Plant growth affects soil moisture, mineral N and organic C availability in soil, all of which influence denitrification. With increasing plant growth, root exudation may stimulate denitrification, while N uptake restricts nitrate availability. We conducted a double labeling pot experiment with either maize (Zea mays L.) or cup plant (Silphium perfoliatum L.) of the same age but differing in size of their shoot and root systems. The 15N gas flux method was applied to directly quantify N2O and N2 fluxes in situ. To link denitrification with available C in the rhizosphere, 13CO2 pulse labeling was used to trace C translocation from shoots to roots and its release by roots into the soil. Plant water and N uptake were the main factors controlling daily N2O + N2 fluxes, cumulative N emissions, and N2O production pathways. Accordingly, pool-derived N2O + N2 emissions were 30–40 times higher in the treatment with highest soil NO3− content and highest soil moisture. CO2 efflux from soil was positively correlated with root dry matter, but we could not detect any relationship between root-derived C and N2O + N2 emissions. Root-derived C may stimulate denitrification under small plants, while N and water uptake become the controlling factors with increasing plant and root growth.

中文翻译：

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硝酸盐吸收和碳渗出——植物根部是刺激还是抑制反硝化作用？

植物生长影响土壤水分、土壤中矿物质氮和有机碳的有效性，所有这些都会影响反硝化作用。随着植物生长的增加，根系分泌物可能会刺激反硝化作用，而 N 吸收会限制硝酸盐的可用性。我们对相同年龄但地上部和根系大小不同的玉米 (Zea mays L.) 或杯形植物 (Silphium perfoliatum L.) 进行了双重标记盆栽试验。应用 15N 气体通量方法直接定量原位 N2O 和 N2 通量。为了将反硝化作用与根际中的有效碳联系起来，使用 13CO2 脉冲标记来追踪碳从芽到根的易位及其通过根释放到土壤中的过程。植物水分和氮吸收是控制每日 N2O + N2 通量、累积 N 排放和 N2O 生产途径的主要因素。因此，在具有最高土壤 NO3− 含量和最高土壤水分的处理中，池源 N2O + N2 排放量高出 30-40 倍。从土壤中流出的 CO2 与根干物质呈正相关，但我们无法检测到根源 C 与 N2O + N2 排放之间的任何关系。根源性C可能会刺激小植物下的反硝化作用，而N和吸水成为植物和根系生长增加的控制因素。