Loss of a Foundation Species, Eastern Hemlock (Tsuga canadensis), May Lead to Biotic Homogenization of Fungal Communities and Altered Bacterial Abundance in the Forest Floor

Determinants of temperature sensitivity of soil respiration with the decline of a foundation species

“…Other work on this study site showed that macrofungal communities of the forest floor did not demontrate strong differences in morphospecies richness in hemlock stands compared to black birch stands, but had more rare fungi taxa [44]. Even though bacterial community richness has not been quantified at this study site, the data show the abundance of bacterial colony forming units in the soil organic horizon follow a seasonal pattern that differs between hemlock and black birch stands [44]. Specifically, the timing of peak abundance of bacteria showed that abundance found within hemlock stands peaks in the summer and abundance found within black birch stands peaks in the fall [44].…”

“…Since substrate quality can exhibit a strong influence on temperature sensitivities of soil respiration [11,43], I expected similar factors to influence the temperature sensitivities in this study. The hemlock stands have more persistent soil organic carbon, due to a thick organic layer (4.1 cm; [44]). Though not formerly tested, hemlock forests are thought to have more recalcitrant organic matter, as they may be comprised of needles containing high concentrations of lignin and polyphenolic compounds, as well as humic compounds [20].…”

“…Though not formerly tested, hemlock forests are thought to have more recalcitrant organic matter, as they may be comprised of needles containing high concentrations of lignin and polyphenolic compounds, as well as humic compounds [20]. Given the environmental conditions of hemlock forests, there has been greater accumulation of organic material relative to black birch stands [20,44]. The mature birch stands have a 6.8× decline in soil organic layer carbon storage due to their higher decomposition of soil organic material with lower C:N [20].…”

“…Acidic soils have been shown to have a high ratio of percent fungal to bacterial respiration [54], and soil bacterial communities can be linked to forest litter characteristics and soil pH [55]. Fungal vs. bacterial communities should be greatly affected by the transition from hemlock stands to black birch stands, since previous research found nitrogen availability and C:N of the soil as a strong influencing factor [44]. Other work on this study site showed that macrofungal communities of the forest floor did not demontrate strong differences in morphospecies richness in hemlock stands compared to black birch stands, but had more rare fungi taxa [44].…”

“…Fungal vs. bacterial communities should be greatly affected by the transition from hemlock stands to black birch stands, since previous research found nitrogen availability and C:N of the soil as a strong influencing factor [44]. Other work on this study site showed that macrofungal communities of the forest floor did not demontrate strong differences in morphospecies richness in hemlock stands compared to black birch stands, but had more rare fungi taxa [44]. Even though bacterial community richness has not been quantified at this study site, the data show the abundance of bacterial colony forming units in the soil organic horizon follow a seasonal pattern that differs between hemlock and black birch stands [44].…”