Soil freeze-thaw cycles (FTCs) profoundly influence biophysical conditions and modify biogeochemical processes across many northern-hemisphere and alpine ecosystems. How FTCs will contribute to global processes in seasonally snow-covered ecosystems in the future is of particular importance as climate change progresses and winter snowpacks decline. Our understanding of these contributions is limited because there has been little consideration of inter- and intrayear variability in the characteristics of FTCs, in part due to a limited appreciation for which of these characteristics matters most with respect to a given biogeochemical process. Here, we introduce the concept of effective FTCs: those that are most likely linked to changes in key soil processes. We also propose a set of parameters to quantify and characterize effective FTCs using standard field soil temperature data. To put these proposed parameters into effective practice, we present FTCQuant, an R package of functions that quantifies FTCs based on a set of user-defined parameter criteria and, importantly, summarizes the individual characteristics of each FTC counted. To demonstrate the utility of these new concepts and tools, we applied the FTCQuant package to re-analyze data from two published studies to help explain over-winter changes to N2 O emissions and wet-aggregate stability. We found that effective FTCs would be defined differently for each of these response variables and that effective FTCs provided a 76 and 33% increase in model fit for wet-aggregate stability and cumulative N2 O emission, respectively, relative to conventional FTC quantification methods focusing on fluctuations around 0 °C. These results demonstrate the importance of identifying effective FTCs when scaling soil processes to regional or global levels. We hope our contributions will inform future deductions, hypothesis generation, and experimentation with respect to expected changes in freeze-thaw cycling globally.

中文翻译：

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有效冻融循环作为生态系统变化驱动因素的新确定

土壤冻融循环 (FTC) 深刻影响了许多北半球和高山生态系统的生物物理条件并改变了生物地球化学过程。随着气候变化的进展和冬季积雪的减少，未来 FTC 将如何为季节性积雪覆盖的生态系统的全球进程做出贡献尤为重要。我们对这些贡献的理解是有限的，因为很少考虑 FTC 特征的年际和年内变化，部分原因是对这些特征中哪些对给定的生物地球化学过程最重要的认识有限。在这里，我们引入了有效 FTC 的概念：最有可能与关键土壤过程变化相关的那些。我们还提出了一组参数，以使用标准的现场土壤温度数据量化和表征有效的 FTC。为了将这些提议的参数付诸有效实践，我们提出了 FTCQuant，这是一个 R 函数包，它根据一组用户定义的参数标准量化 FTC，并且重要的是，总结了所计数的每个 FTC 的个体特征。为了证明这些新概念和工具的实用性，我们应用 FTCQuant 包重新分析了来自两项已发表研究的数据，以帮助解释 N2 O 排放和湿集料稳定性的越冬变化。我们发现，对于这些响应变量中的每一个，有效 FTC 的定义不同，并且有效 FTC 分别使湿集料稳定性和累积 N2 O 排放的模型拟合增加了 76% 和 33%，相对于关注 0 °C 左右波动的传统 FTC 量化方法。这些结果证明了在将土壤过程扩展到区域或全球水平时确定有效 FTC 的重要性。我们希望我们的贡献能够为未来关于全球冻融循环的预期变化的推论、假设生成和实验提供信息。