References

Interactions Between Mycorrhizal Fungi and Bacteria 207
tative area within a desertified semi-arid ecosystem in southeast Spain.
The existing natural vegetation was a degraded shrubland, in which Anthyllis
cytisoides, a drought-tolerant legume able to form symbioses with
both rhizobial and mycorrhizal microsymbionts, was the dominant species
(Requena et al. 1997). The experimental variables tested, as inoculants for
Anthyllis cytisoides seedlings to be transplanted, involved three microsymbiont
inoculation treatments, including: (1) an exotic mycorrhizal fungi
from culture collection, (2) a mixture of five taxa of indigenous mycorrhizal
fungi representing the natural abundance and diversity at the site,
and (3) an indigenous rhizobial inoculum (Requena et al. 1997). A timecourse
(every 6 months) sampling was established over 5 years after transplanting.
A long-term improvement in the physicochemical properties in
the soil around Anthyllis plants inoculated with a mycorrhizal inoculum
based on indigenous taxa was observed. The benefits included an increased
content of both N and organic matter, and in the number of hydro-stable
macroaggregates.
As described before, it can be assumed that the increase in N content
in the rhizosphere of the legume can be accounted to an improvement in
nodulation and N-fixation rates resulting from inoculation with mycorrhizal
fungi (Barea et al. 1992), while increases in organic matter content
and improvement in soil aggregation are due to the role of the mycorrhizal
mycelium on soil structure stabilization (Miller and Jastrow 2000). Because
rhizobial species are usually recognized for their ability to produce
exo-polysaccharides (Spaink et al. 1998), it can be assumed that, given the
Fig. 3. Time-course changes in soil aggregation in the rhizosphere of field-established nodulated
plants of Anthyllis cytisoides growing under natural conditions, either noninoculated
with AMF (white columns), or inoculated with G. intraradices (light gray columns), or with
native AMF (dark gray columns). For each response variable, means (n = 5), not sharing
aletterincommondiffersignificantly(p = 0. 05) from each other according to Duncan’s
multirange test. Data points on the y-axis represent background values in the bare soil
before transplanting. (Requena et al. 2001)