Glomalin-related Soil Protein Fractions Research Articles

Evaluation of the relation between soil biomass of arbuscular mycorrhizal fungi and glomalin-related soil protein in conservation agriculture

Arbuscular mycorrhizal fungi (AMF) are indicators of soil health and are associated with various soil benefits, primarily linked to glomalin accumulation from hyphal turnover. However, the direct connection between glomalin-related soil protein (GRSP) and AMF has been questioned. The study aimed to investigate the correlation between different fractions of GRSP and fatty acid fractions in soil, as well as the impact of conservation agriculture practices on AMF biomass and GRSP content. Findings revealed a positive correlation between easily extractable (EE) GRSP and phospholipid fatty acid (PLFA) 16:1ω5, while no significant correlations were found for difficultly extractable (DE) or total GRSP fractions. These results highlight the complexity of GRSP dynamics and the need for further research on different fractions and their relation to AMF biomass. Additionally, the study demonstrated that mechanical soil management had a greater impact on AMF hyphal biomass and EE-GRSP compared to residue management. Direct seeding, a reduced tillage approach, led to higher hyphal biomass and EE-GRSP, indicating AMF sensitivity to tillage intensity. This suggests that tillage practices exert a stronger influence on AMF abundance and GRSP content than residue management.

Soil glomalin-related protein affects aggregate N2O fluxes by modulating denitrifier communities in a fertilized soil

Agricultural ecosystems contribute significantly to atmospheric emissions of soil nitrous oxide (N2O), which exacerbate environmental pollution and contribute to global warming. Glomalin-related soil protein (GRSP) stabilizes soil aggregates and enhances soil carbon and nitrogen storage in agricultural ecosystems. However, the underlying mechanisms and relative importance of GRSP on N2O fluxes within soil aggregate fraction remain largely unclear. We examined the GRSP content, denitrifying bacterial community composition, and potential N2O fluxes across three aggregate-size fractions (2000–250 μm, 250–53 μm, and <53 μm) under a long-term fertilization agricultural ecosystem, subjected to mineral fertilizer or manure and their combination. Our findings indicated that various fertilization treatments have no discernible impact on the size distribution of soil aggregates, paving the way to further research into the impact of soil aggregates on GRSP content, the denitrifying bacterial community composition, and potential N2O fluxes. GRSP content increased with the increase in soil aggregate size. Potential N2O fluxes (including gross N2O production and N2O reduction and net N2O production) among aggregates were highest in microaggregates (250–53 μm), followed by macroaggregates (2000–250 μm) and lowest in silt + clay (<53 μm) fractions. Potential N2O fluxes had a positive response to soil aggregate GRSP fractions. The non-metric multidimensional scaling analysis revealed that soil aggregate size could drive the denitrifying functional microbial community composition, and deterministic processes play more critical roles than stochasticity processes in driving denitrifying functional composition under soil aggregate fractions. Procrustes analysis revealed a significant correlation between denitrifying microbial community, soil aggregate GRSP fractions, and potential N2O fluxes. Our study suggests that soil aggregate GRSP fractions influence potential nitrous oxide fluxes by affecting denitrifying microbial functional composition within soil aggregate.

Biostimulatory Response of Easily Extractable Glomalin-Related Soil Protein on Soil Fertility Mediated Changes in Fruit Quality of Citrus

Arbuscular mycorrhizal fungi secrete glomalin deposited into the soil as glomalin-related soil protein (GRSP), which possess multiple utility to benefit both soil as well as plant health. The present study aimed to assess the effects of the foliar application of an easily extractable GRSP (EE-GRSP) on the fruit quality, soil nutrients, and soil structural changes in three important citrus varieties (Satsuma mandarin Oita 4, Newhall navel orange, and Cocktail grapefruit). The exogenous EE-GRSP significantly elevated root mycorrhizal fungal colonization and soil hyphal length in Newhall and Oita 4 varieties, but without any such response in Cocktail grapefruit variety. The foliar spray of the EE-GRSP improved different external (e.g., pericarp, sarcocarp, and single fruit weight) and internal (e.g., soluble solids, titratable acids, and sugar contents) qualities of fruits to varying magnitudes, depending on citrus variety, with a more prominent effect on Cocktail grapefruit. EE-GRSP-treated fruits of Newhall and Oita 4 were more suitable for processing than non-treated control because of a low fruit hardness. However, no significant effect of the EE-GRSP was observed on the internal quality parameters of Newhall. EE-GRSP-treated citrus trees represented higher soil available nutrients over control, to some extent, especially on Oita 4. The foliar application of the EE-GRSP also increased various GRSP fractions to varying proportions and improved the distribution of water-stable aggregates in the size fraction of 0.25–2 mm, thereby increasing the mean weight diameter, particularly in Newhall and Cocktail grapefruit varieties. These observations provided clues about the stimulatory role of the EE-GRSP through soil structure and nutrient pool-mediated improvements in fruit quality.

Characterization of Different Molecular Size Fractions of Glomalin-Related Soil Protein From Forest Soil and Their Interaction With Phenanthrene.

As a natural organic compound secreted by arbuscular mycorrhizal fungi (AMF), glomalin-related soil protein (GRSP) is an important part in soil, affecting the bioavailability of polycyclic aromatic hydrocarbons (PAHs) in it. Previous research have demonstrated that GRSP could enhance the availability of PAHs in the soil and favor their accumulation in plant roots. However, a scarcity of research exists on the different molecular weights of GRSP interacting with PAHs due to their complexation and heterogeneity. In this research, the extracted GRSP in soil was divided into three molecular weight (Mw) fractions of GRSP (<3,000, 3,000–10,000, and >10,000 Da), whose characteristics and binding capacity of PAHs were conducted by using UV–visible absorption, quenching fluorometry and, Fourier transform infrared spectroscopy. The results showed that the GRSP was composed of abundant compounds, it has a wide distribution of molecular weight, and the >10,000 Da Mw fraction was dominant. For three Mw fractions of GRSP, they have some difference in spectral features, for example, the >10,000 Da fraction showed higher dissolved organic carbon (DOC) contents, more phenolic hydroxyl groups, and stronger UV adsorption capacity than the low and middle Mw fractions. In addition, the interaction between GRSP and phenanthrene is related to the characteristics of the Mw fractions, especially the phenolic hydroxyl group, which has a significantly positive correlation with a binding coefficient of KA (k = 0.992, p < 0.01). Simultaneously, hydrophobic, NH-π, and H-bound also played roles in the complexation of phenanthrene with GRSP. These findings suggested that different GRSPMw fractions could influence the fate, availability, and toxicity of PAHs in soil by their interaction.

Glomalin-related soil protein: The particle aggregation mechanism and its insight into coastal environment improvement

Glomalin-related soil protein (GRSP), a ubiquitous microbial product, plays a crucial role in particle aggregation and metal adsorption, but the underlying mechanisms remain unknown. Here, GRSP fraction was extracted from estuarine ecosystems and systematically characterized to elucidate the aggregation mechanisms and its impact on coastal environment improvement. We found that GRSP fraction (gravimetric mass of extracted GRSP, 5.1–24.3 mg g−1) was a globally relevant novel bioflocculant and that protein (linked to Bradford protein assay, 1.64–4.37 mg g−1) was the active flocculant constituent. The zeta potential, FTIR, XPS, and 13C NMR analyses identified its key constituents and structure, and revealed that the charge neutralization and bridging were GRSP fraction aggregation mechanisms. Thermogravimetric-infrared spectrometry analysis showed that GRSP fraction was highly thermostable, and the main volatile pyrolysis products included H2O, CO2, CO, and CH4. The SEM-EDX and XPS Fe valence spectroscopy suggested that GRSP fraction contained rich Fe (11.91 ± 0.48%) and could form Fe-rich flocs with particles. We also found that GRSP fraction has a high adsorption capacity (76–95%) for Cu, Zn, Pb and Cd, and its flocculation properties provide new insights into metal adsorption. The analysis of particle aggregation mechanism and its metal adsorption capacity is of great significance to elucidate the role of GRSP fraction in coastal environment improvement.

Carbon sequestration in artificial silicate soils facilitated by arbuscular mycorrhizal fungi and glomalin‐related soil protein

AbstractIn urban areas, pre‐existing concrete‐based demolition wastes and purposely introduced crushed dolerite have been used to create artificial soils, which capture carbon (C) as carbonate minerals and offset greenhouse gas (GHG) emissions. Arbuscular mycorrhizal fungi (AMF) can enhance capture of C in artificial soils through production of glomalin‐related soil protein (GRSP), which facilitates soil organic carbon (SOC) storage and aggregation, and may also enhance precipitation of soil inorganic carbon (SIC). In this paper, we show how different mixtures of dolerite and concrete affect AMF community structure and function, GRSP fractions, and soil organic and inorganic carbon contents. We used nine demonstration plots, 1 m deep, to simulate a constructed urban soil, consisting of different proportions (0, 30, 50, 70 and 100%) of either crushed concrete demolition waste or dolerite quarry fines and sown to a species‐rich meadow mixture, to investigate AMF colonization and community structure (using DNA terminal restriction fragment length polymorphism), contents of easily‐extractable and difficultly‐extractable GRSP, and both organic and inorganic carbon contents. All artificial soils supported functioning AMF communities with different levels of GRSP, SIC and SOC. The 100% dolerite and 100% concrete soils had higher values of difficultly‐to‐extract GRSP andSOC than pure sand, whereas 100% concrete had higher AMF colonization and SOC than sand. AMF community analysis indicated that high GRSP producing species were abundant in 100% dolerite and 100% concrete. These findings demonstrate that there is potential to incorporate demolition waste or dolerite products into the land to support environmental sustainability and enhance soil C sequestration.Highlights In constructed soils, crushed concrete and dolerite more effectively enhance GRSP and soil organic and inorganic carbon contents than sand. Use of crushed concrete and dolerite in plant‐growing substrates is a novel way to combat climate change.

Can soil properties and land use explain glomalin-related soil protein (GRSP) accumulation? A nationwide survey in France

Organic matter plays essential roles in soil, including physical stabilization, nutrient storage and carbon sequestration. An operationally defined fraction of soil organic matter known as glomalin or glomalin-related soil protein, GRSP, is obtained by autoclaving soil in citrate solution. It is reputed to be of fungal origin, very stable and responsible for enhanced soil physical stability. This is the first nationwide survey of GRSP content in soil and was conducted to test the hypotheses on the origin and identity of GRSP. Nearly 200 archived soils were selected on the basis of organic matter content from the French National Soil Inventory, representing mostly cropland, grassland and woodland land uses. Two fractions of GRSP were measured, easily extractable (GRSPEE) and total (GRSPT), extraction. The median values of GRSPEE and GRSPT were 0.7 and 2 g kg−1 respectively, with a strong correlation between the two fractions. Scatter plots and cubist modelling were used to explore the relationships between the contents of the two GRSP fractions and both soil properties and land use. Land use effects were almost entirely attributable to soil characteristics. No evidence was found to support the hypotheses that GRSP is solely of fungal origin, nor that easily extracted GRSP is more recent that the total fraction, although this does not disprove either hypothesis. Soil organic matter was enriched in GRSP C-depleted cropland soils and lower in C-rich woodland, this may result from inherent stability or differences in plant-related composition of carbon input.

Mycorrhiza-released glomalin-related soil protein fractions contribute to soil total nitrogen in trifoliate orange

Glomalin released from arbuscular mycorrhizal fungi (AMF) has important roles in soil nutrient cycles, whereas contributing to glomalin-related soil protein (GRSP) fractions to soil nitrogen (N) is unknown. In this study, a two-chambered root-box that was divided into root chamber (root and mycorrhizal fungi hypha) and hypha chamber (free of the root) was used, and three AMF species including Diversispora epigaea, Paraglomus occultum, and Rhizoglomus intraradices were separately inoculated into the root chamber. Plant growth, soil total N, N content of purified GRSP fractions, and its contribution to soil total N, and leaf and root N contents were analysed. After four months, total biomass and root total length, surface area, and volume were improved by all AMF inoculations. AMF inoculations dramatically increased soil total N content in two chambers. The N content of purified easily extractable GRSP (EE-GRSP) and difficultly extractable GRSP (DE-GRSP) was 0.10 ± 0.01 mg/g and 0.16 ± 0.02 mg/g, respectively, accounted for 15.6 ± 1.6% and 18.1 ± 1.8% of soil total N, respectively. AMF inoculations stimulated the N accumulation in EE-GRSP and DE-GRSP, especially in the hypha chamber. It concluded that GRSP, especially DE-GRSP, acts as a soil N pool accounting for 33.8 ± 1.9% of soil total N in orchards.

Health risk assessment of heavy metal and its mitigation by glomalin-related soil protein in sediments along the South China coast

Knowledge regarding the exposure risk of heavy metals in estuarine wetland is important for people (especially fishermen and consumers of local fish) living in the coastal area and the coastal reclamation. Here, we assessed the ecological and human health risks of sediment-associated metals in the large-scale estuary area based on different sediment textures (Mud, Mud-Sand, and Sand). To investigate the potential impact of terrestrial material on the contamination risks, glomalin-related soil protein (GRSP), a recalcitrant soil protein fraction, was used. Results showed that the estuarine sediment texture played a rather important role in the heavy metal distribution, risk assessment, and the metal sequestration capacity of the land-derived GRSP fraction. We found arsenic, Pb, Cd, and Cr had the highest enrichment in the estuarine wetlands by calculating multiple contamination indices, and that confirmed similar findings of heavy metal contents, except Cd. The average pollution load index (PLI) was 1.67 in all the estuarine sediments, indicating multi-element contamination, with the Muddy sediments (PLI = 2.07) significantly higher than the Mud-Sand mixed sediments (PLI = 1.85), and the lowest (0.78 < 1) in the Sandy sediments. The health risk assessment suggested that the potential cancer risk occurred (>1.00E-6) but no obvious non-carcinogenic effects occurred (<1). Arsenic was found to be the primary contributor to non-carcinogenic risk, accounting for 44.2% of hazard index, while Ni is the primary control metal for carcinogenic risk (except arsenic in the Sandy sediments). As a proxy of terrestrial organic matter, GRSP fraction possessed a high sequestration capacity for heavy metal, especially in the Sandy sediments, and it was significantly associated with the mitigation of ecological and health risks, which may provide new insights into the in situ remediation of anoxic estuarine wetlands.

Contribution of glomalin-related soil proteins to soil organic carbon in trifoliate orange

Arbuscular mycorrhizal fungi (AMF) produce glomalin-related soil protein (GRSP) that influences organic carbon (C) storage in soil; however, how much purified GRSP fractions contribute to soil organic carbon (SOC) is yet not known. The present study evaluated the contribution of GRSP towards changes in SOC in trifoliate orange grown in a rootbox divided into a roots + hyphae chamber (roots colonized by AMF hyphae and AMF extraradical hyphae) and a hyphae chamber (only the presence of AMF extraradical hyphae, without roots). Three AMF species (Diversispora epigaea, Paraglomus occultum and Rhizoglomus intraradices) were inoculated into the roots + hyphae chamber. Following four months of plant growth, P. occultum showed higher AMF hyphal growth in roots, soils and nylon mesh than D. epigaea or R. intraradices. Mycorrhizal inoculation improved the plant growth performance and increased easily extractable GRSP (EE-GRSP) and difficultly extractable GRSP (DE-GRSP) concentrations in both chambers, regardless of AMF species. The C content observed in total GRSP of the soil after purification was 2.71 ± 0.49 mg g−1, while purified EE-GRSP and DE-GRSP showed the C content of 1.01 ± 0.19 mg g−1 and 1.70 ± 010.34 mg g−1, respectively. The C contribution by purified EE-GRSP and DE-GRSP accounted for 8.67 ± 0.95% and 14.59 ± 2.21%, respectively, of total SOC, with a total C contribution of purified GRSPs accounting for 23.26 ± 2.67% of total SOC. A significantly higher C content of GRSP and the C contribution of GRSP to SOC were observed in DE-GRSP than in EE-GRSP, as well as the soil of the roots + hyphae chamber than the soil of the hyphae chamber. The proportionate distribution of water-stable aggregate in 2–4 and 1–2 mm sizes and their stability were higher under AMF hyphae than under non-AMF hyphae. This study thus provided a database evidence of increased contribution of GRSP towards build-up of SOC in response to mycorrhizal symbiosis.

Interactions of soil metals with glomalin-related soil protein as soil pollution bioindicators in mangrove wetland ecosystems

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.

Soil organic matter and glomalin-related soil protein contents do not explain soil aggregate stability after freeze-thaw cycles at contrasting soil moisture contents

ABSTRACT Soil organic carbon (SOC) and glomalin-related soil protein (GRSP) contributes to the formation and stability of soil aggregates, but it remains unknown whether the frequency of freeze-thaw cycles (FTCs) and soil moisture content (SMC) at freezing changes aggregate stability and whether SOC and GRSP regulate these changes. Effects of FTCs (0, 1, 3 and 9 times) and initial SMC (40% and 80% field capacity) on aggregate distribution, SOC, and easily extractable, difficultly extractable and total GRSP content in soil aggregates (> 2000 μm, 250–2000 μm, and <250 μm) were evaluated in Chinese pine forest soil. FTCs significantly reduced MWD by disrupting large macro-aggregates. On the other hand, higher SMC increased MWD by binding soil particles, the effect of which was much greater than the disruptive effects of FTCs. SOC in bulk soil and aggregate fractions slightly decreased with the frequency of FTCs. Bulk and aggregate-associated GRSP fractions first decreased, and then increased with the frequency of FTCs. SOC and GRSP fractions correlated insignificantly with MWD. Our results indicated that increasing SMC could augment soil aggregate stability, and that SOC and GRSP might not be the primary control on aggregate stabilization during freeze-thaw conditions in Chinese pine forest soil.

Glomalin-related soil protein affects soil aggregation and recovery of soil nutrient following natural revegetation on the Loess Plateau

The glomalin-related soil protein (GRSP) is an important fraction of soil organic carbon (SOC) and soil nitrogen (N), and is important for stabilization of SOC and soil aggregates. However, the effects of natural restoration on the concentration and allocation of GRSP differ for different soil aggregate sizes, and how size further affects SOC and soil N restoration, and stabilization of SOC and soil aggregates is not well understood. Here, we present the first characterization of the distribution of GRSP fractions and soil nutrients in soil aggregates following natural restoration by choosing fields of 0, 7, 12, 17, 22, 32 years after cropland abandonment, and a natural grassland as reference. GRSP concentration increased most in microaggregates after 32 years of natural restoration. The processes of rapid accumulation of GRSP (22 to 32 years) occurred simultaneously with the formation of macroaggregates, reduction of microaggregates, and rapid increase of mean weight diameter (22 to 32-years). The soil aggregate stability and contents of GRSP, SOC, labile carbon, total N and phosphorus in each soil aggregate fraction significantly increased in the late stage of natural restoration (22 to 32 years). The most recalcitrant carbon fraction in microaggregates significantly increased between 7 and 32 years (0.887 g kg−1). Our study suggests that abandoning farmland is effective for the restoration of GRSP, soil nutrients and structure and that microaggregates promote the accumulation of recalcitrant carbon and increase the stability of SOC largely through its ability to retain GRSP.

Apatite Stimulates the Deposition of Glomalin-Related Soil Protein in a Lowbush Blueberry Commercial Field

Many wind-sensitive and unproductive soils could benefit from increased glomalin-related soil protein (GRSP), an operationally defined soil protein pool known to improve soil quality and nutrient storage. We expect at least part of this GRSP fraction to originate from fungal biomass. Although P-rich minerals such as apatite are known to increase C allocation from plants to mycorrhizal fungi, there are no studies directly linking apatite with GRSP. We investigated the effect of apatite on GRSP deposition rates in a cultivated field of wild lowbush blueberry (Vaccinium angustifolium Aiton; Vaccinium myrtilloides Michx.) in the Saguenay‒Lac-Saint-Jean region of Quebec (Canada). A field incubation technique (145 days) using sterilized porous sand bags (50 µm pores) was used to measure in situ easily extractable GRSP (EE-GRSP) deposition rates from bags with (n = 10) and without (n = 10) apatite. Half of the bags (n = 10) were also soaked in Proline® 480 SC (Bayer CropScience, Calgary, Alberta, Canada) (Prothioconazole) to determine if EE-GRSP deposition rates were affected by this commonly applied fungicide. Our results indicated that adding apatite into sand bags significantly increased (+70%) EE-GRSP deposition rates, whereas soaking the bags in fungicide had no significant effect. Although the direct linkage between GRSP and lowbush blueberry plants remains to be detailed, our study reports for the first time GRSP concentrations from lowbush blueberry soils. Implications of these findings are discussed.

Tree growth rate regulate the influence of elevated CO2 on soil biochemical responses under tropical condition

Tree growth rate can complicate our understandings of plant belowground responses to elevated CO2 (eCO2) in tropical ecosystems. We studied the effects of eCO2 on plant growth parameters, and rhizospheric soil properties including soil organic carbon (SOC), glomalin related soil protein (GRSP), microbial biomass C (Cmic), CO2 efflux (Cefflux), and microbial extracellular enzyme activities under two tropical tree saplings of fast-growing Tectona grandis (Teak) and slow-growing Butea monosperma (Butea). We exposed these saplings to eCO2 (∼550 ppm) and ambient CO2 (aCO2; ∼395 ppm) in the Indo-Gangetic plain region, and further (after 10 and 46 months) measured the changes in their rhizospheric soil properties. With respect to aCO2 treatment, eCO2 significantly increased plant height, stem and shoot weight, and total plant biomass of Teak. However, these plant traits did not considerably differed between eCO2 and aCO2 treatments of Butea. The eCO2 induced greater extent of increase in rhizospheric soil properties including SOC fractions (particulate OC, non-particulate OC and total OC), GRSP fractions (easily extractable- GRSP, difficulty extractable- GRSP and total- GRSP), Cmic, Cefflux and extracellular enzyme activities (phosphatase, dehydrogenase, β-glucosidase and fluorescein diacetate) were observed under Teak compared with Butea. Compared with aCO2 treatment, eCO2 slightly reduced soil available N and P under the Teak, but no changes were apparent between eCO2 and aCO2 treatments of the Butea. The greater extent of responses from soil variables observed after longer period (46 months) of CO2 exposure. The multivariate analysis confirmed that eCO2 treatment with Teak is more responsive compared with other treatments of Teak and Butea. This contrasting rhizospheric soil feedback to eCO2 between two tropical trees, suggesting fast-growing species will be more responsive to future climate. Such species will have a competitive advantage over coexisting less responsive species (e.g. Butea) under future eCO2 climate.

Distribution of soil organic carbon and glomalin related soil protein in reclaimed coal mine-land chronosequence under tropical condition

The revegetation on mine spoiled lands has potential to improve the status of reclaimed mine-soil quality. However, to date the temporal dynamics of labile and stable fractions of soil organic carbon (SOC) and glomalin related soil protein (GRSP) have not been satisfactorily demonstrated. We investigated SOC and GRSP fractions including labile particulate OC (POC) and easily extractable GRSP (EE-GRSP) and stable non-particulate OC (NPOC) and difficulty extractable GRSP (DE-GRSP) along with other important soil properties in six reclaimed mine lands chronosequence (1 to 26 years old) and a reference forest site in Raniganj Coalfield, India. Our results demonstrated that the accumulation of SOC and GRSP significantly increased with increasing age of the sites, with greater extent of increment after 26 years were seen in labile POC (6.6×) and EE-GRSP (11.5×) compared to stable NPOC (1.8×) and DE-GRSP (6.2×). The higher contribution of GRSP-C in NPOC compared to TOC across the sites, indicate the proximate role of GRSP in accumulation and stabilization of SOC during the pedogenesis. The multivariate analysis revealed strong association among arbuscular mycorrhizal fungi (AMF) spore density, microbial biomass carbon, SOCs and GRSPs, suggesting the factors involved in SOC accumulation likely contributed to AMF proliferation and GRSP enrichment during the reclamation process. Moreover, strong correlation of GRSP and SOC with soil's bulk density, pH, total N and C/N ratio, suggest increasing GRSP and SOC content resulted in multi-level improvement in soil properties. Our results highlight the importance of using GRSP and SOC as indicator during mine land reclamation.

Glomalin-related soil protein deposition and carbon sequestration in the Old Yellow River delta

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±0.04mgg−1 (0.24MgCha−1), accounting for 6.41±0.17% of total organic C and 3.75±0.13% of total N in the 0–10cm marine sediments, indicating that the coastal marine system is an important sink of GRSP. GRSP also contained 1.46±0.06% Fe (20.7kgFeha−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.

Spatial distribution of glomalin-related soil protein and its relationship with sediment carbon sequestration across a mangrove forest

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 1.20–2.22mgg−1, 1.38–2.61mgg−1, 1.45–10.78mgg−1 and 10.35–39.65mgL−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 0–50cm 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.

Effect of long term land use systems on fractions of glomalin and soil organic carbon in the Indo-Gangetic plain

Long-term history of tillage and cropping mediated disturbed and undisturbed use soils effect on glomalin related soil protein (GRSP) and soil organic carbon (SOC) and on their sub fractions were investigated in Indo-Gangetic plain region. In this study, shallow soils were collected from 50-year-old monoculture treatments of undisturbed (Dendrocalamus calostachyus, Mangifera indica and Saccharum munja Roxb.) and disturbed (Oryza sativa cultivated field) land use. Our results showed that compared with undisturbed soils, soils under the disturbed use dramatically depleted in SOC, particulate OC (POC), non-particulate OC (NPOC), GRSP, easily extractable GRSP (EE-GRSP) and difficulty extractable GRSP (DE-GRSP). The depletion in labile POC was found to be little higher than physically protected NPOC, and were almost similar among the fractions of GRSP (each decreased by 50%). Further, a linear correlation was found among the fractions of GRSP and SOC, and in turn resulted in the similar relationship with soils bulk density, porosity, pH, available phosphorus, total phosphorus, organic nitrogen's, cations (calcium and potassium), arbuscular mycorrhizal (AM) abundance, and with microbial activity. These results indicate that the factors involve in SOC accumulation simultaneously encourage AM proliferation and in turn GRSP enrichment. Apart from this, the higher contribution of GRSP-C in NPOC (13 to 17%), tended to increase with decreasing soil disturbance, suggesting the role of GRSP in accumulation and stabilization of SOC in this zone. A two component factor structure showed component 1 considerably occupied by fractions of GRSP, SOC and those other variables favouring GRSP and SOC, primarily scored by undisturbed (M. indica and D. calostachyus treatments) soils. The second component which has fewer influence over soil variables, considerably occupied by microbial activity, electrical conductivity, cations and nutrients (available nitrogen, phosphorus) was also exemplified by undisturbed soils (except D. calostachyus treatment). Thus, improving GRSP and SOC stock in disturbed agricultural soil in studied area is of urgent requirement for the long-term goal of C sequestration and sustainable soil health. Our finding should stimulate management plans for degraded lands aimed at recovering the landscape heterogeneity.

Exogenous application of EE-GRSP and changes in citrus rhizosphere properties

Mycorrhization-induced secretion of glomalin-related soil protein (GRSP) is known to contribute in improving soil fertility and aggregate stability. But, there is hardly any evidence that exogenous GRSP could produce the similar type of response. The present study was, therefore, carried out to extract easily extractable GRSP (EE-GRSP) from citrus rhizosphere soils and evaluate the response at 1/4, 1/2 and full strength EE-GRSP solutions watered into the rhizosphere of 27-year-old Satsuma mandarin (Citrus unshiu) grafted on the rootstock of Poncirus trifoliata. After ~5 months, exogenous EE-GRSP treatments produced significantly positive responses on endogenous EE-GRSP, difficultly-extractable GRSP (DE-GRSP), total GRSP production and soil organic carbon (SOC) content. A significantly positive correlation of these endogenous GRSP fractions with SOC indicated an active participation of GRSP on soil C pool. Exogenous GRSP showed a key role in binding water-stable aggregate (WSA) at 2–4, 1–2, 0.5–1, and 0.25– 0.5 mm size and enhancing WSA stability through changes in mean weight diameter (MWD). A stronger correlation of EE-GRSP and total GRSP with MWD was observed than DE-GRSP fraction. On the other hand, exogenous EEGRSP showed a positive effect on soil phosphatase activity, and soil endogenous EE-GRSP was significantly and positively correlated only with neutral phosphatase. Our studies suggest that exogenous EE-GRSP could be used as an effective regulator to affect soil fertility and soil structure within citrus rhizosphere.