COS 67-1 - The impacts of logging to mycorrhizal fungi associated with the tallest trees on earth (Sequoia sempervirens – coast redwoods)

Abstract: Across the globe the rate of deforestation has steadily increased, leading to the expansion of second-growth forests. Despite their critical role in forest function, there is limited knowledge surrounding the impact of deforestation on mycorrhizal fungi. In the coast redwood range (Sequoia sempervirens) of the US Pacific Coast, old-growth forests are hosts for arbuscular mycorrhiza (AM) and ectomycorrhiza (EM). However, the abundance of AM is concentrated in the rhizonode, a specialized root structure that facilitates AM associations. Despite the ability of old-growth forests to regenerate from cut stumps, the encroachment of pine woodland (Pinaceae) has diminished the recovery of second-growth forests. The goal of this study was to determine how AM and EM associations are impacted by logging using ITS2 DNA sequencing. Additionally, we sought to determine how the removal of pine woodland, which is only associated with EM, will impact mycorrhizal associations of redwoods. Lastly, we expected the rhizonodes of second-growth redwood forests would be less abundant and diverse in AM compared to old-growth.

While we expected EM associations to be most abundant and diverse in second-growth forests, only the abundance of EM in soils was significantly higher in second-growth forests. In the soil community of old-growth forests, the species richness of AM was 16.2. In comparison, AM richness of second-growth forests where significantly lower at 5.0 and 4.0 following the removal of pine woodland. The relative abundance of AM was highest in old-growth forests at 22.9% in soils, whereas as second-growth forests were 3.3% and < 1% following the removal of pines. The species richness of AM in the rhizonode was highest at 15.7 in old-growth compared to second-growth at 6.4. The results of our study indicate AM in redwood forests are more sensitive to logging compared to EM. While the removal of pine woodland had no immediate effect on the diversity and abundance of mycorrhiza, AM communities can potentially recover over time following the eradication of pines. Therefore, the removal of pine woodlands is critical to the long-term recovery of second-growth redwood forests.