Effects of ecological restoration on carbon sink and carbon drawdown of degraded salt marshes with carbon‐rich additives application

Abstract Plant biomass resources have been gradually used to restore and improve saline soils. However, little is known about whether the applications of reed straw (PA) and biochar (BC) in degraded coastal salt marshes are beneficial for blue carbon sink enhancement and carbon drawdown. Here, we evaluated the effects of 3% PA and 3% BC applications on the vegetation, soil and blue carbon sink function of degraded salt marsh ecosystems and assessed their CO 2 reduction capacities based on the life cycle. The results showed that the applications of PA and BC improved the soil quality of degraded salt marshes. Suaeda salsa recovered after 3% PA and 3% BC additions, and its carbon sequestration increased by 133% and 12%, respectively. The carbon pool of the degraded salt marshes was elevated by 0.4%–2.8% compared with that before restoration. The structural equation modelling indicated that both PA and BC application decreased soil electrical conductivity, while promoted the recovery of the plant carbon pool and an increase in the soil carbon pool. We calculated a CO 2 drawdown of 137 kg·t −1 for the 3% PA addition in comparison with a CO 2 emission of 175 kg·t −1 for the 3% BC addition based on a life cycle assessment. These findings indicate that PA and BC can be effectively used to restore degraded salt marshes and enhance blue carbon sinks while PA application is a better choice for degraded coastal wetlands rehabilitation to achieve carbon drawdown from a life cycle perspective.