Removal of sulfamethoxazole and Cu, Cd compound pollution by arbuscular mycorrhizal fungi enhanced vertical flow constructed wetlands.

The combined pollution of antibiotics and heavy metals (HMs) has a serious impact on the water ecological environment. Previous researches mainly focused on the removal of antibiotics or HMs as single pollutants, with limited investigation into the treatment efficiencies and underlying mechanisms associated with their co-occurring pollution. In this study, 16 micro vertical flow constructed wetlands (MVFCWs) were constructed to treat composite wastewater consisting of sulfamethoxazole (SMX), copper (Cu) and cadmium (Cd), involving two different inoculation treatments (arbuscular mycorrhizal fungi (AMF) inoculated and uninoculated) and eight kinds of pollutant exposure (Control Check (CK), SMX, Cu, Cd, SMX + Cu, SMX + Cd, Cu + Cd, SMX + Cu + Cd). The findings of this study demonstrated that the inoculation of AMF in MVFCWs resulted in removal efficiencies of SMX, Cu, and Cd ranging from 18.70% to 80.52%, 75.18% to 96.61%, and 40.50% to 89.23%, respectively. Cu and CuCd promoted the degradation of SMX in the early stage and inhibited the degradation of SMX in the later stage. Cd did not demonstrate a comparable promotive impact on SMX degradation, and its addition hindered Cu removal. However, comparatively, the presence of Cu exerted a more pronounced inhibitory effect on Cd removal. Furthermore, the addition of Cu augmented the abundances of Proteobacteria, Bacteroidetes (at the phylum level) and Rhodobacter, Lacunisphaera and Flavobacterium (at the genus level), and Cu exposure showed a substantially stronger influence on the microbial community than that of Cd and SMX. AMF might confer protection to plants against HMs and antibiotics by enriching Nakamurella and Lacunisphaera. These findings proved that AMF-C. indica MVFCW was a promising system, and the inoculation of AMF effectively enhanced the simultaneous removal of compound pollution.

The functional division of arbuscular mycorrhizal fungi and earthworm to efficient cooperation on phytoremediation in molybdenum (Mo) contaminated soils.

Single phytoremediation has limited capacity to restore soil contaminated with extreme Mo due to its low metal accumulation. Soil organisms can help compensate for this deficiency in Mo-contaminated soils. However, there is limited information available on the integrated roles of different types of soil organisms, particularly the collaboration between soil microorganisms and soil animals, in phytoremediation. The objective of this study is to investigate the effects of a combination of arbuscular mycorrhizal fungi (AMF) and earthworms on the remediation of Mo-contaminated soils by alfalfa (Medicago sativa L.). The results indicated that in the soil-alfalfa system, earthworms effectively drive soil Mo activation, while AMF significantly improve the contribution of the translocation factor to total Mo removal (TMR) in alfalfas (p < 0.05). Meanwhile, compared to individual treatments, the combination of AMF and earthworm enhanced the expression of alfalfa root specific Mo transporter - MOT1 family genes to increase alfalfa uptake Mo (p < 0.05). This alleviated the competition between P/S nutrients and Mo on non-specific Mo transporters-P/S transporters (p < 0.05). Additionally, the proportion of organelle-bound Mo in the root was reduced to decrease Mo toxicity, while the cell wall-bound Mo proportion in the shoot was increased to securely accumulate Mo. The contributions of inoculants to alfalfa TMR followed the order (maximum increases): AMF + E combination (274.68 %) > alone treatments (130 %). Overall, the "functional division and cooperation" between earthworm and AMF are of great importance to the creation of efficient multi-biological systems in phytoremediation.

Afforestation enhances glomalin-related soil protein content but decreases its contribution to soil organic carbon in a subtropical karst area.

Afforestation on degraded croplands has been proposed as an effective measure to promote ecosystem functions including soil organic carbon (SOC) sequestration. Glomalin-related soil protein (GRSP) plays a crucial role in promoting the accumulation and stability of SOC. Nevertheless, mechanisms underlying the effects of afforestation on GRSP accumulation have not been well elucidated. In the present study, 14 pairs of maize fields and plantation forests were selected using a paired-site approach in a karst region of southwest China. By measuring soil GRSP and a variety of soil biotic and abiotic variables, the pattern of and controls on GRSP accumulation in response to afforestation were explored. The average content of total GRSP (T-GRSP) and its contribution to SOC in the maize field were 5.22 ± 0.29 mg g-1 and 42.33 ± 2.25%, and those in the plantation forest were 6.59 ± 0.32 mg g-1 and 25.77 ± 1.17%, respectively. T-GRSP content was increased by 26.4% on average, but its contribution to SOC was decreased by 39.1% following afforestation. T-GRSP content decreased as soil depth increased regardless of afforestation or not. Afforestation increased T-GRSP indirectly via its positive effects on arbuscular mycorrhizal fungi biomass, which was stimulated by afforestation through elevating fine root biomass or increasing the availability of labile C and N. The suppressed contribution of T-GRSP to SOC following afforestation was due to the relatively higher increase in other SOC components than T-GRSP and the significant increase of soil C:N ratio. Our study reveals the mechanisms underlying the effects of afforestation on T-GRSP accumulation, and is conducive to improving the mechanistic understanding of microbial control on SOC sequestration following afforestation.

Arbuscular Mycorrhizal Fungi Shift Soil Bacterial Community Composition and Reduce Soil Ammonia Volatilization and Nitrous Oxide Emissions.

Arbuscular mycorrhizal fungi (AMF) establish mutualistic relationships with the majority of terrestrial plants, increasing plant uptake of soil nitrogen (N) in exchange for photosynthates. And may influence soil ammonia (NH3) volatilization and nitrous oxide (N2O) emissions directly by improving plant N uptake, and/or indirectly by modifying soil bacterial community composition for the soil C availability increasing. However, the effects of AMF on soil NH3 volatilization and N2O emissions and their underlying mechanisms remain unclear. We carried out two independent experiments using contrasting methods, one with a compartmental box device (in 2016) and the other with growth pot experiment (in 2020) to examine functional relationships between AMF and soil NH3 volatilization and N2O emissions under varying N input. The presence of AMF significantly reduced soil NH3 volatilization and N2O emissions while enhancing plant biomass and plant N acquisition, and reducing soil NH4+ and NO3-, even with high N input. The presence of AMF also significantly reduced the relative abundance within the bacterial orders Sphingomonadales and Rhizobiales. Sphingomonadales correlated significantly and positively with soil NH3 volatilization in 2016 and N2O emissions, whereas Rhizobiales correlated positively with soil N2O emissions. High N input significantly increased soil NH3 volatilization and N2O emissions with increasing relative abundance of Sphingomonadales and Rhizobiales. These findings demonstrate the contribution of AMF in regulating NH3 and N2O emission by improving plant N uptake and altering soil bacterial communities. They also suggest that altering the rhizosphere microbiome might offer additional potential for restoration of N-enriched agroecosystems.

Mycorrhizal Infection Can Ameliorate Abiotic Factors in Urban Soils.

Once abandoned, urban and post-industrial lands can undergo a re-greening, the natural regeneration and succession that leads to surprisingly healthy plant communities, but this process is dependent upon microbial activity and the health of the parent soil. This study aimed to evaluate the effects of arbuscular mycorrhizal fungi (AMF) in facilitating plant production in post-industrial soils. In so doing, we helped to resolve the mechanism through which AMF ameliorate environmental stress in terrestrial plants. An experiment was established in which rye grass (Lolium perenne) was grown in two heavy metal-contaminated soils from an urban brownfield in New Jersey, USA, and one non-contaminated control soil. One set of the treatments received an AMF inoculum (four species in a commercial mix: Glomus intraradices, G. mosseae, G. etunicatum and G. aggregatum) and the other did not. Upon harvest, dried plant biomass, root/shoot ratio, AMF colonization, and extracellular soil phosphatase activity, a proxy for soil microbial functioning, were all measured. Plant biomass increased across all treatments inoculated with AMF, with a significantly higher average shoot and root mass compared to non-inoculated treatments. AMF colonization of the roots in contaminated soil was significantly higher than colonization in control soil, and the root/shoot ratio of plants in contaminated soils was also higher when colonized by AMF. Mycorrhizal infection may help plants to overcome the production limits of post-industrial soils as is seen here with increased infection and growth. The application of this mechanistic understanding to remediation and restoration strategies will improve soil health and plant production in urban environments.

Arbuscular mycorrhizal fungi reduce potassium, cadmium and ammonium losses but increases nitrate loss under high intensity leaching events.

BACKGROUND: Nutrients and heavy metals can be lost from soils via leaching, and arbuscular mycorrhizal fungi (AMF) can influence these events. Soil column experiments were carried out to examine whether leaching intensity and AMF can alter nutrient and Cd uptake in white clover plants and the extent of their losses through leaching. RESULTS: The presence of AMF significantly increased shoot and total biomass, as well as increased N, P, Cu and Zn uptake independent of water amount applied; while root P and Cu uptakes were promoted by AMF at any water amount treatments. Higher water amounts led to reductions in total N, K and Zn uptake for AMF-colonized plants in comparison to moderate water amount treatments. In the absence of AMF, white clover at low water amount treatment exhibited maximal root Cd uptake. At high water amount treatments, the presence of AMF significantly decreased leachate volumes and the amount of leached NH4+, K and Cd while AMF significantly increased the amounts of leached NO3-. CONCLUSIONS: Overall we found that AMF-colonized white clover plants reduced NH4+, K and Cd loss from soils but increased the risk of NO3- loss under high intensity leaching conditions.

Arbuscular mycorrhizal fungi affecting the growth, nutrient uptake and phytoremediation potential of different plants in a cadmium-polluted soil.

Heavy metals stress is of great concern as it contaminates the environment affecting human health and the growth and quality of different plants including the medicinal ones. The use of soil microbes is among the most efficient methods for treating heavy-metal polluted soils. The objective was to investigate the effects of arbuscular mycorrhizal (AM) fungi (Glomus mosseae) on the nutrient uptake (N, P, K, Fe, and Mn,) and Cd removal of different plants including rosemary (Salvia rosmarinus), amaranth (Amaranthus sp.), and ornamental cabbage (Brassica oleracea) in a Cd-polluted soil. The experiment was a three-way factorial on the basis of a randomized complete block design with three replicates. The experimental soil was sprayed with Cd (0, 10, 25, 50, 75 and 100 mg kg-1), and after 2 months it was inoculated with 100 g of mycorrhizal inoculums, and was planted in 4-kg pots. Plant growth (root and aerial part) and nutrient uptake as well as Cd removal from the contaminated soil were significantly affected by the experimental treatments. AM fungi significantly increased plant P uptake (35%) compared with N (24%), K (4%), Fe (24%) and Mn (13%). According to the results, rosemary was the most effective plant for the bioremediation of the soil. There were significant differences between plant roots and aerial part in terms of plant nutrient uptake and phytoremediation potential. Although increasing Cd concentration decreased plant growth and nutrient uptake, mycorrhizal fungi was able to alleviate the stress by significantly increasing plant growth, nutrient uptake and phytoremediation potential.

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.

Cadmium transfer between maize and soybean plants via common mycorrhizal networks.

More than 80% terrestrial plants establish mutualistic symbiosis with soil-borne arbuscular mycorrhizal fungi (AMF). These fungi not only significantly improve plant nutrient acquisition and stress resistance, but also mitigate heavy metal phytotoxicity, Furthermore, the extraradical mycorrhizal mycelia can form common mycorrhizal networks (CMNs) that link roots of multiple plants in a community. Here we show that the networks mediate migration of heavy metal cadmium (Cd) from maize (Zea mays L.) to soybean (Glycine max (Linn.) Merr.) plants. CMNs between maize and soybean plants were established after inoculation of maize plants with AMF Funneliformis mosseae. Application of CdCl2 in maize plants led to 64.4% increase in the shoots and 48.2% increase in the roots in Cd content in CMNs-connected soybean plants compared to the control without Cd treatment in maize. Meanwhile, although the CMNs-connected soybean plants did not directly receive Cd supply, they upregulated transcriptional levels of Cd transport-related genes HATPase and RSTK 2.13- and 5.96-fold, respectively, induced activities of POD by 44.8% in the leaves, and increased MDA by 146.2% in the roots. Furthermore, Cd addition inhibited maize growth but mycorrhizal colonization improved plant performance in presence of Cd stress. This finding demonstrates that mycorrhizal networks mediate the transfer of Cd between plants of different species, suggesting a potential to use CMNs as a conduit to transfer toxic heavy metals from main food crops to heavy metal hyperaccumulators via intercropping.

Dual RNA and 16S ribosomal DNA sequencing reveal arbuscular mycorrhizal fungi-mediated mitigation of selenate stress in Zea mays L. and reshaping of soil microbiota.

Excessively high concentrations of selenium (Se) in soil are toxic to crop plants, and inoculation with arbuscular mycorrhizal fungi (AMF) can reverse Se stress in maize (Zea mays L.). To investigate the underlying mechanisms, maize seedlings were treated with sodium selenate (5 mg Se[VI] kg-1) and/or AMF (Funneliformis mosseae and Claroideoglomus etunicatum). Dual RNA sequencing in mycorrhiza and 16 S ribosomal DNA sequencing in soil were performed. The results showed that Se(VI) application alone decreased plant dry weight, but increased plant Se concentration, total Se content (mainly selenocysteine), and root superoxide content. Inoculation with either F. mosseae or C. etunicatum increased plant dry weight, decreased Se accumulation and selenocysteine proportion, enhanced root peroxidase activity, and alleviated oxidative stress in Se(VI)-treated plants. Inoculation also downregulated the expression of genes encoding Se transporters, assimilation enzymes, and cysteine-rich receptor-like kinases in Se(VI)-stressed plants, similar to plant-pathogen interaction and glutathione metabolism related genes. Conversely, genes encoding selenium-binding proteins and those related to phenylpropanoid biosynthesis were upregulated in inoculated plants under Se(VI) stress. Compared with Se(VI)-free plants, Se tolerance index, symbiotic feedback percentage on plant dry weight, and root colonization rate were all increased in inoculated plants under Se(VI) stress, corresponding to upregulated expression of 'key genes' in symbiosis. AMF inoculation increased bacterial diversity, decreased the relative abundances of selenobacteria related to plant Se absorption (e.g., Proteobacteria and Firmicutes), and improved bacterial network complexity in Se(VI)-stressed soils. We suggest that stress-mediated enhancement of mycorrhizal symbiosis contributed to plant Se(VI) tolerance, whereas AMF-mediated reshaping of soil bacterial community structure prevented excessive Se accumulation in maize.

Metabolic alterations elicited by Cd and Zn toxicity in Zea mays with the association of Claroideoglomus claroideum.

The concentrations of cadmium (Cd) and zinc (Zn) in arable lands exceed the maximum permissible levels due to the excessive use of phosphorus fertilizers and fungicides by farmers. The increasing issues related to the application of agrochemicals have lead to the demand for the implementation of sustainable agricultural approaches. Association of arbuscular mycorrhizae with crop plants is an appropriate strategy due to the potential of these microorganisms to augment the metals tolerance of plants through the immobilization of Cd and Zn in an eco-friendly manner. In the present study, 45 d old Zea mays (var. CoHM6) plants inoculated with AM fungi (Claroideoglomus claroideum) were exposed to 1.95 g Zn Kg-1 soil and 0.45 g Cd Kg-1 soil. The major objective of this study was to determine the metabolic alterations in the leaves and roots of mycorrhizal and non-mycorrhizal plants exposed to CdCl2 and ZnSO4. Both non AM and AM plants exhibited alterations in the quantity of primary and secondary metabolites on exposure to Zn and Cd toxicity. Moreover, Zn and Cd-induced accumulation of γ-sitosterol reduced the quantity of neophytadiene (a well-known terpenoid) and aided the production of 3-ß-acetoxystigmasta-4,6,22-triene in maize leaves. Mycorrhization and heavy metal toxicity induced significant metabolic changes in the roots by producing 4,22-stigmastadiene-3-one, eicosane, 9,19-cyclolanost-24-en-3-ol, pentacosane, oxalic acid, heptadecyl hexyl ester, l-norvaline, and n-(2-methoxyethoxycarbonyl). In addition, the metal-induced variations in leaf and root lignin composition were characterized with the aid of the FTIR technique. Mycorrhization improved the tolerance of maize plants to Cd and Zn toxicity by stabilizing these metal ions in the soil and/or limiting their uptake into the plants, thus ensuring normal metabolic functions of their roots and shoots.

Ozone does not diminish the beneficial effects of arbuscular mycorrhizas on Medicago sativa L. in a low phosphorus soil.

Enriched surface ozone (O3) can impose harmful effects on plants. Conversely, arbuscular mycorrhizal (AM) symbiosis can enhance plant tolerance to various environmental stresses and facilitate plant growth. The interaction of AM fungi and O3 on plant performance, however, seldom has been investigated. In this study, alfalfa (Medicago sativa L.) was used as a test plant to study the effects of O3 and AM symbiosis on plant physiology and growth under two O3 levels (ambient air and elevated O3 with 60 nmol·mol-1 O3 enrichment) and three AM inoculation treatments (inoculation with exogenous or indigenous AM fungi and non-inoculation control). The results showed that elevated O3 decreased plant net photosynthetic rate and biomass, and increased malondialdehyde concentration, while AM inoculation (with both exogenous and indigenous AM fungi) could promote plant nutrient acquisition and growth irrespective of O3 levels. The positive effects of AM symbiosis on plant nutrient acquisition and antioxidant enzyme (superoxide dismutase and peroxidase) activities were most likely offset by increased stomatal conductance and O3 intake. As a result, AM inoculation and O3 generally showed no significant interactions on plant performance: although elevated O3 did not diminish the beneficial effects of AM symbiosis on alfalfa plants, AM symbiosis also did not alleviate the harmful effects of O3 on plants.

Transfer of La, Ce, Sm and Yb to alfalfa and ryegrass from spiked soil and the role of Funneliformis mosseae.

Rare earth elements (REEs) are widely used in high-tech industries, and REE waste emissions have become a concern for ecosystems, food quality and human beings. Arbuscular mycorrhizal fungi (AMF) have repeatedly been reported to alleviate plant stress in metal-contaminated soils. To date, little information is available concerning the role of AMF in REE-contaminated soils. We recently showed that there was no transfer of Sm to alfalfa by Funneliformis mosseae, but only a single REE was examined, while light and heavy REEs are present in contaminated soils. To understand the role of AMF on the transfer of REEs to plants, we carried out an experiment using alfalfa (Medicago sativa) and ryegrass (Lolium perenne) in compartmented pots with separate bottom compartments that only were accessible by F. mosseae fungal hyphae. The bottom compartments contained a mixture of four REEs at equal concentrations (La, Ce, Sm and Yb). The concentration of REEs in plants was higher in roots than in shoots with higher REE soil-root than root-shoot transfer factors. Moreover, significantly higher light-REEs La and Ce were transferred to ryegrass shoots than Sm and the heavy-REE Yb, but this was not observed for alfalfa. Alfalfa dry weight was significantly increased by F. mosseae inoculation, but not ryegrass dry weight. For both plant species, there was significantly higher P uptake by the mycorrhizal plants than the nonmycorrhizal plants, but there was no significant transfer of La, Ce, Sm or Yb to alfalfa and ryegrass roots or shoots due to F. mosseae inoculation.

Altering microbial community for improving soil properties and agricultural sustainability during a 10-year maize-green manure intercropping in Northwest China.

Maize is a crop that is cultivated worldwide. The Hexi Oasis is one of the most important areas for high-yield maize seed production in China. Green manure, a plant fertilizer, has great potential for increasing crop yield and agricultural sustainability. However, the role of microorganisms in soil health and the microbiological mechanism of green manure in improving soil fertility and crop production in the Hexi Oasis area remain unknown. The effects of maize-green manure intercropping on the soil microbial community structure and diversity and the mechanism of soil improvement were investigated in a 10-year field experiment. The study revealed that microbial phylotypes were grouped into four major ecological clusters. Module #2 is a soil core ecological cluster enriched with many plant growth-promoting rhizobacteria and arbuscular mycorrhizal fungi. The application of green manure led to significantly increased soil pH, nutrient contents, and enzyme activities, and significantly reduced the relative abundance of potential plant pathogens compared with monocropping, which should ensure high and stable maize yield under long-term continuous cropping. It also increased the economic benefits by 56.39% compared with monocropping, owing to the additional products produced by the green manure. These improvements were associated with changes in the microbial community structure and activity, consistent with the structural equation model results. Therefore, soil microorganisms are the key drivers of the potential benefits of maize-green manure on agricultural sustainability.

Effects of solid waste-based soil conditioner and arbuscular mycorrhizal fungi on crop productivity and heavy metal distribution in foxtail millet (Setaria italica).

Shanxi is a large coal-producing province, and it also produces a lot of solid waste. Solid waste can leach heavy metals, which can harm soil and affect food security at the beginning of the food chain. To investigate the impacts of solid waste-based soil conditioner (SWSC) and arbuscular mycorrhizal fungi (AMF) on millet safety and crop production, a field experiment with foxtail millet (Setaria italica) was conducted in Tunliu. The results of this study demonstrate that SWSC + AMF, SWSC and AMF can increase millet yield by 28.0%, 27.1% and 19.5%, respectively, compared with CK. This is mainly due to increased mycorrhizal infection. Besides, the pollution index (Pi) and the Nemerow-integrated pollution index (PN) of the soil with SWSC and AMF were both below 0.7, indicating safe pollution levels. The application of AMF and SWSC inhibits plants from absorbing heavy metals from the soil and reduces the TFroot/soil of the millet. SWSC + AMF application inhibited the transfer of heavy metals from the roots to the upper part of the ground and reduced the TFshoot/root of the millet. The TFgrain/soil of the millet was below 1. The HQ and HI of the millet grains did not exceed 1, indicating the absence of a potential health risk. Therefore, SWSC combined with AMF is applicable for millet production in Tunliu, and the combined treatment can decrease heavy metal phytoavailability and post-harvest transfer risks. This work provides a way to utilize solid waste while also improving millet yields in dry farming. Based on the review, we suggested future researches to better understand the mechanisms of SWSC + AMF long-term application to promote awareness on its role over time through alterations in its surface chemistry, soil microbial community and environmental implications.

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 0-20 cm soil layer in the greenspace of Nanchang, China (505 km2). 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 0.57 mg g-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 1.4 mg g-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.

Enrichment of nosZ-type denitrifiers by arbuscular mycorrhizal fungi mitigates N2 O emissions from soybean stubbles.

Hotspots of N2 O emissions are generated from legume residues during decomposition. Arbuscular mycorrhizal fungi (AMF) from co-cultivated intercropped plants may proliferate into the microsites and interact with soil microbes to reduce N2 O emissions. Yet, the mechanisms by which or how mycorrhizal hyphae affect nitrifiers and denitrifiers in the legume residues remain ambiguous. Here, a split-microcosm experiment was conducted to assess hyphae of Rhizophagus aggregatus from neighbouring maize on overall N2 O emissions from stubbles of nodulated or non-nodulated soybean. Soil microbes from fields intercropped with maize/soybean amended with fertilizer nitrogen (SS-N1) or unamended (SS-N0) were added to the soybean chamber only. AMF hyphae consistently reduced N2 O emissions by 20.8%-61.5%. Generally, AMF hyphae promoted the abundance of N2 O-consuming (nosZ-type) denitrifiers and altered their community composition. The effects were partly associated with increasing MBC and DOC. By contrast, AMF reduced the abundance of nirK-type denitrifiers in the nodulated SS-N0 treatment only and that of AOB in the non-nodulated SS-N1 treatment. Taken together, our results show that AMF reduced N2 O emissions from soybean stubbles, mainly through the promotion of N2 O-consuming denitrifiers. This holds promise for mitigating N2 O emissions by manipulating the efficacious AMF and their associated microbes in cereal/legume intercropping systems.

The influence of alfalfa-switchgrass intercropping on microbial community structure and function.

The use of nitrogen fertilizer on bioenergy crops such as switchgrass results in increased costs, nitrogen leaching and emissions of N2 O, a potent greenhouse gas. Intercropping with nitrogen-fixing alfalfa has been proposed as an environmentally sustainable alternative, but the effects of synthetic fertilizer versus intercropping on soil microbial community functionality remain uncharacterized. We analysed 24 metagenomes from the upper soil layer of agricultural fields from Prosser, WA over two growing seasons and representing three agricultural practices: unfertilized switchgrass (control), fertilized switchgrass and switchgrass intercropped with alfalfa. The synthetic fertilization and intercropping did not result in major shifts of microbial community taxonomic and functional composition compared with the control plots, but a few significant changes were noted. Most notably, mycorrhizal fungi, ammonia-oxidizing archaea and bacteria increased in abundance with intercropping and fertilization. However, only betaproteobacterial ammonia-oxidizing bacteria abundance in fertilized plots significantly correlated to N2 O emission and companion qPCR data. Collectively, a short period of intercropping elicits minor but significant changes in the soil microbial community toward nitrogen preservation and that intercropping may be a viable alternative to synthetic fertilization.

Physiological and biochemical responses of soybean plants inoculated with Arbuscular mycorrhizal fungi and Bradyrhizobium under drought stress.

BACKGROUND: The present study aims to study the effects of biofertilizers potential of Arbuscular Mycorrhizal Fungi (AMF) and Bradyrhizobium japonicum (B. japonicum) strains on yield and growth of drought stressed soybean (Giza 111) plants at early pod stage (50 days from sowing, R3) and seed development stage (90 days from sowing, R5). RESULTS: Highest plant biomass, leaf chlorophyll content, nodulation, and grain yield were observed in the unstressed plants as compared with water stressed-plants at R3 and R5 stages. At soil rhizosphere level, AMF and B. japonicum treatments improved bacterial counts and the activities of the enzymes (dehydrogenase and phosphatase) under well-watered and drought stress conditions. Irrespective of the drought effects, AMF and B. japonicum treatments improved the growth and yield of soybean under both drought (restrained irrigation) and adequately-watered conditions as compared with untreated plants. The current study revealed that AMF and B. japonicum improved catalase (CAT) and peroxidase (POD) in the seeds, and a reverse trend was observed in case of malonaldehyde (MDA) and proline under drought stress. The relative expression of the CAT and POD genes was up-regulated by the application of biofertilizers treatments under drought stress condition. Interestingly a reverse trend was observed in the case of the relative expression of the genes involved in the proline metabolism such as P5CS, P5CR, PDH, and P5CDH under the same conditions. The present study suggests that biofertilizers diminished the inhibitory effect of drought stress on cell development and resulted in a shorter time for DNA accumulation and the cycle of cell division. There were notable changes in the activities of enzymes involved in the secondary metabolism and expression levels of GmSPS1, GmSuSy, and GmC-INV in the plants treated with biofertilizers and exposed to the drought stress at both R3 and R5 stages. These changes in the activities of secondary metabolism and their transcriptional levels caused by biofertilizers may contribute to increasing soybean tolerance to drought stress. CONCLUSIONS: The results of this study suggest that application of biofertilizers to soybean plants is a promising approach to alleviate drought stress effects on growth performance of soybean plants. The integrated application of biofertilizers may help to obtain improved resilience of the agro ecosystems to adverse impacts of climate change and help to improve soil fertility and plant growth under drought stress.

Differential strategies of two species of arbuscular mycorrhizal fungi in the protection of maize plants grown in chromium-contaminated soils.

Chromium (Cr) is a nonessential element for plants that is extremely toxic at high concentrations. Zea mays L. is a species of plant that has developed adaptive mechanisms to increase its tolerance and absorption capacity for this metal. One effective mechanism is to form associations with arbuscular mycorrhizal fungi (AMF), which help the plant cope with stress from heavy metals such as Cr. However, it is still not clear which species of AMF are more efficient as bioremediating agents for plants of agricultural importance. Here, we evaluated the effect of Gigaspora gigantea and Rhizophagus irregularis as protective agents of maize plants in soils contaminated with Cr at concentrations of 0, 48.5, 97 and 194 mg kg-1 under greenhouse conditions. Maize tolerance to Cr was corroborated, as well as increased absorption of this element by plants associated with both species of AMF. G. gigantea caused an increase in nitrogen content and greater translocation of Cr to the aerial part of the plant; R. irregularis registered an increase in the formation of arbuscules and vesicles with increasing metal concentration and greater retention of Cr in the roots of the plants. Based on these results, we can conclude that the analyzed species of fungi use different strategies, with similar effectiveness, to enhance the absorption capacity of Cr by the plant and influence the differential deposition of this metal in various parts of the plant.