PS 11-158 - CANCELLED - Wildfire-induced changes to soil chemistry inhibit growth and re-establishment of a harmful, annual invasive

Abstract: Wildfires can fundamentally alter species interactions among plants indirectly through changes to the soil chemistry, including acidification, mobilization of additional nutrients, and active carbon deposits. As climate change-exacerbated droughts, invasive grasses, arson, and accidental ignitions of dry litter increase the frequency of wildfires throughout much of the world, studying how fire-induced changes to interactions between native and invasive species is quickly becoming of greater importance. My previous work showed that fire resulted in reduced abundance of a harmful, allelopathic invasive black mustard (Brassica nigra) in Southern California sage scrub and increased replacement by native "fire-followers" in the second year of post fire vegetative recovery. Since active carbon can bond to and neutralize active sites on allelopathic exudates, I hypothesize that carbon is the primary driver of reduced competitiveness and hence abundance of B. nigra. However, the exact mechanisms of changes to plant-soil feedback remain elusive. To tease apart the effects of fire-induced alteration of soil chemistry and how it affects plant-soil feedbacks, and thus species interactions, a full-factorial greenhouse experiment examining how active carbon, additional nutrients, and soil acidification interact to affect interactions between B. nigra and the native "fire-follower" deerweed (Acmispon glaber) was conducted. Active carbon resulted in the greatest reduction in B. nigra shoot DW, leaf count, and inflorescence (proxy for fitness), but additional nutrients and acidification of soils also had significant affects on species interactions. Taken together, results suggested that contrary to commonly held wisdom, fire can inhibit the establishment of one of the more harmful invasives that threaten native plant diversity in Southern California.