Understanding the mechanisms that control diversity is vital to understanding and predicting changes is community composition. Here we investigate possible mechanisms responsible for the low rate of regeneration near mature Platanus occidentalis, (sycamore). Using the US Forest Service Forest Inventory and Analysis database, we determined that sycamore exhibits a strong pattern of conspecific regeneration inhibition near mature trees across its range in the eastern US. We tested the impact of negative soil feedback and shading in limiting seedling recruitment using a glasshouse experiment. Soil was collected near (2m) and far (25-30m) from five different adult sycamore trees. Seedlings were grown in near or far live soil treatments and sterilized near and far soils for control. Two light treatments (5% and 40% of full PAR) were applied to the 2x2 soil treatments. Seedlings were grown for 105 days.  Final plant biomass was quantified and analyzed in an ANOVA. To determine if mycorrhizal colonization affected the results, four individuals were randomly chosen from each treatment and evaluated for colonization.

Results/Conclusions

Sycamore seedlings had significantly larger biomass in live soil treatments compared to sterilized soil regardless of distance from mature trees (p < 0.0001). Seedlings grown in far live soil had significantly greater biomass than seedlings grown in near live soil (p < 0.0001), suggesting a negative feedback in near soil. Surprisingly, shade significantly affected biomass for seedlings grown in near soil (p = 0.046) where seedlings grown under the shaded conditions had greater biomass. As expected, seedlings grown in live soil had significantly greater colonization by arbuscular mycorrhizae (p = 0.0007). However, the interaction between live soil and distance treatments had no statistically significant difference in colonization (p = 0.145). Overall, our results suggest that shade resulting from canopy closure is not a mechanism inhibiting regeneration of sycamore seedlings near adult trees. These results show that sycamore has a beneficial association with mycorrhizae, but potentially a negative feedback in the soil near adult trees. Additional investigation is underway to determine the mechanism of this negative feedback phenomenon.