Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Skogsmarksgränd 17, 90183 Umeå, Sweden; Global Change Research Institute of the Czech Academy of Sciences, Bělidla 986/4a, 603 00 Brno, Czech Republic.
Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Skogsmarksgränd 17, 90183 Umeå, Sweden.
Sci Total Environ. 2024 Dec 1;954:176243. doi: 10.1016/j.scitotenv.2024.176243. Epub 2024 Sep 13.
Tree stems exchange greenhouse gases with the atmosphere but the magnitude, variability and drivers of these fluxes remain poorly understood. Here, we report stem fluxes of carbon dioxide (CO), methane (CH) and nitrous oxide (NO) in a boreal riparian forest, and investigate their spatiotemporal variability and ecosystem level importance. For two years, we measured CO and CH fluxes on a monthly basis in 14 spruces (Picea abies) and 14 birches (Betula pendula) growing near a headwater stream affected by historic ditching. We also measured NO fluxes on three occasions. All tree stems were net emitters of CO and CH, while NO fluxes were around zero. CO fluxes correlated strongly with air temperature and peaked in summer. CH fluxes correlated modestly with air temperature and solar radiation and peaked in late winter and summer. Trees with larger stem diameter emitted more CO and less CH and trees closer to the stream emitted more CO and CH. The CO and CH fluxes did not differ between spruce and birch, but correlations of CO fluxes with stem diameter and distance to stream differed between the tree species. The absence of vertical trends in CO and CH fluxes along the stems and their low correlation with groundwater levels and soil CO and CH partial pressures suggest tree internal production as the primary source of stem emissions. At the ecosystem level, the stem CO, CH and NO emissions represented 52 ± 16 % of the forest floor CO emissions and 3 ± 1 % and 11 ± 40 % of the forest floor CH and NO uptake, respectively, during the snow-free period (median ± SE). The six month snow-cover period contributed 11 ± 45 % and 40 ± 29 % to annual stem CO and CH emissions, respectively. Overall, the stem gas fluxes were more typical for upland rather than wetland ecosystems likely due to historic ditching and subsequent groundwater level decrease.
树木茎干与大气交换温室气体，但这些通量的幅度、可变性和驱动因素仍知之甚少。在这里，我们报告了北方河岸林的二氧化碳 (CO)、甲烷 (CH) 和氧化亚氮 (NO) 的茎干通量，并研究了它们的时空变异性和生态系统水平的重要性。在两年的时间里，我们每月在受历史沟渠影响的一条溪流附近生长的 14 棵云杉 (Picea abies) 和 14 棵桦树 (Betula pendula) 上测量 CO 和 CH 通量。我们还进行了三次 NO 通量测量。所有树木茎干都是 CO 和 CH 的净排放源，而 NO 通量接近零。CO 通量与空气温度强烈相关，在夏季达到峰值。CH 通量与空气温度和太阳辐射适度相关，在冬季末和夏季达到峰值。茎干直径较大的树木排放更多的 CO 和较少的 CH，而靠近溪流的树木排放更多的 CO 和 CH。云杉和桦木的 CO 和 CH 通量没有差异，但 CO 通量与茎干直径和与溪流距离的相关性在树种之间有所不同。CO 和 CH 通量沿茎干没有垂直趋势，并且与地下水位以及土壤 CO 和 CH 分压的相关性较低，这表明树木内部的生产是茎干排放的主要来源。在生态系统水平上，在无雪期（中位数 ± SE），茎干 CO、CH 和 NO 排放分别占林地步 CO 排放的 52 ± 16%，占林地步 CH 和 NO 吸收的 3 ± 1%和 11 ± 40%。六个月的积雪期分别贡献了年度茎干 CO 和 CH 排放的 11 ± 45%和 40 ± 29%。总的来说，由于历史沟渠和随后的地下水位下降，茎干气体通量更典型的是旱地而不是湿地生态系统。
