Wheat root trait plasticity, nutrient acquisition and growth responses are dependent on specific arbuscular mycorrhizal fungus and plant genotype interactions

Tradeoffs among root functional traits for phosphorus acquisition in 13 soybean genotypes contrasting in mycorrhizal colonization

BACKGROUND AND AIMS

Plants have adapted to acquire phosphorus (P) primarily through advantageous root morphologies, responsive physiological pathways and associations with mycorrhizal fungi. Yet, to date, little information exists on how variation in arbuscular mycorrhizal (AM) colonization is coordinated with root morphological and physiological traits to enhance P acquisition.

METHODS

Thirteen root functional traits associated with P acquisition were characterized at full bloom stage in pot cultures under low soil P availability conditions for 13 soybean genotypes contrasting in AM colonization.

KEY RESULTS

Significant variation in root functional traits was observed in response to low P stress among the 13 tested soybean genotypes contrasting in AM colonization. Genotypes with low AM colonization exhibited greater root proliferation but with less advantageous root physiological characteristics for P acquisition. In contrast, genotypes with high AM colonization exhibited less root growth but higher phosphatase activities and carboxylate content in the rhizosheath. Root dry weights, and contents of carbon and P were positively correlated with root morphological traits of different root orders and whole root systems, and were negatively correlated with AM colonization of fine roots and whole root systems, as well as rhizosheath phosphatase activities and carboxylate contents. These results taken in combination with a significant positive correlation between plant P content and root morphological traits indicate that root morphological traits play a primary role in soybean P acquisition.

CONCLUSIONS

The results suggest that efficient P acquisition involves tradeoffs among carbon allocation to root proliferation, mycorrhizal symbiosis or P-mobilizing exudation. Complementarity and complexity in the selection of P acquisition strategies was notable among soybean genotypes contrasting in AM colonization, which is closely related to plant C budgeting.

Maize, wheat, and soybean root traits depend upon soil phosphorus fertility and mycorrhizal status

Strong effects of plant identity, soil nutrient availability or mycorrhizal fungi on root traits have been well documented, but their interactive influences on root traits are still poorly understood. Here, three crop species (maize, wheat and soybean) were grown under four phosphorus (P) addition levels (0, 20, 40 and 60 mg P kg-1 dry soil), and plants were inoculated with or without five combined arbuscular mycorrhizal fungal (AMF) species. Plant biomass, nutrient contents, root traits (including total root length, average root diameter, specific root length and root tissue density) and plants' mycorrhizal responses were measured. Crop species, P level, AMF, and their interactions strongly affected plant biomass and root traits. P fertilization promoted plant growth but reduced mycorrhizal benefits on plant biomass and nutrient uptake. Root traits of maize were sensitive to P addition only under the non-mycorrhizal condition, whilst most root traits of soybean and wheat plants were responsive to mycorrhizal inoculation but not P addition. Mycorrhizal colonization reduced the root plasticity in response to P fertility for maize but not for wheat or soybean. This study highlights the importance of soil nutrient fertility and mycorrhizal symbiosis in influencing root traits.

Assessment of halotolerant bacterial and fungal consortia for augmentation of wheat in saline soils

Adaptations of green technologies to counter abiotic stress, including salinity for crops like wheat by using halotolerant microbes, is a promising approach. The current study investigated 17 salt-affected agroecological zones from the Punjab and Sindh provinces of Pakistan to explore the potential of indigenous microbial flora, with their multiple biochemical characteristics in addition to plant growth promoting (PGP) traits, for enhanced wheat production in saline areas. Initially, 297 isolated pure bacterial colonies were screened for salt tolerance, biochemical, and PGP traits. Three bacterial strains belonging to Pantoea spp. and Erwinia rhaphontici with possession of multiple characteristics were selected for the development of the halotolerant bacterial consortium. Inoculation of two local wheat varieties, Faisalabad 2008 and Galaxy 2013, with the consortium for in vitro seed germination assay and sand microcosm experiments exhibited significant improvement of selected plant growth parameters like germination percentage and root structure. Two previously reported PGP fungal strains of Trichoderma harzianum and T. viridae were also used as fungal consortium separately for pot experiments and field trials. The pot experiments exhibited a positive correlation of consortia with metabolic viz. catalase, peroxidase, and proline and agronomical parameters including shoot length, dry weight, number of spikes, spike length, and 100 grain weight. To evaluate their performance under natural environmental conditions, field trials were conducted at three salt-affected sites. Agronomical attributes including days of flowering and maturity, flag leaf weight, length and width, shoot length, number of spikes, spike length, spike weight, number of seeds spike-1, 1,000 grain weight, and plot yield indicated the efficiency of these microbes to enhance wheat growth. Concisely, the bacterial consortium showed better performance and Faisalabad 2008 was a more resistant variety as compared to Galaxy 2013. Initial promising results indicate that further extensive research on indigenous microbes might lead to the development of Pakistan's first saline-specific biofertilizers and sustainable eco-friendly agriculture practices.

Individual and combined effects of arbuscular mycorrhizal fungi and phytohormones on the growth and physiobiochemical characteristics of tea cutting seedlings

Both arbuscular mycorrhizal fungi (AMF) and phytohormones collectively regulate plant growth and root development, but their individual and combined effects on tea [Camellia sinensis (L.) O. Kuntze] cutting seedings remain unclear. This study examined the individual and combined effects of two species of AMF (Rhizophagus intraradices, RI and Funneliformis mosseae, FM) and two types of palnt hormones (strigolactones, SLs; polyamines, PAs) on tea cutting seedings, by evaluating the growth and physiobiochemical characteristics of plants treated with the AMFs and/or hormones. The results showed that inoculation with either AMF individually or hormones treatment alone could significantly enhanced mycorrhizal colonization, growth target and physiobiochemical characteristics of tea cutting seedlings. Interestingly, the addition of a combination of AMFs and hormones showed superior effects, while SL and RI exhibited the most improvements to the colonization rate, plant growth, root-morphological traits, root DHA activity, photosynthesis, chlorophyll content, soluble sugar content in leaves, and the activities of antioxidant enzymes (SOD, POD, and CAT), compared to other treatment combinations (SL + FM, PA + RI, and PA + FM). Correlation analyses revealed a significantly (p < 0.05) positive correlation of root AMF colonization with root-related traits (e.g., DHA, root total length, surface area, and volume) and leaf-related traits (e.g., leaf area, shoot biomass, total chlorophyll, and antioxidant enzyme activities). This study demonstrated that while the apllication of individual AMF or plant hormones had a certain good effects on most growth and physiobiochemical characteristics parameters of tea cutting seedings, the additive effect was from specific combined of AMF and plant hormones. These results highlight the possibility for combined of AMF and plant hormones to improve the asexual reproduction of tea plants via cuttings.

New Insights into the Phosphorus Acquisition Capacity of Chilean Lowland Quinoa Roots Grown under Low Phosphorus Availability

Reducing phosphate fertilizer inputs while increasing food nutritional quality has been posited as a major challenge to decrease human undernourishment and ensure food security. In this context, quinoa has emerged as a promising crop due to its ability to tolerate different stress conditions and grow in marginal soils with low nutrient content, in addition to the exceptional nutritional quality of its grains. However, there is scarce information about the phosphorus acquisition capacity of quinoa roots. This work aimed to provide new insights into P acquisition and functional root traits, such as root biomass, rhizosphere pH, carboxylate exudation, and acid phosphatase activity of thirty quinoa genotypes grown under P limiting conditions (7 mg P kg^-1). Significant genotypic variation was observed among genotypes, with average P accumulation ranging from 1.2 to 11.8 mg. The shoot biomass production varied more than 14 times among genotypes and was correlated with the P accumulation on shoots (r = 0.91). Despite showing high variability in root traits, only root biomass production highly correlated with P acquisition (r = 0.77), suggesting that root growth/morphology rather than the measured biochemical activity possesses a critical role in the P nutrition of quinoa.

Symbiotic Fungi Alter the Acquisition of Phosphorus in Camellia oleifera through Regulating Root Architecture, Plant Phosphate Transporter Gene Expressions and Soil Phosphatase Activities

Plant roots can be colonized by many symbiotic fungi, whereas it is unclear whether and how symbiotic fungi including arbuscular mycorrhizal fungi and endophytic fungi promote phosphorus (P) uptake in Camellia oleifera plants. The objective of the present study was to analyze the effect of inoculation with a culturable endophytic fungus (Piriformospora indica), three arbuscular mycorrhizal fungi (Funneliformis mosseae, Diversispora versiformis, and Rhizophagus intraradices), and mixture of F. mosseae, D. versiformis and R. intraradices on plant growth, root architecture, soil Olsen-P, soil phosphatase activities, leaf and root P concentrations, and phosphate transporter gene expressions, in order to explore the potential and mechanism of these symbiotic fungi on P acquisition. All the symbiotic fungi colonized roots of C. oleifera after 16 weeks, with P. indica showing the best effect on fungal colonization. All the symbiotic fungi significantly increased acid, neutral, and total phosphatase activities in the soil, accompanied with an elevation of soil Olsen-P, of which P. indica presented the best effect. All symbiotic fungal treatments, except D. versiformis, significantly promoted plant growth, coupled with an increase in root total length, area, and volume. Symbiotic fungi almost up-regulated root CoPHO1-3 expressions as well as leaf CoPHO1-1, CoPHO1-3, and CoPHT1;4 expressions. Correlation analysis showed that P concentrations in leaves and roots were significantly positively correlated with root morphological variables (length, volume, and surface area) and soil acid, neutral and total phosphatase activities. It is concluded that symbiotic fungi, especially P. indica, played an important role in P uptake of C. oleifera plants through regulating root architecture, part plant phosphate transporter gene expressions and soil phosphatase activities.

Shifts in biochemical and physiological responses by the inoculation of arbuscular mycorrhizal fungi in Triticum aestivum growing under drought conditions

BACKGROUND

A decrease in rainfall is one of the main constraints on wheat production, although the association of wheat with arbuscular mycorrhizal fungi (AMF) may be an alternative for crop production under drought conditions. In the present study, we used three wheat cultivars (Purple, Ilustre and Maxi Baer) inoculated with two AMF strains, one obtained from the hyperarid Atacama Desert (northern Chile; Fm) and the other obtained from southern Chile (Cc). Plants were maintained under two irrigation conditions (normal irrigation and drought) and the physiological behaviour and enzymatic and nonenzymatic antioxidant activities in the shoots were determined. In addition, the phenolic compounds were identified by high-performance liquid chromatography-dioide array detection-electrospray ionization-tandem mass spectrometry and quantified.

RESULTS

AMF colonization produced higher levels of efficiency of photosystem II and photosynthetic pigments. High values of catalase in Purple-Cc, ascorbate peroxidase in Purple-Cc, glutathione reductase in Maxi-Cc and superoxide dismutase in Purple-Cc, all under stress, were registered. Of the inoculated cultivars, Purple-Cc showed the highest flavonoid levels, whereas hydroxycinnamic acids were higher in Maxi-Fm without drought, with apigenin and luteolin being the most abundant. High levels of phenols were present in the Ilustre-Fm plants without drought. Under normal irrigation, high levels of antioxidant activity were registered in the AMF treatments, whereas, under stress conditions, in general, high values were observed under the Fm inoculation.

CONCLUSION

Our results showed that the greatest antioxidant activity and phenolic content occurred in wheat plants inoculated with AMF, indicating their influence on coping with water stress, which is of importance in vast areas where global climate change is resulting in diminished rainfall. © 2021 Society of Chemical Industry.