Can litter quality-enzyme efficiency interactions impact on subsequent decomposition?

Background/Question/Methods

Litter quality controls decomposition and soil organic matter turnover. Recently, enzyme efficiency, defined as the relationship between cumulative litter decomposition and enzyme activities over time, was shown to increase with low litter quality. This apparent paradox suggests that residue quality could preselect soil microbial community and functions. To test this concept, a controlled condition incubation was performed with either low (maize roots) or high (maize leaves) quality litter. After 62 days incubation, a 13C-labeled low quality litter (flax stem) was added to maize leaf or root-amended soils or to soil without previous amendment. C mineralization, C biomass and enzymes kinetics were measured regularly. Our hypothesis was that the decomposition of litter having a contrasted quality would lead to different patterns of enzyme production and would then impact differently the decomposition of a litter added subsequently.

Results/Conclusions

Flax stem C mineralization rate was lower when added to soil recently amended with maize leaf or root compared to mineralization rate measured in soil without previous litter addition. The effects of subsequent litter addition on enzymes dynamics were minor compare to those related to litter quality. Indeed, lignocellulolytic enzymes produced in presence of maize root or leave i.e., before flax stem addition, did not contribute much to the decomposition of flax stem. However, laccase activities increase after the addition of flax stem for all treatments and this increase was more pronounced in the soil with previous addition of maize root than with flax stem alone. This suggests that recalcitrant residue could preselect microbial community for oxidative enzyme thus increasing enzyme efficiency. Overall, our results support the hypothesis of “microbial economics” with a decrease in enzyme production when assimilable resources are available in sufficient amount, resulting in less degradation of more complex substrates