Soil Pathogens and Prunus Serotina Seedling and Sapling Growth Near Conspecific Trees

Soil pathogens close to mature Prunus serotina trees reduce the survival of conspecific seedlings. We examined whether the soil community associated with P. serotina trees has continued negative effects on seedling growth. P. serotina seedlings and saplings were harvested after being followed for 1-3 years in the field, and above- and belowground biomasses were measured. Linear regression models including distance to adult P. serotina tree, conspecific seedling density, and seedling age explained 13.9% of the variation in biomass. Distance and age were positively correlated with total biomass, while density was negatively correlated with total biomass. A similar model for saplings established prior to the beginning of the study, and of unknown age, predicted 11.3% of the variation in total biomass, with distance to adult positively correlated with biomass. To separate the effects of distance from density and remove confounding environmental factors, seedlings were grown in the greenhouse at high or low density in soil collected 0-5 m or 25-30 m from adult P. serotina trees. Half of the soil collected at each distance was sterilized by autoclaving. The experiment was repeated in 1998 and 1999, and in both years there was a significant sterilization-by-distance interaction. Sterilization of soil collected close to the tree resulted in higher root:shoot ratios, while sterilization of soil collected away from the tree resulted in lower root:shoot ratios. This suggests that soil biota vary with distance to adults and that elimination of soil biota changes plant allocation patterns differentially with distance. Distance-dependent effects of soilborne pathogens may continue beyond seedling mortality and suppress juvenile growth. Reduced growth could increase an individual's chance of later mortality, suggesting that initial escape from damping-off pathogens close to parental trees does not ensure longer-term survival.