Long-term effects of timber harvesting on hemicellulolytic microbial populations in coniferous forest soils

Abstract

Forest ecosystems need to be sustainably managed, as they are major reservoirs of biodiversity, provide important economic resources and modulate global climate. We have a poor knowledge of populations responsible for key biomass degradation processes in forest soils and the effects of forest harvesting on these populations. Here, we investigated the effects of three timber-harvesting methods, varying in the degree of organic matter removal, on putatively hemicellulolytic bacterial and fungal populations 10 or more years after harvesting and replanting. We used stable-isotope probing to identify populations that incorporated 13C from labeled hemicellulose, analyzing 13C-enriched phospholipid fatty acids, bacterial 16 S rRNA genes and fungal ITS regions. In soil microcosms, we identified 104 bacterial and 52 fungal hemicellulolytic operational taxonomic units (OTUs). Several of these OTUs are affiliated with taxa not previously reported to degrade hemicellulose, including the bacterial genera Methylibium, Pelomonas and Rhodoferax, and the fungal genera Cladosporium, Pseudeurotiaceae, Capronia, Xenopolyscytalum and Venturia. The effect of harvesting on hemicellulolytic populations was evaluated based on in situ bacterial and fungal OTUs. Harvesting treatments had significant but modest long-term effects on relative abundances of hemicellulolytic populations, which differed in strength between two ecozones and between soil layers. For soils incubated in microcosms, prior harvesting treatments did not affect the rate of incorporation of hemicellulose carbon into microbial biomass. In six ecozones across North America, distributions of the bacterial hemicellulolytic OTUs were similar, whereas distributions of fungal ones differed. Our work demonstrates that diverse taxa in soil are hemicellulolytic, many of which are differentially affected by the impact of harvesting on environmental conditions. However, the hemicellulolytic capacity of soil communities appears resilient.

Analysis of microbial utilization of rice straw in paddy soil using a DNA‐SIP approach

“…In our study, fungal community showed lower α‐diversity (Supplemental Table ) and fewer specific fungal OTUs were identified compared with bacterial community (Table ). Consistent with previous studies using SIP method (Leung et al., ; Stursová, Zifčáková, Leigh, Burgess, & Baldrian, ), Ascomycota also accounted for the majority of total community in 13 C‐heavy fraction (Figure 5b). The genera Chaetomium , Mortierella and Curvularia , which are known to be involved in hemicellulose degradation (Zeng et al., ), were the initial fungal groups assimilating straw‐derived 13 C at Day 3.…”

“…Generally, bacteria degrade labile organic matter more actively in the early phase of straw decomposition, while fungi are responsible for the degradation of complex and recalcitrant substrates at later stages (Paterson et al., ). For instance, members of the genera Bacillus and Paenibacillus have been identified as decomposers of labile C (Verastegui et al., ), while members of the phylum Ascomycota have strong cellulolytic and hemicellulolytic capabilities (Leung, Maas, Wilhelm, & Mohn, ). Recently, it was also suggested that, like fungi, bacteria potentially play a significant role in the mineralization of recalcitrant components (Bastian, Bouziri, Nicolardot, & Ranjard, ; España et al., ).…”

Effects of tillage managements and maize straw returning on soil microbiome using 16S rDNA sequencing

“…Soil is the major sink for COS from the atmosphere, and rotary tillage would expose to the soil to more COS than no tillage or deep tillage treatments. It is well known that Methylibium possess the ability to degrade hemicellulose, which is abundant in crop straw (Leung et al ). Although few studies have investigated the relationship between Methylibium and tillage practices, it is known to be a monoaromatic hydrocarbon degrading bacterium (Salvador et al ).…”

Bacterial and fungal contributions to delignification and lignocellulose degradation in forest soils with metagenomic and quantitative stable isotope probing

“…Microcosms were wetted and pre-incubated in the dark at 20° C for one-week prior to the addition of 1% (w/w) 13 C-labeled cellulose or 0.8% (w/w) lignin. The hemicellulose-amended incubations were performed as part of a previous study examining the impacts of timber harvesting on decomposition using identical methods as described here for cellulose (Leung et al , 2016). Each microcosm with 13 C-labeled substrate was paired with an identical ‘ 12 C-control’ microcosm amended with the corresponding unlabeled substrate (~1.1% atom 13 C).…”

“…Microcosms were incubated at 20° C for 14 days (cellulose) or 60 days (lignin) or 2 days (hemicellulose; Leung et al , 2016). The incubation length for this study was optimized by preliminary time-course experiments described in Wilhelm et al (2014).…”