Arbuscular Mycorrhizal Fungal Biomass Research Articles

Impact of Silver Nanoparticles on Arbuscular Mycorrhizal Fungi and Glomalin-Related Soil Proteins in the Rhizosphere of Maize Seedlings

Glomalin-related soil protein (GRSP), an important arbuscular mycorrhizal (AM) fungal by-product, plays a key role in preserving or sequestrating soil organic carbon (C). Silver nanoparticles (AgNPs) have become an emerging contaminant and their impacts on soil ecosystems attract increasing concerns. The dynamics of AM fungi and GRSP could therefore form the basis for an in-depth exploration of the influences of AgNPs on soil ecosystems. This study investigated the effects of AgNPs on mycorrhizal growth and AM fungal communities, as well as the GRSP contents in maize (Zea mays L.) soils, with a pot experiment. The contributions of GRSP to soil organic C and the correlations of GRSP with soil organic C were also evaluated. The results indicated that AgNPs decreased the mycorrhizal colonization, AM fungal biomass, and diversity indices, and strongly shifted the community composition of AM fungi with a reduction in Acaulosporaceae and an enrichment in Glomeraceae. Additionally, AgNPs also decreased the soil’s easily extractable (EE) GRSP and total (T) GRSP contents, resulting in lower contributions of EE-GRSP-C and T-GRSP-C to the soil organic C. Linkage analyses revealed that AM fungal abundances have positive correlations with EE- and T-GRSP, and EE- and T-GRSP also positively correlated with soil organic C, indicating that the negative effects of AgNPs on AM fungal abundances and communities were extended to AM-fungal-associated C processes. Altogether, our study found that AgNPs decreased the AM fungal abundances shaped AM fungal communities, and reduced the soil GRSP content, which might subsequently be unfavorable for soil C storage.

Arbuscular mycorrhizal fungi affect the response of soil CO2 emission to summer precipitation pulse following drought in rooted soils

Drought and extreme precipitation are projected to occur more frequently as a consequence of climate change, with uncertain implications for soil CO2 emission. Although studies have revealed the response patterns of soil CO2 emission to precipitation pulse, the effects of forest plant roots on this relationship after drought are still poorly understood. Here, a field experiment was performed to examine the differences in soil CO2 emission and microbial community between rootless and rooted soils, pretreated with three drought intensities (control, moderate, and severe), and rewetted with different water additions (0, 5, 10, and 20 mm) in a temperate forest. Compared with control soils, whether the water was added or not, severe drought suppressed soil CO2 emission for both root-excluded and -included soils. Regardless of drought intensities, significantly positive effects (19.4–44.9%) of precipitation pulse on soil CO2 emission were only detected in the root-included soils. Both the contribution of root-derived CO2 to the stimulated soil CO2 emission and biomass of soil arbuscular mycorrhizal fungi (AMF) substantially increased with elevated precipitation levels. The enhanced soil CO2 emission following precipitation pulse is primarily due to the increase in root-derived CO2 in the rooted soils, likely resulting from the enhanced biomass of soil AMF. This study provides empirical evidence on the primacy of AMF in root-derived CO2 and thus the response of soil CO2 emission to precipitation pulse in forest ecosystems.

Distinct response patterns of soil micro-eukaryotic communities to early-season and late-season precipitation in a semiarid grassland

Semiarid ecosystems are susceptible to changes in precipitation regimes. However, how soil micro-eukaryote communities in semi-arid ecosystems respond to variations in the seasonal distribution of precipitation remains elusive. A 5-year field experiment was performed to investigate the effect of changed precipitation distributions throughout the growing season on soil micro-eukaryotic communities in the temperate steppe. Early-season precipitation did not significantly affect the biomass of arbuscular mycorrhizal fungi (AMF) nor the composition and structure of AMF and protist communities. Late-season precipitation significantly increased the biomass of AMF while significantly altering the relative abundance of dominant genera in AMF and protist communities. There was a clear difference in the community structure of AMF and protists between the late-season precipitation and natural precipitation. In addition, late-season precipitation decreased the amount of consumer protists but enhanced the abundance of parasitic protists. These results indicate that the impact of precipitation limitations in the middle growing season can be weakened by increased precipitation in the early growing seasons, while an increase in precipitation later in the growing season does not improve the impact of a decrease in precipitation in the middle growing season. Our findings highlight the potential impact of intra-annual changes in precipitation in soil micro-eukaryotic communities in arid and semiarid regions.

Optimum planting density of Amorpha fruticosa promotes the recovery of understory vegetation and the arbuscular mycorrhizal fungal community in plantations in arid coal mining areas

AbstractEstablishment of plantations may be a useful means of vegetation reconstruction in coal mining areas, especially in fragile environments. However, the influence of shrub planting on the relationship between understory vegetation and soil microorganisms remains poorly understood. Here, we describe a field experiment in which the relationships between understory vegetation and soil microorganisms under different planting densities of Amorpha fruticosa L. (A. fruticosa) were investigated. Compared with areas allowed to recover naturally, shrub planting changed the community and increased the biomass of understory vegetation and soil microbes, especially of arbuscular mycorrhizal fungi (AMF). Planting density was also a key factor that influenced understory vegetation and the soil AMF community and biomass. The maximum diversity of understory vegetation and the AMF community occurred at an intermediate density of introduced shrubs, which was considered to be the optimum density of A. fruticosa. The major soil nutrient cycles that influence understory vegetation and the AMF community were also investigated. An optimum density of introduced shrubs was important in the ecological reconstruction of vegetation in the coal mining area. There may also have been an optimum relationship between the understory vegetation and soil microorganisms especially with AMF in the experimental conditions.

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.

Trophic interactions in soil micro-food webs drive ecosystem multifunctionality along tree species richness.

Rapid biodiversity losses under global climate change threaten forest ecosystem functions. However, our understanding of the patterns and drivers of multiple ecosystem functions across biodiversity gradients remains equivocal. To address this important knowledge gap, we measured simultaneous responses of multiple ecosystem functions (nutrient cycling, soil carbon stocks, organic matter decomposition, plant productivity) to a tree species richness gradient of 1, 4, 8, 16, and 32 species in a young subtropical forest. We found that tree species richness had negligible effects on nutrient cycling, organic matter decomposition, and plant productivity, but soil carbon stocks and ecosystem multifunctionality significantly increased with tree species richness. Linear mixed-effect models showed that soil organisms, particularly arbuscular mycorrhizal fungi (AMF) and soil nematodes, elicited the greatest relative effects on ecosystem multifunctionality. Structural equation models revealed indirect effects of tree species richness on ecosystem multifunctionality mediated by trophic interactions in soil micro-food webs. Specifically, we found a significant negative effect of gram-positive bacteria on soil nematode abundance (a top-down effect), and a significant positive effect of AMF biomass on soil nematode abundance (a bottom-up effect). Overall, our study emphasizes the significance of a multitrophic perspective in elucidating biodiversity-multifunctionality relationships and highlights the conservation of functioning soil micro-food webs to maintain multiple ecosystem functions.

Drought reduces productivity and anti-herbivore defences, but not mycorrhizal associations, of perennial prairie forbs.

During drought, plants allocate resources to aboveground biomass production and belowground carbohydrate reserves, often at the expense of production of defence traits. Additionally, drought has been shown to alter floral resources, with potential implications for plant-pollinator interactions. Although soil symbionts, such as arbuscular mycorrhizal (AM) fungi, can alleviate drought stress in plants, certain levels of drought may negatively impact this relationship, with potential cascading effects. Because of their importance to plant and animal community diversity, we examined effects of drought on biomass production, physical defence properties, nectar production, and associated AM fungal abundance of five common prairie forb species in a greenhouse study. Reduced soil moisture decreased vegetative biomass production. Production of trichomes and latex decreased under drought, relative to well-watered conditions. Ruellia humilis flowers produced less nectar under drought, relative to well-watered conditions. Intra-radical AM fungal colonization was not significantly affected by drought, although extra-radical AM fungal biomass associated with S. azurea decreased following drought. Overall, grassland forb productivity, defence, and nectar production were negatively impacted by moderate drought, with possible negative implications for biotic interactions. Reduced flower and nectar production may lead to fewer pollinator visitors, which may contribute to seed limitation in forb species. Reduced physical defences increase the likelihood of herbivory, further decreasing the ability to store energy for essential functions, such as reproduction. Together, these results suggest drought can potentially impact biotic interactions between plants and herbivores, pollinators, and soil symbionts, and highlights the need for direct assessments of these relationships under climate change scenarios.

Responses of the arbuscular mycorrhizal fungi community to warming coupled with increased drought in an arid desert region

Warming coupled with precipitation changes induced by climate change profoundly affect desert ecosystem functions in global drylands. Arbuscular mycorrhizal fungi (AMF) play a crucial role in such ecosystems by regulating energy and nutrient exchange. However, little is known about how AMF communities respond to warming coupled with reduced precipitation (W + RP). We evaluated the impacts of 0.5 °C and 1.5 °C increase in temperature coupled with 5 % and 8 % reductions in total annual precipitation (0.5 °C W + 5 % RP, 1.5 °C W + 8 % RP) on AMF communities and the main ecological processes structuring AMF community assemblies in the rhizosphere soil of typical winter annual plants in the Tengger Desert, northwest China. The results showed that warming coupled with reduced precipitation could significantly alter the composition, abundance, and diversity of AMF communities. Both AMF biomass and AMF diversity increased in the 0.5 °C W + 5 % RP treatment but decreased in the 1.5 °C W + 8 % RP treatment. The 1.5 °C W + 8 % RP treatment significantly reduced root biomass and the AMF colonization rate but increased the specific root length, indicating a trade-off between fine roots and their symbiotic AMF. The AMF community was phylogenetically random in the 0.5 °C W + 5 % RP treatment but appeared clustered in the 1.5 °C W + 8 % RP treatment, implying that more pronounced warming coupled with reduced precipitation can promote the deterministic assembly of the AMF community. We provide a conceptual framework for comprehending the mechanisms underlying the effects of warming coupled with reduced precipitation on AMF communities, incorporating biological and geochemical processes. Overall, the findings of this study suggest that AMF abundance and diversity and the main ecological processes driving AMF assemblages respond differently to more pronounced compared to less intensive warming coupled with reduced precipitation. Importantly, higher warming coupled with a reduction in precipitation reduced plant dependence on AMF and resulted in stronger environmental filtration by significantly reducing soil water content.

Exploring the potentialities of an improved triglyceride 16:1ω5 extraction technique for quantitative estimation of arbuscular mycorrhizal fungi in the rhizosphere of olive trees

A method combining solid-phase extraction (SPE) on silica (Si) and aminopropyl-bonded silica (NH2) columns has been applied for the separation of phospholipids (PL), glycolipids (GL), neutral lipids (NL) and triglyceride fatty acids from the spores of Rhizophagus irregularis DAOM 197198 and in olive rhizosphere with and without arbuscular mycorrhizal (AM) fungi. Chromatography on the Si-column resulted in the separation of NL, GL and PL. Chromatography on the NH2- column led to the separation of TG from NL, previously coeluted on the Si-column. The fatty acid composition of TG of Rhizophagus irregularis spores obtained using this method showed higher amounts of 16:1ω5 (40%). The TGFA 16:1ω5 was present in higher levels in rhizosphere with AM fungi than in rhizosphere without AM fungi. This Si/NH2 method provided a rapid separation of TGFA 16:1ω5, commonly found in living cells, and will be useful to quantify the biomass of AM fungi in soil.

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

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

Tree species richness and functional composition drive soil nitrification through ammonia-oxidizing archaea in subtropical forests

Understanding the links between plant diversity and functional microbiota is crucial for unraveling the mechanisms by which plant communities regulate ecosystem functions. However, the underlying mechanism of how tree diversity influences soil nitrification remains elusive in forest ecosystems. Here we investigated the impacts of tree species richness and their functional composition (including functional identity and functional trait diversity) on the dynamics of ammonia-oxidizing archaea (AOA), ammonia-oxidizing bacteria (AOB) and arbuscular mycorrhizal (AM) fungi using a tree diversity experiment established with 32 native tree species in a subtropical forest biome. Our study revealed that tree species richness had a positive concave-down relationship with the abundance of AOA. Furthermore, the community-weighted mean of leaf nitrogen and specific root length were significant positive factors for the abundances of AOA and AOB, respectively. By contrast, functional trait diversity of specific root length was negatively associated with the biomass of AM fungi. Regression analysis showed that the abundance of AOA was positively correlated with soil net nitrification rates, while the biomass of AM fungi was negatively correlated with soil net nitrification rates. The structural equation model showed that the positive effect of leaf nitrogen on nitrification was driven by the increase in AOA. By contrast, the functional trait diversity of specific root length indirectly increased soil nitrification via a negative impact on the biomass of AM fungi. Taken together, our findings demonstrate that both tree species richness and tree functional composition promoted soil nitrification by increasing the AOA abundance, and emphasize the key role of the interplay between tree diversity and functional microbiota in predicting ecosystem functions.

Long-term manuring facilitates glomalin-related soil proteins accumulation by chemical composition shifts and macro-aggregation formation

Glomalin-related soil proteins (GRSP), derived from arbuscular mycorrhizal fungi (AMF), contributes significantly to soil stability and carbon sequestration. However, the responses of GRSP accumulation and associated AMF community and diversity to long-term fertilization regimes remain unclear. Here, we investigated the dynamics of GRSP contents, AMF biomass and diversity based on a 29-year fertilization experiment (including control, mineral fertilization, manuring and straw returning treatments). Results showed that GRSP contents increased over years across fertilization treatments. Compared with no fertilization, long-term manuring and straw returning significantly increased bulk soil GRSP by 100% and 80%, respectively, and altered the chemical composition of GRSP by increasing the recalcitrant (aromatic) C proportion. The proportion of aromatic C in GRSP was positively correlated with AMF biomass and diversity (Shannon and Chao1), indicating that the chemical composition of GRSP could be regulated by AMF community and diversity. Moreover, manuring facilitated the formation of macro-aggregates (>250 µm), thus increasing the physical protection of GRSP. The structural equation modeling further demonstrated that GRSP content was positively regulated by soil macro-aggregates, AMF biomass and diversity and their linkage with GRSP chemical composition. Collectively, long-term manuring could facilitate GRSP accumulation by shifts in AMF-mediated GRSP chemical composition (aromatic C) along with enhanced protection of macro-aggregates. This study highlights a feasible way forward for soil quality improvement and carbon sequestration for sustainable agriculture.

Soil organic matter dynamics mediated by arbuscular mycorrhizal fungi - an updated conceptual framework.

Arbuscular mycorrhizal (AM) fungi play an important role in soil organic matter (SOM) formation and stabilization. Previous studies have emphasized organic compounds produced by AM fungi as persistent binding agents for aggregate formation and SOM storage. This concept overlooks the multiple biogeochemical processes mediated by AM fungal activities, which drive SOM generation, reprocessing, reorganization, and stabilization. Here, we propose an updated conceptual framework to facilitate a mechanistic understanding of the role of AM fungi in SOM dynamics. In this framework, four pathways for AM fungi-mediated SOM dynamics are included: 'Generating', AM fungal exudates and biomass serve as key sources of SOM chemodiversity; 'Reprocessing', hyphosphere microorganisms drive SOM decomposition and resynthesis; 'Reorganizing', AM fungi mediate soil physical changes and influence SOM transport, redistribution, transformation, and storage; and 'Stabilizing', AM fungi drive mineral weathering and organo-mineral interactions for SOM stabilization. Moreover, we discuss the AM fungal role in SOM dynamics at different scales, especially when translating results from small scales to complex larger scales. We believe that working with this conceptual framework can allow a better understanding of AM fungal role in SOM dynamics, therefore facilitating the development of mycorrhiza-based technologies toward soil health and global change mitigation.

Conversion of native grassland to coniferous forests decreased stocks of soil organic carbon and microbial biomass

AimsEncroachment of woody species into grasslands is a global phenomenon that affects ecosystem services, including soil organic carbon (SOC) storage and microbial community structure. We determined stocks of SOC and soil microbial biomass as affected by conversion of grasslands to coniferous forests.MethodsWe examined SOC and soil δ13C signatures under three vegetation covers: native grasslands, eastern redcedar (Juniperus virginiana), and ponderosa pine (Pinus ponderosa), at six soil depths (0 − 10, 10 − 30, 30 − 100, 100 − 170, 170 − 240, 240 − 300 cm). Fatty acid methyl esters (FAMEs) were used to quantify soil microbial biomass (MB) and as biomarkers for bacteria, arbuscular mycorrhizal fungi (AMF), and saprophytic fungi (SF) which includes ectomycorrhizal fungi (ECM).ResultsNative grasslands had higher overall SOC and MB stocks in the top 300 cm soil depth (7.39 kg SOC m− 2 and 65.6 mmol MB m− 2) than converted cedar (6.80 kg SOC m− 2 and 38.4 mmol MB m− 2) or pine (5.87 kg SOC m− 2 and 39.9 mmol MB m− 2) forest. Losses of AMF biomass occurred on conversion of native grasslands to pine forest. Stocks of SF biomass only differed with vegetation type in topsoil.ConclusionsConversion of native grasslands to cedar or pine forest increased topsoil (0 − 10 cm) SOC storage due to needle litter accumulation. Conversion of native grasslands to forests decreased subsoil (10 − 300 cm) SOC stocks and had replaced, by increasing depth, 30 to 19% and 45 to 26% of grassland C with cedar and pine C, respectively. Changes in soil pH, nutrients, and soil microbial communities accelerated SOC turnover.

Biotic and abiotic drivers of ecosystem multifunctionality: Evidence from the semi-arid grasslands of northern China

Ecosystem functioning plays a crucial role in maintaining human welfare. Terrestrial ecosystems provide multiple ecosystem services simultaneously, such as carbon sequestration, nutrient cycling, water purification, and biodiversity conservation, known as ecosystem multifunctionality (EMF). However, the mechanisms by which biotic and abiotic factors, and their interactions regulate EMF in grasslands are unclear. We conducted a transect survey to illustrate the single and combined effects of biotic factors (including plant species diversity, trait-based functional diversity, community-weighted mean (CWM) of traits, and soil microbial diversity) and abiotic factors (including climate and soil) on EMF. Eight functions were investigated, including aboveground living biomass and litter biomass, soil bacterial biomass, fungal biomass, arbuscular mycorrhizal fungi biomass, and soil organic carbon storage, total carbon storage and total nitrogen storage. We detected a significant interactive effect between plant species diversity and soil microbial diversity on the EMF; Structural equation model showed that soil microbial diversity indirectly affected EMF by regulating plant species diversity. These findings highlight the importance of the interaction effect of above- and below-ground diversity on EMF. Both plant species diversity and functional diversity had similar explanatory power for the variation in EMF, implying that niche differentiation and multifunctional complementarity among plant species and traits are essential in regulating the EMF. Furthermore, the effects of abiotic factors on EMF were stronger than those of biotic factors via direct and indirect pathways affecting above- and below-ground biodiversity. As a dominant regulator, the soil sand content was negatively correlated with EMF. These findings indicate the vital role of abiotic mechanisms in affecting EMF, and deepen our understanding of the single and combined effects of biotic and abiotic factors on EMF. We conclude that soil texture and plant diversity, representing crucial abiotic and biotic factors, respectively, are important determinants of the EMF of grasslands.

Response of Sagebrush Steppe Grass Species to AMF Inoculum Sources and Biochar.

The sagebrush steppe has presented increasing levels of degradation. The addition of arbuscular mycorrhizal fungi (AMF) and biochar have been suggested to restore ecosystems. However, little is known about their effects on sagebrush steppe plants. We tested three sources of AMF inoculum: soil from a disturbed site (Inoculum A), soil from an undisturbed site (Inoculum B), and commercial inoculum (Inoculum C), all with and without biochar, to test if they could mediate growth of Pseudoroegneria spicata (native perennial), Taeniatherum caput-medusae (early seral; exotic annual) and Ventenata dubia (early seral; exotic annual) under greenhouse conditions. We measured AMF colonization and biomass. We hypothesized that the plant species would be differently affected by the inoculum types. The colonization of T. caput-medusae and V. dubia was greatest when inoculated with Inoculum A (38.8% and 19.6%). In contrast, the colonization of P. spicata was greatest with Inoculum B and Inoculum C (32.1% and 32.2). Biochar decreased biomass production but increased colonization with Inoculum A for P. spicata and V. dubia and with Inoculum C for T. caput-medusae. This study reveals the response of early and late seral sagebrush steppe grass species to contrasting sources of AMF and suggests that late seral plant species respond better to late seral inocula.

Deciphering the effects of genotype and climatic factors on the performance, active ingredients and rhizosphere soil properties of Salvia miltiorrhiza.

Salvia miltiorrhiza Bunge is an important medicinal herb, which is widely cultivated in most parts of China. It has attracted considerable attention because of its pharmacological properties and potential health benefits. We used a field experiment to determine the effects of different genotypes and climatic factors on the performance (plant biomass, morphological parameters), active ingredients, rhizosphere soil physicochemical properties and microbial composition of S. miltiorrhiza at five cultivation locations. The results showed that these parameters were significantly different in the six different genotypes of S. miltiorrhiza from five producing areas. Genotype and soil physicochemical properties were the main factors affecting the growth traits of S. miltiorrhiza, while genotype, climate and soil physicochemical properties were the main factors affecting the content of active components of S. miltiorrhiza. Microbial phospholipid fatty acid analysis showed that the biomass of Gram-positive and Gram-negative bacteria was affected by the genotypes of S. miltiorrhiza plants, while the biomass of arbuscular mycorrhizal fungi, fungi, Gram-positive and Gram-negative bacteria was affected by climate factors. Based on the main results, DS993 was the most suitable genotype for S. miltiorrhiza in the five producing areas from the perspective of comprehensive growth traits and medicinal components, while DS993 and DS2000 were suitable for planting in Shandong province from the perspective of origin. DS996 is not suitable for all of the above production areas. These results are helpful to understand the ecological adaptability of different genotypes of S. miltiorrhiza resources, and to select appropriate S. miltiorrhiza genotypes for specific planting areas, so as to maximize yield and quality.

The balance between arbuscular mycorrhizal fungal diversity and plant growth benefits from optimizing nitrogen inputs in agroecosystems

Excessive nitrogen (N) inputs exacerbate ecological problems and compromise multiple ecosystem services delivered by soil biodiversity. Arbuscular mycorrhizal fungi (AMF) facilitated nutrient acquisition by plants from soil and alleviated reliance on external inputs. However, how N inputs influence the relationships between AMF diversity and crop performance, especially whether there exists an optimal threshold to maximize crop reliance on AMF and minimize reliance on external N remains unclear. A field experiment was conducted to monitor the responses of AMF diversity and maize growth among N input levels (0, 120, 240, and 360 kg urea-N ha−1). Results showed that increasing N inputs decreased AMF colonization rate and spore density. Across the N input levels, the N inputs at 120 and 240 kg N ha−1 increased AMF richness and biomass, respectively. Moreover, N input level at 360 kg ha−1 (local doses) increased maize growth including yield and total biomass but decreased plant P content, indicating that the role of AMF was constrained under high N inputs. Notably, an optimal N input level that resulted in win-win support of AMF diversity and crop growth was obtained, which was ca. 52 % of local doses (i.e. 190 kg ha−1). Together, understanding the relationships between beneficial microbes and crop with nutrient input gradients was critical for advancing future sophisticated fertilizer management harnessing multiple ecological services and crop productivity at the lowest external economic and environmental cost.

Carbohydrate and lipid balances in the positive plant phenotypic response to arbuscular mycorrhiza: increase in sink strength.

The exchange of phosphorus (P) and carbon (C) between plants and arbuscular mycorrhizal fungi (AMF) is a major determinant of their mutualistic symbiosis. We explored the C dynamics in tomato (Solanum lycorpersicum) inoculated or not with Rhizophagus irregularis to study their growth response under different NaH2 PO4 concentrations (Null P, 0 mM; Low P, 0.065 mM; High P, 1.3 mM). The percentage of AMF colonization was similar in plants under Null and Low P, but severely reduced under High P. However, the AMF mass biomarker 16:1ω5 revealed higher fungal accumulation in inoculated roots under Low P, while more AMF spores were produced in the Null P. Under High P, AMF biomass and spores were strongly reduced. Plant growth response to mycorrhiza was negative under Null P, showing reduction in height, biovolume index, and source leaf (SL) area. Under Low P, inoculated plants showed a positive response (e.g., increased SL area), while inoculated plants under High P were similar to non-inoculated plants. AMF promoted the accumulation of soluble sugars in the SL under all fertilization levels, whereas the soluble sugar level decreased in roots under Low P in inoculated plants. Transcriptional upregulation of SlLIN6 and SlSUS1, genes related to carbohydrate metabolism, was observed in inoculated roots under Null P and Low P, respectively. We conclude that P-limiting conditions that increase AMF colonization stimulate plant growth due to an increase in the source and sink strength. Our results suggest that C partitioning and allocation to different catabolic pathways in the host are influenced by AMF performance.

Decoding the PLFA profiling of microbial community structure in soils contaminated with municipal solid wastes

This study aimed to assess the influence of municipal solid waste (MSW) disposal on soil microbial communities. Soil samples from 20 different locations of an MSW dumping site contaminated with toxic heavy metals (HMs) and a native forest (as control) were collected for phospholipid fatty acid (PLFA) profiling to predict microbial community responses towards unsegregated disposal of MSW. PLFA biomarkers specific to arbuscular mycorrhizal fungi (AMF), Gram-negative and Gram-positive bacteria, fungi, eukaryotes, actinomycetes, anaerobes, and microbial stress markers-fungi: bacteria (F/B) ratio, Gram-positive/Gram-negative (GP/GN) ratio, Gram-negative stress (GNStr) ratio and predator/prey ratio along with AMF spore density and the total HM content (Cu, Cr, Cd, Mn, Zn, and Ni) were assessed.The results showed that all of the PLFA microbial biomarkers and the F/B ratio were positively correlated, while HMs and microbial stress markers were negatively correlated. The significant correlation of AMF biomass with all microbial groups, the F/B ratio, and T. PLFA confirmed its significance as a key predictor of microbial biomass. With AMF and T. PLFA, Cd and Cr had a weak or negative connection. Among the toxic HMs, Zn and Cd had the greatest impact on microbial populations. Vegetation did not have any significant effect on soil microbial communities. This research will aid in the development of bioinoculants for the bioremediation of MSW-polluted sites and will improve our understanding of the soil microbial community's ability to resist, recover, and adapt to toxic waste contamination.