Dual purpose secondary compounds: phytotoxin of Centaurea diffusa also facilitates nutrient uptake

Abstract

Summary Traits that allow more efficient foraging for a deficient resource could increase the competitiveness of a species in resource‐poor habitats. Considering the metal‐nutrient mobilization ability of many allelochemicals, it is hypothesized that, along with the reported toxic effect on the neighbors, these compounds could be directly involved in resource acquisition by the allelopathic plant. Using nutrient manipulation treatments in hydroponic culture, this hypothesis was tested using Centaurea diffusa, an invasive species that produces the putative phytotoxin 8‐hydroxyquinoline (8HQ). The exudation of 8HQ by C. diffusa was very limited and transient. It was further shown that: C. diffusa utilizes 8HQ for its own acquisition of iron, a nutrient deficient in many of its alkaline, invaded habitats; there possibly exists a unique mechanism for the uptake of the 8HQ‐complexed iron (Fe) in C. diffusa, which is novel to the nongraminaceous species; although phytotoxic at very low concentrations, the toxic effect of 8HQ showed a conditional response in the presence of metals, and was significantly reduced when 8HQ was complexed with copper (Cu) and Fe. This study, in addition to elucidating one of the possible adaptive mechanisms conferring competitive advantage to C. diffusa, also outlines measures to negate the phytotoxicity of its putative allelochemical. The results indicate that the exudation of 8HQ by C. diffusa could be primarily for nutrient acquisition.

Soil microbial communities alter allelopathic competition between Alliaria petiolata and a native species

“…These differences can result from methodological differences (Blair et al 2009), but can also stem from context dependency in the behavior of allelochemicals. For instance, the toxicity of the putative allelochemical in Centaurea diffusa differs based on which metal it chelates R. Lankau (&) Illinois Natural History Survey, Institute of Natural Resource Sustainability, University of Illinois at Urbana-Champaign, 1816 S. Oak Street, Champaign, IL 61820, USA e-mail: ralankau@illinois.edu; ralankau@gmail.com (Tharayil et al 2009). This context dependency suggests that allelopathy may not be a constant trait of a species, but the outcome of specific plantenvironment interactions.…”

Phytotoxic compounds from roots ofCentaurea diffusaLam.

“…As we have discussed, the allelopathic potential of C. diffusa has been a subject of contradictory and controversial studies. [2][3][4][5]18 Phytotoxic compounds identified in this report could be one of the factors involved in the success of this noxious weed in the colonization of new ecosystems. In addition, lipids present in the root exudates could promote the growth of mycorrhizal fungi in the C. diffusa rhizosphere, which would make it more resistant to soil-borne pathogen attacks.…”

“…However, it should be noted that in a recent study 8-hydroxyquinoline was reported to be secreted by the roots of hydroponically-grown C. diffusa plants following a diurnal pattern. 18 In this study the authors reported that 8-hydroxyquinoline was secreted at its maximum by the roots after 6 continuous hours of sun light following a dark period, after 8 hours of sun light the compound started to degrade and after 10 h the compound could not be detected. These studies herbicides for control of grasses and aquatic weeds.…”

Spatial and Temporal Dynamics of Root Exudation: How Important is Heterogeneity in Allelopathic Interactions?

“…Transport of allelochemicals through the CMN may also protect allelochemicals from rapid degradation by moving them away from microbial "hot zones" in the rhizosphere. Others (Belz and Hurle 2005;Tharayil et al 2009Tharayil et al , 2010) have reported diurnal fluctuations in the exudation of allelochemicals, and Thayaril and Triebwasser (2010) suggest that the pulsing of allelochemical release may be important in overcoming biotic and abiotic degradation mechanisms in soil. While we have measured greater release of thiophenes over daylight hr, the magnitude of diurnal variation seems generally modest in comparison to other variation observed in this study.…”