Spruce and beech as local determinants of forest fungal community structure in litter, humus and mineral soil

Beech forests reaches its native distribution limit in SE Norway, but is expected to expand substantially northwards due to climate warming. This may potentially result in a fundamental transformation of contemporary Northern European forests, with tentative effects on the associated belowground fungi. Fungal communities mediate vital ecosystem processes such as ecosystem productivity and carbon sequestration in boreal forests. To investigate how soil fungi is affected by the vegetation transition from spruce to beech forest, we sampled litter, humus and mineral soil in a forest landscape dominated by beech, spruce or a mixture of these. The fungal communities in the soil samples were analyzed by DNA metabarcoding of the rDNA ITS2 region. Although soil layers were the most important structuring gradient, we found clear differences in fungal species composition between spruce and beech plots. The differences in fungal community composition were most evident in the litter and least in the mineral soil. Decomposers, most notably Mycena, dominated the litter layer while various mycorrhizal fungi dominated the humus and mineral layers. Some ectomycorrhizal taxa, such as Cenoccocum and Russula, were more abundant in spruce forests. Differences in fungal community composition between forest types can potentially have large impacts on carbon sequestration rates.

山毛榉林在挪威东南部已达到其自然分布上限，但受气候变暖影响，预计其分布范围将大幅向北扩张。这可能引发当代北欧森林的根本性转型，并对相关地下真菌群落产生潜在影响。真菌群落介导着寒温带森林中诸多关键生态系统过程，如生态系统生产力与碳封存。为探究土壤真菌如何响应云杉向山毛榉林的植被演替，我们在以山毛榉、云杉或二者混交为主的森林景观中，采集了枯落物、腐殖质与矿质土壤样本。我们通过对核糖体DNA（rDNA）ITS2区域开展DNA宏条形码技术（DNA metabarcoding）分析，对土壤样本中的真菌群落进行了分析。尽管土壤层次是塑造真菌群落结构的最主要分异因子，我们仍发现云杉样地与山毛榉样地的真菌物种组成存在显著差异。真菌群落组成的差异在枯落物层最为显著，在矿质土壤层则最为微弱。分解者类群（尤以小菇属（Mycena）为代表）在枯落物层占据主导地位，而腐殖质层与矿质土层则以各类菌根真菌为主。部分外生菌根类群（如Cenoccocum与红菇属（Russula））在云杉林中的丰度更高。不同林型间的真菌群落组成差异，可能会对碳封存速率产生显著影响。