The soil organic carbon (C) cycle is primarily mediated by soil microorganisms and their genes that function in the C cycle (C-cycle genes), both of which are strongly affected by land cover disturbance. However, the mechanism underlying microbially mediated soil C loss after conversion of primary natural broadleaf forests (BF) to plantation forests (PF) and secondary forests (SF) remains unknown. Here, we measured soil physicochemical properties and soil microbial community properties, and examined their linkages with microbial C-cycle genes. Forest conversion dramatically decreased the richness of the soil fungal community but not of the bacterial community, and altered the composition of both communities. Analysis of C-cycle genes revealed that the abundance of genes associated with C fixation, methane metabolism, and C degradation decreased by 51.3%, 57.9%, and 67.0%, respectively with the conversion of BF to PF; and by 6.3%, 4.1%, and 15.6%, respectively, with the conversion of BF to SF. The reductions in the abundance of C-cycle genes, especially the reduction of hemicellulose- and lignin-degradation genes, were primarily associated with the declines in the abundance of forest conversion-sensitive microbes indexed by operational taxonomic units (fsOTUs, 𝛽$\beta$$\beta$ = 0.41). fsOTUs were taxonomically diverse and included members frequently co-occurring with numerous other microbes in the microbial communities, indicating that the manipulation of fsOTUs by forest management could improve soil fertility and soil C sequestration. Forest conversion-induced shifts in fsOTUs abundance were associated with changes in soil potassium permanganate oxidizable organic carbon (PXC) concentration, dissolved organic carbon (DOC) concentration, and soil pH. Our results indicate that alterations in soil substrate supply (e.g., DOC and PXC) and soil pH induced by forest conversion may strongly shape fsOTUs structure and decrease the abundance of hemicellulose and lignin degradation genes, and consequently increase C loss.

中文翻译：

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原生阔叶林向人工林和次生林转变后土壤微生物群落组成及其碳循环基因的变化

土壤有机碳 (C) 循环主要由土壤微生物及其在 C 循环中起作用的基因（C-循环基因）介导，这两者都受到土地覆盖干扰的强烈影响。然而，在原生天然阔叶林（BF）转变为人工林（PF）和次生林（SF）后，微生物介导的土壤碳损失的机制仍然未知。在这里，我们测量了土壤理化特性和土壤微生物群落特性，并检查了它们与微生物 C 循环基因的联系。森林转化显着降低了土壤真菌群落的丰富度，但没有降低细菌群落的丰富度，并改变了两个群落的组成。对 C 循环基因的分析表明，与 C 固定、甲烷代谢、随着BF向PF的转化，C降解分别降低了51.3%、57.9%和67.0%；BF 转化为 SF，分别降低了 6.3%、4.1% 和 15.6%。C循环基因丰度的减少，尤其是半纤维素和木质素降解基因的减少，主要与操作分类单位索引的森林转化敏感微生物丰度的下降有关。fsOTU ,𝛽$\beta$$\beta$ = 0.41)。fs OTU 在分类学上是多样化的，并且包括经常与微生物群落中的许多其他微生物共存的成员，这表明通过森林管理对fs OTU 的操作可以提高土壤肥力和土壤固碳。森林转化引起的fs OTUs 丰度变化与土壤高锰酸钾可氧化有机碳 (PXC) 浓度、溶解有机碳 (DOC) 浓度和土壤 pH 值的变化有关。我们的研究结果表明，森林转化引起的土壤基质供应（例如，DOC 和 PXC）和土壤 pH 值的变化可能强烈影响 fsOTU 结构并降低了半纤维素和木质素降解基因的丰度，从而增加了 C 损失。