Plant residue chemistry impacts soil processes and microbial community structure: A study with Arabidopsis thaliana cell wall mutants

The C:N ratio and concentrations of resistant compounds such as lignin in plant residues influences their biodegradation by microbial communities in soil. Soil texture is expected to modulate biodegradation rates through physical protection of residues and feedback on microbial communities. The model plant Arabidopsis thaliana can be modified genetically to produce residues with variable C:N ratio and acid unhydrolyzable fraction (AUF) concentrations for controlled biodegradation studies. This study assessed the C:N ratio and AUF concentration of stem and root residues of A. thaliana wild ecotypes and single gene knockout mutants of cinnamoyl-CoA reductase 1 (CCR1) and production of anthocyanin pigment 1 (PAP1/MYB75). Ground stem and root residues from A. thaliana lines were then mixed separately with soil (clay loam or sandy loam) and incubated for 63 d at 25 degrees C to evaluate the soil carbon dioxide (CO2-C) production, mineral nitrogen (N) concentration, microbial biomass carbon (MBC) and microbial community structure by phospholipid fatty acid (PLFA) profiling. The CCR1 mutant had 29% lower C:N ratio and 38% less AUF in stems than the wild ecotype, while MY875 mutant had similar to 2-fold higher C:N ratio in stems than the wild ecotype. The AUF concentration of roots did not differ among mutant lines and their wild ecotypes, but roots had similar to 2-fold higher AUF concentration than stems. Cumulative CO2-C production was higher from soils (both texture types) amended with stem residues of CCR1 and was lower from sandy loam soil amended with stem residues of MY875, compared to their wild ecotypes. There was more CO2-C production from soils amended with stem than root residues. Mineral N concentration was greater in soils (both texture types) amended with stem residue of the CCR1 mutant line than its wild ecotype. There was more MBC in stem-amended than root-amended soils. PLFA profiling revealed lower fungal abundance in stem-amended than root-amended soils. In conclusion, A. thaliana stem residues with altered C:N ratio and AUF concentration affected the CO2-C production, mineral N concentration, MBC and fungal:bacterial ratio of soil. Residue chemistry had a stronger influence on soil processes and microbial community structure than soil texture. (C) 2012 Elsevier B.V. All rights reserved.