Concentrations of the Allelochemical (±)-Catechin IN Centaurea maculosa Soils

Abstract

The phytotoxin (+/-)-catechin has been proposed to mediate invasion and autoinhibition by the Eurasian plant Centaurea maculosa (spotted knapweed). The importance of (+/-)-catechin to C. maculosa ecology depends in part on whether sufficient catechin concentrations occur at appropriate times and locations within C. maculosa soil to influence neighboring plants. Previous research on catechin in C. maculosa soils has yielded conflicting results, with some studies finding high soil catechin concentrations and other, more recent studies finding little or no catechin in field soils. Here, we report the most extensive study of soil catechin concentrations to date. We examined soil catechin concentrations in 402 samples from 11 C. maculosa sites in North America sampled in consecutive months over 1 yr, excluding winter months. One site was sampled on seven dates, another was sampled twice, and the remaining nine sites were each sampled once on a range of sampling dates. Methods used were similar to those with which we previously measured high soil catechin concentrations. We detected catechin only in the site that was sampled on seven dates and only on one sampling date in that site (May 16 2006), but in all samples collected on that date. The mean soil catechin concentration on that date was 0.65 +/- 0.45 (SD) mg g(-1), comparable to previously reported high concentrations. There are a number of possible explanations for the infrequency with which we detected soil catechin in this work compared to previous studies. Differences in results could reflect spatial and temporal variation in catechin exudation or degradation, as we examined different sites in a different year from most previous studies. Also, large quantities of catechin were detected in blanks for two sampling periods in the present study, leading us to discard those data. This contamination suggests that previous reports of high catechin concentrations that did not include blanks should be viewed with caution. Our results suggest that pure catechin is only rarely present in C. maculosa bulk soils. Thus, although catechin may play a role in C. maculosa invasion, the infrequency of soil catechin that we determined in this study suggests that we cannot be as certain of its role as previous reports of high soil catechin concentrations suggested.

Bioavailability of Allelochemicals in Soil

“…Perry et al (2007) report that detection of (+/-)-catechin in soils associated with SK was infrequent and, when detected, the levels were lower then previously reported. Similarly, Blair et al (2006) report that (+/-)-catechin measured in soils associated with long-term infested SK sites was either undetected or detected at low levels (three orders of magnitude less than levels reported earlier and responsible for growth inhibition in sensitive native species), and that soil moisture appears to be an important factor regulating (+)-catechin soil levels.…”

“…Recent studies question the importance of (+/-)-catechin as the allelochemical responsible for the successful spread of SK (Blair et al, 2006;Perry et al, 2007). Perry et al (2007) report that detection of (+/-)-catechin in soils associated with SK was infrequent and, when detected, the levels were lower then previously reported.…”

Species-specific effects of polyploidisation and plant traits of Centaurea maculosa and Senecio inaequidens on rhizosphere microorganisms

“…For each geocytotype, individuals with the same number come from the same population which suggests that a belowground mechanism may be involved in the invasive success of this species. The invasion success of C. maculosa has long been thought to be due to the release of an allelopathic chemical into the soil (Ridenour and Callaway 2001;Callaway and Ridenour 2004), but opinions vary on this question (Blair et al 2006;Perry et al 2007). Our findings suggest a possible invasion mechanism related to the ability to modify bacterial communities.…”

“…C. maculosa has been demonstrated to be allelopathic (Ridenour and Callaway 2001). This species is known for its release of (±) catechin into the soil (Bais et al 2002), and catechin has been thought to be responsible for allelopathic effects, although recent arguments claim that the amount released into the soil is too small to be able to induce allelopathic effects (Blair et al 2006;Perry et al 2007).…”

Allelopathy, an alternative tool to improve cropping systems. A review

“…(-)-catechin is considered a potent phytotoxin, whereas (+)-catechin is a weaker phytotoxin with some antimicrobial activity (Bais et al 2002(Bais et al , 2003Ridenour and Callaway, 2001). However, its role has recently been criticised due to the low concentration of (-)-catechin found in soils with C. maculosa, that exhibit values considered very low to cause significant damage (Duke et al, 2009;Perry et al, 2007). These last authors also report this phytotoxin cannot cause oxidative damage because this molecule can be quickly degraded by extracellular root enzymes.…”