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1.
Components of organic phosphorus in soil extracts that are hydrolysed by phytase and acid phosphatase 总被引:8,自引:0,他引:8
Extracts were prepared from soil using water, 50 mM citric acid (pH ∼2.3) or 0.5 M NaHCO3 (pH 8.5), and were incubated with excess phytase from Aspergillus niger to determine the amounts of labile P. Two A. niger phytase preparations were used: (1) a purified form which exhibited a narrow substrate specificity and high specific activity
against phytate; and (2) a commercial preparation (Sigma) with activity against a broad range of P compounds. A comparatively
large proportion (up to 79%, or 5.7 μg g–1 soil) of the organic P (Po) extracted with citric acid was hydrolysed by the commercial phytase, while between 28% and 40% (up to 3.1 μg g–1 soil) was hydrolysed using purified phytase. By comparison, only small quantities of the Po in water and NaHCO3 soil extracts were enzyme labile. While extractable Po was increased both with increasing concentrations of citric acid (up to 50 mM) and increasing pH (pH 2.3–6.0), enzyme-labile
P increased only with citric acid concentration. The labile component of Po in citric acid extracts from soils with contrasting fertiliser histories indicated that enzyme-labile Po is a relatively large soil P pool and is potentially an important source of P for plants.
Received: 29 October 1999 相似文献
2.
Influence of low-molecular-weight organic acids on the solubilization of phosphates 总被引:18,自引:0,他引:18
Dr N. S. Bolan R. Naidu S. Mahimairaja S. Baskaran 《Biology and Fertility of Soils》1994,18(4):311-319
A range of low-molecular-weight organic acids were identified in rhizosphere soil, leaf litter, and poultry manure compost. Laboratory and greenhouse experiments were carried out to examine the effects of seven low-molecular-weight organic acids on phosphate adsorption by soils, and the solubilization and plant uptake of P from soil pre-incubated with monocalcium phosphate and North Carolina phosphate rock. Acetic, formic, lactic (monocarboxylic), malic, tartaric, oxalic (dicarboxylic), and citric (tricarboxylic) acids were used in the study. The addition of organic acids decreased the adsorption of P by soils in the order tricarboxylic acid>dicarboxylic acid>monocarboxylic acid. The decreases in P adsorption with organic acid addition increased with an increase in the stability constant of the organic acid for Al (logK
Al). Organic acids extracted greater amounts of P from soils meubated with both monocalcium phosphate and phosphate rock than water did. Although more phosphate was extracted by the organic acids from monocalcium phosphate — than from phosphate rock — treated soils in absolute terms, when the results were expressed as a percentage of dissolved phosphate there was little difference between the two fertilizers. The amount of P extracted by the organic acids from both fertilizers increased with an increase in logK
Al values. The addition of oxalic and citric acids increased the dry matter yield of ryegrass and the uptake of P in soils treated with both fertilizers. The agronomic effectiveness of both fertilizers increased in the presence of organic acids and the increase was greater with the phosphate rock than with the monocalcium phosphate. The results indicated that organic acids increase the availability of P in soils mainly through both decreased adsorption of P and increased solubilization of P compounds. 相似文献
3.
Kinetics of soil microbial uptake of free amino acids 总被引:8,自引:0,他引:8
Amino acids and proteins typically form the biggest input of organic-N into most soils and provide a readily available source
of C and N for soil microorganisms. Amino acids can also be taken up directly by plant roots, providing an alternative source
of available soil N. However, the degree to which plants can compete against the soil microbial population for amino acids
in soil solution remains poorly understood. The aim of this study was to measure the rate of microbial uptake of three contrastingly
charged 14C-labelled amino acids (glutamate1–, glycine0, lysine0.9+) over a wide concentration range (0.1–5 mM) and in two contrastingly managed soils varying in their degree of erosion, organic-C
content and microbial biomass. Amino acid uptake was concentration dependent and conformed to a single Michaelis-Menten equation.
The mean maximum amino acid uptake rate (V
max) for the non-eroded (control) soil (high organic-C, high biomass) was 0.13±0.02 mmol kg–1 h–1, while half maximal uptake occurred at a concentration (K
m) of 2.63±0.07 mM. Typically, V
max was fourfold lower and K
m twofold lower in the eroded soil (low available organic-C, low biomass) compared to the non-eroded (control) soil. Amino
acid substrate concentration had little effect on the proportion of amino acid utilized in catabolic versus anabolic metabolism
and was similar for both. While the results obtained here represent the summation of kinetics for a mixed soil population,
they indicate that amino acid uptake is saturated at concentrations within the millimolar range. Because the affinity constants
also were similar to those described for plant roots, we hypothesized that competition for amino acids between plants and
microbes will be strong in soil but highly dependent upon the spatial distribution of roots and microbes in soil.
Received: 2 March 2000 相似文献
4.
有机酸对高岭石, 针铁矿和水铝英石吸附镉的影响 总被引:12,自引:0,他引:12
Effects of organic acids (oxalic, acetic, and citric) on adsorption characteristics of Cadmium (Cd) on soil clay minerals (kaolinite, goethite, and bayerite) were studied under different concentrations and different pH values. Although the types of organic acids and minerals were different, the effects of the organic acids on the adsorption of Cd on the minerals were similar, i.e., the amount of adsorbed Cd with an initial solution pH of 5.0 and initial Cd concentration of 35 mg L^-1 increased with increasing concentration of the organic acid in solution at lower concentrations, and decreased at higher concentrations. The percentage of Cd adsorbed on the minerals in the presence of the organic acids increased considerably with increasing pH of the solution. Meanwhile, different Cd adsorption in the presence of the organic acids, due to different properties on both organic acids and clay minerals, on kaolinite, goethite, or bayerite for different pHs or organic acid concentrations was found. 相似文献
5.
Summary Recent developments in biotechnology industries produce increasing amounts of byproducts with potential uses in agriculture. The present research focused on the nitrification of NH
inf4
sup+
-N in biotechnology byproducts added to soils, and on the effects of 29 naturally occurring organic acids (19 aliphatic and 10 aromatic) on nitrification in soils. A 10-g soil sample was incubated for 10 days at 30°C with 2.0 mg NH
inf4
sup+
-N in a byproduct or with 10 or 50 mol organic acid and 2.0 mg reagent-grade NH
inf4
sup+
-N. In condensed molasses-fermentation solubles, produced during the microbial fermentation of sugar derived from corn (Zea mays L.) and molasses derived from beets (Beta sp.), in the production of lysine as a supplement in animal food, the nitrification of NH
inf4
sup+
-N was similar to that of byproduct or reagent-grade (NH4)2SO4. Nitrite accumulated when either of these materials was added to a calcareous Canisteo soil. The NH
inf4
sup+
-N in slops (produced during microbial fermentation processes occurring in the production of citric acid) was not nitrified in soils. Some organic acids inhibited, whereas others activated, nitrification in soils. Formic, acetic, and fumaric acids enhanced the production of NO
inf2
sup-
-N in a calcareous Canisteo soil, whereas all other aliphatic and aromatic acids studied decreased the accumulation of NO
inf2
sup-
-N. It is concluded that the addition or production of organic acids in soils affects the microbial dynamics, leading to significant changes in rates of nitrification and possibly in other N-transformation processes in soils. 相似文献
6.
Chemical and biological characteristics of alkaline saline soils from the former Lake Texcoco as affected by artificial drainage 总被引:3,自引:0,他引:3
M. L. Luna-Guido R. I. Beltrán-Hernández N.A. Solís-Ceballos N. Hernández-Chávez F. Mercado-García J. A. Catt V. Olalde-Portugal L. Dendooven 《Biology and Fertility of Soils》2000,32(2):102-108
Soils from the former Lake Texcoco are alkaline saline and were artificially drained and irrigated with sewage effluents
since the late 1980s. Undrained soil and soil drained for 1, 5 and 8 years were sampled, characterized and incubated aerobically
for 90 days at 22±1 °C while production of CO2, available P and concentrations of NH4
+, NO2
– and NO3
– were monitored. Artificial drainage decreased pHH2O, water holding capacity, organic C, total N, and Na+, K+, Mg2+, B, Cl– and SO4
2– concentrations, increased inorganic C and Ca2+ concentrations more than 5-fold while total P was not affected. Microbial biomass C decreased with increased length of drainage
but bacteria, actinomycetes, denitrifiers and cellulose-utilizing bacteria tended to show opposite trends. CO2 production was less in soils drained ≥5 years compared to undrained soil but more than in soils drained for 1 year. Emission
of NH3 was negligible and concentrations of NH4
+ remained constant over time in each soil. Nitrification, as witnessed by increases in NO3
– concentrations, occurred in soil drained for 8 years. NO2
– concentrations decreased in soils drained ≤1 year in the first 7 days of the incubation and remained constant thereafter.
It was found that artificial drainage of soils from the former Lake Texcoco profoundly affected soil characteristics. Decreases
in pH and Na+, K+, Cl– and SO4
2– concentrations made conditions more favourable for plant growth, although low concentrations of inorganic N and available
P might be limiting factors.
Received: 1 December 1999 相似文献
7.
The solubility and forms of phosphorus (P) were investigated in manures from chicken and pigs, eight whole soil samples and
clay-, silt-, and sand-size separates from an arable and a grassland soil. Total P (Pt) in liquid pig manure (16.2 g kg–1) and dry chicken manure (26.2 g kg–1) was distributed between residual P (39–41% Pt), H2SO4–P (17–27% Pt), labile resin- and NaHCO3–P (24–39% Pt), and NaOH-P (3–10% Pt). Most soils had larger proportions of NaOH-P and residual P, indicating reactions of manure-derived P compounds with pedogenic
oxides and humic substances. Clay-size separates had the highest P-concentrations in all fractions and were particularly enriched
in exchangeable and labile P forms. Solution 31P-nuclear magnetic resonance (NMR) spectra of 0.5 M NaOH extracts from manures and some soil samples showed greater signal intensities for orthophosphate and monoester P than
0.1 M NaOH extracts. This can be explained by alkaline hydrolysis phosphate diesters at higher NaOH concentrations and/or by preferential
extraction of diesters at lower concentrations. The 31P-NMR spectra showed differences between the two manures and confirmed that increasing proportions of ester-P can be expected
if they are spread to soils. The NaOH extracts of soil samples were characterized by large proportions of orthophosphate-P
(mean 77% of assigned P compounds), which seemed to be slightly enriched in clay fractions whereas the extracts from silt
contained more ester-P. Sequential extractions and 31P-NMR spectroscopy both showed that these excessively manured soils are likely to lose large amounts of P.
Received: 15 July 1996 相似文献
8.
A study was conducted to investigate the effects of cow manure and sewage sludge application on the activity and kinetics
of soil l-glutaminase. Soil samples were collected from a farm experiment in which 0, 25, and 100 Mg ha−1 of either cow manure or sewage sludge had been applied annually for 4 consecutive years to a clay loam soil (Typic Haplargid).
A chemical fertilizer treatment had also been applied. Results indicated that the effects of chemical fertilizer and the solid
waste application on pH in the 18 surface soil (0–15 cm) samples were not significant. The organic C content, however, was
affected significantly by the different treatments, being the greatest in soils treated with 100 Mg ha−1 cow manure, and the least in the control treatment. l-Glutaminase activity was generally greater in solid-waste applied soils and was significantly correlated (r = 0.939, P < 0.001) with organic C content of soils. The values of l-glutaminase maximum velocity (Vmax) ranged from 331 to 1,389 mg NH4
+–N kg−1 2 h−1. Values of the Michaelis constant (K
m) ranged from 35.1 to 71.7 mM. Organic C content of the soils were significantly correlated with V
max (r = 0.919, P < 0.001) and K
m (r = 0.763, P < 0.001) values. These results demonstrate the considerable influence that solid waste application has on this enzymatic
reaction involved in N mineralization in soil. 相似文献
9.
A critical assessment of methods for determining organic phosphorus in savanna soils 总被引:1,自引:0,他引:1
Two newly introduced extraction techniques for determining total organic P (P0) were compared with the standard high-temperature ignition method in selected savanna soils of Nigeria. The two extraction
techniques were: (1) concentrated H2SO4 and dilute base sequential extraction (18 N H2SO4 and 0.5 N NaOH) and (2) basic EDTA method (0.25 M NaOH plus 0.05 M Na2EDTA). The concentrated H2SO4 and dilute base method extracted significantly higher total P0 than the high-temperature ignition method and the basic EDTA extraction. The high-temperature ignition and the basic EDTA
extraction gave similar total P0 values (mean=91 mg kg–1 for ignition and 90 mg kg–1 for basic EDTA). The precision of the methods, determined by coefficients of variation (CV, %) associated with each P0 determination method in the soils, was better for the concentrated H2SO4 and dilute base extraction method (CV=13%) than the ignition method (CV=18%) and the basic EDTA method (CV=15%). The high
C : P0 ratios determined for the high-temperature ignition and basic EDTA extraction indicated that the two methods underestimated
total P0 in the soils. The concentrated H2SO4 and dilute base sequential extraction appears to be suitable for the rapid determination of P0 in savanna soils because the method can be simplified to a single-step analysis.
Received: 14 November 1997 相似文献
10.
We hypothesized that the integration of trees and shrubs in agricultural landscapes can reduce NO3
– leaching and increase utilization of subsoil N. A field survey was conducted on 14 farms on acid soils in the subhumid highlands
of Kenya, where there is little use of fertilizers, to determine the effect of vegetation types (VT) on soil NH4
+ and NO3
– to 4 m depth. The VT included maize (Zea mays) with poor growth and good growth, Markhamia lutea trees scattered in maize, natural weed fallow, banana (Musa spp.), hedgerow, and eucalyptus woodlot. The effect of VT on NH4
+ was small (<1 mg N kg–1). NO3
– within a VT was about constant with depth below 0.25 m, but subsoil NO3
– varied greatly among VT. Mean NO3
–-N concentrations at 0.5–4 m depth were low beneath hedgerow and woodlot (<0.2 mg kg–1), intermediate beneath weed fallow (0.2–0.7 mg kg–1), banana (0.5–1.0 mg kg–1) and markhamia (0.5–1.6 mg kg–1), and high beneath both poor (1.0–2.1 mg kg–1) and good (1.9–3.1 mg kg–1) maize. Subsoil NO3
– (0.5–4 m) was agronomically significant after maize harvest with 37 kg N ha–1 m–1 depth of subsoil beneath good maize and 27 kg N ha–1 m–1 depth beneath poor maize. In contrast, subsoil NO3
– was only 2 kg N ha–1 m–1 depth beneath woodlot and hedgerow. These results demonstrate that the integration of perennial vegetation and the rotation
of annual and perennial crops can tighten N cycling in agricultural landscapes.
Received: 8 July 1999 相似文献
11.
Improving the precision in estimating the nitrogen (N) requirement for citrus trees on sandy soils is important for increasing
N efficiency by the trees and minimizing potential losses of N in commercial citrus production areas. In this study, representative
Florida soils were sampled from major citrus production areas and the electro-ultrafiltration (EUF) technique was used to
measure the concentrations of total EUF-extractable nitrogen (EUF-Nt), ammonium-N (EUF-NH4
+–N) and nitrate-N (EUF-NO3
––N). Available organic N (Norg) was calculated as: EUF-Nt–(NH4
+–N+NO3
––N). The N concentrations in the EUF extraction were greater than those by the KCl or CaCl2 method. The Norg fraction, estimated by the EUF method, varied from 4.4 to 40.8 mg kg–1 soil, equivalent to 10 to 91 kg N ha–1 (for the top 15 cm depth soil) and was positively correlated with the total soil N determined by the Kjeldahl method. The
presence of appreciable amounts of Norg in these soils indicates that these soils contain high proportions of the total soil N in easily mineralizable Norg forms. This study demonstrates that the EUF-extractable organic bound N must be considered in developing N fertilizer recommendations
for citrus.
Received: 13 January 1999 相似文献
12.
Previous studies have shown that carbon (C) mineralization in saline or sodic soils is affected by various factors including
organic C content, salt concentration and water content in saline soils and soil structure in sodic soils, but there is little
information about which soil properties control carbon dioxide (CO2) emission from saline-sodic soils. In this study, eight field-collected saline–sodic soils, varying in electrical conductivity
(ECe, a measure of salinity, ranging from 3 to 262 dS m−1) and sodium adsorption ratio (SARe, a measure of sodicity, ranging from 11 to 62), were left unamended or amended with mature wheat or vetch residues (2% w/w). Carbon dioxide release was measured over 42 days at constant temperature and soil water content. Cumulative respiration
expressed per gram SOC increased in the following order: unamended soil<soil amended with wheat residues (C/N ratio 122)<soil
with vetch residue (C/N ratio 18). Cumulative respiration was significantly (p < 0.05) negatively correlated with ECe but not with SARe. Our results show that the response to ECe and SARe of the microbial community activated by addition of organic C does not differ from that of the less active microbial community
in unamended soils and that salinity is the main influential factor for C mineralization in saline–sodic soils. 相似文献
13.
The simultaneous impact of three successive crops of wheat (Triticum aestivum L.) and of the earthworm (Lumbricus terrestris L.) on the mineralisation of 15N-labelled organic compounds adsorbed to different soil size fractions (sand and organic residues >50 μm; silt 50–2 μm; coarse
clay 2–0.2 μm and fine clay <0.2 μm) was studied under controlled conditions in the greenhouse. Unplanted soils (UPS) were
used as controls. In planted soils without earthworm (PS) total plant biomass decreased with each cropping by up to 50%. However,
in planted soils with earthworms (PES) the total plant biomass loss was only 17%. This pattern was explained by the earthworm
effect. Compared to the unplanted soils, the planted soils had an increased (mean +37%) mineralisation of 15N adsorbed onto fine clays and a partial transfer of 15N to silt and coarse clay. The quantities of 15N mineralised and transferred were higher in the planted soils with earthworms, indicating an amplification of the phenomenon
in the presence of earthworms. The simultaneous effect of the rhizosphere and the drilosphere did not lead to increased mineralisation
of N adsorbed onto coarse clays and silts but instead a greater transfer of N associated with the fine fractions towards the
coarser fractions.
Received: 25 April 2000 相似文献
14.
An open incubation technique was used to measure S mineralization in a range of upland soils of north China. Six mineralization
patterns were examined, and a soil S-exhaustion experiment with ryegrass (Lolium multiflorum L.) was conducted to investigate the availability of various organic S pools to plants. For all of the 12 soils tested, the
release of S as SO4
2– was curvilinear with time, and during a 28-week incubation at 30 °C the amount of S mineralized ranged from 14.0 mg S kg–1 soil to 37.4 mg S kg–1 soil. A first-order model and Gompertz model appeared to best describe S mineralization. Examination of the soils after incubation
revealed the bulk of the mineralized S was mainly derived from the C-bonded S pool, while the majority of mineralized S under
soil S exhaustion by ryegrass was derived from the HI-reducible S pool.
Received: 9 July 1998 相似文献
15.
Soil-released carbon dioxide from microbial biomass carbon in the cultivated soils of karst areas of southwest China 总被引:1,自引:0,他引:1
Soil microbial biomass and the emission of CO2 from the soil surface were measured in yellow soils (Ultisols) of the karst areas of southwest China. The soils are relatively
weathered, leached and impoverished, and have a low input of plant residues. The measurements were made for a 1-year period
and show a reciprocal relationship between microbial biomass and surface CO2 efflux. The highest (42.6±2.8 mg CO2-C m–2 h–1) and lowest (15.6±0.6 mg CO2-C m–2 h–1) CO2 effluxes are found in the summer and winter, respectively. The cumulative CO2 efflux is 0.24 kg CO2-C m–2 year–1. There is also a marked seasonal variation in the amount of soil microbial biomass carbon, but with the highest (644±71 μg
C g–1 soil) and lowest (270±24 μg C g–1 soil) values occurring in the winter and summer, respectively. The cumulative loss of soil microbial biomass carbon in the
top 10 cm of the soil was 608 μg C g–1 year–1 soil over 17 sampling times. The mean residence time of microbial biomass is estimated at 105 days, suggesting that the carbon
in soil microbial biomass may act as a source of the CO2 released from soils.
Received: 13 July 1999 相似文献
16.
The kinetics of nitric oxide consumption in four tropical soils were studied under oxic and anoxic conditions in a flow-through
system in the laboratory. Under anoxic conditions the soils had a very high affinity for NO, resulting in K
M values of 0.02–0.27 ppmv NO (equivalent to 0.04–0.50 nM NO in the aqueous phase). These K
M values were lower than literature values for NO consumption by denitrifying bacteria. Under oxic conditions the kinetics
of NO consumption in the tropical soils were completely different, exhibiting K
M values higher than 1.7 ppmv. These higher K
M values were similar to literature values for NO consumption by aerobic heterotrophic bacteria. Thus, the tropical soils studied
seem to contain two different NO consumption activities which can be distinguished by their kinetics and which predominate
under aerobic and anaerobic conditions, respectively. However, it was not possible to quantify the contribution of each process
to total NO consumption under natural conditions. Under aerobic conditions NO turnover kinetics were positively correlated
with soil respiration, N mineralisation and soil organic carbon, whereas under anaerobic conditions they were positively correlated
with potential and actual denitrification rates and pH.
Received: 26 September 1996 相似文献
17.
Humic acids stimulate growth and activity of in vitro tested axenic cultures of soil autotrophic nitrifying bacteria 总被引:2,自引:0,他引:2
In the present study, the effect of humic acids on activity and growth of Nitrosomonas europaea and Nitrobacter agilis was investigated in vitro under axenic conditions. Humates from compost-stabilized vegetable waste or leonardite were added
to the chemolithotrophic culturing medium at concentrations of 0, 5, 50 and 100 mg l–1. It was found that both types of humic acids increased either NH4
+ or NO2
– oxidation and cell growth of nitrifying bacteria in a dose-independent manner. By combining these results with data from
a comparative growth evaluation of N. agilis based on possible utilization of humates or pyruvate in heterotrophic conditions, evidence was obtained that nitrifiers cannot
use humic acids as an alternative carbon and energy source. Thus, the stimulating effect of this fraction of soil organic
matter on chemolithotrophic ammonia and nitrite oxidizers might be attributed to an increase in microbial membrane permeability
favouring a better utilization of nutrients.
Received: 15 April 1996 相似文献
18.
Microwave irradiation was evaluated as a non-toxic alternate to chloroform fumigation for routine measurement of soil microbial
biomass C. Microwave energy was applied to moist soil to disrupt microbial cells. The flush of C released was then measured
after extraction or incubation. Microwave irradiation at 800 J g–1 soil was optimal because this level resulted in an almost instantaneous rise in soil temperature (≥80 °C), an abrupt reduction
in microbial activity, maximal release of biomass C, and minimal solubilization of humic substances. Both incubation-CO2 titration and extraction-colorimetry methods were used on separate 20-g subsamples to compare the labile C in the microwave-treated
and untreated soil samples. The incubation-titration method was also used to measure C in chloroform-fumigated soil samples.
Averaged across soils, the chloroform fumigation yielded 123.3±5.1 mg CO2-C kg–1. Microwave irradiation yielded 93.6±3.9 mg CO2-C kg–1 soil determined by incubation and 52.4±2.4 mg C kg–1 soil determined by extraction, accounting for 76% and 42% of the net flush of C measured by the chloroform fumigation. Microwave-stimulated
net flushes of C were correlated closely (r
2=0.974 for incubation or 0.908 for extraction) with microbial biomass C measured by the chloroform fumigation. Little correlation
was found with the total soil organic C (r
2=0.241 for incubation or for 0.166 extraction). Mean efficiency factors for incubation (K
MI) or extraction (K
ME) were used to calculate microbial biomass C from net flushes of C between microwaved and unmicrowaved soils. Values of K
MI and K
ME were not affected by soil pH, bulk density or clay contents. Extraction of microwaved soil by 0.5M K2SO4 proved to be a simple, fast, precise, reliable, and safe method to measure soil microbial biomass C.
Received: 12 September 1997 相似文献
19.
Influence of N and non-N salts on atmospheric methane oxidation by upland boreal forest and tundra soils 总被引:10,自引:0,他引:10
S. C. Whalen 《Biology and Fertility of Soils》2000,31(3-4):279-287
The short-term (24 h) and medium-term (30 day) influence of N salts (NH4Cl, NaNO3 and NaNO2) and a non-N salt (NaCl) on first-order rate constants, k (h–1) and thresholds (CTh) for atmospheric CH4 oxidation by homogenized composites of upland boreal forest and tundra soils was assessed at salt additions ranging to 20 μmol
g–1 dry weight (dw) soil. Additions of NH4Cl, NaNO3 and NaCl to 0.5 μmol g–1 dw soil did not significantly decrease k relative to watered controls in the short term. Higher concentrations significantly reduced k, with the degree of inhibition increasing with increasing dose. Similar doses of NH4Cl and NaCl gave comparable decreases in k relative to controls and both soils showed low native concentrations of NH4
+-N (≤1 μmol g–1dw soil), suggesting that the reduction in k was due primarily to a salt influence rather than competitive inhibition of CH4 oxidation by exogenous NH4
+-N or NH4
+-N released through cation exchange. The decrease in k was consistently less for NaNO3 than for NH4Cl and NaCl at similar doses, pointing to a strong inhibitory effect of the Cl– counter-anion. Thresholds for CH4 oxidation were less sensitive to salt addition than k for these three salts, as significant increases in CTh relative to controls were only observed at concentrations ≥1.0 μmol g–1 dw soil. Both soils were more sensitive to NaNO2 than to other salts in the short term, showing a significant decrease in k at an addition of 0.25 μmol NaNO2 g–1 dw soil that was clearly attributable to NO2
–. Soils showed no recovery from NaCl, NH4
+-N or NaNO3 addition with respect to atmospheric CH4 oxidation after 30 days. However, soils amended with NaNO2 to 1.0 μmol NaNO2 g–1 dw showed values of k that were not significantly different from controls. Recovery of CH4-oxidizing ability was due to complete oxidation of NO2
–-N to NO3
–-N. Analysis of soil concentrations of N salts necessary to inhibit atmospheric CH4 oxidation and regional rates of N deposition suggest that N deposition will not decrease the future sink strength of upland
high-latitude soils in the atmospheric CH4 budget.
Received: 30 April 1999 相似文献
20.
The total N content in the acid forest soils studied ranged between 0.41% and 1.43%, and in more than 98% was composed of
organic N. Total hydrolysable organic N, hydrolysable unknown N (HUN) and α-aminoacidic N represented around 70%, 34% and
20% of the organic N, respectively, and varied in wide ranges. The percentages of amidic N and of the organic N compounds
solubilised to NH4
+ were approximately 6% and 5%, respectively, and ranged in narrow intervals. Aminoglucidic N reached a maximum of 3.8% of
the organic N and was undetectable in some of the samples analysed. Most of the hydrolysable N, HUN and α-aminoacidic N was
solubilised with 1 N and 3 N HCl, while a high amount of the compounds recovered as NH4
+ (60%) was obtained with 6 N HCl. The distribution of aminoglucidic N in the four fractions of increasing hydrolytic intensity
was very irregular. The organic N composition in the 0 to 5-cm and 5 to 10-cm layers was not significantly different. The
variation among samples was determined mainly by the organic N compounds less resistant to acid hydrolysis (hydrolysable N
and HUN less resistant to acid hydrolysis, amidic N and labile ammoniacal N) and by all α-aminoacidic N fractions. Aminoacidic
N was positively correlated with electrical conductivity and negatively correlated with exchangeable Al. The net N mineralisation
over 10 weeks of incubation was positive in all the soil samples analysed. The inorganic N content after the incubation and
the microbial N content were positively correlated with other variables – mainly with amidic N and α-aminoacidic N, as well
as with HUN and the hydrolysable N less resistant to hydrolysis.
Received: 13 July 1999 相似文献