Distinct arbuscular mycorrhizal fungal communities associate with different manioc landraces and Amazonian soils

Multiple taxa inoculants of arbuscular mycorrhizal fungi enhanced colonization frequency, biomass production, and water use efficiency of cassava (Manihot esculenta)

Increasing water use efficiency (WUE) in crops is critical to maintaining agricultural production under climate change-exacerbated drought. One of these approaches may consist of leveraging on the beneficial interactions between crops and arbuscular mycorrhizal fungi (AMF). In this study, we investigated how inoculation with AMF from three different taxa (Claroideoglomus etunicatum (T1), Gigaspora margarita (T2), and Rhizophagus irregularis (T3)) and their combination (T123) and a non-inoculated "control" treatment in a greenhouse could achieve increased biomass production and water use efficiency in cassava under three levels of water availability (100% PC, 60%-moderate stress, and 30%-severe stress). Whereas T1 and T2 resulted in a lower growth rate for the plants than the control, T123 enhanced cassava height and the number of petioles and leaves. T123 and T3 increased the total plant dry biomass in comparison with uninoculated plants by 30% and 26%, respectively. The T123 and plants inoculated with T3 significantly increased cassava above-ground biomass by 19% as compared to T1 (8.68 ± 2.44 g) and T2 (8.68 ± 2.44 g) inoculated plants. T123 resulted in higher WUE, which was validated by the leaf carbon (δ13C) isotopic signature, significantly outperforming cassava with T1 and T2, yet there was no difference between the control and T3. Overall, this study demonstrated that the use of multiple AMF from different taxa can increase cassava growth and WUE under greenhouse conditions.

Diversity of Arbuscular Mycorrhizal Fungi in Distinct Ecosystems of the North Caucasus, a Temperate Biodiversity Hotspot

BACKGROUND

Investigations that are focused on arbuscular mycorrhizal fungus (AMF) biodiversity is still limited. The analysis of the AMF taxa in the North Caucasus, a temperate biodiversity hotspot, used to be limited to the genus level. This study aimed to define the AMF biodiversity at the species level in the North Caucasus biotopes.

METHODS

The molecular genetic identification of fungi was carried out with ITS1 and ITS2 regions as barcodes via sequencing using Illumina MiSeq, the analysis of phylogenetic trees for individual genera, and searches for operational taxonomic units (OTUs) with identification at the species level. Sequences from MaarjAM and NCBI GenBank were used as references.

RESULTS

We analyzed >10 million reads in soil samples for three biotopes to estimate fungal biodiversity. Briefly, 50 AMF species belonging to 20 genera were registered. The total number of the AM fungus OTUs for the "Subalpine Meadow" biotope was 171/131, that for "Forest" was 117/60, and that for "River Valley" was 296/221 based on ITS1/ITS2 data. The total number of the AM fungus species (except for virtual taxa) for the "Subalpine Meadow" biotope was 24/19, that for "Forest" was 22/13, and that for "River Valley" was 28/24 based on ITS1/ITS2 data. Greater AMF diversity, as well as number of OTUs and species, in comparison with that of forest biotopes, characterized valley biotopes (disturbed ecosystems; grasslands). The correlation coefficient between "Percentage of annual plants" and "Glomeromycota total reads" r = 0.76 and 0.81 for ITS1 and ITS2, respectively, and the correlation coefficient between "Percentage of annual plants" and "OTUs number (for total species)" was r = 0.67 and 0.77 for ITS1 and ITS2, respectively.

CONCLUSION

High AMF biodiversity for the river valley can be associated with a higher percentage of annual plants in these biotopes and the active development of restorative successional processes.

The function and community structure of arbuscular mycorrhizal fungi in ecological floating beds used for remediation of Pb contaminated wastewater

Arbuscular mycorrhizal fungi (AMF) have been demonstrated to be ubiquitous in aquatic ecosystems. However, their distributions and ecological functions are rarely studied. To date, a few studies have combined sewage treatment facilities with AMF to improve removal efficiency, but appropriate and highly tolerant AMF strains have not been explored, and the purification mechanisms remain unclear. In this study, three ecological floating-bed (EFB) installations inoculated with different AMF inocula (mine AMF inoculum, commercial AMF inoculum and non-AMF inoculated) were constructed to investigate their removal efficiency for Pb-contaminated wastewater. The AMF community structure shifts in the roots of Canna indica inhabiting EFBs during the three phases (pot culture phase, hydroponic phase and hydroponic phase with Pb stress) were tracked utilizing quantitative real-time polymerase chain reaction and Illumina sequencing techniques. Furthermore, transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS) were used to detect the Pb location in mycorrhizal structures. The results showed that AMF could promote host plant growth and enhance the Pb removal efficiency of the EFBs. The higher the AMF abundance, the better the effect of the AMF on Pb purification by EFBs. Both flooding and Pb stress decreased the AMF diversity but did not significantly inhibit the abundance. The three inoculation treatments showed different community compositions with different dominant AMF taxa in different phases, and an uncultured Paraglomus species (Paraglomus sp. LC516188.1) was found to be the most dominant (99.65 %) AMF in the hydroponic phase with Pb stress. The TEM and EDS analysis results showed that the Paraglomus sp. could accumulate Pb in plant roots through their fungal structures (intercellular mycelium, intracellular mycelium, etc.), which alleviated the toxic effect of Pb on plant cells and limited Pb translocation. The new findings provide a theoretical basis for the application of AMF in plant-based bioremediation of wastewater and polluted waterbodies.

Spatial variability and environmental drivers of cassava-arbuscular mycorrhiza fungi (AMF) associations across Southern Nigeria

Cassava, forming starch-rich, tuberous roots, is an important staple crop in smallholder farming systems in sub-Saharan Africa. Its relatively good tolerance to drought and nutrient-poor soils may be partly attributed to the crop's association with arbuscular mycorrhiza fungi (AMF). Yet insights into AMF-community composition and richness of cassava, and knowledge of its environmental drivers are still limited. Here, we sampled 60 cassava fields across three major cassava-growing agro-ecological zones in Nigeria and used a DNA meta-barcoding approach to quantify large-scale spatial variation and evaluate the effects of soil characteristics and common agricultural practices on AMF community composition, richness and Shannon diversity. We identified 515 AMF operational taxonomic units (OTUs), dominated by Glomus, with large variation across agro-ecological zones, and with soil pH explaining most of the variation in AMF community composition. High levels of soil available phosphorus reduced OTU richness without affecting Shannon diversity. Long fallow periods (> 5 years) reduced AMF richness compared with short fallows, whereas both zero tillage and tractor tillage reduced AMF diversity compared with hoe tillage. This study reveals that the symbiotic relationship between cassava and AMF is strongly influenced by soil characteristics and agricultural management and that it is possible to adjust cassava cultivation practices to modify AMF diversity and community structure.

Improved genotypes and fertilizers, not fallow duration, increase cassava yields without compromising arbuscular mycorrhizal fungus richness or diversity

Arbuscular mycorrhizal fungi (AMF) are ubiquitous in agroecosystems, but their role in mediating agricultural yield remains contested. Field experiments testing effects of realistic agronomic practices of intensification on AM fungus composition and yields are scarce, especially in the low-input systems of sub-Saharan Africa. A large, full-factorial field experiment was conducted in South-Kivu (DR Congo), testing effects of fallow duration (6 vs. 12 months), genotype (landrace vs. improved), and fertilizer management (control vs. five combinations omitting N, P, K, and/or secondary macro- and micronutrients) on yields of cassava, an important staple crop strongly colonized by AMF. Furthermore, we used DNA-metabarcoding to evaluate effects of these agronomic practices on the AM fungal communities on the roots. The shorter fallow duration strongly increased diversity and richness of AMF, but this did not correspond with increased yields. Cassava yield was mainly determined by genotype, being largest for the improved genotype, which coincided with a significantly higher sum of AM fungal sequences. Effects of fertilizer or genotype on community composition were minor to absent. We found no evidence that increased AMF richness and diversity enhanced cassava yields. In contrast, the use of the improved genotype and mineral fertilizers strongly benefitted yields, without compromising richness or diversity of AMF. Cassava-AMF associations in this work appear robust to fertilizer amendments and modern genotype improvement.

Arbuscular Mycorrhizal Fungal Communities Are Influenced by Host Tree Species on the Loess Plateau, Northwest China

Arbuscular mycorrhizal (AM) fungi can establish mutualistic symbioses with most terrestrial plants and therefore play a crucial role in the re-vegetation and rehabilitation of degraded ecosystems. Yet, little information is available on AM fungal communities associated with dominant tree species in the semi-arid region of the Loess Plateau, Northwest China. In this study, topsoil (0–20 cm) and subsoil (20–40 cm) samples were collected from the rhizosphere of five dominant tree species in northern Shaanxi Province, to investigate the distribution and diversity of their associated AM fungi. The tree species were Hippophae rhamnoides Linn., Juniperus communis L., Populus cathayana Rehd., Robinia pseudoacacia L., and Salix matsudana Koidz. In total, 24 AM fungal species of eight genera were isolated from the rhizosphere soil samples and identified based on their spore morphology. Funneliformis and Funneliformis monosporum were respectively the most abundant genus and species of AM fungi. The distribution and diversity of AM fungi differed among the five tree species and also between the two soil depths. Across different tree species, the spore density of AM fungi varied from 2.85 to 15.32 spores g−1 fresh soil, with a species richness of 3–7, Shannon–Wiener index of 0.81–1.08, and evenness index of 0.30–0.53. The mycorrhizal colonization rate had a significant negative correlation with both the Shannon-Wiener index and species richness, whereas it was positively correlated with the evenness index. Permutational multivariate analysis of variance, non-metric multidimensional scaling, and structural equation modeling revealed that tree species, rather than soil depth or its interactions with tree species, had significant effects on the composition of AM fungal communities. In conclusion, the distribution and diversity of AM fungi associated with the dominant tree species were mainly affected by host tree species identity in the semi-arid ecosystem. Claroideoglomus etunicatum (W.N. Becker & Gerdemann) C. Walker & A. Schüßler and Glomus reticulatum Bhattacharjee & Mukerji appeared to be promising candidates for ecological restoration in the Loess Plateau region because of their adaptation to its semi-arid conditions with a broad spectrum of host tree species.