Unearthing the Role of Ectomycorrhizal Fungi in Pine Invasions on Maui

Abstract

Pines are one of the most invasive trees in the world, invading with the aid of belowground ectomycorrhizal fungal mutualists. Pinus radiata is currently invading multiple parts of the Hawaiian Islands, including near the Haleakalā National Park on the island of Maui. While there are no pines or their associated ectomycorrhizal (EM) fungi that are native to Hawai‘i, previous studies have shown EM fungal species, especially suilloid species, associating with P. radiata up to 1000 m away from the original plantations. In order to predict areas on Maui that are susceptible to future pine invasions, we must understand how the distribution of EM fungi, specifically Suillus spp., varies across the landscape and how these invasive fungi affect pine seedling success. To do so, a bioassay experiment was performed in which P. radiata seeds were grown from soil collected at varying distances from the existing plantation at the Kula Forest Reserve. Pine seedling roots were visually analyzed for percent colonization of EM fungi, weighed, and sequenced for EM fungal community composition using Illumina amplicon sequencing. The community of EM fungi found 2000 m away from the plantation was significantly different than the community within and around the plantation, and largely comprised of Suillus spp. The percent colonization of bioassay roots by EM fungi increased with distance from the plantation and increased colonization was positively correlated with increased seedling biomass. With the aid of Suillus spp., P. radiata appears to have the symbiotic partners needed to aid in the dispersal and survivorship of seedling out into this landscape.