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1.
《Soil biology & biochemistry》2001,33(4-5):651-657
The direct uptake of organic nitrogen compounds from the soil solution by plant roots has been hypothesised to constitute a significant source of N to the plant particularly in N limiting ecosystems. The experiments undertaken here were designed to test whether wheat roots could out-compete the rhizosphere microflora for a pulse addition of organic N in the form of three contrasting amino acids, namely lysine, glycine and glutamate. Amino acids were added at a concentration reflecting reported soil solution concentrations (100 μM) and the uptake into either plant biomass or respiration or microbial biomass and respiration determined over a 24 h chase period. The results showed that the plant roots could only capture on average 6% of the added amino acid with the remainder captured by the microbial biomass. We therefore present direct in vivo evidence to support earlier work which has hypothesised that organic N may be of only limited consequence in high input agricultural systems. We suggest that this is a result of the higher concentrations of NO3− in agricultural soil solutions, the slow movement of amino acids in soil relative to NO3−, the rapid turnover of amino acids by soil microorganisms, and the poor competitive ability of plant roots to capture amino acids from the soil solution. 相似文献
2.
The critical S concentration and S requirement of the soil microbial biomass of a granitic regosol was examined. S was applied
at the rate of 0, 5, 10, 20, 30 and 50 μg S as MgSO4·7H2O, together with either 3000 μg glucose-C or 3333 μg cellulose-C, 400 μg N, and 200 μg P g –1 soil and 200 μg K g–1 soil. Microbial biomass, inorganic SO4
2–-S, and CO2 emission were monitored over 30 days during incubation at 25 °C. Both glucose and cellulose decomposition rates responded
positively to the S made available for microbial cell synthesis. The amounts of microbial biomass C and S increased with the
level of applied S up to 10 μg S g–1 soil and 30 μg S g–1 soil in the glucose- and cellulose-amended soil, respectively, and then declined. Incorporated S was found to be concentrated
within the microbial biomass or partially transformed into soil organic matter. The concentration of S in the microbial biomass
was higher in the cellulose- (4.8–14.2 mg g–1) than in the glucose-amended soil (3.7–10.9 mg g–1). The microbial biomass C:S ratio was higher in the glucose- (46–142 : 1) than in the cellulose-amended soil (36–115 : 1).
The critical S concentration in the microbial biomass (defined as that required to achieve 80% of the maximum synthesis of
microbial biomass C) was estimated to be 5.1 mg g–1 in the glucose- and 10.9 mg g–1 in the cellulose-amended soil. The minimum requirement of SO4
2–-S for microbial biomass formation was estimated to be 11 μg S g–1 soil and 21 μg S g–1 soil for glucose- and cellulose-amended soil, respectively. The highest levels of activity of the microbial biomass were
observed at the SO4
2–-S concentrations of 14 μg S g–1 soil and 17 μg S g–1 soil, for the glucose and cellulose amendments, respectively, and were approximately 31–54% higher during glucose than cellulose
decomposition.
Received: 20 October 1999 相似文献
3.
A study of the effects of different qualities (fresh and composted) and rates (equivalent to 120, 240, and 360 kg N ha–1) of mustard meal application on wheat yields on humid tropical vertisol was started in 1990 at Ginchi Research Station in
Ethiopia. After continuous wheat cropping for 7 years and without any further fertilisation, soil microbial parameters (basal
respiration, microbial biomass-C and N, organic-C, and ecophysiological quotients) were studied during one growth period.
After 7 years of application, mustard meal still exerted a significant positive effect on microbial biomass, basal respiration,
organic-C, Cmic : Nmic ratio, and metabolic quotient (qCO2). Organic-C, qCO2 and Cmic : Nmic ratios were higher for the compost-amended plots than plots amended with fresh mustard meal. Basal respiration, Cmic, and Cmic : Nmic ratio showed a clear seasonality, but only in manured plots. The data indicate shifts in microbial community structure (from
bacteria to fungi and from r to K strategists) and suggest positive medium-term effects of mustard meal on humid tropical
vertisol biological qualities.
Received: 25 May 1999 相似文献
4.
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
5.
Spatial changes of soil fungal and bacterial biomass from a sub-alpine coniferous forest to grassland in a humid, sub-tropical region 总被引:7,自引:0,他引:7
Fungal and bacterial biomass were determined across a gradient from a forest to grassland in a sub-alpine region in central
Taiwan. The respiration-inhibition and ergosterol methods for the evaluation of the microbial biomass were compared. Soil
fungal and bacterial biomass both significantly decreased (P<0.05) with the shift of vegetation from forest to grassland. Fungal and bacterial respiration rates (evolved CO2) were, respectively, 89.1 μl CO2 g–1 soil h–1 and 55.1 μl CO2 g–1 soil h–1 in the forest and 36.7 μl CO2 g–1 soil h–1 and 35.7 μl CO2 g–1 soil h–1 in the grassland surface soils (0–10 cm). The fungal ergosterol content in the surface soil decreased from the forest zone
(108 μg g–1) to the grassland zone (15.9 μg g–1). A good correlation (R
2=0.90) was exhibited between the soil fungal ergosterol content and soil fungal CO2 production (respiration) for all sampling sites. For the forest and grassland soil profiles, microbial biomass (respiration
and ergosterol) declined dramatically with depth, ten- to 100-fold from the surface organic horizon to the deepest mineral
horizon. With respect to fungal to bacterial ratios for the surface soil (0–10 cm), the forest zone had a significantly (P<0.05) higher ratio (1.65) than the grassland zone (1.05). However, there was no fungal to bacterial ratio trend from the surface
horizon to the deeper mineral horizons of the soil profiles.
Received: 30 March 2000 相似文献
6.
This study examines the effects of atrazine on both microbial biomass C and C mineralization dynamics in two contrasting agricultural
soils (organic C, texture, and atrazine application history) located at Galicia (NW Spain). Atrazine was added to soils, a
Humic Cambisol (H) and a Gleyic Cambisol (G), at a recommended agronomic dose and C mineralization (CO2 evolved), and microbial biomass measurements were made in non-treated and atrazine-treated samples at different time intervals
during a 12-week aerobic incubation. The cumulative curves of CO2–C evolved over time fit the simple first-order kinetic model [Ct = Co (1 − e
−kt
)], whose kinetic parameters were quantified. Differences in these parameters were observed between the two soils studied;
the G soil, with a higher content in organic matter and microbial biomass C and lower atrazine application history, exhibited
higher values of the total C mineralization and the potentially mineralizable labile C pool than those for the H soil. The
addition of atrazine modified the kinetic parameters and increased notably the C mineralized; by the end of the incubation
the cumulative CO2–C values were 33–41% higher than those in the corresponding non-added soils. In contrast, a variable effect or even no effect
was observed on the soil microbial biomass following atrazine addition. The data clearly showed that atrazine application
at normal agricultural rates may have important implications in the C cycling of these two contrasting acid soils. 相似文献
7.
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
8.
Conservation tillage, and especially no-tillage, induce changes in the distribution of organic pools in the soil profile.
In long-term field experiments, marked stratification of the total soil microbial biomass and its activity have been observed
as consequence of the application of no-tillage to previously tilled soils. Our objective was to study the evolution of the
total and active soil microbial biomass and mineralized C in vitro during the first crop after the introduction of no-tillage
to an agricultural soil. The experiment was performed on a Typic Hapludoll from the Argentinean Pampa. Remaining plant residues,
total and active microbial biomass and mineralized C were determined at 0–5 cm and 5–15 cm depths, at three sampling times:
wheat tilling, silking and maturity. The introduction of no-tillage produced an accumulation of plant residues in the soil
surface layer (0–5 cm), showing stratification with depth at all sampling dates. Active microbial biomass and C mineralization
were higher under no-tillage than under conventional tillage in the top 5 cm of the profile. The total soil microbial biomass
did not differ between treatments. The active soil biomass was highly and positive correlated with plant residues (r
2=0.617;P<0.01) and with mineralized C (r
2=0.732;P<0.01). Consequently, the active microbial biomass and mineralized C reflected immediately the changes in residue management,
whereas the total microbial biomass seemed not to be an early indicator of the introduction of a new form of soil management
in our experiment.
Received: 23 February 1999 相似文献
9.
Giancarlo Renella Amar M. Chaudri Céline M. Falloon Loretta Landi Paolo Nannipieri Philip C. Brookes 《Biology and Fertility of Soils》2007,43(6):751-758
We investigated Cd, Zn, and Cd + Zn toxicity to soil microbial biomass and activity, and indigenous Rhizobium leguminosarum biovar trifolii, in two near neutral pH clay loam soils, under long-term arable and grassland management, in a 6-month laboratory incubation,
with a view to determining the causative metal. Both soils were amended with Cd- or Zn-enriched sewage sludge, to produce
soils with total Cd concentrations at four times (12 mg Cd g−1 soil), and total Zn concentrations (300 mg Zn kg−1 soil) at the EU upper permitted limit. The additive effects of Cd plus Zn at these soil concentrations were also investigated.
There were no significant differences in microbial biomass C (B
C), biomass ninhydrin N (B
N), ATP, or microbial respiration between the different treatments. Microbial metabolic quotient (defined as qCO2 = units of CO2–C evolved unit−1 biomass C unit−1 time) also did not differ significantly between treatments. However, the microbial maintenance energy (in this study defined
as qCO2-to-μ ratio value, where μ is the growth rate) indicated that more energy was required for microbial synthesis in metal-rich sludge-treated soils (especially
Zn) than in control sludge-treated soils. Indigenous R.
leguminosarum bv. trifolii numbers were not significantly different between untreated and sludge-treated grassland soils after 24 weeks regardless of
metal or metal concentrations. However, rhizobial numbers in the arable soils treated with metal-contaminated sludges decreased
significantly (P < 0.05) compared to the untreated control and uncontaminated sludge-treated soils after 24 weeks. The order of decreasing
toxicity to rhizobia in the arable soils was Zn > Cd > Cd + Zn. 相似文献
10.
Sulfate adsorption by variable charge soils: Effect of low-molecular-weight organic acids 总被引:1,自引:0,他引:1
C. E. Martinez A. W. Kleinschmidt M. A. Tabatabai 《Biology and Fertility of Soils》1998,26(3):157-163
Sulfate (SO4
2–) movement and transport in soils has received considerable attention in recent years. In most soils, SO4
2– coexists with a variety of natural organic compounds, especially organic acids. Studies were conducted to assess the effect
of low-molecular-weight organic acids (eight aliphatic and five aromatic acids) on SO4
2– adsorption by variable charge soils from Chile and Costa Rica. The effects of type of organic acid, pH, type of soil, and
organic acid concentration were investigated. In one experiment, a 1.0 g soil sample was equilibrated with 25 ml 0, 0.5, 1.0,
2.0, 4.0, or 6.0 mM K2SO4 in 1 mM NaCl in the presence or absence of 5 mM citric acid. In the second set of experiments, the adsorption of 2 mM SO4
2– in soils at pH 4 or pH 5 in the presence or absence of one of 13 organic acids at a concentration of 2 mM or 5 mM was studied. Results showed that citric acid significantly decreased SO4
2– adsorption by the two soils. Sulfate adsorption decreased with increasing pH of the equilibrium solution. Aliphatic acids,
with the exception of cis-aconitic acid, decreased the amount of SO4
2– adsorbed by the two soils, with oxalic, tartaric, and citric acid showing the greatest effect. The differences in pH values
of the equilibrium solutions in the presence and absence of organic acids were significantly, but negatively, correlated with
the amount of SO4
2– adsorbed, suggesting chemisorption of SO4
2– and the release of hydroxide ions. The ionization fraction values of the organic acids at the equilibrium pH were correlated
with the amounts of SO4
2– adsorbed, suggesting that the protonation of surface hydroxyl groups of the mineral phase increased as the strength of the
ionization of the acid increased, thus creating more positively charged surfaces.
Received: 12 February 1997 相似文献
11.
Huan Ll Xiaolin Li Zhengxia Dou Junling Zhang Chong Wang 《Biology and Fertility of Soils》2012,48(1):75-85
The interactive impacts of arbuscular mycorrhizal fungi (AMF, Glomus intraradices) and earthworms (Aporrectodea trapezoides) on maize (Zea mays L.) growth and nutrient uptake were studied under near natural conditions with pots buried in the soil of a maize field.
Treatments included maize plants inoculated vs. not inoculated with AMF, treated or not treated with earthworms, at low (25 mg kg−1) or high (175 mg kg−1) P fertilization rate. Wheat straw was added as feed for earthworms. Root colonization, mycorrhiza structure, plant biomass
and N and P contents of shoots and roots, soil available P and NO3−–N concentrations, and soil microbial biomass C and N were measured at harvest. Results indicated that mycorrhizal colonization
increased markedly in maize inoculated with AMF especially at low P rate, which was further enhanced by the addition of earthworms.
AMF and earthworms interactively increased maize shoot and root biomass as well as N and P uptake but decreased soil NO3−–N and available P concentrations at harvest. Earthworm and AMF interaction also increased soil microbial biomass C, which
probably improved root N and P contents and indirectly increased the shoot N and P uptake. At low P rate, soil N mobilization
by earthworms might have reduced potential N competition by arbuscular mycorrhizal hyphae, resulting in greater plant shoot
and root biomass. Earthworms and AMF interactively enhanced soil N and P availability, leading to greater nutrient uptake
and plant growth. 相似文献
12.
Influence of soil phosphorus status and nitrogen addition on carbon mineralization from 14C-labelled glucose in pasture soils 总被引:2,自引:0,他引:2
This study examines the effect of soil P status and N addition on the decomposition of 14C-labelled glucose to assess the consequences of reduced fertilizer inputs on the functioning of pastoral systems. A contrast
in soil P fertility was obtained by selecting two hill pasture soils with different fertilizer history. At the two selected
sites, representing low (LF) and high (HF) fertility status, total P concentrations were 640 and 820 mg kg–1 and annual pasture production was 4,868 and 14,120 kg DM ha–1 respectively. Soils were amended with 14C-labelled glucose (2,076 mg C kg–1 soil), with and without the addition of N (207 mg kg–1 soil), and incubated for 168 days. During incubation, the amounts of 14CO2 respired, microbial biomass C and 14C, microbial biomass P, extractable inorganic P (Pi) and net N mineralization were determined periodically. Carbon turnover was greatly influenced by nutrient P availability.
The amount of glucose-derived 14CO2 production was high (72%) in the HF and low (67%) in the LF soil, as were microbial biomass C and P concentrations. The 14C that remained in the microbial biomass at the end of the 6-month incubation was higher in the LF soil (15%) than in the
HF soil (11%). Fluctuations in Pi in the LF soil during incubation were small compared with those in HF soil, suggesting that P was cycling through microbial
biomass. The concentrations of Pi were significantly greater in the HF samples throughout the incubation than in the LF samples. Net N mineralization and nitrification
rates were also low in the LF soils, indicating a slow turnover of microorganisms under limited nutrient supply. Addition
of N had little effect on biomass 14C and glucose utilization. This suggests that, at limiting P fertility, C turnover is retarded because microbial biomass becomes
less efficient in the utilization of substrates.
Received: 18 October 1999 相似文献
13.
Organic matter, microbial biomass and enzyme activity of soils under different crop rotations in the tropics 总被引:8,自引:0,他引:8
Soil organic matter level, soil microbial biomass C, ninhydrin-N, C mineralization, and dehydrogenase and alkaline phosphatase
activity were studied in soils under different crop rotations for 6 years. Inclusion of a green manure crop of Sesbania aculeata in the rotation improved soil organic matter status and led to an increase in soil microbial biomass, soil enzyme activity
and soil respiratory activity. Microbial biomass C increased from 192 mg kg–1 soil in a pearl millet-wheat-fallow rotation to 256 mg kg–1 soil in a pearl millet-wheat-green manure rotation. Inclusion of an oilseed crop such as sunflower or mustard led to a decrease
in soil microbial biomass, C mineralization and soil enzyme activity. There was a good correlation between microbial biomass
C, ninhydrin-N and dehydrogenase activity. The alkaline phosphatase activity of the soil under different crop rotations was
little affected. The results indicate the green manuring improved the organic matter status of the soil and soil microbial
activity vital for the nutrient turnover and long-term productivity of the soil.
Received: 7 January 1996 相似文献
14.
Haiyan Chu Jianguo Zhu Xiangui Lin Rui Yin Zubin Xie Zhihong Cao Takeshi Fujii 《Biology and Fertility of Soils》2007,43(6):811-814
In this study, we investigated the effects of lanthanum (La), one of the rare earth elements (REEs), on microbial biomass
C as well as the decomposition of 14C-labelled glucose in a fluvo-aquic soil in 28 days. The soil was collected from the field plots under maize/wheat rotation
in Fengqiu Ecological Experimental Station of Chinese Academy of Sciences, Henan Province, China. Application of La decreased
soil microbial biomass C during the experimental period, and there was a negative correlation (P < 0.01) between microbial biomass and application rate of La. La increased microbial biomass 14C after 14C glucose addition, and the increase was significant (P < 0.05) at the rates of more than 160 mg kg−1 soil. La slightly increased 14CO2 evolution at lower rates of application but decreased it at higher rates 1 day after 14C glucose addition, while there was no significant effect from days 2 to 28. For the cumulative 14CO2 evolution during the incubation of 28 days, La slightly increased it at the rates of less than 120 mg kg−1 soil, while significantly decreased (P < 0.05) it at the rate of 200 mg kg−1 soil. The results indicated that agricultural use of REEs such as La in soil could decrease the amount of soil microbial
biomass and change the pattern of microbial utilization on glucose C source in a short period. 相似文献
15.
L. Landi G. Renella J. L. Moreno L. Falchini P. Nannipieri 《Biology and Fertility of Soils》2000,32(1):8-16
This study was carried out to investigate the effect of very high cadmium concentrations (50 and 500 μg Cd g–1 soil) on some biochemical and microbiological measurements under laboratory conditions involving daily soil samplings. The
data for both DTPA- and water-soluble Cd showed two distinctive patterns during soil incubation; from 0 to 4 days, values
were about 50–500 and 1–100 μg g–1 dry weight soil, whereas they decreased markedly after 7 days. Both daily respiration and the ATP content but not the microbial
biomass C determined by the fumigation–extraction method were lowered by high DTPA- and water-soluble Cd concentrations. Dehydrogenase
and phosphatase activities as well as both enzyme activity : microbial biomass ratios were decreased by the high DTPA- and
water-soluble Cd concentrations. In the first 2 days of incubation, the metabolic quotient (qCO2) was also decreased by the highest values of available Cd. The early (after 6 h) mineralization of l- but not d-glutamic acid to CO2 was inhibited during the 0–4 day incubation period by the highest Cd concentration. Possibly the l-enantiomer was used by a larger fraction of soil microorganisms than the d-enantiomer or, if they were used by the same fraction of soil microorganisms, the d-enantiomer was mineralized at a lower rate. The l- : d-glutamic acid respiration ratio was decreased by the high available Cd content because under polluted conditions soil microorganisms
probably discriminated less between the two stereoisomers of glutamic acid.
Received: 13 July 1999 相似文献
16.
Long-term winter cover cropping effects on corn (Zea mays L.) production and soil nitrogen availability 总被引:1,自引:0,他引:1
This study was conducted to determine effects of long-term winter cover cropping with hairy vetch, cereal rye and annual
ryegrass on soil N availability and corn productivity. From 1987 to 1995, with the exception of the first year of the study,
the cover crops were seeded each year in late September or early October after the corn harvest and incorporated into the
soil in late April or early May. Corn was seeded 10 days to 2 weeks after the cover crop residues had been incorporated, and
N fertilizer was applied as a side-dressing at rates of 0, 67, 134, or 201 kg N ha–1 each year. While the average annual total N input from the above-ground biomass of the cover crops was highest for hairy
vetch (72.4 kg N ha–1), the average annual total C input was highest for cereal rye (1043 kg C ha–1) compared with the other cover crops. Hairy vetch was the only cover crop that significantly increased pre-side-dressed NO3
–-N (Ni) corn biomass and N uptake at 0 N. At an N fertilizer rate of 134 kg N ha–1 or higher, the cover crops had a minimal effect on corn biomass. This indicated that even after 9 years of winter cover cropping,
the effect of the cover crops on corn growth resulted primarily from their influence on soil N availability. The amount of
available N estimated from the cover crops (Nac) was significantly correlated with relative corn biomass production (r
2=0.707, P<0.001). The total amount of available N, comprising Nac and N added from fertilizer (Nf), was strongly correlated (r
2=0.820, P<0.001)) with relative corn biomass production. The correlation was also high for the available N comprising Ni and Nf (r
2=0.775, P<0.001). Although cereal rye and annual ryegrass did not improve corn biomass production in the short term, they benefited
soil organic N accumulation and gradually improved corn biomass production compared with the control over the long term.
Received: 10 August 1999 相似文献
17.
We investigated some aspects of soil quality and community-level physiological profiles (CLPP) of bacteria in soil under a
long-term (37 years) trial with either exclusive inorganic fertilizers or fertilizers combined with farmyard manure cultivated
with jute–rice–wheat system. The treatments consisted of 100% recommended dose (RD) of NPK, 150% RD of NPK, 100% RD of N,
100% RD of NPK + FYM (10 t ha−1 year−1), and untreated control. Long-term application of 150% RD of NPK lowered the soil pH considerably while the soils in the
other treatments remained near neutral. The 100% RD of NPK + FYM treated plot showed significantly highest accumulation of
organic carbon, total nitrogen, microbial biomass carbon, basal soil respiration, and fluorescein diacetate hydrolyzing activity
among the treatments. CLPP analysis in Biolog Ecoplates revealed that utilization of carbohydrates was enhanced in all input
treated regimes, while the same for polymers, carboxylic acids, amino acids, and amines/amides were similar or less than the
untreated control. However, within these groups of carbon sources, heterogeneity of individual substrate utilization between
treatments was also noted. Taken together, addition of organic supplements showed significantly increased microbial biomass
carbon and microbial activity, but input of nutrient supplements, both inorganic and organic, only marginally affected the
overall substrate utilization pattern of soil microorganisms. 相似文献
18.
Combining field incubation with nitrogen-15 labelling to examine nitrogen transformations in low to high intensity grassland management systems 总被引:2,自引:0,他引:2
D. J. Hatch S. C. Jarvis R. J. Parkinson R. D. Lovell 《Biology and Fertility of Soils》2000,30(5-6):492-499
The 15N isotope dilution method was combined with a field incubation technique to provide simultaneous measurements of gross and
net rates of N turnover in three long-term swards: unfertilized (Z) or receiving N either from N fixation as clover (C), or
as 200 kg fertilizer N ha–1 year–1 (F). Uniform N enrichment of soil microplots was achieved with a multi-point soil injector to measure mineralization/immobilization
turnover and nitrification over a 4-day incubation. Net rates of mineralization ranged between 0.6 and 2.9 μg N g–1 day–1 and in all three treatments were approximately half the gross rates. Nitrification rates (gross) were between 1.0 and 1.6 μg
N g–1 day–1. In the F treatment, the turnover of NH4
+-N and NO3
–-N pools was on a 2- and 4-day cycle, respectively, whereas in the N-limited treatments (C and Z) turnover rates were faster,
with the NO3
–-N pools turning over twice as fast as the NH4
+-N pools. Therefore, available N was recycled more efficiently in the C and Z treatments, whereas in the F treatment a higher
N pool size was maintained which would be more vulnerable to leakage. A large proportion of the added 15N was recovered in the soil microbial biomass (SMB), which represented a 4–5 times larger sink for N than the plant biomass.
Although the C treatment had a significantly lower SMB than the grass-only treatments, there were no differences in microbial
activity. Gross rates of nitrification increased along the gradient of N input intensity (i.e. Z<C<F), and the addition of
a nitrification inhibitor (C2H2) tended to increase microbial immobilization, but did not influence plant N uptake. In this study, the value of combining
different techniques to verify net rates was demonstrated and the improved methodology for 15N labelling of soil enabled measurements to be obtained from relatively undisturbed soil under natural field conditions.
Received: 25 May 1999 相似文献
19.
《Soil biology & biochemistry》2001,33(7-8):1137-1140
Amino acids constitute a major reserve of soil organic-N and studies demonstrating direct uptake of amino acids by plants has indicated that understanding their bioavailability and fate in soil is important to understanding terrestrial N cycling. The aim of this study was to determine the effects of temperature and sorption on the mineralisation of three amino acids (glycine, lysine glutamate) in soil. Amino acid sorption followed the series lysine>glycine>glutamate, whereas mineralisation rate followed the series glutamate>glycine>lysine. These observations support the concept that sorption reduces the bioavailability of amino acids to the soil microbial population. Although the amino acids were used preferentially for making new biomass rather than respiration, differences were apparent between the individual amino acids with microbial assimilation efficiency (biomass production) following the series, lysine>glycine>glutamate. Our results suggest divergences in the uptake and metabolism of the individual amino acids with a rapid mineralisation of amino acids which readily enter general metabolic cycles (e.g. glutamate) compared to the amino acids which typically form the terminus of metabolic pathways (e.g. lysine). Temperature significantly affected the rate of amino acid mineralisation which increased up to 30°C (Q10=2.0) followed by a decline as the temperature approached 40°C. Rapid mineralisation occurred even at very low temperatures (1°C). Amino acid mineralisation across three experimental soil treatments followed the trend acidified>control>eroded soil. In summary, the results indicate that mineralisation is highly amino acid species dependent, has a mesophilic optimum, is retarded by sorption and is most rapid in soils which are not degraded. 相似文献
20.
Dwipendra Thakuria Narayan C. Talukdar Chandan Goswami Samarendra Hazarika Mohan C. Kalita Gary D. Bending 《Biology and Fertility of Soils》2009,45(3):237-251
To achieve higher yields and better soil quality under rice–legume–rice (RLR) rotation in a rainfed production system, we
formulated integrated nutrient management (INM) comprised of Azospirillum (Azo), Rhizobium (Rh), and phosphate-solubilizing bacteria (PSB) with phosphate rock (PR), compost, and muriate of potash (MOP). Performance
of bacterial bioinoculants was evaluated by determining grain yield, nitrogenase activity, uptake and balance of N, P, and
Zn, changes in water stability and distribution of soil aggregates, soil organic C and pH, fungal/bacterial biomass C ratio,
casting activities of earthworms, and bacterial community composition using denaturing gradient gel electrophoresis (DGGE)
fingerprinting. The performance comparison was made against the prevailing farmers’ nutrient management practices [N/P2O5/K2O at 40:20:20 kg ha−1 for rice and 20:30:20 kg ha−1 for legume as urea/single super-phosphate/MOP (urea/SSP/MOP)]. Cumulative grain yields of crops increased by 7–16% per RLR
rotation and removal of N and P by six crops of 2 years rotation increased significantly (P < 0.05) in bacterial bioinoculants-based INM plots over that in compost alone or urea/SSP/MOP plots. Apparent loss of soil
total N and P at 0–15 cm soil depth was minimum and apparent N gain at 15–30 cm depth was maximum in Azo/Rh plus PSB dual
INM plots. Zinc uptake by rice crop and diethylenetriaminepentaacetate-extractable Zn content in soil increased significantly
(P < 0.05) in bacterial bioinoculants-based INM plots compared to other nutrient management plots. Total organic C content in
soil declined at 0–15 cm depth and increased at 15–30 cm depth in all nutrient management plots after a 2-year crop cycle;
however, bacterial bioinoculants-based INM plots showed minimum loss and maximum gain of total organic C content in the corresponding
soil depths. Water-stable aggregation and distribution of soil aggregates in 53–250- and 250–2,000 μm classes increased significantly
(P < 0.05) in bacterial bioinoculants-based INM plots compared to other nutrient management plots. Fungal/bacterial biomass
C ratio seems to be a more reliable indicator of C and N dynamics in acidic soils than total microbial biomass C. Compost
alone or Azo/Rh plus PSB dual INM plots showed significantly (P < 0.05) higher numbers of earthworms’ casts compared to urea/SSP/MOP alone and bacterial bioinoculants with urea or SSP-applied
plots. Hierarchical cluster analysis based on similarity matrix of DGGE profiles revealed changes in bacterial community composition
in soils due to differences in nutrient management, and these changes were seen to occur according to the states of C and
N dynamics in acidic soil under RLR rotation. 相似文献