Decreased soil pH weakens the positive rhizosphere effect on denitrification capacity

• Published in: Pedosphere 2024-10, Vol.34 (5), p.905-915
• Main Authors: WANG, Jun, ZHANG, Zongxiang, LIANG, Fei, CHE, Zhao, WEN, Yongkang, ZHANG, Manyu, JIN, Wenjun, DONG, Zhaorong, SONG, He
• Format: Article
• Language: English
• Subjects: bacterial abundance; denitrifier community; dissolved organic carbon; operational taxonomic unit; soil acidification
• ISSN: 1002-0160
• DOI: 10.1016/j.pedsph.2023.07.011

The stimulating effect of rhizosphere on denitrification is considered to be an unavoidable loss of soil nitrogen (N) and detrimental to crop N use efficiency, which is regulated by crop growth and soil properties. Soil acidification, occurring rapidly in many intensive farming lands, affects both crop growth and soil properties, thereby altering rhizosphere effect on denitrification. However, the mechanism by which soil acidification regulates rhizosphere denitrification still remains unclear. Here, we determined the denitrification capacity (DC) and associated community compositions of nirK- and nirS-type denitrifiers in maize rhizosphere and bulk soils at four acidity gradients (pH = 6.8, 6.1, 5.2, and 4.2). Results showed that the stimulating effect of rhizosphere on DC strongly depended on soil pH. Compared to bulk soil, rhizosphere soil had significantly higher DC at pH ≥ 5.2, but not at pH of 4.2. With increasing soil acidity, the stimulation of rhizosphere on DC (calculated as the difference in DC between rhizosphere and bulk soils) decreased from 8.01 to 0.01 mg N kg-1 d-1. Moreover, soil acidification significantly reduced the differences in dissolved organic carbon (DOC) and abundance of key nirK-type denitrifier taxa between rhizosphere and bulk soils, both of which were positively related to the stimulation of rhizosphere on DC. These findings demonstrated that soil acidification could weaken the positive rhizosphere effect on denitrification via regulated C availability and associated nirK-type denitrifier community, potentially reducing N loss risk in rhizosphere soil. The independent role of soil pH should be fully considered when modelling N behaviour in plant-soil systems.