Increased root-derived carbon buffers soil carbon loss under simultaneous warming and nitrogen addition

Area of Science:

• Ecology
• Soil Science
• Global Change Biology

Background:

• Plant roots are key drivers of soil organic matter dynamics, influencing carbon cycling belowground.
• Interactions between rising temperatures and nitrogen availability on these processes are not well understood in field conditions.

Purpose of the Study:

• To quantify the long-term effects of soil warming, nitrogen enrichment, and their combination on root-derived carbon inputs and soil organic carbon (SOC) dynamics in a temperate forest.
• To assess how these global change factors influence root production, exudates, and microbial respiration.

Main Methods:

• A 16-year field experiment manipulating soil temperature (+5°C) and nitrogen availability (+5 g N m⁻² year⁻¹).
• Measurement of fine-root production, root exudates, root respiration, and microbial respiration.
• Quantification of carbon inputs to soil organic matter from various root-related sources.

Main Results:

• Warming alone reduced root-derived carbon inputs and increased microbial respiration, leading to net soil carbon loss.
• Nitrogen enrichment increased SOC accumulation and reduced root respiration, resulting in a near-neutral carbon balance.
• Combined warming and nitrogen addition quadrupled root-derived SOC, fully offsetting warming effects and maintaining soil carbon stocks.

Conclusions:

• Interacting global change factors can have balancing effects on belowground carbon allocation and losses.
• Soil nitrogen availability is a critical factor determining whether warming leads to soil carbon depletion or stabilization.
• Species-specific root traits, like fine-root production and exudate composition, significantly control carbon stabilization.