PARENT SESSION
Wednesday, August 9, 8:00-11:30 am
COS 49 - Biogeochemical processes and dynamics
L-13, Lobby Level, Cook Convention Center
Presiders: J Edwards and C Cleveland
Effects of pH and calcium on soil organic matter dynamics across a glacial chronosequence in Alaskan tundra.
Whittinghill, Kyle*,1, Hobbie, Sarah1, 1 University of Minnesota, Minneapolis, MN
ABSTRACT- In Northern Alaska, the tundra comprises a mosaic of different aged geologic substrates because of expansion and contraction of glaciers in Brooks Range throughout the Pleistocene. Past research suggests younger landscapes have slower soil organic matter (SOM) decomposition and dissolved organic matter (DOM) production than older landscapes, but for unknown reasons. We aimed to determine the relative importance of variation in pH versus variation in multivalent cation ′′bridging′′ in influencing microbial respiration and DOM production along a chronosequence of sites that developed on glacial drift deposited during the last four distinct glacial advances near Toolik Lake, AK, USA. To tease apart the effects of pH and polyvalent cations on microbial respiration and DOM production, we manipulated pH and Ca concentration factorially using soils collected from replicated sites on each of the four different glacial ages. Soils from the youngest sites contained significantly more multivalent cations (primarily Ca2+), had higher pH (6.5 vs. 4.5-5), and lower respiration than all older sites. Soils with similar Ca concentration exhibited higher cumulative respiration at pH 6.5 than at pH 4.5, but the pH effect was greater at the low Ca concentration. At equal pH, cumulative respiration was less in high Ca than low Ca treatments. The inhibition of respiration by high Ca was stronger at pH 6.5 than pH 4.5. Our results indicate that both pH and Ca influence microbial respiration suggesting that heterogeneity in these factors associated with landscape age should be considered in models of SOM dynamics in tundra ecosystems.
Key words: Biogeochemistry, Arctic, Decomposition