Glomalin-related Soil Protein Content Research Articles

Spatial Changes in Glomalin-Related Soil Protein and Their Correlation with Soil Properties in the Black Soil Region of Northeast China

Glomalin-related soil protein (GRSP), soil nutrients, and soil enzyme activities are closely related to soil fertility and land productivity, which play an important role in indicating soil quality. Little is known about the spatial variation in GRSP and its relationship with edaphic factors. Here, the spatial distribution of GRSP, soil chemical properties, and the soil enzyme activities of 0–20 cm depth farmland soil in the black soil region of northeast China were investigated, and the relationships among edaphic factors were analyzed collected from 41 sampling sites. The results indicate that GRSP, soil organic matter, total nitrogen, and acid phosphatase activities showed significant patterns of spatial variation, generally decreasing from north to south along a latitudinal gradient. Principal component analysis revealed that total GRSP (by 80.19%) and soil organic matter content (by 80.15%) were the greatest contributing factors accounting for the variations. Edaphic factors such as soil organic matter, total nitrogen, total phosphorus, and acid phosphatase were significantly positively correlated with GRSP, while urease was negatively correlated with GRSP. Mantel tests also showed that soil organic matter, total nitrogen, urease, and acid phosphatase were positively correlated with GRSP. The results reflect the soil fertility characteristics of the black soil region of northeast China and reveal the relationship among edaphic factors. These findings could be used to inform agricultural production and provide new insight into the role of GRSP in soil quality.

Effects of urbanization intensity on glomalin-related soil protein in Nanchang, China: Influencing factors and implications for greenspace soil improvement.

Glomalin-related soil protein (GRSP) is a stable and persistent glycoprotein secreted by arbuscular mycorrhizal fungi that plays an important role in sequestering soil organic carbon (SOC) and improving soil quality. Rapid urbanization disturbs and degrades the soil quality in the greenspace. However, few studies have investigated the effects of urbanization on GRSP and its influencing factors. This study selected impervious surface area as a measure of urbanization intensity. A total of 184 soil samples were collected from the 0-20cm soil layer in the greenspace of Nanchang, China (505km2). The GRSP content, soil properties, urban forest characteristics, and land-use configuration were determined. The total GRSP (TG) and easily extractable GRSP (EEG) contents were 2.38 and 0.57mgg-1, respectively. TG and EEG decreased by 16.22% and 19.35%, respectively, from low to heavy urbanized areas. Moreover, SOC decreased from 39.9 to 1.4mgg-1, while EEG/SOC and TG/SOC increased by approximately 17% and 34%, respectively, indicating the significant contribution of GRSP to the SOC pool. Pearson and redundancy analysis showed that GRSP was positively correlated with SOC, phosphorus, nitrogen, vegetation richness, and tree height, but negatively correlated with pH, bulk density, and impervious area. The partial least squares path model demonstrated that urbanization affected soil properties, forest characteristics, and land use factors, resulting in GRSP changes. This study clarifies the key factors of urbanization that affect GRSP and provides insight for urban greenspace soil improvement from the new perspective of enhancing the GRSP content.

Linking the chemical nature of soil organic carbon and biological binding agent in aggregates to soil aggregate stability following biochar amendment in a rice paddy

Changes in soil aggregation with biochar amendment have been investigated extensively, but how biochar affects the chemical composition of organic carbon (C) and biological binding agents in aggregates and their linkage with soil aggregate stability remains unclear. Soil samples were collected in a rice paddy treated with 0 (C0, control), 10 t ha−1 (C10), 20 t ha−1 (C20) and 40 t ha−1 (C40) biochar for twenty months. The amount and chemical composition of soil organic C (SOC), microbial abundances and glomalin-related soil protein (GRSP) were determined in bulk soil and four fractions: large macroaggregates (>2000 μm), small macroaggregates (250–2000 μm), microaggregates (53–250 μm), and silt + clay (<53 μm). Our results showed that the proportion of >250 μm water-stable aggregates and mean weight diameter were gradually increased with increasing biochar addition rate. The concentrations of SOC, readily oxidizable C and microbial biomass C increased most in the small macroaggregates, followed by microaggregates under biochar amendment. Increasing biochar addition rate gradually decreased the relative contents of alkyl C, O-alkyl C and carbonyl C, but increased those of aromatic C across the aggregates, resulting in a higher aromaticity and hydrophobicity of SOC with respect to the control. The abundances of bacteria, fungi and archaea and the content of GRSP were significantly enhanced in the large and small macroaggregates under the C40 treatment. The proportion of >250 μm aggregates was significantly correlated with the contents of soil organic C fractions, GRSP and microbial abundance. Structural equation modeling further revealed that changes in SOC hydrophobicity and GRSP content under biochar amendment had significant and direct effects on the soil aggregate size distribution. In summary, our findings suggest that biochar amendment in rice paddy could improve soil aggregation through altering the chemical composition of soil organic C and the abundance of biological binding agents.

Inhibition of native arbuscular mycorrhizal fungi induced increases in cadmium loss via surface runoff and interflow from farmland

Arbuscular mycorrhizal fungi (AMF) can form symbiotic relationships with most crops, but their impact on the environmental migration of cadmium (Cd) in farmland is limited. A field experiment was performed in the rainy season (May–October) for two years in Cd-polluted farmland used for maize cultivation. A fungicide (benomyl) was used to specifically inhibit native AMF growth in the farmland. The growth and Cd uptake of maize and the Cd concentration and loss in runoff and interflow were investigated. Benomyl strongly and significantly inhibited AMF colonization rate in maize roots, reduced the contents of total and easily extractable glomalin-related soil protein (GRSP) in soil and the Cd uptake in maize roots, and increased the Cd uptake in shoots. Particulate Cd was the main form of Cd loss in runoff, while dissolved Cd was the main form of Cd leaching loss at depths of 20 cm and 40 cm. Inhibiting AMF increased the Cd concentration in runoff and interflow and promoted dissolved Cd loss in runoff and interflow at 20 cm depth by 34.7% and 68.0% and particulate Cd loss by 46.4% and 19.7%, respectively. Furthermore, the AMF colonization rate in maize roots and the GRSP content in soil were significantly positively correlated with Cd uptake in roots and negatively correlated with the concentration and loss of Cd in runoff and interflow. These results indicated that the benomyl-induced inhibition of native AMF promoted Cd transfer to maize shoots and increased Cd loss via runoff and interflow from polluted farmland.

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.

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.

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.

Efeitos micorrízicos nos teores de proteína do solo relacionada à glomalina e de clorofila em cafeeiro na Amazônia peruana

ABSTRACT The inoculation of vegetatively propagated coffee plants with arbuscular mycorrhizal fungi (AMF) prior to field establishment may positively influence the plant growth and physiology. This study aimed to evaluate the AMF effects on the glomalin-related soil protein and chlorophyll contents in vegetatively propagated coffee plants inoculated in a greenhouse and transplanted to an open field, in the Peruvian Amazon. The experiment consisted of eight treatments, in a 2 × 4 factorial design, being two coffee varieties (Caturra and Pache) and four AMF inocula (control, Moyobamba, El Dorado and Huallaga). The inocula were collected from organic coffee crops and named according to the province from which they were collected. The mycorrhizal colonization and chlorophyll content were statistically higher in the plants inoculated with AMF, if compared to the non-inoculated plants, while the glomalin-related soil protein content ranged from 61.6 to 69.1 mg g-1 and showed no statistically significant differences among the inocula, although the Moyobamba inoculum showed to be numerically superior. The effect of the coffee variety was not statistically significant among the variables under study.

Earthworm (Pheretima guillelmi)-mycorrhizal fungi (Funneliformis mosseae) association mediates rhizosphere responses in white clover

Earthworms and arbuscular mycorrhizal fungi (AMF) are beneficial organisms in the soil and play an important role in improving soil fertility and plant growth. The objective of this study was to analyze the response of single versus dual inoculation of earthworms (Pheretima guillelmi) and AMF (Funneliformis mosseae) on mycorrhizal growth, root morphology, and rhizosphere properties of white clover (Trifolium repens). Addition of earthworms significantly increased the degree of root AMF colonization, while decreased hyphal length and spore number in the soil. Single or dual inoculation of F. mosseae and P. guillelmi significantly increased root traits (total length, area, volume, and average diameter), soil phosphatase activities (acid, neutral, and alkaline), easily extractable and total glomalin-related soil protein content, the percentage of soil water-stable aggregates at the size of 2–4 mm, 1–2 mm and 0.5–1 mm, aggregate stability, Bray-P, and soil organic carbon (SOC) contents. Among them, the dual inoculation further amplified the effect on glomalin production, phosphatase activity, and aggregate stability, but did not show a superposition effect on root improvement, Bray-P, and SOC. Our study, hence, suggested that AMF and earthworms have synergistic roles in elevating rhizosphere properties vis-à-vis agronomic responses of white clover.

Field Inoculation of Arbuscular Mycorrhizal Fungi Improves Fruit Quality and Root Physiological Activity of Citrus

Soil arbuscular mycorrhizal (AM) fungi form a mutualistic symbiosis with plant roots and produce many benefits on host plants under potted conditions, while field inoculation of AM fungi on citrus (a woody plant) has been rarely reported. The present study aimed to analyze the changes in mycorrhizal growth, root vitality, and fruit quality of Citrus reticulata Blanco var. Ponkan mandarin cv. Jinshuigan grafted on Poncirus trifoliata L. after inoculation with a mix of AM fungi (Diversispora versiformis, Funneliformis mosseae, and Rhizophagus intraradices) and single F. mosseae. After the second year of AM fungal inoculations, root mycorrhizal colonization (%), root vitality, hyphal length in soil, and easily extractable glomalin-related soil protein content were significantly increased, while difficult-to-extract glomalin-related soil protein content was decreased. Two mycorrhizal fungal inoculation treatments collectively improved fruit quality parameters such as polar diameter, equatorial diameter, the weight of single fruits, fruit peel, and sarcocarp, coloration value, and soluble solids content. Our study, therefore, suggested that field inoculation with AM fungi improved root physiological activities in terms of mycorrhizal growth and root vitality and thus improved fruit quality. The effect of mixed-AM treatment was more significant than that of F. mosseae alone.

Contrasting effects of long term phosphorus fertilization on glomalin-related soil protein (GRSP)

Glomalin-related soil protein (GRSP) is believed to be produced by arbuscular mycorrhizal fungi (AMF). However, this fraction of organic matter is influenced by various soil and land-use parameters and its link with AMF has been questioned. The aim of this study was to advance the understanding of the origin of GRSP and its value as a marker of AMF activity by focusing on the effects of soil P status. Archived soils from two phosphorus fertilization field trials on sandy soils under maize cultivation in the south-west of France were studied. Trends in GRSP and soil organic carbon (SOC) were compared. Grain yield and available P (Olsen-P) were monitored and compared to assess P sufficiency/limitation. The time trends of GRSP for each site were not significant. No significant P-fertilization effect on GRSP was observed for the P-sufficient continuously cropped soil, for which the crop yield increase was small. For the P-deficient, former forest soil, P fertilization led to a marked increase in crop production and a significantly larger GRSP content. These trends are coherent with GRSP input linked to crop C-inputs, including the incorporation of crop residue.

Dynamics of arbuscular mycorrhizal fungi and glomalin in the rhizosphere of Gymnocarpos przewalskii in Northwest Desert, China

Relict plants, remnants of Tertiary flora, survived geochronological ages, however, studies intended to ascertain the background of their fungal symbionts are limited. Different from many other relict plants, Gymnocarpos przewalskii Maxim. inhabits arid deserts region, mainly distributed in northwest China. In order to inquire the arbuscular mycorrhizal fungi (AMF) associated to G. przewalskii and their ecological significance in desert ecosystems, the seasonal dynamics of AMF and glomalin were surveyed in Anxi and Minqin in Gansu Province, northwest China. Soil samples in the rhizosphere of G. przewalskii were collected in July, September and December 2019, respectively. In total, 41 and 46 AMF species were identified via morphological techniques in Anxi and Minqin, respectively. Meanwhile, high throughput sequencing (HTS) data diagnosed 29 and 61 AMF OTUs in Anxi and Minqin, respectively. Glomus was the dominant genus in different seasons and locations in both morphological investigation and HTS data. AMF colonization (44.67–75.30%) and spore densities (19–248 per 20 g soil) varied sharply among seasons and locations. AMF colonization and spore densities showed significant positive correlations to most edaphic factors, except soil carbon: nitrogen ratio. Glomalin-related soil protein (GRSP) dramatically contributed to local soil carbon pool (51.54% in Anxi, 40.37% in Minqin), and the GRSP contents in soil were significantly affected by soil properties, season, and location. Random forest analysis indicated that soil humidity and total GRSP were the main factors shaping AMF communities. Our results showed that AMF colonization, spore density, and species diversity were higher and AMF community composition was less variable in Minqin where the soil nutrition levels were lower, which emphasized the necessity of AMF symbiosis for plants in harsh environments. The present research demonstrated the seasonal dynamics of soil AMF communities and glomalin and determined influential environmental factors in desert ecosystems. Our findings provide novel views on desert soil resource management and relict plant protection from an aspect of plant-AMF symbiosis.

Effect of root‐glomalin on soil carbon storage in trees' rhizosphere and interspace of a tropical dry forest

AbstractIncreasing soil organic carbon (SOC) concentration is a desirable aspect of afforestation. Glomalin‐related soil protein (GRSP) is a ubiquitous component of SOC, preferentially produced by arbuscular mycorrhizal fungi (AMF) during symbiotic association with the plant roots. Although the role of AMF in GRSP production is well established, the role of root in GRSP production is not yet clear. Hence, we aimed to assess the glomalin in different tree roots (i.e., glomalin‐related root protein; GRRP) and its influence on GRSP and SOC storage in trees’ rhizosphere and interspace. The experiment was conducted in a tropical dry forest (India) with six native trees (Hardwickia binata, Lagerstroemia parviflora, Diospyros melanoxylon, Terminalia tomentosa, Shorea robusta, and Anogeissus latifolia) and a planted Teak (Tectona grandis). The fine roots (from the rhizosphere) and topsoils (0–15 cm) were collected from the rhizosphere and interspace of each tree. We found GRRP concentration varying between trees, with higher values observed in the roots of native trees than those of Teak. The AMF colonization was positively correlated with GRRP (r2 = 0.88), and GRRP positively correlated with GRSP and SOC. The higher correlation of GRRP was observed with GRSP (r2 = 0.70–0.79) compared with SOC (r2 = 0.56–0.58), while the correlation was much stronger between GRSP and SOC (r2 = 0.91). These results indicate that GRRP influences SOC storage via mediating GRSP concentration. We suggest that GRRP can be used as an indicator for species screening during afforestation with the aim to improve SOC storage on an afforested landscape.

Responses of soil microbial community composition and enzyme activities to long-term organic amendments in a continuous tobacco cropping system

Organic amendment may be an effective management practice for alleviating soil degradation in continuous cropping systems. However, few studies focus on the effects of long-term organic amendments on soil microbial community and microbial nutrient status in continuous tobacco fields. Here, an 11-year field experiment was conducted to investigate the effects of organic amendments on plant and soil physiochemical properties, microbial communities, ecoenzymatic stoichiometry, and glomalin-related soil protein (GRSP) accumulation in a continuous tobacco field. Five treatments were applied: CK (no fertilizer); CF (chemical fertilizer only); CFS (chemical fertilizer plus corn straw); CFO (chemical fertilizer plus oilseed residues); CFM (chemical fertilizer plus composted pig manure). Organic amendments increased soil microbial abundances. Application of organic fertilizers significantly reduced gram-positive to gram-negative bacterial ratios, but significantly increased fungi/bacteria ratios, probably because gram-negative bacteria and fungi are the dominant decomposers of increased available nutrients and recalcitrant materials, respectively. Organic amendments significantly enhanced soil enzyme activities, except for the difference in β-1,4-N-acetylglucosaminidase, Leucine aminopeptidase, and polyphenol oxidase (PPO) activities between the CF and CFO. The lowest soil organic carbon (SOC) content in CFS among organic amendments treatments was probably because the positive priming effects of straw and the highest peroxidase and PPO activities increased stable SOC mineralization rates due to the high C:N:P ratio of nutrients input. Microbial activities were limited by carbon, nitrogen, and phosphorus in CFS, while carbon and phosphorus were the limiting factors in CK, CF, CFO, and CFM. Relative to CF, CFO significantly enhanced microbial carbon and phosphorus limitation, whereas CFM significantly decreased microbial carbon limitation. CFM had the highest GRSP content among treatments. Our results demonstrated that combined application of composted pig manure and chemical fertilizers is a consistently effective measure for alleviating soil degradation in continuous tobacco fields.

Mycorrhizal Fungal Diversity and Its Relationship with Soil Properties in Camellia oleifera

Arbuscular mycorrhizal fungi (AMF) are well known for their important physiological implications on diversified host plants, while the information on AMF diversity and its relationship with soil properties of Camellia oleifera is yet not fully understood. In the proposed study, high-throughput sequencing of small subunit ribosomal RNA was performed to analyze the AMF diversity of the rhizosphere and endosphere of 20-year-old C. oleifera Xianglin in the field at Wuhan (China) and their relationship with soil physico-chemical properties. As high as 30.73–41.68% of the roots of C. oleifera were colonized by indigenous AMF with a spore density of 66–111 spores/10 g soil. The surface soil (0–20 cm) showed significantly higher root fungal colonization, spore density, soil hyphal length, and easily extractable glomalin-related soil protein content than the sub-surface soil (20–40 cm). Soil pH value, available K, and NO3−-N content affected the root and soil mycorrhizal development, whilst soil pH proved to be the most influential soil property governing their variability. A total of 467 OTUs associated with AMF were detected from the endosphere and rhizosphere, representing 10 genera and 138 species, of which 295 OTUs and 9 genera were jointly observed. The genus Glomus displayed maximum relative abundance (&gt;86%) in both endosphere and rhizosphere. Scutellospora was detected in the endosphere, but absent in the rhizosphere. The endosphere recorded a relatively higher number of OTUs and alpha diversity indices (Shannon, Simpson, and PD index) of AMF than rhizosphere. Our study, hence, revealed that C. oleifera in fields was mainly colonized by Glomus, coupled with comparatively greater AMF diversity in the endosphere than in the rhizosphere, governed predominantly by soil pH, NO3−-N content, and available K content.

Glomalin-related soil protein analysis and its role in erodibility in a semiarid zone in San Luis Potosi, Mexico

The relationship between erodibility (susceptibility to erosion) and soil biological parameters has not been thoroughly investigated in Palomas Valley (PV), a region in San Luis Potosí, México that includes gully-eroded microcatchments. Previous reports have shown the potential of Glomalin-related soil protein (GRSP) as an erodibility marker. Thus, our first goal was to develop an optimized autoclaving-free extraction method for GRSP suitable for 1D-SDS-PAGE analysis. Samples from horizon A (0–10 cm) were collected in three sites in PV. Total GRSP and organic matter contents were obtained, and GRSP was used for correlation analysis (Pearson correlation coefficient) with the K factor, an erodibility index. Our novel total protein-extraction method allowed to obtain moderated resolution electrophoretic patterns and GRSP detection was achieved by molecular weight comparison. GRSP contents ranged 11–203 μg·g−1 soil, and organic matter contents ranged from 2.1 to 12.8%. A multiple regression analysis was performed, obtaining a strong correlation (R = 0.79; R2 = 0.63) among organic matter and GRSP contents and K factor. The results suggested a strong dependence of K from organic components, mainly from GRSP. This is the first time that K factor and GRSP correlation analysis has been reported. Also, this work provides interesting data that could improve the analysis of factor K. All these results suggest GRSP content may play an important role in soil erodibility, but further research is required.

Deciphering the dynamics of glomalin and heavy metals in soils contaminated with hazardous municipal solid wastes

Heavy metals (HMs) accumulation in the soils poses risks towards the environment and health. Glomalin related soil protein (GRSP) produced by arbuscular mycorrhizal fungi (AMF) has metal-sorption and soil aggregation properties and is critical in the survival of plants and AMF. For the first time, this study attempted to examine the GRSP mediated bio-stabilization of HMs in soils contaminated with municipal solid wastes (MSW). The content and interrelationship of GRSP and HMs, along with soil physicochemical properties were studied in 20 different soil samples from the dumping site. Higher amount of GRSP indicated potential bio-stabilization of HMs at some sites. GRSP exhibited weak positive correlation with essential (Zn, Cu) and toxic HMs (Cd, Ni). Cr and Mn were possibly sequestered in AMF structures and thus found to be negatively correlated with GRSP. The positive correlation observed between GRSP and soil nutrients like N, P and soil organic carbon (SOC) indicating potential of AMF-GRSP in sustaining soil health. Results revealed that AMF residing at contaminated sites produced higher amount of GRSP potentially to bio-stabilize the HMs, and reduce their bioavailability and also facilitate SOC sequestration.

Effects of residue stoichiometric, biochemical and C functional features on soil aggregation during decomposition of eleven organic residues

Soil aggregation is deeply impacted by the quality of organic materials. However, the organic material features that control soil aggregation dynamics are still largely unknown. In this study, a total of 11 organic residues including vetch (alfalfa, hairy, and Chinese milk), straw (rice, maize, wheat, miscanthus, soybean, and sorghum) and manures (cattle and pig) were characterized by stoichiometric, biochemical and C functional features. The soil respiration, mean weight diameter (MWD) and glomalin-related soil protein (GRSP) levels were measured during 56 d of incubation. The results showed that stoichiometric features had no impact on soil respiration and aggregate stability except the N content. Residue decomposition was positively affected by soluble sugars but negatively affected by lignin and cellulose in the first 14 d (P < 0.05). Soluble sugars positively influenced the MWD up to 28 d, and cellulose continued this effect at 56 d (P < 0.05). Soil respiration and MWD were positively associated with alkyl and carbonyl C but negatively related to the alkyl and di-O-alkyl C fractions in the first two weeks, while adverse effects on the MWD were found at 56 d of incubation (P < 0.05). Organic residue input increased the GRSP level in the order of manure > straw > vetch. The GRSP content had a negative effect on the MWD up to 28 d (P < 0.05) but was not related at 56 d of incubation. Overall, high levels of soluble sugars of residues resulted in transient aggregate stability, but persistent aggregate stability was mainly contributed by the cellulose, O-alkyl C and di-O-alkyl C features.

Effects of atrazine application on soil aggregates, soil organic carbon and glomalin-related soil protein

Atrazine is still widely used in China. Atrazine residue (1.86–1 100 mg/kg) in the soil has exceeded the allowable limit (1.0 mg/kg), affecting soil structure and soil aggregate composition. To understand the long-term application of atrazine on soil aggregates and the binding agent, four treatments were established in cornfield planted since 1998, including without atrazine applied (AT&lt;sub&gt;0&lt;/sub&gt;), atrazine applied (28% atrazine, 1 200–1 350 mL/ha/year) once a year from 2012 to 2018 (AT&lt;sub&gt;6&lt;/sub&gt;, 167 mg/kg), from 2008 to 2018 (AT&lt;sub&gt;10&lt;/sub&gt;, 127.64 mg/kg) as well as from 2002 to 2018 (AT&lt;sub&gt;16&lt;/sub&gt;, 102 mg/kg) with three replications. Along with the increase of atrazine application time, the mass fraction of soil aggregates &amp;gt; 5 mm and 2–5 mm decreased significantly while the mass fraction of soil aggregates 0.5–2 mm and &amp;lt; 0.5 mm increased gradually, and the change of aggregate binding agents contents were the same as that of aggregates. The contents of soil organic carbon (SOC) and glomalin-related soil protein (GRSP) in the aggregates &amp;gt; 5 mm and 2–5 mm were significantly negatively correlated with the years of atrazine application. Our results show that although atrazine residue in the soil does not increase with the increased yearly application, its concentration is still markedly higher than the permitted limit value and seriously affected the content of SOC and GRSP of aggregates &amp;gt; 2 mm, which can lead to a decrease of soil aggregate stability and soil quality.

Co-inoculation of Arizona cypress with mycorrhizae and rhizobacteria affects biomass, nutrient status, water-use efficiency, and glomalin-related soil protein concentration

Inoculation of Arizona cypress seedlings with beneficial microorganisms can improve the overall growth and establishment under water stress conditions by reducing the transplantation shock and better nutrient and water uptake. Water plays a key role in determining successful seedling establishment, especially in arid and semi-arid climates. Drought is the major environmental stressor that leads to a reduction in growth rate and decline in Arizona cypress. One of the most promising methods to improve seedling establishment in droughty climates is the application of beneficial microorganisms, including mycorrhizae and rhizobacteria. This study aimed to evaluate the effectiveness of mycorrhizae and rhizobacteria inoculation on Arizona cypress (Cupressus arizonica Greene) seedlings establishment under water stress conditions. A factorial experiment with a completely randomized design with three replications was established. The factors included four mycorrhizae regimes (control, Rhizophagus irregularis, Funneliformis mosseae, and Rhizophagus irregularis–Funneliformis mosseae mixture), two rhizobacteria regimes (control, Pseudomonas fluorescens), and two irrigation regimes (well-watered [WW] and water deficit [WD]). Both mycorrhizae and rhizobacteria inoculation increased seedling biomass compared with control under the WD regime. Moreover, mycorrhizae inoculation improved glomalin-related soil protein (GRSP) concentration by 24 %, although this treatment was not statistically significant. Co-inoculated seedlings had improved water use efficiency (WUE) compared with those inoculated with either mycorrhizae or rhizobacteria. The WD regime negatively affected nutrient uptake, especially in control seedlings. Both mycorrhizae and rhizobacteria inoculation increased nutrient uptake (except for zinc) compared with control. Although WUE was affected by irrigation regime, nutrient uptake was dependent on an association with beneficial microorganisms. Our novel finding was that co-inoculation of Arizona cypress seedlings with mycorrhizae and rhizobacteria significantly increased seedling biomass, WUE, and nutrient uptake, as well as improved water stress tolerance.