American Society of Plant Biologists 
Biochemical composition and decomposition among several C3 and C4 species
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Poster: Global Change

Abs # 164: Biochemical composition and decomposition among several C3 and C4 species

Presenter: Johnson, Jane M-F,
Barbour, Nancy W. (A)  
Affiliations: (A): USDA-Agricultural Research Service
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Understanding decomposition of plant residue is vital to understanding the cycling of C, N, S and P, both in terms of plant nutrient needs and global change. The rate of residue decomposition reflects decomposition of the degrading substrates. Composition data (e.g., lignin, cellulose, hemicellulose, protein concentrations) while abundant for forest species are limited in comparison for agronomic species, especially data on root composition. Roots typically constitute less than half the total plant biomass, but literature suggests they contribute 1.4 to 1.8 times as much C to the soil. This study addresses the related issues of plant composition, residue decomposition, and will make inferences to C, N and P cycling. The first objective is to compare root biochemical composition among species and to above- ground components. The second objective is to evaluate the decomposition of roots and above-ground components among species as it relates to C, N and P mineralization rates. Plant material from C3 (alfalfa, cuphea, soybean, wheat) and C4 (corn, big blue stem, switchgrass)was collected from field-grown and growth chamber-grown plants at physiological maturity. Structural and nonstructural components were isolated from roots, stems and leaves. Ground plant material was mixed with soil. Decomposition was monitored by total respired CO2 at 25oC and 60% water-filled pore space. Soluble sugar and starch concentrations varied among species and among plant organs. Chemical composition also varied between plants grown in a growth chamber compared to plant of the same species grown in the field. It is hypothesized that rates will vary with lignin, lignin:N and C:N ratio.

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