PARENT SESSION
Symposium 19: The Role of Plant-Microbe Feedbacks in Plant Invasions
Organized by: K Reinhart and R Callaway
Thursday, August 7. 1:30 PM to 5:00 PM, SITCC Oglethorpe Auditorium.

Interactions between black cherry seedlings and the microbial soil community across a successional gradient.

Packer, Alissa ^*,1, Clay, Keith¹, ¹ Indiana University- Bloomington, Bloomington, IN

ABSTRACT- Plant interactions with soil microbes may strongly affect the structure and dynamics of natural communities. Negative feedback between black cherry (Prunus serotina) and soil-borne fungal pathogens (Pythium spp.) is known to result in high mortality of conspecific seedlings close to trees. Based on these findings we expect uniform, rather than aggregated, spatial distributions of trees. However black cherry trees at early successional sites in the Midwest are often aggregated. We asked whether the plant/pathogen interaction intensifies with succession, as might be predicted if host-specific pathogens accumulate over time. We expected that seedling mortality near conspecific trees in the field would be greater in later successional sites than earlier successional sites. In greenhouse experiments we compared seedling survival and growth in sterile and unsterile soil collected beneath trees at each site, which allowed us to examine the effect of soil biota independent of confounding factors in the field. Seedling survival did not vary predictably with successional age in the field. In greenhouse experiments sterilization of field soil improved seedling survival regardless of successional age, suggesting that the soil microbial community negatively affects seedlings at all sites. We also examined the rate at which the soil community develops by repeatedly planting seedlings in soil collected from conspecific trees at both a young and a mature successional site (four sequential 5-week growth cycles). Host-induced alteration of the soil community was inferred from changes in seedling survival in field soil relative to sterile soil. Negative effects of soil biota increased with repeated growth cycles, potentially resulting from changes in microbial composition. In field soil, survival decreased with increased growth cycles regardless of the site age. Together these results suggest that negative plant/soil microbe feedback occurs rapidly during plant succession. Aggregated populations of black cherry trees may occur because seedlings establish in the community at the same time.

Key words: pathogens, Prunus serotina, succession