John S. Waid

Does soil biodiversity depend upon metabiotic activity and influences

Abstract A central tenet of biological science is that living organisms modify their environments. Metabiosis is a form of ecological dependence in which one organism or a functional group of organisms must modify the environment before another organism or functional group of organisms can live or thrive in it. Soil ecosystems are modified by metabionts to create habitats or supply resources for which dependent organisms may adapt, evolve and hence diversify. Thus, the diversity of the soil biota and its functional capabilities may to a large extent be the result of and dependent upon metabiotic activity and influences. Examples of metabiotic activity in soil ecosystems are: plants are the main source of O 2 for the soil biota; decomposers deplete soil O 2 thus enabling the growth of microaerophiles or anaerobes; ammonium released by bacterial deamination supports the growth of autotrophic ammonium-oxidisers; burrowing earthworms improve soil drainage and create aeration channels for aerobic biota; detoxification of plant residues by biodegraders permits proliferation of toxin-sensitive organisms; wood decay by microbes creates habitats for arthropods associated with rotting wood; arthropod comminution of litter liberates nutrients that facilitate microbial activity. Some metabionts, the panmetabionts, had a global influence by modifying the biosphere, its evolving biota and by maintaining its biogeochemistry. For example, during the development of the biosphere the cyanobacteria began the transformation of the atmosphere through the production of O 2 . The accumulation of atmospheric O 2 had an overwhelming influence on the formation of soils, their physico-chemistry and biology, in particular the evolution of diverse major groups of aerobic terrestrial organisms (plants, fungi and animals). Many practices to improve soil fertility, e.g. agro-forestry, mulching, legume inoculation, minimum tillage are applications of metabiotic techniques, which maintain or improve soil biodiversity and its functional potentiality. Conversely, where ecosystems are degraded through human activity, e.g. forest destruction, irrigation with saline water, strip-mining, deep tillage, there is an inevitable reduction of species of animals and plants. It can also result in the loss of some components of the soil community, e.g. mycorrhizal fungi, macrobiota such as invertebrates, with a consequent reduction in or a loss of the metabiotic activities of functional groups of the soil biota. Types of metabiotic action include facilitation, ecological engineering, commensalism and keystone predation. Metabiosis must rank with biotic interrelationships and interactions, such as competition, predation or mutualism, in its effects upon soil communities and ecosystems.

Regulated modulation of Trifolium subterraneum inoculated with bacteriocinproducing strains of Rhizobium trifolii

Abstract When a bacteriocin-sensitive and a bacteriocin-resistant strain of Rhizobium were added together to plant-tubes, containing Trifolium subterraneum cv. Dwalganup seedlings, the bacteriocinresistant strain occupied less than 10% of the nodules sites. But when a bacteriocin-producer was added with the inoculum, the bacteriocin-resistant strain occupied 75% of the nodule sites. In a replicate experiment, using a different bacteriocin-sensitive strain, the proportion of the nodules formed by the bacteriocin-resistant strain was increased from 17%, in the absence of the bacteriocin-producer, to 100% in its presence. Similar experiments were set up in non-sterile soil that contained ineffective, bacteriocin-sensitive rhizobia. When an effective bacteriocin-resistant strain was inoculated with a bacteriocin-producing strain, the proportion of nodules formed by the effective strain was greater than in the absence of the bacteriocin-producer. This was because nodulation by the indigenous rhizobia was reduced in the presence of the bacteriocin-producer. Such experiments suggest that bacteriocin-producing strains of R. trifolii that reduce the nodulation success of competing bacteriocin-sensitive strains could be used to increase the proportion of nodules formed by a desired bacteriocin-resistant strain.

Polychlorinated biphenyls and organochlorine pesticides in the Australian fur seal, Arctocephalus pusillus doriferus

Seals occupy a high trophic level in the marine ecosystem and have large reserves of subcutaneous fats. It is, therefore, not surprising that they accumulate high concentration of lipophilic substances such as organochlorine pesticides. Seal tissue concentration of pesticides are considered by some workers to be a good indication of local environmental loads. The Australian fur seals at Seal Rocks occupy a breading colony from which they can range into Bass Strait, Westernport Bay and Port Phillip Bay. It is, therefore, reasonable that results obtained for local seals should provide an indication of pesticides and PCBs in local squid and schooling fish. Previous results indicate that biota in Port Phillip Bay and Bass Strait, adjacent to the colony are exposed to elevated concentrations of PCBs. The authors have determined PCB and pesticide levels in local seals.

Biological and biochemical analysis of soils

There is an immense literature on biological and biochemical analyses of soils. Such analyses have revealed the enormous richness of species in soil and their vast range of metabolic potentials and ecological diversity. Accordingly, the approaches used to investigate the soil biota and its biochemistry usually have to be modified or adapted depending upon the purpose of the investigation. Studies of micro-organisms in the soil environment, are complicated because microbial cells are commonly attached to surfaces where they live side-by-side with other populations in consortia usually containing different morphological and physiological types. Such assemblages of organisms cannot be described quantitatively using cultural techniques, such as plate counts, which underestimate both cell numbers and viable biomass. The development of more powerful observational and staining techniques has improved our knowledge of the diverse morphological and biochemical composition of soil micro-communities. Such findings have been amplified at a grosser level by laboratory studies with multi-component systems (microcosms) to mimic field situations and to assess the range of biochemical potentials of microbial consortia. But despite notable advances in analytical methods we are still, with a few exceptions, unable to detect or identify those microorganisms which carry out specific biochemical transformations or determine whether particular cells are alive, dormant or dead at the time of observation. Considerable work has been done to define some of the fundamental ecological attributes of microbial assemblages in soil. Productive work on the metabolic activities of the soil microbiota, specially geochemical transformations of C, N, S and P, has been under way for more than a century. But only in more recent years have more sensitive and reproducible analytical methods become available to measure viable biomass in soil. This will enable some insight to be gained into the role that microbial biomass plays as a labile source and sink for plant nutrients.SummaryThere is an immense literature on biological and biochemical analyses of soils. Such analyses have revealed the enormous richness of species in soil and their vast range of metabolic potentials and ecological diversity. Accordingly, the approaches used to investigate the soil biota and its biochemistry usually have to be modified or adapted depending upon the purpose of the investigation.Studies of micro-organisms in the soil environment, are complicated because microbial cells are commonly attached to surfaces where they live side-by-side with other populations in consortia usually containing different morphological and physiological types. Such assemblages of organisms cannot be described quantitatively using cultural techniques, such as plate counts, which underestimate both cell numbers and viable biomass. The development of more powerful observational and staining techniques has improved our knowledge of the diverse morphological and biochemical composition of soil micro-communities. Such findings have been amplified at a grosser level by laboratory studies with multi-component systems (microcosms) to mimic field situations and to assess the range of biochemical potentials of microbial consortia.But despite notable advances in analytical methods we are still, with a few exceptions, unable to detect or identify those microorganisms which carry out specific biochemical transformations or determine whether particular cells are alive, dormant or dead at the time of observation.Considerable work has been done to define some of the fundamental ecological attributes of microbial assemblages in soil. Productive work on the metabolic activities of the soil microbiota, specially geochemical transformations of C, N, S and P, has been under way for more than a century. But only in more recent years have more sensitive and reproducible analytical methods become available to measure viable biomass in soil. This will enable some insight to be gained into the role that microbial biomass plays as a labile source and sink for plant nutrients.

RELEASE OF NITROGEN FROM DECOMPOSING LEGUME ROOTS AND NODULES

At present there is a considerable world-wide research effort under way to boost biological nitrogen fixation. The areas of research thrust(1) include (a) the improvement of legume inoculation (rhizobial technology), (b) the modification of farming systems and the creation of new legume cultivars so that legume green manures, forage legumes and legumes intercropped with non-legumes are used in agriculture more extensively and more efficiently, (c) the use of the techniques of genetic engineering to fashion and improve hosts as well as symbiotic N2-fixing micro-organisms, (d) efforts to harness to the needs of agriculture symbiotic combinations, such as the Azo11a-Anabaena or actinomycete (Frankia)-nodulated angiosperm associations, which hitherto have not been exploited to the full nor have the conditions under which such associations fix N2 optimally been determined and, (e) investigations to understand and to use biological N2-fixing associations with grasses, grain cereals and other non-legumes.