Allelopathy as a mechanism for resisting invasion: the case of Polygonella myriophylla - Invasive Plants: Ecological and Agricultural Aspects - page 148

Figure 3. Summary results of bioassays with bahiagrass ( Paspalum notatum ) conducted on soils col-
lected biweekly for one year from beneath Polygonella myriophylla , the surrounding bare zones, and
adjacent grassed areas (predominantly P. notatum ). The data presented here are averages for the entire
year. Soils were assayed in 6-month sets, and differences in both germination and growth were sig-
nificant between the three soil types. The original data and statistical analyses are presented in [9].
Environmental activation of plant allelochemicals
Glycosides of hydroquinone and gallic acid are the major allelochemicals of P.
myriophylla , and occur in high concentrations in the foliage. Microorganisms
readily degrade these compounds in soil. Arbutin is rapidly converted to
hydroquinone, and hydroquinone is rapidly converted to benzoquinone (Fig. 4)
[11]. Whole plant bioassays with soil treated with hydroquinone and gallic
acid show increasing toxicity to bahiagrass long after these compounds disap-
pear, suggesting the importance of microbial and non-microbial oxidation
products in the allelopathic activity of this plant [12].
Environmental activation processes appear to be important for other scrub
species as well. Aqueous leaf washes of Ceratiola ericoides contain the inac-
tive dihydrochalcone ceratiolin. On exposure to light, ceratiolin degrades to
the much more phytotoxic hydrocinnamic acid [4, 13]. Microorganisms rapid-
ly degrade hydrocinnamic acid to acetophenone, which also has activity as a
germination and growth inhibitor [14].
The importance of environmental and microbial processes in activating rel-
atively non-toxic allelochemicals in Florida scrub plants implies that the use of
bioassay-guided fractionation of crude plant extracts may be misleading when
environmental transformation of plant allelochemicals is significant. The