Recovery of the ectomycorrhizal community after termination of long-term nitrogen fertilisation of a boreal Norway spruce forest. N addition fungal ITS

Ectomycorrhizal fungi (ECM) are a fundamental component of boreal forests promoting tree growth and participating in soil nutrient cycling. Increased nitrogen (N) input is known to largely influence ECM communities but their potential recovery is not well understood. Therefore, we studied the effects of long-term N-fertilisation on ECM communities, and their recovery after termination of N treatment. Fungal ITS sequencing data indicated that N-fertilisation (34 kg N ha−1 y−1) for 46 y decreased the relative abundance of ECM species in the fungal community and suppressed originally dominating medium-distance fringe exploration types adapted to N-limited conditions, while the ECM diversity remained unaffected. In other plots, 23 y after termination of fertilisation at 73 kg N ha−1 y−1 for 23 y, the relative abundance of ECM species shifted closer to, but did not reach, control levels. These observations indicate only slow recovery of ECM community, likely due to a high soil N retention capacity.

外生菌根真菌（Ectomycorrhizal fungi，ECM）是北方针叶林的核心组成组分，可促进林木生长并参与土壤养分循环。已知氮（N）输入增加会对ECM群落产生显著影响，但目前学界对其潜在的恢复能力尚缺乏深入认知。为此，本研究探究了长期施氮对ECM群落的影响，以及施氮处理终止后ECM群落的恢复情况。真菌ITS测序数据显示，持续46年施氮（34 kg N ha⁻¹ y⁻¹）降低了真菌群落中ECM物种的相对丰度，抑制了原本适应氮限制环境的优势中等距离边缘探索型ECM类群，但ECM多样性未受显著影响。在另一组样地中，以73 kg N ha⁻¹ y⁻¹的施氮强度处理23年后终止施氮，时隔23年采样时，ECM物种的相对丰度虽已向对照组水平趋近，但未达到对照组标准。上述观测结果表明ECM群落的恢复过程较为缓慢，这可能与土壤较强的氮固持能力有关。