Molecular monitoring of the poplar wood chip microbiome as a function of storage strategy

One of the most challenging aspects of using wood chips as renewable energy source is the loss of biomass related to storage. Therefore, we installed three outdoor industrial-scale piles (250 m³) of poplar wood chips and monitored the bacterial and fungal communities by next-generation sequencing over a storage period of 120 d. Two of the three piles were supplemented with calcium dihydroxide (Ca(OH)₂) (1.5%, 3% w/w) in order to test its potential as alkaline stabilization agent to preserve woody biomass during storage. Shifts in the microbial community composition occurred almost entirely in the beginning of the storage experiment, which we attribute to the temperature rise of up to 60 °C within the first week of storage. Later, however, we found little changes. Independent of Ca(OH)₂ concentration, a consortium of lignocellulolytic and thermotolerant microorganisms dominated the stored wood chip microbiota emphasizing their role as key players during wood decomposition. Although the addition of Ca(OH)₂ altered the physicochemical properties of wood chips, it did not prevent loss of biomass. Especially the pH was increased in Ca(OH)₂ treated piles. However, only minor differences in the microbial communities’ composition were detected following Ca(OH)₂ addition, highlighting the microbes tolerance towards and adaptation to changing environmental conditions.