Widespread Higher Soil Respiration Rates at Nighttime Than Daytime Across Global Forest Ecosystems

Area of Science:

• Terrestrial Ecosystem Ecology
• Biogeochemical Cycles
• Climate Change Science

Background:

• Soil respiration (Rs) is a major terrestrial carbon flux influencing the soil carbon budget.
• Seasonal and annual Rs dynamics and temperature sensitivity are understood, but diel (24-hour) patterns are not.
• Earth System Models (ESMs) often assume constant Rs temperature response over diel cycles, predicting lower nighttime Rs.

Purpose of the Study:

• To investigate diel patterns of soil respiration (Rs) across global forest ecosystems.
• To compare observed diel Rs patterns with predictions from Earth System Models (ESMs).
• To assess the implications of diel Rs dynamics for carbon-climate feedbacks.

Main Methods:

• Analysis of extensive in situ Rs datasets from 36 global forest sites.
• Comparison of daytime and nighttime Rs-temperature relationships.
• Evaluation of ESM predictions against observed diel Rs patterns.

Main Results:

• A widespread pattern of higher nighttime than daytime Rs was observed across 36 forest sites.
• This pattern is likely driven by a temporal lag between photosynthesis and Rs due to photosynthate transport.
• Daytime Rs-temperature relationships underestimated nighttime Rs by 2.5%–28.7% at 31 sites.
• ESMs inaccurately predict lower nighttime Rs due to underestimating root respiration dynamics.

Conclusions:

• Significant diel Rs patterns exist across forest ecosystems, with higher nighttime respiration.
• Diel differences in Rs temperature response are substantial and not captured by current ESMs.
• Incorporating diel Rs dynamics is essential for improving carbon-climate feedback predictions under global warming.