Microbial carbon limitation plays a key role in shaping the blue carbon outcomes of mangrove restoration, according to a new study. It suggests that restoration not only increases soil organic carbon (SOC) but also alters the source composition and potential biochemical quality of the restored carbon pool.

The study, led by researchers from the South China Botanical Garden (SCBG) of the Chinese Academy of Sciences (CAS), was published in Catena on June 16.

Mangrove SOC accumulation is jointly controlled by plant inputs, microbial transformation, and nutrient supply. However, how microbial metabolic limitation affects the balance between plant-derived and microbial-derived carbon during restoration remains poorly understood.

To address this gap, the researchers compared degraded mudflats with restored stands of Sonneratia apetala and Kandelia obovata on Qi'ao Island, Zhuhai, in South China's Guangdong province.

They found that degraded mudflat soils were limited by both carbon and phosphorus. Following mangrove restoration, microbial carbon limitation was strongly reduced and was no longer detectable in either restored forest type, whereas phosphorus limitation persisted. Importantly, available nutrients and soil carbon quality exerted stronger control over microbial carbon limitation than microbial life-history strategies, with SOC, total nitrogen, and the ratio of labile to recalcitrant carbon emerging as key predictors.

In addition, restoration increased the absolute abundance of both lignin phenols—used as indicators of plant-derived carbon—and amino sugars—used as indicators of microbial necromass. However, when standardized by SOC, the restored soils showed a higher relative contribution of plant-derived carbon and a lower relative contribution of microbial-derived carbon.

According to the researchers, these findings indicate that restoration changes not only the quantity of carbon stored but also the types of carbon that accumulate. Although the study did not directly measure long-term persistence, it identifies microbial carbon limitation as a key link between restoration, SOC accumulation, and blue carbon source composition.

The researchers suggest that microbial carbon limitation, phosphorus availability, and biomarker-based indicators of carbon sources should be incorporated into mangrove restoration monitoring. These indicators could improve the evaluation of carbon-sequestration outcomes and support more targeted blue carbon management.

Dr. HUANG Xingyun, a postdoctoral researcher at the SCBG, is the first author of the study, and Prof. WANG Faming from SCBG is the corresponding author.

The study was supported by the National Natural Science Foundation of China, the National Key Research and Development Program of China, the EU-China C-BLUES collaborative project, and other sources.