A study conducted by researchers at the Institute of Applied Ecology of the Chinese Academy of Sciences has uncovered how widely used agricultural chemicals, designed to enhance fertilizer efficiency, may reshape soil microbial ecosystems. 

The findings, published in Geoderma and Applied Soil Ecology, demonstrate that urease inhibitors—chemicals added to slow the breakdown of urea fertilizers—trigger compensatory mechanisms in soil microbes.

The researchers examined two common synthetic urease inhibitors, N-butyl-thiophosphate triamide (NBPT) and phenyl-phosphoryl-diamine (PPD), both of which are employed to reduce nitrogen loss in the soil. While both inhibitors effectively suppress extracellular urease activity, an enzyme responsible for the hydrolysis of urea into ammonia and carbon dioxide, their impact led to an unexpected rise in intracellular urease activity—an enzyme found within soil microorganisms that also hydrolyzes urea. This suggests that soil organisms actively compensate for the chemical disruption through a biological "homeostatic response."

Central to this adaptation were bacteria that carried the ureC gene, which encodes the catalytic subunit of urease. The researchers observed that both urease inhibitors increased the abundance of ureC-containing microbial groups. However, their effects on the structure of microbial communities differed. PPD was found to reduce the genetic diversity of ureC-bearing bacteria, simplifying the functional community of soil microbes. In contrast, NBPT promoted more complex microbial networks, strengthening the connections between bacterial clusters characterized by the ureC gene.

With global urea use exceeding 180 million tonnes annually and up to half lost to environmental leakage, urease inhibitors remain critical tools for curbing pollution and greenhouse gas emissions. However, the study highlights nuanced challenges. While these inhibitors offer short-term nitrogen retention benefits, their suppression of extracellular urease activity forces microbes to rely on intracellular urease reserves. This shift is primarily driven by bacteria. The research suggests that the choice of urease inhibitor plays a critical role in shaping the microbial community: NBPT, with its milder ecological impact, may be preferable to PPD for preserving microbial diversity and maintaining functional bacterial networks.

The study provides novel insights into the microbial homeostasis mechanisms in regulating enzymatic activity and offers a fresh perspective on how soil urease activity changes in response to the application of urease inhibitors.