Changes in Fungal Community Composition in Response to Elevated Atmospheric CO2 and Nitrogen Fertilization Varies with Soil Horizon

Abstract

Increasing levels of atmospheric carbon dioxide (CO2) and rates of nitrogen (N)-deposition to forest ecosystems are predicted to alter the structure and function of soil fungal communities, but the spatially heterogeneous distribution of soil fungi has hampered investigations aimed at understanding such impacts. We hypothesized that soil physical and chemical properties and fungal community composition would be differentially impacted by elevated atmospheric CO2 (eCO2) and N-fertilization in spatially separated field samples, in the forest floor, 0–2, 2–5, and 5–10 cm depth intervals in a loblolly pine Free-Air Carbon Dioxide Enrichment (FACE) experiment. In all soils, quantitative PCR-based estimates of fungal biomass were highest in the forest floor. Fungal richness, based on pyrosequencing of the fungal ribosomal large subunit gene, increased in response to N-fertilization in 0–2 cm and forest floor intervals. Composition shifted in forest floor, 0–2 and 2–5 cm intervals in response to N-fertilization, but the shift was most distinct in the 0–2 cm interval, in which the largest number of statistically significant changes in soil chemical parameters (i.e., phosphorus, organic matter, calcium, pH) was also observed. In the 0–2 cm interval, increased recovery of sequences from the Thelephoraceae, Tricholomataceae, Hypocreaceae, Clavicipitaceae, and Herpotrichiellaceae families and decreased recovery of sequences from the Amanitaceae correlated with N-fertilization. In this same depth interval, Amanitaceae, Tricholomataceae, and Herpotriciellaceae sequences were recovered less frequently from soils exposed to eCO2 relative to ambient conditions. These results demonstrated that vertical stratification should be taken into consideration in future efforts to elucidate environmental impacts on fungal communities and their feedbacks on ecosystem processes.

Fungal Communities Respond to Long-Term CO 2 Elevation by Community Reassembly

“…Interestingly, decreased and increased overall relative abundances of Ascomycota and Basidiomycota in eCO 2 samples were observed for the 119 OTU. Compared to the recent study in a forest FACE site by Weber et al (31), our results were generally consistent that eCO 2 had no significant effects on high-level fungal groups when relative abundances for all OTU were considered. Our results were also consistent with a previous study that the fungal richness was not significantly affected by eCO 2 (57).…”

“…The grassland soil ecosystem in the BioCON experimental site in Minnesota was dominated by Ascomycota (81% at aCO 2 and 77% at eCO 2 ) and Basidiomycota (11% at aCO 2 and 14% at eCO 2 ). Compared to the reports by previous studies (31,(58)(59)(60)(61), fungal community composition in soil varied greatly across different types of soil ecosystems. Such variations in fungal community composition between different studies might be caused by different coverage of different primer sets or phylogenetic markers (such as ITS versus 28S) (62), but more likely caused by plant species, soil, and/or climate differences (58).…”

“…Previous studies of fungal responses to eCO 2 were mainly carried out using approaches such as phospholipid fatty-acid analysis, denaturing gradient gel electrophoresis, extracellular enzyme assays, and clone library analysis (6,12,16,(21)(22)(23) and mostly focused on mycorrhizal fungi (15,(24)(25)(26), which have major influences on plant biodiversity and productivity (27). Those previous studies were focused on fungal carbon degradation, nitrogen cycling, and interactions with plants (26,28,29); however, knowledge about fungal community-level responses to eCO 2 is still limited, though some efforts have been made recently (12,30,31).…”

Temporal variation overshadows the response of leaf litter microbial communities to simulated global change

“…For instance, drought reduced the relative abundance of Proteobacteria in our study, as previously reported in a constructed old-field ecosystem (Castro et al, 2010); two abundant Proteobacteria OTUs (Methylobacterium 2 and Mitsuaria) had a significantly lower relative abundance in the drought treatment. In contrast, Weber et al (2013) reported a positive response of Ascomycetes to nitrogen addition, whereas many of the abundant Ascomycete OTUs decreased in relative abundance in our nitrogen treatment. Also, in contrast to prior studies, added nitrogen or drought did not increase the relative abundance of Actinobacteria (Ramirez et al, 2012;Barnard et al, 2013).…”

“…Broadly speaking, the taxonomic composition observed in this study is similar to that found in other terrestrial litter and soil systems. The majority of fungal sequences in this study were Ascomycota and Basidiomycota (Barnard et al, 2013;Voriskova and Baldrian, 2013;Weber et al, 2013), and Proteobacteria, Bacteriodetes and Actinobacteria made up most of the bacterial diversity (Castro et al, 2010;Sheik et al, 2011;Barnard et al, 2013;Kim et al, 2014). In contrast, many soils contain a large fraction of Acidobacteria (Castro et al, 2010;Sheik et al, 2011;Barnard et al, 2013;Kim et al, 2014), but they represented o1% of our litter communities.…”