Decomposition in soil and chemical changes of maize roots with genetic variations affecting cell wall quality

Abstract

Roots of brown-midrib (F2bm1 and F292bm3) maize mutants and their normal isogenic counterparts (F2 and F292) were used to evaluate the changes in chemical cell wall features with regard to polysaccharides, lignin composition and interconnecting phenolic acids during root degradation in soil. To this end, the chemical variability of roots of brown-midrib mutants and their normal counterparts was compared and its subsequent impact on carbon (C) mineralization determined under controlled conditions. The bm1 mutation mainly caused an increase in lignin content and a decrease in polysaccharide content of maize roots whereas the bm3 mutation caused only a decrease in polysaccharide content. The lignin composition of bm roots differed from that of normal lines and the proportion of cell wall ester-linked hydroxycinnamic acids was also different. C mineralization kinetics differed markedly between the genotypes. Certain relevant factors concerning root decomposition in soil were studied from the relationships between the chemical characteristics of maize roots at different stages of decomposition and C mineralization rates. The Klason lignin-to-glucose ratio (KL/Glu), the Klason lignin-to-arabinoxylans ratio (KL/AX) and the arabinose-to-xylose ratio (A/X) were proposed as promising predictive indicators of C mineralization kinetics. Future estimations of soil residue decomposition could be improved by taking these initial chemical criteria into account on a wider range of residues.Décomposition dans le sol et évolution de la qualité chimique des racines de maïs présentant des modifications génétiques de la qualité des parois cellulaires' RésuméLes racines des maı¨s mutants brown-midrib (F2bm1 et F292bm3) et celles de leurs ligne´es isoge´niques normales (F2 et F292) ont e´te´utilise´es pour e´valuer les modifications des caracte´ristiques chimiques des parois cellulaires, a`travers la composition des polysaccharides, de la lignine et la nature des acides phe´noliques, au cours de la de´gradation des racines dans le sol. Pour cela, nous avons examine´, en conditions controˆle´es, l'impact d'une variabilite´de la qualite´chimique des racines, en comparant les mutants bm et leurs ligne´es isoge´niques normales, sur la mine´ralisation du C. La mutation bm1 engendre principalement une augmentation de la teneur en lignine et une diminution de la teneur en polysaccharides dans les racines de maı¨s alors que la mutation bm3 cause uniquement une diminution de la teneur en polysaccharides. Dans les racines des mutants bm, la composition de la lignine ainsi que les proportions en acides hydroxycinnamiques este´rifie´s des parois cellulaires diffe`rent de celles des ligne´es non mutantes. Les cine´tiques de mine´ralisation du C varient fortement entre les ge´notypes. Les relations entre les caracte´r-istiques chimiques des racines de maı¨s a`diffe´rents stades de de´composition et les taux de mine´ralisation du C ont permis d'e´tudier certains facteurs pertinents concernant la de´composition des racines dans le sol. Les rapports lig...

Litter decay rates are determined by lignin chemistry

“…In these systems, lignin structures can be modified by altering the expression of genes coding for enzymes in the lignin biosynthesis pathway, or by chemically modifying the lignin as it polymerizes in the cell wall. Previous studies have used genetically or chemically modified plant systems in laboratory studies to examine lignin chemistry effects on cell wall degradation by rumen microbes (Grabber 2005;Grabber et al 2009;Jung and Casler 1991;Jung and Buxton 1994;Jung et al 1999;Vailhe et al 1996), extracellular enzyme preparations (Grabber 2005;Grabber et al 1998c;Grabber et al 1997;Li et al 2010), or microbes in soil microcosms (Hénault et al 2006;Machinet et al 2009;Webster et al 2005). These studies have found mixed evidence for the hypothesis that lignin chemical composition affects plant cell wall degradation.…”

Tissue density determines the water storage characteristics of crop residues

“…Incubation was performed under controlled conditions. The soil used in these experiments, sampled from the 0-10 cm layer at the INRA experimental station in northern France (49°80′N, 3°6 0′E), was a silty loam comprised of 17.8 % clay, 77.3 % silt, 3.8 % sand, and 0.95 % organic C, with a pH H2O of 7.6 (Machinet et al 2009). The moist soil was sieved through a 2-mm mesh-size sieve and stored at 4°C until the initiation of incubation.…”

Impact of fine litter chemistry on lignocellulolytic enzyme efficiency during decomposition of maize leaf and root in soil

“…Chemical characteristics of decomposing leaves and roots were expressed in relation to the initial dry matter (non-decomposed dry matter, ND-DM) by taking into account the loss of mass by decomposition, calculated from the cumulative amounts of mineralized C (Machinet et al 2009). These chemical analyses were performed on only two replicates at each date, as previous experiments demonstrated extremely low variation in similar results (Bertrand et al 2006;Machinet et al 2009Machinet et al , 2011a. This low number of replicates decreased the power of statistical analyses so that significant results should be viewed as conservative.…”

“…These arabinose substitutions can be esterified by ferulic acid (FA) and form diferulate bridges and ether linkages with lignin, thereby crosslinking arabinoxylan chains and arabinoxylan/lignin connections, respectively. The presence of lignin and cross-linking phenolic acids is well known to regulate enzyme access to cellulose and hemicelluloses in forage digestibility and bioreffinery studies (Chesson 1988(Chesson , 1997Lam et al 2003;Berlin et al 2006) and appears to affect decomposition in soils (Machinet et al 2009(Machinet et al , 2011aTalbot et al 2012).…”

“…The recalcitrance of residues to decomposition is mainly related to cell wall polymer content, i.e., lignin (Melillo et al 1982;Berg and McClaugherty 2008). Recently, finer scale residue chemical characteristics related to hemicellulose substitution level (i.e., arabinose to xylose ratio), and interactions between cellulose, hemicellulose and lignin have provided new insights to chemical controls on decomposition (Machinet et al 2009(Machinet et al , 2011a. These studies demonstrated that C mineralization of maize roots in soil was described by both cell wall polymer content, cross linking agents (hydroxycinnamic acids) between hemicellulose and lignin, and the substitution level of hemicelluloses.…”