Decipher soil organic carbon dynamics and driving forces across China using machine learning.

Area of Science:

• Environmental Science
• Soil Science
• Climate Change Research

Background:

• Soil organic carbon (SOC) dynamics are critical for regulating global warming.
• Long-term, large-scale SOC changes and their driving forces remain poorly understood.
• Understanding SOC dynamics is essential for climate change mitigation strategies.

Purpose of the Study:

• To investigate the spatiotemporal dynamics of SOC in various soil layers across China from the 1980s to 2010s.
• To quantify the impacts of key driving factors, including climate change, vegetation growth, and human activities, on SOC dynamics.
• To enhance understanding of SOC's role in carbon sequestration and climate modulation.

Main Methods:

• Utilized a machine learning approach to analyze SOC dynamics across different soil depths.
• Conducted factorial simulation experiments to quantify the influence of primary driving factors.
• Examined relationships between SOC and forest canopy height to assess vegetation impact.

Main Results:

• The latest SOC stock (2000-2014) in the top meter of soil was 80.68 ± 3.49 Pg C, with 42.6% in the top 20 cm.
• SOC has been sequestering carbon at a rate of 30.80 ± 12.37 g C m⁻² yr⁻¹ since the 1980s.
• Climate change was the dominant driver of SOC dynamics, especially in topsoil, with warming/drying causing SOC loss. Vegetation growth's influence increased with soil depth.
• Coupled influence of climate and environment (CE) controlled SOC in 71% of topsoil, while CE and climate-vegetation interactions dominated 82.05% of the first meter soil.
• National cropland topsoil organic carbon increased by 23.6 ± 7.6 g C m⁻² yr⁻¹ since the 1980s, stimulated by nitrogenous fertilizer application.

Conclusions:

• Climate change significantly impacts SOC dynamics, with varying influence across soil depths.
• Vegetation growth plays an increasingly important role in deep soil carbon sequestration, particularly in mature forests.
• Human activities, such as nitrogenous fertilizer use, are key drivers of SOC changes in croplands.
• This study provides crucial insights into large-scale SOC dynamics and the complex interplay of factors influencing carbon cycling.