Fungi associated with invasive pine roots on Maui

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 Haleakala National Park on the island of Maui. While there are no pines or their associated ectomycorrhizal (EM) fungi that are native to Hawaii, 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.

松树是全球入侵性最强的树木类群之一，其入侵过程依赖地下外生菌根真菌（ectomycorrhizal fungal）共生伙伴的协助。辐射松（Pinus radiata）目前正在夏威夷群岛的多个区域扩散入侵，其中包括毛伊岛哈莱亚卡拉国家公园周边地带。尽管夏威夷本土并无松树及其相关外生菌根（ectomycorrhizal，EM）真菌，但已有研究表明，在距离原始种植园最远1000米的区域，仍有外生菌根真菌类群（尤其是乳牛肝菌类群）与辐射松形成共生关系。为了预测毛伊岛上未来易受松树入侵的区域，我们需要明确外生菌根真菌（尤其是乳牛肝菌属（Suillus spp.）类群）的空间分布格局，以及这些入侵性真菌如何影响松树幼苗的定植成功率。为此，本研究开展了生物测定实验：将辐射松种子播种于从库拉森林保护区现有种植园不同距离处采集的土壤中进行培育。随后对松树幼苗根系进行可视化分析以统计外生菌根真菌侵染率，测定幼苗生物量，并采用Illumina扩增子测序技术分析外生菌根真菌群落组成。实验结果显示，距离种植园2000米区域的外生菌根真菌群落与种植园内部及周边的群落存在显著差异，且该区域群落主要由乳牛肝菌属类群构成。生物测定实验中，幼苗根系的外生菌根真菌侵染率随与种植园的距离增加而升高，且较高的侵染率与幼苗生物量提升呈显著正相关。借助乳牛肝菌属类群的协助，辐射松似乎已获得了所需的共生伙伴，能够助力其幼苗在该区域的扩散与存活。