Effects of elevated atmospheric CO₂ enrichment and N fertilization on extraradical and mycorrhizal fungi: Implications for carbon flow into southeastern forest soils

Seth Pritchard, College of Charleston

Abstract

We propose to mine an archive of minirhizotron images for information regarding the influence of atmospheric CO₂ enrichment on mycorrhizas and extraradical fungal hyphae. In addition to ongoing studies, archived images are available for both a loblolly pine forest experiment (Duke University FACE site, Chapel Hill, NC) and a model regenerating longleaf pine ecosystem (National Soil Dynamics Laboratory, Auburn, AL).

This research will take place at the Duke FACE site in Durham NC and also at the College of Charleston in Charleston, South Carolina.

Hypothesis 1: CO₂-enrichment will stimulate fungal growth in both experiments.
Hypothesis 2: CO₂-enrichment will increase the lifespan of ectomycorrhizal root tips, rhizomorphs, and fungal extraradical hyphae in both experiments.
Hypothesis 3: Addition of N in the Duke experiment will decrease lifespan of fugal structures.
Hypothesis 4: Addition of N will reduce percent root length colonized by mycorrhizas and total visible mycorhizae and extraradical hyphae (Duke experiment).
Hypothesis 5: Stimulation of fungal growth by CO₂-enrichment will be greatest in shallow soil in the Duke experiment and in deep soil in the USDA experiment.
Hypothesis 6: Fungal structures produced in deep soil will persist longer than those in shallow soil.

A microvideo camera, inserted into the soil profile through a clear access tube, is being used to capture digital images of roots and their fungal partners. Images of the soil/tube interface are available from two key climate change experiments in the Southeast. Image collection began (monthly) in 1998 at the Duke University Forest (loblolly pine) FACE experiment and will continue through 2007. Images from the USDA-ARS National Soil Dynamics laboratory were collected during a three year experiment that ran from 1998 through 2001. Analysis of sequential images collected over long time periods (6+ years at Duke and 3 years at USDA site) provides a unique opportunity to directly observe how fungi, both mycorrhizal and extraradical, are influenced by exposure of the plant canopy to elevated CO₂. Data extracted from archived images will then be compared to future data collected at the Duke FACE site following the initiation of a N treatment scheduled for January 2005.

This study will provide important insight into the effects of CO₂ enrichment on C allocation to soil fungi at the ecosystem level, and will also provide valuable data concerning the potential of fungi to contribute to soil C sequestration. Finally, the fate of mycorrhizae in a higher CO₂ environment may influence the extent to which forest ecosystem productivity is limited by nutrient availability.

Publications

Pritchard SG, Strand AE, McCormack ML, Davis MA, and Oren R. 2008. Effects of Free-Air CO₂-enrichment (FACE) on mycorrhizae and rhizomorph production and turnover. Global Change Biology (accepted).

Pritchard SG, Strand AE, McCormack ML, Davis MA, Finzi AC, Jackson RB, Matamala R, Rogers HH, and Oren R. 2008. Fine root dynamics in a loblolly pine forest are influenced by Free-Air-CO₂-Enrichment (FACE): a six year minirhizotron study. Global Change Biology (accepted).

Pritchard SG, Strand AE. 2008. Can you believe what you see? Reconciling minirhizotron and isotopic estimates of fine root longevity. New Phytologist (in press).

Finzi AC, Norby RJ, Calfapietra C, Gallet-Budynek A, Gielen B, Holmes WE, Hoosbeek MR, Iverson C, Kubiske ME, Liberloo M, Oren R, Polle A, Pritchard SG, Jackson RB, Zak DR, Schlesinger, WH, and Ceulemans R. 2007. Increases in nitrogen uptake rather than nitrogen-use efficiency support higher rates of temperate forest productivity under elevated CO₂. Proceedings of the National Academy of Sciences 104:14014-14019.