Effects of N rhizodeposition on rhizosphere N transformation in clonal ramets of Moso bamboo forest

N rhizodeposition plays a vital role in regulating rhizosphere soil N dynamics. However, its effects on the rhizosphere soil N cycle in clonal plants and the underlying mechanism remain unclear.

¹⁵N solutions with different concentrations were injected into young or connected mature ramets of Moso bamboo (Phyllostachys edulis), respectively, in the field, to explore the response of rhizosphere N transformation to N rhizodeposition.

¹⁵N injection increased the ¹⁵N abundance in the rhizosphere soil of both young and mature ramets, with higher ¹⁵N abundance in 20–40-cm layer than that in 0–20-cm layer. Functional genes involved in nitrification and denitrification in the rhizosphere were upregulated when young ramets received low- and medium-N solutions. However, the genes showed diverse responses to high-N treatment in young ramets, with increased abundances of ammonia-oxidizing bacteria and decreased levels of ammonia-oxidizing archaea, comammox, and denitrifiers. In contrast, the functional genes involved in denitrification in the 20–40-cm layer of rhizosphere soil were upregulated by high-N treatment in mature ramets. Additionally, partial-least-squares path modeling revealed ¹⁵N abundance in the soil indirectly affected N mineralization, N mineralization directly affected nitrification, and nitrification directly affected denitrification in a positive manner.

The variations of N rhizodeposition and transformation process in both connected ramets is highly consistent in responding to different N treatments, but the nitrifiers and denitrifiers in the deeper rhizosphere soil were more sensitive to N rhizodeposits than those in the upper rhizosphere soil.