Showing papers on "Native plant published in 1996"

A native nitrogen-fixing shrub facilitates weed invasion

Abstract: Invasions by exotic weedy plants frequently occur in highly disturbed or otherwise anthropogenically altered habitats. Here we present evidence that, within California coastal prairie, invasion also can be facilitated by a native nitrogen-fixing shrub, bush lupine (Lupinus arboreus). Bush lupines fix nitrogen and grow rapidly, fertilizing the sandy soil with nitrogen-rich litter. The dense lupine canopy blocks light, restricting vegetative growth under bushes. Heavy insect herbivory kills lupines, opening exposed nitrogen-rich sites within the plant community. Eventual re-establishment of lupine occurs because of an abundant and long-lived seed bank. Lupine germination, rapid growth, shading and fertilization of sites, and then death after only a few years, results in a mosaic of nutrient-rich sites that are available to invading species. To determine the role of bush lupine death and nitrogen enrichment in community composition, we examined nutrient dynamics and plant community characteristics within a site only recently colonized by lupine, comparing patches where lupines had recently died or were experimentally killed with adjacent areas lacking lupine. In experimentally killed patches, instantaneous pool sizes of exchangeable ammonium and nitrate nitrogen were higher than in adjacent sites free of lupine. Seedlings of the introduced grass Bromus diandrus accumulated 48% greater root biomass and 93% more shoot biomass when grown in a greenhouse in soil collected under experimentally killed lupines compared to B. diandrus seedlings grown in soil collected at least 1 m away from lupines. At the end of the spring growing season, total above-ground live plant biomass was more than twice as great in dead lupine patches as in the adjacent lupine-free grassland, but dead lupine patches contained 47% fewer plant species and 57% fewer native species. Sites where lupines have repeatedly died and reestablished during recent decades support an interstitial grassland community high in productivity but low in diversity, composed of mostly weedy introduced annual plants. In contrast, at a site only recently colonized by bush lupines, the interstitial grassland consists of a less productive but more diverse set of native and introduced species. We suggest that repeated bouts of lupine germination, establishment, and death can convert a rich native plant community into a less diverse collection of introduced weeds.

Dynamics of energy and nutrient concentration and construction cost in a native and two alien C4 grasses from two neotropical savannas.

Abstract: In Venezuela, the alien grasses Melinis minutiflora Beauv. and Hyparrhenia rufa (Nees.) Stapf tend to displace the native savanna plant community dominated by Trachypogon plumosus (Humb. and Bonpl.) Nees. This occurs in either relatively wetter and fertile highland savannas or in drier and less fertile lowland savannas. Although the native and aliens are perennial C4 grasses, higher net assimilation leaf biomass per plant and germination rate of the latter are some causes for their higher growth rates and for their competitive success. The objective of this study is to compare seasonal tissue energy, N, P and K concentrations and the calculated construction costs (CC) between the native grass and either one of the alien grasses from lowland and highland savannas. We predict that, in order to out-compete native plants, alien grasses should be more efficient in resource use as evidenced by lower tissue energy and nutrient concentrations and CC.

Using native plants as problem-solvers

Abstract: / The Federal Highway Administration encourages state highway agencies to use native plants in erosion control, revegetation, and landscaping solutions. This paper explains both policy reasons and technical reasons for the use of native plants. How native species can be used is shown through a roadside case study. Other applications of native plant use will be explained through a plant community approach. KEY WORDS: Native plants; Plant community; Federal Highway Administration; State highway agencies; Native plant definition

The biology, ecology and taxonomy of Phytophthora citricola in native plant communities in Western Australia

Abstract: The objectives of the project were to develop an understanding of the disease dynamics caused by Phytophthora citricola in native plant communities in the south of Western Australia. Prior to 1983, the pathogen had only been reported twice from Australian forests. Since then, P. citricola has been extensively recorded from plant communities north and south of Perth, and is currently the second most frequently recovered Phytophthora species from the northern jarrah forest and the northern sandplains. The objectives were addressed by examining the biology, ecology and taxonomy of isolates of P. citricola local to the southwest. Examination of the intraspecific variation of P. citricola by isozyme analysis resolved three major electrophoretic subgroups (SG), and these were aligned with morphological and cultural variation within the species. One electrophoretic SG was confined to forested areas. This SG differed from other SGs in sporangial dimensions, growth rate on two media and in vitro sensitivity to phosphonate. A redescription of the species may be warranted. P. citricola was positively associated with two roads in the northern jarrah forest. Road surfaces were sampled, then soil overburden was removed and the surface of the concreted lateritic layer beneath was sampled. Isolation of P. citricola declined away from the road into the adjacent forest and was more frequently recovered from the caprock (up to 1 metre below soil surface) than from the soil surface. The most probable source of introduction was from infested soil on vehicles using the roads. Oospores were shown to be produced in two soils, a lateritic gravelly loam and sand, and in plants. In soil, the electrophoretic SG confined to the forest (loamy soil) produced only limited numbers of oospores in the sandy soil of the northern sandplain. The restriction of this SG to the forested areas is probably physiological, rather than limited dispersal, with the SG currently occupying the full extent of its range. Estimation of the relative persistence of oospores, zoospores and plant material colonised by P. citricola established that only oospores (either free in soil or in colonised plant material) were important in long tern survival in soil. Oospores were still viable after six months at two field sites, and after 18 months in soil in the laboratory. Phosphonate is currently the most promising method of control of Phytophthora induced disease in native plant cornmunites of the southwest. The efficacy of phosphonate against P. citricola was examined in vivo and in vitro against two SGs. Phosphonate successfully inhibited lesion growth of both SGs in vivo, but of only one electrophoretic subgroup in vitro. The ecological implications of infestation of native plant communities in the southwest of Australia are discussed.

Control of African Striga Species by Natural Products From Native Plants.

Abstract: Obligate root-parasitic flowering plants o f the genus Striga (fam ily Scrophulariaceae) cause considerable yield reductions o f various crops in tropical and semi-tropical countries. Mature Striga species (witchweeds) plants produce copious quantities o f minute seeds which remain dormant in the soil fo r many years until exudates from roots o f various host plants induce germination. Economically effective means o f control o f Striga species are not yet available fo r small-scale farmers in developing countries. In the present study data is presented which indicate that the two most effective Striga control measures are crop rotation and suicidal germination. For the firs t time we have analyzed the dichloromethane extracts of dry and conditioned Striga species seeds by means of gas chromatography coupled to mass spectrometry. Sixteen compoimds were identified on the basis o f their mass spectra and their retention indices. A ll Striga species extracts contained tetradecanoic acid, cis,cis9,12-octadecadienoic acid, c/j-9-octadecenoic acid and sitosteroL Also, 2,6-dimethoxyp-benzoquinone (2,6-DMB(3) and several long chain aldehydes and n-hydrocarbons were detected in some o f the extracts. The nature of the chemical changes induced by seed conditioning are discussed. Dichloromethane and water extracts of various parts o f legume cultivars were tested fo r stimulation o f germination o f Striga species seeds as described in the experimental sections. Also, several pure compounds isolated were assayed. Dilution methods, which are very sensitive and better suited fo r quantifying germination stimulant activity, were employed in identification o f high and low stimulant producing legume cultivars. New and interesting relationships between stimulatory activity and concentration emerged. Most pure compounds tested induced significant germination o f isolates o f Striga species seeds across a broad concentration range, from 10*3 to 10' 20 M. The mechanism o f Striga germination proposed may foster synthesis o f more effective germination stimulants and/or inhibitors.

Wildflowers for indiana highways

Abstract: Questions concerning wildflower usage on Indiana highway rights-of-way were investigated. Native prairie wildflower seed quality was found to be highly variable among supply companies, species, and years. Less variability was found among "garden" wildflower species and suppliers. Direct seeding was found to be successful with six species of native prairie forbs: Butterfly Milkweed (Asclepias tuberosa), Wild Bergamot (Monarda fistulosa), New England Aster (Aster novae-angliae), Pale-purple Coneflower (Echinacea pallida), Gray-headed Coneflower (Ratibida pinnata), and Ironweed (Vernonia fasciculata). Five species of "garden" wildflowers performed well: Common Cosmos (Cosmos bipinnatus), Yellow Cosmos (Cosmos sulphureus), Cornflower (Centaurea cyanus), Goldenwave (Coreopsis tinctoria), and Black-eyed Susan (Rudbeckia hirta). Significant variation was found for species establishment success with respect to soil type. Seedling transplanting was found to be a successful method for establishment of forb species, especially those that are difficult to establish by direct seeding. Eight-inch deep seedling tubes increased plant survival compared to plants produced in five-inch deep tubes. Use of water-holding polymers in the growing medium, or inoculation with vesicular-arbuscular mycorrhizal fungi did not improve forb transplant survival. VAM inoculation did result in larger plants after the first growing season. The costs of establishment and management of wildflowers varied with the type and management strategy. Wildflowers were found to be cost-effective when compared to the current grass monoculture vegetation strategy used by the Indiana Department of Transportation. "Garden" wildflowers were less costly to establish, but were more costly on an annual basis. Prairie plant community wildflowers were more costly initially, but became cost effective when low, long-term management costs were factored into the analysis.