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1.
Low molecular weight (LMW) organic compounds in soil solution are easily biodegradable and could fuel respiration by soil microorganisms. Our main aim was to study the mineralization kinetics of monosaccharides using 14C-radiolabelled glucose. Based on these data and the soil solution concentrations of monosaccharides, we evaluated the contribution of monosaccharides to basal respiration for a variety of tropical forest soils. Further, the factors controlling the mineralization kinetics of monosaccharides were examined by comparing tropical and temperate forest soils. Monosaccharides comprised on average 5.2 to 47.7% of dissolved organic carbon in soil solution. Their kinetic parameters (V max and KM ), which were described by a single Michaelis-Menten equation, varied widely from 11 to 152?nmol?g?1?h?1 and 198 to 1294?µmol?L?1 for tropical soils, and from 182 to 400?nmol?g?1?h?1 and 1277 to 3150?µmol?L?1 for temperate soils, respectively. The values of V max increased with increasing microbial biomass-C in tropical and temperate soils, while the KM values had no correlations with soil biological or physicochemical properties. The positive correlation between V max values and microbial biomass-C indicates that microbial biomass-C is an essential factor to regulate the V max values in tropical and temperate forest soils. The biodegradation kinetics of monosaccharides indicate that the microbial capacity of monosaccharide mineralization far exceeds its rate at soil solution concentration. Monosaccharides in soil solution are rapidly mineralized, and their mean residence times in this study were very short (0.4–1.9?h) in tropical forests. The rates of monosaccharide mineralization at actual soil solution concentrations made up 22–118% of basal respiration. Probably because of the rapid and continuous production and consumption of monosaccharides, monosaccharide mineralization is shown to be a dominant fraction of basal respiration in tropical forest soils, as well as in temperate and boreal forest soils.  相似文献   

2.
Amending soils with glucose (5 mg g?1) resulted in an immediate increase in microbial activity and within 30 min the rates of heat output and respiration at 22° C were increased by up to 17.8 and 23.4 times, respectively. The increased rate of heat output remained stable for up to 6 h and there was good correlation with the amount of CO2 respired. The soil biomass was calculated by the method of Anderson and Domsch (1978). The rate of heat output of the biomass varied in different soils and ranged from 11.5 to 83.7 Jh?1 g?1 biomass C. In glucose-amended soils, however, the rate of heat output was much more consistent; the soils were in two groups having between 169–265 Jh?1g?1 biomass C or 454–482 J h?1 g?1 biomass C, both the latter two soils were from pasture. The increased rate of heat output from the amended soils was lower than expected from the respiration rate and the heat of oxidation of glucose, suggesting that a proportion of the CO2 respired was from catabolism of substrates other than glucose. Use of 14C-glucose confirmed that between 57–91% of the CO2 was derived from the glucose substrate.  相似文献   

3.
A method for determining microbially available N and P in an organic soil   总被引：3，自引：0，他引：3  
Summary A bioassay of microbially available soil N and P is described. It is based on the addition of glucose together with N or P to soil, followed by monitoring of the respiration rate. The addition of glucose + N resulted in an immediate increase in the soil respiration rate followed by a short period of exponential increase, reflecting the growth of microorganisms on the added substrate. The exponential phase levelled off, when lack of P prevented further growth of the soil microorganisms. The soil respiration rate then remained constant for several hours before decreasing, when glucose became limiting. The addition of glucose + P resulted in a lower plateau of the soil respiration rate, indicating that microbial growth was more limited by N than P in this forest soil (0.28 and 0.79 mg CO2 g-1 organic matter h-1, respectively). Additions of the limiting nutrient resulted in a proportional increase in the constant level of the soil respiration rate. This was used to calculated the increase in the soil respiration rate per mg N (0.71 mg CO2 h-1) or mg P (4.6 mg CO2 h-1) added to this particular soil. Microbially available N was then calculated in two ways from the regression equation (0.15 or 0.40 mg g-1 organic matter) and P (0.13 or 0.17 mg g-1 organic matter). A comparison with 2 M KCl extraction showed that in nutrient-poor forest soils the microbially available N was 6.3 or 18.5 times higher than the KCl extractable N.  相似文献   

4.
Microbial biomass C and soil respiration measurements were made in 17–20 yr old soils developed on sluiced and tipped coal‐combustion ashes. Topsoil (0–30 cm) and subsoil (30–100 cm) samples were collected from three soil profiles at two abandoned disposal sites located in the city area of Halle, Saxony‐Anhalt. Selected soil physical (bulk density and texture) and chemical (pH, organic C, total N, CEC, plant available K and P, and total Cd and Cu) properties were measured. pH values were significantly lower while organic C and total N contents and the C : N ratio were significantly higher in the topsoil than in the subsoil indicating the effects of substrate weathering and pedogenic C accumulation. Likewise, microbial biomass C, K2SO4‐extractable C, and soil respiration with median values of 786 μg biomass C g–1, 262 μg K2SO4‐C g–1, and 6.05 μg CO2‐C g–1 h–1, respectively, were significantly higher in the topsoil than in the subsoil. However, no significant difference was observed in metabolic quotient between the topsoil and the subsoil. Metabolic quotient with median values of 5.98 and 8.54 mg CO2‐C (g biomass C)–1 h–1 for the 0–30 cm and 30–100 cm depths, respectively, was higher than the data reported in the literature for arable and forest soils. Microbial biomass C correlated significantly with extractable C but no relationship was observed between it and total N, Cd, and Cu contents, as well as plant‐available K and P. We conclude that the presence of the remarkable concentration of extractable C in the weathered lignite ashes allowed the establishment of microbial populations with high biomass. The high metabolic quotients observed might be attributed to the heavy‐metal contamination and to the microbial communities specific to ash soils.  相似文献   

5.
Estimation of microbial biomass and activity in soil using microcalorimetry   总被引：2，自引：0，他引：2  
Relationships between the rate of heat output from soil, the rate of respiration and the soil microbial biomass were investigated for 25 soils from northern Britain. The rate of heat output, measured in a Calvet microcalorimeter at 22°C, correlated well with the rate of carbon dioxide respiration. The average amount of heat evolved per cm3 of gas respired. 21.1 J cm?3, suggests that the biomass metabolism was largely aerobic. The rate of heat output per unit of total microbial biomass was remarkably uniform over a wide range of soils, but showed differences depending upon whether the soil had been stored or amended. Mineral soils that had been stored at 4°C had the lowest heat output, 12.0 mW g?1 biomass C, compared with a mean of 20.4 mW g?1 biomass C for freshly-collected soils. Amendment with glucose (0.5% w/w) caused an immediate increase in respiration and heat output, up to 59.4 mW g?1 biomass C for stored soils and 188.2 mW g?1 biomass C for freshly collected soils. There was a consistent relationship between the biomass and the rate of heat output from freshly collected and amended mineral and organic soils which gave a linear fit using log transformed data: y= 0.6970+ 1.025x (r= 0.98, P < 0.001) (y=log10 biomass C, μgC g?1; x=log10 rate of heat output at 22°C, μW g?1). The overall relationship between biomass and the rate of heat output for all the amended samples was: 1 g biomass C= 180.05 ± 34.61 mW.  相似文献   

6.
1.3-β-Glucanase (laminarinase) activity in soil was measured using laminarin as the substrate. Activity was optimal in sodium acid-maleate buffer at pH 5.4 and followed Michaelis-Menten kinetics. Three methods of analysing kinetic data gave Km values of 0.23, 0.21 and 0.20 mg.ml?1. Vmax values were 0.41, 0.39 and 0.39 μmole glucose, g?1. h?1. The activation energy of the reaction was 49 kJ. mole?1. A proportion of the activity was highly resistant to storage at various temperatures: at 50 C 1,3-β-glucanase had a half-life of 28 days.  相似文献   

7.
Anaerobic ammonium oxidation (anammox process) widely occurs in paddy soil and may substantially contribute to permanent N removal; however, little is known about the factors controlling this process. Here, effects of temperature, pH, organic C, and substrates on potential rate of anammox and the relative contribution of anammox to total N2 production in a paddy soil were investigated via slurry incubation combined with 15N tracer technique. Anammox occurred over a temperature range from 5 to 35 °C with an optimum rate at 25 °C (1.7 nmol N g?1 h?1) and a pH range from 4.8 to 10.1 with an optimum rate at pH 7.3 (1.7 nmol N g?1 h?1). The presence of glucose and acetate (5–100 mg C L?1) significantly inhibited anammox activities and the ratio of anammox to total N2 production. The response of potential rates of anammox to ammonium concentrations fitted well with Michaelis-Menten relationship showing a maximum rate (Vmax) of 4.4 nmol N g?1 h?1 and an affinity constant (Km) of 6.3 mg NH4+-N L?1. Whereas, nitrate addition (5–15 mg 15NO3?-N L?1) significantly inhibited anammox activities and the ratio of anammox to total N2 production. Our results provide useful information on factors controlling anammox process and its contribution to N loss in the paddy soil.  相似文献   

8.
Bacteria, Pseudomonas paucimobilis, were inoculated at two concentrations (6.56 × 104 g?1 and 6.56 × 106g?1) into sterilized soil amended with 700 μg glucose-C g?1. Two levels of NH+4-N (11.0μg g?1 and 81.0 μg g?1) were used. The subsequent development was followed for three days by measurement of several biological, chemical and physiological parameters.The amount of bacterial biomass-C (μg g?1 soil) became twice as great in high as in low N treatments, and significantly decreased between 39.5 and 63.5 h for the high inoculum, high N level treatment due to decreasing cell size. By the end of the experiment the cumulative respired carbon was twice as great and more inorganic P was immobilized for high compared to low N treatments and all available NH+4-N was taken up by the final sample time. Soil ATP concentrations were twice as large in high N treatments but the turnover times were twice as long compared to low N systems. The yield coefficient (Y), calculated from respiration and biomass-C values, equalled 0.61 while substrate was plentiful. Nitrogen limitation did not alter the efficiencey with which glucose was transformed into biomass, but rather controlled the total amount of glucose used and biomass produced.  相似文献   

9.
The soils of the Antarctic dry valleys are exposed to extremely dry and cold conditions. Nevertheless, they contain small communities of micro-organisms that contribute to the biogeochemical transformations of the bioelements, albeit at slow rates. We have determined the dehydrogenase, β-glucosidase, acid and alkaline phosphatase and arylsulphatase activities and the rates of respiration (CO2 production) in laboratory assays of soils collected from a field experiment in an Antarctic dry valley. The objective of the field experiment was to test the responses of the soil microbial community to additions of C and N in simple (glucose and NH4Cl) and complex forms (glycine and lacustrine detritus from the adjacent lake comprising principally cyanobacterial necromass). The soil samples were taken 3 years after the experimental treatments had been applied. In unamended soil, all enzyme activities and respiration were detected indicating that the enzymatic capacity to mineralize organic C, P and S compounds existed in the soil, despite the very low organic matter content. Relative to the control (unamended soil), respiration was significantly increased by all the experimental additions of C and N except the smallest NH4Cl addition (1 mg N g−1 soil) and the smallest detritus addition (1.5 mg C g−1 soil and 0.13 mg N g−1 soil). The activities of all enzymes except dehydrogenase were increased by C and combined large C (10 mg C g−1 soil) and N additions, but either unchanged or diminished by addition of either N only or N (up to 10 mg N g−1 soil) with only small C (1 mg C g−1 soil) additions in the form of glucose and NH4Cl. This suggests that in the presence of a large amount of N, the C supply for enzyme biosynthesis was limited. When normalized with respect to soil respiration, only arylsulphatase per unit of respiration showed a significant increase with C and N additions as glucose and NH4Cl, consistent with S limitation when C and N limitations have been alleviated. Based on the positive responses of enzyme activity, detritus appeared to provide either conditions or resources which led to a larger biological response than a similar amount of C and more N added in the form of defined compounds (glucose, NH4Cl or glycine). Assessment of the soil microbial community by ester-linked fatty acid (ELFA) analysis provided no evidence of changes in the community structure as a result of the C and N supplementation treatments. Thus the respiration and enzyme activity responses to supplementation occurred in an apparently structurally stable or unresponsive microbial community.  相似文献   

10.
The substrate availability for microbial biomass (MB) in soil is crucial for microbial biomass activity. Due to the fast microbial decomposition and the permanent production of easily available substrates in the rooted top soil mainly by plants during photosynthesis, easily available substrates make a very important contribution to many soil processes including soil organic matter turnover, microbial growth and maintenance, aggregate stabilization, CO2 efflux, etc. Naturally occurring concentrations of easily available substances are low, ranging from 0.1 μM in soils free of roots and plant residues to 80 mM in root cells. We investigated the effect of adding 14C-labelled glucose at concentrations spanning the 6 orders of magnitude naturally occurring concentrations on glucose uptake and mineralization by microbial biomass. A positive correlation between the amount of added glucose and its portion mineralized to CO2 was observed: After 22 days, from 26% to 44% of the added 0.0009 to 257 μg glucose C g?1 soil was mineralized. The dependence of glucose mineralization on its amount can be described with two functions. Up to 2.6 μg glucose C g?1 soil (corresponds to 0.78% of initial microbial biomass C), glucose mineralization increased with the slope of 1.8% more mineralized glucose C per 1 μg C added, accompanied by an increasing incorporation of glucose C into MB. An increased spatial contact between micro-organisms and glucose molecules with increasing concentration may be responsible for this fast increase in mineralization rates (at glucose additions <2.6 μg C g?1). At glucose additions higher than 2.6 μg C g?1 soil, however, the increase of the glucose mineralization per 1 μg added glucose was much smaller as at additions below 2.6 μg C g?1 soil and was accompanied by decreasing portions of glucose 14C incorporated into microbial biomass. This supports the hypothesis of decreasing efficiency of glucose utilization by MB in response to increased substrate availability in the range 2.6–257 μg C g?1 (=0.78–78% of microbial biomass C). At low glucose amounts, it was mainly stored in a chloroform-labile microbial pool, but not readily mineralized to CO2. The addition of 257 μg glucose C g?1 soil (0.78 μg C glucose μg?1 C micro-organisms) caused a lag phase in mineralization of 19 h, indicating that glucose mineralization was not limited by the substrate availability but by the amount of MB which is typical for 2nd order kinetics.  相似文献   

11.
The rate of organic matter turnover in soil is a critical component of the terrestrial carbon cycle and is frequently estimated from measurements of respiration. For estimates to be reliable requires that isotopically labelled substrate uptake into the soil microbial biomass and its subsequent mineralization occurs almost simultaneously (i.e. no time delay). Here we investigated this paradigm using glucose added to an agricultural soil. Immediately after collection from the field, various concentrations of 14C-labeled glucose (1 μM to 10 mM) were added to soil and the depletion from the soil solution measured at 1–60 min after substrate addition. 14CO2 production from the mineralization of glucose was simultaneously measured. The microbial uptake of glucose from soil solution was concentration-dependent and kinetic analysis suggests the operation of at least two distinct glucose transport systems of differing affinity. At glucose concentrations reflecting those naturally present in the soil solution (54±10 μM), the half-time (t1/2) of exogenous glucose was extremely rapid at ca. 30 s. At higher glucose concentrations (100 μM to 10 mM), the t1/2 values for the high-affinity carrier were altered little, but increasing proportions of glucose were taken up by the low affinity transport system. Glucose mineralization by the soil microbial community showed a significant delay after its uptake into the microbial biomass suggesting a decoupling of glucose uptake and subsequent respiration, possibly by dilution of glucose in labile metabolite pools. By fitting a double first order kinetic equation to the mineralization results we estimated the t1/2 for the first rapid phase of respiration at natural soil solution glucose concentrations to be 6–8 min, but at least 87% of the added glucose was retained in the microbial biomass prior to mineralization. Our results suggest that in this soil the soil solution glucose pool turns over 100–1000 times each day, an order of magnitude faster than when determined from measurements of mineralization. These results imply that traditional isotopic based measurements of substrate turnover measured using CO2 may vastly underestimate their rate of cycling in soil.  相似文献   

12.

Purpose

The nitrification inhibitor dicyandiamide (DCD) has been shown to be highly effective in reducing nitrate (NO3 ?) leaching and nitrous oxide (N2O) emissions when used to treat grazed pasture soils. However, there have been few studies on the possible effects of long-term DCD use on other soil enzyme activities or the abundance of the general soil microbial communities. The objective of this study was to determine possible effects of long-term DCD use on key soil enzyme activities involved in the nitrogen (N) cycle and the abundance of bacteria and archaea in grazed pasture soils.

Materials and methods

Three field sites used for this study had been treated with DCD for 7 years in field plot experiments. The three pasture soils from three different regions across New Zealand were Pukemutu silt loam in Southland in the southern South Island, Horotiu silt loam in the Waikato in the central North Island and Templeton silt loam in Canterbury in the central South Island. Control and DCD-treated plots were sampled to analyse soil pH, microbial biomass C and N, protease and deaminase activity, and the abundance of bacteria and archaea.

Results and discussion

The three soils varied significantly in the microbial biomass C (858 to 542 μg C g?1 soil) and biomass N (63 to 28 μg N g?1), protease (361 to 694 μg tyrosine g?1 soil h?1) and deaminase (4.3 to 5.6 μg NH4 + g?1 soil h?1) activity, and bacteria (bacterial 16S rRNA gene copy number: 1.64?×?109 to 2.77?×?109 g?1 soil) and archaea (archaeal 16S rRNA gene copy number: 2.67?×?107 to 3.01?×?108 g?1 soil) abundance. However, 7 years of DCD use did not significantly affect these microbial population abundance and enzymatic activities. Soil pH values were also not significantly affected by the long-term DCD use.

Conclusions

These results support the hypothesis that DCD is a specific enzyme inhibitor for ammonia oxidation and does not affect other non-target microbial and enzyme activities. The DCD nitrification inhibitor technology, therefore, appears to be an effective mitigation technology for nitrate leaching and nitrous oxide emissions in grazed pasture soils with no adverse impacts on the abundance of bacteria and archaea and key enzyme activities.  相似文献   

13.
Large amounts of low molecular weight (LMW;<250 Da) carbon (C) are lost from roots into the rhizosphere as a consequence of root turnover and exudation. Their rates of turnover after release into the soil remain poorly understood. We extracted soil solution from a temperate grassland Eutric Cambisol, isotopically labeled the glucose and amino acid components, and then re-injected the solution back into the soil. We followed the subsequent evolution of 14CO2 and incorporation of the LMW C into the soil microbial biomass or grasses for 48 h. The experiments were performed both on grazed and un-grazed swards in the field, and in the laboratory. In the field, we showed that glucose and amino acids had short half-lives (t1/2) in soil solution (t1/2=20-40 min), but that they persisted in soil microbes for much longer. A first-order double exponential model fitted the experimental data well and gave rate constant (k) values of 1.21-2.14 h−1 for k1 and 0.0025-0.0048 h−1 for k2. Only small amounts of the added 14C were recovered in plant biomass (<5% of total added to soil) indicating that plant roots are poor competitors for LMW dissolved organic C (DOC) in comparison to soil microorganisms. The first phase of glucose and amino acid mineralization in the laboratory was slower (t1/2=40-60 min) than measured in the field reinforcing the importance of making flux measurements in situ. Whilst grazing stimulated below-ground respiration, it exerted only a small influence on the turnover of LMW DOC suggesting that the increase in respiration was due to increased root respiration and not turnover of soil organic matter (SOM). Our results suggest that some components of the LMW DOC pool are turned over extremely rapidly (ca. 4000 times annually).  相似文献   

14.
Gas exchange rates over soils were measured in a closed, flowing-gas system. 14CO was rapidly oxidized to 14CO2 with only a minor loss in atmospheric radioactivity. Incorporation of 14C into the soil was slight and was via 14CO2 rather than 14CO. CO oxidation was a microbial process and no oxidation occurred when soils had been autoclaved. The rate of CO depletion was concentration dependent and followed Michaelis-Menten kinetics. The rate constants Km and Vmax ranged from 18 to 51 μ 1?1 CO and from 0.58 to 4.35 mg C kg?1 dry soil h?1 respectively. The maximum rate of reaction for Hubbard Brook soil was about an order of magnitude greater than any soil previously reported. The oxidation reaction was accompanied initially by a reduction in net soil respiration. This was then followed by a period of high respiration which continued until CO levels were reduced to about 5μll?1. Thereafter respiration fell below the pretreatment rate and only returned to that rate 45 min after CO had been depleted from the atmosphere. The data suggest that at high CO concentrations (40–100 μll?1CO) autotrophic carboxydobacteria comprise the main component of the CO-oxidizing population and, as the concentration declines towards ambient levels they are replaced by heterotrophic microorganisms possessing a cometabolic process.  相似文献   

15.
Soil respiration is an important process for carbon geochemical cycling. Based on our five long‐term fertilizer experiments, soil respiration was measured using pot experiments with or without planting soybean. Soil respiration rates and soybean root biomass were determined at different observation times. Soil respiration rates due to soil microbial activity could be estimated by extrapolating a newly derived regressive equation at zero root biomass. Soil microbial respiration rates in the control were also observed directly, ranging from 16.0 to 42.7 mg carbon (C) m?2 h?1. Average soil microbial respiration rates from the regression analyses and direct observations were 32.9 and 27.8 mg C m?2 h?1, respectively. The average proportions of soil respiration rates due to the soybean growth were 63.0% using the regressive equation and 69.8% from direct observation. Therefore, the application of these two methods could provide new insight for separating plant root respiration from soil microbial respiration, which is important for estimating their individual contributions to atmospheric carbon dioxide.  相似文献   

16.
Cassava is an important subsidiary food in the tropics. In Tamil Nadu, India, microbial cultures were used to eradicate the tuberous root rot of cassava. Hence, an experiment was conducted for two consecutive years to test the effects of coinoculation of microbes on soil properties. The surface soil from the experimental site was analysed for soil available nutrients, soil enzyme activities and microbial biomass carbon. The treatment of Azospirillum with Trichoderma at the 50% recommended N:P2O5:K2O (NPK) rate (50:25:50 kg ha?1) significantly increased soil available nitrogen (142.81 kg ha?1) by 72.66% over uninoculated control. There was a significant increase in available phosphorus in soil by the inoculation of AM (arbuscular mycorrhizal) fungi with Trichoderma at the 50% recommended NPK rate (41.04 kg ha?1) compared to other treatments. The application of Pseudomonas fluorescens with Trichoderma at the 50% recommended NPK rate significantly increased available iron (19.34 µg g?1) in soil. The treatment of Azospirillum with Trichoderma increased urease enzyme activity at the recommended NPK rate (816.32 μg urea hydrolyzed g?1 soil h?1). Soil application of all cultures at the 50% recommended NPK rate significantly increased dehydrogenase activity (88.63 μg TPF g?1 soil) and β-glucosidase activity (48.82 μg PNP g?1 soil) in soil. Inoculation of Trichoderma alone at the 50% recommended NPK rate significantly increased microbial biomass carbon (3748.85 μg g?1 soil). Thus, the microbial inoculations significantly increased soil available nutrient contents, enzyme activities such as urease, dehydrogenase and β-glucosidase activity and microbial biomass carbon by reducing the amount of the required fertilizer.  相似文献   

17.
Agricultural soil CO2 emissions and their controlling factors have recently received increased attention because of the high potential of carbon sequestration and their importance in soil fertility. Several parameters of soil structure, chemistry, and microbiology were monitored along with soil CO2 emissions in research conducted in soils derived from a glacial till. The investigation was carried out during the 2012 growing season in Northern Germany. Higher potentials of soil CO2 emissions were found in grassland (20.40 µg g?1 dry weight h?1) compared to arable land (5.59 µg g?1 dry weight h?1) within the incubating temperature from 5°C to 40°C and incubating moisture from 30% to 70% water holding capacity (WHC) of soils taken during the growing season. For agricultural soils regardless of pasture and arable management, we suggested nine key factors that influence changes in soil CO2 emissions including soil temperature, metabolic quotient, bulk density, WHC, percentage of silt, bacterial biomass, pH, soil organic carbon, and hot water soluble carbon (glucose equivalent) based on principal component analysis and hierarchical cluster analysis. Slightly different key factors were proposed concerning individual land use types, however, the most important factors for soil CO2 emissions of agricultural soils in Northern Germany were proved to be metabolic quotient and soil temperature. Our results are valuable in providing key influencing factors for soil CO2 emission changes in grassland and arable land with respect to soil respiration, physical status, nutrition supply, and microbe-related parameters.  相似文献   

18.
 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   

19.
The response of microbial biomass carbon (Cmic), nitrogen (Nmic), basal respiration, and the metabolic quotient to 3 years of a natural succession fallow were studied in a field experiment on sandy soil in Northeast Saxony/Germany from 1996 to 1998. Soil samples were taken from Eutric Cambisol and Mollic Cambisol every six weeks during the vegetation period at soil depths of 0—10 and 10—30 cm. The Cmic content in the topsoils increased with time of succession in both soil types. This trend was more distinct in the Mollic Cambisol (70.7 μg g—1 in June 1996 to 270.9 μg g—1 in October 1998 at 0—10 cm) than in the Eutric Cambisol (69.7 μg g—1 in June 1996 to 175.0 μg g—1 in October 1998 at 0—10 cm). By contrast, the Nmic content slightly decreased in the Eutric Cambisol from 18.9 μg g—1 to 17.7 μg g—1 during the same time period. In the Mollic Cambisol, the Nmic increased from 18.8 μg g—1 in spring 1996 to 35.5 μg g—1 in fall 1998, however to a lower extent than the Cmic. Subsequently, the (C:N)mic ratio increased from 4.3 to 5.8 at soil depth of 0—10 cm and from 3.5 to 6.5 at 10—30 cm during the 3‐year‐study at the Eutric Cambisol. In the Mollic Cambisol, the enhancement of (C:N)mic ratio was more pronounced (i.e. from 4.3 to 6.7 at 0—10 cm and from 3.5 to 7.2 at 10—30 cm). Most likely this results from a shift in microbial populations towards a dominance of soil fungi. The already low basal respiration of, on average, 0.26 mg CO2 g—1 (24h)—1 (0—10 cm) in June 1996 decreased with time of succession fallow to 0.15 and 0.22 mg CO2 g—1 (24h)—1 in October 1998 in the Eutric and the Mollic Cambisol, respectively. Thus, the metabolic quotient as an indicator for the efficiency of organic matter turnover in soil was very low in both soils. During the summer months, the metabolic quotients reached minimum levels of ≤ 0.1 μg CO2 C (g Cmic)—1 h—1, probably because of low soil moisture contents. Correlation analyses revealed close relationships between Nmic and total N, Nmic and water content, and Nmic and pH values. These relationships became even more pronounced with the time period of natural succession. For the samples from fall 1998, highly significant correlations were determined between Nmic and total N (coefficients were rs = 0.91***), Nmic and water content (rs = 0.91***), and Nmic and pH value (rs = 0.76***). The values for all biological parameters studied were larger in the Mollic than in the Eutric Cambisol. This indicates higher turnover rates of different C and N fractions in the Mollic Cambisol. In general, set aside of formerly agricultural managed sandy soils resulted in greater Cmic : Nmic ratios and thus, in a change in the microbiological community structure as well as in reduced C and N turnover rates (i.e. low metabolic quotient) under the climatic conditions of the East German lowlands.  相似文献   

20.
Microbial biomass, respiratory activity, and in‐situ substrate decomposition were studied in soils from humid temperate forest ecosystems in SW Germany. The sites cover a wide range of abiotic soil and climatic properties. Microbial biomass and respiration were related to both soil dry mass in individual horizons and to the soil volume in the top 25 cm. Soil microbial properties covered the following ranges: soil microbial biomass: 20 µg C g–1–8.3 mg C g–1 and 14–249 g C m–2, respectively; microbial C–to–total organic C ratio: 0.1%–3.6%; soil respiration: 109–963 mg CO2‐C m–2 h–1; metabolic quotient (qCO2): 1.4–14.7 mg C (g Cmic)–1 h–1; daily in‐situ substrate decomposition rate: 0.17%–2.3%. The main abiotic properties affecting concentrations of microbial biomass differed between forest‐floor/organic horizons and mineral horizons. Whereas microbial biomass decreased with increasing soil moisture and altitude in the forest‐floor/organic horizons, it increased with increasing Ntot content and pH value in the mineral horizons. Quantities of microbial biomass in forest soils appear to be mainly controlled by the quality of the soil organic matter (SOM), i.e., by its C : N ratio, the quantity of Ntot, the soil pH, and also showed an optimum relationship with increasing soil moisture conditions. The ratio of Cmic to Corg was a good indicator of SOM quality. The quality of the SOM (C : N ratio) and soil pH appear to be crucial for the incorporation of C into microbial tissue. The data and functional relations between microbial and abiotic variables from this study provide the basis for a valuation scheme for the function of soils to serve as a habitat for microorganisms.  相似文献   

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