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Summary THE ANTHROPOGENIC ECOLOGY OF SOIL FUNGI

  Microscopic fungi take part in the major soil processes, primarily in the destruction of organic compounds in ecosystems, and also participate in various processes of biogeochemical transformation in soils of mineral elements, such as N, P, K, S, etc.
At the same time soil fungi are major components of food chains in soils. In total, their influence on other organisms in terrestrial ecosystems may be great.

Soil - is one of the most complex inhabitancies on the Earth. Fungi can exist in soils as the mycelium (actively growing, inactive, or dead), spores and as some other structures. The biomass formed by fungi in soils usually surpasses the biomass of other soil organisms. The most advanced methods of mycological analyses do not still allow assessment of all microfungal species in soils. Methods of the molecular analysis are under development, and their application to soil conditions is rather problematic. At present soil inhabiting microscopic fungi are investigated primarily by their isolation on solid media or «baits» which does not allow estimation of the ratio between the dormant spores and actively growing mycelium, isolation of all the ecological and trophic fungal groups, as well as detection of not cultivated forms. Nevertheless, these ways of analysis, in combination with commonly used ecological approaches allow establishment of the basic tendencies in changes induced by anthropogenous factors in soil fungal communities.

We haye examined modem forms of human impact of different types (industrial pollution - by heavy metals, acid rains; agricultural pollution - by mineral fertilisers, recreation and pasturing impact, urbanisation influence) in different zone soils. The main tendencies in the modification of the structural and functional characteristics of the soil microfungal communities have been revealed. The quantitative and qualitative changes have been investigated as determined by changes in different forms of fungal biodiversity (a, (3), species and genera structure, by survival and growth of the resistant microfungal groups, by changes in the ratio of the stenotopic and everytopic species present, by the character of successia, by changes in the fungal biomass content, etc.

Under very strong human impact there occurs unification of soil microfungal communities found at different ecosystem levels, namely:

• At the local level: on small territories unification manifests itself in greater similarity of microfungal species structure and composition in samples of anthropogenically disturbed soils, as compared to samples of natural soils; At the regional level: on the territories characterized by extensive anthropogenically disturbed sites the diversity of soil microfungal communities tends to decrease as compared to the background ecosystems, with the dominaiting species becoming more numerous and rare species becoming smaller in number; At the zone level: similar microfungal communities can form under the influence of identical anthropogenous factors in soils of different types, or in soils of the same type situated, however, rather far from each other.

High levels of human impact can cause pauperization of the vertical ecosystem structure and increased of similarity of microfungal communities in the different ecosystem components (in soils, on the surface of plants, in ground layers of air).

Anthropogenically disturbed soils tend to contain microfungal communities, characteristic of more southern latitudes. It can be revealed by changes in the occurrence of particular microfungal genera and species, as well as by inter genera reorganizations. For example, in the section composition of the genus Penicillium, there are changes similar to those in case of promotion «from the north to the south». This phenomenon is most evidently seen in urbanized soils in northern or moderate latitudes where microfungal communities, characteristic of more southern regions, currently tend to form.

The course of fungal succession maybe changed by anthropogenous factors, depending on their character and intensity, as well as the type of ecosystem. In the course of fungal succession the values of species diversity indexes can originally increase in soils with unstable pollution, or under the impact of the physical soil properties or vegetative cover.

In case of high-level stable pollution (high dozes of heavy metals, industrial air pollution) microfungal species diversity may decrease even at the begining of succession. Anthropogenically- induced changes in succession of microfungal communities can manifest themselves not only in alteration of the species diversity, but also in changed composition of microfungal species. Thus, high levels of impact (e.g., strong pollution by heavy metals) are usually found to influence the microfungal species composition and structure as early as at the initial stages of microfungal succession, while the influence of lower levels or weaker forms of impact (e.g., pollution by acid deposits, recreational trampling) becomes evident only gradually and is registered at later stages of fungal succession.

Anthropogenous factors may induce elimination of stenotropic species in soils. No species-indicators of any particular types of anthropogenous influences have been revealed among microscopic fungi. The most obvious nonspecific sensitivity to different types of anthropogenic influences has been displayed by species Micromucor ramannianus. Anthropogenically disturbed soils are characterized by an increased number of the everytopic microfungal species, many of which show resistance to several anthropogenous factors simultaneously.

The highest modification of the zone microfungal communities has been noted in urban soils. In urban ecosystems the mycobiota may form having properties different from those of zone fungal communities. Namely urban soils are characterized by the structure of fungal biomass, species composition, and dominant micro fungal species different from those in zone soils. These modifications of microfungal communities are noted in various components of urban environment (soils, river beaches, snow, upper-soil air layers), thus creating a very specific «mycological environment» for man. Spore content in the fungal biomass of urban soils increases manifold. Urban soils are characterized by higher microfungal species diversity as compared to zone soils.

The microfungal species composition of urban soils, and especially of soils in industrial northern cities, is modified as compared to that under natural zone conditions. In urban soils there may be noted an increased frequency of occurrence and great abundance of species, which are inherent in soils, located farther to the south, for example, the decreasing number of the species of the genus Penicillium and the increasing number of the species of the genus Aspergillus. In urban soils there are increased diversity and abundance of everytopic species, which are more obvious of the northern conditions. In urban soils is increased occurrence of dark colored microfungal species. This accumulation is most frequently observed in the road side soils.

The mycological properties of soil can offer information about ancient man-landscape interaction and the related environmental changes. To this end it might be of interest to study soil properties, such as diversity of microfungal communities, species composition, the presence of specific fungal groups, the fungal biomass content and its structure, etc. This preposition has been confirmed in our investigations of the occupation deposits in the medieval Russian settlements. The examined cultural layers differ from the horizons of the surrounding natural soils by a bigger rate of fungal spores in spore biomass, more diverse morphology of fungal spores, higher species diversity of microscopic fungi, etc. Some mycological characteristics of the occupation deposits in the excavated medieval settlements were found to be similar to mycological properties of modem urban soils. We believe that the very existence of these properties in occupation deposits can be interpreted as a kind of «soil mycological memory» of the ancient anthropogenic impacts and can be used as bioindicating criteria in reconstruction of the character of ancient human activities.

Preservation of soil fungi i s now determined primarily by preservation of their natural habitats.

At present the basic problem connected with anthropogenous transformation of fungal communities in soils implies not only disappearance of rare species and the necessity of their protection, but also distribution of everytopc, ruderal species.

Changes of microfungal communities under the human impact are defined by changes of microfungal life cycles of particular species. We were first to investigate reactions of soil fungi to the influence of anthropogenous factors at different stages of the life cycle.

Influence of anthropogenous factors on the spore germination in soils and on solid media can manifest itself in: 1) changed duration of the lag-phase (its increase or reduction), 2) changed speed of spore germination (stimulation or inhibition, 3) changed level of germination (stimulation or inhibition).

The delay of spore germination - the fungistatic effect - is frequently caused by various anthropogenous factors: industrial pollution, agricultural pollution, deterioration of physical soil properties. This effect is observed in species, that are sensitive to these types of impact and whose occurrence, as a rule, decreases in anthropogenically disturbed soils (for example, M. ramannianus under Cd pollution). By contrast, the species whose allocation grows under the influence of particular anthropogenous factors, the log-period may be found to decrease (for example, P funiculosum under Pb pollution). Under low-level impact conditions resistant fungal species frequently demonstrate accelerated spore germination.

The changed level of spore germination is one of the most distinct reactions of soil fungi to anthropogenous impact. The decreased level of spore germination is usually registered in the species, which are considered to be sensitive to the impact (for example, Ulocladium botrytis under pollution by acid rains). By contrast, the increased level of spore germination is usually observed in species, that prove to be resistant to certain anthropogenus factors (for example, A.

niger, P funiculosum under Pb pollution). It is especially clearly seen at low and average levels of influence.

The mycelial growth has the determinative meaning for the soil formation, because both colonization of the soil space by fungi and the fungal biomass formation depend on it. We have established that anthropogenic factors may influence the main indexes of the hyphal growth patterns of the soil microfungi, namely: (1) the possibility of the mycelial growth from the germ-tubes, (2) the hyphal exponential rate, (3) the linear growth rate, (4) branch production, (5) some morphological properties, for example, the diameter of hypha, frequency of the septum formation, etc.

The basic increase of fungal mycelium occurs as a result of linear growth. It has been established, that the speed of microscopic fungi linear growth can vary essentially under the influence of anthropogenous factors. Under low- level impact conditions, the linear growth speed of the fungal species rather resistant to this type of impact tends to increase (for example, Zygorhynchus heterogamus under low doses of Pb pollution), while that of species sensitive to this factor is usually reduced (for example, M. ramannianus under Cd pollution). At a high level of impact the growth rate of rather resistant species is also found to diminish.

Growth of fungal colonies occurs as a system of the ramified mycelium. IVficrofimgi frequently react to the unfavorable ecological conditions in soils by reduction in the number of growing tips in the fungal colony, that can be registered as an increase in the parameter of «hyphal growth unit» (HGU), determined as the ratio between the general mycelial length and the number of growing tips. Such mycelium reaction to the unfavorable impact has been most clearly demonstrated by the species of the order Mucorales, having unicellular mycelium. This reaction has been observed upon exposure to different anthropogenous influences, e.g., increase in the soil density, pollution by heavy metals, etc. Anthropogenous factors have been also shown to induce changes in the morphological parameters of fungal mycelium, for example, in its thickness. Such kind of mycelium reaction could influence on the fungal biomass content in soils. This type of reaction also was most frequently observed for the Mucorales species. Under influence of anthropogenous factors on the soil microfungi, having septate mycelium, the density of septum formation could increase. That was shown, for example, for the species Alternaria alternata during acidification.

The sporulation of soil fungi appeared to be controlled under the human impact. It could be observed 1) in the autolysis of mycelium before sporulation, changes in the duration of sporulation period, 3) changes in the intensity of sporulation, 4) in the formation of defective spores.

Under anthropogenic factors in soil condition for species, which are sensitive to particular types of human impact, the reproduction usually does not come. The same phenomenon was observed also for rather resistant species under the high level of impact. In this condition the lysis of germ tubes and mycelium could be observed.

Most often, the disturbance of reproduction of soil microfungi became apparent in earlier sporulation. Under influence of anthropogenous factors both increase and reduction of intensity of spore formation can occur. For species rather steady to impact the increasing of reproduction is frequently observed at low levels of influences. The changes in the reproduction level could depends from the stage of live cycles (dormant spores, germinating spores, growing mycelium), at which a particular species has tested human impact.

Under influence of anthropogenous factors in soils the change in the duration of particular stages of life cycles and even the reduction of some it’s stages can take place. For example, the microcyclic life cycle, when the formation of spores begins directly on the germ tubes without development of mycelium system, was observed for A.niger in soils polluted by cadmium, for Ulocladium botrytis in soils under recreation tramping, etc.

Process of reproduction of microscopic fungi in soils occurs both as asexual - by spores, and as vegetative way - by mycelial fragments. As it was established by us, during the process of vegetative reproduction for different microfungal species exist the special «critical size» of mycelial fragment. The fragments, with a less size are lacking vitality. The anthropogenous factors can render essential influence on process of vegetative reproduction of soil microscopic fungi. It is shown in: 1) a growth inhibition (fungistasis) of mycelial fragments, 2) smaller viability of short fragments (increasing the «critical size» of fragments) under anthropogenic stress conditions.

Vegetative and asexual stages of fungi in some cases can have various sensitivity to the anthropogenous factors. Also in most cases a direction of reaction to anthropogenic changes in environment conditions on viability of mycelial fragments and spore germination is the same. For example, for P. spinulosum viability of spores is the greatest in an interval pH 3,5-5,0, and viability of fragments - at pH 6,0-7,0. High dozes of Cd inhibit the growth of this microfungi from mycelial fragments, on the contrary, for spores can be observed the increasing of germination.

At the influences of anthropogenous factors (at pollution by heavy metals, acid deposits) the increasing of formation of dormant fungal structures (chlamydospores for Foxysporum, gemma for M. ramannianus) was marked in the soils.

So, anthropogenic factors can influence on the all stages of life cycle of soil microscopic fungi. The influence of anthropogenic factors is shown by inhibition or stimulation of microfungal growth at separate stages of life cycle, that is expressed in change of period and duration of stages, and also the quantity indices, describing a concrete stage of life cycle. For the species, which are sensitive to influence, the reaction is usually shown in increase of the lag-period, decrease of the level of spore germination, a stop of the growth of germ tubes, decrease of mycelium growth rate, change of its branching, reduction of a reproduction, mycelium lysis prior to the beginning of sporulation. For the microfungal species, which are rather resistant to the particular anthropogenic factors, the passage of life cycles in anthropogenic conditions could occurs as activation (reduction of time and increase of a level) of spore germination, increase of mycelial growth rate, faster transition to a reproduction and increase of sporulation level.

As the result of these changes - one microfungal species are eliminated and their role in a habitat is reduced. Populations of resistant species change the time positions and increase their pool (spore and mycelium content) in soils. Consequences of reorganizations of soil microfungal communities can have the major value for other organisms in ecosystems.

The microscopic fungi enter into close relationships with other organisms. Anthropogenous transformation of soil microfungal communities can change usual relation between organisms and to render negative influence on the humans, animals and plants. Until recently, the potential danger, determined by presence of microscopic fungi in terrestrial ecosystems, was connected mainly with active growth of phytopathogenic and phytotoxic species, negatively influencing on the plants. But negative consequences of development of the microscopic fungi having properties dangerous for human and animals are investigated while insufficiently.

The anthropogenous factors, changing the composition and structure of soil microfungal communities, can break the animal and fungal relationships. It is established, that anthropogenic factors can: 1) results in growth stimulation of microfungal species, which are toxic and repellent for soil invertebrates, 2) to break the food chains of soil invertebrates, 3) to influence negative on the population growth of these animals. The following mechanisms are revealed: 1) production of repellent metabolites during the growth of the certain microfungal species, 2) impossibility of animals to use as a food the microfungal species surviving in anthropogenically disturbed soil, 3) toxic influence of fungal metabolites on animals, 4) distraction population processes at animals as a result of feeding by «a poor-quality fungal food». So, for the major group of soil invertebrate animals - the earthworms, these effects can be observed in the case of active growth in anthropogenicaly disturbed soils the species of genus Aspergillus (A.niger, Aflavus), which 1) are not used by animals as a food, 2) metabolites of which frighten off earthworms, 3) and even cause the death of young animals.

Negative influence on a population of soil invertebrates can occur during the consumption by animals the fungal mycelium, which could accumulate the polluting substances. At feeding of soil collembola by the fungal mycelium, brought up on the substrata polluted with herbicides, a deterioration of population growth of that invertebrate animals (lengthening the period of the beginning of egg production, reduction of number of eggs, high death rate of animals etc.) was established.

Last years the big attention of physicians and mycologists causes growth of human diseases caused by pothentially pathogenic (opportunistic) microfimgi. Increase of distribution of opportunistic microfimgi in an environment also can have the important influence on an opportunity of diseases of the person. However till now the distribution of potentially pathogenic microfimgi in terrestrial ecosystems and their dynamics depending on ecological factors was not investigated.

The distribution of the microscopic fungi, which are known as species, which could cause opportunistic mycoses of human, was investigated by us in the different climate zones at the European part of Russia, in the natural and disturbed ecosystems, in the different environments (snow, soils, air) and in different seasons of the year.

From the soils and the connected environments it was isolated more than 50 species of the microfimgi, categorized to opportunistic. Among them - half of species are most known as potentially pathogenic, including species known as sources of the deep human mycosises, categorized to group BSL-2 - A.flavus, A. fumigatus, F. oxysporum, F verticilloides, Paecilomyces variotii, etc. Distribution of potentially pathogenic microfungi in the environment is determined by natural and anthropogenous factors. In northern latitudes (Murmansk region) the main part of selected opportunistic microfimgi is submitted by species, which pathogenic properties are marked seldom. At this areas, from the species categorized as belonging to group BSL-2, usually is isolated Acremonium kiliense and rather rare species Foxysporum, Fverticilloides. In a zone of moderate latitudes (the Moscow, Tula, Vladimir region) are frequently isolated A. fumigatus, Pae.c.variotii, species of the genus Fusarium. Southern, in chernozem zone (the Voronezh, Kursk region, Krasnodar territory), most frequently are isolated microfimgal species A. flavus, A. fumigatus, A.terreus, Foxysporum, F solani, etc.

The greatest level of presence of opportunistic microfungi is revealed in urban environment. Among all investigated cities the biggest occurrence of opportunistic species at northern and boreal areas was determined in large industrial centers. The occurrence of opportunistic species was high also in investigated southern cities. In urban soils the amount of opportunistic species can make up to 40%, and an abundance about one half from all isolated, including species of group BSL-2 up to 25%.

For people’s health the important role can have the distribution of potentially pathogenic microfungi in the ground layers of air as separate spores and with particles of a soil dust. The contents of potentially pathogenic microfungi in ground layers of air in the city environment usually is higher, than in urban soils and makes in various seasons from 60 up to 80 %. In the late summer and an autumn the diversity and an abundance of potentially pathogenic microfungi is usually the greatest. The established laws of accumulation of opportunistic filamentous microfimgi can be used for the forecast of danger of fungal diseases and mycological monitoring of an environment.

One of forms of possible negative effects of microfimgi for human are mycogenic allergies - the high sensitivity of some persons to the substances of fungal origin. We have carried out the analysis of occurrence of microscopic fungi with potentially allergenic properties in anthropogenous ecosystems in comparison with natural. As allergenic took into account species, which allergenic properties are now registered most frequently - AL alternata, Clherbarum, A.flavus,A. fumigatus, A. niger, P chrysogenum,P tardum, some dark colored fungi. In urban environment in comparison with natural territories, is increased presence of the microfimgal species most frequently showing allergenic properties. First of all there are melanized microfimgi - species of genera Alternaria, Cladosporium, Ulocladium etc. It is marked especially in ground layers of air and also in soils, on a plants surface, in a snow cover. Accumulation of dark colored species to the greatest degree (and on their number, and on their abundance) is traced in roadside zones of city highways, where constantly is present active transport of the soil particles and consequently, the probability of accumulation of the fungal spores in an organism of the person is higher.

Thus, the available data allow to propose, that in conditions of various anthropogenous influences among the most resistant to these influences microfuni are species, potentially dangerous to human health. The number of such species and their abundance both potentially pathogenic, and allergenic, is especially great in cities. «Contamination» potentially dangerous microfungal species is high not only in soils, but also in the environments connected to them: for example, in ground layers of air, that essentially increase the risk of negative influences on human.

We have analysed also in anthropogenic conditions the distribution of some microfungal species, which are known as mycotoxic. One of the most dangerous to the human mycotoxins are considered - aflatoxins, produced by strains of Aflavus. The analysis of changes of occurrence and an abundance of this species in various ecosystems in moderate conditions has shown, that it’s occurrence essentially can grow in anthropogenic ecosystems in comparison with zonal soil, firstly at urbanized and recreational territories. Also it is established, that some species of the genus Penicillium (R chrysogenum, P. granulatum, R vulpinum etc.), which abundance frequently was some times higher in anthropogenically disturbed ecosystems in comparison with non- contaminated, has well defined mycotoxic properties, due to their ability to produce alkaloids. To extrapolate direct communications between increase of a level of ecological danger and allocation of microfungal species, for which strains are known mycotoxic properties, is represented poorly correct. However, the increasing of the abundance in anthropogenous ecosystems (especially at urban conditions) of the species already known as mycotoxic and established for some allocated in anthropogenic ecosystems strains an opportunity to produce significant amounts of mycotoxins, give us the basis to propose, that in aggregate these phenomena can have ecotoxicological meaning.

The major, but a poorly studied problem of anthropogenous ecology of soil fungi is their role in transformation of polluting substances in biosphere. At transfonnation there can be as soil treating in result of biodegradation, and a secondary pollution of environment that is connected to transformation initial pollutants in more toxic substances connections or with their output in an environment. An important aspect of this problem can be secondary pollution by steady pollutants, first of all, by heavy metals. In model experiments with industrially polluted soils we on an example of two species (Mucor hiemalis and Trichoderma viride) show an opportunity of participation of micro fungi in change of mobility of heavy metals (Cu, Ni, Zn) in soils. The microfungal growth in polluted soils conducts to mobilization of metals. Increase of mobility Cu, Ni, Zn as a result of viability of microscopic fungi can be connected with active decomposition of soil organic matter and increasing of migration capacity of the metals fixed in it. 

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Источник: Марфенина О.E.. Антропогенная экология почвенных грибов. 2005

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