Influence of genetically modified cell wall mutants on carbon dioxide and nitrous oxide emissions from soil: A study with Arabidopsis thaliana

Increasing atmospheric concentrations of the greenhouse gases (GHGs) carbon dioxide (CO2) and nitrous oxide (N2O) are of environmental concern. Genetically modified (GM) cell wall mutants that have altered lignin concentration in their plant tissues may reduce the magnitude of one or both of these GHGs emitted from soil. Taking Arabidopsis thaliana as a model plant species, this study examined how A. thaliana cell wall mutants may influence emission of CO2 and N2O from soil during their growth and development and after incorporation of their residues in soil. Down-regulated (k/o) and over-expression (o/x) KNOTTED ARABIDOPSIS THALIANA 7 (KNAT7), k/o and o/x of PRODUCTION OF ANTHOCYANIN PIGMENT 1 (PAP1) also known as MYB75 and k/o cinnamoyl-CoA reductase 1 (CCR1 ) mutant lines and their wild ecotypes were considered in the present study. KNAT7 k/o and MYB75 k/o had similar morphological traits and caused no alteration in emission of CO2 and N2O from soil during their growth and development as compared to their wild ecotypes. CCR1 mutant line had lower crown cover of rosette leaves, reduced fertility, and on average lower biomass. This line had lower transpiration and greater mineral N concentration in rhizosphere and bulk soil, which did not affect CO2 emission but increased N2O emission from root-associated soil of the CCR1 mutant line at the reproductive stage. Residues of KNAT7 k/o and MYB75 k/o had higher lignin and C:N ratio while CCR1 had lower lignin and C:N ratio in inflorescence stems, compared to their wild ecotypes. Decomposition of KNAT7 k/o and MYB75 k/o stem residues tended to decrease CO2 while CCR1 stem residues caused higher CO2 emissions from soil. Root residues that had higher lignin than stems, caused lower CO2 emissions from soil. Stem residues of CCR1 increased mineral N concentration and microbial biomass of soil, whereas MYB75 k/o stem residues increased microbial biomass in clay loam soil. Microbial biomass was higher in soil amended with stem residues than soil amended with root residues. Root residues increased fungal:bacterial ratio of soil. In conclusion, the altered morphological traits and residue chemistry of A. thaliana cell wall mutants influenced soil abiotic and biotic factors (i.e. evapotranspiration, mineral N concentration, microbial biomass, microbial community structure e.g. fungal:bacterial ratio of soil) that contribute to CO2 and N2O emissions from soil.