Search

PREMISE: Sparse understory communities, in association with non‐native tree species, are often attributed to allelopathy, the chemical inhibition of a plant by another. However, allelopathy is a difficult ecological phenomenon to demonstrate as many studies show conflicting results. Eucalyptus globulus, a tree native to Australia, is one of the most widely planted trees around the world. Sparse understories are common beneath E. globulus plantations and are often attributed to allelopathy, but the ecological impacts of E. globulus on native plant communities outside Austrialia are poorly understood. METHODS: To assess allelopathy as a mechanism of understory inhibition, we tested volatile‐ and water‐soluble leaf extracts from E. globulus, Salvia apiana, and Quercus agrifolia on seed germination of California native plants. We also quantified germination rates and early seedling growth of California native plants grown in soil from E. globulus plantations versus soil from an adjacent native plant community. RESULTS: Volatile compounds from E. globulus did not significantly reduce germination for any species. Inhibition from water‐soluble E. globulus compounds was comparable to that of a native tree, Quercus agrifolia (10%). Eucalyptus globulus soil supported germination and early seedling growth of native species equal to or better than coastal scrub soil, although species responses were variable. CONCLUSIONS: In contrast to previous studies, our results fail to support the hypothesis that E. globulus chemically inhibits germination of native species. California native plants germinate and grow well in soils from E. globulus plantations, which may have significant implications for management and restoration of land historically occupied by E. globulus plantations. [ABSTRACT FROM AUTHOR]

Weeds are a major constraint to canola (Brassica napus L.) production, reducing grain yield and quality. The repeated use of pre- and post- emergent herbicides to control several grasses and broadleaf weeds has escalated the problem of herbicide resistance in weeds. The development of herbicide-tolerant canola cultivars has increased the flexibility of weed management but has also increased the risks of outcrossing with wild relatives and weed shifts to resistance. Herbicide-resistant weed species, and the related biological repercussions, pose a major threat to sustainable weed management. These developing risks have led researchers to examine integrated weed management (IWM) techniques for sustainable weed control. Weed control strategies using non-chemical tactics have valid roles for managing weeds. However, in broad-acre commercial fields, the effectiveness of several non-chemical selections are less proven than commercial chemical herbicides. Canola competition and allelopathy for weed suppression are potential components for integrated weed management in canola. This review examines current chemical and non-chemical options available for developing IWM strategies for profitable canola production, as well as future research directions. [ABSTRACT FROM AUTHOR]

The establishment and productivity of new forest plantations can be significantly impacted by the presence of native vegetation. In a study site in New South Wales, Australia, the growth of a Pinus radiata plantation has been virtually halted in areas dominated by the native shrub Allocasuarina nana , effects that persist for decades even after its physical removal. To determine the mechanism by which A. nana impedes P. radiata growth, we compared the fungal soil community and metabolomic profile of soils in patches rich in A. nana with adjacent healthy P. radiata patches and the transition zone between them. This data was complemented by a pot experiment to assess P. radiata growth in soils from the different vegetation areas with and without a viable soil community or the addition of A. nana roots or exudates. Together, the data demonstrates that these A. nana soils are likely inhibitory to P. radiata growth through a dual mechanism: impacting the growth of the pine directly through root associated metabolites and indirectly through the inhibition of the fungal community supporting P. radiata health, including ectomycorrhizal fungi. • The Australian native shrub Allocasuarina nana severely impacts Pinus radiata growth. • Soils occupied by A. nana show a reduction in mycorrhizal fungi beneficial to pine. • A. nana root exudates have a negative effect on growth of pine and beneficial fungi. [ABSTRACT FROM AUTHOR]

Abstract: Acacia dealbata Link, an Australian tree legume, is one of the most invasive species in south-eastern Europe. The invasive success of A. dealbata is partially attributed to its ability to release allelopathic compounds that affect native plant species, but the allelopathic effect on soil microbes has been little explored. Here, we used natural leachates to assess the bioactivity of these allelochemicals on soil microorganisms in native Mediterranean pine and mixed forests. Soil samples were treated either with acacia canopy leachate or the corresponding canopy leachate. Soil microbial communities were analyzed using Biolog Ecoplates™ and PCR–DGGE. Allelochemicals naturally released by A. dealbata clearly modified soil bacterial functional diversity in the pine forest where acacia leachate significantly increased the consumption of carbohydrates and amino acids and reduced the utilization of carboxylic acids. Acacia leachates also lead to a significant reduction in bacterial richness and diversity in the pine forest soil. However, the soil microorganisms of mixed oak forest were insensitive to allelochemical activity. Our results show that the allelopathic effects of A. dealbata on soil microbes depend on ecosystem type and that soil bacteria are more sensitive than soil fungi to the allelochemicals released by A. dealbata. We conclude that the higher sensitivity of pine forest soil microbiota to allelochemicals introduced by A. dealbata can contribute to the process of invasion. [Copyright &y& Elsevier]

Background: The invasive success of Acacia dealbata is partially attributed to the release of allelopathic compounds and changes in soil characteristics. However, both mechanisms have been studied separately, which does not reflect field conditions. Aims: To test whether interactions of allelopathy, soil origin and soil microbiota affect plant germination and growth of A. dealbata. Methods: Soil sampling and collection of natural canopy leachates were conducted in Coimbra, Portugal. Germination and seedling growth were tested in sterilised and control soils from native forests and invasive acacia stands, watered either with acacia or native canopy leachates. Sapling growth was further studied in soils from native forests and invasive acacia stands. Results: No interaction between Acacia leachates and soil microbiota was detected. Leachates of A. dealbata had a negative effect on the growth of its own seedlings in native soils. Soil microbiota reduced seedling growth in native forests. Saplings of A. dealbata grew bigger in the invaded soil than in soil from native forests. Conclusions: Soil microorganisms have a positive effect on the initial establishment and growth of A. dealbata. The effect of Acacia leachates depends on the origin of the soil. Soil previously modified by A. dealbata seems to favour its own growth. [ABSTRACT FROM PUBLISHER]

Abstract: During November 1997, an extreme rainfall event caused flooding in the Olary Creek and created a terminal lake within mallee vegetation on Nagaela Station, far western New South Wales. To assess the effect of this rare event on native flora, six 25×25m2 grazing exclusion plots were established on flooded (4), and un-flooded control (2) areas. We investigated (i) the distribution of Nicotiana glauca in relation to the 1997 flooding event (ii) the variation in density of N. glauca soil-stored seed between soil in control and exclosure plots (iii) the allelopathic effects of N. glauca on germination of Lactuca sativa seeds. Analysis of N. glauca stem sections revealed a maximum of five growth rings, confirming an origin following the 1997 flood event. At a September 1998 assessment, no N. glauca were found across flooded and control plots. In October 2000 N. glauca occurred at densities of 24 and 12 N. glauca seedlings ha−1 in the flooded unfenced and fenced plots respectively. No N. glauca individuals were recorded either from control fenced or unfenced plots. The soil-stored seed study revealed that larger numbers of N. glauca seeds were recovered from the flooded open plot (1936±968) than in flooded fenced plots (856±428.12) but none was found in the control plots. Leachates obtained from dry leaves and twigs had a significantly greater negative impact (p>0.001) on germination of L. sativa seeds than leachates obtained from fresh leaves and bark. This study showed that the density of N. glauca is high in areas where grazing had eliminated competition from native shrubs and grasses. N. glauca is potentially a serious weed along the Olary Creek and ephemeral lake boundaries. Management strategies such as reducing grazing pressure from native and introduced animals and/or effective eradication programs should be adopted, to minimize further infestation. [Copyright &y& Elsevier]

Abstract. Two field experiments were performed on the Great Barrier Reef, Australia, at Orpheus Island and Lizard Island, respectively, to investigate the effects of allelopathic soft corals on survivorship and community structure of scleractinian coral spat. Ceramic tiles were placed around the allelopathic soft corals Sinularia flexibilis (Quoy & Gaimard 1833) and Sarcophyton glaucum (Quoy & Gaimard 1833), and controls. One control consisted of settlement plates surrounding a scleractinian coral (non-allelopathic planktivore); another control had no adult soft or scleractinian coral present. The experimental soft corals affected the recruitment of various taxonomic groups of coral spat differentially, as evidenced by the diversity of coral spat settling in treatments and controls. At Orpheus Island (O.I., n = 1038 spat) and Lizard Island (L.I., n = 7032 spat), there were significant differences between recruitment success of the two dominant coral taxa, Pocilloporidae (O.I., 61.4 %; L.I., 20.5 %) and Acroporidae (O.I., 33.7 %; L.I., 53 %). Settlement plates exposed to Sinularia flexibilis at either site had the lowest proportion of acroporid recruits. Diversity indices (Shannon-Wiener Indices) varied significantly between treatments at both Orpheus and Lizard Islands. This appears to be due to selective inhibition of acroporid spat by Sinularia flexibilis at both sites. Growth of coral spat was higher on settlement plates in the presence of Sarcophyton at Lizard Island. Settlement of most associated epibiota was generally inhibited under these conditions. Coral spat survivorship was highest in the presence of Sinularia at Orpheus ­Island; at Lizard Island, this was the case with the Sarcophyton treatment. Higher survivorship, and in some cases growth, of coral spat near soft corals was apparently due to reduced competition for space between spat and associated epibiota. This hypothesis is supported by the results of a sister experiment where a coating of Sinularia flexibilis extract on settlement tiles significantly decreased fouling by sessile epibiota. Soft corals have an allelopathic effect on recruitment and early development of scleractinian corals and, consequently, on early coral reef community succession. [ABSTRACT FROM AUTHOR]

Agricultural productivity is very dependent upon the successful establishment of crops and pastures. High populations of vigorous seedlings enable the crop or pasture to withstand competition from weeds and infection from diseases as well as providing good utilisation of nutrient inputs and water. Residues of weed and pasture species can interfere with crop establishment and pasture regeneration. Research at Charles Sturt University (CSU) and elsewhere in Australia has focused on a better understanding of these relationships and the management of each situation to advantage the pasture and to minimise the impact of the allelopathic effects. Such effects include poor germination and early seedling growth and are influenced by the variety and species of agricultural plants being grown. [ABSTRACT FROM PUBLISHER]

Parthenium weed (Parthenium hysterophorus L.) is an invasive plant species in around 50 countries and a 'Weed of National Significance' in Australia. This study investigated the relative toxicity of the leaf, shoot and root extracts of two geographically separate and morphologically distinct biotypes of parthenium weed in Queensland, Australia. Parthenium weed exhibited higher phytotoxic, cytotoxic and photocytotoxic activity in leaf tissue extracts in contrast to shoot and root. The germination and seedling growth of a dicot species (garden cress) were inhibited more than those of a monocot species (annual ryegrass) using a phytotoxicity bioassay. The cytotoxicity of leaf extracts was assessed in a mouse fibroblast cell suspension assay and increased under high ultraviolet A(UV-A) radiation. A major secondary metabolite, parthenin, was found in abundance in leaf extracts and was positively correlated with cytotoxicity but not with photocytotoxicity or phytotoxicity. Ambrosin and chlorogenic acid were also detected and were positively correlated with germination inhibition and the inhibition of radicle elongation, respectively. In addition, other currently unidentified compounds in the leaf extracts were positively correlated with phytotoxicity, cytotoxicity and photocytotoxicity with two to three molecules strongly correlated in each case. Both parthenium weed biotypes investigated did not differ with respect to their relative toxicity, despite their reported differences in invasive potential in the field. This suggests that secondary chemistry plays a limited role in their invasion success. [ABSTRACT FROM AUTHOR]

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., (© 2021 Botanical Society of America.)