The aeroponic rhizosphere microbiome: community dynamics in early succession suggest strong selectional forces

Evaluating Propagation Techniques for Cannabis sativa L. Cultivation: A Comparative Analysis of Soilless Methods and Aeroponic Parameters

Given the rapid growth of the Cannabis industry, developing practices for producing young plants with limited genetic variation and efficient growth is crucial to achieving reliable and successful cultivation results. This study presents a multi-faceted experiment series analyzing propagation techniques for evaluating proficiency in the growth and development of Cannabis vegetative cuttings. This research encompasses various (1) soilless propagation methods including aeroponics, horticultural (phenolic) foam, and rockwool; (2) transplant timings; (3) aeroponic spray intervals; and (4) aeroponic reservoir nutrient concentrations, to elucidate their impact on rooting and growth parameters amongst two Cannabis cultivars. Aeroponics was as effective as, and in some cases more effective than, soilless propagation media for root development and plant growth. In aeroponic systems, continuous spray intervals, compared to intermittent, result in a better promotion of root initiation and plant growth. Moreover, raised nutrient concentrations in aeroponic propagation demonstrated greater rooting and growth. The effects of experimental treatment were dependent on the cultivar and sampling day. These findings offer valuable insights into how various propagation techniques and growth parameters can be tailored to enhance the production of vegetative cuttings. These results hold critical implications for cultivators intending to achieve premium harvests through efficient propagule methods and optimization strategies in the competitive Cannabis industry. Ultimately, our findings suggest that aeroponic propagation, compared to alternative soilless methods, is a rapid and efficient process for cultivating vegetative cuttings of Cannabis and offers sustainable advantages in resource conservation and preservation.

Nutrient availability and plant phenological stage influence the substrate microbiome in container-grown Impatiens walleriana 'Xtreme Red'

BACKGROUND

The microbiome plays a fundamental role in plant health and performance. Soil serves as a reservoir of microbial diversity where plants attract microorganisms via root exudates. The soil has an important impact on the composition of the rhizosphere microbiome, but greenhouse ornamental plants are commonly grown in soilless substrates. While soil microbiomes have been extensively studied in traditional agriculture to improve plant performance, health, and sustainability, information about the microbiomes of soilless substrates is still limited. Thus, we conducted an experiment to explore the microbiome of a peat-based substrate used in container production of Impatiens walleriana, a popular greenhouse ornamental plant. We investigated the effects of plant phenological stage and fertilization level on the substrate microbiome.

RESULTS

Impatiens plants grown under low fertilization rates were smaller and produced more flowers than plants grown under optimum and high fertilization. The top five bacterial phyla present in the substrate were Proteobacteria, Actinobacteria, Bacteriodota, Verrucomicrobiota, and Planctomycetota. We found a total of 2,535 amplicon sequence variants (ASV) grouped into 299 genera. The substrate core microbiome was represented by only 1.8% (48) of the identified ASV. The microbiome community composition was influenced by plant phenological stage and fertilizer levels. Phenological stage exhibited a stronger influence on microbiome composition than fertilizer levels. Differential abundance analysis using DESeq2 identified more ASVs significantly affected (enriched or depleted) in the high fertilizer levels at flowering. As observed for community composition, the effect of plant phenological stage on microbial community function was stronger than fertilizer level. Phenological stage and fertilizer treatments did not affect alpha-diversity in the substrate.

CONCLUSIONS

In container-grown ornamental plants, the substrate serves as the main microbial reservoir for the plant, and the plant and agricultural inputs (fertilization) modulate the microbial community structure and function of the substrate. The differences observed in substrate microbiome composition across plant phenological stage were explained by pH, total organic carbon (TOC) and fluoride, and across fertilizer levels by pH and phosphate (PO4). Our project provides an initial diversity profile of the bacteria occurring in soilless substrates, an underexplored source of microbial diversity.

Labile carbon inputs boost microbial contribution to legacy mercury reduction and emissions from industry-polluted soils

Soils is a crucial reservoir influencing mercury (Hg) emissions and soil-air exchange dynamics, partially modulated by microbial reducers aiding Hg reduction. Yet, the extent to which microbial engagements contribute to soil Hg volatilization remains largely unknown. Here, we characterized Hg-reducing bacterial communities in natural and anthropogenically perturbed soil environments and quantified their contribution to soil Hg(0) volatilization. Our results revealed distinct Hg-reducing bacterial compositions alongside elevated mercuric reductase (merA) gene abundance and diversity in soils adjacent to chemical factories compared to less-impacted ecosystems. Notably, solely industry-impacted soils exhibited increased merA gene abundance along Hg gradients, indicating microbial adaption to Hg selective pressure through quantitative changes in Hg reductase and genetic diversity. Microcosm studies demonstrated that glucose inputs boosted microbial involvement and induced 2-8 fold increments in cumulative Hg(0) volatilization in industry-impacted soils. Microbially-mediated Hg reduction contributed to 41.6% of soil Hg(0) volatilization in industry-impacted soils under 25% water-holding capacity and glucose input conditions over a 21-day incubation period. Alcaligenaceae, Moraxellaceae, Nitrosomonadaceae and Shewanellaceae were identified as potential contributors to Hg(0) volatilization in the soil. Collectively, our study provides novel insights into microbially-mediated Hg reduction and soil-air exchange processes, with important implications for risk assessment and management of industrial Hg-contaminated soils.

The Hydroponic Rockwool Root Microbiome: Under Control or Underutilised?

Land plants have an ancient and intimate relationship with microorganisms, which influences the composition of natural ecosystems and the performance of crops. Plants shape the microbiome around their roots by releasing organic nutrients into the soil. Hydroponic horticulture aims to protect crops from damaging soil-borne pathogens by replacing soil with an artificial growing medium, such as rockwool, an inert material made from molten rock spun into fibres. Microorganisms are generally considered a problem to be managed, to keep the glasshouse clean, but the hydroponic root microbiome assembles soon after planting and flourishes with the crop. Hence, microbe–plant interactions play out in an artificial environment that is quite unlike the soil in which they evolved. Plants in a near-ideal environment have little dependency on microbial partners, but our growing appreciation of the role of microbial communities is revealing opportunities to advance practices, especially in agriculture and human health. Hydroponic systems are especially well-suited to active management of the root microbiome because they allow complete control over the root zone environment; however, they receive much less attention than other host–microbiome interactions. Novel techniques for hydroponic horticulture can be identified by extending our understanding of the microbial ecology of this unique environment.

Plant Beneficial Bacteria and Their Potential Applications in Vertical Farming Systems

In this literature review, we discuss the various functions of beneficial plant bacteria in improving plant nutrition, the defense against biotic and abiotic stress, and hormonal regulation. We also review the recent research on rhizophagy, a nutrient scavenging mechanism in which bacteria enter and exit root cells on a cyclical basis. These concepts are covered in the contexts of soil agriculture and controlled environment agriculture, and they are also used in vertical farming systems. Vertical farming-its advantages and disadvantages over soil agriculture, and the various climatic factors in controlled environment agriculture-is also discussed in relation to plant-bacterial relationships. The different factors under grower control, such as choice of substrate, oxygenation rates, temperature, light, and CO₂ supplementation, may influence plant-bacterial interactions in unintended ways. Understanding the specific effects of these environmental factors may inform the best cultural practices and further elucidate the mechanisms by which beneficial bacteria promote plant growth.

Plants Dictate Root Microbial Composition in Hydroponics and Aquaponics

The role of the microbial community in mediating fish and plant co-culture is often considered the black box of aquaponics. Despite widespread recognition regarding the dependency of plants on their rhizosphere, the extent to which upstream aquaculture influences downstream hydroponic root communities has been poorly described in the literature. In this study we performed a taxonomic survey (16S rRNA metabarcoding) of microbial communities originating in the facility water source, hydroponic nutrient solution (HNS) sump, nutrient supplemented biofilter effluent (BF) sump, and recirculating aquaculture system tanks stocked with Nile tilapia (Oreochromis niloticus). Lettuce (Lactuca sativa) was then grown using the HNS and BF effluent under sterilized or mature (prior aquaponics/hydroponics lettuce culture water) conditions, likewise, the influence of probiotic addition or inoculation with soil-grown lettuce rhizosphere was assessed. Compositional similarities across treatments suggest that under soil-less conditions, plants are able to exert a stronger discriminatory influence on their rhizosphere composition than is done by colonization from upstream sources. Furthermore, cluster dendrograms grouped the sterilized and unsterilized treatments more consistently together than hydroponics and aquaponics treatments. These findings contradict conventional beliefs that microbial communities in the water column colonize roots based on their presence alone, ignoring the role that plants play in rhizosphere community selection.

Root-Associated Bacterial Community Shifts in Hydroponic Lettuce Cultured with Urine-Derived Fertilizer

Recovery of nutrients from source-separated urine can truncate our dependency on synthetic fertilizers, contributing to more sustainable food production. Urine-derived fertilizers have been successfully applied in soilless cultures. However, little is known about the adaptation of the plant to the nutrient environment. This study investigated the impact of urine-derived fertilizers on plant performance and the root-associated bacterial community of hydroponically grown lettuce (Lactuca sativa L.). Shoot biomass, chlorophyll, phenolic, antioxidant, and mineral content were associated with shifts in the root-associated bacterial community structures. K-struvite, a high-performing urine-derived fertilizer, supported root-associated bacterial communities that overlapped most strongly with control NPK fertilizer. Contrarily, lettuce performed poorly with electrodialysis (ED) concentrate and hydrolyzed urine and hosted distinct root-associated bacterial communities. Comparing the identified operational taxonomic units (OTU) across the fertilizer conditions revealed strong correlations between specific bacterial genera and the plant physiological characteristics, salinity, and NO₃⁻/NH₄⁺ ratio. The root-associated bacterial community networks of K-struvite and NPK control fertilized plants displayed fewer nodes and node edges, suggesting that good plant growth performance does not require highly complex ecological interactions in hydroponic growth conditions.

Getting to the roots of aeroponic indoor farming

Vertical farming is a type of indoor agriculture where plants are cultivated in stacked systems. It forms a rapidly growing sector with new emerging technologies. Indoor farms often use soil-free techniques such as hydroponics and aeroponics. Aeroponics involves the application to roots of a nutrient aerosol, which can lead to greater plant productivity than hydroponic cultivation. Aeroponics is thought to resolve a variety of plant physiological constraints that occur within hydroponic systems. We synthesize existing studies of the physiology and development of crops cultivated under aeroponic conditions and identify key knowledge gaps. We identify future research areas to accelerate the sustainable intensification of vertical farming using aeroponic systems.