Terrestrial organic matter (OM) is an essential energy source that fuels many food webs. The factors contributing to OM decomposition and the rate at which OM decomposes can influence carbon fluxes through ecosystems. Previous research demonstrates that the factors driving OM decomposition can vary with environmental condition, prompting more research that characterizes the relative importance of each factor driving OM decomposition under differing environmental conditions. This is especially important for ecosystems that may be particularly vulnerable to climate change, like temperate, montane ecosystems. We used a 126-day leaf-pack study to compare and identify the most important factors (i.e., physical abrasion, microbial activity, and shredding macroinvertebrates) regulating OM decomposition rates ( k ) in two montane rivers. We used a structural equation model (SEM) to evaluate the relative importance of each factor contributing to OM decomposition. We found that k were significantly faster in the Blacksmith Fork. But when temperature differences were accounted for, k were approximately 1.5 times faster in the Logan River. Macroinvertebrate abundance and biomass, physical abrasion, nutrients, and temperature were significantly greater in the Blacksmith Fork, while microbial activity was the only factor significantly greater in the Logan River. We estimated that by day 100, microbes contributed 2.1 times more to decomposition in the Logan River (0.88 g; 14.6%) compared to the Blacksmith Fork (0.41 g; 6.9%). Relative to shredders (0.39 g; 6.5%), microbial contributions were approximately 2.2 times greater in the Logan River by day 100. Our SEM also revealed that microbes were more important to decomposition in this system relative to shredding macroinvertebrates. The reversal of k when day was replaced with degree-day and the significant direct effect of degree-days in our SEM suggests that temperature is a key factor regulating OM decomposition in these montane rivers. These findings contrast with many other studies conducted in montane systems, showing that microbes are less important contributors to OM decomposition at higher elevations, and further demonstrate that the relative importance of the factors driving OM decomposition is highly context dependent, even across small geographic scales.

中文翻译：

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在犹他州西部山间河流中，导致叶子分解的因素随温度变化

陆地有机物 (OM) 是一种必不可少的能源，可为许多食物网提供燃料。促成有机质分解的因素和有机质分解的速率会影响通过生态系统的碳通量。先前的研究表明，驱动 OM 分解的因素会随着环境条件而变化，这促使更多的研究表征在不同环境条件下驱动 OM 分解的每个因素的相对重要性。这对于可能特别容易受到气候变化影响的生态系统尤其重要，例如温带、山地生态系统。我们使用了一项为期 126 天的叶包研究来比较和确定调节两条山地河流中 OM 分解率 (k) 的最重要因素（即物理磨损、微生物活动和大型无脊椎动物的切碎）。我们使用结构方程模型 (SEM) 来评估有助于 OM 分解的每个因素的相对重要性。我们发现在 Blacksmith Fork 中 k 明显更快。但是当考虑到温差时，洛根河中的 k 大约快 1.5 倍。铁匠叉的大型无脊椎动物丰度和生物量、物理磨损、营养和温度显着更高，而微生物活动是洛根河中显着更高的唯一因素。我们估计，到第 100 天，微生物对洛根河分解的贡献（0.88 克；14.6%）是铁匠叉（0.41 克；6.9%）的 2.1 倍。相对于粉碎机（0.39 克；6.5%），到第 100 天，洛根河中的微生物贡献大约高出 2.2 倍。我们的 SEM 还显示，相对于切碎大型无脊椎动物，微生物对于该系统中的分解更为重要。当日被度日取代时 k 的逆转以及我们SEM中度日的显着直接影响表明温度是调节这些山地河流中OM分解的关键因素。这些发现与在山地系统中进行的许多其他研究形成对比，表明微生物在较高海拔处对 OM 分解的贡献不太重要，并进一步证明驱动 OM 分解的因素的相对重要性高度依赖于环境，即使在小地理尺度上也是如此。当日被度日取代时 k 的逆转以及我们SEM中度日的显着直接影响表明温度是调节这些山地河流中OM分解的关键因素。这些发现与在山地系统中进行的许多其他研究形成对比，表明微生物在较高海拔处对 OM 分解的贡献较小，并进一步证明驱动 OM 分解的因素的相对重要性高度依赖于环境，即使在小地理范围内也是如此。当日被度日取代时 k 的逆转以及我们SEM中度日的显着直接影响表明温度是调节这些山地河流中OM分解的关键因素。这些发现与在山地系统中进行的许多其他研究形成对比，表明微生物在较高海拔处对 OM 分解的贡献较小，并进一步证明驱动 OM 分解的因素的相对重要性高度依赖于环境，即使在小地理范围内也是如此。