Effects of cultivation of herbaceous perennials on soil microbial community structure and nitrogen cycling functions

Abstract

This study aimed to elucidate the impacts of cultivating different herbaceous perennials on the rhizosphere microenvironment, nitrogen-cycling microbial communities, and functional genes in black soils of urban green spaces in Northeast China, thereby providing a scientific basis for rational urban plant configuration and interspecific differences in soil nutrient cycling. Focusing on five commonly utilized herbaceous perennials in Changchun ( Lycopus lucidus [P-LL], Salvia japonica [P-SJ], Hemerocallis fulva [P-HF], Hosta ensata [P-HE], and Pseudolysimachion spicatum [P-PS]), this study integrated conventional physicochemical analyses, metagenomic sequencing, co-occurrence networks, and Random Forest modeling to analyze rhizosphere soil nutrient profiles, nitrogen-cycling microbial community structures, and key functional gene abundances after two years of continuous cultivation. Different floral treatments significantly altered rhizosphere nutrient status and microbial community composition. The P-LL treatment exhibited relatively higher contents of total nitrogen (TN), soil microbial biomass nitrogen (SMBN), available phosphorus, and available potassium, demonstrating a high-level soil multifunctionality index (SMI). The P-PS treatment showed higher available nitrogen and ammonium nitrogen but lower SMBN, accompanied by a higher relative abundance of Actinomycetota and the assembly of a microbial co-occurrence network with enhanced connectivity and robustness, indicating a potent organic nitrogen mineralization potential in its rhizosphere. The composition of nitrogen-cycling genes remained broadly stable across treatments, dominated by ammonia assimilation genes ( glnA and gltB ), with a relatively low abundance of denitrification genes ( nirK ). Multivariate and Random Forest analyses revealed that SMBN exerted the strongest positive regulatory effect on nitrogen-sensing genes (e.g., ntrY and ntrX ), whereas TN, nitrate nitrogen (NO 3 - -N), and available potassium (AK) emerged as the paramount direct drivers determining the abundance variations of core ammonia assimilation genes. Different herbaceous perennials shaped species-specific rhizosphere nutrient and microbial functional profiles. P-LL and P-PS exhibited superior comprehensive nutrient traits and potential nitrogen mineralization characteristics, respectively, making them excellent candidate species for urban green space configuration and future mixed-planting trials in cold regions.