MICROBIAL DRIVERS SUPPORT LEHMANN’S LOVEGRASS GERMINATION AND PERSISTENCE AT THE SANTA RITA EXPERIMENTAL RANGE

Abstract

Invasive plants often have traits that promote their success in novel landscapes. Among these may be a propensity to form symbioses with beneficial fungi that promote the establishment of the invader. Lehmann’s lovegrass (Eragrostis lehmanniana, ERLE) was introduced to southern Arizona in 1913 to improve grazing for livestock. It now displaces native grasses and dominates the landscape. Diverse hypotheses have been proposed to explain its success, focusing on phenology and tolerance of fire. I have examined how fungal symbionts contribute cryptically to its success and found that fungal endophytes commonly associated with ERLE increase seed germination of that species but decrease germination of native grasses in vitro. As these endophytes complete their life cycles in litter and soil, I proposed that ERLE seeds exposed to soils from areas with a high density of ERLE would germinate well, whereas seeds of native species would not. I found that seed germination of two native grasses (Bouteloua curtipendula, Eragrostis intermedia) decreased in the presence of ERLE-dominated soils. ERLE seeds germinated equally well in the presence and absence of these soil fungi. A complementary litter-degradation experiment showed litter decomposition rates of a native grass (Digitaria californica) were higher than decomposition rates of ERLE in patches of native grasses. These patterns persist regardless of shrub canopy cover, suggesting that microclimate is less important than the action of litter-degrading fungi associated with ERLE vs. native species. Together, these results suggest important and understudied roles of diverse fungi in shaping invasion success in grasslands.