Belowground acquisition strategies in a warmed peatland

Camille E. Defrenne, Paul J. Hanson and Colleen Iversen, Climate Change Science Institute and Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN, Katherine Duchesneau, Caitlin Petro and Joel Kostka, Georgia Institute of Technology, Atlanta, GA, Avni Malhotra, Department of Earth System Science, Stanford University, Stanford, CA, Jessica A. M. Moore, Bioscience Division, Oak Ridge National Laboratory, Oak Ridge, TN

Background/Question/Methods
As climate changes, northern peatlands are becoming warmer and drier, which may alter the acquisition of soil resources by plant fine roots and mycorrhizal fungi. Ericaceous shrubs are expected to directly rely on roots for resource acquisition while trees could increase their dependence on ectomycorrhizal fungi. Such changes could affect the ability of peatlands to store carbon into the future as plant fine roots and fungi play key roles in carbon cycling. However, empirical evidence are scarce and root-mycorrhizal interactions in peatlands have received little attention. Here we used the ingrowth core approach in a forested bog where the SPRUCE (Spruce and Peatland Responses Under Changing Environments) experiment is located to explore belowground resource acquisition strategies used by the root-mycorrhiza-bacteria continuum and how these may be affected by whole-ecosystem warming.
Results/Conclusions
Spruce (Picea mariana) and larch (Larix laricina) adopt two viable belowground resource acquisition strategies: the first one consisted of increasing fine-root spatial coverage and root mass in soil while the second strategy consisted of increasing root colonization and shifting ectomycorrhizal exploration type assemblage. The relative contribution of these strategies was species-specific; spruce tended to rely more on mycorrhizal fungi whereas larch relied more on fine roots for resource acquisition. Whole ecosystem warming directly increased the reliance of larch on fine roots while it indirectly increased the reliance of spruce on mycorrhizal fungi via soil drying. In both cases, warming enhanced the acquisitive capacity of fine roots. In addition, these strategies were related to shifts in rhizosphere fungal bacterial community structure. Alterations in multitrophic interactions in the rhizosphere of trees under experimental warming have important implications for peat carbon accumulation on the boreal landscape.