Mountain ecosystems, contributing substantially to the global carbon (C) and nitrogen (N) biogeochemical cycles, are heavily impacted by global changes. Although soil respiration and microbial activities have been extensively studied at different elevation, little is known on the relationships between environmental drivers, microbial functions, and greenhouse gas fluxes (GHGs; carbon dioxide [CO2], methane [CH4] and nitrous oxide [N2O]) in soils of different elevation. Here, we measured how in situ GHG fluxes were linked to soil properties, soil organic matter (SOM) quantity and composition (the proportion of humic-like vs. protein-like OM), microbial biomass, enzyme activities and functional gene abundances in natural soils spanning an elevational gradient of ∼2400 m in Switzerland. Soil CO2 fluxes did not significantly vary from low (lowland zone) to higher (montane and subalpine zones) elevation forests, but decreased significantly (P<0.001) from the treeline to the mountain summit. Multivariate analyses revealed that CO2 fluxes were controlled by C-acquiring enzymatic activities which were mainly controlled by air mean annual temperature (MAT) and SOM quantity and composition. CH4 fluxes were characterized by uptake of atmospheric CH4, but no trend was observed along the elevation. N2O fluxes were also dominated by uptake of atmospheric N2O. The flux rates remained stable with increasing elevation below the treeline, but decreased significantly (P<0.001) from the treeline to the summit. N2O fluxes were driven by specific nitrifying and denitrifying microbial genes (ammonia-oxidizing amoA and N2O-producing norB), which were again controlled by SOM quantity and composition. Our study indicates the treeline as a demarcation point changing the patterns of CO2 and N2O fluxes along the elevation, highlighting the importance of SOM quantity and composition in controlling microbial enzyme activities and GHG fluxes.

中文翻译：

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土壤有机质特性沿海拔梯度驱动微生物酶活性和温室气体通量


山地生态系统对全球碳 （C） 和氮 （N） 生物地球化学循环有重大贡献，受到全球变化的严重影响。尽管不同海拔的土壤呼吸和微生物活动已被广泛研究，但对不同海拔土壤中环境驱动因素、微生物功能和温室气体通量（温室气体、二氧化碳 [CO2]、甲烷 [CH4] 和一氧化二氮 [N2O]）之间的关系知之甚少。在这里，我们测量了原位温室气体通量如何与瑞士 ∼2400 m 海拔梯度的天然土壤中的土壤特性、土壤有机质 （SOM） 数量和组成（腐殖质与蛋白质样 OM 的比例）、微生物生物量、酶活性和功能基因丰度相关联。土壤 CO2 通量在低海拔 （低地区） 到高海拔 （山地和亚高山区） 森林之间没有显著变化，但从林线到山顶显著下降 （P<0.001）。多因素分析显示，CO2 通量受 C 获取酶活性控制，主要受空气平均年温度 （MAT） 和 SOM 数量和组成控制。CH4 通量的特征是吸收大气中的 CH4，但沿海拔没有观察到趋势。N2O 通量也以大气中 N2O 的吸收为主。随着林线以下海拔的增加，磁通率保持稳定，但从林线到山顶的磁通速率显著降低 （P<0.001）。N2O 通量由特定的硝化和反硝化微生物基因 （氨氧化 amoA 和产生 N2O 的 norB） 驱动，这些基因再次受到 SOM 数量和组成的控制。 我们的研究表明，林线作为分界点改变了沿海拔的 CO2 和 N2O 通量模式，强调了 SOM 数量和组成在控制微生物酶活性和 GHG 通量方面的重要性。