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mineralization as a result of nematode excretion and nematode effects on
bacterial populations (De Ruiter et al. 1993). In addition, (±)-catechin in
the rhizosphere may affect soil mycorrhizal fungi. Catechin concentrations
in the roots of several tree species have been shown to decline in association
with mycorrhizal infection (Münzenberger et al. 1990, 1995; Beyeler and
Heyser 1997), suggesting either that tree roots reduce catechin concentra-
tions to allow mycorrhizal infection to occur, or that mycorrhizal fungi use
the catechin in infected roots as a carbon source (Beyeler and Heyser 1997).
Several fungi have been shown to degrade catechin (Galiotou-Panayotou
et al. 1988; Vasudevan and Mahadevan 1990). In either case, high soil (±)-
catechin concentrations would be expected to influence the abundance of
soil mycorrhizal fungi. (±)-Catechin exudation may increase the abundance
of soil microbes that can survive high soil (±)-catechin concentrations, or
that can use (±)-catechin as a carbon source, and reduce the abundance
of those microbes that cannot. Such changes have the potential to alter
nutrient mineralization, immobilization, and transformation rates, as well
as mutualistic associations that affect resource availability (Laakso et al.
2000; Hamel 2004). Research on the effects of (±)-catechin on soil com-
munities, particularly mycorrhizal communities, and on nutrient cycling
is needed to determine the effects of C. maculosa (±)-catechin exudation
on soil processes.
27.7
Conclusions and Future Prospects
In summary, (±)-catechin, a secondary metabolite exuded from the roots of
C. maculosa , has been shown to mediate positive and antagonistic plant-
plant and plant-microbe communication, with the potential for strong
effects on (1) survival and growth of interspecific competitors, (2) conspe-
cific seedling establishment, (3) survival of pathogenic and nonpathogenic
soil organisms, and (4) soil processes. Given the numerous functions that
(±)-catechin may have in plant communities, it will be difficult to deter-
mine the selection pressures that resulted in the evolution of C. maculosa
(±)-catechin production and that continue to select for its production in
its native and exotic ranges. It is likely that some or perhaps many of the
potential effects of C. maculosa (±)-catechin production are unintended
consequences of a compound produced for a particular function or com-
bination of functions. More research will be needed to determine the field
conditions under which (±)-catechin operates as an allelochemical, au-
toinhibitor, antimicrobial agent, or soil nutrition enhancer, and whether
and when these functions might act in concert. Regardless, the myriad of
roles that (±)-catechin may play in communities occupied by C. maculosa
 
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