ELEVATED ATMOSPHERIC CARBON-DIOXIDE EFFECTS ON COTTON PLANT RESIDUE DECOMPOSITION

Assessing the impact of elevated atmospheric CO2 concentration on the global environment is hampered due to a lack of understanding of globa l C cycling. Carbon fixed within plant biomass ultimately enters the s oil via plant residues, but the effects of elevated-CO2-grown plant ma terial on decomposition rates and long-term soil C storage are unknown . The objective of this study was to determine the decomposition rate of plant residues grown under an elevated CO2 environment as affected by soil type. Cotton (Gossypium hirsuturn L. 'Delta Pine 77') samples were collected from a free-air CO2 enrichment (550 mu L L(-1)) experim ent. The plant residues were incubated under ambient CO2 conditions to determine decomposition rates of leaves, stems, and roots and potenti al N and P mineralization-immobilization in three soil series: a Blant on loamy sand (loamy siliceous, thermic Grossarenic Paleudult), a Deca tur silt loam (clayey, kaolinitic, thermic Rhodic Paleudult), and a Ho uston clay loam (very fine, montmorillonitic Typic Chromudert). No sig nificant difference was observed between plant residue grown under CO2 enrichment vs. ambient CO2 conditions for soil respiration or P miner alization-immobilization. Significantly greater net N immobilization w as observed during the incubation in all soil types for plant residue grown at elevated CO2. These results indicate that while decomposition of plant residue may not be reduced by CO2 enrichment, N dynamics may be markedly changed.