The Effect of Synthetic Cow Urine on Microorganisms and Their Potential Phosphorus Mining Activity in Rhizosphere and Bulk Soil

ABSTRACT Background and aims Soil microbes adapt to varying nutrient inputs by modifying their utilization strategies, with root exudates and animal urine serving as key carbon (C) and nutrient sources in grasslands. Nonetheless, the specific mechanisms by which cow urine and root exudates influence microbial community and resource utilization remain elusive. This study investigates the differential effects of cow urine on microbial biomass, community composition and enzymatic activity in C‐rich (rooted) and C‐poor (vegetation‐free) soil. Methods A laboratory experiment was conducted using synthetic cow urine applied to a Vertic Cambisol soil, either densely rooted with Dactylis glomerata (C‐rich) or vegetation‐free (C‐poor). Destructive sampling occurred on days 1, 4 and 14. Microbial biomass (MBC, MBN and MBP), phospholipid fatty acids, DNA and enzymatic activities (acid phosphatase, β‐glucosidase) were analysed to assess microbial responses. Results DNA content was twice as high in C‐rich rooted as in C‐poor bulk soil. In C‐poor soil, urine strongly reduced DNA‐to‐MBC (−166%, day 14) and MBP‐to‐MBC (−23%, day 14), while increased MBN‐to‐MBC (+23% day 14). After 14 days of urine addition, phosphatase‐to‐β‐glucosidase ratios increased from 0.76 to 1.1 in C‐rich but declined in C‐poor soil. In C‐poor bulk soil, urine shaped the microbial community, whereas in C‐rich soil, root exudates dominated. Abundance of bacterial fatty acids increased from 2% to 22% over 14 days. Conclusions In C‐rich soil, urine stimulated microbial growth through C and nutrients availability from both roots and urine, thereby shifting enzymatic activity towards P mining. In contrast, microbial communities in C‐poor soil exhibited restrained growth and stable stoichiometric ratios, adapting to low nutrient supply. These findings highlight that microbial responses to urine input varied between rooted and bulk soil, emphasizing their relevance in soil microbial ecology.