A response surface methodology approach to improve nitrogen use efficiency in maize by an optimal mycorrhiza-to-Bacillus co-inoculation rate

Survival of beneficial microbes in liquid bioformulation and optimization of different carrier materials using RSM technique

Soil salinity in rice cultivation areas is considered a severely limiting factor that adversely affects the quantity and quality of rice production in wetlands. Recently, the alternative use of salt-tolerant plant growth-promoting rhizobacteria (PGPR) inhabiting extreme saline conditions has gained remarkable attention and had positive effects on soil and crops. Therefore, a study has been initiated to develop a liquid biofertilizer formulation from locally isolated multi-strain salt-tolerant PGPR strains such as Bacillus tequilensis and Bacillus aryabhattai, using glycerol (5 mM), trehalose (10 mM), and polyvinylpyrrolidone (PVP) at 1% as additives to prolong the shelf-life of the bacteria. After 3 months of incubation, the bacterial population in the trehalose-supplemented mixed strain was highest at 9.73×107 CFU/mL, followed by UPMRE6 and UPMRB9 at 9.40×107 CFU/mL and 8.50×107 CFU/mL respectively. The results showed that the optimal trehalose concentration successfully prolonged the shelf-life of bacteria with minimal cell loss. Validation of quadratic optimization by response surface methodology revealed that the cell density of the mixed strain was 4.278×107 log CFU/mL after 24 h. The precision ratio was 99.7% higher than the predicted value in the minimized medium formulation: 0.267 g/mL trehalose, 1% glycerol, at 120 rpm agitation using the data analysis tools of Design Expert software. The population study confirmed the better and longer survival of salt-tolerant PGPR fortified with 10 mM trehalose, which was considered the best liquid biofertilizer formulation. Moreover, the optimized trehalose-glycerol liquid formulation can be used commercially as it is cost-effective.

Association between host nitrogen absorption and root-associated microbial community in field-grown wheat

Plant roots and rhizosphere soils assemble diverse microbial communities, and these root-associated microbiomes profoundly influence host development. Modern wheat has given rise to numerous cultivars for its wide range of ecological adaptations and commercial uses. Variations in nitrogen uptake by different wheat cultivars are widely observed in production practices. However, little is known about the composition and structure of the root-associated microbiota in different wheat cultivars, and it is not sure whether root-associated microbial communities are relevant in host nitrogen absorption. Therefore, there is an urgent need for systematic assessment of root-associated microbial communities and their association with host nitrogen absorption in field-grown wheat. Here, we investigated the root-associated microbial community composition, structure, and keystone taxa in wheat cultivars with different nitrogen absorption characteristics at different stages and their relationships with edaphic variables and host nitrogen uptake. Our results indicated that cultivar nitrogen absorption characteristics strongly interacted with bacterial and archaeal communities in the roots and edaphic physicochemical factors. The impact of host cultivar identity, developmental stage, and spatial niche on bacterial and archaeal community structure and network complexity increased progressively from rhizosphere soils to roots. The root microbial community had a significant direct effect on plant nitrogen absorption, while plant nitrogen absorption and soil temperature also significantly influenced root microbial community structure. The cultivar with higher nitrogen absorption at the jointing stage tended to cooperate with root microbial community to facilitate their own nitrogen absorption. Our work provides important information for further wheat microbiome manipulation to influence host nitrogen absorption. KEY POINTS: • Wheat cultivar and developmental stage affected microbiome structure and network. • The root microbial community strongly interacted with plant nitrogen absorption. • High nitrogen absorption cultivar tended to cooperate with root microbiome.

Apple Antioxidant Properties as an Effect of N Dose and Rate-Mycorrhization Involvement: A Long-Term Study

The genetic and/or the agronomic approaches are two main ways to enhance concentrations of biologically active compounds in fruits and vegetables. In this study, the apple antioxidant status was evaluated from the second to the fourth year after planting in relation to an increasing N-dose applied-with or without plant microbial inoculation in the field conditions. Cultivar 'Šampion Arno' was selected to test these relationships. In the growing season, N treatment and inoculation effects were monitored for the apple peel total phenolics and selected individual phenolic compounds ((+)-catechin, (-)-epicatechin, chlorogenic and caffeic acids, rutin and phloridzin) and total ascorbate concentration. Additionally, as an environmental stress marker measurement of glutathione reductase, ascorbate peroxidase and catalase activity were conducted. The year effect was most pronounced, while the N or applied inoculum effects were much weaker. Great differences in antioxidative enzyme activity and phenolic concentrations between years were revealed. Nitrogen fertilization reduced the fruit's global phenolic accumulation compared to the control, but the N-effect varied depending on individual phenolic compounds, N dose and N application method. None of the tested factors influenced the ascorbate concentration. There was a certain tendency to increase antioxidant properties in the control group (without mineral N fertilization) but with the application of bio-fertilizer, which may seem promising for future research in this scope.