Nitrogen fertilization affected microbial carbon use efficiency and microbial resource limitations via root exudates

Area of Science:

• Soil Science
• Microbial Ecology
• Agricultural Science

Background:

• Nitrogen (N) fertilizer influences nutrient cycling and microbial acquisition in soils.
• The impact of long-term N fertilizer rates on soil microbial resource limitations in greenhouse vegetable systems is understudied.
• Root exudation plays a role in nutrient availability and microbial processes.

Purpose of the Study:

• To investigate the effects of varying long-term N fertilizer application rates on root carbon and nitrogen exudation.
• To assess the impact on soil microbial resource limitations and microbial carbon use efficiency (CUE_ST).
• To elucidate the relationship between root exudation, microbial limitations, and CUE_ST in greenhouse vegetable systems.

Main Methods:

• Experiment conducted over 15 years in a greenhouse vegetable system with four N treatments (N0, N1, N2, N3).
• Measured root carbon and nitrogen exudation rates, microbial C, N, P limitations, and CUE_ST.
• Utilized Random Forest analysis and structural equation modeling (SEM) to identify key factors and relationships.

Main Results:

• N fertilizer treatments significantly decreased root C and N exudation rates compared to the control (N0).
• Microbial C and N/P limitations were positively correlated with root exudation rates and negatively with CUE_ST.
• Root exudation rates were identified as key factors influencing microbial resource limitations and CUE_ST; soil NH₄⁺ content directly affected root exudation.

Conclusions:

• Increased root exudation, driven by N fertilizer, enhances microbial resource limitations, potentially due to competition.
• Reduced microbial carbon use efficiency (CUE) may decrease soil carbon sequestration.
• Root exudation is critical in modulating microbial resource limitations and CUE, impacting plant-soil interactions and carbon dynamics.