Nitrogen inhibitors improve soil ecosystem multifunctionality by enhancing soil quality and alleviating microbial nitrogen limitation

Soil quality (SQI) is a comprehensive indicator reflecting the agricultural productivity of soil, and soil ecosystem multifunctionality (performing multiple functions simultaneously; EMF) can reflect complex biogeochemical processes. However, the effects of enhanced efficiency nitrogen fertilizers (EENFs; urease inhibitors (NBPT), nitrification inhibitors (DCD), and coated controlled-release urea (RCN)) application on the SQI and soil EMF and their relationships are still unclear. Therefore, we conducted a field experiment to study the effects of different EENFs on the SQI, enzyme stoichiometry and soil EMF in semiarid areas of Northwest China (Gansu, Ningxia, Shaanxi, Shanxi). Across the four study sites, DCD and NBPT increased SQI by 7.61-16.80 % and 2.61 %-23.20 % compared to mineral fertilizer, respectively. N fertilizer application (N200 and EENFs) alleviated microbial N limitation, and EENFs alleviated microbial N and C limitations to a greater extent in Gansu and Shanxi. Moreover, nitrogen inhibitors (Nis; DCD and NBPT) improved the soil EMF to a greater extent than N200 and RCN, DCD increased by 205.82-340.00 % and 145.00-215.47 % in Gansu and Shanxi, respectively; NBPT increased by 332.75-778.59 % and 364.44-929.62 % in Ningxia and Shanxi, respectively. A random forest model showed that the microbial biomass carbon (MBC), microbial biomass nitrogen (MBN) and soil water content (SWC) of the SQI factors were the main driving forces of soil EMF. Moreover, SQI improvement could alleviate microbial C and N limitations and promote the improvement of soil EMF. It is worth noting that soil EMF was mainly affected by microbial N limitation rather than C limitation. Overall, NIs application is an effective way to improve the SQI and soil EMF in the semiarid region of Northwest China.