Mike Dixon

• PhD
• Professor (Full) at University of Guelph

Medicinal plants (MPs) are valued for their contributions to human health. However, the growing demand for MPs and the concerns regarding their quality and sustainability have prompted the reassessment of conventional production practices. Controlled environment cropping systems, such as vertical farms, offer a transformative approach to MP product...

Capturing and reusing fertigation drainage is a key strategy for maximizing greenhouse production efficiency while minimizing the impact of wastewater discharge on receiving ecosystems. Fertigation drainage, in this regard, refers to irrigation water mixed with fertilizer that has once passed through soilless culture. Although an economically and e...

Future space missions will likely include plants to provide fresh foods and bioregenerative life support capabilities. Current spacecraft such as the International Space Station (ISS) operate at 1 atm (101 kPa) pressure, but future missions will likely use reduced pressures to minimize gas leakage and facilitate rapid egress (space walks). Plants f...

Composting has been used extensively as a sustainable approach for the management organic waste streams and conversion into stabilized soil amendments and horticultural growth media. In addition to these products, the composting process also generates by-products of microbial metabolism that includes gas (CO2) and energy (heat). High rates of food...

The blue water footprint (WF) is an indicator of freshwater required to produce a given end product. Determining the blue WF for milk production, the seasonal water use and the impact of water conservation are important sustainability considerations for the dairy industry in Ontario (Canada). In this study, a water footprint network (WFN) method wa...

Controlled environment agriculture (CEA), specifically advanced greenhouses, plant factories, and vertical farms, has a significant role to play in the urban agri-food landscape through provision of fresh and nutritious food for urban populations. With the push towards improving sustainability of these systems, a circular or closed-loop approach fo...

Adventitious root development, an auxin mediated process, is critical for clonal propagation of ornamental crops such as Kalanchoe blossfeldiana. Understanding and manipulating auxin transport as it relates to adventitious rooting can lead to improved rooting success and faster production cycles. Auxin dynamics are known to be heavily influenced by...

Boron-Doped Diamond (BDD) anodes and stainless-steel cathodes were employed in an electrochemical flow cell and evaluated for inactivation efficacy on the plant pathogen Rhizoctonia solani in hydroponic fertigation water. The electrochemical system showed promise as an electrochemical advanced oxidation process (EAOP) in that significant reductions...

The capture and re-use of greenhouse fertigation water is an efficient use of fertilizer and limited water resources, although the practice is not without risk. Plant pathogens and chemical contaminants can build up over successive capture and re-use cycles; if not properly managed they can lead to reduced productivity or crop loss. There are numer...

Abstract: The capture and re-use of greenhouse irrigation/fertigation water is an efficient use of ever more limited water resources. Although an efficient use of water and fertilizer resources, the recycling of fertigation water is not without obstacles. When capturing and re-applying fertigation solutions there is a greater risk for both pathogen...

Controlled application of drought can increase secondary metabolite concentrations in some essential oil-producing crops. To evaluate the effects of drought on cannabis ( Cannabis sativa L.) inflorescence dry weight and cannabinoid content, drought stress was applied to container-grown cannabis plants through gradual growing substrate drying under...

Return of samples from the surface of Mars has been a goal of the international Mars science community for many years. Strategies for the collection of such samples have ranged from “grab and go” acquisition from the surface, to dust collection in the atmosphere, to scientific selection by geologically capable rovers. As comprehension of the comple...

Executive Summary Return of samples from the surface of Mars has been a goal of the international Mars science community for many years. Affirmation by NASA and ESA of the importance of Mars exploration led the agencies to establish the international MSR Objectives and Samples Team ( iMOST ). The purpose of the team is to re‐evaluate and update the...

This report requested by the International Mars Exploration Working Group (IMEWG). Return of samples from the surface of Mars has been a goal of the international Mars science community for many years. Affirmation by NASA and ESA of the importance of Mars exploration led the agencies to establish the international MSR Objectives and Samples Team (i...

Electrochemical in situ regenerative hypochlorination for the continuous disinfection of fertigation solutions. A process was developed that allowed for the regeneration of free chlorine such that complete inactivation of pathogens could be achieved without breaching free chlorine phytotoxic thresholds. The system is effective with only trace level...

The influence of light spectral quality on cannabis (Cannabis sativa L.) development is not well defined. It stands to reason that tailoring light quality to the specific needs of cannabis may increase bud quality, consistency, and yield. In this study, C. sativa L. ‘WP:Med (Wappa)’ plants were grown with either no supplemental subcanopy lighting (...

In typical ornamental nursery operations, irrigation schedules are predominantly determined by the nursery manager’s subjective assessment of crop water requirements. In lieu of quantitative assessment strategies, managers tend to err on the side of caution and water to excess. This results in poor water use efficiency and significant fertilizer le...

Cannabis producers lack reliable information on the horticultural management of their crops. This thesis research was designed to improve horticultural practices for controlled environment cannabis production; topics included propagation, growing substrates, fertilization, and irrigation. To optimize the procedures for taking vegetative stem cuttin...

Executive Summary: Return of samples from the surface of Mars has been a goal of the international Mars science community for many years. Affirmation by NASA and ESA of the importance of Mars exploration led the agencies to establish the international MSR Objectives and Samples Team (iMOST). The purpose of the team is to re-evaluate and update the...

The tree nursery industry is the largest water consumer in the ornamental horticulture sector in Canada. In most nurseries, subjective irrigation scheduling protocols have conditioned the trees to receive daily irrigation, however, rising environmental concerns and cost of water have prompted the industry to reduce its use of water. These water sav...

This study evaluated the influence of several factors and their interactive effects on the propagation success of stem cuttings of cannabis (Cannabis sativa L.). Factors included (i) leafnumber(twoorthree),(ii) leaftip removal (one-third of leaf tips removed), (iii) basal/apical position of stem cutting on the stock plant, and (iv) rooting hormone...

In typical ornamental nurseries, irrigation schedules are frequently established subjectively, often resulting in excessive water use and significant fertilizer leaching. Using stem psychrometers to directly measure plant water status (PWS), the relationship between water stress, prevailing environmental conditions, and species-specific stress-tole...

In the expanding North American medical cannabis industry, growers lack reliable and systematically investigated information on the horticultural management of their crops, especially with regard to nutrient management and growing substrates. To evaluate organic substrates and their optimal nutrient management, five rates that supplied 57, 113, 170...

Details, in brief, how advanced life support research aligns well with Canada’s Space policy framework: 1) Puts Canadian interests first 2) Excellence in key capabilities 3) Private sector driven 4) Progress made through partnerships 5) Inspires Canadians (e.g., Tomatosphere)

Cannabis producers, especially those with organic operations, lack reliable information on the fertilization requirements for their crops. To determine the optimal organic fertilizer rate for vegetative-stage cannabis (Cannabis sativa L.), five rates that supplied 117, 234, 351, 468, and 585 mg N/L of a liquid organic fertilizer (4.0N–1.3P– 1.7K) w...

Presented our lab’s research on coir-based growing substrates and organic fertilizer use for cannabis production

Extreme hypobaria is a novel abiotic stress that is outside the evolutionary experience of terrestrial plants. In natural environments, the practical limit of atmospheric pressure experienced by higher plants is about 50 kPa or about 0.5 atmospheres; a limit that is primarily imposed by the combined stresses inherent to high altitude conditions of...

Research and technology developments surrounding Advanced Life-Support (ALS) began at the University of Guelph in 1992 as the Space and Advanced Life Support Agriculture (SALSA) program, which now represents Canada’s primary contribution to ALS research. The early focus was on recycling hydroponic nutrient solutions, atmospheric gas analysis and ca...

Controlled hypobaria presents biology with an environment that is never encountered in terrestrial ecology, yet the apparent components of hypobaria are stresses typical of terrestrial ecosystems. High altitude, for example, presents terrestrial hypobaria always with hypoxia as a component stress, since the relative partial pressure of O2 is consta...

Differentially expressed genes in response to 50 kPa/NormOx (50 kPa/pO2 = 21 kPa) and 25 kPa/NormOx (25 kPa/pO2 = 21 kPa) in roots and shoots of 10 d plants. There are 40 genes showing statistically significant (p < 0.01) differential expression by at least 2-fold in at least in one of 50 kPa/NormOx and 25 kPa/NormOx in roots, and 3 genes in shoots...

Confirmation of gene expression profiles using qRT-PCR. The transcript levels of AHB1 (AT2G16060) and PDC1 (AT4G33070) were determined by Taqman quantitative RT-PCR for RNA samples from the same 10 d roots tissues used for microarray analysis and additional experimental replications. The UBQ11 (AT4G05050) was used as the internal control. The Log2...

Full list of differentially expressed genes in response to 50 kPa and 50 kPa/NormOx (50 kPa/pO2 = 21 kPa) in roots of 10 d and 5 d plants. In a comparison between 10 and 5 d plants, 221 genes show statistically significant (p < 0.01) differential expression by at least 2-fold in at least one condition (in response to 50 kPa and 50 kPa/NormOx in roo...

Full list of differentially expressed genes in response to 50 kPa and 50 kPa/NormOx (50 kPa/pO2 = 21 kPa) in roots and shoots of 10 d plants. There are 151 genes that present significant (p < 0.01) differential expression by at least 2-fold in at least one condition (including responses to 50 kPa and 50 kPa/NormOx in roots or shoots) in 10 d plants...

Full list of differentially expressed genes in response to 25 kPa, 25 kPa/NormOx (25 kPa/pO2 = 21 kPa), and 97 kPa/HypOx (97 kPa/pO2 = 5 kPa) in roots and shoots of 10 d plants. There are 372 genes showing statistically significant (p < 0.01) differential expression by at least 2-fold in at least one condition—including responses to 25 kPa, 25 kPa/...

List of genes in pathway enrichment. The differentially expressed genes mapped to KEGG pathways in the enrichment analysis (Benjamini corrected p < 0.05) were listed. Responses include 50 kPa, 50 kPa/NormOx (50 kPa/pO2 = 21 kPa), 25 kPa, 25 kPa/NormOx (25 kPa/pO2 = 21 kPa), and 97 kPa/HypOx (97 kPa/pO2 = 5 kPa) in roots and shoots of 10 d plants.

Plant growth promoting microorganisms (PGPMs) of the plant root zone microbiome have received limited attention in hydroponic cultivation systems. In the framework of a project aimed at the development of a biological life support system for manned missions in space, we investigated the effects of PGPMs on four common food crops (durum and bread wh...

Details, in brief, how advanced life support research aligns well with Canada’s Space policy framework: 1) Puts Canadian interests first 2) Excellence in key capabilities 3) Private sector driven 4) Progress made through partnerships 5) Inspires Canadians (e.g., Tomatosphere)

Soybean is traditionally grown in soil, where root symbiosis with Bradyrhizobium japonicum can supply nitrogen (N), by means of bacterial fixation of atmospheric N2. Nitrogen fertilizers inhibit N-fixing bacteria. However, urea is profitably used in soybean cultivation in soil, where urease enzymes of telluric microbes catalyze the hydrolysis to am...

Rearing of yellow mealworm (Tenebrio molitor L.) will provide good animal nutrition for astronauts in a bioregenerative life support system. In this study, growth and biomass conversion data of T. molitor larvae were tested for calculating the stoichiometric equation of its growth. Result of a respiratory quotient test proved the validity of the eq...

Plant cultivation in large-scale closed environments is challenging and several key technologies necessary for space-based plant production are not yet space-qualified or remain in early stages of development. The EDEN ISS project foresees development and demonstration of higher plant cultivation technologies, suitable for future deployment on the...

Conventional irrigation practices are based on physical factors and observations, however this fails to include plant water status measurements. This study examined the relationship between cumulative water potential with concurrent cumulative vapour pressure deficit (VPD) for the common nursery species Thuja occidentalis 'Smaragd' (emerald pyramid...

High mortality rates among most species of nursery trees after transplanting is generally attributed to water stress imposed by a range of soil and other environmental conditions. This study examined the efficacy of a consortium of mycorrhizae (Root Rescue Landscape Powder), comprised of 20 species of both endo-And ecto-mycorrhizae, in mitigating w...

Abstract High phosphate content in wastewater is currently a major issue facing the North American greenhouse industry. Phosphate-sorbing material filters could provide a means of removing phosphate from wastewater prior to discharge to the environment, but characterization of economically viable materials and specific recommendations for greenhous...

Investigating the use of ion-selective optical sensors for characterizing biologically significant water chemistry in extreme environments.

Soybean [Glycine max (L.) Merr.] is one of the plant species selected within the European Space Agency (ESA) Micro-Ecological Life Support System Alternative (MELiSSA) project for hydroponic cultivation in Biological Life Support Systems (BLSSs), because of the high nutritional value of seeds. Root symbiosis of soybean with Bradirhizobium japonicum...

Robust, real-time, ion-selective sensors are much needed by the greenhouse and controlled environment plant production sectors. Ion-selective sensors will provide growers with the capability to minimize nutrient and water requirements while improving crop yields. Such considerations are more critical requirements for space-based plant production sy...

Hanging basket (HB) production alters the light environment in the lower canopy of ornamental greenhouses by intercepting and altering the spectral quality of incoming light. If shading is sufficiently high, the quality of the lower crops can be reduced. This work investigated changes in light quantity and quality at the lower crop level caused by...

At the dawn of the space age, the Chapman report set Canada on a path to a robust space program responding to Canadian socio-economic challenges. Canada’s leadership in radar and communications satellite technology is a direct result of this wise allocation of funds. Canada’s strategy to concentrate limited funding on niche areas that support Canad...

In the last decade, indoor air pollution has been unanimously recognised as a public health hazard worldwide, both in developed and developing countries. Accumulation of indoor air pollutants appears to significantly contribute to "sick building syndrome" (SBS) and other reported diseases in affected spaces. Botanical biofiltration has received a g...

Ensuring high plant yields is critical for the application of higher plants to spacebased biological life support systems. An imager capable of monitoring several fluorescent biological markers in real-time would provide a robust health monitoring system and allow growers to minimize environmental stressors. This article reports the results of the...

Greenhouse ornamental plants in Canada make up a billion dollar industry. This large industry requires substantial amounts of growing substrates. At present, most of the substrates are composed of primarily peat moss and perlite. Current environmental concerns surrounding the over use of peat has increased the demand for more environmentally sustai...

The ability to monitor and control plant nutrient ions in fertigation solutions, on an ion-specific basis, is critical to the future of controlled environment agriculture crop production, be it in traditional terrestrial settings (e.g., greenhouse crop production) or as a component of bioregenerative life support systems for long duration space exp...

Presents the development of extreme environment plant production systems for spaceflight applications and how that technology is directly transferable to Food Security issues in northern communities.

A model development approach, which aims to build sufficiently simple models so as to ensure parameter identifiability, is presented and used to develop a dynamic mass balance model of photosynthesis and respiration reactions. The model was developed for the control of a highly automated plant growth chamber within the context of the MELiSSA projec...

Highly efficient and reliable plant growth such as that required in biological life support systems for future space-based missions can be better achieved with knowledge of ion concentrations within the hydroponic nutrient solution. This paper reports on the development and application of ion-selective bulk optodes to plant growth systems. Membrane...

To investigate the feasibility of using a sensor-based automated irrigation system in pot-in-pot tree production and to determine the optimum substrate moisture contents at which the irrigation events should be triggered to turn on, a trial was conducted in a commercial nursery in Southwest Ontario, Canada, in the growing season of 2011. Acer rubru...

Aqueous ozone is increasingly used to treat irrigation source water in greenhouse and nursery operations; however, the ozone is typically removed prior to crop application. Until recently, this was appropriate as there was a paucity of data to suggest any other course of action. Recent research examining the application of aqueous ozone, through dr...

As part of an ESA MELiSSA investigation into advanced life support (ALS) candidate crop cultivar selection and growth requirements, the University of Guelph’s Controlled Environment Systems Research Facility (CESRF) conducted a case study on growth and development of four durum wheat cultivars (Triticum turgidum var durum) grown hydroponically unde...

Fusarium foetens was recently reported on greenhouse Hiemalis begonia (Begonia × hiemalis Fotsch) in Canada, causing disease symptoms which consist of a dull green leaf colour, wilting, and vascular necrosis. During our greenhouse trials, a concentration of 100 conidia mL added to the growing substrate was sufficient to cause severe disease symptom...

Marchantia polymorpha L. (a thalloid liverwort) is a common plant pest in nursery and greenhouse production systems. The rapid growth and dissemination of this pest can result in heavy mats of thallus tissue on the surface of pots, which restrict water penetration, compete for nutrients, and provide a habitat for other pests and disease vectors. Th...

Long-term space exploration missions to the Moon or Mars will require food production facilities to sustain human life. Considering that the atmospheric pressure on the Moon and Mars is much less than that on Earth, scientists have been studying plant production in controlled environments with reduced pressures in order to better understand effects...

Soybean [Glycine max (L.) Merr.] is one of the plant species selected as a candidate for hydroponic cultivation in biological life support systems (BLSS) for human space exploration, because of the high nutritional value of seeds, rich in proteins and lipids. Nitrate based recipes are the most common to feed crops in hydroponics, however, they requ...

The deployment of complex biological systems in urban settings has evolved as a technology to mitigate what has come to be known as the sick building syndrome. Indoor air quality (IAQ) is a rising concern as people are spending more time indoors and buildings are increasingly sealed to reduce energy consumption. Accumulation of gaseous contaminants...

During the growth of red beet plants in a closed environment plant growth chamber, a change in metabolism was observed (decreasing photosynthetic quotient) which was not predicted by a previously developed simple dynamic model of photosynthesis and respiration reactions. The incorporation of developmental stages into the model allowed for the repre...

Plant productivity is mediated by numerous environmental parameters and for a bioregenerative life support system to supply the needs of the crew and be sustainable with current technological limitations, photosynthesis must be optimized. The objectives of this study were to evaluate the change in the quantum efficiency of radish grown at reduced t...

Recycling of greenhouse irrigation water in hydroponic tomato production requires a water remediation process to reduce the risk of pathogen proliferation and the accumulation of other chemical compounds. The dissolution of ozone into bulk irrigation solutions is an effective technology for reducing chemical contaminant and pathogen levels in green...

Radish (Raphanus sativus), lettuce (Latuca sativa), and wheat (Triticum aestivum) plants were grown at either 98 kPa (ambient) or 33 kPa atmospheric pressure with constant 21 kPa oxygen and 0.12 kPa carbon dioxide in atmospherically closed pressure chambers. All plants were grown rockwool using recirculating hydroponics with a complete nutrient sol...

In North America the demand for organically produced food has increased rapidly during the past several years. In Canada, more than 2000 ha of organic vegetables are produced in the field in 2005, but a major proportion of organic vegetables consumed are imported, especially when seasonally cold conditions preclude field production. Research has sh...

The advantages of plant growth promoting rhizobacteria in an Advanced Life Support system on the Moon or Mars may be limited by a low partial pressure of oxygen (pO 2). Raphanus sativus 'Cherry Bomb II Hybrid' was inoculated with Bradyrhizobium japonicum Tal 629 and grown hydroponically at ambient and low (7 kPa) pO 2 for 18 days. Inoculation with...

Zeolite in substrates for growing plants has been shown to reduce nutrient leaching and to increase water retention. Zeolite was incorporated in organic growing substrates to evaluate the effects of this mineral on the growth of tomato transplants. Initially, 25 substrates were evaluated and the most promising were chosen for further investigation....

Simultaneous measurements of electrical resistance (or impedance (Z)) and water potential have been made on avocado Perseaamericana Mill. in the laboratory and on white spruce Piceaglauca (Moench) Voss in the field.A significant correlation was found between electrical impedance (corrected to standard temperature of 20 °C) and water potential of ne...

Simultaneous measurements were made of the water potentials of the stem and fruit of intact tomato plants (Lycopersicon esculentum Mill. var. Heinz 2653) using in situ temperature-corrected stem psychrometers. Water potential of the fruit remained consistently lower than the water potential of the stem except when the plant had been subjected to pr...

The presence of an abscission zone in the stem of greenhouse roses (Rosa hybrida) between the vegetative and reproductive components was verified. This led to a description of the hydraulic architecture of the rose stem. The structural aspects of the xylem conducting system in stem, abscission zone and peduncle were examined to define their relativ...

Aqueous ozone (O 3(aq)) solutions were applied to the rockwool substrate of hydroponically cultured tomato and cucumber plants. Single applications of high concentration solutions (0, 5, 10, 15, 20 mg/L), as well as repeated application of lower concentration solutions (0, 2, 4, 6 mg/L), had no impact on leaf area and shoot dry weight accumulation....

This paper presents a simple mass balance model for plant growth. This work is a first step in the development of a model intended to enable the prediction and control of a plant production chamber for MELiSSA, a regenerative life support system project developed by the ESA. Photosynthesis and respiration were selected as key reactions for biomass...

Hiemalis begonias Fotsch (Begonia × hiemalis), a member of the family Begoniaceae, is a commercially important potted flowering plant in Europe and North America. In the spring of 2010, stunted growth and dull green leaves of H. begonias were observed in a commercial greenhouse in southern Ontario, Canada. Symptoms began with dull green foliage, fo...

Six individual growing substrate components were selected. From the individual components, 35 growing substrates were constructed. Preliminary analyses, which included pH, electrical conductivity, and macro- and micronutrient concentrations, combined with environmental and cost implications were conducted to identify which substrates had the approp...

To determine the optimum feeding nutrient solution concentrations for the production of potted miniature roses (Rosa chineersis minima 'Fall Festival') under recirculating subirrigation conditions, plants were grown under four different nutrient solution concentrations [25%, 50%, 75%, and 100% of the full strength with an electrical conductivity (E...

Low pressure atmospheres were suggested for Space Greenhouses (SG) design to minimize sys-tem construction and re-supply materials, as well as system manufacturing and deployment costs. But rarified atmospheres modify heat exchange mechanisms what finally leads to alter-ations in thermal control for low pressure closed environments. Under low atmos...

Micro-Ecological Life Support System Alternative (MELiSSA) is an artificial closed ecosystem that is considered a tool for the development of a bioregenerative life support system for manned space missions. One of the five compartments of MELiSSA loop -Higher Plant Chamber was recently integrated into the MELiSSA Pilot Plant facility at Universitat...

The Canadian Advanced Life Support Systems (CanALSS) roadmap was initially prepared for the CSA in 2008, providing a plan to align Canadian technology development and mission priorities with the global space exploration strategy and the ESA MELiSSA project. An enhanced Canadian advanced life support system strategy based on life support and technol...

The Arthur Clarke Mars Greenhouse is a unique research facility dedicated to the study of greenhouse engineering and autonomous functionality under extreme operational conditions, in preparation for extraterrestrial biologically-based life support systems. The Arthur Clarke Mars Greenhouse is located at the Haughton Mars Project Research Station on...