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Use of microbial inoculations for soil revitalization
As a consequence of extensive brown coal mining, thousands of hectars of the north western part of Bohemia are covered by spoil banks. The surface of the spoil banks is mostly formed by miocene clays with unfavourable physical properties, especially of high compactness and low water permeability. Successfull establishment of a vegetation cover at these stands is influenced by factors such as nutrient availability, pH, humidity and microbial activity of the substrate (Visser 1985). Soil microbial communities act in many important biogeochemical processes, which are indespensible for the soil development and plant growth (Pfleger et al. 1994). Important components of the soil microbial communitiy are symbiotic arbuscular mycorrhiza fungi (AMF), colonising the roots of the majority of terrestrial plants, and rhizospheric bacteria promoting plant growth (PGPR) inhabiting the plant rhizosphere, the root surface and intercellular root spaces.
AM fungi can influence the growth and survival of plants by reducing stresses connected to nutrient deficits, unfavourable water conditions, soil structure, pH, toxic metals, soil organic matter deficits and biotic factors such as soil pathogens (Sylvia and Williams 1992). Enhancement of nutrient uptake by mycorrhizal plants is particularly facilitated by extraradical mycelium (ERM) expanding into a much larger soil volume than the root system and reaching up to several dozens metres per gram of soil (Jakobsen et al., 1992). Li et al. (1991b) estimated than more than 70-80 % of the total plant phosphorus content can be taken up via ERM. Under low soil pH, AMF can positively affect nitrogen uptake from ammonium ions (Smith and Read 1997). AM fungi can also enhance resistance of host plants to drought, especially by incresing the absorption surface of the root system (Hardie 1985).
PGPR can influence plant growth in several manners: by fixation of aerial nitrogen, increasing nutrient availability in the rhizosphere, affecting root growth and morphology or support the plant symbiosis with other benefitial microorganisms (Vessey 2003). On the other hand, symbiosis with AMF can increase the fixation of aerial nitrogen by symbiotic Rhizobium bacteria (Barea et al., 1989).
AMF inhabit almost all undisturbed ecosystems, however, mechanical or chemical disturbance of soil can lead to the reduction or even elimination of their populations (Sylvia and Williams 1992, Schafer and Schoeneberger 1994). Mechanical disturbance of soil connected with mine activities has been proved to cause a decrease in AMF spore numbers and drop in their species diversity. Densities of AM spores in young spoil banks and in abandoned surface mines were considerably lower than at surrounding undisturbed areas, and AMF root colonisation of sawn grasses did not reach levels similar to those before disturbation until 3 to 7 years after mining (Waaland and Allen 1997, Mott and Zuberer 1987). Most authors agreee that the amendment of top soil into the waste substrate can be a suitable way for the introduction of native AMF (Lambert and Cole 1980, Lore and Williams 1987), however, mechanical disturbance of the top soil and its long-term storage lead to a reduction in its mycorrhizal inoculation potential (e.g. Miller et al 1985, Harris et al. 1987).
Another way of biological revitalisation of waste substrates consists in applying various types of organic matter. Johnson and McGraw (1988 a,b) studied the succesion of AM fungi on recultivated waste substrate after ore-mining, where sewage slugdes from paper-mills or straw had been applied. After recultivation, fast colonisation by AM fungi was observed. After two vegetation seasons, spore densities were 10- to 100-fold higher than in unaffected grass ecosystems. Noyd et al. (1996) observed that the amendment of composted manure into waste substrate after ore-mining was connected to higher plant cover and biomass, higher spore density and mycorrhizal infectivity of the substrate. Saif (1986) pointed out that farm organic matter can positively influence AM fungi also undirectly via its effect on soil structure, nutrient mineralization and water capacity of the soil. It has been proved that hyphae of AM fungi can transport significant amount of phosphorus originating from decaying organic matter towards host plant (Joner and Jakobsen 1994, 1995b).
Specific tasks
Task 1
Verification of the potential of microbial inoculations for the revitalizations of spoil banks after brown coal mining with selected model crops
Task 2
Development of an optimal regime of microbial inoculation and fertilization for the establishment of stable vegetation cover in order to economise the costs for the management of recultivated areas
Task 3
Evaluation of the effect of cultivated crops, microbial inoculations and fertilization on the revitalization of degraded soils
Conception and Methods
Targeted inoculation with soil microorganisms capable to support plant growth will be exploited for improving the effectiveness of recultivation procedures for spoil banks after brown coal mining. Current recultivation procedures based on the selection of appropriate crop species and fertilisation regime will be complemented with introduction of microbial communities with the aim to increase the crops' yield, accelerate the process of soil revitalisation and decrease the recultivation costs. The recultivation procedure will be optimised for 2 model crop species utilised in the recultivation of degraded soils, Cannabis sativa and Phalaris arundinacea. Fertilisation regime and microbial inoculum will be devised for each crop species separately. The microbial inoculum will contain symbiotic arbuscular mycorrhizal fungi (AMF) as its main component and nitrogen fixing soil bacteria Azotobacter, phosphorus solubilising bacteria and symbiotic nitrogen fixing bacteria Sinorrhizobium meliloti as supporting components. The composition of the microbial inoculum will be optimised for the given conditions especially by selecting effective AMF isolates.
In the first step of the project, the microbial inoculum as the key component of the revitalisation system will be optimised in pot experiments. The optimisation will include a pre-selection of AMF isolates best adapted to the soil conditions of the given type of spoil banks. In addition to isolates from the collection of the Institute of Botany, AMF strains isolated from the direct vicinity of the model locality will be included into the pre-selection. The AM fungal mixture will be further optimised for each of the model crop species separately and in interaction with the supporting bacteria and fertilisation. Detection and identification of the inoculated microorganisms in the soil and plant roots will enable to economise the composition of the microbial inoculation mixture so that it will contain only microorganisms actually proliferating in the system.
In the second step of the project, the effectiveness of the revitalisation systems, designed on the basis of pot experiments, will be verified in field experiments on the model locality. The aim of the experiments is to obtain reference data essential for further applications of the devised system. The 3-years-experimental period guarantees representative data and enables the generalisation of the results in correlation with climatic data.
A complex monitoring of the field experiments will include recording of plant growth and develepment parameters as well as of the chemical and microbiological soil parameters in accordance with the requirements on complex revitalisation systems.
In addition to the yield parameters of the cultivated crops, qualitative biomass parameters will be recorded such as the health state and biomass contents of nutrients and risk elements. In the roots and soil, the inoculated microorganisms will be detected by means of molecular methods to confirm the establishment of their populations and the effectiveness of the inoculation. Chemical and microbiological parameters of the soil (e.g. contents of organic carbon and available phosphorus, soil respiration, inoculation potential) will be recorded, which can serve as indicators of the soil quality.
The complex documentation of the effectiveness of the designed recultivation procedures will prove on a particular case the potential of microbial inoculations in increasing the effectiveness of revitalisation procedures for degraded soils and decreasing their costs.
