Soil microorganisms help transform plant inputs into mineral-associated soil organic carbon (SOC) – the largest and slowest-cycling pool of organic carbon on land. However, the microbial traits that influence this process are widely debated. While current theory and biogeochemical models have settled on carbon-use efficiency (CUE) and growth rate as positive predictors of mineral-associated SOC, empirical tests are sparse, with contradictory observations. Using C-labeling of an annual grass () under two moisture regimes, we found that microbial traits associated with formation of C-mineral-associated SOC varied by soil habitat, as did active microbial taxa and SOC chemical composition. In the rhizosphere, bacterial-dominated communities with fast growth, high biomass, and high extracellular polymeric substance (EPS) production were positively associated with C-mineral-associated SOC. In contrast, the detritusphere held communities dominated by fungi and more filamentous bacteria, and with greater exoenzyme activity; there, C-mineral-associated SOC was associated with slower microbial growth and lower microbial biomass. CUE was a negative predictor of C-mineral-associated SOC in both habitats. Using C-quantitative stable isotope probing, we found that the majority of C assimilation in the rhizosphere and detritusphere at week 12 of the experiment was performed by very few bacterial and fungal taxa (3–5% of the total taxa that assimilated C). Several complementary chemical analyses (C-NMR, FTICR-MS, and STXM-NEXAFS) suggested that SOC in the rhizosphere had a more oxidized chemical signature, while SOC in the detritusphere had a less oxidized, more lignin-like chemical signature. Our findings challenge current theory by demonstrating that microbial traits linked with mineral-associated SOC are not universal, but vary with soil habitat and moisture conditions, and are shaped by a small number of active taxa. Emerging SOC models that explicitly reflect these interactions may better predict SOC storage, since climate change causes shifts in soil moisture regimes and the ratio of living versus decaying roots.

中文翻译：

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从根系输入到与矿物质相关的土壤碳的路径由栖息地特定的微生物特征和土壤湿度决定

土壤微生物有助于将植物输入转化为与矿物质相关的土壤有机碳（SOC）——陆地上最大且循环最慢的有机碳库。然而，影响这一过程的微生物特征存在广泛争议。虽然当前的理论和生物地球化学模型已将碳利用效率（CUE）和增长率确定为与矿物相关的 SOC 的积极预测因子，但实证测试很少，且观察结果相互矛盾。在两种湿度条件下对一年生草进行 C 标记，我们发现与 C 矿物相关 SOC 形成相关的微生物特征因土壤栖息地而异，活性微生物类群和 SOC 化学成分也是如此。在根际，以细菌为主的群落具有快速生长、高生物量和高细胞外聚合物（EPS）产量，与碳矿物质相关的 SOC 呈正相关。相比之下，碎屑圈中的群落以真菌和更多的丝状细菌为主，并且具有更强的外酶活性。在那里，C-矿物质相关的 SOC 与微生物生长较慢和微生物生物量较低有关。 CUE 是两个栖息地中与 C 矿物相关的 SOC 的负预测因子。使用 C 定量稳定同位素探测，我们发现实验第 12 周根际和碎屑圈中的大部分 C 同化是由极少数细菌和真菌类群（占同化 C 的总类群的 3-5%）进行的。几种补充化学分析（13C-NMR、FTICR-MS 和 STXM-NEXAFS）表明，根际中的 SOC 具有更多氧化的化学特征，而碎屑圈中的 SOC 具有氧化程度较低、更类似于木质素的化学特征。我们的研究结果挑战了当前的理论，证明与矿物相关的 SOC 相关的微生物特征并不普遍，而是随土壤栖息地和湿度条件而变化，并且由少数活跃类群决定。明确反映这些相互作用的新兴 SOC 模型可能会更好地预测 SOC 存储，因为气候变化会导致土壤湿度状况以及活根与腐烂根的比率发生变化。