Biotic and abiotic forces together drive forest soil carbon response

Forests cover about 30% of the world’s land area and play a crucial role in absorbing and releasing carbon. A key part of this process is soil respiration, which is the release of CO₂ from soil as plants and microbes break down organic matter. How sensitive this soil breathing is to changes in temperature — known as Q₁₀ — is an important measure for predicting how forests might respond to global warming.

A new study published in Forest Ecosystems by researchers from the Institute of Botany at the Chinese Academy of Sciences shows that both biotic and abiotic factors work together to shape this temperature sensitivity.

The research team collected data on 766 soil Q₁₀ values from forests around the world, covering different climates, soil types, and tree species. With this global dataset, they used a random forest model to find out which factors best predict Q₁₀.

The study found that microbial biomass carbon (MBC) — a measure of how much living microbial material is in the soil — was the strongest single predictor of soil Q₁₀. The more active the soil microbes, the more sensitive soil respiration is to warming. Besides microbes, the researchers also found that soil Q₁₀ increased when leaves had more phosphorus but decreased when the ratio of leaf nitrogen to phosphorus was high. This means the nutrients in leaves, which eventually become leaf litter, help shape how soil processes carbon.

Not surprisingly, abiotic factors like temperature, rainfall, and soil type were also important. For example, forests in warmer and wetter places tended to have lower soil Q₁₀ values. Soil organic carbon and clay content also influenced how the soil breathes CO₂.

The researchers also looked at how tree diversity affects soil Q₁₀. They compared mixed forests with a variety of tree types to forests with only one species. They found that mixed forests, especially those combining needle-leaved and broad-leaved trees, tended to have slightly lower soil Q₁₀ values than monocultures. It can be concluded that forests with diverse tree species might be more stable and less sensitive to temperature swings.

These findings are meaningful because many climate models still treat soil Q₁₀ as a fixed value, ignoring how microbes, leaves, and soil interact. This study is the first time introducing biotic factors into a forest soil Q₁₀ predictive model. By showing that both biotic and abiotic factors shape soil respiration, the study points the way to better, more accurate predictions of how forests will store or release carbon as the planet warms.

“Our study highlights the need to include both biotic and abiotic factors to better predict forest carbon dynamics,” said the corresponding author Dr. Haihua Shen. “This could help refine carbon cycle models and guide forest management strategies.”