Symbiotic Fungi: Principles and Practice (Soil Biology)

Chapter 12
Interaction with Soil Microorganisms
R. Hampp and M. T. Tarkka
12.1 Introduction
Roots constitute important plant organs for water and nutrient uptake. However,
they also release a wide range of carbon compounds of low molecular weight.
These can amount to between 10 and 20% of total net fixed carbon (Rovira 1991)
and form the basis for an environment rich in diversified microbiological populations,
the rhizosphere (Hiltner 1904). Its specific conditions lead to the selection of
distinct microbial communities (Smalla et al. 2001), where fungi play an important
role (Linderman 1988; Andrade et al. 1997; Frey-Klett et al. 2005; de Boer et al.
2005). This is due to the fact that the fungal hyphae, which emanate from mycorrhizas,
release a substantial amount of the acquired plant carbon to the soil. The
energy-rich plant compounds promote bacterial growth and survival (Hobbie 1992),
and the soil volume filled with mycorrhizal fungal hyphae is therefore often depicted
as the mycorrhizosphere (Foster and Marks 1967).
The mycorrhizosphere effect leads to the enrichment of microorganisms that
improve plant fitness (Frey-Klett et al. 2005). Some of the mycorrhizosphere
organisms directly influence the development and physiology of the plants through
the production of plant growth regulators (Azcon et al. 1978), by increasing the root
branching rate or root permeability. Others may interact in a more indirect way
that supports plant growth. For example, the interacting organisms may improve
nitrogen or phosphate availability, lead to better survival of the hyphae and the
plants in a contaminated soil, assist the plant resistance against pathogens by
R. Hampp (*)
Institute of Microbiology, Department of Physiological Ecology of Plants, University of Tuebingen,
Auf der Morgenstelle 172076 Tuebingen, Germany
e-mail: ruediger.hampp@uni-tuebingen.de
T. Tarkka
UFZ, Helmholtz-Centre for Environmental Research, Department of Soil Ecology, Theodor-
Lieser-Strasse 4, D-06120 Halle, Germany
A. Varma and A.C. Kharkwal (eds.), Symbiotic Fungi, Soil Biology 18, 197
DOI: 10.1007/978‐3‐540‐95894‐9_12, # Springer‐Verlag Berlin Heidelberg 2009