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Title: Mineralization of soil organic matter in two elevated CO2 by warming experiments in grassland

Author
item PENDALL, ELISE - UNIVERSITY OF WYOMING
item HOVENDEN, MARK - UNIVERSITY OF TAZMANIA
item WILLIAMS, DAVID - UNIVERSITY OF WYOMING
item Dijkstra, Feike
item Morgan, Jack

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 10/15/2007
Publication Date: 12/10/2007
Citation: Pendall, E., Hovenden, M., Williams, D., Dijkstra, F.A., Morgan, J.A. 2007. Mineralization of soil organic matter in two elevated CO2 by warming experiments in grassland. In: Proceedings of the American Geophysical Union fall meeting. Abstract.

Interpretive Summary:

Technical Abstract: Experimentally elevated atmospheric CO2 has enhanced carbon (C) allocation belowground, while ecosystem warming has led to losses of soil C due to enhanced mineralization of soil organic matter (SOM). Few investigations of possible interactions between elevated CO2 and temperature have been reported, but the potential for C cycling effects not to be simply additive is high. We have taken advantage of two multi-factor global change experiments being conducted in mixed C3/C4 grasslands to evaluate similarities and differences in responses of SOM mineralization rates. The TasFACE experiment in Tasmania, Australia, has been running for over 5 years, while the Prairie Heating and CO2 Enrichment (PHACE) experiment in Wyoming, USA, has been running for less than 2 years. Both experiments employ mini-FACE systems (enriched plots targeted at 550 at TasFACE and 600 ppm at PHACE) and overhead ceramic infrared emitters (heated plots targeted at +2 degrees C at TasFACE and +1.5/+3 degrees day/night at PHACE). Soil samples collected after 5 years at TasFACE and at the beginning of the second year at PHACE were incubated for three weeks to evaluate changes in labile SOM pool sizes and turnover rates. We hypothesized that elevated CO2 would enhance labile SOM pool size and that warming would reduce it, and that warming would stimulate decomposition rate. Preliminary results suggested that five years of warming enhanced decomposition rate in the TasFACE soils, but only under the C4 grass species, whereas the first two months of warming had no effects on decomposition rate at PHACE. Elevated CO2 increased mineralizable C pool sizes by 10 to 30 percent, depending on depth, in the TasFACE soils, but did not significantly alter C cycling in the PHACE soils. Short experimental duration likely explained the lack of treatment effects seen at PHACE. We plan to continue conducting parallel experiments to track temporal changes in C cycling with the expectation that interactive effects of elevated CO2 and warming may appear over the long term.