Low-molecular-weight organic carbon (LMWOC) from root exudate influences soil organic carbon cycling via priming of microbial activity. However, the mechanisms underlying the uptake and utilization of specific exudates by microorganisms in soils remain unclear. To address this gap in knowledge, a one-month C (0.1 mg C﹒g soil) tracer incubation study was conducted to investigate the fate of the most abundant root exudate groups (using C-labeled glucose, acetic acid, and oxalic acid) in paddy vs. upland soil. After 2 days of incubation, the microbial substrate use efficiency (SUE) was >80% in paddy soil, which was approximately 1.9, 2.9, and 1.3 times that in uplands with glucose, acetic acid, and oxalic acid addition, respectively. The SUE in paddy soil with glucose or acetic acid addition was always higher than that in uplands over time ( < 0.05). In both soils, the SUE of glucose was 1–4 times that of carboxylic acids ( < 0.05). The recovery of C-labeled total phospholipid fatty acids (PLFAs) in paddy soils was 1.5–2 times that in uplands ( < 0.05). In both soils, bacteria preferred to utilize glucose and acetic acid to synthesize cellular components. Throughout the incubation period, bacteria dominated over fungi in terms of LMWOC consumption. Gram-positive and -negative bacteria were dominant in upland and paddy soils, respectively. From days 11–30, the contribution of fungi and actinomycetes to LMWOC utilization began to appear. Temperature positively regulated C distribution in microbial groups ( < 0.05), and increased dissolved organic carbon in upland soil accelerated microbial SUE. The results of this study clarify microbial effects on the high soil carbon sequestration capacity of paddy soil as compared with upland in subtropical areas.

中文翻译：

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水稻与旱地土壤中低分子量有机物的命运：微生物生物标志物方法

根系分泌物中的低分子量有机碳（LMWOC）通过启动微生物活动影响土壤有机碳循环。然而，土壤中微生物吸收和利用特定渗出物的机制仍不清楚。为了解决这一知识差距，进行了为期一个月的 C（0.1 mg C﹒g 土壤）示踪剂孵育研究，以调查最丰富的根系分泌物组的命运（使用 C 标记的葡萄糖、乙酸和草酸）在水稻与旱地土壤中。培养2天后，水稻土的微生物底物利用效率（SUE）>80%，分别约为添加葡萄糖、乙酸和草酸的旱地的1.9、2.9和1.3倍。随着时间的推移，添加葡萄糖或乙酸的稻田土壤的 SUE 始终高于旱地土壤的 SUE（< 0.05）。在两种土壤中，葡萄糖的 SUE 是羧酸的 1-4 倍 (< 0.05)。水稻土中C标记总磷脂脂肪酸(PLFA)的回收率是旱地的1.5-2倍(<0.05)。在这两种土壤中，细菌更喜欢利用葡萄糖和乙酸来合成细胞成分。在整个培养期间，就LMWOC消耗而言，细菌优于真菌。旱地和水稻土中革兰氏阳性菌和阴性菌分别占优势。从第 11 天到第 30 天，真菌和放线菌对 LMWOC 利用率的贡献开始显现。温度正向调节微生物群体中的碳分布（<0.05），而旱地土壤中溶解有机碳的增加加速了微生物的SUE。本研究的结果阐明了微生物对亚热带地区水稻土与旱地高土壤固碳能力的影响。