After extensive logging and fire suppression many oak dominated woodlands or forests are in danger of being replaced by a mix of non-pyrogenic and shade tolerant tree species that benefit from fire suppression. Successful advanced regeneration by oaks in forests and woodlands depends both on the persistence of seedlings in the shade and growth within canopy gaps. Through the sharing of carbon and/or water between adults and seedlings, connection to a commycorrhizal network potentially provides a mechanism by which oak seedlings could persist in shade and/or grow rapidly in dry soils within canopy gaps. A study was conducted to determine the effects of commycorrhizal networks on seedling growth and survival using four plots with variable canopy density and fire history in north Mississippi. Oak seedlings were grown adjacent to mature oak trees in root exclusion cylinders that alloseedlings access to fungal networks but isolated them from direct root competition. A subset of seedlings was trenched to disconnect them from the network. Response variables were relative growth rate of height and diameter, above and belowground biomass, root:shoot ratio, lateral root length, total number mycorrhizal tips and mycorrhizal tip density. Contrary to predictions, connection to a commycorrhizal network did not alleviate either shade stress or water stress, but rather had a negative effect on aboveground biomass. Isolation from roots and commycorrhizal networks led to an increase in total biomass. Connection to a commycorrhizal network led to increased mycorrhizal root tips and an increase in the density of mycorrhizal tips per cm lateral root length. Survival was very high and any treatment effects were negligible. Negative effects of commycorrhizal connections between adults and seedlings of the same genus could be a previously unappreciated mechanism of negative density-dependent seedling growth. We suggest that research into the effect of CMN interaction with oak seedlings include fire or clipping, and drought as treatments to determine the effects of CMNs on oak seedlings during stressful times to further complete the picture of oak seedling interactions with commycorrhizal networks
