Effects of bioethanol residues on the functional and genetic diversity of soil microbiota

Summary

Regarding the use of residual material from bioethanol conversion, a series of experiments were performed. The work included two NZ soils from organic farming systems (Templeton and Ballantray, respectively) and treatments with three types of biomaterials: 1) residual material from bio-ethanol conversion (based on rye straw; 2) untreated rye straw; 3) grass-clover mixture - as well as a control with no amendment. The dried and ground biomaterials were supplied at 2 and 10 mg kg-1 dry soil, incubated in 1-L glass vials and harvested destructively after 3, 5 and 21 days. In this way, four experimental series were performed, each with three sequential harvests. The soil was analyzed for various microbial parameters: bacterial colony-forming units (not in all experiments), phospholipid fatty acid composition (PLFA; genetic diversity), catabolic response profiling (CRP; functional diversity); content of labile organic carbon (hot-water extractable C) and mineral N concentration and loss of organic C via accumulated respiration.
Analysis of the CRP data showed that the functional diversity of the soil microbial community is generally very high and not significantly different between any of the soils, treatments or time of harvest (Table 1). Principal component analysis (PCA) of the CRP profiles showed that this method can distinguish between the treatments – not least at 10 mg biomaterial g-1 dry soil. The PCAs also shows that right after soil amendment, the functional diversity is affected differently, according to the type of material applied. However, after 21 days the data points representing the three applied materials tend to group up together, indicating that it is the added materials which have the largest impact on the soil microbial function, but also that this impact is getting less within a relatively short time (weeks).