References

412 L.G. Perry et al.
27.4
(±)-Catechin and C. maculosa Autoinhibition
In addition to reducing the success of C. maculosa’s interspecific competitors,
(±)-catechin appears to reduce C. maculosa seedling recruitment
in well-established populations. In C. maculosa stands in North America,
adult plants are sometimes widely spaced, with the interspaces between
plants unoccupied, occupied by C. maculosa seedlings that fail to establish,
or occupied by other species. Perry et al. (2005b) examined whether this
pattern might be accounted for by (±)-catechin inhibition of C. maculosa
seedling establishment (i.e., autoinhibition).
To test whether organic compounds in the soil in C. maculosa stands
limited C. maculosa seedling establishment, Perry et al. (2005b) added activated
carbon, which adsorbs organic compounds (Mahall and Callaway
1992), to the soil around adult C. maculosa plants in a well-established
population in the field. Activated carbon addition increased C. maculosa
seedling densities by more than 30%, indicating a strong negative effect of
organic compounds in the soil around C. maculosa adults on C. maculosa
seedling establishment. Seedling densities were still visibly greater in the
soil with activated carbon than in the soil without activated carbon in some
plots 1 year after the start of the experiment (L. Perry, personal observation),
indicating that the effects of organic compounds in the soil around
C. maculosa adults on C. maculosa seedling establishment are persistent.
Measurements of soil (±)-catechin around adult C. maculosa at the field
site indicated that (±)-catechin concentrations in the site were extremely
high (mean 1.55 mg g −1 dry soil). C. maculosa seedling densities at the site
were very low (mean 28 seedlings per square meter). To test whether the
high soil (±)-catechin concentrations could account in part for the low
C. maculosa seedling establishment, Perry et al. (2005b) examined the response
of C. maculosa seedlings to (±)-catechin in laboratory experiments.
Treatment with 1.0 mg ml −1 of (±)-catechin reduced C. maculosa seedling
root lengths by 50%, demonstrating that C. maculosa soil (±)-catechin
concentrations are sufficient to substantially reduce C. maculosa seedling
growth. Higher (±)-catechin concentrations (2 and 4 mg ml −1 ) reduced
C. maculosa root elongation by as much as 75%. Reduced root elongation
did not result in seedling mortality under laboratory conditions, but would
be expected to reduce survival under field conditions with limited water. In
addition, when (±)-catechin was maintained in solution in 10% methanol
for 2 days after treatment, treatment with 1.0 mg ml −1 of (±)-catechin reduced
C. maculosa germination by more than 70%. Tetrazolium analyses of
seed viability indicated that (±)-catechin treatment did not reduce seed survival,
suggesting that (±)-catechin dissolved in methanol may have delayed
germination of C. maculosa seeds.