Fluorescence spectroscopy is a common tool to assess optical dissolved organic matter (DOM) and a number of characteristics, including DOM biodegradability, have been inferred from these analyses. However, recent findings on soil and DOM dynamics emphasize the importance of ecosystem-scale factors, such as physical separation of substrate from soil microbial communities and soil physiochemical cycles driving DOM stability. We apply this principle to soil derived DOM and hypothesize that optical properties can only supply information on biodegradability when evaluated in the larger ecosystem because substrate composition and the activity/abundance of the microbial community ultimately drive DOM degradation. To evaluate biodegradability in this context, we assessed aqueous soil extracts for water extractable organic carbon (WEOC) content, biodegradability, microbial biomass and DOM characteristics using fluorescence spectroscopy across a range of environmental conditions (covariant with season and land use) in northern Vermont, USA. Our results indicate that changes in environmental conditions affect composition, quantity, and biodegradability of DOM. WEOC concentrations were highest in the fall and lowest in the summer, while no significant differences were found between land covers; however, DOM biodegradability was significantly higher in the agricultural site across seasons. Despite a shift in utilized substrate from less aromatic DOM in summer to more aromatic DOM in winter, biodegradability was similar for all seasons. The only exception was cold temperature incubations where microbial activity was depressed, and processing was slowed. These results provide examples on how fluorescence based metrics can be combined with context relevant environmental parameters to evaluate bioavailability in the context of the larger ecosystem.

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测量环境条件对溶解有机物生物降解性和光学特性的影响：结合现场和实验室研究

荧光光谱是评估光学溶解有机物 (DOM) 的常用工具，并且从这些分析中推断出许多特性，包括 DOM 的生物降解性。然而，最近关于土壤和 DOM 动态的发现强调了生态系统尺度因素的重要性，例如基质与土壤微生物群落的物理分离以及驱动 DOM 稳定性的土壤理化循环。我们将此原理应用于土壤衍生的 DOM，并假设光学特性只能在更大的生态系统中评估时提供有关生物降解性的信息，因为底物组成和微生物群落的活动/丰度最终会驱动 DOM 降解。为了评估在这种情况下的生物降解性，我们评估了含水土壤提取物的水可提取有机碳 (WEOC) 含量，在美国佛蒙特州北部的一系列环境条件（与季节和土地利用协变）中使用荧光光谱法分析生物降解性、微生物生物量和 DOM 特征。我们的结果表明，环境条件的变化会影响 DOM 的组成、数量和生物降解性。WEOC浓度在秋季最高，夏季最低，土地覆盖之间没有显着差异；然而，跨季节农业场地的 DOM 生物降解性显着更高。尽管利用的底物从夏季芳香度较低的 DOM 转变为冬季芳香度较高的 DOM，但所有季节的生物降解性都相似。唯一的例外是低温孵化，微生物活动受到抑制，加工速度减慢。