Glyphosate retention in grassland riparian areas is reduced by the invasion of exotic trees

Gustavo Carlos María Giaccio, P Laterra, VC Aparicio, JL Costa


In this study, we examined some aspects regarding theeffect of willow trees (Salix fragilis L.) invasion of grassland riparianenvironments in the Argentinean Pampas on the runoff reduction,sedimentation and glyphosate retention in the riparian vegetationstrip (RVS). To assess the influence of willows on the filtering mechanisms,we performed runoff simulation experiments in plots of 1.5 x2.5 m, in coastal environments characterized by the presence of willowsor the lack of trees. Despite the short length of the experimentalplots, the retention of glyphosate in the controls, with no trees, washigher and reached almost 74%. Nevertheless, sediment retentiondid not differ significantly between the tree areas and the grassycontrols. The runoff reduction in plots with willows was of 63%.The presence of willow trees significantly altered the measured biophysicalproperties, such as soil moisture and aboveground biomass,compared to areas without trees. Analysis of partial correlations forenvironments with and without trees showed that the reduction inrunoff volume increased significantly with the soil sand content andthe groundwater table depth, while it decreased with bulk density,soil moisture and the riparian slope. Sediment retention increasedsignificantly with aboveground biomass, litter and root biomass;and decreased with the riparian slope. In turn, glyphosate retentionincreased significantly with sediment retention and decreased withthe riparian slope and litter biomass. The mechanisms involving theeffect of willows could not be well explained. Due to the increasedintensification of agriculture, treeless RVS are important to reduceglyphosate concentration in streams and their sinks. Nevertheless,the presence of trees is also important in the context of agroecosystemsand agricultural landscapes, as they contribute to reduce therunoff flow.

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Phyton. International Journal of Experimental Botany. ISSN print 0031-9457 ISSN en line 1851-5657 Fundación Rómulo Raggio Gaspar Campos 861,  Vicente López, Buenos Aires, Argentina (C.P. 1638) Tel 54 11 4791-0868 / 4796-1456