Plant allelopathic interactions matter in arid ecosystems of Patagonia: An analysis across a wide aridity gradient

Abstract

Shrubs and perennial grasses coexist in most semi-arid and arid ecosystems of the world. We analyzed changes in shrub/perennial grass cover ratios and the concentrations of two phytochemicals with high (soluble phenols) and low (lignin) allelochemical potential across a wide aridity gradient in Patagonia. We asked whether shrubby canopies create ecological/environmental contexts favorable for allelopathic interactions between shrubs and perennial grasses. Shrub/perennial grass cover ratio increased with increasing aridity. Evergreen tall shrubs, accounting among the dominant shrub morphotypes at the driest sites, showed many-fold higher soluble phenol and lower lignin concentrations in their green leaves than tall deciduous, medium, and dwarf shrub morphotypes. Studies in the Patagonian Monte (driest extreme of the gradient) indicated that leaf leachates and propagules of evergreen tall shrubs, and their associated soils had high concentrations and diversity of soluble phenols negatively affecting in different ways the germination, establishment, and biomass of perennial grass species with differential plant traits. No evidence of allelopathic interactions was reported when shrubby canopies were dominated by other shrub morphotypes with high concentration of lignin in leaves (wettest extreme of the gradient). We concluded that aridity shapes ecological/environmental contexts, which could promote allelopathic interactions between shrubs and perennial grasses.