Decomposition of Litter and Root Residues From Perennial Intermediate Wheatgrass Governed by the Soil Microbiome and Different Earthworm Species

Introduction
Perennial intermediate wheatgrass (IWG, Kernza®) establishes an extensive root system which positively impacts nutrient retention and biodiversity and therefore offers a regenerative alternative to current annual wheat production. However, the effect of its components on the soil ecosystem, for example, on the macrofauna and microbiota, is not yet understood.

Materials and Methods
Litter and root samples of IWG and annual wheat were sampled and used in an experimental design consisting of two pot experiments under controlled conditions to investigate the effect of earthworms and microorganisms on litter and root decomposition differing in starch and element composition. From the experiment, two lifeforms of earthworms (anecic, endogeic) and the soil microbiome were analysed.

Results
Both litter and root samples had higher lignin and starch content for IWG as compared to annual wheat. A possible greater nutrient retention for IWG was also indicated by higher nitrogen and carbon contents in both the litter and the root samples. Accordingly, the C/N ratio was lower than for annual wheat, which resulted in a faster decomposition rate and a significantly lower ratio of fungi to bacteria. Both cropping systems showed significant differences in the underlying soil bacterial community composition. Most notably, the IWG root substrate led to a higher diversity in the underlying soil in comparison to the annual wheat substrate.

Conclusion
The beneficial substrate composition of IWG supports macrofauna and microbial uptake and decomposition. The rhizosphere harbours a higher microbial diversity and an increased nutrient retention in comparison to annual wheat, recommending IWG for a sustainable and regenerative agriculture.