Effects of precipitation on belowground carbon allocation and storage by fine roots and mycorrhizal fungi in pine savannas

Robert J. Mitchell, Joseph W. Jones Ecological Research Center

Co-investigators: Erik Hobbie, University of New Hampshire
Chelcy Ford, Coweeta Hydrological Laboratory

Abstract

We propose a study that addresses one under-investigated area-the long-term experimental manipulation of precipitation-and uses multiple approaches to examine the key role of fine roots and mycorrhizal fungi in belowground carbon cycling and in ecosystem responses to precipitation shifts.

We hypothesize that the estimated allocation to roots and mycorrhizal fungi will not differ between direct measures and estimates derived from the indirect, carbon balance approach. We further hypothesize that increased water supply will increase absolute belowground allocation to mycorrhizal fungi more than to roots. In addition, patterns of production and respiration in mycorrhizal fungi and roots will correlate with precipitation inputs. Lastly, we hypothesize that carbon derived from ectomycorrhizal fungi (associated with pines) is preferentially preserved in soil organic matter relative to root-derived carbon or carbon from arbuscular mycorrhizal fungi (associated with wiregrass).

This work will be conducted in longleaf pine-wiregrass savanna, in long-term experimental and control plots, the former has received 33% greater precipitation inputs compared to the latter for the last five years.

To address the hypotheses we will use the carbon balance approach and direct observation of growth and mortality of roots to assess carbon allocation to roots. We will also employ recently developed methods to address productivity, turnover, and respiration of the mycorrhizal component of belowground ecosystems to determine the proportion of belowground carbon allocated to mycorrhizal fungi. Lastly, we will use stable isotope measurements of carbon and nitrogen to address potential changes in sources of soil carbon storage resulting from increases in precipitation on belowground dynamics (e.g., from ectomycorrhizal fungi, arbuscular mycorrhizal fungi, and fine roots).

This work will address gaps in climate change impacts on carbon cycling, and will result in four refereed publications in leading ecological journals.