Nitrogen-salt interaction in Pennisetum giganteum: Effects on soil, rhizosphere, and ion transport processes

Abstract

The continuous expansion of soil salinization poses challenges to agricultural development. Nitrogen (N), the most commonly used fertilizer, helps alleviate salt stress either at appropriate concentrations or through N assimilation. Fertilization management is crucial for plant survival and saline soil quality. Although the individual effects of N and salt have been widely studied, their combined impact on Pennisetum giganteum (P. giganteum) remains insufficiently explored. In this study, laboratory and field experiments were combined to investigate changes in soil N transformation, salt ion transport in P. giganteum, and the effects of N-salt interaction on the rhizosphere microbial community (RMC). The results indicated that N-salt interaction increased P. giganteum height and yield by 50.80 % and 67.23 %, respectively. The structural equation model indicated that N uptake had the most significant effect on yield (path coefficient = 0.963), with NO₃⁻-N positively affecting N uptake. NO₃⁻-N was more strongly correlated with height and yield than NH₄⁺-N. 16S sequencing, principal coordinate analysis, and redundancy analysis revealed that denitrifying genera (e.g., Dechloromonas) decreased significantly under high-level N-salt interaction, while nitrification-related genera (e.g., Nitrospira) increased, thereby generating more NO₃⁻-N to promote P. giganteum growth. Soil electrical conductivity was the key factor affecting the RMC at the tillering stage. Additionally, P. giganteum may adapt to different salinity levels through distinct salt tolerance mechanisms. This study confirmed that N alleviates salt stress, and revealed the mechanisms of N transformation in the rhizosphere microenvironment and the transport of salt ions in P. giganteum under N-salt interaction.