Propagule bank and plant emergence of macrophytes in artificial channels of a temperate irrigation area in Argentina

The irrigation district of the lower valley of Rio Colorado (62 degrees 37' W, 39 degrees 23' S) was examined during 1995 and 1996 to evaluate propagu le bank abundance and regeneration in five irrigation and five drainage cha nnel sites. Six 15 cm deep cores from each site were collected in late wint er and sectioned into two subsamples. One was sieved to identify taxa and p ropagule density and the other was placed under controlled laboratory condi tions to record emergence over 90 days. Mean propagule density of Potamoget on pectinatus (260 tubers. m(-2), 173 rhizome nodes. m(-2) and 246 seeds. m (-2)) and Zannichellia palustris (968 seeds. m(-2)) was higher in irrigatio n than in drainage channels. By contrast, higher values in drainage channel s were recorded for Ruppia maritima (4352 seeds. m(-2)) and Chara contraria (35633 oospores. m(-2)). Plant emergence in P. pectinatus was independent of channel type. Higher and lower values were registered in irrigation chan nels for Z. palustris and the other two species, respectively. Plant emerge nce in relation to propagule density for all the species ranged from 24% to 56%, and no differences were found between irrigation and drainage channel s. Results are discussed in relation to the established vegetation and the different management and environmental conditions of both types of channels .