PARENT SESSION
Monday, August 7, 8:00-11:30 am
COS 4 - Carbon cycling I
Ballroom E, Ballroom Level, Cook Convention Center
Presiders: A Diochon and K Stephan
Response of soil carbon pools and fractions to a century of land use change.
Lewis, David*,1, 2, Kaye, Jason2, 1 Global Institute of Sustainability, Tempe, AZ, USA2 Department of Crop and Soil Sciences, University Park, PA, USA
ABSTRACT- Global and regional budgets recognize that soils are potentially large reservoirs of carbon (C). Uncertainties include (i) the proportion of C that is labile and (ii) interactive effects of past and contemporary land use on C pools. Here, we test the hypothesis that former and contemporary land use interactively effect the size and fractionation of the C pool in surface (0-15 cm) soils of arid central Arizona, USA. Our 2 x 2 design examines the effects of history (desert vs. agrarian in 1912) and conversion status in 2004 (still in original 1912 use vs. converted to residential). Generally, soil C fractions were greater in residential land than in non-residential land, and were greater in soil with any agrarian history than in soil without agrarian history. The signal of former agrarian use persists for > 40 y after subsequent residential development. We observed this pattern for total, organic, and inorganic C, and two labile C fractions—respired CO2-C and leached dissolved organic C in 400 d incubations. Past and present interacted to influence leached dissolved inorganic C, which was greater from residential soils than from non-residential soil only if the 1912 land use was desert. When determining land use effects on fractions of the soil C pool, it is also relevant to express fractions as proportions of total C. The proportion of total C that was labile was unaffected by agrarian history and was suppressed by contemporary residential land use. There were no effects of land use on the organic-to-inorganic C ratio. Our hypothesis is supported, and suggests that land conversion in arid biomes produces potentially greater fluxes of C from soil. Classifying land by contemporary use for biogeochemical budgets is overly simplistic, as lands of a type vary owing to differences in provenance.
Key words: carbon sequestration, biogeochemistry, soil incubation