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

Abstract

Residue recalcitrance controls decomposition and soil organic matter turnover. We hypothesized that the complexity of the cell wall network regulates enzyme production, activity and access to polysaccharides. Enzyme efficiency, defined as the relationship between cumulative litter decomposition and enzyme activities over time, was used to relate these concepts. The impact of two contrasting types of cell walls on xylanase, cellulase and laccase efficiencies was assessed in relation to the corresponding changes in residue chemical composition (xylan, glucan, lignin) during a 43-day incubation period. The selected residues were maize roots, which are rich in secondary cell walls that contain lignin and covalent bridges between heteroxylans and lignin, and maize leaves having mostly nonlignified primary cell walls thus making the cellulose and hemicelluloses less resistant to enzymes. Relationships between C mineralization and change in residue quality through decomposition indicated that the level of substitution of arabinoxylans (arabinan to xylan ratio) provides a good explanation of the decomposition process. In leaves enriched in primary cell walls, arabinose substitution of xylan controlled C mineralization rate but hampered polysaccharide decomposition, but to a lesser extent than in roots in which arabinoxylans were mostly cross-linked with lignin. Enzyme activity was higher in leaf than root amended soils while enzyme efficiency was systematically higher in the presence of roots. This apparent paradox suggests that residue quality could preselect the microbial community. Indeed, we found that microorganisms exhibited an initial rapid growth in the presence of a high quality litter and produced enzymes that are not efficient in degrading recalcitrant cell walls while, in the presence of the more recalcitrant maize roots, microbial biomass grew more slowly but produced enzymes of higher efficiency. This high enzyme efficiency could be explained by the synergistic action of hydrolytic and oxidative enzymes even in the early stage of decomposition.

Enzymatic Strategies and Carbon Use Efficiency of a Litter-Decomposing Fungus Grown on Maize Leaves, Stems, and Roots

“…The lowest enzyme efficiencies in the root treatment were compensated for by the highest investments in enzyme activities. The relationships between the enzyme efficiencies and the chemical recalcitrance of the substrate remain unclear (Sinsabaugh et al, 2002; Wickings et al, 2012; Amin et al, 2014; Fanin et al, 2016). In the present work, differences in the enzyme efficiencies observed between the stems and roots could not be explained by differences in the lignin content, which was similar for the two litters.…”

“…We calculated the enzyme efficiencies between dates and summed the values over the entire incubation period for the C-acquiring hydrolase activity by summing the βG, EX, and EG activities and for the oxidative enzyme activity by using the LAC value. The enzyme activity efficiencies can be assessed against the CO 2 mineralized as an index of microbial metabolism (Sinsabaugh et al, 2002; Moorhead et al, 2013b; Amin et al, 2014). We proposed in this study to calculate the efficiency of the enzyme activity for fungal-C biosynthesis (in μg fungal-C mol -1 ) by dividing the amount of recovered C in fungal biomass by the cumulative enzyme activity (in μmol g -1 DM).…”

“…Indeed, once enzymes have been secreted, their activities have shown different efficiencies, meaning that the amount of enzyme activity required for substrate decomposition can vary markedly. High contents of lignin may decrease enzyme efficiency (Sinsabaugh et al, 2002; Wickings et al, 2012), and recalcitrant substrates may alternatively induce the synthesis of an enzyme “cocktail” in which hydrolytic enzymes act in synergy with oxidative enzymes, thereby resulting in a higher efficiency relative to enzymes secreted on labile substrates (Amin et al, 2014). Enzyme activities per unit microbial biomass synthetized over a specific period are used to characterize the microbial “investment” in enzymes.…”

Long-term application of Jatropha press cake promotes seed yield by enhanced soil organic carbon accumulation, microbial biomass and enzymatic activities in soils of semi-arid tropical wastelands

“…This view is supported by Amin et al [69] who have recently reported a decrease in specific activities of measured enzymes during decomposition of maize roots as compared to leaf residues and ascribed it to the presence of higher ligno-cellulosic fractions of the roots besides other chemical features of the wall constituents. Further, lower enzymatic activities does not necessary reflect lower efficiency [70] and we hypothesize that higher efficiency of the enzymes in Jatropha press cake amended soil might have resulted in more resource allocation to increase biomass by some group of microorganisms for ecological or competitive advantage over others.…”

Effects of water management practices on residue decomposition and degradation of Cry1Ac protein from crop-wild Bt rice hybrids and parental lines during winter fallow season

“…In addition, it was reported that the chemistry of a single litter type diverged when it was decomposed in management systems with distinct decomposer communities (Wickings et al, 2012).Collectively, these investigations may provide an explanation for the results that the k m value for the roots was significantly higher under the aerobic condition compared with the flooded condition. Furthermore, it was reported that the enzyme activity was higher in maize leaf than root amended soils while enzyme efficiency was systematically higher in the presence of roots, which demonstrated that litter quality is regulating decomposer strategy (Amin et al, 2014). Thus, the opposite pattern of differed process of decomposition between leaves and roots under aerobic and flooded condition indicated that the chemistry of different litter types diverged, rather than converged, during decomposition due to the activities of decomposers, as suggested by Wickings et al (2012).…”