<b>Microbial life history strategies explain dissolved organic matter response to warming</b>

Soil dissolved organic carbon (DOC) and dissolved organic nitrogen (DON), as the main component of dissolved organic matter (DOM), play pivotal roles in regulating soil carbon and nitrogen cycles and environmental effect. Warming alter microbial life history strategies, but the extent to whether these changes account for the effects of warming on DOC and DON remains unclear. To explore the effect variation, this study reviewed updated datasets with 321 individual DOC and 187 DON independent experiments globally combined with soil microbial properties. Our results indicated that while warming does not significantly affect DOC concentrations, it led to a notable increase in DON (8.84%), consequently reducing the DOC/DON by 10.79%. Soil moisture emerged as the most influential factor (19.0%) driving DOC responses to warming, whereas soil nitrate nitrogen was the primary driver (33.2%) of DON responses to warming. Under conditions of warming-induced carbon or/and water limitation and environmental stress, microbial tend to shift their life history strategies from a focus on Y (yield) to prioritizing resource acquisition (A) or stress tolerance (S), manifesting by increased soil enzyme activity. The increased DON is a result of microbes intensifying their consumption of carbon to maintain stability under stress, which in turn reduces soil organic carbon (-3.2%) and increases CO₂ emissions (48.8%). The reduced DOC/DON ratio under warming had implications for nitrogen cycling. Specifically, soil ammonium nitrogen exhibited a positive linear relationship with the DOC/DON ratio, while soil nitrate nitrogen responded negatively as the DOC/DON ratio increased. This studies highlights the sensitivity and adaptability of soil carbon and nitrogen cycles to warming due to microbial shift from Y- toward A- or S-strategies.土壤溶解性有机碳（dissolved organic carbon, DOC）与溶解性有机氮（dissolved organic nitrogen, DON）作为溶解性有机质（dissolved organic matter, DOM）的核心组分，在调控土壤碳氮循环与环境效应方面发挥着关键作用。气候变暖可改变微生物的生活史策略，但此类变化在多大程度上能够解释变暖对DOC与DON的影响，目前仍不明确。为探究该效应的变异规律，本研究整合了全球范围内321项独立DOC实验与187项独立DON实验的最新数据集，并结合土壤微生物属性展开分析。研究结果显示：尽管变暖对DOC浓度无显著影响，但可使DON含量显著提升8.84%，进而导致DOC/DON比值降低10.79%。土壤含水量是驱动DOC对变暖响应的最关键因素（解释度达19.0%），而土壤硝态氮则是调控DON对变暖响应的首要驱动因子（解释度为33.2%）。在变暖诱导的碳或/和水分限制以及环境胁迫条件下，微生物倾向于将其生活史策略从以产量（Y）为核心，转向优先获取资源（A）或耐受胁迫（S），具体表现为土壤酶活性升高。DON含量的提升源于微生物为维持胁迫下的生存稳态而增强了碳消耗，这一过程进而导致土壤有机碳减少3.2%，并使二氧化碳（CO₂）排放量增加48.8%。变暖下DOC/DON比值的降低对氮循环具有重要意义。具体而言，土壤铵态氮与DOC/DON比值呈正线性相关，而土壤硝态氮则随DOC/DON比值升高呈现负向响应。本研究揭示了土壤碳氮循环对变暖的敏感性与适应性，其核心机制为微生物从Y策略向A或S策略的转变。