PREMISE Invasion processes involve several mechanisms, some of which have received little attenti... more PREMISE Invasion processes involve several mechanisms, some of which have received little attention. Allelopathy has been invoked as an invasion driver according to the novel weapon hypothesis (NWH), and polyploidization can also be an important factor for invasion success. However, very few studies have addressed both topics together. We analyzed the allelopathic effect of the polyploid Oxalis pes-caprae, an invader in mediterranean-climate areas worldwide, from different origins and ploidy levels (native: South Africa; invaded: Chile, Australia, California, and the Mediterranean Basin) on Lactuca sativa as a model species. METHODS We measured seed germination, initial plant height, and aboveground and belowground biomass of Lactuca grown in field soil mixed with Oxalis material and with or without activated carbon in a common garden experiment. We performed the experiment twice, when Oxalis was vigorous and when senescent. RESULTS Vigorous plants of Oxalis tended to reduce Lactuca germination, but both vigorous and senescent Oxalis plants increased Lactuca biomass, probably due to an increase in nutrients provided by plant material. The highest increase in Lactuca traits occurred with Oxalis plants from the Iberian Peninsula. Allelopathy only happened when Oxalis was senescent and was especially strong with plants from Chile. CONCLUSIONS Although we did not find broad evidence for the NWH considering all areas together, we reported differences in the allelopathic potential of Oxalis plants depending on their origin. These results highlight the independent evolution of invasiveness traits in distant introduced ranges and the importance of the invaders' origin when testing hypotheses about invasion drivers.
Acacia dealbata (Fabaceae) is an Australian species and invader in temperate regions worldwide.Th... more Acacia dealbata (Fabaceae) is an Australian species and invader in temperate regions worldwide.This species is based on a network of functional attributes, and from an ecophysiological point of view this confers a competitive advantage over cohabiting species. The invasion process of A. dealbata is partially mediated by releasing allelopathic compounds that affect native plants and soil microbes. However, chemical compounds responsible for the allelopathic effects as well as morphological and intracellular damage in target species remain unknown. We examined (through bioassays based in aqueous extracts and the direct effect of plant parts) different plant materials of A. dealbata: leaf litter, fresh leaves, flower litter, pod litter and seeds, as well as the evolution of phytotoxicity from the litter on germination and early seedling growth of Lactuca sativa L. (indicator species), Helenium aromaticum (native grass) and Quillaja saponaria (native tree). These plant materials were qu...
The leguminous tree Acacia dealbata is one of the most widespread invasive of Australian Acacia s... more The leguminous tree Acacia dealbata is one of the most widespread invasive of Australian Acacia species around the world reducing plant biodiversity and altering soil microorganisms. The invasion success of A. dealbata was partially related to the release of chemical compounds that interfere with native plants and soil microorganisms and promote the growth of its own seedlings. However, this positive autoallelopathic effect was reduced in the presence of field soils. Therefore, other factors should be influencing the colonization of A. dealbata in non-native ranges and the role of allelopathy remains unclear. Recent studies have shown that the establishment of A. dealbata seems to be promoted by high irradiance and environmental disturbances. Nevertheless, this species is also capable of invading communities where no obvious alterations were observed. Therefore these factors seem important but not determinant. Although there is abundant literature compiling A. dealbata impacts, stud...
... The oxidative stress results from deleterious effects of reduced oxygen ... protection, preve... more ... The oxidative stress results from deleterious effects of reduced oxygen ... protection, prevention of enzyme-especially photosynthesising-denaturation and/or their stress-induced aggregation and post ... signalling as follows (see Figure 3): 'All biotic and abiotic stressors, natural and ...
... Allelopathy was implicated by Duhan and Lakshminarayana (1995), Rafiqul-Hoque et al. (2003), ... more ... Allelopathy was implicated by Duhan and Lakshminarayana (1995), Rafiqul-Hoque et al. (2003), El-Khawas and Shehata (2005), Al-Wakeel et al. (2007), and Lorenzo et al. ... (1991) in their studies of Eucalyptus spp. and Lorenzo et al. ...
PREMISE Invasion processes involve several mechanisms, some of which have received little attenti... more PREMISE Invasion processes involve several mechanisms, some of which have received little attention. Allelopathy has been invoked as an invasion driver according to the novel weapon hypothesis (NWH), and polyploidization can also be an important factor for invasion success. However, very few studies have addressed both topics together. We analyzed the allelopathic effect of the polyploid Oxalis pes-caprae, an invader in mediterranean-climate areas worldwide, from different origins and ploidy levels (native: South Africa; invaded: Chile, Australia, California, and the Mediterranean Basin) on Lactuca sativa as a model species. METHODS We measured seed germination, initial plant height, and aboveground and belowground biomass of Lactuca grown in field soil mixed with Oxalis material and with or without activated carbon in a common garden experiment. We performed the experiment twice, when Oxalis was vigorous and when senescent. RESULTS Vigorous plants of Oxalis tended to reduce Lactuca germination, but both vigorous and senescent Oxalis plants increased Lactuca biomass, probably due to an increase in nutrients provided by plant material. The highest increase in Lactuca traits occurred with Oxalis plants from the Iberian Peninsula. Allelopathy only happened when Oxalis was senescent and was especially strong with plants from Chile. CONCLUSIONS Although we did not find broad evidence for the NWH considering all areas together, we reported differences in the allelopathic potential of Oxalis plants depending on their origin. These results highlight the independent evolution of invasiveness traits in distant introduced ranges and the importance of the invaders' origin when testing hypotheses about invasion drivers.
Acacia dealbata (Fabaceae) is an Australian species and invader in temperate regions worldwide.Th... more Acacia dealbata (Fabaceae) is an Australian species and invader in temperate regions worldwide.This species is based on a network of functional attributes, and from an ecophysiological point of view this confers a competitive advantage over cohabiting species. The invasion process of A. dealbata is partially mediated by releasing allelopathic compounds that affect native plants and soil microbes. However, chemical compounds responsible for the allelopathic effects as well as morphological and intracellular damage in target species remain unknown. We examined (through bioassays based in aqueous extracts and the direct effect of plant parts) different plant materials of A. dealbata: leaf litter, fresh leaves, flower litter, pod litter and seeds, as well as the evolution of phytotoxicity from the litter on germination and early seedling growth of Lactuca sativa L. (indicator species), Helenium aromaticum (native grass) and Quillaja saponaria (native tree). These plant materials were qu...
The leguminous tree Acacia dealbata is one of the most widespread invasive of Australian Acacia s... more The leguminous tree Acacia dealbata is one of the most widespread invasive of Australian Acacia species around the world reducing plant biodiversity and altering soil microorganisms. The invasion success of A. dealbata was partially related to the release of chemical compounds that interfere with native plants and soil microorganisms and promote the growth of its own seedlings. However, this positive autoallelopathic effect was reduced in the presence of field soils. Therefore, other factors should be influencing the colonization of A. dealbata in non-native ranges and the role of allelopathy remains unclear. Recent studies have shown that the establishment of A. dealbata seems to be promoted by high irradiance and environmental disturbances. Nevertheless, this species is also capable of invading communities where no obvious alterations were observed. Therefore these factors seem important but not determinant. Although there is abundant literature compiling A. dealbata impacts, stud...
... The oxidative stress results from deleterious effects of reduced oxygen ... protection, preve... more ... The oxidative stress results from deleterious effects of reduced oxygen ... protection, prevention of enzyme-especially photosynthesising-denaturation and/or their stress-induced aggregation and post ... signalling as follows (see Figure 3): 'All biotic and abiotic stressors, natural and ...
... Allelopathy was implicated by Duhan and Lakshminarayana (1995), Rafiqul-Hoque et al. (2003), ... more ... Allelopathy was implicated by Duhan and Lakshminarayana (1995), Rafiqul-Hoque et al. (2003), El-Khawas and Shehata (2005), Al-Wakeel et al. (2007), and Lorenzo et al. ... (1991) in their studies of Eucalyptus spp. and Lorenzo et al. ...
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