Submitted to: Acta Oecologica
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 28, 2010
Publication Date: September 1, 2010
Citation: Reinhart, K.O., Royo, A.A., Kageyama, S.A., Clay, K. 2010. Canopy gaps decrease microbial densities and disease risk for a shade-intolerant tree species. Acta Oecologica 36(6):530-536. Interpretive Summary: • Forest disturbances appear to reduce the densities of some soil-borne pathogens and other soil microbes. • Reduced densities of soil-borne pathogens (Pythium) reduce disease expression of susceptible tree species but have no affect on those that appear resistant to disease. • Theoretical implications- Results suggest that forest disturbances create refuges from pathogens where susceptible (and likely shade-intolerant) species can recruit. Our results suggest that successional processes may be affected by shade tolerance adaptations and variation in and susceptibility to pest pressure. Results from this study suggest that shade tolerant species are less susceptible to soil-borne pathogens than shade intolerant species but more comparisons are needed to confirm this as a generalization. • Management implications- Black cherry (Prunus serotina) is a highly valuable timber species that is susceptible to soil-borne diseases caused by Pythium. Results from this study suggest that forest gaps reduce pathogen loads and create opportunities for this tree species to re-establish.
Technical Abstract: Canopy disturbances such as windthrow events have obvious impacts on forest structure and composition aboveground, but changes in soil microbial communities and the consequences of these changes are less understood. We characterized the densities of a soil-borne pathogenic oomycete (Pythium) and a common saprotrophic zygomycete (Mortierella) in nine pairs of forest gaps created by windthrows and adjacent forest understories. We determined the levels of Pythium necessary to cause disease by performing pathogenicity experiments using two Pythium species, a range of Pythium densities, and two common tree species (Acer rubrum and Prunus serotina) from the study sites. Three years post-disturbance, densities of Pythium and Mortierella remained suppressed in soil from forest gaps compared to levels in intact forest understories. Expression of disease symptoms increased with increasing inoculum density for seedlings of P. serotina with each Pythium spp. having a similar effect on this species. Conversely, A. rubrum appeared resistant to Pythium. These results suggest that Pythium densities in the field are sufficient to cause disease and have the potential to affect establishment of susceptible species like P. serotina. Because early seral environments have lower pathogen loads, susceptible species are more likely to become established in those settings than in late-seral forests. Forest disturbances that alter the disease landscape may provide an additional mechanism for explaining succession of temperate forests in addition to the shade-tolerance paradigm.