Effects of Leachates From Shrub Patches on the Survival and Biomass of Native Perennial Grasses and Shrubs in Disturbed Rangelands of the Patagonian Monte, Argentina

The eventual negative effect of allelochemicals released from shrub canopies has been scarcely studied in arid ecosystems. We analyzed the effects of leachates from shrub canopies with high concentrations of soluble phenols, their associated soils, and neighboring seedlings on the survival and biomass of seedlings of perennial grasses and shrubs in arid rangelands of the Patagonian Monte. We conducted a microcosm experiment using soils from plant patches dominated by Schinus johnstonii (Sj) and Larrea divaricata (Ld). Microcosms with recently emerged seedlings (two per microcosm) with individual perennial grass species (Pappostipa speciosa, Nassella tenuis, and Poa ligularis), individual shrub species with high concentrations of soluble phenols (Ld, Sj), and combinations of shrub and perennial grass species were installed under inert shrub canopies mimicking natural Ld and Sj canopies. Microcosms were exposed to low (5%–10%) and high (10%–20%) ranges of soil moisture using water and leachates from canopy patches of Ld or Sj for 14 months. Both shrub canopy leachates had high soluble phenols concentrations, but Sj leachates exhibited a more phenolic complex structure than Ld leachates. Seedling survival was not affected by leachates or patch soils, reaching the highest values when both life forms coexisted. The total biomass of both life forms was only negatively affected by Sj leachates. Our results highlighted that those shrubby canopies with phenolics of complex structure may exert negative allelopathic interactions during the early establishment of both perennial grasses and shrubs, being allelopathy a complementary mechanism to the facilitation/competition balance to be considered in the dynamics of plant patches in arid ecosystems.