Soil microbial function and fungal community data along an ectomycorrhizal basal area gradient, Vermont, May 2019

Mycorrhizal fungi can affect soil organic matter cycling through several mechanisms including priming, nutrient competition, and direct enzyme production. Differences in nutrient foraging strategies between ectomycorrhizal (EcM) and arbuscular mycorrhizal (AM) fungi produce divergent belowground dynamics: where EcM can take up organic nitrogen and directly break down SOM by producing enzymes, AM fungi are limited to scavenging mineral N. EcM-associated tree species also have leaf litter with relatively higher ratios of carbon to nitrogen (C:N), and belowground saprotrophic communities more dominated by fungi. Consequently, free-living microbes in EcM-dominated soils should experience nitrogen limitation, with subsequent increases in enzyme production and decreased carbon use efficiency (CUE). However, the relative importance of the effects of substrate quality and fungal community composition on enzyme production and CUE are unclear. To assess this distinction, we sampled the organic horizon and 10 cm of the mineral horizon in northern temperate forest soils along a gradient of EcM dominance (see SCxTS_DBH.csv for full tree species information). We characterized fungal community composition by measuring EcM relative abundances from extracted fungal DNA (To run raw ASV data through R code, use SCxTS_ASV_taxonomy.csv, and R code ITS_processing.Rmd; to see processed data with EcM relative abundance, use file SCxTS_sum_afitch_Feb18.20.csv) and the fungal to bacterial ratios (see data file SCxTS_plfa.csv) from phospholipid fatty acid analysis. Soil microbial functions were measured as potential activities of five hydrolytic and two oxidative enzymes ( To run raw data through R code us SCxTS_metadata.csv, hydrolytic_oxidative_raw.csv, MUBraw.csv, Enzyme_soilweight.csv, and incubationtime.csv, and R code SCxTS_enzymes.Rmd; to use Enzyme data ready to run through statistics code, use file Enzyme.data.csv) and microbial carbon use efficiency (see file SCxTS_CUE.csv and for full calculations file 18O_CUEcalcs_SCxTS_2019.xlsx). We assessed soil substrate quality as the soil carbon:nitrogen ratio (See file Organic_CN.csv). Statistical analysis can be run using R code from file SCxTS_analysis.Rmd.

菌根真菌（Mycorrhizal fungi）可通过激发效应、养分竞争及直接产酶作用等多种机制调控土壤有机质循环。外生菌根（ectomycorrhizal, EcM）与丛枝菌根（arbuscular mycorrhizal, AM）真菌在养分觅取策略上的差异，会导致地下生态过程产生分化：外生菌根真菌可吸收有机氮并通过分泌酶类直接分解土壤有机质（soil organic matter, SOM），而丛枝菌根真菌仅能摄取矿质态氮。与外生菌根真菌共生的树种，其凋落叶的碳氮比（carbon to nitrogen, C:N）相对更高，且地下腐生微生物群落以真菌为主导。因此，以外生菌根真菌为主导的土壤中的自由生活微生物，会面临氮素限制，进而表现为产酶活性上升、碳利用效率（carbon use efficiency, CUE）下降。然而，底物质量与真菌群落组成对产酶活性及碳利用效率的相对重要性尚不明确。为评估这一科学问题，我们沿外生菌根真菌占比梯度，采集了北温带森林土壤的有机层及10 cm深度的矿质层样品（完整树种信息详见SCxTS_DBH.csv文件）。我们通过提取真菌DNA并测定外生菌根真菌的相对丰度，以表征真菌群落组成（若需通过R代码处理原始扩增子序列变体（Amplicon Sequence Variant, ASV）数据，可使用SCxTS_ASV_taxonomy.csv与ITS_processing.Rmd文件；若需查看已处理的外生菌根真菌相对丰度数据，可使用SCxTS_sum_afitch_Feb18.20.csv文件），并通过磷脂脂肪酸分析测定真菌与细菌的生物量比（相关数据见SCxTS_plfa.csv文件）。土壤微生物功能通过以下指标表征：5种水解酶与2种氧化酶的潜在活性（若需通过R代码处理原始酶活数据，可使用SCxTS_metadata.csv、hydrolytic_oxidative_raw.csv、MUBraw.csv、Enzyme_soilweight.csv与incubationtime.csv文件，以及R代码文件SCxTS_enzymes.Rmd；若需使用可直接用于统计分析的酶活性数据集，可使用Enzyme.data.csv文件），以及微生物碳利用效率（相关数据见SCxTS_CUE.csv文件，完整计算过程详见18O_CUEcalcs_SCxTS_2019.xlsx文件）。我们以土壤碳氮比表征土壤底物质量（相关数据见Organic_CN.csv文件）。统计分析可通过文件SCxTS_analysis.Rmd中的R代码完成。