The product from the burning of a combination of carbonaceous materials.

Toxicity to soil microorganisms

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

toxicity to soil microorganisms

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

no data

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Non-GLP compliant, non-guideline experimental study. Study published in a scientific, peer reviewed journal.

Reason / purpose for cross-reference:

reference to same study

Qualifier:

no guideline available

Principles of method if other than guideline:

A laboratory study using microcosms was used for determing the impact of wood ash amendments on soil micro-organisms. The microcosms were later on disturbed with drought.

GLP compliance:

no

Details on sampling:

First sampling 15 weeks after the start of the experiment, second sampling week 17, third sampling week 27, fourth sampling week 54. At each sampling five replicates per treatment were taken.

Details on preparation and application of test substrate:

Humus was collected from a pine forest near the city of Jyväskylä, central Finland, sieved through a 1-cm sieve and autoclaved. After sieving soil pH was 4,2, water content 58 % of fresh mass and loss on ignition 48 %. Because the acidity of the soil increased during autoclaving (pH 3,7), 1,0 g CaCO3 to 1 kg fresh mass soil was added, raising the pH to 4,7. Then the soil was stored in plastic bags for 1 month at room temperature. Litter materials (pH 5,8, water content 46 %, LOI 91 %) consisting on bierch leaves, spruce and pine needles, were cut into pieces, mixed in equal proportions and defaunated by heating (+60 ◦C for 24 h). Half of the material was treated with wood ash which was carefully mixed into the soil and litter, and the other part was left as ash free controls. Each ash treated microcosm received 2,8 g wood ash corresponding to 5000 kg wood ash per hectare. Microbes and microfauna were reonoculated into the systems by adding 5 ml water-soil suspension, which was first filtered through 500 µm and then 45 µm mesh to remove soil macro- and mesofauna.

Test organisms (inoculum):

soil

Total exposure duration:

54 wk

Test temperature:

Incubation conditions were set up to simulate summer (+17°C), autumn (day +7°C, night + 5°C), winter (+2,5-+4°C) and spring (day +7°C, night +5°C).

Nominal and measured concentrations:

Ca 350 mg/kg; Mg 17mg/kg;K 26 mg/kg; P 9 mg/kg; Mn 10 mg/kg; Zn 2,5 mg/kg; Cd 15 mg/kg; Al 12 mg/kg; Cu 72 mg/kg; Fe 9 mg/kg

Reference substance (positive control):

no

Remarks on result:

not measured/tested

Remarks:

Microbial biomass and microbial composition were analysed in the humus soil using the PLFA method (phospholipid fatty acids). The total amount of PLFA was used as an indicator of the microbial biomass, and the sum of PLFAs considered to be predominantly of bacterial origin

Details on results:

Before the drought the PLFAs indicating total microbial and bacterial biomasses were lower in the ash-treated soils than in the ash free soils. After the drought, the PLFAs indicating total microbial, bacterial and fungal biomasses were lower in the ash-treated soils. Ash application also decreased fungal to bacterial ratio.

Reported statistics and error estimates:

- Before the drought the PLFAs indicating total microbial (F=8,21, P<0,05) and bacterial biomasses (F=20,97, P<0,001) were lower in the ash-treated soils than in the ash free soils.
- After the drought, the PLFAs indicating total microbial (F=18,45, P<0,01), bacterial (F=19,49, P< 0,001) and fungal (F=21,56, P<0,001) biomasses were lower in the ash-treated soils.
- Ash application also decreased fungal to bacterial ratio (F=8,35, P<0,05).

The PLFAs indicating total microbial (F=8,21, P< 0,05), and bacterial biomasses (F=20,97, P<0,001) were lower in the ash treated soils than in the ash free soils.

Validity criteria fulfilled:

not applicable

Conclusions:

The microbial community structure and microbial biomass were affected by the ash treatment (biomass was lower in the ash-treated soil).

Executive summary:

A non-GLP, non-guideline laboratory experiment was established to estimate the chronic effects of wood ash amendments on soil micro-organisms. A simulated coniferous forest floor with humus and litter layers, and a seedling of silver birch (Betula pendula) was prepared without and with wood ash amendment corresponding to 5000 kg wood ash per hectar. The microbial biomass and microbial composition were analysed in the humus soil using the PLFA method (phospholipid fatty acids).The microbial community structure and microbial biomass were affected by the ash treatment (biomass was lower in the ash-treated soil).

Reference 2

Endpoint:

toxicity to soil microorganisms

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

May 1999-

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Non-GLP compliant, non guideline experimental study. Study published in a scientific, peer reviewed journal.

Qualifier:

no guideline available

Principles of method if other than guideline:

The effects of wood ash amendments on functional complexicity of the soil decomposer food web and consequently on ecosystem functioning was studied with lysimeters in a field experiment.

GLP compliance:

no

Details on sampling:

The soils outside of lysimeters (experimental plots) and the soils inside the lysimeters were sampled five times during the experiment (weeks 40, 58, 95, 111 and 152). At each sampling two soil samples were taken both from the soil outside and inside of the lysimeters. Microbial biomasses and community structure were analysed.

Details on preparation and application of test substrate:

The forest floor was constructed by spreading sand on the bottom of the lysimeter followed by organic layer consisting of humus and litter. Each ash-treated lysimeter received 24.5 g of wood ash (19.6 g in the humus and 4.9 g in the litter).

Test organisms (inoculum):

soil

Total exposure duration:

152 wk

Test temperature:

Ambient field temperature

Moisture:

Varied from 9.30±3.0 % to 74.4±1.9 % depending on the season and place (inside or outside of lysimeter)

Details on test conditions:

Lysimeters were placed on eight experimental plots of 30 x 30 cm2 in size. Half of the plots had received 3000 kg of wood ash per ha two years prior to the experiment and the other half was left as ash-free control plots. Two to four lysimeters were placed in each experimental plot so that ash-free lysimeters were planted in ash-free control plots. The lysimeters were covered with a 45 µm or 1 mm mesh. Pine seedlings were planted in the center of each lysimeter 40 weeks after the lysimeters were placed in the experimental area.

Nominal and measured concentrations:

The ash used in the experiment contained P 4.2 mg/g, K 13.5 mg/g, Ca 78.5 mg/g, Mg 7 mg/g, Fe 8.6 mg/g, Mn 4.3 mg/g, Zn 947 mg/kg, Cu 189 mg/kg, B 121.5 mg/kg, Al 42.3 mg/kg, Cr 159,8 mg/kg, Ni 31.7 mg/kg, Cd 6.4 mg/kg

Remarks on result:

not measured/tested

Remarks:

The effects of wood ash amendments on functional complexicity of the soil decomposer food web and consequently on ecosystem functioning was studied with lysimeters in a field experiment.

Details on results:

Ash application had a negative effect on soil microbial biomasses as calculated per dry mass of the soil. However, when expressed in relation to the organic matter content, microbial biomasses were unaffected by ash-treatment. Ash-treatment had no effect on fungal-to-bacterial ratio inside the lysimeters. Outside the lysimeters, ash changed neither the microbial biomasses nor fungal-to-bacterial ration compared to ash-free plots. Ash-treatment had a clear effect on the structure of the microbial community in the lysimeters. The substrate utilisation potential of the bacterial community was also affected by the ash-treatment. In the soils outside of the lysimeters, ash-treatment had no influence on the structure of the soil microbial communities.

Reported statistics and error estimates:

- Fungal biomass in the lysimeters with 45 μm mesh (F=12.9,P<0.001) decreased due to ash-treatment.
- Ash-treatment had a clear effect on the structure of the microbial community in the lysimeters. The factor scores of the first PCA-axis of PLFA composition differed clearly between the ash-free and ash-treated lysimeters at each sampling (October 1998:F=36.53,P<0.001; June 1999:F=166.71,P<0.001, October 1999:F=476.54,P<0.001; July 2000:F=251.22,P<0.001). At the October 1998 sampling also the factor scores of the second PCA-axis were separated with respect to ash-treatment (F=5.56,P=0.03).
- The substrate utilisation potential of the bacterial community was also affected by the ash-treatment, which was indicated by the difference between the factor scores of the first PCA-axis of the ash-free and ash-treated mesocosms in the October 1998 (F=35.91,P<0.001) and June 1999 (F=79.70,P<0.001) samplings.

Inside the lysimeters, ash application had a negative effect on soil microbial biomasses as calculated per dry mass of the soil: bacterial biomass in the lysimeters with both 1 mm and 45 μm mesh, and fungal biomass in the lysimeters with 45 μm mesh decreased due to ash-treatment. However, when expressed in relation to the organic matter content of the soil, microbial biomasses were unaffected by the ash-treatment. Ash-treatment had no effect on fungal-to-bacterial ratio inside the lysimeters. Outside the lysimeters, ash changed neither the microbial biomasses nor fungal-to-bacterial ratio compared to the ash-free plots.

Ash-treatment had a clear effect on the structure of the microbial community in the lysimeters. The factor scores of the first PCA-axis of PLFA composition differed clearly between the ash-free and ash-treated lysimeters at each sampling (see above). At the October 1998 sampling also the factor scores of the second PCA-axis were separated with respect to ash-treatment. The substrate utilisation potential of the bacterial community was also affected by the ash-treatment, which was indicated by the difference between the factor scores of the first PCA-axis of the ash-free and ash-treated mesocosms in the October 1998 and June 1999 samplings. In the soils outside the lysimeters, ash-treatment had no influence on the structure of the soil microbial communities.

Conclusions:

The complexity of the decomposer food web was manipulated by application of wood ash. Clear changes in the composition of the soil microbial community after ash application were observed, but the fungal-to-bacterial ratio remained unchanged. Wood ash-treatment increased mainly the relative abundance of PLFAs common in Gram-negative bacteria. However, the reason for the observed change in the substrate utilisation potential after wood ash application may also be the altered humus pH changing the incubation conditions on Biolog plates instead of the sensitivity of the Biolog analysis in characterising this kind of high organic matter containing humus. However, the number of nematodes, and especially number of bacterial feeding nematodes increased in the ash-treated soils, which indicates enhanced microbial production in these soils.

Executive summary:

A non GLP, non Guideline 3 yr experiment, using field lysimeters with seedlings of Scots pine (Pinus sylvestris) growing in raw humus, was established to study how functional complexity of the soil decomposer food web affects ecosystem functioning. The functional complexity of the decomposer system was manipulated by treating half of the lysimeters with wood ash. To test whether altering functional complexity of the decomposer community is related to the system's ability to resist disturbance, the lysimeters were later on disturbed with drought. The structure and biomass of soil fauna and soil microbial communities were analysed. Wood ash increased the number of nematodes and changed microbial community structure. The system's ability to resist disturbance was not affected by the treatments. The changes in the structure and biomass of soil fauna were not reflected as changes in system functioning.

Reference 3

Endpoint:

toxicity to soil microorganisms

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

2002

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Non-GLP compliant, non-guideline experimental study. Study published in a scientific, peer reviewed journal.

Qualifier:

no guideline available

Principles of method if other than guideline:

A laboratory study using microcosms and humus soil from 60 years old Scots pine stand of Empetrum-Calluna site type.

GLP compliance:

no

Test organisms (inoculum):

soil

Total exposure duration:

21 d

Moisture:

60% WHC

Reference substance (positive control):

no

Remarks on result:

not measured/tested

Remarks:

xperiment using microcosms was established in order to separate the effects of DOC and/or pH on soil microbial activity using suspensions of humus extracts and bacteria that had not previously been exposed to wood ash fertilization.

The addition of wood ash increased the DOC concentration ca. four times over the control DOC value. This increase was already observed on the second incubation day when the DOC concentration was 40.1±5.0 mg C l⁻¹in the ash treatment and 10.2±0.2 mg C l⁻¹in the control. In both treatments the DOC concentration remained quite constant during the incubation (data not shown). At the end of the experiment the DOC concentration in the ash treatment was 32.5±2.0 mg C l⁻¹, which was significantly higher (F=4216.3,P<0.001) than that in the control (9.1±0.8 mg C l⁻¹).

Conclusions:

Direct and indirect pH effects are mainly responsible for the increase in microbial activities following ash fertilization. At neutral pH, the microbial activities are stimulated as compared to acidic conditions, the concentration of DOC is higher and its quality is enhanced. The increase in microbial activity is due the preferential growth of certain members of the bacterial community that are favoured by a higher pH rather than all members being equally stimulated.

Executive summary:

A non GLP, non-guideline laboratory experiment using microcosms was established in order to separate the effects of DOC and/or pH on soil microbial activity using suspensions of humus extracts and bacteria that had not previously been exposed to wood ash fertilization.

Wood ash fertilization increases the pH and concentration of dissolved organiccarbon(DOC) in the soil solution and enhances the activity of soil microorganisms.

Both DOC and pH influence microbial activity and a subset of the bacterial community. The addition of wood ash increased the DOC concentration.

Description of key information

Toxicity of ash to soil micro-organisms was estimated based on three scientific publications from literature. In the first laboratory investigation microcosms was used for determing the impact of wood ash amendments on soil micro-organisms. In the second investigation, the impact of the ash treatment effects on the bacterial community was studied in microcosm. In the third investigation, the effects of wood ash amendments on functional complexicity of the soil decomposer food web and consequently on ecosystem functioning was studied with lysimeters in a field experiment.
Wood ash application induces increase in microbial activity, decrease in microbial biomass and a change in bacterial community structure. 

Additional information

Microbial communities respond in many ways to changes in pH and because of that, ash amendment has a large impact on the microbiology in the upper part of the soil. Wood ash fertilization increases the pH and concentration of dissolved organic carbon (DOC) in the soil solution and enhances the activity of soil microorganisms.The type and species distribution will change and microbial processes will be influenced.The changes in the structure and biomass of soil fauna were not reflected as changes in system functioning.