Interactions among roots, mycorrhizas and free-living microbial communities differentially impact soil carbon processes

Journal Article · Tue Oct 20 00:00:00 EDT 2015 · Journal of Ecology

DOI:https://doi.org/10.1111/1365-2745.12484· OSTI ID:1326499

Moore, Jessica A. M. ^[1]; Jiang, Jiang ^[1]; Patterson, Courtney M. ^[1]; Mayes, Melanie A. ^[2]; Wang, Gangsheng ^[2]; Classen, Aimée T. ^[3]

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1. Univ. of Tennessee, Knoxville, TN (United States)
2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
3. Univ. of Tennessee, Knoxville, TN (United States); Univ. of Copenhagen, Kobenhavn O (Denmark)

1. Plant roots, their associated microbial community and free-living soil microbes interact to regulate the movement of carbon from the soil to the atmosphere, one of the most important and least understood fluxes of terrestrial carbon. Our inadequate understanding of how plant–microbial interactions alter soil carbon decomposition may lead to poor model predictions of terrestrial carbon feedbacks to the atmosphere. 2. Roots, mycorrhizal fungi and free-living soil microbes can alter soil carbon decomposition through exudation of carbon into soil. Exudates of simple carbon compounds can increase microbial activity because microbes are typically carbon limited. When both roots and mycorrhizal fungi are present in the soil, they may additively increase carbon decomposition. However, when mycorrhizas are isolated from roots, they may limit soil carbon decomposition by competing with free-living decomposers for resources. 3. We manipulated the access of roots and mycorrhizal fungi to soil in situ in a temperate mixed deciduous forest. We added ¹³C-labelled substrate to trace metabolized carbon in respiration and measured carbon-degrading microbial extracellular enzyme activity and soil carbon pools. We used our data in a mechanistic soil carbon decomposition model to simulate and compare the effects of root and mycorrhizal fungal presence on soil carbon dynamics over longer time periods. 4. Contrary to what we predicted, root and mycorrhizal biomass did not interact to additively increase microbial activity and soil carbon degradation. The metabolism of ¹³C-labelled starch was highest when root biomass was high and mycorrhizal biomass was low. These results suggest that mycorrhizas may negatively interact with the free-living microbial community to influence soil carbon dynamics, a hypothesis supported by our enzyme results. Our steady-state model simulations suggested that root presence increased mineral-associated and particulate organic carbon pools, while mycorrhizal fungal presence had a greater influence on particulate than mineral-associated organic carbon pools. 5. Synthesis. Our results suggest that the activity of enzymes involved in organic matter decomposition was contingent upon root–mycorrhizal–microbial interactions. Using our experimental data in a decomposition simulation model, we show that root–mycorrhizal–microbial interactions may have longer- term legacy effects on soil carbon sequestration. Overall, our study suggests that roots stimulate microbial activity in the short term, but contribute to soil carbon storage over longer periods of time.

• Research Organization: Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
• Sponsoring Organization: USDOE Office of Science (SC)
• Grant/Contract Number: AC05-00OR22725; SC0010562
• OSTI ID: 1326499
• Alternate ID(s): OSTI ID: 1400939; OSTI ID: 1501382
• Journal Information: Journal of Ecology, Vol. 103, Issue 6; ISSN 0022-0477
• Publisher: Wiley
• Country of Publication: United States
• Language: English

Related Subjects

59 BASIC BIOLOGICAL SCIENCES
54 ENVIRONMENTAL SCIENCES
decomposition
extracellular enzyme activity
forest
nutrient cycling
plant-microbe interactions
plant-soil (below-ground) interactions
rhizosphere
simulation model
stable isotope