2019 ASHS Annual Conference

Desert plants have evolved diverse tools for accessing limited water and soil nutrients, including inhibition of seed germination and growth of potential competitors. One tool for doing so is allelopathy – the exudation of compounds that inhibit the growth or germination of other plants. The desert shrub Larrea tridentata (creosote) is known for allelopathy and thus for forming monodominant stands of evenly spaced plants with few competitors in its extreme natural environments. Increasingly it is appreciated that plant microbiomes – the suite of microbes that live on, in, and in association with plant tissues – alter the chemical expression of their host plants. However, the potential roles of rhizosphere microbes in allelopathy are not well known. The aim of this study was to evaluate potential contributions of microbes to allelopathy of creosote. In phase one we surveyed the root microbiome of creosote in monodominant stands west of Tucson, Arizona, USA. Surveys encompassed aerobic, anaerobic, and oligotrophic microbes and were designed to provide a rich culture library that, after identification with molecular barcoding, was used in phase two (inhibition assays, designed to measure the capacity of these microbes, individually and in the context of infecting root tissue of creosote, to inhibit seed germination and growth of representative desert plants). Overall this study advances our understanding of the diversity of microbes associated with an iconic desert shrub and provides a first perspective on the capacity of microbes, or plant-microbe interactions, to influence the powerful allelopathic properties of one of the Southwest’s most distinctive plants.