Mechanisms of Plant Species Coexistence: Roles of Rhizosphere Bacteria and Root Fungal Pathogens

Abstract

Abstract. Two independent experiments were conducted to investigate the influence of rhizosphere bacteria on the growth of Anthoxanthum odoratum and Panicum sphaerocarpon. We tested whether host-specific populations of Bacillus mycoides affected the growth of their Anthoxanthum and Panicum hosts and whether host-specific differences in Bacillus populations modified the strong detrimental effect of the root fungal pathogen, Pythium macrosporum. Our results showed both positive and negative effects of Bacillus inoculation and that Anthoxanthum and Panicum plants responded differently to Bacillus isolates that originated from different host plants. Anthoxanthum grew relatively better with isolates from Panicum, while Panicum grew relatively better with isolates from Anthoxanthum, consistent with a negative feedback. In both experiments Pythium infection was detrimental to plant growth, and Panicum was more negatively affected by inoculation with Pythium. Overall, Bacillus ameliorated the pathogenic effect of Pythium. However, there was no evidence that host-specific Bacillus populations had different effects on the interaction between these plant species and Pythium. Both host-specific differences in rhizosphere bacteria and host-specific accumulation of a fungal pathogen can generate negative feedback between these two plant species.

Plant-soil feedback as a mechanism of invasion by Carpobrotus edulis

“…As pointed out before, we observed an accumulation of chytrids in the long-term invaded soils and the role of these symbiotic fungi in the plant community needs to be elucidated. The accumulation of soil fungi in the invaded soils could be detrimental for other plants and not for C. edulis, a mechanism that has been observed in other invasive plants (Mangla and Inderjit 2008;Eppinga et al 2006;Westover and Bever 2001).…”

An invasive aster (Ageratina adenophora) invades and dominates forest understories in China: altered soil microbial communities facilitate the invader and inhibit natives

“…The direction of soil biota feedback can be positive, neutral, or negative, and depends on the balance between negative effects of accumulating soilborne pathogens, herbivores, and parasites (Brown and Gange 1989;van der Putten 2001;Packer and Clay 2002) and the positive effects of accumulating mycorrhizal fungi, nitrogen-fixing bacteria, and other beneficial soil organisms (Allen and Allen 1984;Garbaye 1994;Horiuchi et al 2005). These feedbacks occur when plants change the components of the soil microbial community and affect plant establishment, growth, competition, and community succession (Westover and Bever 2001;Reynolds et al 2003).…”

Bacterial inoculation of maize affects carbon allocation to roots and carbon turnover in the rhizosphere

“…Among discussed possible mechanisms leading to plant growth promoting effects are such diverse processes as associative nitrogen fixation (Boddey and Döbereiner, 1988;Dobbelaere et al, 2001), Psolubilization (Schilling et al, 1998;Singh and Ka- * FAX No: +49 551 39 55 70. E-Mail: jschulz2@gwdg.de poor, 1999;Reyes et al, 2002), bacterial hormone excretion (Scholz-Seidel and Ruppel, 1992;Okon and Itzigsohn, 1995;Bent et al, 2001) or defense against pathogenic organisms (Kumar et al, 2001;Westover and Bever, 2001), all of which are strongly dependent on environmental conditions. Thus it becomes understandable that defining and sustaining beneficial mechanisms of bacterial inoculation in the complex soil-rhizosphere-plant system is not a trivial task.…”