COS 102-4
Experimental pH and P manipulation alters root-associated fungal community structure in temperate hardwood forests
Many temperate hardwood forests in the Northeastern US are affected by chronic acid deposition, which can lower soil pH and limit the availability of nutrients such as phosphorus (P). However, previous studies have found a lack of above-ground responses to changes in soil pH and P availability, suggesting that forest trees possess mechanisms for overcoming nutrient limitations associated with acidified conditions. Potential mechanisms for overcoming pH-induced P limitation include increased mycorrhizal colonization and alterations in mycorrhizal community structure. To examine this, we conducted a manipulative, ecosystem-level soil pH and P availability experiment, which increased pH by more than 1.5 units and/or doubled P availability in hardwood forests of eastern Ohio. Seventy-two experimental plots were established in a complete randomized block design with two regions (north and south) and four treatments (control, elevated pH, elevated P, and elevated pH+P). Two years after treatment initiation, we sampled roots of hardwood trees to examine effects of soil chemistry on colonization and community structure of ectomycorrhizal (EcM) and arbuscular mycorrhizal (AM) fungi. The EcM community was profiled using tag-encoded 454 pyrosequencing of the internal transcribed spacer region of rDNA, while the less diverse AM fungal community was profiled with TRFLP.
Results/Conclusions
Using root tips that were visibly colonized by EcM fungi, our 454-pyrosequencing effort detected over 72,000 sequences that met quality control criteria, which were grouped into 3174 OTUs (97% similarity) that matched with 184 genera. Non-metric multidimensional scaling (NMS) of EcM communities indicated that both region and pH influenced community structure. This pattern was confirmed with PERMANOVA, which found significant differences in EcM communities between northern and southern Ohio (P=0.04) and between elevated and ambient pH plots (P=0.01). Some EcM taxa (e.g., Sebacinaceae and Thelephoraceae) were significant indicators of elevated pH plots. Likewise, AM communities (profiled with TRFLP) were found to vary with region and pH treatment in both NMS ordination and PERMANOVA analysis (P=0.01 for region and P=0.02 for pH treatment). Elevated pH plots had higher AM colonization (P<0.001) and this was consistent across regions. Although P addition had no treatment effect on fungal communities in general, EcM and AM community patterns were significantly correlated with measured P fractions. These differences in fungal communities with changes in pH and P availability may have functional consequences for forest health and may be important in mediating above-ground responses to global change.