Department of Biology, University of British Columbia, Kelowna, British Columbia, Canada.
Department of Environment and Primary Industries, Biosciences Research Division, Bundoora, Victoria, Australia.
ISME J. 2014 Mar;8(3):699-713. doi: 10.1038/ismej.2013.195. Epub 2013 Oct 31.
Soils of northern temperate and boreal forests represent a large terrestrial carbon (C) sink. The fate of this C under elevated atmospheric CO2 and climate change is still uncertain. A fundamental knowledge gap is the extent to which ectomycorrhizal fungi (EMF) and saprotrophic fungi contribute to C cycling in the systems by soil organic matter (SOM) decomposition. In this study, we used a novel approach to generate and compare enzymatically active EMF hyphae-dominated and saprotrophic hyphae-enriched communities under field conditions. Fermentation-humus (FH)-filled mesh bags, surrounded by a sand barrier, effectively trapped EMF hyphae with a community structure comparable to that found in the surrounding FH layer, at both trophic and taxonomic levels. In contrast, over half the sequences from mesh bags with no sand barrier were identified as belonging to saprotrophic fungi. The EMF hyphae-dominated systems exhibited levels of hydrolytic and oxidative enzyme activities that were comparable to or higher than saprotroph-enriched systems. The enzymes assayed included those associated with both labile and recalcitrant SOM degradation. Our study shows that EMF hyphae are likely important contributors to current SOM turnover in sub-boreal systems. Our results also suggest that any increased EMF biomass that might result from higher below-ground C allocation by trees would not suppress C fluxes from sub-boreal soils.
北方温带和北方森林的土壤代表了一个大型陆地碳（C）汇。在大气 CO2 升高和气候变化下，这种 C 的命运仍然不确定。一个基本的知识差距是外生菌根真菌（EMF）和腐生真菌在土壤有机质（SOM）分解过程中对 C 循环的贡献程度。在这项研究中，我们使用了一种新的方法，在野外条件下生成和比较酶活性旺盛的 EMF 菌丝占主导地位和腐生真菌菌丝丰富的群落。填充发酵腐殖质（FH）的网袋，周围有一层沙障，有效地捕获了 EMF 菌丝，其群落结构在营养和分类水平上与周围的 FH 层相似。相比之下，没有沙障的网袋中超过一半的序列被鉴定为腐生真菌。EMF 菌丝占主导地位的系统表现出的水解和氧化酶活性水平与腐生真菌丰富的系统相当或更高。测定的酶包括与易降解和难降解 SOM 降解相关的酶。我们的研究表明，EMF 菌丝可能是北方亚森林系统中当前 SOM 转化的重要贡献者。我们的结果还表明，树木通过增加地下 C 分配可能导致的 EMF 生物量增加，不会抑制北方亚土壤的 C 通量。
