Invasive Species Compendium

Detailed coverage of invasive species threatening livelihoods and the environment worldwide

Abstract Full Text

Does plant response to the limiting resource explain invasibility? An experimental test using two invasive weeds and their non-invasive native congeners.


Alternanthera philoxeroides (alligator weed) and Phyla canescens (lippia) are two exotic weeds invading wetlands and riparian habitats in Australia. Preliminary studies showed that at low nutrient levels, lippia and alligator weed were healthy but their growth rates were reduced. Tissue analyses of plants collected from the field revealed nitrogen/phosphorus ratios <14, which indicate nitrogen is probably the primary nutrient limiting plant growth. In a glasshouse study, the growth responses of both invasive plants and their 'native non-invasive' congeners to differing nitrogen concentrations were compared. A. philoxeroides to A. denticulata and P. canescens to P. nodiflora were contrasted. Plants were grown individually in a washed peat-sand (20:80) substrate at five levels of nitrogen (1 to 30 mmol/litre). Dry biomass (roots, stems and leaves), shoot characteristics, leaf area and physiological characteristics were measured. Relative growth rate, the below-ground biomass to above-ground biomass ratio and the physiological responses were compared between the nitrogen concentrations and among the four species. The results are presented during the conference.