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How invasive plants get that way

If I can wait long enough, maybe privet will learn to be a proper guest.
How invasive plants get that way
Manipulation of soil communities enables some introduced species to turn into 'monsters' | By Stuart Blackman

While most introduced species never become established, some have just
gone crazy [and] changed, from being nice guysgood citizens coexisting
with other speciesinto these competitive monsters, according to
University of Montana plant ecologist Ragan Callaway. One secret to
invasive species' success is a knack for manipulating soil organisms in
their adoptive habitat to their own advantage, according to a paper by
Callaway and colleagues in the February 19 Nature (Nature, 427:731-733,
February 19, 2004).

The competitive monster studied by Callaway and colleagues was spotted
knapweed (Centaurea maculosa), a European native that has spread to all
50 US states since its introduction in the late 1800s. They took a
biogeographic approach, comparing the feedback effects that arise
between the plant and soil microbes when it is grown in soil taken from
its native versus adoptive habitat.

The authors showed that soil microbes from the plant's home range have
stronger inhibitory effects on its growth than do those from its US
habitat. Sterilization of European soil resulted in a 166% increase in
plant biomass compared with a 24% increase following the same treatment
of soil from Montana. Additionally, plants grown in nonsterilized
European soil were smaller if the soil had been precultured with other
C. maculosa plants rather than a European grass species. Conversely, in
Montana soil, plants did better in C. maculosaprimed soil.

John Klironomos of the University of Guelphwho 2 years ago showed that
within a given habitat, invasive plants were associated with positive
microbial feedback interactions, while natives displayed the more stable
negative relationship with soil flora and faunadescribed the findings
as a fantastic breakthrough.

This invader makes use of native species to pull itself up by its
bootstraps, said Charles Mitchell, an ecologist who works on invasive
species at Cornell University. The effect is compatible with the enemy
escape hypothesis, which holds that transplantation of a species from
its native habitat separates it from natural enemies such as herbivorous
insects or, in this case, soil pathogens.

Mitchell notd that the generality of Callaway's reported effects remains
to be established, and observed that similar studies on less successful
introduced species could reveal a correlation between the degree of
positive feedback and invasiveness. It remains unclear, said Mitchell,
whether the plant manipulates the native microbes by inhibiting
pathogens, promoting beneficial organismswhich are generally considered
to be less host-specific than pathogensor both.

Soil contains a diverse suite of organisms, including fungi, bacteria,
and protozoans, totaling 2000 species per gram of soil, according to
Klironomos. And the interactions between these organisms and Centaurea
remain squarely inside a very dark black box, said Mitchell.

As for the future dynamics of the invader and its adoptive habitat:
Callaway has evidence that native US plants are already adapting to
Centaurea's presence and pointed out that the rapid nature of microbial
evolution could mean that native ecosystems are more able than is
generally believed to respond to the pressures exerted by introduced
species. In a hundred years, Centaurea maculosa may not be the monster
that we see now, he said.

Links for this article
Ragan Callaway

US Invasive Species

R.M. Callaway et al., Soil biota and exotic plant invasion, Nature, 427:731-733, February 19 2004.

Centaurea maculosa
http://www.fs.fed.us/database/feis/plants/forb/cenmac/distribut ion_and_occurrence.html 

John N. Klironomos
http://www.uoguelph.ca/botany/people/faculty/klironomos/index.h tml 

J.N. Klironomos, Feedback with soil biota contributes to plant rarity
and invasiveness in communities, Nature, 417:69-70, May 2, 2002.

[PubMed Abstract]  

Charles Mitchell

C.E. Mitchell, A.G. Power, Release of invasive plants from fungal and viral pathogens, Nature, 421:625-627, February 6, 2003.
[PubMed Abstract]  

Bonnie Zone 6+ ETN

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