Abstract
Arbuscular mycorrhiza (AM) is a mutualistic association between most plant species and the ancient fungal phylum Glomeromycota in roots, and it plays a key role in a plant’s nutrient uptake ...from the soil. Roots synthesize strigolactones (SLs), derivatives of carotenoids, and exude them to induce energy metabolism and hyphal branching of AM fungi. Despite the well-documented roles of SLs in the pre-symbiotic phase, little is known about the role of SLs in the process of root colonization. Here we show that the expansion of root colonization is suppressed in the mutants of rice (Oryza sativa) SL biosynthesis genes, carotenoid cleavage dioxygenase D10 and more severely in D17. Interestingly, most of the colonization process is normal, i.e. AM fungal hyphae approach the roots and cling around them, and epidermal penetration, arbuscule size, arbuscule number per hyphopodium and metabolic activity of the intraradical mycelium are not affected in d10 and d17 mutants. In contrast, hyphopodium formation is severely attenuated. Our observations establish the requirement for SL biosynthesis genes for efficient hyphopodium formation, suggesting that SLs are required in this process. Efficient hyphopodium formation is required for the punctual internalization of hyphae into roots and maintaining the expansion of colonization.
El estudio de la composición de los hongos micorrizógenos arbusculares (HMA) permite analizar patrones temporales de estos microorganismos en distintos ecosistemas, así como identificar especies ...tolerantes a los cambios ambientales. El objetivo fue evaluar si existen cambios a lo largo del tiempo en la composición de los HMA en un bosque templado mexicano. Se recolectaron muestras de suelo (300 g) en ocho parcelas a dos altitudes diferentes durante 2015, 2017 y 2019, en la temporada lluviosa y seca. Las esporas de HMA se extrajeron con la técnica de tamizado húmedo y gradiente de sacarosa. Se usó el índice de Jaccard para calcular la similitud de especies entre años. Se construyó un diagrama de Venn para conocer el número de especies compartidas y exclusivas, y un clúster de dos vías para determinar el agrupamiento de las especies. Se realizó un análisis de correspondencia canónica (CCA) para relacionar la composición de HMA y los factores abióticos. Se registraron 38 especies de HMA, agrupadas en 15 géneros y 6 familias. Se encontraron especies presentes en los tres años y ambas temporadas: Acaulospora delicata, Acaulospora laevis, Acaulospora mellea, Funneliformis geosporus, Funneliformis mosseae y Rhizophagus fasciculatus. El CCA mostró influencia de la temperatura, materia orgánica y pH en la composición de HMA. Estas especies tienen un potencial uso para la restauración o reforestación debido a su capacidad de tolerar los cambios en las condiciones ambientales. En conclusión, la composición de HMA es sujeta a los cambios temporales a lo largo de los años
Global increase in nitrogen (N) deposition influences the belowground allocation of plant photosynthates and the formation of roots and rhizosphere-associated symbionts as well as soil nutrient ...availability, thereby affecting the nutrient acquisition by trees. Trees obtain nutrients primarily through fine root growth or mycorrhizal symbioses. These two mechanisms have an antagonistic relationship, but how they are modified by N deposition remains unknown. Arbuscular mycorrhizae (AM) and ectomycorrhizae (EM) are the two dominant types of mycorrhizal fungi that form symbioses with the roots of most trees. However, the divergent adaptive mechanisms and nutrient acquisition strategies of trees with a symbiotic relationship with AM (AM trees) or with EM (EM trees) in response to N deposition are unclear. To clarify these points, we conducted a meta-analysis of 116 studies on global forest ecosystems. Following prolonged (>2 years) or high-load (>140 kg ha−1 y−1) N addition, both AM and EM trees decrease the amount of energy allocated to mycorrhizal symbioses and increasingly rely on fine roots to obtain nutrients. The faster growth of AM trees than of EM trees under N deposition is partly attributed to their divergent nutrient acquisition strategies: the fine root biomass and length decreased significantly in EM trees (−13% and −17%, respectively), but not in AM trees. Furthermore, the acid phosphatase activity increased more for the AM trees than for the EM trees (28% and 4%, respectively), indicative of a greater abundance of available P for the AM trees than for the EM trees after N addition. Consequently, AM trees have advantages in terms of root morphology and phosphatase activity over EM trees, suggesting they are better adapted to high N deposition.
•Trees shifted from mycorrhizal fungi to fine roots for nutrient acquisition under N addition.•Fine root biomass and length significantly decreased for ECM not for AM trees.•AM trees increased acid phosphatase activity 7-fold compared with that of ECM trees.•N deposition can influence belowground traits and plant nutrient acquisition.
•New insights into the effects of biochar on fine root dynamics are presented.•An increase of fine root biomass occurred immediately after biochar application.•Fine root biomass increment during ...water shortage could be attributed to radial growth.•Biochar had no significant effect on the annual production of arbuscular mycorrhiza.
Application of biochar to the soil is globally recognised as a means to improve soil structure and fertility, increase carbon sequestration, enhance crop production and mitigate climate change. However, although the fine root system is fundamental for plant growth, crop productivity, carbon and nutrient cycling, little is known about the effect of biochar on plant fine roots. This study, conducted in a Montepulciano (Vitis vinifera L.) vineyard, was aimed at investigating the impact of biochar application (at the rate of 10tha−1) on soil chemical and physical properties, fine root dynamics and arbuscular mycorrhizal fungi (AMF) production during a one-year sampling period. To this aim, seasonal variation of fine root mass, length and diameter was measured by the sequential coring technique, whereas fine root annual production was calculated by minimum-maximum procedure and turnover rate of live roots by maximum standing biomass. For AMF annual production, in-growth mesh bags were used to measure glomalin as quantitative indicator of mycorrhizae presence. Results showed that biochar significantly increased organic carbon (20.7%), available ammonium (84.4%), and available water content of the soil (11.8%), while it also promoted the formation of the large fraction of macro aggregates (ø>2mm; 3.1% control; 5.5% treated). Cation exchange capacity, pH, total nitrogen content, and total and available phosphorus content remained unaffected. Immediately after biochar soil amendment, while fine root length remained unchanged, a significant increase in fine root biomass was measured resulting in a higher mean annual biomass (8.56gm−2 control; 13.34gm−2 treated), annual production (8.71gm−2 control; 12.7gm−2 treated) and lifespan (as evidenced by a lower turnover rate; 1.02 yr−1 control; 0.95 yr−1 treated). Moreover, the increase of fine root biomass resulted to be associated with radial growth since mean fine root diameter was significantly higher in biochar-treated plants (0.56mm) than in control plants (0.46mm). Biochar had no significant effect on the annual production of AMF. The results of the present study show that the improvements of soil chemical and physical features due to biochar application have an immediate effect on fine root dynamics and morphology. Furthermore, the increase of fine root biomass is mainly due to radial growth and occurs during the water shortage period, supporting fruit setting and ripening in grapevine plants.
Arbuscular mycorrhizal (AM) fungi contribute to plant nitrogen (N) acquisition. Recent studies demonstrated the transport of N in the form of ammonium during AM symbiosis. Here, we hypothesize that ...induction of specific ammonium transporter (AMT) genes in Sorghum bicolor during AM colonization might play a key role in the functionality of the symbiosis.
For the first time, combining a split-root experiment and microdissection technology, we were able to assess the precise expression pattern of two AM-inducible AMTs, SbAMT3;1 and SbAMT4. Immunolocalization was used to localize the protein of SbAMT3;1.
The expression of SbAMT3;1 and SbAMT4 was greatly induced locally in root cells containing arbuscules and in adjacent cells. However, a split-root experiment revealed that this induction was not systemic. By contrast, a strictly AM-induced phosphate transporter (SbPt11) was expressed systemically in the split-root experiment. However, a gradient of expression was apparent. Immunolocalization analyses demonstrated that SbAMT3;1 was present only in cells containing developing arbuscules.
Our results show that the SbAMT3;1 and SbAMT4 genes are expressed in root cortical cells, which makes them ready to accommodate arbuscules, a process of considerable importance in view of the short life span of arbuscules. Additionally, SbAMT3;1 might play an important role in N transfer during AM symbiosis.
An increase in root hair length and density and the development of arbuscular mycorrhiza symbiosis are two alternative strategies of most plants to increase the root-soil surface area under ...phosphorus (P) deficiency. Across many plant species, root hair length and mycorrhization density are inversely correlated. Root architecture, rooting density and physiology also differ between species. This study aims to understand the relationship among root hairs, arbuscular mycorrhizal fungi (AMF) colonization, plant growth, P acquisition and mycorrhizal-specific Pi transporter gene expression in maize.
Using nearly isogenic maize lines, the B73 wild type and the rth3 root hairless mutant, we quantified the effect of root hairs and AMF infection in a calcareous soil under P deficiency through a combined analysis of morphological, physiological and molecular factors.
Wild-type root hairs extended the rhizosphere for acid phosphatase activity by 0.5 mm compared with the rth3 hairless mutant, as measured by in situ zymography. Total root length of the wild type was longer than that of rth3 under P deficiency. Higher AMF colonization and mycorrhiza-induced phosphate transporter gene expression were identified in the mutant under P deficiency, but plant growth and P acquisition were similar between mutant and the wild type. The mycorrhizal dependency of maize was 33 % higher than the root hair dependency.
The results identified larger mycorrhizal dependency than root hair dependency under P deficiency in maize. Root hairs and AMF inoculation are two alternative ways to increase Pi acquisition under P deficiency, but these two strategies compete with each other.
Arbuscular mycorrhizal (AM) symbiosis is stimulated by phosphorus (P) limitation and contributes to P and nitrogen (N) acquisition. However, the effects of combined P and N limitation on AM formation ...are largely unknown.
Medicago truncatula plants were cultivated in the presence or absence of Rhizophagus irregularis (formerly Glomus intraradices) in P-limited (LP), N-limited (LN) or combined P- and N-limited (LPN) conditions, and compared with plants grown in sufficient P and N.
The highest AM formation was observed in LPN, linked to systemic signaling by the plant nutrient status. Plant free phosphate concentrations were higher in LPN than in LP, as a result of cross-talk between P and N. Transcriptome analyses suggest that LPN induces the activation of NADPH oxidases in roots, concomitant with an altered profile of plant defense genes and a coordinate increase in the expression of genes involved in the methylerythritol phosphate and isoprenoid-derived pathways, including strigolactone synthesis genes.
Taken together, these results suggest that low P and N fertilization systemically induces a physiological state of plants favorable for AM symbiosis despite their higher P status. Our findings highlight the importance of the plant nutrient status in controlling plant–fungus interaction.
Rice (Oryza sativa L.), being a high silicon (Si)-accumulator, is a major global food crop for more than half of the world's population. However, both salinity and drought, two of the most ...challenging abiotic stresses in rice-growing areas globally, threaten world food security. Both symbiosis with arbuscular mycorrhizal fungi (AMF) and supplementing paddy soils with Si have been shown to improve rice growth during drought and salinity-stress. However, their combined impact is poorly understood. AMF may absorb Si through their spores and hyphae and thus help accumulate root Si. In turn, Si can affect mycorrhizal responsiveness but the underlying mechanisms remain largely unknown. This review explores (i) how Si and AMF act to mitigate salinity and drought stress in rice plants and (ii) how they can be applied together. We also identify areas for future study and discuss how the combined presence of arbuscular mycorrhizas (AMs) and Si in paddy soils can generate more sustainable rice productivity.
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•The benefits of Si nutrition, although significant, are limited due to its restricted uptake by rice plant.•AMF improve Si uptake, Si translocation from external solution to intraradical mycelium, and from fungal cell to root cell.•Mycorrhizal effectiveness is dependent on various factors (i.e., like soil conditions).•Si increases mycorrhizal effectiveness in plant via various mechanisms.•Research on their interaction in the combination is further required as it is a novel field.
The identity and diversity of arbuscular mycorrhizal (AM) fungal symbionts strongly affect the functioning of mycorrhiza, but little is still known about the functional relevance of the individual ...taxa abundances within AM fungal communities. We hypothesized that proportions of AM fungal taxa influence mycorrhizal benefits to the host, and that a community with spontaneously established ratios of AM fungal species is more beneficial than communities with artificially manipulated ratios. Medic (Medicago truncatula) was inoculated with synthetic AM fungal communities composed of five fungal species in different proportions, and a ‘functionally optimized’ community generated by previous co-cultivation of the five AM fungi. The composition of the communities was monitored along with the host plant responses to mycorrhiza in three sequential harvests.
Most of the artificial AM fungal communities differed compositionally and functionally from the presumably ‘functionally optimized’ community, which indeed promoted plant growth to the greatest extent. The higher ability to promote plant growth was partly explained by higher intraradical fungal biomass, but functional differences between the communities were also related to the abundances of certain AM fungal species. Thus, the experiment demonstrated functional relevance of species' abundances within AM fungal communities. The observed ‘functional optimization’ of the AM fungal community is discussed in context with the host plant's and AM fungal species' traits.
•Species ratios in mycorrhizal fungal communities influence mycorrhiza functioning.•A spontaneously established mycorrhizal community induced the highest plant benefits.•Manipulation of the fungal species abundances mostly decreased plant benefits.•Fungal species traits explain the differences in the functioning of the communities.
•ST and DT enhanced AM fungal ERH density and root colonization as compared with NT.•AM fungal spore density and OTU richness was decreased by DT as compared with NT.•Tillage practice had stronger ...effect on AM fungal community than residue retention.•Residue retention did not influence AM fungal biomass and OTU richness.
Arbuscular mycorrhizal (AM) fungi are one of the most important soil microbes in an agrarian ecosystem, and consequently affected by various agricultural practices. To elucidate the effects of tillage practices and residue management on AM fungi, a field trial was conducted on the Songnen Plain, Northeast China. We examined the effects of different tillage practices including no-tillage (NT), rotary tillage (RT), subsoil tillage (ST) and deep tillage (DT) on the AM fungal biomass, diversity and community under residue removal and residue retention. AM root colonization and extraradical hyphal (ERH) density were significantly higher in DT treatment compared with NT treatment, whereas an opposite trend was observed for AM fungal spore density. Structural equation modeling indicated that AM fungal spore density was directly affected by tillage practices. Albeit, the effect of tillage practices on ERH density was mainly mediated through root length of maize. By Miseq sequencing of 18S rDNA, 66 AM fungal operational taxonomic units (OTUs) were identified and Glomeraceae was the most abundant group in this study. AM fungal OTU richness was highest in treatment NT, and significantly higher than that in treatment DT. Non-metric multidimensional scaling analysis indicated that treatment DT and ST induced a distinct AM fungal community composition compared with treatment NT. On the other hand, residue did not significantly influence AM fungal biomass, OTU richness and community composition. Overall, our findings indicated that tillage practice is a stronger determinant than residue management in AM fungal development and community composition in black soil on the Songnen Plain.
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