Live and Dead Root Biomass in Alaskan Tundra and Boreal Forest Ecosystems.

Abstract:

High-latitude ecosystems are important sinks, as well as potentially large sources of carbon as the climate continues to change. Belowground biomass of vegetation can act as both a sink and source of carbon; with live root biomass acting as a sink of carbon stores, and dead root biomass acting as a source of carbon to the atmosphere. There is significant literature citing the large ratio of belowground to aboveground biomass in tundra ecosystems, yet understanding of allocation in forested regions of the artic is less understood. Arctic vegetation is investing more resources and energy into belowground biomass relative to aboveground biomass compared to other ecosystems. However, permafrost ecosystems have low decomposition rates as a result of their cold and saturated soils. This allows for the accumulation of a thick organic layer mainly composed of decomposing belowground biomass. Fine roots are of particular importance because their rapid turnover rates makes them important contributions to soil carbon pools.

To quantify the ratio of dead to live roots in tundra and boreal forest ecosystems, soils were collected along a latitudinal gradient throughout Interior Alaska, the Arctic North Slope and Coastal Western Alaska. Several sites located in close proximity were chosen to control for geological and climatic differences among sites, allowing differences to be attributed to the proximal ecosystem. Soil samples were washed, sieved and the roots were sorted into the four categories, including fine-live, fine-dead, coarse-live, and coarse-dead. Classification of these roots followed well established protocols based on visual and physical cues with coarse roots being greater than 2mm. Dead to live ratios of root biomass varied from 4.91 to 45.98, averaging at 14.29 +/- 11.39. Belowground allocation of plant biomass and associated resources may not be significantly larger than aboveground allocation because the majority of the belowground biomass is dead and non-functioning. As global temperatures continue to increase so will decomposition rates, allowing the carbon stored in these dead roots to be released into the environment creating a potentially large carbon source.