Nitrogen input enhances microbial carbon use efficiency by altering plant-microbe-mineral interactions

Area of Science:

• Soil Science
• Microbiology
• Environmental Science

Background:

• Microbial growth and respiration are central to the soil carbon (C) cycle, determining C fate and influencing climate feedback.
• Microbial carbon use efficiency (CUE) quantifies C partitioning between growth and respiration, a key factor in soil C dynamics.
• The impact of nitrogen (N) input on CUE and its underlying mechanisms are poorly understood, creating uncertainty in soil C predictions.

Purpose of the Study:

• To investigate how nitrogen (N) addition affects microbial carbon use efficiency (CUE) in soil.
• To elucidate the mechanisms, particularly plant-microbial-mineral interactions, driving CUE responses to N input.
• To improve predictions of soil C dynamics under ongoing N deposition.

Main Methods:

• A multi-level field N addition experiment over 6 years.
• Substrate-independent 18O-H2O labeling technique.
• High-throughput sequencing and mineral analysis to assess plant-microbial-mineral interactions.

Main Results:

• Microbial CUE significantly increased after 6 years of N addition, linked to enhanced microbial growth.
• Elevated microbial growth and CUE were primarily associated with increased soil C accessibility due to weakened mineral protection.
• N-induced changes in plant community and increased soil oxalic acid correlated with attenuated organo-mineral associations.

Conclusions:

• Nitrogen input enhances soil microbial CUE by increasing C accessibility through altered mineral protection, rather than solely through stoichiometric changes.
• Plant community shifts and organic acid production mediate the relationship between N input, mineral association, and microbial physiology.
• Understanding complex plant-microbe-mineral interactions is crucial for accurately predicting soil C responses to anthropogenic N input.