Riqueza, composición y abundancia de especies en una comunidad vegetal ribereña en el río Santa Catarina, Monterrey, Nuevo León

La vegetación ribereña constituye un elemento clave para el mantenimiento de los ecosistemas fluviales, en especial, en aquellos que se encuentran circundados por zonas urbanas. El objetivo del presente trabajo fue evaluar la variación espacial de la riqueza, la composición y la estructura de la vegetación ribereña en un tramo del río Santa Catarina sobre dos municipios de la Zona Metropolitana de Monterrey. Para el análisis de la vegetación, se establecieron transectos de muestreo, en un tramo de 15.65 km. El estrato alto (plantas arbustivas y arbóreas), se analizó mediante un modelo de ordenación Bray-Curtis y una gráfica de dominancia-diversidad. Para el estrato bajo (plantas herbáceas), se utilizó el coeficiente de similitud de Jaccard. En el estrato alto, se registraron 16 familias pertenecientes a 25 géneros y 28 especies. Las especies con mayor número de individuos fueron Salix nigra, Leucaena leucocephala, Ricinus communis y Parkinsonia aculeata. La composición de la vegetación tiene una similitud de intermedia a alta, ya que los grupos variaron con valores de 60 % a 71.53 %. En el estrato bajo, se registraron 25 familias, 53 géneros y 60 especies, con una similitud de baja a intermedia, debido a que los primeros tres grupos variaron entre 23 % a 47 %. Las especies que se reportaron con mayor distribución en el estrato bajo, fueron Cyperus involucratus y Phragmites australis en 7 sitios cada una, Eragrostis mexicana, Heliantus annuus, Melinis repens, Polygonum pensylvanicum y Typha domingensis, en 6 sitios cada una. La composición de la vegetación se encuentra en un estado sucesional secundario, debido a que las especies con mayor presencia son introducidas, como Leucaena leucocephala y Ricinus communis para el estrato alto, y Cypereus involucratus y Melinis repens, para el estrato bajo.

Banded herbicide, rotary hoeing and cultivation effects on weed populations in ridge-tilled soybean

Can banded herbicide be eliminated in ridge-tilled soybean (Glycine max)? The effects of banded herbicide, rotary hoeing and cultivation on weed populations and soybean yield in a ridge-tillage system were tested on three farms in Iowa, USA in 1989 and 1990. In 1989, plots either had no herbicide or had herbicide banded in the row at planting in mid-May; all plots received two rotary hoeings and two cultivations. In 1990, treatments were banded herbicide with no rotary hoeing, banded herbicide with one rotary hoeing, and no herbicide with one or two rotary hoeings; all plots received two or three cultivations. In both years, over all weed species [primarily giant foxtail (Setaria faberi), Pennsylvania smartweed (Polygonum pensylvanicum) and redroot pigweed (Amaranthus retroflexus)], seedling emergence was highest in late May and early June, with few seedlings emerging after mid-June. Weed populations were highest in May and June, after which rotary hoeing and cultivation reduced weed numbers in all plots. There were no consistent differences among treatments in weed numbers in early August for the 2 years. In both years, there was no significant difference in soybean yield among treatments. Within-farm mean yields ranged from 2.26 to 3.01 Mg ha−1among farms in 1989 and from 2.07 to 2.93 Mg ha−1among farms in 1990. Ridge-tillage without herbicide was generally equivalent to ridge-tillage with banded herbicide, with respect to total number of weeds and number of broad-leaved weeds remaining in August after tillage, and to soybean yield.

Germination Techniques for Common Lambsquarters (Chenopodium album) and Pennsylvania Smartweed (Polygonum pensylvanicum)

A laboratory bioassay was conducted to describe the effects of cold stratification and solid matrix priming (SMP®) on the germination response of common lambsquarters and Pennsylvania smartweed seeds. Treating seeds of common lambsquarters with a combination of cold stratification and SMP resulted in 78% germination compared with 13% in control seeds. Analogous treatments of Pennsylvania smartweed seeds resulted in 22% germination compared with 1% for control. Improved germination of common lambsquarters and Pennsylvania smartweed seeds suggested that the combination of cold stratification and SMP treatments have potential for improving seed germination in other weed species that exhibit high levels of seed dormancy.

Genotypic variation in Polygonum pensylvanicum: nutrient effects on plant growth and aphid infestation

Variation in the performance of 20 genotypes of Polygonum pensylvanicum under two nutrient treatments was studied in a garden experiment. Nutrient fertilization enhanced vegetative biomass and fruit biomass production, but did not result in significant genotype–environment interactions, suggesting that nutrient variation of the range used in the experiment has little potential as a microevolutionary factor in this species. Leaf nitrogen concentration was not affected by a nutrient pulse. The degree of transient aphid infestation that occurred during the experiment had a weak positive correlation with final reproductive biomass of plants. Mean density of aphids per leaf was negatively correlated with percent leaf nitrogen and was not affected by genotypic identity of host plants. Key words: Polygonum pensylvanicum, genotype–environment interaction, phenotypic plasticity, aphids, nutrients.

Allozyme variation in the Polygonum lapathifolium complex

The Polygonum lapathifolium complex consists of populations that are widely distributed in the Northern Hemisphere and that have been classified at different taxonomic levels. Allozyme data were used to test the current North American taxonomic status of members of the complex (including P. lapathifolium var. lapathifolium, P. lapathifolium var. salicifolium, and P. scabrum) and to verify diploidy in the P. lapathifolium complex and polyploid origins of the morphologically similar P. persicaria and P. pensylvanicum. Of the 15 enzyme systems surveyed in 50 populations of the complex, only 3 of the 23 loci (Acon, Lap, and Skdh) were polymorphic in the North American populations and a total of 6 loci in European populations. Fifteen multilocus genotypes were evident in the complex. Four genotypes (all with Lap-10.67 were exclusive to North American populations of P. lapathifolium, providing support for a North American element of the complex. Nine genotypes (all with Lap-10.63) were found in North American and European populations of P. scabrum, all European populations of the P. lapathifolium complex, and three populations of North American P. lapathifolium var. lapathifolium. Lap-10.67 was also found in the native tetraploid P. pensylvanicum, whereas Lap-10.63 was found in the introduced tetraploid P. persicaria. Genetic distances among populations did not support the current taxonomic divisions within the complex, nor did it support separate species status of P. scabrum. Allozyme data provided support for the allotetraploid origins of P. pensylvanicum and P. persicaria, with members of the P. lapathifolium complex as one of the parents of each. Key words: Polygonum lapathifolium, Polygonum scabrum, Polygonum pensylvanicum, Polygonum persicaria, allozymes.

Mutant Weeds of Iowa:S-Triazine Resistant Pennsylvania Smartweed (Polygonum pensylvanicum)

Suspected triazine resistant Pennsylvania smartweed plants were discovered near Holy Cross, Dubuque County, IA. Subsequent variable chlorophyllafluorescence assays confirmed these selections to be triazine resistant. This is the first reported evidence ofs-triazine resistance in Pennsylvania smartweed.

Comparison of Ronstar Formulations for Efficacy and Phytotoxicity in Container Grown Landscape Plants

Three formulations of Ronstar [oxadiazon-2-tert-butyl-4-(2,4-dichloro-5-isopropoxyphenyl)-2-1 ,3,4-oxadiazolin-5 one], were evaluated for control of 3 weed species and injury to 3 woody landscape plants over 90 days. Wettable powder (WP) 50%, 20% granular and 0.24 kg/L (2 lb/gal) emulsifiable concentrate (EC) were evaluated at 3 rates, 2.2, 4.5 and 9.0 kg/ha (2,4 and 8 lb/A). The WP formulation was generally more effective than the G formulation for control of goosegrass [Eleusine indica (L.) Gaert] and Pennsylvania smartweed (Polygonum pensylvanicum L.). Ronstar at the 4.5 kg/ha (4 lb/A) rate of WP and EC formulations provided excellent control of goosegrass and Pennsylvania smartweed. Prostrate spurge (Euphorbia humistrata Eagelm. ex gray) was controlled only by the 9.0 kg/ha (8 lb/A) rate of all 3 formulations. Pronounced injury to Compact Japanese Holly (Ilex crenata Thumb. ‘Compacta’) and ‘Hershey Red’ Azalea Rhododendron obtusum was evident at 14 and 30 days after treatment with the WP and EC formulations. Ninety days after treatment the species were marketable plants. Evergreen euonymus (Euonymus japonica) was not injured with any formulation or rate of Ronstar.