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DIVISION S-3-SOIL BIOLOGY & BIOCHEMISTRY

Use of Carbon-13 and Carbon-14 to Measure the Effects of Carbon Dioxide and Nitrogen Fertilization on Carbon Dynamics in Ponderosa Pine

^a Dep. of Crop and Soil Sciences, Michigan State Univ., East Lansing, MI 48824-1325 USA
^b Environmental Studies Dep., Univ. of California, Santa Cruz, CA 95064 USA
^c Earth and Ecosystem Science, Desert Research Institute, 2215 Raggio Parkway, Reno, NV 89512 USA
^d Biological Science Center, Desert Research Institute, Reno, NV 89512 USA

hailemar{at}pilot.msu.edu

Soil C sequestration in predicted, future elevated CO₂ environments will be important to atmospheric CO₂ levels, soil tilth, and fertility. An elevated CO₂ study with ponderosa pines (Pinus ponderosa Laws) grown in chambers produced above ground vegetation with a ¹³C of -44 and roots with -42. This together with carbon dating made it possible to follow soil C dynamics. Fifty percent of the California upland soil C, resistant to acid hydrolysis, was designated as the resistant fraction. Carbon dating showed the mean residence times of this fraction to be 400 to 1500 yr greater than the total soil C for the horizons sampled. Young ponderosa pines grown in CO₂ chambers produced negligible leaf litter. There were 32% more roots in the presence of either added N or double CO₂ but 77% more in the presence of both. Root-derived soil C was equivalent to 10% of the root C after the 6-yr growth period. Analysis of laboratory CO₂ evolution during extended incubation showed the active soil C pool represented 1 to 2% of the soil C with a field-equivalent mean residence time (MRT) of 24 to 53 d. The slow pool represented 46 to 52% of the C with MRT of 24 to 67 yr depending on treatment and soil depth. Analysis of the ¹³CO₂ label during incubation from the elevated CO₂ treatments, showed the root-derived ¹³C of the active fraction to have residence times similar to those of the total soil non labeled C at 35 d. Root-derived C of the slow pool at 10 yr MRT turned over three to four time as fast as the general soil C. The ¹³C of the light fraction (LF), showed it to be most closely associated with the active pool. The particulate organic matter (POM) was part of the slow pool as determined with incubation.

Abbreviations: FACE, free-air CO₂ enrichment • LF, light fraction • MRT, mean residence time • POM, particulate organic matter • SOC, soil organic carbon

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				S. Haile-Mariam, H. P. Collins, S. Wright, and E. A. Paul Fractionation and Long-Term Laboratory Incubation to Measure Soil Organic Matter Dynamics Soil Sci. Soc. Am. J., January 25, 2008; 72(2): 370 - 378. [Abstract] [Full Text] [PDF]

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