonium availability along the sere regulates rates of nitrification. 相似文献
3.
Spatial variability of soil total nitrogen (N), available N (KCl extractable NH4+ and NO3−), and spatial patterns of N mineralization and nitrification at a stand scale were characterized with geostatistical and
univariate analysis. Two extensive soil spatial samplings were conducted in an evergreen broadleaf forest in Sichuan province,
southwestern China in June and August 2000. In a study area of 90 × 105 m2, three soil samples were collected from each 5 × 5 m2 plot (n = 378) in June and August, and were analyzed for total N and available N contents. Net N mineralization and nitrification
were measured by in situ core incubation and the rates were estimated based on the difference of NH4+ and NO3− contents between the two sampling dates. Total N, NH4+, and NO3− were all spatially structured with different semivariogram ranges (from high to low: NH4+, NO3−, and total N). The semivariograms of mineralization and nitrification were not as spatially structured as available N. NH4+ was the dominant soil inorganic N form in the system. Both NH4+ and NO3− affected spatial patterns of soil available N, but their relative importance switched in August, probably due to high nitrification
as indicated by greatly increased soil NO3− content. High spatial auto-correlations (>0.7) were found between available N and NH4+, available N and NO3− on both sampling dates, as well as total N measurements between both sampling dates. Although significant, the spatial auto-correlation
between NH4+ and NO3− were generally low. Topography had significant but low correlations with mineralization (r = −0.16) and nitrification (r = −0.14), while soil moisture did not. The large nugget values of the calculated semivariograms and high-semivariance values,
particularly for mineralization and nitrification, indicate that some fine scale (<5 m) variability may lie below the threshold
for detection in this study. 相似文献
4.
The short-term effect of a single fire, and the long-term effect of recent fire history and successional stage on total and mineral N concentration, net nitrogen mineralization, and nitrification were evaluated in soils from a steep semi-arid shrubland chronosequence in southeast Spain. A single fire significantly increased soil mineral N availability and net nitrification. Increasing fire frequency in the last few decades was. associated with a sharp decrease in surface soil organic matter and total N concentrations and pools, and with changes in the long-term N dynamic patterns. The surface-soil extractable NH4
+:NO3
– ratio increased throughout the chronosequence. All net mineralized N in laboratory incubations from all sites was converted to nitrate, suggesting that allelochemic inhibition of net nitrification is probably not important in this system. Net nitrification in samples during incubation increased through the sere. The maximum rate of net nitrification (kmax) increased through the first three stages of the sere. A linear relationship was found between total soil N and N mineralization, and both kmax and net nitrification for the first three stages of the sere, suggesting that total N and ammonification are likely to be the control mechanisms of nitrification within the sere. The oldest site exhibited the lowest specific kmax and the highest, potential soil respiration rate suggesting that a lower N quality and increasing competition for ammonium might also limit nitrification at least in the long-unburned garrigue site. 相似文献
5.
Robert G. Björk Leif Klemedtsson Ulf Molau Jan Harndorf Anja Ödman Reiner Giesler 《Plant and Soil》2007,294(1-2):247-261
The spatial distribution of organic soil nitrogen (N) in alpine tundra was studied along a natural environmental gradient,
covering five plant communities, at the Latnjajaure Field Station, northern Swedish Lapland. The five communities (mesic meadow,
meadow snowbed, dry heath, mesic heath, and heath snowbed) are the dominant types in this region and are differentiated by
soil pH. Net N mineralization, net ammonification, and net nitrification were measured using 40-day laboratory incubations
based on extractable NH4+ and NO3−. Nitrification enzyme activity (NEA), denitrification enzyme activity (DEA), amino acid concentrations, and microbial respiration
were measured for soils from each plant community. The results show that net N mineralization rates were more than three times
higher in the meadow ecosystems (mesic meadow 0.7 μg N g−1 OM day−1 and meadow snowbed 0.6 μg N g−1 OM day−1) than the heath ecosystems (dry heath 0.2 μg N g−1 OM day−1, mesic heath 0.1 μg N g−1 OM day−1 and heath snowbed 0.2 μg N g−1 OM day−1). The net N mineralization rates were negatively correlated to organic soil C/N ratio (r = −0.652, P < 0.001) and positively correlated to soil pH (r = 0.701, P < 0.001). Net nitrification, inorganic N concentrations, and NEA rates also differed between plant communities; the values
for the mesic meadow were at least four times higher than the other plant communities, and the snowbeds formed an intermediate
group. Moreover, the results show a different pattern of distribution for individual amino acids across the plant communities,
with snowbeds tending to have the highest amino acid N concentrations. The differences between plant communities along this
natural gradient also illustrate variations between the dominant mycorrhizal associations in facilitating N capture by the
characteristic functional groups of plants.
Responsible Editor: Bernard Nicolardot 相似文献
6.
Summary The sensitivity of the mineralization of nitrogen by a range of soils contaminated with heavy metals (up to 340 μg Cd g−1, 7500 μg Pb g−1 and 34000 μg Zn g−1) to the addition of heavy metals in solution were studied using pot incubations (ammonification) and a soil perfusion technique
(nitrification). The ammonification of peptone showed little correlation between treatments with Cd, Zn (1000 and 5000 μg
g−1) and Pb (10000 and 20000 μg g−1) and origin of the soil. Nitrification was considerably more sensitive to heavy metals than ammonification. All the soils
had active, often large, populations of ammonifying and nitrifying organisms which showed substantial similarities between
the soils. The rate of nitrifying activity (NO3−N production) was logrithmic in most cases. The presence of tolerant populations of nitrifying organisms in the contaminated
soils was demonstrated. Tolerance was also eventually acquired after a longer lag phase, by the non-contaminated soil populations
although the rate of activity was often reduced. Metals added in solution were adsorbed by the soil within 4 hours. Differences
in toxicity between metal salts (chlorides, sulphates and acetate) were attributed to the amount left in solution. However,
in many instances, acetate was found to stimulate all the stages in the mineralisation of nitrogen. 相似文献
7.
Soil nitrogen cycling and nitrous oxide flux in a Rocky Mountain Douglas-fir forest: effects of fertilization,irrigation and carbon addition 总被引:6,自引:4,他引:2
Pamela A. Matson Stith Thoma Gower Carol Volkmann Christine Billow Charles C. Grier 《Biogeochemistry》1992,18(2):101-117
Nitrous oxide fluxes and soil nitrogen transformations were measured in experimentally-treated high elevation Douglas-fir
forests in northwestern New Mexico, USA. On an annual basis, forests that were fertilized with 200 kg N/ha emitted an average
of 0.66 kg/ha of N2O-N, with highest fluxes occurring in July and August when soils were both warm and wet. Control, irrigated, and woodchip
treated plots were not different from each other, and annual average fluxes ranged from 0.03 to 0.23 kg/ha. Annual net nitrogen
mineralization and nitrate production were estimated in soil and forest floor usingin situ incubations; fertilized soil mineralized 277 kg ha−1 y−1 in contrast to 18 kg ha−1 y−1 in control plots. Relative recovery of15NH4-N applied to soil in laboratory incubations was principally in the form of NO3-N in the fertilized soils, while recovery was mostly in microbial biomass-N in the other treatments. Fertilization apparently
added nitrogen that exceeded the heterotrophic microbial demand, resulting in higher rates of nitrate production and higher
nitrous oxide fluxes. Despite the elevated nitrous oxide emission resulting from fertilization, we estimate that global inputs
of nitrogen into forests are not currently contributing significantly to the increasing concentrations of nitrous oxide in
the atmosphere. 相似文献
8.
Low Nitrification Rates in Acid Scots Pine Forest Soils Are Due to pH-Related Factors 总被引:1,自引:0,他引:1
In a previous study, ammonia-oxidizing bacteria (AOB)-like sequences were detected in the fragmentation layer of acid Scots
pine (Pinus sylvestris L.) forest soils (pH 2.9–3.4) with high nitrification rates (>11.0 μg g−1 dry soil week−1), but were not detected in soils with low nitrification rates (<0.5 μg g−1 dry soil week−1). In the present study, we investigated whether this low nitrification rate has a biotic cause (complete absence of AOB)
or an abiotic cause (unfavorable environmental conditions). Therefore, two soils strongly differing in net nitrification were
compared: one soil with a low nitrification rate (location Schoorl) and another soil with a high nitrification rate (location
Wekerom) were subjected to liming and/or ammonium amendment treatments. Nitrification was assessed by analysis of dynamics
in NH4
+-N and NO3
−-N concentrations, whereas the presence and composition of AOB communities were assessed by polymerase chain reaction–denaturing
gradient gel electrophoresis and sequencing of the ammonia monooxygenase (amoA) gene. Liming, rather than ammonium amendment, stimulated the growth of AOB and their nitrifying activity in Schoorl soil.
The retrieved amoA sequences from limed (without and with N amendment) Schoorl and Wekerom soils exclusively belong to Nitrosospira cluster 2. Our study suggests that low nitrification rates in acidic Scots pine forest soils are due to pH-related factors.
Nitrosospira cluster 2 detected in these soils is presumably a urease-positive cluster type of AOB. 相似文献
9.
Jirko Holst Chunyan Liu Nicolas Brüggemann Klaus Butterbach-Bahl Xunhua Zheng Yuesi Wang Shenghui Han Zhisheng Yao Jin Yue Xingguo Han 《Ecosystems》2007,10(4):623-634
Gross rates of N mineralization and nitrification, and soil–atmosphere fluxes of N2O, NO and NO2 were measured at differently grazed and ungrazed steppe grassland sites in the Xilin river catchment, Inner Mongolia, P. R.
China, during the 2004 and 2005 growing season. The experimental sites were a plot ungrazed since 1979 (UG79), a plot ungrazed
since 1999 (UG99), a plot moderately grazed in winter (WG), and an overgrazed plot (OG), all in close vicinity to each other.
Gross rates of N mineralization and nitrification determined at in situ soil moisture and soil temperature conditions were
in a range of 0.5–4.1 mg N kg−1 soil dry weight day−1. In 2005, gross N turnover rates were significantly higher at the UG79 plot than at the UG99 plot, which in turn had significantly
higher gross N turnover rates than the WG and OG plots. The WG and the OG plot were not significantly different in gross ammonification
and in gross nitrification rates. Site differences in SOC content, bulk density and texture could explain only less than 15%
of the observed site differences in gross N turnover rates. N2O and NO
x
flux rates were very low during both growing seasons. No significant differences in N trace gas fluxes were found between
plots. Mean values of N2O fluxes varied between 0.39 and 1.60 μg N2O-N m−2 h−1, equivalent to 0.03–0.14 kg N2O-N ha−1 y−1, and were considerably lower than previously reported for the same region. NO
x
flux rates ranged between 0.16 and 0.48 μg NO
x
-N m−2 h−1, equivalent to 0.01–0.04 kg NO
x
-N ha−1 y−1, respectively. N2O fluxes were significantly correlated with soil temperature and soil moisture. The correlations, however, explained only
less than 20% of the flux variance. 相似文献
10.
Donald R. Zak William E. Holmes Matthew J. Tomlinson Kurt S. Pregitzer Andrew J. Burton 《Ecosystems》2006,9(2):242-253
Sugar maple (Acer saccharum Marsh.)-dominated northern hardwood forests in the upper Lakes States region appear to be particularly sensitive to chronic
atmospheric NO3− deposition. Experimental NO3− deposition (3 g NO3− N m−2 y−1) has significantly reduced soil respiration and increased the export of DOC/DON and NO3− across the region. Here, we evaluate the possibility that diminished microbial activity in mineral soil was responsible for
these ecosystem-level responses to NO3− deposition. To test this alternative, we measured microbial biomass, respiration, and N transformations in the mineral soil
of four northern hardwood stands that have received 9 years of experimental NO3− deposition. Microbial biomass, microbial respiration, and daily rates of gross and net N transformations were not changed
by NO3− deposition. We also observed no effect of NO3− deposition on annual rates of net N mineralization. However, NO3− deposition significantly increased (27%) annual net nitrification, a response that resulted from rapid microbial NO3− assimilation, the subsequent turnover of NH4+, and increased substrate availability for this process. Nonetheless, greater rates of net nitrification were insufficient
to produce the 10-fold observed increase in NO3− export, suggesting that much of the exported NO3− resulted directly from the NO3− deposition treatment. Results suggest that declines in soil respiration and increases in DOC/DON export cannot be attributed
to NO3−-induced physiological changes in mineral soil microbial activity. Given the lack of response we have observed in mineral
soil, our results point to the potential importance of microbial communities in forest floor, including both saprotrophs and
mycorrhizae, in mediating ecosystem-level responses to chronic NO3− deposition in Lake States northern hardwood forests. 相似文献
11.
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
12.
We assessed the potential impact of global warming resulting from a doubling of preindustrial atmospheric CO2 on soil net N transformations by transferring intact soil cores (0–15 cm) from a high-elevation old-growth forest to a forest about 800 m lower in elevation in the central Oregon Cascade Mountains, USA. The lower elevation site had mean annual air and soil (10-cm mineral soil depth) temperatures about 2.4 and 3.9 °C higher than the high-elevation site, respectively. Annual rates of soil net N mineralization and nitrification more than doubled in soil transferred to the low-elevation site (17.2–36.0 kg N ha–1 and 5.0–10.7 kg NO3––N ha–1, respectively). Leaching of inorganic N from the surface soil (in the absence of plant uptake) also increased. The reciprocal treatment (transferring soil cores from the low- to the high-elevation site) resulted in decreases of about 70, 80, and 65% in annual rates of net N mineralization, nitrification, and inorganic N leaching, respectively. Laboratory incubations of soils under conditions of similar temperature and soil water potential suggest that the quality of soil organic matter is higher at the high-elevation site. Similar in situ rates of soil net N transformations between the two sites occurred because the lower temperature counteracts the effects of greater substrate quantity and quality at the high elevation site. Our results support the hypothesis that high-elevation, old-growth forest soils in the central Cascades have higher C and N storage than their low-elevation analogues primarily because low temperatures limit net C and N mineralization rates at higher elevations. 相似文献
13.
Seasonal patterns of ammonium and nitrate uptake in nine temperate forest ecosystems 总被引:11,自引:2,他引:9
Summary Seasonal patterns of net N mineralization and nitrification in the 0–10 cm mineral soil of 9 temperate forest sites were analyzed using approximately monthlyin situ soil incubations. Measured nitrification rates in incubated soils were found to be good estimates of nitrification in surrounding forest soils. Monthly net N mineralization rates and pools of ammonium-N in soil fluctuated during the growing season at all sites. Nitrate-N pools in soil were generally smaller than ammonium-N pools and monthly nitrification rates were less variable than net N mineralization rates. Nitrate supplied most of the N taken up annually by vegetation at 8 of the 9 sites. Furthermore, despite the large fluctuations in ammonium-N pools and monthly net N mineralization, nitrate was taken up at relatively uniform rates during the growing season at most sites. 相似文献
14.
Net nitrogen mineralization and net nitrification along a tropical forest-to-pasture chronosequence 总被引:8,自引:0,他引:8
Soil inorganic nitrogen pools, net mineralization and net nitrification rates were compared during the dry season along a chronosequence of upland (terra firme) forest, 3-, 9- and 20-year-old pastures in the western Brazilian Amazon Basin state of Rondônia to investigate the influence of forest conversion to pasture on soil nitrogen cycles. Surface soil (0 to 10 cm) from forest had larger extractable inorganic nitrogen pools than pasture soils. In the forest, NO
3
–
pools equaled or exceeded NH
4
+
pools, while pasture inorganic N pools consisted almost exclusively of NH
4
+
. Rates of net N mineralization and net nitrification in seven -day laboratory incubations were higher in the seven - day forest than in the pastures. Net N mineralization rates did not differ significantly among different-aged pastures, but net nitrification rates were significantly lower in the 20-year-old pasture. Higher net N mineralization and net nitrification rates were measured in laboratory and in situ incubations of sieved soil, compared with in situ incubations of intact soil cores. Rates calculated in seven-day incubations were higher than determined by longer incubations. Sieving may increase N mineralization and/or decrease N immobilization compared with intact cores. We concluded that 7-day laboratory incubation of sieved soil was the most useful index for comparing N availability across the chronosequence of forest and pasture sites. High net nitrification rates in forest soils suggest a potential for NO
3
–
losses either through leaching or gaseous emissions. 相似文献
15.
Laboratory incubation and field experiments were conducted to evaluate thiourea, ATC (4-amino-1, 2, 4 triazole hydrochloride)
and N-Serve 24 E (2-chloro-6-trichloromethyl-pyridine) as inhibitors of nitrification of fertilizer N. In the incubation experiment,
most of the added aqueous NH3 or urea was nitrified at 14 days on both soils, but addition of the inhibitors to fertilizer N decreased the conversion of
NH4−N to NO3−N markedly. There was less nitrification for ATC and thiourea but not for N-Serve 24 E when the fertilizers and the inhibitors
were placed at a point as opposed to when mixed into soil. After 28 days, ATC and N-Serve 24 E were more effective in inhibiting
nitrification than thiourea. ATC and N-Serve 24 E also inhibited release of mineral N (NH4−N+NO3−N) from native soil N. In the uncropped field experiment, which received N fertilizers in the fall, nitrification of fall-applied
N placed in the 15-cm bands was almost complete by early May in the Malmo soil, but not in the Breton soil. When ATC or thiourea
had been applied with urea, nitrification of fall-applied N was depressed by May and the recovery of applied N as NH4−N was greater with increasing band spacing to 60 cm or placing N fertilizer in nests (a method of application where urea
prills were placed at a point in the soil in the center of 60×60 cm area). In late June, the percentage recovery of fall-applied
N in soil as NH4−N or mineral N increased with wide band spacing, or nest placement, or by adding ATC to fertilizer N on both soils. These
results indicate that placing ammonium-based N fertilizers in widely-spaced bands or in nests with low rates of inhibitors
slows nitrification enough to prevent much of the losses from fall-applied N.
Scientific Paper No. 552, Lacombe Research Station, Research Branch, Agric, Can. 相似文献
16.
Microclimatic controls of nitrogen mineralization and nitrification in shortgrass steppe soils 总被引:6,自引:0,他引:6
Summary The depth distributions of rates of net nitrogen mineralization and nitrification were measured in a series of field and laboratory
incubations. Field studies suggested that the highest rates of mineralization and nitrification occurred in the surface 2.5
cm such that forty to sixty percent of the N mineralization in 20-cm soil column occurred in the surface 2.5cm. Some upward
nitrate movement occurred but laboratory studies suggested that surface rates were not an artifact of nitrate mobility alone.
Microclimatic data indicate that either dew or upward movement and condensation of soil water vapor may drive biological activity
at the soil surface. High rates of N mineralization even in dry horizons were sustained as long as water was stored within
the 0-to 20-cm depth. High rates of nitrification were found in all incubations, and field measurements showed NO
3
−
to be the predominant form of inorganic N, despite previous characterization of the shortgrass steppe as an NH
4
+
-dominated system. 相似文献
17.
Dissolved organic carbon affects soil microbial activity and nitrogen dynamics in a Mexican tropical deciduous forest 总被引:1,自引:0,他引:1
Seasonal variation of dissolved organic C (DOC) and its effects on microbial activity and N dynamics were studied during two
consecutive years in soils with different organic C concentrations (hilltop and hillslope) in a tropical deciduous forest
of Mexico. We found that DOC concentrations were higher at the hilltop than at the hillslope soils, and in both soils generally
decreased from the dry to the rainy season during the two study years. Microbial biomass and potential C mineralization rates,
as well as dissolved organic N (DON) and NH4+ concentrations and net N immobilization were higher in soils with higher DOC than in soils with lower DOC. In contrast, net
N immobilization and NH4+ concentration were depleted in the soil with lowest DOC, whereas NO3− concentrations and net nitrification increased. Negative correlations between net nitrification and DOC concentration suggested
that NH4+ was transformed to NO3− by nitrifiers when the C availability was depleted. Taken together, our results suggest that available C appears to control
soil microbial activity and N dynamics, and that microbial N immobilization is facilitated by active heterotrophic microorganisms
stimulated by high C availability. Soil autotrophic nitrification is magnified by decreases in C availability for heterotrophic
microbial activity. This study provides an experimental data set that supports the conceptual model to show and highlight
that microbial dynamics and N transformations could be functionally coupled with DOC availability in the tropical deciduous
forest soils.
Responsible Editor: Chris Neill 相似文献
18.
晋西北不同年限小叶锦鸡儿灌丛土壤氮矿化和硝化作用 总被引:1,自引:0,他引:1
利用PVC管顶盖埋管法研究了晋西北黄土高原区小叶锦鸡儿人工灌丛不同定植年限(5,10,20,30,40a)土壤氮矿化与硝化速率的动态和净矿化与硝化总量。结果表明,⑴小叶锦鸡儿灌丛土壤无机氮主要以NO_-~3-N形式存在,不同生长年限相同月份的土壤硝态氮(NO-3-N)含量分别是铵态氮(NH+4-N)含量的1.5—15.4倍;⑵土壤氮素硝化速率和矿化速率随生长年限延长而加快,30年生时达到高峰,数值达40.2,44.1 mg m~(-2)d~(-1)。从季节性变化看,7—8月份是硝化速率和矿化速率快速增长期,30年生小叶锦鸡儿灌丛土壤硝化速率和矿化速率分别达到86.9,93.1 mg m~(-2)d~(-1),显著高于其它生长年限(P0.05);(3)土壤氮素硝化与矿化总量同样随小叶锦鸡儿生长年限延长而增加,30年生时达到最高,与5年生相比,分别增加了3.7和3.1倍。(4)5—10月份小叶锦鸡儿生长期内,各年限土壤全氮量的2.3%被矿化成无机氮,其中87%最终被转化成NO-3-N形式存在于土体中。 相似文献
19.
The exotic annual grass Bromus tectorum has replaced thousands of hectares of native perennial vegetation in semi-arid ecosystems of the western United States. Inorganic N availability and production were compared in soil from monodominant patches of Bromus tectorum, the perennial bunchgrass Elymus elymoides, and the shrub Artemisia tridentata, in Curlew Valley, a salt-desert shrub site in Northern Utah. Bromus-dominated soil had greater %N in the top 10 cm than Artemisia or Elymus-dominated soils. As determined by spring isotope-dilution assays, gross mineralization and nitrification rates were higher in Bromus-dominated than Artemisia-dominated soils, but gross rates of NH4
+ and NO3
– consumption were also higher. Litterbags had greater mass loss and N mineralization when buried in Bromus stands than in Artemisia stands, indicating the soil environment under the annual grass promotes decomposition. As determined by nitrification potential assays, nitrifier populations were higher under Bromus than under Artemisia and Elymus. Soil inorganic N concentrations were similar among vegetation types in the spring, but NO3
– accumulated under Bromus once it had senesced. An in situ net mineralization assay conducted in autumn indicated that germinating Bromus seedlings are a strong sink for soil NO3
–, and that net nitrification is inherently low in soils under Artemisia and Elymus. Results of the study suggest that differences in plant uptake and the soil environment promote greater inorganic N availability under Bromus than under perennial species at the site. 相似文献
20.
Denitrification and N mineralization from hairy vetch (Vicia villosa Roth) and rye (Secale cereale L.) cover crop monocultures and bicultures 总被引:1,自引:1,他引:0
N mineralization, N immobilization and denitrification were determined for vetch, rye and rye-vetch cover crops using large
packed soil cores. Plants were grown to maturity from seed in cores. Cores were periodically leached, allowing for quantification
of NO3
− and NH4
+ production, and denitrification incubations were conducted before and after cover crop kill. Gas permeable tubing was buried
at two depths in cores allowing for quantification of N2O in the soil profile. Cover crops assimilated most soil N prior to kill. After kill, relative rates of N mineralization were
vetch > rye-vetch mixture > fallow > rye. After correcting for N mineralization from fallow cores, net N mineralization was
observed in vetch and rye-vetch cores, while net N immobilization was observed in rye cores. Denitrification incubations were
conducted 5, 15 and 55 days after kill, with adjustment of cores to 75% water filled pore space (WFPS). The highest denitrification
was observed in vetch cores 5 days after kill, when soil NO3
− and respiration rates were high. Substantially lower denitrification was observed on subsequent measurement dates and in
other treatments probably due to either limited NO3
− or organic carbon in the soil. On day 5, 3%, 23%, 31% and 31% of the N2O was recovered in the headspace of fallow, vetch, rye and rye-vetch cores, respectively. The rest was stored in the soil
profile. In a field study using intact soil cores, denitrification rates also peaked 1 week after cover crop kill and decreased
significantly thereafter. Results suggest greater potential N losses from vetch than rye or rye-vetch cover crops due to rapid
N-mineralization in conjunction with denitrification and potential leaching, prior to significant crop N-assimilation.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献