Data_Sheet_1_Understory species composition mediates soil greenhouse gas fluxes by affecting bacterial community diversity in boreal forests.docx

IntroductionPlant species composition in forest ecosystems can alter soil greenhouse gas (GHG) budgets by affecting soil properties and microbial communities. However, little attention has been paid to the forest types characterized by understory vegetation, especially in boreal forests where understory species contribute significantly to carbon and nitrogen cycling.MethodIn the present study, soil GHG fluxes, soil properties and bacterial community, and soil environmental conditions were investigated among three types of larch forest [Rhododendron simsii-Larix gmelinii forest (RL), Ledum palustre-Larix gmelinii forest (LL), and Sphagnum-Bryum-Ledum palustre-Larix gmelinii forest (SLL)] in the typical boreal region of northeast China to explore whether the forest types characterized by different understory species can affect soil GHG fluxes.ResultsThe results showed that differences in understory species significantly affected soil GHG fluxes, properties, and bacterial composition among types of larch forest. Soil CO2 and N2O fluxes were significantly higher in LL (347.12 mg m−2 h−1 and 20.71 μg m−2 h−1) and RL (335.54 mg m−2 h−1 and 20.73 μg m−2 h−1) than that in SLL (295.58 mg m−2 h−1 and 17.65 μg m−2 h−1), while lower soil CH4 uptake (−21.07 μg m−2 h−1) were found in SLL than in RL (−35.21 μg m−2 h−1) and LL (−35.85 μg m−2 h−1). No significant differences between LL and RL were found in soil CO2, CH4, and N2O fluxes. Soil bacterial composition was mainly dominated by Proteobacteria, Actinobacteria, Acidobacteria, and Chloroflexi among the three types of larch forest, while their abundances differed significantly. Soil environmental variables, soil properties, bacterial composition, and their interactions significantly affected the variations in GHG fluxes with understory species. Specifically, structural equation modeling suggested that soil bacterial composition and temperature had direct close links with variations in soil GHG fluxes among types of larch forest. Moreover, soil NO3−−N and NH4+ − N content also affected soil CO2, CH4, and N2O fluxes indirectly, via their effects on soil bacterial composition.DiscussionOur study highlights the importance of understory species in regulating soil GHG fluxes in boreal forests, which furthers our understanding of the role of boreal forests in sustainable development and climate change mitigation.

引言：森林生态系统中植物物种组成的变化可通过对土壤性质和微生物群落的影响，调节土壤温室气体（GHG）收支。然而，对以林下层植被为特征的森林类型的关注尚显不足，尤其是在北方针叶林中，林下层物种对碳和氮循环的贡献尤为显著。方法：本研究在东北中国典型的北方地区，对三种类型的落叶松林（杜鹃叶松林（RL）、越橘叶松林（LL）和苔藓-苔草-越橘叶松林（SLL））的土壤GHG通量、土壤性质、细菌群落以及土壤环境条件进行了调查研究，旨在探究不同林下层物种特征的森林类型是否会影响土壤GHG通量。结果：研究表明，林下层物种的差异显著影响了落叶松林类型之间的土壤GHG通量、性质和细菌组成。LL和RL的土壤CO2和N2O通量（分别为347.12 mg·m−2·h−1和20.71 μg·m−2·h−1，335.54 mg·m−2·h−1和20.73 μg·m−2·h−1）明显高于SLL（295.58 mg·m−2·h−1和17.65 μg·m−2·h−1），而SLL的土壤CH4吸收率（−21.07 μg·m−2·h−1）低于RL（−35.21 μg·m−2·h−1）和LL（−35.85 μg·m−2·h−1）。LL和RL之间的土壤CO2、CH4和N2O通量无显著差异。在三种类型的落叶松林中，土壤细菌组成主要由变形菌门、放线菌门、酸杆菌门和绿弯菌门主导，而其丰度存在显著差异。土壤环境变量、土壤性质、细菌组成及其相互作用显著影响了土壤GHG通量随林下层物种的变化。具体而言，结构方程模型表明，土壤细菌组成和温度与落叶松林类型之间土壤GHG通量的变化存在直接的紧密联系。此外，土壤NO3−−N和NH4+−N含量也通过影响土壤细菌组成间接影响了土壤CO2、CH4和N2O通量。讨论：本研究突出了林下层物种在调节北方森林土壤GHG通量中的重要性，进一步加深了我们对北方森林在可持续发展与气候变化缓解中所起作用的认知。