In a new study published in New Phytologist on Nov. 23, Prof. ZENG Fanjiang's team from the Xinjiang Institute of Ecology and Geography of the Chinese Academy of Sciences, has identified the key pathway driving the soil carbon sinks in arid regions.

For years, understanding the intricate pathways through which photosynthetic carbon is allocated and stabilized in arid soils has been a significant challenge. To solve this puzzle, the researchers conducted an in-situ 13CO₂ pulse-labeling experiment on Alhagi sparsifolia, a keystone desert plant species in the southern Taklamakan Desert. They tracked the dynamics of photosynthetic carbon over a remarkable 360-day period.

The researchers found that photosynthetic carbon, captured by the plant's leaves, was swiftly transported down to its extensive root system and then into the surrounding soil and microbes. While the direct accumulation of plant residue carbon remained modest, contributing only 0.2% to 1.1% of the total soil organic carbon (SOC), the contribution from microbial necromass – the remains of dead microorganisms – was significantly larger, accounting for 12% to 30% of SOC.

In addition, they found that in the topsoil layers (0-100 cm), this microbial necromass initially increased and then stabilized over time. However, it continued to accumulate in the deeper subsoil layers (100-200 cm). 

Further analysis demonstrated that microbial processes were the primary drivers of SOC variations, explaining a substantial 59% of the variance, a figure that outstripped the contribution from plant-derived carbon (38%).

"Our study demonstrates that microbial necromass is the primary contributor to SOC stability in hyper-arid desert ecosystems," said Dr. CONG Mengfei, the first author of the study.

This study significantly advances our understanding of carbon cycle dynamics in arid regions, providing critical insights for assessing the carbon sink potential of desert ecosystems.