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M.a ROSARIO DE FELIPE ANTÓN AN. R. ACAD. NAC. FARM.

Palabras clave: Biofertilizantes.— Control biológico.— Fijación biológica

de N2.— Rhizobiaceas.— Simbiosis hongo-planta.— Micorrizas.— Rizosfera.— Ri-
zobacterias.

ABSTRACT

Plant-soil-microorganisms interactions on the protection
of the Environment and Health

Soil microorganisms stablish beneficious symbiosis with plants and can be
considered as biofertilizers and also useful in biological control applications. The
beneficious symbiosis: «bacteria-plant» and «fungy-plant», have great interest for
its great impact in Agriculture, Forestry and Environment and constitute an alter-
native to the application of chemical fertilizers, avoiding its negative effects at
health and environmental level. The nitrogen-fixing bacteria and mycorrizal fungi
are among the plant symbionts more extended and ecologycally more important.
The potential of soil microorganisms is unlimited. It is necessary to study more
deeply the interaction between endogenous organisms with plant roots, to get a
better knowledge of them. With these technologies we are trying both: the self-
supplying and self-defending of the plants under adverse environmental conditions
and to let to our planet in good health for the future generations.

Key words: Biofertilizers.— Biological control.— Biological N2 fixation.— Rhi-
zobiaciae.— Symbiosis fungi-plants.— Rhizosphere.— Rhizobacteria.

EXTENSIVE ABSTRACT

This dissertation deals at a field of increasing interest, the interactions between
microorganisms, soil and plants, which needs to be studied more deeply, since
given its complexity, our knowledge is still very limited. It starts with a previous
comments on the soil, as a living agent, the fundamental role played by soil micro-
organisms on the soil structure, growth of the plants and C and N cycles. Between
all ecosystems, the soil presents the major richness of species, living together a
great amount of microorganisms as bacteria, fungi, virus, protozoae, and algae.
From all of these groups, the bacteria is one of the most abundant and diverse,
possibly because they are able of a rapid growth by using a great amount on
nitrogen and carbon sources. The bacteria interact with plant roots and colonize
the root surface that has a high concentration of nutrients.

Plant life is conditioned by the presence of these wide range of microorganisms
associated to the roots which can alter the nutrient absorption, by direct effect on
the roots, on the environment or by competition for soil nutrients. The plant
rhizosphere is considered as a zone with intense microbial activity surrounding
the root surface and stimulating the plant growth. The microbial density in the
rhizosphere is higher with respect to the rest of the soil. It is a dinamic and
changeable zone with different characteristics to the rest of the soil.

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