Individual trees directly modify the soils they occupy, which in turn can affect survival and growth of tree seedlings–a process known as plant-soil feedbacks (PSFs). PSFs critically influence tree species composition and diversity. Despite their importance, persistence of PSFs after tree death remains virtually unstudied. Our preliminary work used Prunus serotina, which has shown strong negative PSFs, to examine PSFs at a range of times since tree death (0.5, 1.5, 3.5 & ~15 years since harvest) and found a release from prior negative PSFs between 0.5 and 1.5 years. Building upon this work, we collected soil cores from the vicinity of P. serotina stumps (spanning 0.5-1.5 years since harvest) and live trees and assessed PSF persistence by growing conspecific seedlings in soil cores under two light levels (5% & 30% full sun) and monitored survival for 12 weeks. We also identified potential soil pathogens causing the PSF by baiting field collected soils, culturing on selective media, and sequencing the ITS 4 and 6 regions for identification. To confirm pathogenicity, P. serotina seedlings grown in sterile potting media will be inoculated with each isolate and seedling survival and growth will be monitored.
Results/Conclusions
Negative PSFs persisted after tree removal, but only for 0.5 years after harvest and under 5% full sun, typical of light levels in a single tree fall gap. Seedlings were released from negative PSFs at 1.5 years after tree harvest, despite the potential for fungal and oomycete components of PSFs to persist long term in resting forms. Three dominant potential pathogens were identified: Phytopythium vexans, Pythium irregulare, and Pythium intermedium. Phytopythium vexans was detected at all live trees and stumps regardless of time since harvest, while P. irregulare and P. intermedium were detected at all live trees and stumps harvested 0.5 years prior, but only found at two stumps harvested 1.5 years prior. Interestingly, seedling survival at these two stumps was poorer than seedling survival at other stumps harvested 1.5 years prior where P. irregulare and P. intermedium were not detected. Results of the pathogenicity trial, where P. serotina seedlings are inoculated with each isolate, will illuminate which of these potential pathogens is driving seedling survival responses and the PSF legacy effect. Though PSF legacies were short-lived, this study provides estimates of PSF persistence after tree death, demonstrates their importance, and identifies particular agents of early seedling death.