Hol Et Al. Species Loss and Antifungal Volatiles 1 Running Head: Species Loss and Antifungal Volatiles Non-random Species Loss in Bacterial Communities Reduces Antifungal Volatile Production

12 The contribution of low-abundance microbial species to soil ecosystems is easily overlooked 13 because there is considerable overlap between metabolic abilities (functional redundancy) of 14 dominant and subordinate microbial species. Here we studied how loss of less abundant soil 15 bacteria affected the production of antifungal volatiles, an important factor in the natural control 16 of soil-borne pathogenic fungi. We provide novel empirical evidence that the loss of soil bacterial 17 species leads to a decline in the production of volatiles that suppress root pathogens. By using 18 dilution-to-extinction for seven different soils we created bacterial communities with a decreasing 19 number of species and grew them under carbon-limited conditions. Communities with high 20 bacterial species richness produced volatiles that strongly reduced the hyphal growth of the 21 pathogen Fusarium oxysporum. For most soil origins loss of bacterial species resulted in loss of 22 antifungal volatile production. Analysis of the volatiles revealed that several known antifungal 23 Hol et al. Species loss and antifungal volatiles 2 compounds were only produced in the more diverse bacterial communities. Our results suggest 24 that less abundant bacterial species play an important role in antifungal volatile production by 25 soil bacterial communities and, consequently, in the natural suppression of soil-borne pathogens. 26