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1.
Changes in soil microbial biomass, metabolic quotient, and organic matter turnover under Hieracium (H. pilosella L.) 总被引:9,自引:0,他引:9
In New Zealand Hieracium is an opportunistic plant that invades high country sites more or less depleted of indigenous vegetation. To understand the
invasive nature of this weed we assessed the changes in soil C, N and P, soil microbial biomass C, N and P contents, microbial
C : N and C : P ratios, the metabolic quotient, and turnover of organic matter in soils beneath Hieracium and its adjacent herbfield resulting from the depletion of tussock vegetation. The amounts of soil organic C and total N
were higher under Hieracium by 25 and 11%, respectively, compared to soil under herbfield. This change reflects an improvement in both the quantity and
quality of organic matter input to mineral soil under Hieracium, with higher percentage organic C and a lower C : N ratio. The microbial biomass C, N and P contents were also higher under
Hieracium. The amount of C respired during the 34-week incubation indicated differences in the nature of soil organic matter under
Hieracium, the unvegetated "halo" zone surrounding Hieracium patches, and herbfield (depleted tussock grassland). Decomposition of organic matter in these zones showed that the Hieracium soil had the greatest rate of CO2 respired, and the halo soil had the lowest. We relate the enhanced organic C turnover to the invasive nature of Hieracium. Net N mineralization was significantly lower from the Hieracium soil (57 mg N g–1 soil N) than from herbfield and halo soils (74 and 71 mg N g–1 soil N, respectively), confirming that the nature of organic N in Hieracium soil is different from adjoining halo and herbfield soils. It seems plausible that specific compounds such as polyphenols
and lignins released by Hieracium are not only responsible for increased organic N, but also control the form and amount of N released during organic matter
transformations. We conclude that the key to the success of Hieracium in the N-deficient South Island high country of New Zealand lies in its ability to control and sequester N supply through
modifying the soil organic matter cycle.
Received: 1 December 1998 相似文献
2.
S. S. Arnold I. J. Fernandez L. E. Rustad L. M. Zibilske 《Biology and Fertility of Soils》1999,30(3):239-244
Effects of increased soil temperature on soil microbial biomass and dehydrogenase activity were examined on organic (O) horizon
material in a low-elevation spruce-fir ecosystem. Soil temperature was maintained at 5 °C above ambient during the growing
season in the experimental plots, and soil temperature, moisture, microbial biomass, and dehydrogenase activity were measured
during the experiment. An incubation study was also conducted under three temperature regimes, 5, 15, and 25 °C, and under
four moisture regimes of 20, 120, 220, and 320% to further evaluate these environmental factors on dehydrogenase activity
and microbial biomass. Soil moisture content and microbial biomass controls were significantly lower (30% and 2 μg g–1 soil, respectively) in the heated plots during the treatment period, suggesting that moisture content was important in controlling
microbial biomass. In the incubation study, temperature appeared more important than moisture in controlling microbial biomass
and dehydrogenase activity. Increasing temperature between 5 °C and 25 °C resulted in significant decreases in microbial
biomass and dehydrogenase activity.
Received: 7 August 1998 相似文献
3.
Seasonal responses in microbial biomass carbon, phosphorus and sulphur in soils under pasture 总被引:28,自引:0,他引:28
The response of the soil microbial biomass to seasonal changes was investigated in the field under pastures. These studies
showed that over a 9-month period, microbial biomass carbon, phosphorus and sulphur (biomass C, P, S), and their ratios (C:P,
C:S, and P:S) responded differently to changes in soil moisture and to the input of fresh organic materials. From October
to December (1993), when plant residues were largely incorporated into the soils, biomass C and S increased by 150–210%. Biomass
P did not increase over this time, having decreased by 22–64% over the dry summer (July to September). There was no obvious
correlation between biomass C, P, and S and air temperature. The largest amounts of biomass C and P (2100–2300μg and 150–190μgg–1 soil, respectively) were found in those soils receiving farmyard manure (FYM or FYM+NPK) and P fertilizer, whereas the use
of ammonium sulphate decreased biomass C and P. The C:P, C:S, and P:S ratios of the biomass varied considerably (9–276:1;
50–149:1; and 0.3–14:1, respectively) with season and fertilizer regime. This reflected the potential for the biomass to release
(when ratios were narrow) or to immobilize (wide ratios) P and S at different times of the year. Thus, seasonal responses
in biomass C, P, and S are important in controlling the cycling of C, P, and S in pasture and ultimately in regulating plant
availability of P and S. The uptake of P in the pasture was well correlated with the sum of P in the biomass and soil available
pools. Thus, the simultaneous measurement of microbial biomass P and available P provide useful information on the potential
plant availability of P.
Received: 25 May 1996 相似文献
4.
Relationships of soil microbial biomass carbon and organic carbon with environmental parameters in mountainous soils of southwest China 总被引:5,自引:0,他引:5
The relationships between microbial biomass C, organic C, and environmental parameters were studied in soils under corn (Zea mays. L) in the mountainous areas of southwest China. Three yellowish-red (Ultisols), yellow (Ultisols) and yellowish-brown (Alfisols) soils were relatively weathered, leached and impoverished, with most having a low input of aboveground corn residues. Seasonal changes in soil microbial C at 0-10 cm depth were significant at each sampling site, with the highest value (120 g C m-2) in winter, and lowest value in summer (21 g C m-2). Microbial biomass C was significantly and negatively correlated with site elevation and positively correlated with mean annual temperature. The seasonal change in microbial biomass C was significantly correlated with total soil organic C. The decline in microbial biomass C estimated as a percentage of the total soil organic C was negatively correlated with the elevation above sea level, ranging from 3.9ǂ.9% below 600 m to 1.4ǂ.5% above 1,500 m, suggesting higher turnover rates of soil microbial biomass C at warmer air temperatures. Temperature influenced the decomposition of organic C in soils mainly through its effects on microbial biomass C, and the microbial biomass C/organic C ratio appears to be a sensitive index of the change in organic matter content of soil. 相似文献
5.
P. M. Groffman 《Biology and Fertility of Soils》1999,29(4):430-433
The effects of acetate additions to northern hardwood forest soils on microbial biomass carbon (C) and nitrogen (N) content,
soil inorganic N levels, respirable C and potential net N mineralization and nitrification were evaluated. The experiment
was relevant to a potential watershed-scale calcium (Ca) addition that aims to replace Ca depleted by long-term exposure to
acid rain. One option for this addition is to use calcium-magnesium (Mg) acetate, a compound that is inexpensive and much
more readily soluble than the Ca carbonate that is generally used for large-scale liming. Field plots were treated with sodium
(NA) acetate, Na bicarbonate or water (control) and were sampled (forest floor – Oe and Oa combined) 2, 10 and 58 days following
application. It was expected that the addition of C would lead to an increase in biomass C and N and a decrease in inorganic
N. Instead, we observed no effect on biomass C, a decline in biomass N and an increase in N availability. One possible explanation
for our surprising results is that the C addition stimulated microbial activity but not growth. A second, and more likely,
explanation for our results is that the C addition did stimulate microbial growth and activity, but there was no increase
in microbial biomass due to predation of the new biomass by soil fauna. The results confirm the emerging realization that
the effects of increases in the flow of C to soils, either by deliberate addition or from changes in atmospheric CO2, are more complex than would be expected from a simple C : N ratio analysis. Evaluations of large-scale manipulations of
forest soils to ameliorate effects of atmospheric deposition or to dispose of wastes should consider microbial and faunal
dynamics in considerable detail.
Received: 13 March 1998 相似文献
6.
Water and N availability are the major limiting factors of primary production in desert ecosystems, and the response of soil
biota to these two factors is of great importance. We examined the immediate response of soil nematodes and the microbial
biomass to a single pulse of water amendment in N-treated plots in the Israeli Negev desert. Plots were treated with 0, 50
and 100 kg NH4NO3 ha–1 in December 1992, and at the end of the summer period (August 1993) the plots were exposed to a 15 mm water. Soil samples
from the 0–10 cm layer were collected daily and analysed soil moisture, total soluble N, nematode populations and microbial
biomass. Soil moisture increased to 8.5%, then gradually decreased to 2% during the 11 days of the study. Microbial biomass,
soil respiration and metabolic quotient values did not exhibit any significant correlation with soil N levels. Free-living
nematode population levels in the different plots were found to increase from a mean level of 45 500 to a mean level of 92 300
individuals m–2. N treatment was found to affect the patterns of free-living nematode population dynamics. The results of this study demonstrated
the importance of moisture availability levels and the ability to mobilize previous N inputs into available N which, occurring
in pulses, can affect the microbial ecophysiological status, nematode population dynamics and the interrelationship between
these two important components in the desert soil milieu.
Received: 5 November 1998 相似文献
7.
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
8.
Gross N mineralization and nitrification rates and their relationships to microbial biomass C and N and enzyme (protease,
deaminase and urease) activities were determined in soils treated with dairy shed effluent (DSE) or NH4
+ fertilizer (NH4Cl) at a rate equivalent to 200 kg N ha–1 at three water potentials (0, –10 and –80 kPa) at 20 °C using a closed incubation technique. After 8, 16, 30, 45, 60 and
90 days of incubation, sub-samples of soil were removed to determine gross N mineralization and nitrification rates, enzyme
activities, microbial biomass C and N, and NH4
+ and NO3
– concentrations. The addition of DSE to the soil resulted in significantly higher gross N mineralization rates (7.0–1.7 μg
N g–1 soil day–1) than in the control (3.8–1.2 μg N g–1 soil day–1), particularly during the first 16 days of incubation. This increase in gross mineralization rate occurred because of the
presence of readily mineralizable organic substrates with low C : N ratios, and stimulated soil microbial and enzymatic activities
by the organic C and nutrients in the DSE. The addition of NH4Cl did not increase the gross N mineralization rate, probably because of the lack of readily available organic C and/or a
possible adverse effect of the high NH4
+ concentration on microbial activity. However, nitrification rates were highest in the NH4Cl-treated soil, followed by DSE-treated soil and then the control. Soil microbial biomass, protease, deaminase and urease
activities were significantly increased immediately after the addition of DSE and then declined gradually with time. The increased
soil microbial biomass was probably due to the increased available C substrate and nutrients stimulating soil microbial growth,
and this in turn resulted in higher enzyme activities. NH4Cl had a minimal impact on the soil microbial biomass and enzyme activities, possibly because of the lack of readily available
C substrates. The optimum soil water potential for gross N mineralization and nitrification rates, microbial and enzyme activities
was –10 kPa compared with –80 kPa and 0 kPa. Gross N mineralization rates were positively correlated with soil microbial biomass
N and protease and urease activities in the DSE-treated soil, but no such correlations were found in the NH4Cl-treated soil. The enzyme activities were also positively correlated with each other and with soil microbial biomass C and
N. The forms of N and the different water potentials had a significant effect on the correlation coefficients. Stepwise regression
analysis showed that protease was the variable that most frequently accounted for the variations of gross N mineralization
rate when included in the equation, and has the potential to be used as one of the predictors for N mineralization.
Received: 10 March 1998 相似文献
9.
To assess cultivation-induced changes followed during the Green Revolution on continuous rice–rice and rice–wheat cropping,
fence-line comparisons between cultivated and adjacent noncultivated soils were made to (a) quantify changes in selected soil
chemical and biological properties at two moisture conditions, (b) determine the N, P, and K uptake of rice and wheat as affected
by changes in soil properties, and (c) determine the relationship between N, P, and K uptake and soil properties. Two parallel
experiments were conducted: laboratory incubation and a greenhouse experiment with soils collected from seven rice–wheat and
two rice–rice soils. As an average, NH4OAc-extractable K, water soluble organic carbon, and hot water soluble organic carbon were all lower by 48%, total carbon
by 35%, total nitrogen by 33%, and microbial biomass carbon by 38% in the cultivated soils, whereas no significant change
was observed in the enzyme activities. Changes were mostly associated with the existing fertilizer practices and moisture
status of the soil during cultivation. In general, fertilizers were not sufficient to replenish crop removal. Soil type also
influenced cultivation changes especially soil carbon parameters. Lighter soil texture had higher decomposable organic C and
total C declined than heavy soils. Soils with higher declined in both decomposable organic C and total C had higher reduction
in functional diversity of culturable microorganisms. The declining C pools caused lower N uptake and there was a clear association
between organic matter parameters and N uptake. Olsen P was correlated with P uptake and extractable K with K uptake. As expected,
crop biomass correlated with N, P, and K uptake of plants. Comparison of cultivated and its corresponding uncultivated soil
provides possibility to determine management effect on soil status. 相似文献
10.
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
11.
Soil organic matter quantity and quality in mountain soils of the Alay Range, Kyrgyzia, affected by land use change 总被引:4,自引:0,他引:4
Changes in soil management practices influence the amount, quality and turnover of soil organic matter (SOM). Our objective
was to study the effects of deforestation followed by pasture establishment on SOM quantity, quality and turnover in mountain
soils of the Sui Checti valley in the Alay Range, Kyrgyzia. This objective was approached by analysis of total organic C (TOC),
N, lignin-derived phenols, and neutral sugars in soil samples and primary particle-size soil fractions. Pasture installation
led to a loss of about 30% TOC compared with the native Juniperus turkestanica forests. The pasture soils accumulated about 20% N, due to inputs via animal excrement. A change in land use from forest
to pasture mainly affected the SOM bound to the silt fraction; there was more microbial decomposition in the pasture than
in the forest silt fraction, as indicated by lower yields of lignin and carbohydrates, and also by a more advanced oxidative
lignin side-chain oxidation and higher values of plant : microbial sugar ratios. The ratio of arabinose : xylose was indicative
of the removal of carbohydrates when the original forest was replaced by pasture, and we conclude that this can be used as
an indicator of deforestation. The accumulation of lignin and its low humification within the forest floor could be due to
the extremely cold winter and dry summer climate.
Received: 10 March 1999 相似文献
12.
Soil organic carbon stocks, storage profile and microbial biomass under different crop management systems in a tropical agricultural ecosystem 总被引:3,自引:0,他引:3
We investigated the soil organic C and N stocks, storage profiles and microbial biomass as influenced by different crop management
systems in a tropical agricultural ecosystem. The different crop management systems significantly affected the C and N stocks
and microbial biomass C and N at different soil depths. Amongst the systems evaluated, the rice-wheat system maintained a
higher soil organic C content. Inclusion of legumes in the system improved the soil organic matter level and also soil microbial
biomass activity, vital for the nutrient turnover and long-term productivity of the soil. Irrespective of the cropping system,
approximately 58.4%, 25.7% and 15.9% of the C was distributed in 0–15, 15–30 and 30–60 cm depths, respectively.
Received: 10 October 1999 相似文献
13.
Addition of soluble organic substrates to soil has been shown to either increase or restrict the rate of microbial CO2–C evolution. This has been attributed to a priming effect resulting from accelerated or decreased turnover of the soil organic
matter including the soil microflora. We investigated microbial responses to small glucose-C additions (10–50 μg C g1 soil) in arable soils either amended or not with cellulose. An immediate CO2–C release between 0 and 69 h (equivalent to 59% of glucose-C applied) was measured. However, only half of the CO2–C respired could be attributed to the utilisation of glucose-C substrate, based on the percentage of 14C–CO2 evolved after the addition of a 14C-labelled glucose tracer. Thus, although no evidence of an immediate release of ‘extra’ C above the rate applied as glucose-C
was observed, the pattern of decomposition for 14C-glucose suggested utilisation of an alternate C source. Based on this, a positive priming effect (1.5 to 4.3 times the amount
CO2–C evolved that was attributed to glucose-C decomposition) was observed for at least 170 h in non-cellulose-amended soil and
612 h in cellulose-amended soil. Two further phases of microbial activity in cellulose-amended soils were attributed to either
activation of different microbial populations or end-product inhibition of cellulase activity after glucose addition. During
these subsequent phases, a negative priming effect of between 0.1 and 1.5 times was observed. Findings indicate that the response
of the microbial community to small additions of soluble organic C substrate is not consistent and support the premise that
microbial response varies in a yet to be predicted manner between soil type and ecosystems. We hypothesise that this is due
to differences in the microbial community structure activated by the addition of organic C and the timing of soluble organic
substrate addition with respect to the current dissolved organic C status of the soil. 相似文献
14.
The present research was conducted to determine the relationship between the degradation of rimsulfuron and soil microbial
biomass C in a laboratory-incubated clay loam soil (pH=8.1; organic matter=2.1%) under different conditions and at different
initial dosages (field rate, 10 and 100 times the field rate). The half-life values varied between 0.4 and 103.4 days depending
on temperature, soil moisture and initial dose. Evidence suggested that rimsulfuron could pose environmental risks in cold
and dry climatic conditions. Significant decreases in microbial biomass C content in rimsulfuron-treated soil, compared to
untreated soil, were observed initially, especially at higher temperatures and low moisture levels, but never exceeded 20.3%
of that in control soil. The microbial biomass C content then returned to initial values at varying times depending on incubation
conditions. The relationship between herbicide degradation and microbial biomass C content gave parabolic curves (P<0.005 in all cases) under all conditions tested. Generally, maximum biomass C decrease coincided with the decrease in the
concentration of rimsulfuron to about 50% of the initial dose, except at 10 °C and 100×, when biomass began to recover as
early as 65–70% of the initial dose. The final equations could be useful to deduce the decrease of soil microbial biomass
in relation to herbicide concentration. From the degradation kinetics of the herbicide, the time required to reach this decrease
can also be calculated.
Received: 19 July 1999 相似文献
15.
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
16.
Effects of 17-year fertilization on soil microbial biomass C and N and soluble organic C and N in loessial soil during maize growth 总被引:2,自引:0,他引:2
As labile organic pools, soluble organic matter and soil microbial biomass are sensitive to changes in soil management and
therefore good indicators of soil quality. Effects of a 17-year long-term fertilization on soil microbial biomass C (SMBC)
and N (SMBN), soluble organic C, and soluble organic N during the maize growing season were evaluated in a loess soil (Eum-Orthic
Anthrosol) in northwest China. The fertilization treatments included no fertilizer (CK), inorganic N, P, and K fertilizer
(NPK), cattle manure plus NPK fertilizer (MNPK), and straw plus NPK fertilizer (SNPK). Our results showed that C storage in
the 0–20 cm soil layer was 28% to 81% higher in the fertilized treatments compared to the unfertilized treatment. In the 0–10 cm
soil layer, SMBC and SMBN in the three fertilized treatments were higher than in the unfertilized treatment on all sampling
dates, while microbial biomass C and N in the 0−10 cm soil layers were the highest at grain filling. In the same soil layer,
soil-soluble organic C generally decreased in the order MNPK > SNPK > NPK > CK, while soluble organic N was the highest in
the MNPK followed by the SNPK treatment. There was no significant difference in soluble organic N in the NPK and CK treatments
throughout most of the maize growing season. Changes in soluble organic N occurred along the growing season and were more
significant than those for soluble organic C. Soluble organic N was the highest at grain filling and the lowest at harvest.
Overall, our results indicated that microbial biomass and soluble organic N in the surface soil were generally the highest
at grain filling when maize growth was most vigorous. Significant positive relationships were found between soluble organic
C and SMBC and between soluble organic N and SMBN. 相似文献
17.
Influence of soil properties on microbial populations, activity and biomass in humid subtropical mountainous ecosystems of India 总被引:1,自引:0,他引:1
Microbial populations, biomass, soil respiration and enzyme activities were determined in slightly acid organic soils of
major mountainous humid subtropical terrestrial ecosystems, along a soil fertility gradient, in order to evaluate the influence
of soil properties on microbial populations, activity and biomass and to understand the dynamics of the microbial biomass
in degraded ecosystems and mature forest. Although the population of fungi was highest in the undisturbed forest (Sacred Grove),
soil respiration was lowest in the 7-year-old regrowth and in natural grassland (approximately 373 μg g–1 h–1). Dehydrogenase and urease activities were high in "jhum" fallow, and among the forest stands they were highest in the 7-year-old
regrowth. Microbial biomass C (MBC) depended mainly on the organic C status of the soil. The MBC values were generally higher
in mature forest than in natural grassland, 1-year-old jhum fallow and the 4-year-old alder plantation. The MBC values obtained
by the chloroform-fumigation-incubation technique (330–1656 μg g–1) did not vary significantly from those obtained by the chloroform-fumigation-extraction technique (408–1684 μg g–1), however, the values correlated positively (P<0.001). The enzyme activities, soil respiration, bacterial and fungal populations and microbial biomass was greatly influenced
by several soil properties, particularly the levels of nutrients. The soil nutrient status, microbial populations, soil respiration
and dehydrogenase activity were greater in Sacred Grove, while urease activity was greater in grassland.
Received: 14 October 1998 相似文献
18.
A. S. Raghubanshi 《Biology and Fertility of Soils》1991,12(1):55-59
Summary Three dry tropical forest soils along a topographic sequence were examined to determine the seasonal dynamics of microbial C, N, and P. The lowest microbial biomass was found in forest soils at the foot of the hill followed by midslope forest soils. The hilltop soil, which had the most fine particles, water-holding capacity, organic C, and total N, reflected the presence of greater amounts of microbial C, N, and P. Mean annual microbial C, N, and P ranges were 466–662, 48–72 to 21–30 g g-1, respectively. The seasonal pattern of microbial biomass, C, N, and P was similar at all sites, the values being greatest during the dry season and lowest during the wet season. The seasonal values for microbial biomass C, N, and P were positively correlated with each other and a negative correlation was found between microbial biomass and the fine root mass in these forest soils. 相似文献
19.
A field study was conducted to investigate the effect of abandonment of management on net N mineralization (NNM) in subalpine
meadows. NNM, soil microbial biomass N (SMBN), fungal biomass and physicochemical characteristics (total C, total N, dissolved
organic carbon (DOC) and pH) were determined in surface (0–10 cm) soil from May to October 1997 in an intensively managed
and an abandoned meadow at 1770 m a.s.l.. The cumulative NNM was lower in the abandoned area and ranged from 150 to 373 and
from 25 to 85 μg N g–1 soil in the intensively managed and the abandoned areas, respectively. The total organic C increased in the abandoned area,
while total N showed no difference between abandoned and managed meadow. SMBN showed no difference between the investigated
sites, whereas ergosterol, a measure of fungal biomass, increased significantly at the abandoned site. The cumulative NNM
was negatively correlated with total organic C, C : N ratio, DOC and ergosterol content, and positively correlated with the
NH4
+-N content of soil. The decrease in NNM at the abandoned site may be explained by the lower availability of N in substrates
characterized by a high C : N ratio which, together with a decrease in pH in the litter layer, may have increased fungal biomass.
Received: 8 January 1999 相似文献
20.
Thomas L. Kieft 《Biology and Fertility of Soils》1994,18(2):155-162
The major objectives of this study were to determine the influence of grazing on the soil microbial biomass and activity in semiarid grassland and shrubland areas and to quantify the canopy effect (the differences in soil microbial biomass and activities between soils under plant canopies and soils in the open between plants). We also quantified changes in microbial biomass and activity during seasonal transition from dry to moist conditions. Chronosequences of sites withdrawn from grazing for 0, 11, and 16 years were sampled in a grassland (Bouteloua spp.) area and a shrubland (Atriplex canescens) area on and near the Sevilleta National Wildlife Reguge in central New Mexico, USA. Samples were obtained from beneath the canopies of plants (Yucca glauca in the grassland and A. canescens in the shrubland) and from open soils; they were collected three times during the spring and summer of a single growing season. Organic C, soil microbial biomass C, and basal respiration rates (collectively called the soil C triangle) were measured. We also calculated the microbial: organic C ratio and the metabolic quotient (ratio of respiration to microbial C) as measures of soil organic C stability and turnover. Although we had hypothesized that individual values of the soil C triangle would increase and that the ratios would decrease with time since grazing, differences in microbial parameters between sites located along the chronosequences were generally not significant. Grazing did not have a consistion effect on organic C, microbial C, and basal respiration in our chronosequences. The microbial: organic C ratio and the metabolic quotient generally increased with time since grazing on the shrubland chronosequence. The microbial: organic C ratio decreased with time since grazing and the metabolic quotient increased with time since grazing on the grassland chronosequence. The canopy effect was observed at all sites in nearly all parameters including organic C, microbial C, basal respiration, the microbial: organic C ratio, and the metabolic quotient which were predominantly higher in soils under the canopies of plants than in the open at all sites. Microbial biomass and activity did not increase during the experiment, even though the availability of moisture increased dramatically. The canopy effects were approximately equal on the shrubland and grassland sites. The microbial: organic C ratios and the metabolic quotients were generally higher in the shrubland soils than in the grassland soils. 相似文献