Wilhelm Roland C, Cardenas Erick, Leung Hilary, Szeitz András, Jensen Lionel D, Mohn William W
Department of Microbiology and Immunology, Life Sciences Institute, University of British ColumbiaVancouver, BC, Canada.
Pharmaceutical Analytical Suite, Faculty of Pharmaceutical Sciences, University of British ColumbiaVancouver, BC, Canada.
Front Microbiol. 2017 Apr 11;8:537. doi: 10.3389/fmicb.2017.00537. eCollection 2017.
Soil management is vital for maintaining the productivity of commercial forests, yet the long-term impact of timber harvesting on soil microbial communities remains largely a matter of conjecture. Decomposition of plant biomass, comprised mainly of lignocellulose, has a broad impact on nutrient cycling, microbial activity and physicochemical characteristics of soil. At "Long-term Soil Productivity Study" sites in California dominated by Ponderosa pine, we tested whether clear-cut timber harvesting, accompanied by varying degrees of organic matter (OM) removal, affected the activity and structure of the cellulose-degrading microbial populations 16 years after harvesting. Using a variety of experimental approaches, including stable isotope probing with C-labeled cellulose in soil microcosms, we demonstrated that harvesting led to a decrease in net respiration and cellulolytic activity. The decrease in cellulolytic activity was associated with an increased relative abundance of thermophilic, cellulolytic fungi (Chaetomiaceae), coupled with a decreased relative abundance of cellulolytic bacteria, particularly members of Opitutaceae, , and Streptomycetaceae. In general, harvesting led to an increase in stress-tolerant taxa (i.e., also non-cellulolytic taxa), though our results indicated that OM retention mitigated population shifts via buffering against abiotic changes. Stable-isotope probing improved shotgun metagenome assembly by 20-fold and enabled the recovery of 10 metagenome-assembled genomes of cellulolytic bacteria and fungi. Our study demonstrates the putative cellulolytic activity of a number of uncultured taxa and highlights the mineral soil layer as a reservoir of uncharacterized diversity of cellulose-degraders. It also and contributes to a growing body of research showing persistent changes in microbial community structure in the decades following forest harvesting.
土壤管理对于维持商品林的生产力至关重要，但木材采伐对土壤微生物群落的长期影响在很大程度上仍属推测。主要由木质纤维素组成的植物生物量的分解，对土壤的养分循环、微生物活性和理化特性具有广泛影响。在加利福尼亚州以黄松为主的“长期土壤生产力研究”站点，我们测试了皆伐木材采伐（伴随着不同程度的有机质去除）在采伐16年后是否会影响纤维素降解微生物种群的活性和结构。我们采用了多种实验方法，包括在土壤微宇宙中用碳标记的纤维素进行稳定同位素探测，结果表明采伐导致净呼吸和纤维素分解活性下降。纤维素分解活性的下降与嗜热纤维素分解真菌（毛壳菌科）相对丰度的增加以及纤维素分解细菌相对丰度的下降有关，特别是疣微菌科和链霉菌科的成员。总体而言，采伐导致耐胁迫类群（即也是非纤维素分解类群）增加，不过我们的结果表明，有机质保留通过缓冲非生物变化减轻了种群变化。稳定同位素探测使鸟枪法宏基因组组装提高了20倍，并使我们能够获得10个纤维素分解细菌和真菌的宏基因组组装基因组。我们的研究证明了许多未培养类群的假定纤维素分解活性，并突出了矿质土壤层是未表征的纤维素分解者多样性的储存库。它也为越来越多的研究做出了贡献，这些研究表明森林采伐后的几十年里微生物群落结构会持续变化。
