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1.
We measured microbial biomass C and soil organic C in soils from one grassland and two arable sites at depths of between 0 and 90 cm. The microbial biomass C content decreased from a maximum of 1147 (0–10 cm layer) to 24 g g-1 soil (70–90 cm layer) at the grassland site, from 178 (acidic site) and 264 g g-1 soil (neutral site) at 10–20 cm to values of between 13 and 12 g g-1 soil (70–90 cm layer) at the two arable sites. No significant depth gradient was observed within the plough layer (0–30 cm depth) for biomass C and soil organic C contents. In general, the microbial biomass C to soil organic C ratio decreased with depth from a maximum of between 1.4 and 2.6% to a minimum of between 0.5 and 0.7% at 70–90 cm in the three soils. Over a 24-week incubation period at 25°C, we examined the survival of microbial biomass in our three soils at depths of between 0 and 90 cm without external substrate. At the end of the incubation experiment, the contents of microbial biomass C at 0–30 cm were significantly lower than the initial values. At depths of between 30 and 90 cm, the microbial biomass C content showed no significant decline in any of the four soils and remained constant up to the end of the experiment. On average, 5.8% of soil organic C was mineralized at 0–30 cm in the three soils and 4.8% at 30–90 cm. Generally, the metabolic quotient qCO2 values increased with depth and were especially large at 70–90 cm in depth.  相似文献   

2.
In the mountain rainforest region of the South Ecuadorian Andes natural forests have often been converted to pastures by slash-and-burn practice. With advanced pasture age the pasture grasses are increasingly replaced by the tropical bracken leading to the abandonment of the sites. To improve pasture productivity a fertilisation experiment with urea was established. The effects of urea on soil organic matter (SOM) mineralisation and microbial community structure in top soil (0–5 cm depth) of an active and abandoned pasture site have been investigated in laboratory incubation experiments. Either 14C- or 15N-labelled urea (74 mg urea-N kg−1 dw soil) was added to track the fate of 14C into CO2 or microbial biomass and that of 15N into the KCl-extractable NH4-N or NO3-N or microbial biomass pool. The soil microbial community structure was assessed using phospholipid fatty acid analysis (PLFA). In a second experiment two levels of 14C-labelled urea (74 and 110 mg urea-N kg−1 dw soil) were added to soil from 5 to 10 cm depth of the respective sites. Urea fertilisation accelerated the mineralisation of SOC directly after addition up to 17% compared to the non-fertilised control after 14 days of incubation. The larger the amount of N potentially available per unit of microbial biomass N the larger was the positive priming effect. Since in average 80% of the urea-C had been mineralised already 1 day after amendment, the priming effect was strong enough to cause a net loss of soil C. Although the structure of the microbial community was significantly different between sites, urea fertilisation induced the same alteration in microbial community composition: towards a relative lower abundance of PLFA marker characteristic of Gram-positive bacteria and a higher one of those typical of Gram-negative bacteria and fungi. This change was positively correlated with the increase in NH4, NO3 and DON availability. In addition to the activation of different microbial groups the abolishment of energy limitation of the microbes seemed to be an important mechanism for the enhanced mineralisation of SOM.  相似文献   

3.
A microcosm was used to study the effect of the endogeic earthworm Aporrectodea caliginosa (Savigny) on the use of C by microorganisms in a calcareous beech forest soil and its dependence on temperature (5–25%C). Inclusion of 14C-labelled beech leaf litter made it possible to differentiate between C use by litter-colonizing microflora and by autochthonous soil microflora. The effect of temperature on the soil microbial biomass 12C was confined to a significant increase at 15 and 20°C. The size of the 14C-labelled microbial biomass, in contrast, was positively correlated with temperature. The 12C mineralization increased exponentially with temperature. The relationship between 14C mineralization and temperature, in contrast, followed a logistic curve. Significant main effects of A. caliginosa were confined to 12C mineralization, reflecting an increase in 12CO2–C production in the earthworm treatments. The earthworm effects on 12CO2–C production and on 14C incorporation of the microflora were not linear. The effect of A. caliginosa on 12CO2–C production was most pronouned at intermediate temperatures. It is concluded that temperature alterations affect the microbial use of different C sources in different ways and that the temperature effects can be significantly modified by endogeic earthworms.  相似文献   

4.
The effect of endogeic earthworms (Octolasion tyrtaeum) and the availability of clay (Montmorillonite) on the mobilization and stabilization of uniformly 14C-labelled catechol mixed into arable and forest soil was investigated in a short- and a long-term microcosm experiment. By using arable and forest soil the effect of earthworms and clay in soils differing in the saturation of the mineral matrix with organic matter was investigated. In the short-term experiment microcosms were destructively sampled when the soil had been transformed into casts. In the long-term experiment earthworm casts produced during 7 days and non-processed soil were incubated for three further months. Production of CO2 and 14CO2 were measured at regular intervals. Accumulation of 14C in humic fractions (DOM, fulvic acids, humic acids and humin) of the casts and the non-processed soil and incorporation of 14C into earthworm tissue were determined.Incorporation of 14C into earthworm tissue was low, with 0.1 and 0.44% recovered in the short- and long-term experiment, respectively, suggesting that endogeic earthworms preferentially assimilate non-phenolic soil carbon. Cumulative production of CO2-C was significantly increased in casts produced from the arable soil, but lower in casts produced from the forest soil; generally, the production of CO2-C was higher in forest than in arable soil. Both soils differed in the pattern of 14CO2-C production; initially it was higher in the forest soil than in the arable soil, whereas later the opposite was true. Octolasion tyrtaeum did not affect 14CO2-C production in the forest soil, but increased it in the arable soil early in the experiment; clay counteracted this effect. Clay and O. tyrtaeum did not affect integration of 14C into humic fractions of the forest soil. In contrast, in the arable soil O. tyrtaeum increased the amount of 14C in the labile fractions, whereas clay increased it in the humin fraction.The results indicate that endogeic earthworms increase microbial activity and thus mineralization of phenolic compounds, whereas clay decreases it presumably by binding phenolic compounds to clay particles when passing through the earthworm gut. Endogeic earthworms and clay are only of minor importance for the fate of catechol in soils with high organic matter, clay and microbial biomass concentrations, but in contrast affect the fate of phenolic compounds in low clay soils.  相似文献   

5.
In order to study the influence of salinity on the biological activity of soils, experiments were performed in a saline alkaline soil from Tunisia (mediterranean semi-arid climate) and compared with results of similar experiments performed in a pelosol from a semi-continental climate (Lorraine, France). Both soils had received 14C-labelled maize straw.The microbial biomass was estimated by a modified Jenkinson's method and also by measurements of ATP content. The microbial activity was determined by measurements of total and 14CO2 evolved.The results have shown an inverse correlation between the salinity determined by electrical conductivity and the biomass estimations and its activity. The higher ATP con tent (141.5 ng · 100 g?1 soil) was observed in the pelosol and the lower (99.4 ng · 100 g?1) in the saline soil. Simultaneously and respectively in the pelosol and the saline soil the biological carbon evolved was 114 and 54 mgC 100 g?1 soil and the average rate of 14C mineralization was 0.82 and 0.45 mgC · 100 g?1 soil.Results have also shown that CO2 evolved after sterilization and reinoculation is not only provided by mineralization of microbial biomass during fumigation but also from interaction between organic-matter and CHCl3; this interaction is more intense in the saline soil.  相似文献   

6.
Summary A 2-year study (1983–1984 to 1984–1985) was conducted to estimate temporal and seasonal changes and the effects of fertiliser on some soil chemical, biochemical and microbiological characteristics. The soil used was a Typic Vitrandept under grazed pasture. Soil samples were taken regularly to a depth of 75 mm from paired unfertilised and fertilised (500 kg ha– 30% potassic superphosphate) plots. Except for organic C, fertiliser had little or no effect on the characteristics measured. Organic C averaged about 9.2% in unfertilised soil and was about 0.3% higher in the fertilised soil. The size of the microbial biomass fluctuated widely in the 1st year (3000 g C g–1 in February to 1300 g C g–1 in September) but there was less variation in the 2nd year (range 1900 g C g–1 to 2500 g C g–1 soil). CO2 production values (10- to 20-day estimates averaged 600 g of CO2-C g–1 soil) were generally higher in spring compared to the rest of the year. Water extractable C increased over winter and declined through spring in both years (range 50 g C g–1 soil to 150 g C g–1 soil). Mineral-N flush values were higher in summer (300 g N g–1 soil) and lower in winter months (200 g N g–1 soil). The pattern of variation of microbial N values was one of gradual accumulation followed by rapid decline. This rapid decline in values occurred in spring and autumn (range 130–220 g N g–1 soil). N mineralisation and bicarbonate-extractable N showed no clear trend; these values ranged from 100–200 and 122–190 g N g–1 soil, respectively. There was a significant correlation (0.1%) between N mineralisation and bicarbonate-extractable N in the late summer-autumn-early winter period (February–August) in both years but not in spring. These results and their relationships to climatic factors and rates of pasture production are discussed.  相似文献   

7.
Root activity and carbon metabolism in soils   总被引：4，自引：0，他引：4  
Summary Two different soils were amended with 14C-labelled plant material and incubated under controlled laboratory conditions for 2 years. Half the samples were cropped with wheat (Triticum aestivum) 10 times in succession. At flowering, the wheat was harvested and the old roots removed from the soil, so that the soil was continuously occupied by predominantly active root systems. The remaining samples were maintained without plants under the same conditions. During the initial stages of high microbial activity, due to decomposition of the labile compounds, the size of the total microbial biomass was comparable for both treatments, and the metabolic quotient (qCO2-C = mg CO2-C·mg–1 Biomass C·h–1) was increased by the plants. During the subsequent low-activity decomposition stages, after the labile compounds had been progressively mineralized, the biomass was multiplied by a factor of 2–4 in the presence of plants compared to the bare soils. Nevertheless, qCO2-C tended to reach similar low values with both treatments. The 14C-labelled biomass was reduced by the presence of roots and qCO2-14C was increased. The significance of these results obtained from a model experiment is discussed in terms of (1) the variation in the substrate originating from the roots and controlled by the plant physiology, (2) nutrient availability for plants and microorganisms, (3) soil biotic capacities and (4) increased microbial turnover rates induced by the roots.  相似文献   

8.
 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   

9.
C and N mineralization was quantified in an incubation experiment with two samples containing different amounts of microbial biomass. The samples from two layers (0–20, 20–30 cm) of an arable luvisol from loess were fertilized with nitrate, mixed with 14C-labelled straw and incubated for 52 days at different O2 levels. Decreasing O2 concentrations (21, 2, 1 and 0% O2) in soil conducted a decrease in C and N mineralization. More C and N were mineralized in samples with a higher initial microbial biomass. The differences in microbial biomass were still present at the end of the experiment, but more proliferation was detected in samples with the lower initial microbial biomass, leading to equal ratios between microbial biomass-C and soil organic C in both soils.  相似文献   

10.
The effect of soil aeration status on carbon partitioning of a labelled organic substrate (14C-[U]-glucose) into CO2, microbial biomass, and extra-cellular metabolites is described. The soil was incubated in a continuous flow incubation apparatus under four different aeration conditions: (1) permanently aerobic, (2) permanently anaerobic, (3) shifted from anaerobic to aerobic, and (4) shifted from aerobic to anaerobic. The soil was pre-incubated for 10 days either under aerobic or under anaerobic conditions. Afterwards, glucose was added (315 g C g–1) and the soils were incubated for 72 h according to four treatments: aerobic or anaerobic conditions maintained, aerobic conditions shifted to anaerobic conditions and anaerobic conditions shifted to aerobic conditions. Carbon partitioning was measured 0, 8, 16, 24, 48 and 72 h after the glucose addition. In permanently aerobic conditions, the largest part of the consumed glucose was built into microbial biomass (72%), much less was mineralised to CO2 (27%), and only a negligible portion was transformed to soluble extra-cellular metabolites. Microbial metabolism was strongly inhibited when aeration conditions were changed from aerobic to anaerobic, with only about 35% of the added glucose consumed during the incubation. The consumed glucose was transformed proportionally to microbial biomass and CO2. In permanently anaerobic conditions, 42% of the consumed glucose was transformed into microbial biomass, 30% to CO2, and 28% to extra-cellular metabolites. After a shift of anaerobic to aerobic conditions, microbial metabolism was not suppressed and the consumed glucose was transformed mainly to microbial biomass (75%) and CO2 (23%). Concomitant mineralisation of soil organic carbon was always lower in anaerobic than in aerobic conditions.  相似文献   

11.
Summary Mineral N concentrations ranged from 133.1 to 167.8 g g-1 dry soil in fresh casts of the endogeic earthworm Pontoscolex corethrurus fed on an Amazonian Ultisol; this was approximately five times the concentration in non-ingested soil. Most of this N was in the form of NH inf4 sup+ . N also accumulated in microbial biomass, which increased from a control value of 10.5–11.3 to 67.5–74.1 g g-1 in fresh casts. During a 16-day incubation, part of the NH inf4 sup+ -N was nitrified and/or transferred to the microbial biomass. Total labile N (i.e., mineral+biomas N) decreased sharply at first (ca. 50% in the first 12 h), and then more slowly. The exact fate of this N (microbial metabolites, denitrification, or volatilization) is not known. After 16 days, the overall N content of the casts was still 28% higher than that of the control soil. Incubation of the soil before ingestion by the earthworms significantly increased the production of NH inf4 sup+ in casts. We calculate that in a humid tropical pasture, 50–100 kg mineral N may be produced annually in earthworm casts. Part of this N may be conserved in the compact structure of the cast where the cast is not in close contact with plant roots.  相似文献   

12.
During the first few days after rewetting of an air-dried soil (AD-RW), microbial activity increases compared to that in the original moist soil, causing increased mineralisation (a flush) of soil organic carbon (C) and other nutrients. The AD-RW flush is believed to be derived from the enhanced mineralisation of both non-biomass soil organic matter (due to its physical release and enhanced availability) and microbial biomass killed during drying and rewetting. Our aim was to determine the effects of AD-RW on the mineralisation of soil organic matter and microbial biomass during and after repeated AD-RW cycles and to quantify their proportions in the CO2-C flushes that resulted. To do this, a UK grassland soil was amended with 14C-labelled glucose to label the biomass and then given five AD-RW cycles, each followed by 7 d incubation at 25 °C and 50% water holding capacity. Each AD-RW cycle increased the amount of CO2-C evolved (varying from 83 to 240 μg g−1 soil), compared to the control with, overall, less CO2-C being evolved as the number of AD-RW cycles increased. In the first cycle, the amount of biomass C decreased by 44% and microbial ATP by 70% while concentrations of extractable C nearly doubled. However, all rapidly recovered and within 1.3 d after rewetting, biomass C was 87% and ATP was 78% of the initial concentrations measured prior to air-drying. Similarly, by 2 d, extractable organic C had decreased to a similar concentration to the original. After the five AD-RW cycles, the amounts of total and 14C-labelled biomass C remaining in the soil accounted for 60 and 40% of those in the similarly incubated control soil, respectively. Soil biomass ATP concentrations following the first AD-RW cycle remained remarkably constant (ranging from about 10 to 14 μmol ATP g−1 biomass C) and very similar to the concentration in the fresh soil prior to air-drying. We developed a simple mathematical procedure to estimate the proportion of CO2-C derived from biomass C and non-biomass C during AD-RW. From it, we estimate that, over the five AD-RW cycles, about 60% of the CO2-C evolved came from mineralisation of non-biomass organic C and the remainder from the biomass C itself.  相似文献   

13.
The effects of soil texture (silt loam or sandy loam) and cultivation practice (green manure) on the size and spatial distribution of the microbial biomass and its metabolic quotient were investigated in soils planted with a permanent row crop of hops (Humulus lupulus). The soil both between and in the plant rows was sampled at three different depths (0–10, 10–20, and 20–30 cm). The silt loam had a higher overall microbial biomass C concentration (260 g g-1) than the sandy loam (185 g g-1), whereas the sandy loam had a higher (3.1 g CO2-C mg-1 microbial Ch-1) metabolic quotient than the silt loam (2.6 g CO2-C mg-1 microbial C h-1), on average over depth (0–30 cm) and over all treatments. There was a sharp decrease in the microbial biomass with increasing depth for all plots. However, this was more pronounced in the silt loam than in the sandy loam. There was no distinct influence of sampling depth on the metabolic quotient. The microbial biomass was considerably higher in the rows than between the rows, especially in the silt loam plots. There was no significant difference between plots without green manure and plots with green manure for either the microbial biomass or the metabolic quotient.  相似文献   

14.
Ergosterol and microbial biomass C were measured in 26 arable, 16 grassland and 30 forest soils. The ergosterol content ranged from 0.75 to 12.94 g g-1 soil. The geometric mean ergosterol content of grassland and forest soils was around 5.5 g g-1, that of the arable soils 2.14 g g-1. The ergosterol was significantly correlated with biomass C in the entire group of soils, but not in the subgroups of grassland and forest soils. The geometric mean of the ergosterol: microbial biomass C ratio was 6.0 mg g-1, increasing in the order grassland (5.1), arable land (5.4) and woodland (7.2). The ergosterol:microbial biomass C ratio had a strong negative relationship with the decreasing cation exchange capacity and soil pH, indicating that the fungal part of the total microbial biomass in soils increased when the buffer capacity decreased. The average ergosterol concentration calculated from literature data was 5.1 mg g-1 fungal dry weight. Assuming that fungi contain 46% C, the conversion factor from micrograms ergosterol to micrograms fungal biomass C is 90. For soil samples, neither saponification of the extract nor the more effective direct saponification during extraction seems to be really necessary.  相似文献   

15.
The biogas production process generates as side-products biogas residues containing microbial biomass which could contribute to soil organic matter formation or induce CO2 emissions when applied to arable soil as fertilizer. Using an isotope labelling approach, we labelled the microbial biomass in biogas residues, mainly G+ bacteria and methanogenic archaea via KH13CO3, and traced the fate of microbial biomass carbon in soil with an incubation experiment lasting 378 days. Within the first seven days, 40% of the carbon was rapidly mineralized and after that point mineralization continued, reaching 65% by the end of the experiment. Carbon mineralization data with 93% recovery could be fitted to a two-pool degradation model which estimated proportions and degradation rate constants of readily and slowly degrading pools. About 49% of the carbon was in the slowly degrading pool with a half-life of 1.9 years, suggesting mid-term contribution to living and non-living soil organic matter formation. Biogas residues caused a priming effect at the beginning, thus their intensive application should be avoided.  相似文献   

16.
Our aim was to determine whether the soil microbial biomass, which has developed naturally over many years in a given ecosystem, is specially adapted to metabolize the plant‐derived substrate C of the ecosystem within which it developed or whether the nature of recently added substrate is the more important factor. To examine this, soils from three sites in close proximity (woodland, grassland and arable from the Broadbalk Experiment at Rothamsted Research, Harpenden, UK) were each amended with air‐dried wheat straw (Triticum aestivum), ryegrass leaves (Lolium perenne) or woodland leaf litter (mainly Quercus robur and Fagus sylvatica) in a fully replicated 3 × 3 factorial laboratory experiment. The initial mineralization rates (evolved CO2‐C) were determined during the first 6.5 hours and again, together with the amount of microbial biomass synthesized (microbial biomass C), at 7, 14, 21, 30 and 49 days of incubation. The hourly rate of CO2‐C production during the first 6.5 hours was slowest following leaf litter addition, while the added grass gave the fastest rates of CO2‐C evolution both within and between soils. Ryegrass addition to the arable soil led to approximately four times more CO2‐C being evolved than when it was added to the woodland soil, at an overall rate in the arable soils of 41 μg C g?1 soil hour?1. In each soil, the net amounts of CO2‐C produced were in the order grass > straw > leaf litter. In each case, the amount produced by the added leaf litter was significantly less (P < 0.05) than either the added grass or straw. Overall, the trend was for much slower rates of mineralization of all substrates in the woodland soil than in either the arable or grassland soils. During 49 days of incubation in the woodland and grassland soils, the net total amounts of CO2‐C evolved differed significantly (P < 0.01), with grass > straw > leaf litter, respectively. In the arable soil, the amounts of CO2‐C evolved from added grass and straw were significantly larger (P < 0.01) than from the leaf litter treatment. Our findings indicated that the amounts of CO2‐C evolved were not related to soil management or to the size of the original biomass but to the substrate type. The amount of biomass C synthesized was also in the order grass > straw > leaf litter, at all stages of incubation in the woodland and grassland soil. In the arable soil, the same effect was observed up to 14 days, and for the rest of the incubation the biomass C synthesized was in the order grass > straw > leaf litter. Up to three times more biomass C was synthesized from the added grass than from the other substrates in all soils throughout the incubation. The maximum biomass synthesis efficiency was obtained with grass (7% of added C). Overall, the woodland soil was most efficient at synthesizing biomass C and the arable soil the least. We conclude that substrate type was the overriding factor that determined the amount of new soil microbial biomass synthesized. Mineralization of substrate C by soil microorganisms was also influenced mainly by substrate type and less by soil management or size of original biomass.  相似文献   

17.
Changes in the soil microbial biomass following applications of farmyard manure and inorganic fertilizer, alone and in combination, were studied for two annual cycles in a rice-lentil crop sequence grown under rainfed tropical dryland conditions. During the two annual cycles the microbial biomass C range (g g-1) was 146–241 (x = 204), 191–301 (245), 244–382 (305), and 294–440 (365) in control, fertilizer, manure and manure+fertilizer plots, respectively. The corresponding ranges for microbial biomass N (g g-1) were 16.5–21.0 (19.5), 20.4–38.2 (26.0), 23.0–34.6 (27.0) and 26.2–42.4 (33.3), and for microbial biomass P (g g-1) 4.4–8.2 (7.0) 6.0–11.2 (9.6), 11.2–22.0 (17.0), and 10.0–25.4 (18.3). The maximum increase in the microbial biomass, due to these inputs was observed under the manure+fertilizer treatment followed, in decreasing order, by manure alone and fertilizer alone. Within individual crop periods the levels of microbial biomass decreased sharply from the seedling to the flowering stage and then increased slightly with crop maturity. The maximum levels of microbial biomass C and P were observed during the summer fallow. The maximum accumulation of microbial biomass N occurred in the early rainy season, immediately after the soil amendments. Microbial biomass C, N, and P were positively related to each other throughout the annual cycle.  相似文献   

18.
Decomposition rates of the [2-14C]-glucose and [2-14C]-glycine in four different soils of the long-term field trial of Moscow were investigated in a 3-months laboratory experiment in which 14CO2 respiration was measured. A model with three decomposition components and two distribution parameters was developed and validated with the data of the experiment. The decay rate constants of free [2-14C]-glucose (4–32 day-1) were slower than those of [2-14C]-glycine (16–44 day-1). The calculated use efficiency for microbial biosynthesis of the second carbon atom was 47% for glucose and 31% for glycine. The potential half-life of labelled carbon in the microbial soil biomass ranged from 0.6 to 4.4 days, depending on the soil type and the initial amount of added substrate. The calculated total utilisation of carbon by the soil biomass from glycine was about 2–5 times lower than that of glucose.The modelled 14C incorporation into the microbial soil biomass reached its maximum on the first day of the incubation experiment and did not exceed 22% of the 14C input. Both of the investigated substances decomposed most rapidly in the soil samples from sites that have not being fertilised with organic or mineral fertilisers during an 81-years period.  相似文献   

19.
A method is proposed for studying the dynamic behaviour of the soil microbial population involved in the degradation of 2,4-D. The method is based on in situ specific-labelling of that population following treatment of the soil with 14C-labelled herbicide and investigating the kinetics of the incorporation of radioactivity by the soil microflora in treated soil samples subjected to the chloroform-fumigation technique after varying periods of exposure. Non-degraded herbicide still present in the soil after fumigation did not affect the overall flush of CO2 and was not further broken down at a sufficient rate to appreciably contribute to 14CO2 evolution. The validity of the method to assess the soil biomass of the 2,4-D degrading population together with its time variations is discussed in relation to the position of the 14C on the pesticide molecule.  相似文献   

20.
Summary The effects of simulated acid rain on litter decomposition in a calcareous soil (pHH 2 O 5.8) were studied. Litterbags (45 m and 1 mm mesh size) containing freshly fallen beech leaf litter were exposed to different concentrations of acid in a beech forest on limestone (Göttinger Wald. Germany) for 1 year. Loss of C, the ash content, and CO2–C production were measured at the end of the experiment. Further tests measured the ability of the litter-colonizing microflora to metabolize 14C-labelled beech leaf litter and hyphae. The simulated acid rain strongly reduced CO2–C and 14CO2–C production in the litter. This depression in production was very strong when the input of protons was 1.5 times greater than the normal acid deposition, but comparatively low when the input was 32 times greater. acid deposition may thus cause a very strong accumulation of primary and secondary C compounds in the litter layer of base-rich soils, even with a moderate increase in proton input. The presence of mesofauna significantly reduced the ability of the acid rain to inhibit C mineralization. The ash content to the 1-mm litterbags indicated that this was largely due to transport of base-rich mineral soil into the litter.  相似文献   

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