Spatial heterogeneity in chemical composition and stability of glomalin-related soil protein in the coastal wetlands

Advances, Challenges, and Perspectives in Glomalin-Related Soil Protein Research

Glomalin-related soil protein (GRSP), a glycoprotein primarily exuded by arbuscular mycorrhizal fungi (AMF), exerts key roles in ecological processes in terrestrial ecosystems. Nevertheless, the intricate nature of GRSP, coupled with constraints in its extraction and analytical methodologies, impedes a comprehensive understanding of its compositional attributes and ecological functions. Moreover, the scope of current GRSP research has undergone significant expansion, necessitating a comprehensive synthesis in this field. Here, we employed bibliometric analysis to systematically assess research trends and hotspots in the research field of GRSP based on 840 relevant articles indexed in the Web of Science Core Collection database. Among them, key parameters evaluated encompass publications' quantity, highly cited articles, high-frequency keywords, and historical direct citations. These analyses illuminated the state-of-the-art of GRSP research, delineated emergent trends, and provided future perspectives. Current investigations into GRSP predominantly focus on three major topics: (i) GRSP's nature, origin, and quantification methodologies; (ii) GRSP's key influencing factors including agricultural management practices, climate and land use change; and (iii) GRSP's ecological functions enhancing soil aggregate stability, C sequestration, and contamination remediation. Our findings can serve as a scholarly resource for advancing inquiries into the ecological functionalities of GRSP and its prospective applications in sustainable soil management and ecological restoration.

Immobilization mechanisms of Sr(II), Ni(II), and Cd(II) on glomalin-related soil protein in mangrove sediments at the microscopic scale

Glomalin-related soil protein (GRSP) is a significant component in the sequestration of heavy metal in soils, but its mechanisms for metal adsorption are poorly known. This study combined spectroscopic data with molecular docking simulations to reveal metal adsorption onto GRSP's surface functional groups at the molecular level. The EXAFS combined with FTIR and XPS analyses indicated that the adsorption of Cd(II), Sr(II), and Ni(II) by GRSP occurred mainly through the coordination of -OH and -COOH groups with the metal. The -COOH and -OH groups bound to the metal as electron donors and the electron density of the oxygen atom decreased, suggesting that electrostatic attraction might be involved in the adsorption process. Two-dimensional correlation spectroscopy revealed that preferential adsorption occurred on GRSP for the metal in sequential order of -COOH groups followed by -OH groups. The presence of the Ni-C shell in the Ni EXAFS spectrum suggested that Ni formed organometallic complexes with the GRSP surface. However, Sr-C and Cd-C were absent in the second shell of the Sr and Cd spectra, which was attributed to the adsorption of Sr and Cd ions with large hydration ion radius by GRSP to form outer-sphere complexes. Through molecular docking simulations, negatively charged residues such as ASP151 and ASP472 in GRSP were found to provide electrostatic attraction and ligand combination for the metal adsorption, which was consistent with the spectroscopic analyses. Overall, these findings provided new insights into the interaction mechanisms between GRSP and metals, which will help deepen our understanding of the ecological functions of GRSP in metal sequestration.

Microbial Necromass, Lignin, and Glycoproteins for Determining and Optimizing Blue Carbon Formation

Coastal wetlands contribute to the mitigation of climate change through the sequestration of "blue carbon". Microbial necromass, lignin, and glycoproteins (i.e., glomalin-related soil proteins (GRSP)), as important components of soil organic carbon (SOC), are sensitive to environmental change. However, their contributions to blue carbon formation and the underlying factors remain largely unresolved. To address this paucity of knowledge, we investigated their contributions to blue carbon formation along a salinity gradient in coastal marshes. Our results revealed decreasing contributions of microbial necromass and lignin to blue carbon as the salinity increased, while GRSP showed an opposite trend. Using random forest models, we showed that their contributions to SOC were dependent on microbial biomass and resource stoichiometry. In N-limited saline soils, contributions of microbial necromass to SOC decreased due to increased N-acquisition enzyme activity. Decreases in lignin contributions were linked to reduced mineral protection offered by short-range-ordered Fe (FeSRO). Partial least-squares path modeling (PLS-PM) further indicated that GRSP could increase microbial necromass and lignin formation by enhancing mineral protection. Our findings have implications for improving the accumulation of refractory and mineral-bound organic matter in coastal wetlands, considering the current scenario of heightened nutrient discharge and sea-level rise.

Change in glomalin-related soil protein along latitudinal gradient encompassing subtropical and temperate blue carbon zones

Glomalin-related soil protein (GRSP), an abundant and eco-friendly bioproduct associated with arbuscular mycorrhizal fungi (AMF), contributes significantly to the soil particle aggregation and carbon sequestration. Although much research has been conducted on the storage of GRSP at different spatio-temporal scales in terrestrial ecosystems. However, the deposition of GRSP in large-scale coastal environments has not been revealed, which hinders an in-depth understanding of GRSP storage patterns and environmental controls, and this knowledge gap has become one of the key uncertainties in understanding the ecological functions of GRSP as blue carbon components in coastal environments. Therefore, we conducted large-scale experiments (spanning subtropical and warm temperate climate zones, coastlines over 2500 km) to test the relative contributions of environmental drivers that shape unique GRSP storage. In salt marshes of China, we found that the abundance of GRSP ranges from 0.29 mg g-1 to 1.10 mg g-1, and its concentration decreases with increasing latitude (R2 = 0.30, p < 0.01). The GRSP-C/SOC of salt marshes ranged from 4 % to 43 % and increased with the increase in latitude (R2 = 0.13, p < 0.05). The carbon contribution of GRSP does not follow the trend of increasing abundance, but is limited by the total amount of background organic carbon. In salt marsh wetlands, precipitation, clay content and pH are the main factors influencing GRSP storage. GRSP is positively correlated with precipitation (R2 = 0.42, p < 0.01) and clay content (R2 = 0.59, p < 0.01), but negatively correlated with pH (R2 = 0.48, p < 0.01). The relative contributions of the main factors to the GRSP differed across climatic zones. Soil properties, such as clay content and pH, explained 19.8 % of the GRSP in subtropical salt marshes (20°N < 34°N), however, in warm temperate salt marshes (34°N < 40°N), precipitation explained 18.9 % of the GRSP variation. Our study provides insight into the distribution and function of GRSP in coastal environments.