Alteration of plant lignin concentration is expected to affect the C mineralization of crop residues. Mutations of single genes involved in biosynthesis of secondary cell walls such as KNOTTED ARABIDOPSIS THALIANA 7 (KNAT7), PRODUCTION OF ANTHOCYANIN PIGMENT 1 (PAP1) also known as MYB75, and cinnamoyl CoA reductase 1 (CCR1) coding genes could change lignin concentration in specific plant tissues. This study assessed the CO2-C production of soil amended with stem and root tissues of down-regulated (k/o) and over expression (o/x) KNAT7 and MYB75 and the CCR1 k/o mutant lines of A. thaliana. KNAT7 k/o and MYB75 k/o were grown in two different environmental conditions (two cohorts) in the greenhouse. Oven dried, finely ground (<0.5 mm) stem and root residues underwent biochemical analysis, then were mixed separately with sandy loam or clay loam soil to assess CO2-C production under controlled laboratory conditions for 63 days. Compared to wild ecotypes, C:N ratio and acid unhydrolyzable fraction (AUF) concentration tended to be higher in stem residues of KNAT7 k/o and MYB75 k/o mutant lines. The C:N ratio was lower in stem and roots of CCR1 k/o line, and the AUF concentration was lower in CCR1 k/o stem residues than in the wild ecotypes. Hemicelluloses were lower in stem residues of KNAT7 k/o and MYB75 k/o (first cohort) than their wild ecotypes. Cumulative CO2-C production was lower in soil amended with stem residues of KNAT7 k/o (first cohort) and MYB75 k/o (first and second cohorts). CCR1 k/o stem tissues caused higher CO2-C production from soil. After 63 days incubation, the acid/aldehyde ratio (Ad/Al) of vanillin (V) and syringyl (S) lignin monomers of soil was higher for stem amended CCR1 k/o and lower for stem amended MYB75 k/o soils as compared to their wild ecotypes. Generally root residues caused lower CO2-C production from soil than stem residues. There was no difference in CO2-C production for root residues between mutant lines and their wild ecotypes. In conclusion, KNAT7 k/o, MYB75 k/o and CCR1 k/o mutations resulted in altered C:N ratio and resistant compounds (i.e., AUF) especially in stems, and these alterations in residue chemistry influenced CO2-C production and also lignin degradation in soil. (c) 2012 Elsevier GmbH. All rights reserved.
