Litter type control on soil C and N stabilization dynamics in a temperate forest

Area of Science:

• Forest ecology
• Soil science
• Biogeochemistry

Background:

• Plant litters are primary drivers of soil organic matter (SOM) accumulation in forest ecosystems.
• Understanding the factors and processes governing stable SOM formation is crucial for soil health and carbon sequestration.

Purpose of the Study:

• To investigate the influence of litter type (needles vs. fine roots) and placement depth (O vs. A horizon) on carbon (C) and nitrogen (N) dynamics in temperate forest soils over five years.
• To elucidate the transformation pathways of litter-derived C and N into stable SOM fractions.

Main Methods:

• Utilized (13)C/(15)N-labeled needles and fine roots to trace C and N dynamics in situ.
• Analyzed soil samples from O and A horizons after a 5-year incubation period.
• Quantified C and N retention and characterized their distribution within different SOM fractions.

Main Results:

• Litter type, not placement depth, was the primary controller of soil C and N retention after 5 years.
• Fine root inputs led to greater soil C (1.4x) and N (1.2x) retention compared to needle inputs.
• While similar proportions of C and N were incorporated into stable SOM, fine roots exhibited slower transfer rates, and proportionally more remaining needle-derived C and N entered stable SOM fractions.
• Stoichiometric analysis indicated at least two SOM pools with different turnover times and highlighted the importance of N-rich compounds for persistence.

Conclusions:

• Fine root litter promotes greater long-term soil C and N accumulation than needle litter in temperate forests.
• Litter decomposition and transformation pathways into stable SOM differ significantly between plant tissues.
• Current models may underestimate soil C retention from rapidly decomposing litters, emphasizing the need for refined modeling approaches in soil carbon dynamics.