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Glomalin-related soil protein (GRSP) derived from arbuscular mycorrhizal fungi can be transported from land to sea and captured in mangrove wetlands, thereby contributing to soil C and N pools. However, the stable isotope signatures of GRSP and the key influencing factors that affect its isotope values in coastal wetlands remain unknown. In this study, the results showed that total-GRSP (T-GRSP) was a significant contributor of C and N content to mangrove soil. We first compared stable isotope (δ13C and δ15N) values and C/N ratios of GRSP with those of other blue carbon sources in a typical mangrove wetland. The isotope fingerprints of T-GRSP, mangrove soils, mangrove plants, and tidal waters were identified. Unlike those of the conventional sources, the δ13C and δ15N values of T-GRSP were −25.04‰ to −22.83‰ and 3.22‰ to 7.24‰, respectively, and the mean C/N ratio was 12.95 in the mangrove cover sites. These findings indicated that T-GRSP is a novel blue carbon source mainly originating from terrestrial ecosystems. Moreover, the δ13C and δ15N values of T-GRSP in mangrove wetlands were affected by vegetation interception and soil properties. Redundancy analysis results indicated that pH, moisture, depth, and salinity were key factors influencing the T-GRSP isotope fingerprints in mangrove wetlands. Additionally, the simultaneous changes in T-GRSP content, isotope values, and C/N ratios among mangrove cover sites, a mudflat, and tidal waters suggested that this protein is a sensitive tracer between land and sea. Overall, the isotope signatures of GRSP captured by mangroves were identified for the first time, which will have important implications for the estimation of the blue carbon budget and identification of the blue carbon sources in global coastal regions. Unlabelled Image • GRSP is an important terrestrial carbon source that efficiently stores blue carbon. • δ13C and δ15N values of T-GRSP differed from those of other mangrove SOM sources. • The stable isotope values and C/N ratios of T-GRSP revealed its terrestrial origin. • T-GRSP content was significantly positively correlated with soil OC and TN content. • The simultaneous changes in characteristics showed that GRSP is a sensitive tracer. [ABSTRACT FROM AUTHOR]

Glomalin-related soil protein (GRSP), a particular terrigenous-derived carbon (C), is transported to the coastal oceans, where it accumulates in sediments. We hypothesized that terrigenous C (GRSP) accumulation could enhance marine C sequestration, and sediment fertility would increase the C stock in the marine ecosystem. In this study, we tested GRSP contribution to marine sediment C, nitrogen (N) and iron (Fe), and explored whether GRSP deposition varied with sediment fertility levels in the Old Yellow River delta. The mean concentration of total GRSP was 1.10 ± 0.04 mg g − 1 (0.24 Mg C ha − 1 ), accounting for 6.41 ± 0.17% of total organic C and 3.75 ± 0.13% of total N in the 0–10 cm marine sediments, indicating that the coastal marine system is an important sink of GRSP. GRSP also contained 1.46 ± 0.06% Fe (20.7 kg Fe ha − 1 ), accounting for 0.058 ± 0.003% of total Fe in marine sediments. Meanwhile, Fe-content in GRSP significantly decreased with distance from the shore, indicating that Fe was released with GRSP transfer and thus GRSP was a new natural Fe fertilization in marine environment. Furthermore, GRSP enhanced marine C sequestration by its rapid deposition and Fe contribution. Combined indicators of sediment fertility (factor 1) were significantly positively correlated with GRSP concentrations by Principal Component Analysis. Co-deposited with nutrient elements, GRSP fractions were accumulated more in more fertile sediments but less in less fertile sediments. GRSP, a mixture of co-existent multiple elements, can be used as a nutrient controlled-release agent in the marine ecosystem. GRSP fractions were responsive to marine sediment fertility levels and the understanding of their function in sediment C sequestration will provide new insights into the importance of terrestrial-marine linkages. [ABSTRACT FROM AUTHOR]

Arbuscular mycorrhizal (AM) fungi produce a recalcitrant glycoprotein, (glomalin-related soil protein (GRSP)), which can contribute to soil carbon sequestration. Here we made a first study to characterize the spatial distribution of GRSP fractions in a mangrove forest at Zhangjiang Estuary, Southeastern China and to explore potential contributions of GRSP to sediment organic carbon (SOC) in this forest. We identified GRSP fractions in surface sediments, as well as those at a depth of 50 cm. The contents of easily extractable GRSP (EE-GRSP), total GRSP (T-GRSP), GRSP in particulate organic matter (POM-GRSP) and GRSP in pore water (PW-GRSP) ranged between 1.20–2.22 mg g − 1 , 1.38–2.61 mg g − 1 , 1.45–10.78 mg g − 1 and 10.35–39.65 mg L − 1 respectively, and these four GRSPs are significantly affected by sample sites and sediment layers. Carbon in GRSP accounted for 2.8–5.9% of SOC and its contributions can far exceed that of microbial biomass carbon (0.21–0.73%) in the 0–50 cm sediment layers. Our data indicate that GRSP could be transported by pore water and accumulated in sediment profiles. The non-linear regression analysis revealed that as SOC and particulate organic carbon (POC) contents decrease, GRSP proportions increase, indicating the increase of the recalcitrant carbon offsetting the effects of mangrove carbon loss, especially labile C. Regression and ordination analyses indicated that GRSP fractions were mainly positively correlated with sediment carbon fractions and spore density but were negatively correlated with sand, pH. Strikingly, the unfavorable environmental factors for microbial organisms, especially AM fungi, prove to be able to promote the production or accumulation of GRSP. We propose that there are two different pathways for affecting the pool size of GRSP in mangrove ecosystems: (i) directly via indigenous AM fungi propagules; (ii) or via the GRSP transport and deposition by pore water and tides. [ABSTRACT FROM AUTHOR]

Through binding of mineral particles and elements, glomalin-related soil protein (GRSP) plays a critical role in sustaining terrestrial soil quality and contributes to the fate of elements from terrestrial to aquatic ecosystems. There is little knowledge, however, of the metal sequestration patterns of GRSP in both terrestrial and aquatic soils, and this limits progress in understanding how environmental conditions influence GRSP characteristics. Here, we employed microcosm experiments to determine the molecular composition of original GRSP derived from three arbuscular mycorrhizal fungi, Glomus intraradices , Glomus versiforme and Acaulospora laevis. To gain insight into the metal sequestration patterns of environmental GRSP, we investigated major subtropical and tropical mangrove wetlands in southern China. GRSP-bound metals were significantly and positively correlated with total metals, and the metal binding contributed to the metal sequestration of mangrove soils. Fourier-transform infrared spectroscopy results showed that original- and environmental GRSP fractions contained hydroxyl, carboxyl, amide and carbonyl functional groups, which enhanced metal binding. Environmental process had no effect on the type of functional groups of the GRSP, while it significantly changed the relative content of the functional groups. The infrared fingerprint analyses of original- and environmental GRSP revealed field-specific, however, no taxon-specific characteristics of GRSP. Biostatistical analysis of the GRSP molecular composition further revealed that the soil pollution sources regulated the ratios of functional group contents associated with hydrocarbons, proteins, polysaccharides and nucleic acids. By GRSP infrared fingerprints coupled with multivariate analyses, we developed a technique for source identification of heavy metal pollution, giving more reliable evidence about contributing sources. Unlabelled Image • Revealing soil pollution by combining GRSP traits with multivariate analysis. • Soil environment process had no effect on the type of functional groups of GRSP. • Molecular composition ratios of GRSP were field-specific in mangrove soils. • GRSP-bound metals were linked with metal pollution sources in coastal wetlands. • GRSP, a novel bioindicator, provided new perspective for coastal management. [ABSTRACT FROM AUTHOR]