Phytochromes (PHYs) play a dual role in sensing light spectral quality and temperature. PHYs can interconvert between their active and inactive forms upon absorption of red and far-red light (Photoconversion). In addition, the active form can be converted to the inactive form in a temperature-dependent manner (Thermal Reversion). Our recent research found that while far-red (FR; 700-800 nm) light promoted leaf expansion and biomass of lettuce (Lactuca sativa) ‘Rex’ under cooler temperatures (20-24 °C), it reduced plant biomass and leaf area under warm temperature (28 °C). Considering that PHY activity would be driven mainly by photoconversion, not thermal reversion, under higher light intensity (HL), we hypothesized that the magnitude of the interaction between FR light and temperature on plant growth and morphology decreases with increasing light intensity. Lettuce ‘Rex’ was grown under three temperature regimes (20, 24, and 28 oC) x two spectral treatments [0 and 20% of FR light in total photon flux density (TPFD; 400-800 nm)] x two light intensities [150 (lower light intensity; LL) and 300 (HL) μmol·m-2·s- 1 of TPFD]. Our results showed that the effects of FR light on leaf expansion and stem elongation depended on temperature under LL. Specifically, FR light significantly promotes leaf expansion under cooler temperatures (20 oC), while decreasing total leaf area under warmer temperatures (24 and 28 oC). However, the magnitude of the interactive effects between FR light and temperature on plant morphology decreased under HL, leading to a consistent increase in total leaf area by FR light under HL. Similarly, FR light promoted plant growth under HL regardless of temperature, while reducing plant biomass under warm temperature under LL. Crop yield was primarily dependent on photon capture rather than photosynthetic efficiency per unit leaf area. FR light generally decreased the production of secondary metabolites (e.g., phenolics and flavonoids), while warm temperature and HL treatments increased the production of secondary metabolites. We concluded that the interactive effects between FR light and temperature on plant growth and morphology are further dependent on light intensity. The combination of FR light, warm temperature, and HL could maximize crop yield without reducing nutritional quality in terms of antioxidant capacity.
Photoperiod extension in controlled environment agriculture - including the use of 24h continuous light - can be used to reduce light fixture and electricity costs in regions with lower night electricity rates. However, many plant species develop photoperiodic injury characterized by leaf chlorosis and yield reduction at a critical species-specific photoperiod threshold. Here we will discuss the response of different plant species to continuous lighting strategies. We will first challenge the conventional notion that dark adapted chlorophyll fluorescence (Fv/Fm) measurements are the most appropriate when assessing photoperiodic injury. We provide evidence that light adapted (φPSII) measurements allow for a more in-depth understanding of the light capture process at photosystem II. Through RNA-sequencing in tomato, we determined that the use of a dynamic 24h lighting treatment (i.e., red light during the day and blue light during the night) lead to normal gene expression of chlorophyll a/b binding (CAB) proteins. However when tomato plants were grown under a static continuous lighting strategy (i.e., red blue lighting for 24h) at the same daily light integral, gene expression of CAB proteins were drastically reduced, resulting in chlorosis and yield reduction. In comparison to tomatoes, cucumbers tend to be more tolerant to long photoperiods and therefore continuous lighting can have an immediate impact in commercial production. Initial results in cucumbers show that a continuous lighting strategy can decrease the lighting electricity costs by 26% and greenhouse gas emissions by 38.9% per unit of produce compared to a 16h control treatment. Using the knowledge gained throughout our studies, we propose a lighting strategy which gamifies the electricity market to further reduce costs and greenhouse gas emissions.
Plant stress can cause economic loss for plant production and is hard and expensive to identify at times. Thus, a greenhouse experiment was conducted to find an easy and cost-friendly way to identify plant stress, set up thresholds and values for the initiation of plant nitrogen stresses. Four different crops (basil, pepper, marigold, and sage) were included and treated with five different nitrogen levels (0%, 25%, 50%, 75%, and 100%). Plant height, width and leave greenless (indicated by SPAD) were measured weekly. Pictures were taken weekly. Software Image J was used to process pictures and R was used for data analysis. We found that plants with higher nitrogen treatments (75%-100%) all grow better and have higher SPAD than other treatments, except for bail. Also, RGB value could indicate plant nitrogen status with high accuracy. Plants become nitrogen stressed when SPAD falls to 25. Red and green values in RGB have negative correlations directly with SPAD and indirectly with nitrogen stress status. When the R and G values are higher than 150 and 185, respectively, we can safely predict that the plant is nitrogen stressed. In conclusion, using RBG value can be a cost-friendly way for plant stress identification.
Dutch bucket hydroponic systems are used for high-wire crop production such as tomatoes, cucumbers, or peppers, and are typically filled with perlite as a substrate. Through past research, our group identified pine bark and wood fiber as sustainable alternative substrates for high-wire tomato production. Typically, greenhouse tomato growers utilize leachate-based or timed irrigation; however, the use of a water content sensor could precisely identify the irrigation set-point for different substrates, potentially saving water and fertilizers. This study aimed to optimize the irrigation rate for greenhouse tomato ('Favorita F1') production in the Dutch bucket hydroponic system using a soil water content sensor. Three types of substrates (perlite, pine bark, and wood fiber-coir mix (60:40)) and four different gravimetric water contents (100%, 120%, 140%, and 160%) were considered. The experiment was conducted with three replications in a completely randomized design, with the irrigation treatments under the perlite substrate serving as the control. Physical parameters, such as the number of leaves and plant height, were significantly higher in the wood fiber-coir mix and pine bark at 160% irrigation, and lowest under perlite at 100% water content. However, there was no significant difference among the treatments for the number of flower (fruit) clusters. The plant leaf area measurements indicated better vegetative growth with wood fiber-coir mix at 160% water content, whereas pine bark at 160% water content resulted in a higher yield and better fruit quality. In contrast, phytochemicals such as Brix, vitamin C, titratable acidity, lycopene, beta-carotene, and phenolic compounds were significantly higher in the organic substrates (pine bark and wood fiber) with low water content (100% to 120%) and lower in perlite with high water content (140% to 160%). The highest and lowest concentrations of phytochemicals varied between 13% to 67%. There was no significant difference among the treatments (substrates and water contents) in terms of tissue mineral analysis. In general, plants grown in wood fiber-coir mix treatments required 28% and 51% less irrigation compared to those in pine bark and perlite treatments, respectively. Plants grown in organic substrates require less water, and the yield quantity and quality are either similar to or higher than those in perlite. Out of the organic substrates, wood fiber-coir mix can be used in Dutch bucket systems to conserve water and nutrients, enhancing yield quantity and quality, and thereby achieving environmental sustainability.
As legalization continues to change the cannabis industry, we see an influx of creative innovation, funding, and research as more entities enter the field. The two innovative growing management investigated in this study were Mechanical Vibration Training (MVT) and High Stress Training (HST). MVT was carried out using a grid exposing the plants to 200 Hz vibration, and HST is a practice that involves damaging the vascular bundles, pith, and cortex of the main stem while leaving the epidermis intact. MVT is a newer technique still in development, as Thigmo-priming has been shown to change plant morphology and chemistry and even increase the speed and magnitude of future stress responses. Many industry leaders claim that the advantages of using HST include higher canopy, increased biomass and cannabinoid concentrations, and more effective IPM strategies. However, studies validating these claims are still being determined. This study aims to compare each growing management under the overall category of Thigmomorphogenesis or mechanostimulation against control (no artificial mechanical stimulation) and tease out any synergism between the treatments. We hypothesize that applying mechanostimulation to cannabis plants will enhance their growth and increase secondary metabolite production. The environment-controlled growth units housed the treatments consisted of 1-Control, 2-MVT, 3-HST, and 4-MVT HST. Each growth unit contained five-gallon fabric pots with a single Suver Haze plant. An amended coco coir substrate was used with a water-soluble nutrient solution, and optimal growing conditions, including lighting, were maintained equally in all environment-controlled growth units. Weekly plant parameters included stem diameter, plant height, NDVI, chlorophyll concentration, and photosynthetic efficiency. After-harvest parameters included above/below ground biomass, yield mass, bucked biomass, trichome density, and cannabinoid levels. Morphological and numerical differences between treatments indicated the potential for a shorter, more efficient growth cycle with higher cannabinoid levels. Further testing is currently underway.
Climate change challenges all aspects of food production, including standard greenhouse products, such as tomatoes. The cause of climate change can be directly attributed to the rise in carbon dioxide (CO2) levels, leading to increased temperatures and drought severity. Tomatoes are the most produced fruit crop globally, and in addition to their economic benefits contain several vitamins and minerals essential for human health. The objective of this study was to assess the multi-variable effects of simulated climate change on tomato plants by investigating the combination of elevated CO2 (800 ppm vs 400 ppm), increased temperature (28℃ vs 21℃), and water deficit stress (20% decrease from control) across three development stages: juvenile, anthesis, and fully mature tomato. ‘Sweet ‘N’ Neat Scarlet’ tomatoes (Solanum lycopersicum) were grown in four plant growth chambers in a 2 x 2 x 2 factorial design with four replications. Quality parameters included photosynthetic efficiency, growth index, dry weight, flower number, fruit number, and fruit size. Inductively coupled plasma mass spectrometry (ICP-MS) and oxygen radical absorbance capacity (ORAC) analyses were measured at each of the three stages when applicable. Preliminary data suggests that higher temperatures and CO2 increase (p
