Abstract Plant competition can impose species-specific effects on the dynamics of soil carbon (C) and nitrogen (N) through rhizosphere processes and litter input. Therefore, it is crucial to quantify these effects in various terrestrial ecosystems for a better understanding of the mechanisms. Here, we collected subsoils containing low N from a subtropical forest and planted eight dominant tree species (two deciduous and six evergreens) in these soils in a greenhouse to explore the effects of interspecific plant competition on plant growth, soil C and N contents, and soil C and N mineralization rates after the plants had grown for 12 months. Soil labile organic C and N contents were represented by soil extractable organic C (EOC) and extractable organic N (EON) contents. We assessed the magnitude of the interspecific plant competition via the relative interaction intensity (RII) index, which was calculated from the biomass of seedlings in the mixed treatments compared with the single treatments. Our results showed that interspecific plant competition had species-specific effects on plant biomass and soil total C and N contents as well as soil C mineralization rates, whereas it tended to decrease soil N mineralization rates. However, interspecific plant competition significantly decreased plant C and N contents, and significantly increased soil EOC and EON contents with increasing RII. After classifying the communities into two functional types (i.e., deciduous–evergreen versus evergreen–evergreen), similar relationships were observed. These findings address the importance of quantifying interspecific plant competition on soil labile organic C and N contents, which is helpful for understanding soil C and N cycling in forest ecosystems.

中文翻译：

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种间植物竞争增加土壤不稳定有机碳和氮含量

摘要 植物竞争可以通过根际过程和凋落物输入对土壤碳 (C) 和氮 (N) 的动态施加物种特异性影响。因此，量化各种陆地生态系统中的这些影响对于更好地理解这些机制至关重要。在这里，我们从亚热带森林中收集了含低 N 的底土，并在温室中在这些土壤中种植了 8 种优势树种（两种落叶和 6 种常绿植物），以探索种间植物竞争对植物生长、土壤 C 和 N 含量的影响，以及植物生长 12 个月后土壤 C 和 N 矿化率。土壤不稳定有机碳和氮含量以土壤可萃取有机碳（EOC）和可萃取有机氮（EON）含量表示。我们通过相对相互作用强度 (RII) 指数评估了种间植物竞争的程度，该指数是根据混合处理与单一处理相比幼苗的生物量计算得出的。我们的结果表明，种间植物竞争对植物生物量和土壤总碳和氮含量以及土壤碳矿化率具有物种特异性影响，而它往往会降低土壤氮矿化率。然而，种间植物竞争显着降低了植物 C 和 N 的含量，并随着 RII 的增加显着增加了土壤 EOC 和 EON 的含量。将群落分为两种功能类型（即落叶-常绿与常绿-常绿）后，观察到类似的关系。