Nitrogen (N) is a crucial nutrient for the growth and activity of rhizosphere microorganisms, particularly during drought conditions. Plant root-secreted mucilage contains N that could potentially nourish rhizosphere microbial communities. However, there remains a significant gap in understanding mucilage N content, its source, and its utilization by microorganisms under drought stress. In this study, we investigated the impact of four maize varieties (DH02 and DH04 from Kenya, and Kentos and Keops from Germany) on the secretion rates of mucilage from aerial roots and explored the origin of mucilage N supporting microbial life in the rhizosphere. We found that DH02 exhibited a 96% higher mucilage secretion rate compared to Kentos, while Keops showed 114% and 89% higher secretion rates compared to Kentos and DH04, respectively. On average, the four maize varieties released 4 μg N per root tip per day, representing 2% of total mucilage secretion. Notably, the natural abundance of ¹⁵N isotopes increased (higher δ¹⁵N signature) with mucilage N release. This indicates a potential dilution of the isotopic signal from biological fixation of atmospheric N by mucilage-inhabiting bacteria as mucilage secretion rates increase. We proposed a model linking mucilage secretion to a mixture of isotopic signatures and estimated that biological N fixation may contribute to 45 - 75% of mucilage N per root tip. The N content of mucilage from a single maize root tip can support a bacterial population ranging from 10⁷ to 10¹⁰ cells per day. In conclusion, mucilage serves as a significant N-rich resource for microbial communities in the rhizosphere during drought conditions.

氮 (N) 是根际微生物生长和活动的重要营养物质，特别是在干旱条件下。植物根部分泌的粘液含有可能滋养根际微生物群落的氮。然而，对于粘液氮含量、其来源以及干旱胁迫下微生物对其的利用仍存在很大的了解。在本研究中，我们研究了四种玉米品种（肯尼亚的 DH02 和 DH04，以及德国的 Kentos 和 Keops）对气生根粘液分泌率的影响，并探讨了支持根际微生物生命的粘液氮的起源。我们发现，与 Kentos 相比，DH02 的粘液分泌率高出 96%，而与 Kentos 和 DH04 相比，Keops 的分泌率分别高出 114% 和 89%。平均而言，这四个玉米品种每个根尖每天释放 4 微克氮，占粘液分泌总量的 2%。值得注意的是， ¹⁵ N 同位素的自然丰度随着粘液氮的释放而增加（更高的 δ ¹⁵ N 特征）。这表明，随着粘液分泌率的增加，粘液栖息细菌对大气氮的生物固定所产生的同位素信号可能会被稀释。我们提出了一个将粘液分泌与同位素特征混合物联系起来的模型，并估计生物固氮可能贡献每个根尖 45 - 75% 的粘液氮。来自单个玉米根尖的粘液的氮含量可以支持每天10 ⁷至 10 ¹⁰个细胞的细菌种群。总之，在干旱条件下，粘液是根际微生物群落的重要富氮资源。