Glomalin-related Soil Protein Research Articles

Fallow Land Enhances Carbon Sequestration in Glomalin and Soil Aggregates Through Regulating Diversity and Network Complexity of Arbuscular Mycorrhizal Fungi Under Climate Change in Relatively High-Latitude Regions.

Soil aggregation and aggregate-associated carbon (C) play an essential function in soil health and C sequestration. Arbuscular mycorrhizal fungi (AMF) are considered to be primary soil aggregators due to the combined effect of extraradical hyphae and glomalin-related soil proteins (GRSPs). However, the effects of diversity and network complexity of AMF community on stability of soil aggregates and their associated C under long-term climate change (CC) and land-use conversion (LUC) in relatively high-latitude regions are largely unexplored. Therefore, an 8-year soil plot (with a 30-year cropping history) transplantation experiment was conducted to simulate CC and LUC from cropland to fallow land. The results showed that Glomus, Paraglomus, and Archaeospora were the most abundant genera. The diversity of AMF community in fallow land was higher than cropland and increased with increasing of mean annual temperature (MAT) and mean annual precipitation (MAP). Fallow land enhanced the network complexity of AMF community. The abundance families (Glomeraceae and Paraglomeraceae) exhibited higher values of topological features and were more often located in central ecological positions. Long-term fallow land had a significantly higher hyphal length density, GRSP, mean weight diameter (MWD), geometric mean diameter (GMD), and C concentration of GRSP (C-GRSP) than the cropland. The soil aggregate associated soil organic carbon (SOC) was 16.8, 18.6, and 13.8% higher under fallow land compared to that under cropland at HLJ, JL, and LN study sites, respectively. The structural equation model and random forest regression revealed that AMF diversity, network complexity, and their secreted GRSP mediate the effects of CC and LUC on C-GRSP and aggregate-associated SOC. This study elucidates the climate sensitivity of C within GRSP and soil aggregates which response symmetry to LUC and highlights the potential importance of AMF in C sequestration and climate change mitigation.

Sequestration of heavy metals in soil aggregates induced by glomalin-related soil protein: A five-year phytoremediation field study

Glomalin-related soil protein (GRSP) is an essential bioactive component that may respond to heavy metal stress; however, its exact influence on metal bioavailability and the associated mechanism remains poorly understood. This study investigated the speciation and distribution of heavy metals in soil aggregates associated with GRSP through macroscopic and microscopic approaches. A field study showed that the metal ions were distributed to the macro-aggregate fraction by partitioning the particle size classes during phytoremediation. Partial least squares path modeling (PLS-PM) demonstrated that the heavy metal bioavailability was negatively affected by aggregate stability (61.5%) and GRSP content (52.8%), suggesting that the soil aggregate properties regarding GRSP were vital drivers in mitigating environmental risk closely associated with toxic metal migration in soil–plant systems. The nonideal competitive adsorption (NICA)-Donnan model fitting suggested that GRSP were rich in acid site density, and the complexation with deprotonated groups dominated the speciation of heavy metals in soil. Further, the microfocus X-ray absorption/fluorescence spectroscopy analysis indicated that GRSP might promote the formation of stable metal species by binding with sulfur-containing sites. This study highlights the role of GRSP in heavy metal sequestration in contaminated soils, providing new guidance on the GRSP intervention for phytoremediation strategies.

Mapping the scientific knowledge of glomalin-related soil protein with implications for carbon sequestration

ABSTRACT Arbuscular mycorrhizal fungi (AMF) derived refractory organic matter, mainly in glomalin-related soil protein (GRSP), stores globally significant amounts of carbon, attracting wide attention in response to climatic change. However, there is no synthesis review has been done so far toreveal global research progresses on GRSP, especially its ecological role forclimate mitigation. Here,we conducted a bibliometric analysis of the papers on GRSP research from 1998 to 2021, based on the Web of Science (WOS) Core Collection.We collected a total of 634 papers and analyzed the characteristics of publication outputs in various countries and institutions.In addition, keywords analysis was conducted to reveal the main researchdirections and hot trends in the field of GRSP. We confirmed that 1) the number of papers published per year has gradually increased since 2010, and increased sharply in 2019; 2) the United States was the earliest country to conduct GRSP research, while Chinacurrently has the largest number of publications; 3) relevant studies focus on the role from AMF and GRSP in soil health and plant health; 4) the contribution of GRSP to soil carbon and its ecological function in mitigatingclimate change are the hotspot of research. The benefits of GRSP have become a consensus, however, the nature of glomalin and the mechanisms of GRSP-associated benefits still need to explore. As an important soil recalcitrant organic carbon, further studies are need to elucidate the land-ocean biogeochemical processes of GRSP and its contribution to global blue carbon.

Suppression of arbuscular mycorrhizal fungi increased lead uptake in maize leaves and loss via surface runoff and interflow from polluted farmland

Arbuscular mycorrhizal fungi (AMF) are ubiquitous in farmland. But the knowledge on AMF impact on lead (Pb) migration in farmland is limited. A field experiment was conducted in the rainy season (May–October) for two years in a Pb-polluted farmland. Benomyl was used to specifically suppress the native AMF growth in the farmland. The effect of benomyl-induced AMF suppression on the Pb uptake in maize, and Pb loss via surface runoff and interflows (20 cm and 40 cm depth) from the farmland was investigated. The benomyl significantly inhibited the AMF growth, resulting in decreases in the colonization rate, spore number, and contents of total and easily extractable glomalin-related soil protein (GRSP); and promoted the Pb migration into maize shoots and mainly enriched in leaves. The particulate Pb accounted for 83.2%–90.6% of Pb loss via surface runoff, while the proportion of particulate Pb loss via interflow was decreased and the proportion of dissolved Pb loss increased with the increase of soil depth. The AMF suppression led to a decrease in dissolved Pb concentration and loss, but an increase in particulate Pb concentration and loss, and enhanced the total Pb loss via surface runoff and interflows. Moreover, significant or very significant negative correlations were observed between the AMF colonization rate in roots with the Pb uptake in leaves, and the content of easily extractable GRSP with the particulate Pb loss. These results indicated the native AMF contributed to immobilizing Pb in soil and inhibited its migration to crops and the surrounding environment.

Nitrogen fertilization degrades soil aggregation by increasing ammonium ions and decreasing biological binding agents on a Vertisol after 12 years

Degraded soil aggregation arising from nitrogen (N) fertilization has been reported in many studies; however, the mechanisms have not yet been clarified. Elucidating the impact of N fertilization on soil aggregation would help to improve soil structure and sustain high crop production. The objective of this study was to determine the impact of long-term N fertilization on soil aggregation and its association with binding and dispersing agents. A 12-year (2008–2019) N fertilization field experiment on a Vertisol was performed, covering a wide range of N application rates (0, 360, 450, 540, 630, and 720 kg ha-1 year-1) and including straw management (straw return and straw removal) in a wheat (Triticum aestivum L.)-maize (Zea mays L.) cropping system. Soil samples of 0–20 cm depth were collected from 12 field treatments with 3 replications in 2019. Soil aggregate stability (mean weight diameter (MWD)) and contents of soil organic carbon (SOC), glomalin-related soil protein (GRSP), microbial biomass carbon (MBC), and mineral N (NH4+ and NO3-) were determined. Long-term N fertilization under straw removal conditions reduced soil MWD by 12%–18% at N rates from 0 to 720 kg ha-1 compared to that under straw return (P < 0.05). Soil MWD was positively associated with pH (P < 0.05) and MBC (P < 0.05), but negatively correlated with NH4+ (P < 0.05) and NO3- (P < 0.05). Compared with the straw removal treatment, the straw incorporation treatment significantly improved the contents of aggregating agents (SOC, GRSP, and MBC) (P < 0.001), but did not affect that of the dispersing agent (NH4+) (P > 0.05); consequently, it improved soil aggregation. Overall, our results indicate that long-term N fertilization may degrade soil aggregation because of the increases in monovalent ions (H+ and NH4+) and the decrease in MBC during soil acidification, especially when the applied N dose exceeded 360 kg ha-1 year-1. Our finding can minimize the negative structural impacts on Vertisol.

Arbuscular mycorrhizal fungi inoculation stimulates the production of foliar secondary metabolites in Passiflora setacea DC.

Passiflora setacea DC. growing is of interest to the herbal industries since in its leaves are produced secondary metabolites that confer antioxidant, anxiolytic, and antidepressant properties in Passiflora. Therefore, it is important to search for sustainable alternatives that aim to enhance the production of these compounds to add value to the phytomass, such as the inoculation with arbuscular mycorrhizal fungi (AMF) and the application of coconut coir dust, which has not been reported to P. setacea yet. The aim was to select the efficient combination of AMF and coconut coir dust to increase the compounds' production and optimize the antioxidant activity in P. setacea leaves. The P. setacea seedlings that were cultivated in substrates without coconut coir dust and colonized by Gigaspora albida N.C. Schenck & G.S. Sm. produced more total saponins (1,707.43%), total tannins (469.98%), and total phenols (85.81%), in comparison to the non-mycorrhizal plants, in addition to enhancing the glomalin-related soil proteins. On the other hand, in general, the use of coir dust as a substrate has not been shown to increase the production of these bioactive compounds. It is concluded that the production of P. setacea seedlings using G. albida is an alternative to offer phytomass to the herbal medicines industry based on passion fruit.

Arbuscular Mycorrhizal Fungi and Glomalin Play a Crucial Role in Soil Aggregate Stability in Pb-Contaminated Soil.

With the rapid development of industrialization and urbanization, soil contamination with heavy metal (HM) has gradually become a global environmental problem. Lead (Pb) is one of the most abundant toxic metals in soil and high concentrations of Pb can inhibit plant growth, harm human health, and damage soil properties, including quality and stability. Arbuscular mycorrhizal fungi (AMF) are a type of obligate symbiotic soil microorganism forming symbiotic associations with most terrestrial plants, which play an essential role in the remediation of HM-polluted soils. In this study, we investigated the effects of AMF on the stability of soil aggregates under Pb stress in a pot experiment. The results showed that the hyphal density (HLD) and spore density (SPD) of the AMF in the soil were significantly reduced at Pb stress levels of 1000 mg kg−1 and 2000 mg kg−1. AMF inoculation strongly improved the concentration of glomalin-related soil protein (GRSP). The percentage of soil particles >2 mm and 2–1 mm in the AMF-inoculation treatment was higher than that in the non-AMF-inoculation treatment, while the Pb stress increased the percentage of soil particles <0.053 mm and 0.25–0.53 mm. HLD, total glomalin-related soil protein (T-GRSP), and easily extractable glomalin-related soil protein (EE-GRSP) were the three dominant factors regulating the stability of the soil aggregates, based on the random forest model analysis. Furthermore, the structural equation modeling analysis indicated that the Pb stress exerted an indirect effect on the soil-aggregate stability by regulating the HLD or the GRSP, while only the GRSP had a direct effect on the mean weight diameter (MWD) and geometric mean diameter (GMD). The current study increases the understanding of the mechanism through which soil degradation is caused by Pb stress, and emphasizes the crucial importance of glomalin in maintaining the soil-aggregate stability in HM-contaminated ecosystems.

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

GRSP is widely distributed in coastal wetlands, and there is a tendency for it to degrade with increasing burial depth. However, the dynamic changes in the chemical composition and stability of GRSP during the burial process are still unclear. The purpose of this study is to clarify the chemical composition and accumulation characteristics of GRSP during the burial process in the Zhangjiang estuary. In a field study, soil cores to the depth of 100 cm were collected in the estuary from mangrove forests dominated by Kandelia obovata and Avicennia marina, and from mudflat. The results showed that the concentration of GRSP in mangrove forest soil was significantly higher than that in the mudflat (p < 0.05), and the C/N ratio of GRSP increased with depth at all sites. Analysis of Fourier transform infrared (FTIR) data showed that the degradation rates of the GRSP's compositions varied with increasing burial depth, with microbial action and pH possibly being the main factors affecting degradation. Values of recalcitrance index (RI) showed that the stability of GRSP increased with increasing depth, and the contribution of GRSP to soil organic carbon (SOC) also increased. This suggests that the burial process plays a role in screening and storing the stable components of GRSP. Overall, our findings suggest that the concentration and chemical composition of GRSP vary dynamically according to habitat and burial processes. In addition, the improved stability of GRSP could contribute to carbon sequestration in coastal wetlands.

Distributions and Influencing Factors of Soil Organic Carbon Fractions under Different Vegetation Restoration Conditions in a Subtropical Mountainous Area, SW China

Vegetation type is known to affect soil organic carbon (SOC) storage. However, the magnitudes and distributions of SOC sequestration and driving factors for different vegetation types are still largely unknown. Thus, we studied the changes in SOC fractions along soil profiles for different vegetation restoration types and their relationships with soil properties. We selected five vegetation types and collected soil samples from depth intervals of 0–10, 10–30, 30–60, and 60–90 cm. Five soil carbon fractions and the soil properties were tested to evaluate the soil carbon fraction distributions and influencing factors. Our results demonstrated that the concentrations of total organic carbon (TOC) and five carbon fractions were strongly affected by vegetation types and soil depths. The concentrations of all five soil carbon fractions in 0–10 cm depth were higher than those in the other three soil depths and generally increased with vegetation complexity. The Pearson correlations and redundancy analysis showed that the fractions of soil glomalin-related soil protein (GRSP) and Fe oxides as well as the soil bulk densities, were the most significant related to soil TOC levels and carbon fractions, which suggests that soil biochemical and physicochemical processes are among the most important mechanisms that contribute to SOC persistence. Considering the sensitive indices of the soil carbon variables and PCA results, soil permanganate oxidizable carbon (POXC) was considered to be the most sensitive index for differentiating the effects of vegetation types. These results provide important information regarding the distributions and driving factors of the carbon fractions that result from different vegetation restoration types and will help to improve our understanding of soil carbon sequestration during vegetation restoration processes.

Effects of long-term nitrogen addition and precipitation reduction on glomalin-related soil protein and soil aggregate stability in a temperate forest

As a microbial-derived carbon (C) compound, the glomalin-related soil protein (GRSP) is not only a considerable amount of soil active organic C, but also an effective aggregate binder. At present, due to various global change factors, the forest ecosystem C stock and soil stability are facing unprecedented challenges. As the two of important global change factors, the effects of increased nitrogen (N) deposition, precipitation pattern change and their interaction on the soil organic C (SOC) stock, aggregate stability and GRSP and their correlations are not clear. Based on this, we conducted a long-term field experiment in a temperate forest to simulate N addition and precipitation reduction (n = 3). The experimental design included a control, decreased precipitation (DP), N addition (+N) and their interaction (+N×DP). Compared with the control, the negative effect of N addition on the total GRSP (T-GRSP) was not significant, but it significantly reduced the easily extractable GRSP (EE-GRSP) and mean weight diameter (MWD) (P < 0.05). The T-GRSP, EE-GRSP and MWD all showed significant negative responses to the DP treatment (P < 0.05). Compared with the single treatment, the +N×DP treatment further strengthened the negative effects on the EE-GRSP and MWD (P < 0.05). In addition, we found that the MWD was mainly controlled by large aggregates (>2 mm), and the DP and +N×DP treatments destroyed the seasonal stability of aggregate. The correlation analysis showed that the T-GRSP had a strong correlation with the SOC, while the EE-GRSP had a more significant correlation with the MWD (P < 0.001). Through this study, we emphasized the profound impact of global change factors on temperate forest, clarified the ecological functions of the T-GRSP and EE-GRSP, and confirmed the reciprocal mechanism of the GRSP, SOC and MWD. Collectively, our results will be helpful to evaluate the impact of climate change on forest ecosystems from the perspective of microbial derivatives.

Immobilization of lead(Ⅱ) and zinc(Ⅱ) onto glomalin-related soil protein (GRSP): Adsorption properties and interaction mechanisms

Glomalin-related soil protein (GRSP), a microbial product that can be used as a bioflocculant, is critical to metal sequestration in the ecosystem. However, the relationship between GRSP and heavy metal has not been well explored. In this study, the adsorption behaviors and mechanisms of Pb(II) and Zn(II) ions on GRSP were investigated. Results reveal that the Pb(II) and Zn(II) adsorption closely conform to the pseudo second-order model, which indicates that the chemisorption of GRSP occurred after intra-particle diffusion. The adsorption process is influenced by the degree of pollution, pH value, GRSP content in the environment. In addition, scanning electron microscopy coupled with microanalysis (SEM-EDX) reveals that the surface structure of GRSP is irregularly blocky or flaky and metal ions are uniformly distributed on the surface of GRSP. Fourier transform infrared (FT-IR), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD) analysis show that the carboxyl and nitro groups on GRSP act as ligands to form complexes with two divalent metal ions. The interaction between GRSP and the metals is mainly surface complexation. This research further reveals the dynamic response of its structural components when GRSP sequestrates heavy metals in mangrove sediment and aqueous ecosystems, demonstrating a new perspective for the transport and transformation of heavy metals onto GRSP.

Glomalin: A Miracle Protein for Carbon Sequestration

AMF (Arbuscular mycorrhizal fungi)’s hyphae and spore walls releases a special kind of glycoprotein i.e. Glomalin. AMF belongs to the phylem Glomeromycota which was previously known as Zygomycota. There exists a symbiotic relationship of this fungi with terrestrial plants (~80%), that includes major commercial species viz. wheat, sorghum, corn, and forage species. AMF strongly binds and firmly hold the walls of hyphae and spores. On decomposition of hyphae, glomalin is released in soil. Glomalin depicts recalcitrant behavior and hydrophobic characteristics, and hence prevent the loss of water and nutrients from hyphae (ERM). It can remain as such in soil for years. It’s half-life in soil can vary from 6-42 years thus placing it in the category of stable biomolecules. Glomalin Related Soil Protein (GRSP) is quite abundant in wide range of soil The GSRP were found in relative abundance in a wide range of soils (2-15 mg g-1), whether it is acid or calcareous or under various crops, such as cereals, vegetables, forage, and agroforestry systems. It plays a significant role in enhancing the soil organic carbon as it acts as an effective carbon sink. It possess strong cementing ability and hence binds the aggregates to enhance structural stability and prevent loss of carbon and nitrogen. GRSP positively correlates with the carbon present in soil.

Differential Response of Soil Microbial Diversity and Community Composition Influenced by Cover Crops and Fertilizer Treatments in a Dryland Soybean Production System

The response of soil microbial communities to management practices is composite, as it depends on the various environmental factors which contribute to a shift in the microbial communities. In this study we explored the impact of combinations of soil management practices on microbial diversity and community composition in a dryland soybean production system. Soil samples were collected from the experimental field maintained under no till, cover crops, and fertility treatments, at Pontotoc Ridge-Flatwoods Branch Experiment Station, MS, USA. Targeted amplicon sequencing of 16S rRNA and ITS2 genes was used to study the bacterial and fungal community composition. Poultry litter amendment and cover crops significantly influenced soil bacterial diversity. Fertilizer sources had significantly different bacterial communities, as specific microbial taxa were strongly influenced by the changes in the nutrient availability, while cover crops influenced the soil fungal community differences. Differential enrichment of advantageous bacterial (Proteobacteria, Actinobacteria and Acidobacteria) and fungal (Mortierellomycota) phyla was observed across the treatments. Soil pH and easily extractable glomalin-related soil proteins (EE-GRSP) were correlated with bacterial communities and aggregate stability (WSA) was influenced by the poultry litter amendment, thus driving the differences in bacterial and fungal communities. These findings suggest that a long-term study would provide more inferences on soil microbial community response to management changes in these dryland soybean production systems.

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.

Crop\u2013livestock integration enhanced soil aggregate-associated carbon and nitrogen, and phospholipid fatty acid

Integrated crop–livestock (ICL) production enhances diversification and provides ecosystem benefits by improving nutrient cycling and energy efficiency, thus, increasing overall farm productivity. However, a detailed study is needed to understand the influence of crop diversification and grazing animals on soil aggregation and associated carbon (C) and nitrogen (N), and microbial properties, especially compared with a grazed native pasture. We investigated the soil aggregate size distribution and associated C and N fractions, glomalin-related soil protein, and soil phospholipid fatty acid (PLFA) to understand the collective influence of livestock grazing of crop residue and cover crops (CC) and compared it with native pasture and non-grazed traditional production systems. The study was conducted in South Dakota at four different locations consisting of three long-term (> 30 years) on-farm sites: 1 (Salem), 2 (Bristol), 3 (Bristol) with three treatments that included ICL (corn, Zea Mays L.-soybean, Glycine max L.-oats, Avena sativa L.-CC with cattle grazing); natural ecosystem (NE) or native pasture; and control (CNT) (corn–soybean-without grazing or CC). Experimental site 4 (Beresford) with study duration of 3-year consisted of oats, oats with CC, oats with CC + grazing, and grazed pasture mix. Soil samples were collected from 0 to 5 cm depth at all four sites in summer 2019. Data showed that at sites 1 and 2, ICL had significantly (P ≤ 0.5) greater fractionation of 0.053–0.25 mm and > 4 mm aggregates compared with NE and CNT. At site 1, ICL showed significantly higher soil organic carbon (SOC, 36–49%) and higher nitrogen (33–44%) in > 4 mm aggregates than NE and CNT. At site 2, ICL had 32–41% higher SOC than NE and CNT for 0.25–0.5 mm aggregates. At site 1, NE enhanced total phospholipid fatty acid (PLFA), total bacterial biomass, gram (+), gram (−) bacteria than CNT, however, it did not vary significantly than ICL. Grazed pasture mix at site 4 had higher total PLFA (40.81 nmol g−1 soil) than the other treatments. The principal components 1 and 2 accounted for 33% and 22% of the variation, respectively, where the majority of the microbial compositions and aggregate-associated C and N were influenced by ICL and NE compared with corn–soybean without grazing or short-term oats/CC/grazing treatments. Integrated crop–livestock system and NE enhanced C and N concentrations in macroaggregates as well as in microaggregates. It is concluded that ICL and NE systems are sustainable prospects in enhancing overall soil health. Integrating crop and livestock improved physicochemical and microbial properties compared to the traditional corn–soybean system.

Long-term moderate carbon input benefited arbuscular mycorrhizal fungal community diversity and vitality in a sandy loam soil

Soil arbuscular mycorrhizal (AM) fungi play crucial roles in facilitating agroecosystem functioning. However, little is known about their performances in either community composition or ecological function as affected by fertilization with different carbon (C) input levels. Here, an eight-year field experiment established in a sandy loam soil at Northern China, including four treatments of non-fertilization (Control), and NPK-balanced fertilization with no C (F), with relatively low C input level (LCF), and with relatively high C input level (HCF), was adopted to assess soil AM fungal community composition using the Illumina sequencing. Ten genera with the dominance of Glomus followed by Paraglomus and Claroideoglomus were identified, and the communities varied significantly between control and fertilized soils. Long-term fertilization, notably LCF and HCF, increased soil AM fungal diversity, alkaline phosphatase (ALP) activity, and glomalin-related soil protein (GRSP) concentration, which were closely correlated to soil organic C and/or pH. In addition, LCF rather than HCF significantly increased both Chao1 and Shannon indices of AM fungi relative to F, while HCF rather than LCF significantly decreased not only the mycorrhizal colonization relative to control but also the ratio of total GRSP to soil organic C relative to F, suggesting that LCF is better with respect to promoting AM fungal diversity and maintaining their ecological vitality. Our study demonstrated the great value of moderate C input in conserving soil AM fungi and exploring their services.

Short-term modifications of mycorrhizal fungi, glomalin and soil attributes in a tropical agroforestry

Arbuscular mycorrhizal fungi (AMF) community and the Glomalin-related soil protein (GRSP) they produce plays important roles in maintaining soil ecosystem functions, promoting ecological restoration, and are important for monitoring changes in soil health from land use change. This research addressed the subtle modifications of AMF and GRSP in different land use types and their association with soil properties. Our objectives were: 1) to assess land use effects on AMF spore density, diversity, and composition besides glomalin fractions (EEG, easily extracted GRSP; TG, total GRSP), and 2) to quantify the relationships between glomalin, AMF community metrics, soil organic carbon (SOC), and key soil quality parameters. Soils were collected in the dry and rainy seasons of 2018 under five land uses, including: three types of agroforestry systems (AS1, AS2 and AS3), an unmanaged pasture and a secondary forest in the state of Rio de Janeiro, Brazil. Linear mixed-effects model and multivariate analyses showed that land uses had influenced the AMF community, meanly at the family level. On the other hand, seasonality has not proved to be an essential factor that modulates the changes of the AMF community and glomalin production. The management practices had influenced AMF sporulation and the number of total species in agroforestry systems. Glomalin is a potential contributor for SOC, mainly in agroforestry systems and pasture plots. Moreover, we found a correlation between the AMF community and key soil parameters. For example, most of the AMF families and spore density were positively correlated with the stability of soil aggregates and SOC. Our findings shed light on that land-use change can shift the AMF community, glomalin and their relationship to key soil quality parameters. Moreover, the adoption of agroforestry systems indicates maintenance of biodiversity and other soil quality parameters with future implications for their use to recover degraded areas.

Accumulation of glomalin‐related soil protein benefits soil carbon sequestration: Tropical coastal forest restoration experiences

AbstractMany tropical coastal areas experience severe soil erosion due to heavy rainfall, especially after deforestation. Glomalin‐related soil protein (GRSP), the product of arbuscular mycorrhizal fungi (AMF), improves soil structure and soil organic carbon (SOC) sequestration with vegetation restoration. Therefore, the contribution of GRSP to soil property improvement in a tropical coastal area was studied for four different restoration practices: a barren land (BL, unrestored control), a Eucalyptus exserta planted forest (EF), a mixed broadleaved forest (MF), and a secondary natural forest (SF). Results showed that vegetation restoration practices increased easily‐extractable GRSP (EE‐GRSP) and total GRSP (T‐GRSP) by 3.9–12.3‐ and 1.9–4.6‐times, respectively, compared with BL. The proportions of EE‐GRSP/SOC and T‐GRSP/SOC were 1.6%–2.0% and 6.5%–15.8%. The concentrations of GRSP, SOC, and the GRSP/SOC ratio were similar or greater under MF than under SF. 13C NMR analysis showed that the relatively easily degradable O‐alkyl‐C of SOC was significantly higher under MF than under EF and SF, while the recalcitrant aromatic‐C or alkyl‐C were highest under SF or EF, respectively. A significantly positive relationship was found between the GRSP/SOC ratio and aromatic‐C, and between GRSP and soil aggregate stability. Our study indicates that GRSP contributes to a large proportion of SOC, and benefits SOC sequestration through increasing soil aggregate stability and recalcitrant SOC. Among these artificial or naturally growing forest areas, a mixed forest restoration practice with native tree species provides a promising restoration strategy for heavily eroded land restoration, in particular improving soil aggregation and SOC sequestration.

Effect of 50 Years of No-Tillage, Stubble Retention, and Nitrogen Fertilization on Soil Respiration, Easily Extractable Glomalin, and Nitrogen Mineralization

In subtropical regions, we have an incomplete understanding of how long-term tillage, stubble, and nitrogen (N) fertilizer management affects soil biological functioning. We examined a subtropical site managed for 50 years using varying tillage (conventional till (CT) and no-till (NT)), stubble management (stubble burning (SB) and stubble retention (SR)), and N fertilization (0 (N0), 30 (N30), and 90 (N90) kg ha−1 y−1) to assess their impact on soil microbial respiration, easily extractable glomalin-related soil protein (EEGRSP), and N mineralization. A significant three-way tillage × stubble × N fertilizer interaction was observed for soil respiration, with NT+SB+N0 treatments generally releasing the highest amounts of CO2 over the incubation period (1135 mg/kg), and NT+SR+N0 treatments releasing the lowest (528 mg/kg). In contrast, a significant stubble × N interaction was observed for both EEGRSP and N mineralization, with the highest concentrations of both EEGRSP (2.66 ± 0.86 g kg−1) and N mineralization (30.7 mg/kg) observed in SR+N90 treatments. Furthermore, N mineralization was also positively correlated with EEGRSP (R2 = 0.76, p &lt; 0.001), indicating that EEGRSP can potentially be used as an index of soil N availability. Overall, this study has shown that SR and N fertilization have a positive impact on soil biological functioning.

Extraction and purification of glomalin-related soil protein (GRSP) to determine the associated trace metal(loid)s

Glomalin-related soil protein (GRSP) is recalcitrant compound in the soil and sediment and plays a crucial role in metal transportation. However, potential metal speciation changes during GRSP extraction remain unreported. Here, a feasible GRSP extraction and purification procotol is described for robust determination of GRSP-bound metal(loid)s. Several spectrum patterns measured before and after GRSP extraction indicate that the GRSP extraction process does not significantly affect the mineral state of the samples. Potential bias generated by simultaneous metal release during GRSP extraction can be effectively eliminated by applying complete and independent dialysis.•Na signal appeared in the X-ray photoelectron survey spectrum after GRSP extraction, suggesting that Na exchange may be a critical process in releasing metal(loid)s.•Element maps obtained using secondary ion mass spectroscopy exhibited different distribution of C-N and Fe after GRSP extraction, thus suggesting that uncoupling of the Fe-organic framework occurred during GRSP extraction, which could result in the release of organic matter and metal(loid)s.•European Community Bureau of Reference (BCR) subsequent extraction reveals that most of the metal(loid)s were extracted from the acid-exchangeable and residual fraction during GRSP extraction. Remarkable differences in the GRSP-bound metal content before and after dialysis implied that the dialysis could remove most metal(loid)s.