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DIVISION S-3—SOIL BIOLOGY & BIOCHEMISTRY

Carbon and Nitrogen Pools in a Tallgrass Prairie Soil under Elevated Carbon Dioxide

^a Dep. of Agronomy, Kansas State Univ., Manhattan, KS 66506
^b 3121 Miller Plant Sciences Bldg., University of Georgia, Athens, GA 30606
^c Kansas State University, 2004 Throckmorton Plant Sciences Center, Dep. of Agronomy, Manhattan, KS 66506-5501

^* Corresponding author (cwrice{at}ksu.edu).

Soil is a potential C sink and could offset rising atmospheric CO₂. The capacity of soils to store and sequester C will depend on the rate of C inputs from plant productivity relative to C exports controlled by microbial decomposition. Our objective was to measure pools of soil C and N to assess the potential for C accrual and changes to N stocks as influenced by elevated atmospheric CO₂. Treatments (three replications, randomized complete block design) were ambient CO₂—no chamber (NC), ambient CO₂—chamber (AC), and two times ambient CO₂—chamber (EC). Long-term (290 d) incubations (35°C) were conducted to assess changes in the slow soil fractions of potentially mineralizable C (PMC) and potentially mineralizable N (PMN). Potentially mineralizable C was enhanced (P < 0.1) by 19 and 24% in EC relative to AC and NC soil at the 0- to 5- and 5- to 15-cm depths, respectively. Potentially mineralizable N was significantly greater by 14% at the 0- to 5-cm depth in EC relative to AC, but decreased by 12% in EC relative to NC (P < 0.1). Measurements of PMC indicate that increases in total soil C under elevated CO₂ in a previous study were a consequence of accrual into the slow pool. Relatively large amounts of new C deposited as a result of elevated CO₂ (C_new) remained in the soil after the 290-d incubation. In contrast to accumulation of C into the slow fraction, C_new was integrated into a passive fraction of soil organic matter (SOM). Accumulation of N was also detected in the whole soil, which cannot be explained by current estimates of ecosystem N flux.

Abbreviations: AC, ambient CO₂ with chamber • C_new, new carbon • EC, elevated CO₂ with chamber • MRT, mean residence time • NC, ambient CO₂ no chamber • PMC, potentially mineralizable C • PMN, potentially mineralizable N • SOM, soil organic matter