Atmospheric CO 2 and soil extracellular enzyme activity: a meta-analysis and CO 2 gradient experiment

The simultaneous increase of atmospheric CO 2 and nitrogen (N) deposition to terrestrial ecosystems is predicted to alter plant productivity and, consequently, to change the amount and quality of above-and belowground carbon entering forest soils. It is not known how such changes will impact the composition and function of soil fungal communities that play a key role in degrading complex carbon. We sequenced the fungal cellobiohydrolase I gene (cbhI) from soil DNA and cDNA to compare the richness and composition of resident and expressed cbhI genes at a U.S. Department of Energy free air-carbon dioxide enrichment (FACE) site (NC), which had been exposed to elevated atmospheric CO 2 and/or N fertilization treatment for several years. Our results provide evidence that the richness and composition of the cellulolytic fungi surveyed in this study were distinct in the DNA-and cDNA-based gene surveys and were dominated by Basidiomycota that have low or no representation in public databases. The surveys did not detect differences in richness or phylum-level composition of cbhI-containing, cellulolytic fungi that correlated with elevated CO 2 or N fertilization at the time of sampling.

Section: Discussionsupporting

confidence: 91%

“…Like many of these previous studies, our study was conducted at a single time point. It is possible that responses to the treatments are manifest at other times of the year (20). Furthermore, it is possible that subtle compensatory dynamics of various lesser abundant taxa may have gone undetected in our relatively shallow sequencing effort.…”

Section: Discussionmentioning

confidence: 99%

Soil Fungal Cellobiohydrolase I Gene ( cbhI ) Composition and Expression in a Loblolly Pine Plantation under Conditions of Elevated Atmospheric CO ₂ and Nitrogen Fertilization

Weber

Balasch

Gossage

et al. 2012

“…These taxa have different nitrogen demands (18), and two lines of evidence suggest elevated CO 2 increased soil N limitation in our experiment. First, inorganic N availability in the black clay soil declined with increasing CO 2 in the year we sampled fungal communities (25,26). Second, recalcitrant organic N-degrading enzyme activity (likely from saprophytic fungi and bacteria) increased with elevated CO 2 in the black clay (25,27,28).…”

mentioning

confidence: 99%

Fungal Community Responses to Past and Future Atmospheric CO ₂ Differ by Soil Type

Procter

Ellis

Fay

et al. 2014

Self Cite

Soils sequester and release substantial atmospheric carbon, but the contribution of fungal communities to soil carbon balance under rising CO 2 is not well understood. Soil properties likely mediate these fungal responses but are rarely explored in CO 2 experiments. We studied soil fungal communities in a grassland ecosystem exposed to a preindustrial-to-future CO 2 gradient (250 to 500 ppm) in a black clay soil and a sandy loam soil. Sanger sequencing and pyrosequencing of the rRNA gene cluster revealed that fungal community composition and its response to CO 2 differed significantly between soils. Fungal species richness and relative abundance of Chytridiomycota (chytrids) increased linearly with CO 2 in the black clay (P < 0.04, R 2 > 0.7), whereas the relative abundance of Glomeromycota (arbuscular mycorrhizal fungi) increased linearly with elevated CO 2 in the sandy loam (P ‫؍‬ 0.02, R 2 ‫؍‬ 0.63). Across both soils, decomposition rate was positively correlated with chytrid relative abundance (r ‫؍‬ 0.57) and, in the black clay soil, fungal species richness. Decomposition rate was more strongly correlated with microbial biomass (r ‫؍‬ 0.88) than with fungal variables. Increased labile carbon availability with elevated CO 2 may explain the greater fungal species richness and Chytridiomycota abundance in the black clay soil, whereas increased phosphorus limitation may explain the increase in Glomeromycota at elevated CO 2 in the sandy loam. Our results demonstrate that soil type plays a key role in soil fungal responses to rising atmospheric CO 2 .

“…Progressive N limitation theory proposes that ecosystems become more N limited with rising CO 2 , which suggests that the continued sequestration of CO 2 in terrestrial biomass will require greater N fixation inputs (3,4). The increased ecosystem demand for N under elevated CO 2 has been documented after several years of whole-forest CO 2 enrichment (5,6).…”

mentioning

confidence: 99%

Nitrogen Fertilization Has a Stronger Effect on Soil Nitrogen-Fixing Bacterial Communities than Elevated Atmospheric CO ₂

Berthrong

Yeager

Gallegos-Graves

et al. 2014

Self Cite

138

c Biological nitrogen fixation is the primary supply of N to most ecosystems, yet there is considerable uncertainty about how Nfixing bacteria will respond to global change factors such as increasing atmospheric CO 2 and N deposition. Using the nifH gene as a molecular marker, we studied how the community structure of N-fixing soil bacteria from temperate pine, aspen, and sweet gum stands and a brackish tidal marsh responded to multiyear elevated CO 2 conditions. We also examined how N availability, specifically, N fertilization, interacted with elevated CO 2 to affect these communities in the temperate pine forest. Based on data from Sanger sequencing and quantitative PCR, the soil nifH composition in the three forest systems was dominated by species in the Geobacteraceae and, to a lesser extent, Alphaproteobacteria. The N-fixing-bacterial-community structure was subtly altered after 10 or more years of elevated atmospheric CO 2 , and the observed shifts differed in each biome. In the pine forest, N fertilization had a stronger effect on nifH community structure than elevated CO 2 and suppressed the diversity and abundance of N-fixing bacteria under elevated atmospheric CO 2 conditions. These results indicate that N-fixing bacteria have complex, interacting responses that will be important for understanding ecosystem productivity in a changing climate. N itrogen is the most common nutrient limiting productivity in terrestrial ecosystems and enters ecosystems predominantly through bacterial fixation. However, we lack a clear understanding of how N-fixing bacteria respond to climate change drivers or how conserved those responses might be across biomes in a geographic region. Nonagricultural biomes in the eastern United States that experience elevated atmospheric CO 2 and increasing N deposition include hardwood forests to the north, pine forests to the south, and brackish marsh areas along the eastern seaboard. Rising atmospheric CO 2 concentrations and shifting patterns of N deposition can interact and affect N fixation processes in soil (1). To determine if populations of N-fixing bacteria in soils of different biomes showed similarities in composition and in responses to elevated CO 2 , we conducted a systematic survey of soil N-fixing bacterial communities across four biomes in the eastern United States, utilizing long-term, free-air CO 2 enrichment (FACE) experiments (2). One of these field experiments combined elevated CO 2 and N fertilization treatments, allowing us to determine their interactive effects on the N-fixing community in a pine forest in the southeastern United States.Progressive N limitation theory proposes that ecosystems become more N limited with rising CO 2 , which suggests that the continued sequestration of CO 2 in terrestrial biomass will require greater N fixation inputs (3, 4). The increased ecosystem demand for N under elevated CO 2 has been documented after several years of whole-forest CO 2 enrichment (5, 6). N-fixing bacteria, which span many taxonomic groups with high levels of ...