Effects of salinity on iron-organic carbon binding in the rhizosphere of Kandelia obovata: Insights from root exudate analysis

Ying Lei; Yuxin Bi; Xinhan Dong; Hongcheng Li; Xiaoqing Gao; Xiuzhen Li; Zhongzheng Yan

doi:10.1016/j.scitotenv.2024.177214

Effects of salinity on iron-organic carbon binding in the rhizosphere of Kandelia obovata: Insights from root exudate analysis

Sci Total Environ. 2024 Oct 28:177214. doi: 10.1016/j.scitotenv.2024.177214. Online ahead of print.

Authors

Ying Lei¹, Yuxin Bi¹, Xinhan Dong¹, Hongcheng Li¹, Xiaoqing Gao¹, Xiuzhen Li¹, Zhongzheng Yan²

Affiliations

¹ State Key Laboratory of Estuarine and Coastal Research, Institute of Eco-Chongming, East China Normal University, Shanghai, China; Yangtze Delta Estuarine Wetland Ecosystem Observation and Research Station, Ministry of Education, Shanghai Science and Technology Committee, China.
² State Key Laboratory of Estuarine and Coastal Research, Institute of Eco-Chongming, East China Normal University, Shanghai, China; Yangtze Delta Estuarine Wetland Ecosystem Observation and Research Station, Ministry of Education, Shanghai Science and Technology Committee, China. Electronic address: [email protected].

PMID: 39477123
DOI: 10.1016/j.scitotenv.2024.177214

Abstract

Iron (Fe) oxides in wetland soils are crucial for stabilizing soil organic carbon (SOC) by forming stable Fe-OC complexes, thus protecting SOC from microbial breakdown and aiding its preservation. This study delves into the response of Fe (hydr-)oxides to salt stress, a relatively unexplored area, by examining Kandelia obovata, a key mangrove species. Through controlled climate chamber experiments, we investigated how salt stress affects the interactions between Fe (hydr-)oxides and SOC in root exudates (REs) and rhizosphere soils. Our results demonstrate that salinity at 30 ppt significantly increases the release of sugars, amino acids, inorganic nutrients (NH₄⁺, NO₃^-), and phosphorus in K. obovata's REs, while reducing crystalline and amorphous Fe (hydr-)oxides and increasing complexed Fe (hydr-)oxide levels, thereby reducing their crystallinity in rhizosphere soils. Importantly, at elevated salinity (30 ppt), the Fe-OC bond in the rhizosphere shows greater stability, indicating enhanced resilience to salt stress compared to bulk soil. Salt stress also raises the carbon to nitrogen (C/N) ratio in REs. Testing artificial REs (AREs) with different C/N ratios showed that Fe (hydr-)oxide content decreases at C/N ratios of 10 and 30 compared to the control, whereas Fe-OC content increases with higher C/N ratios. Introduction of AREs with a C/N ratio of 20 significantly affected rhizosphere crystalline Fe (hydr-)oxide and Fe-OC content, highlighting AREs' impact on the binding of Fe (hydr-) oxides and OC. The presence of soil microorganisms was critical for the binding of Fe (hydr-) oxides and OC, as sterilized soil exhibited significantly lower levels of Fe (hydr-) oxides and Fe-OC compared to unsterilized soil. This research reveals that under salt stress, mangrove plants play a crucial role in stabilizing rhizosphere SOC by influencing Fe (hydr-) oxide crystallinity and promoting the formation of stable Fe-OC complexes, highlighting the complex interactions between plant REs, salt stress, and soil minerals.

Keywords: Fe redox cycling bacteria; Ferrihydrite; Mangrove; Organic carbon; Root exudates; Salinity.