Abstract Nitrogen is an essential nutrient for the growth and development of plants, aiding many physiological and biological functions. Due to the high demand for the nutrient, it is common for agricultural production systems to fertilize crop fields with large quantities of nitrogen. However, excessive fertilization can be harmful economically and environmentally. Understanding the mechanism by which plants take up nitrogen from their environment is critical to optimize plant growth and agricultural productions. Over the past several decades, researchers have used a variety of methods to quantify nitrogen uptake, including using nitrogen isotopes, measuring uptake through depletion of a solution over time, using compartmented chambers or agarose blocks to target specific root regions, and more recent small‐scale approaches such as nanoscale secondary ion mass spectrometry (nanoSIMS), microdialysis, and biomarkers. Several of these studies have been conducted in maize due to its high nitrogen demand and significance in global food and feed production; however, these techniques can be applied to any plant system. This review will examine the application of these methods, highlighting their advantages and limitations. By exploring existing methods, we aim to provide insights into advancing nitrogen uptake studies, ultimately supporting sustainable nitrogen management and improving crop production efficiency.

Nitrogen is a key nutrient for plant growth and development, and understanding nutrient uptake is central to improving nitrogen use efficiency in crops, including maize. Reducing the need for fertilizer without reducing yield is extremely important, as nitrogen fertilizers come with a high environmental cost, in terms of both emissions from manufacturing and losses to waterways or volatilization off fields. Maize develops multiple different root types, including primary, seminal, crown, and brace roots. Part of improving efficiency in maize involves understanding the differences in nutrient uptake via each distinct root type, but these differences have been largely ignored to date. Here, we describe a protocol that uses stable isotopes for determining nitrogen uptake rates by maize root types. We describe the steps both for intact roots, for which we use rhizoboxes with openable front windows that allow access to the roots without disturbing the rest of the plant, and for field-grown plants, for which intact analysis is not feasible and requires excising the roots. The methods described here can also be modified to measure uptake kinetics and for monitoring nutrient translocation between roots and shoots. Advancing our understanding of root physiology and nutrient dynamics will improve breeding opportunities for efficient nutrient uptake varieties, reducing the need for fertilizer additions.

Nitrogen is an essential element for plant growth and development; however, application of nitrogen (N)-based fertilizers comes with a high environmental cost. This includes the energy required for production, volatilization from fields, and runoff or leaching to waterways triggering algal blooms. As such, a key goal in plant breeding programs is to develop varieties that maintain yield while requiring less fertilization. Central to this goal is understanding how roots take up nitrogen and finding traits that represent improvements in the net uptake. Maize, one of the most widely produced crops in the world, has seminal, crown, and brace root types, each under independent developmental control. Recent evidence suggests that these independent developmental patterns may result in different nutrient uptake characteristics. As such, understanding the uptake dynamics of each root type under different environmental conditions is an essential aspect for the selection of new maize varieties. A key method for tracking nitrogen uptake is the use of the15N stable isotope, which is naturally less abundant than the main14N isotope. This method involves replacing the14N in nutrient solutions with15N, exogenously providing it to the plant tissues (roots in this case), and then measuring the15N content of the tissues after a fixed amount of time. Here, we provide a brief overview of nitrogen uptake and remobilization in maize, and discuss current techniques for measuring nutrient uptake, with a focus on methods using stable isotopes of nitrogen.

Plants have a remarkable ability to generate organs with a different identity to the parent organ, called ‘trans-organogenesis’. An example of trans-organogenesis is the formation of roots from stems (a type of adventitious root), which is the first type of root that arose during plant evolution. Despite being ancestral, stem-borne roots are often contextualised through lateral root research, implying that lateral roots precede adventitious roots. In this review we challenge that idea, highlight what is known about stem-borne root development across the plant kingdom, the remarkable diversity in form and function, and the many remaining evolutionary questions. Exploring stem-borne root evolutionary development can enhance our understanding of developmental decision making and the processes by which cells acquire their fates.

Background and aims Mangrove species respond to variation in soil bulk density (BD). However, very little is known about the regulatory mechanisms that trigger these responses. Methods Endogenous concentrations of different phytohormones were measured in the roots of two mangrove species ( Avicennia marina and Rhizophora stylosa ) grown in low and high BD soils. The potential involvement of ethylene in regulating plant growth responses was tested by applying the ethylene biosynthesis inhibitors cobalt chloride (CoCl 2 ) and aminoisobutyric acid (AIB). Results The two mangrove species responded differently to variation in soil BD. High BD decreased root growth of R. stylosa , but not A. marina . Soil BD had no effect on root phytohormone levels in R. stylosa , but loose soils increased 1-aminocyclopropane-1-carboxylic acid whilst decreasing salicylic acid and gibberellin in A. marina . Applying ethylene inhibitors enhanced R. stylosa root growth, while increasing indole-3-acetic acid but decreasing isopentenyl adenine levels. In contrast, AIB inhibited A. marina root growth, while increasing trans -zeatin levels. Ethylene inhibitors affected salicylic acid levels in both species. Conclusion Salicylic acid is central to root growth responses to variation in BD in A. marina . Conversely, the interaction of ethylene and gibberellin drives responses in R. stylosa. Hormonal interactions involving ethylene potentially reflect the adaptations of the two species to differing conditions within the intertidal zone, with A. marina behaving like an aquatic species and R. stylosa behaving like a terrestrial species.

Brace roots (roots developing from aerial stem nodes) are a type of adventitious root that develop from aboveground stem nodes in many monocots. Brace roots may remain aerial or penetrate the soil as they perform root functions such as anchorage and resource acquisition. Although brace root development in soil or aerial environments influences function, a lot is still unknown about how their anatomy, architecture and development contributes to their function. This article summarizes the current state of knowledge on brace roots.

Allelopathy, that is, plant-plant inhibition via the release of secondary metabolites into the environment, has potential for the management of weeds by circumventing herbicide resistance. However, mechanisms underpinning allelopathy are notoriously difficult to elucidate, hindering real-world application either in the form of commercial bioherbicides or allelopathic crops. Such limited application is exemplified by evidence of limited knowledge of the potential benefits of allelopathy among end users. Here, we examine potential applications of this phenomenon, paying attention to novel approaches and influential factors requiring greater consideration, with the intention of improving the reputation and uptake of allelopathy. Avenues to facilitate more effective allelochemical discovery are also considered, with a view to stimulating the identification of new compounds and allelopathic species. Synthesis and Applications: We conclude that tackling increasing weed pressure on agricultural productivity would benefit from greater integration of the phenomenon of allelopathy, which in turn would be greatly served by a multi-disciplinary and exhaustive approach, not just through more effective isolation of the interactions involved, but also through greater consideration of factors which may influence them in the field, facilitating optimization of their benefits for weed management.

Plants respond to changing and variable environments with molecular and physiological changes that enable adaptation. Many of these responses depend on available energy pools which means trade-offs between prioritised processes are inevitable. The flexibility in these switches can influence plant success in responding to extreme weather events. Trade-offs are also important in the decision to establish symbioses between plants and microbes or mycorrhizae and in plant responses to insect or pathogen attack. The Special Issue ‘Trade-offs in plant responses to the environment’ (Plant, Cell and Environment 2023 Vol. 46;10) explores how plants ‘decide’ on where to best use energy and what those trade-offs mean for plant success, with measures of success ranging from computational models to end products. As experimentalists, we often simplify our research design to changing individual environmental factors and investigating the mechanisms enabling the plant responses. To keep projects manageable we also often limit our research to subsections of whole plant development, physiology or molecular biology (e.g., focusing on roots, or shoots, or specific stages of development, at one or maybe two scales). However, plants exist in complex environments and have evolved complex ways to decide on processes such as resource allocation, whether that be for deciding the direction of growth, investing in secondary metabolites for defence or regulating stomatal conductance to control water use. The articles collated in this Special Issue evaluate functional trade-offs and explore whether or not one response occurs at the expense of another process. Given the interactive nature of the processes, overlap between article topics is inevitable but they can be broadly separated into trade-offs in biotic and abiotic systems. Yet, the review by Leisner et al. (2023) highlights the complexity and importance of multistress interactions. They conclude that more work is needed to fill the knowledge gap that exists in understanding the interactions and trade-offs that occur when plants are exposed to combinations of biotic and abiotic stresses. We couldn't agree more and hope to see more work in this area in the future. When presented with the idea of trade-offs, our first thought often relates to plant defence. Indeed, this is the field where trade-offs have been discussed the most. The typical expectation of plants growing under biotic stresses, is that to make defence compounds (i.e., secondary metabolites), resources for growth need to be killed. However, this generalisation often lacks nuance, a point we find developed in this special issue. A review from Malhotra et al. (2023) nicely details these nuances with examples where growth and defence occur as a trade-off and other times where growth and defence are synergistic. Additional research papers present further evidence of these complexities. In an updated view of the growth defence trade-off, Vega-Alvarez et al. (2023) use Brassica oleracea with differing resistance to Xanthomonas campestris to demonstrate that the immobilisation of sugars, rather than the cost of making secondary metabolites, is the cause of biomass loss. In contrast, Meline et al. (2023) looked at growth defence trade-offs in the context of tomato wilt disease (Ralstonia solanacearum). Studying both wilt resistant and susceptible lines, the authors show that wilt-resistant plants activate both growth and defence, while susceptible plants exhibited the expected trade-off between growth and defence. Thus, each plant−pathogen system has unique attributes, which reinforces the notion that there is no one-size-fits-all for growth defence trade-offs. In addition to studies on pathogens, this Special Issue includes a series of articles on insect defence responses in plants. Again, we see examples for both, existence and absence of trade-offs. For example, Frost (2023) looked at the phytochemical profiles of trees from both an intact and a wound-inducible perspective. They found a trade-off between the diversity of phytochemicals from intact leaves and the diversity of induced phytochemicals in wounded leaves. In other words, plants with a high native phytochemical diversity had a lower inducible diversity, suggesting a trade-off between constitutive inducible defence abilities. In contrast, Guo et al. (2023) found no trade-off between growth and defence in corn borer resistant and corn borer susceptible maize inbred lines. Moving beyond the growth defence trade-off, Zhou et al. (2023) asked whether a rice DREB1A (dehydration-responsive element-binding 1A) line known to enhance abiotic stress tolerance would alter biotic resistance to a phloem-feeding herbivore. They confirm a trade-off exists with DREB1A expressing lines exhibiting reduced resistance to the brown planthopper (Nilaparvata lugens). The articles highlighted thus far have focused on the detrimental plant biotic interactions. A fascinating different aspect of trade-offs in plant biotic interactions is included with the review by Mohd-Radzman and Drapek (2023) discussing trade-offs during symbiosis. This review covers the different degrees by which plants compartmentalise their symbionts and how this could be a strategy to mitigate risks. In summary, compartmentalising different endosymbionts separately helps avoid intraspecies competition between the symbionts and the subsequent reduced symbiont load. It also allows the host to maintain more control over symbiont physiology via resource delivery. This can be an important strategy when plants are growing in nutrient deficient conditions, controlling carbon investment to symbionts and ideally allowing selection for symbionts providing the best nutrient exchange. This Special Issue also touches on trade-offs in the context of abiotic stresses, which is increasingly relevant for plant performance in a changing global climate. A review by Mao et al. (2023) highlights an important signalling pathway, the CBL-CIPK [CALCINEURIN B-LIKE PROTEIN (CBL)-CBL-INTERACTING PROTEIN KINASE (CIPK)], well-known for its role in regulating the crosstalk between growth and stress adaptation. In this review, the authors advocate for modulating the expression of different parts of the CBL-CIPK pathway to fine-tune and optimise the trade-off ‘decision’. In the context of hydraulic physiology, the interactions between carbon fixation and water loss constitute an important trade-off. Stefanski et al. (2023) show that warming and rainfall reduction makes stomatal behaviour more conservative in terms of water loss per unit carbon gain across 21 boreal and temperate tree species. Plants exhibit a typical ‘recession’ behaviour spending less when resources are limited. The authors predict increasingly conservative water-carbon trade-off behaviour in a warming drying world. In a set of simulations, Cai et al. (2023) suggest that the root hydraulic conductivity and/or root length can also contribute to stomatal physiological trade-offs. It will be interesting to explore how a more conservative water-carbon trade-off at the stomatal level will also impact on leaf cooling and energy budgets. On this point, Muller et al. (2023) show that plants can adjust their cooling mechanism to changing environmental conditions by optimising their aerodynamic resistance which is linked to evaporative cooling. Understanding these physiological trade-offs in the context of increasingly harsh environments is an exciting and active area of research. As the exploration of trade-offs grows, there will be an increasing need for accessible and relevant experimental systems. Golan et al. (2023) describe one such system in wheat to study the trade-off of individual plant fitness and community performance. Additional innovation in experimental systems aimed at studying trade-offs at different scales and under different environmental conditions will be needed to drive this field forward. In an excellent conversational and in-depth review, Robinson (2023) delves into a popular theory on how plants manage trade-offs on a global scale, the optimal partitioning theory (OPT). The article argues that plants do not have to trade-off resource allocation between roots and shoot, which is the foundation of the whole-plant OPT. Instead, Robinson proposes a more realistic model that treats plants as groups of semiautonomous modules, which can manage local trade-offs, thus, advocating for consideration of local responses as opposed to solely global responses. Overall, this Special Issue brings together an exciting and diverse set of manuscripts, each detailing a unique aspect of plant trade-offs. Indeed, finding a common theme upon which to structure this editorial was quite the challenge. However, this diversity is inherent to the topic and highlights the broad excitement in the scientific community for exploring trade-offs. Generalising is never the answer in biology.

These data contain information on root traits and concentrations of multiple hormones in root tissue of two mangrove species grown under low and high soil bulk density conditions. Inhibitors were used to assess the role of the phytohormone ethylene. Description of the data and file structure The root trait file contains total root length (cm), mean root length (cm), root dry weight (g), and root number data for two mangrove species (Avicennia marina, Rhizophora stylosa) grown under two different soil bulk densities: 0.2 and 1.0 g cm^-3. Treatment refers to the application of ethylene inhibitors (CoCl2: cobalt chloride, AIB: aminoisobutyric acid, control). The phytohormone file contains the root tissue concentrations (all in ng g^-1) for multiple hormones (ABA: abscisic acid, ACC: 1-aminocyclopropane-1-carboxylic acid, GAx: gibberellins, IAA: indole-3-acetic acid, iP: isopentenyl adenine, JA: jasmonic acid, SA: salicylic acid, tZ: cytokinin trans-zeatin) of two mangrove species (Avicennia marina, Rhizophora stylosa) grown under two different soil bulk densities: 0.2 and 1.0 g cm^-3. Treatment refers to the application of ethylene inhibitors (CoCl2: cobalt chloride, AIB: aminoisobutyric acid, control).

Heightened by the COVID-19 pandemic there has been a global increase in urban greenspace appreciation. Indoor plants are equally important for improving mental health and air quality but despite evolving in humid (sub)tropical environments with aerial root types, planting systems ignore aerial resource supply. This study directly compared nutrient uptake preferences of aerial and soil-formed roots of three common houseplant species under high and ambient relative humidities. Growth and physiology parameters were measured weekly for Anthurium andreanum, Epipremnum aureum and Philodendron scandens grown in custom made growth chambers. Both aerial and soil-formed roots were then fed mixtures of nitrate, ammonium and glycine, with one source labelled with 15 N to determine uptake rates and maximum capacities. Aerial roots were consistently better at nitrogen uptake than soil roots but no species, root type or humidity condition showed a preference for a particular nitrogen source. All three species grew more in high humidity, with aerial roots demonstrating the greatest biomass increase. Higher humidities for indoor niches, together with fertiliser applications to aerial roots will support indoor plant growth, creating lush calming indoor environments for people inhabitants.

Plant root systems provide critical functions to enable plant survival. From anchoring the plant in the soil to finding and acquiring water and nutrients, these organs are essential for plant productivity. Despite a variety of root functions, research typically focuses on defining only one function. In this study, we explore a trade-off hypothesis, that the optimization of one root function (i.e. anchorage) may negatively impact another root function (i.e. nitrogen uptake). Previous work has demonstrated that larger roots are stronger, but may also have a diminished capacity for nutrient acquisition due to a reduced surface area to volume ratio. Using maize brace roots that had entered the soil, we show here that larger roots are both stronger and take up more nitrogen. Despite this general relationship, there are subtle trade-offs between mechanics and uptake that occur when assessing individual genotypes. These trade-offs represent an opportunity to optimize one root function without compromising other root functions. Together these data demonstrate that our original trade-off hypothesis was incorrect for maize brace roots, and that larger roots are both stronger and take up more nitrogen.

Due to climate change, water availability will become increasingly variable, affecting nitrogen (N) availability. Therefore, we hypothesised watering frequency would have a greater impact on plant growth than quantity, affecting N availability, uptake and carbon allocation. We used a gravimetric platform, which measures the unit of volume per unit of time, to control soil moisture and precisely compare the impact of quantity and frequency of water under variable N levels. Two wheat genotypes (Kukri and Gladius) were used in a factorial glasshouse pot experiment, each with three N application rates (25, 75 and 150 mg N kg −1 soil) and five soil moisture regimes (changing water frequency or quantity). Previously documented drought tolerance, but high N use efficiency, of Gladius as compared to Kukri provides for potentially different responses to N and soil moisture content. Water use, biomass and soil N were measured. Both cultivars showed potential to adapt to variable watering, producing higher specific root lengths under low N coupled with reduced water and reduced watering frequency (48 h watering intervals), or wet/dry cycling. This affected mineral N uptake, with less soil N remaining under constant watering × high moisture, or 48 h watering intervals × high moisture. Soil N availability affected carbon allocation, demonstrated by both cultivars producing longer, deeper roots under low N. Reduced watering frequency decreased biomass more than reduced quantity for both cultivars. Less frequent watering had a more negative effect on plant growth compared to decreasing the quantity of water. Water variability resulted in differences in C allocation, with changes to root thickness even when root biomass remained the same across N treatments. The preferences identified in wheat for water consistency highlights an undeveloped opportunity for identifying root and shoot traits that may improve plant adaptability to moderate to extreme resource limitation, whilst potentially encouraging less water and nitrogen use.

Global food production needs to increase by more than 60% by 2050 while concurrently reducing fertiliser applications to crops to reduce greenhouse emissions, production costs and environmental pollution. This chapter explores the role of hormones on nitrogen and phosphate uptake and responses. In particular it focuses on auxin, cytokinin and strigolactones in each nutrient condition and how they interact with each other to control root architectural responses. Past success with stay-green crop varieties, modified in cytokinin regulation of nitrogen remobilisation, demonstrates the real-world significance of a detailed understanding of hormone networks. The chapter also highlights current limitations in our understanding and exciting directions for the future.

Abstract The capability of synthetic pesticides to manage weeds, insect pests and pathogens in crops has diminished due to evolved resistance. Sustainable management is thus becoming more challenging. Novel solutions are needed and, given the ubiquity of biologically active secondary metabolites in nature, such compounds require further exploration as leads for novel crop protection chemistry. Despite improving understanding of allelochemicals, particularly in terms of their potential for use in weed control, their interactions with multiple biotic kingdoms have to date largely been examined in individual compounds and not as a recurrent phenomenon. Here, multi‐kingdom effects in allelochemicals are introduced by defining effects on various organisms, before exploring current understanding of the inducibility and possible ecological roles of these compounds with regard to the evolutionary arms race and dose–response relationships. Allelochemicals with functional benefits in multiple aspects of plant defence are described. Gathering these isolated areas of science under the unified umbrella of multi‐kingdom allelopathy encourages the development of naturally‐derived chemistries conferring defence to multiple discrete biotic stresses simultaneously, maximizing benefits in weed, insect and pathogen control, while potentially circumventing resistance. © 2020 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

The modern workplace requires teamwork bridging distances, time-zones and cultures using virtual collaboration platforms. As such teamwork is a key employability skill for our graduates, and yet we rarely explicitly teach team skills or how to navigate and collaborate in a virtual environment. Here we demonstrate that integrating in-person (synchronous) and online (synchronous and asynchronous) learning environments can prove an extremely resilient teaching method that allowed continuity during COVID-19 lockdown, while providing them with these essential skills. Students were given a semester long documentary video team assignment supported by regular compulsory team training sessions and using the Microsoft Teams online collaboration platform. At the end of semester, the 24 students in the class were sent a survey with questions relating to their perspectives of teamwork in general, the team training sessions and online platform and the impact of COVID-19. Of the 12 respondents only 4 reported negative attitudes to teamwork in general and learning and shared workload were the most reported benefits. Implementing explicit (and compulsory) team training sessions throughout semester were valued by the students for reasons ranging from the explicit intention of each task (team establishment and planning, negotiation, reflection of team behaviours, negotiating team member contributions) to the more general appreciation that regular compulsory sessions ensured the teams met frequently. It was particularly positive that every student reported that this team experience was better than their previous team experiences, and this in spite of the COVID-19 lockdown. Included with this manuscript are all the learning materials provided to the students and a few key lessons we learnt along the way.

Aerial roots have evolved in plants from diverse ecosystems, many facing specific environmental challenges associated with their natural or agricultural setting. In coastal species exposed to wind and waves, including mangroves, soft anoxic substrates have resulted in highly developed aerial root systems. In the rainforest, aerial roots of hemi-epiphytic figs enable life to begin higher in the canopy while climbing plants, such as ivy and Monsteras, depend on structurally very different aerial roots to climb vertical substrates. Maize, globally one of the three most important cereals, develops aerial roots presumably reducing lodging in high winds. In each of these cases, the dominant hypothesized role for aerial roots is to provide support and enabling greater heights to be reached. But do aerial roots of these plant groups also contribute to resource uptake and movement? This article explores the current knowledge of aerial root physiology and structure from each of these interesting and challenging environmental conditions and discusses how understanding these adaptations and niche requirements has value for improving crops, protecting our coastlines, improving our urban green spaces, and managing biodiversity conservation.

Current climate change models project that water availability will become more erratic in the future. With soil nitrogen (N) supply coupled to water availability, it is important to understand the combined effects of variable water and N supply on food crop plants (above- and below-ground). Here we present a study that precisely controls soil moisture and compares stable soil moisture contents with a controlled wetting-drying cycle. Our aim was to identify how changes in soil moisture and N concentration affect shoot-root biomass, N acquisition in wheat, and soil N cycling. Using a novel gravimetric platform allowing fine-scale control of soil moisture dynamics, a 3 × 3 factorial experiment was conducted on wheat plants subjected to three rates of N application (0, 25 and 75 mg N/kg soil) and three soil moisture regimes (two uniform treatments: 23.5 and 13% gravimetric moisture content (herein referred to as Well-watered and Reduced water, respectively), and a Variable treatment which cycled between the two). Plant biomass, soil N and microbial biomass carbon were measured at three developmental stages: tillering (Harvest 1), flowering (Harvest 2), and early grain milk development (Harvest 3). Reduced water supply encouraged root growth when combined with medium and high N. Plant growth was more responsive to N than the water treatments imposed, with a 15-fold increase in biomass between the high and no added N treatment plants. Both uniform soil water treatments resulted in similar plant biomass, while the Variable water treatment resulted in less biomass overall, suggesting wheat prefers consistency whether at a Well-watered or Reduced water level. Plants did not respond well to variable soil moisture, highlighting the need to understand plant adaptation and biomass allocation with resource limitation. This is particularly relevant to developing irrigation practices, but also in the design of water availability experiments.

Societal Impact StatementPlants underpin our society providing food, fuel, medicines, clean air and water, positive mental health, and are central to biodiversity conservation. Despite this importance and an increasing need for people with plant‐identification skills, many societies are becoming increasingly ignorant to the species with which they interact. To benefit both our undergraduates and the society they will enter, we applied mobile technology to improve plant identification and appreciation, while providing opportunities to practice transferable team work and verbal communication skills. Encouraging 'plant vision' will improve conservation efforts while increasing personal connections with green spaces, leading to mental health improvements for society. Summary Despite the importance of plants to human civilization, many societies are becoming increasingly ignorant to the plants that inhabit their surrounding environment. A phenomenon known as ‘plant blindness’. To address plant blindness in undergraduate students we designed an outdoor activity using a mobile phone app. Our aims were to identify the level of ‘plant blindness’ in our students; investigate engagement with the app and activity; determine if we can raise awareness of links between lecture content and real world scenarios; and assess the student experience as a result of the activity in large classes. The app chosen was ActionBound. Students were asked to find and photograph local examples of four plant families, along with identifying physiological benefits of features covered in lectures. Two different first year classes were exposed to this activity – Plant Science and Life on Earth. The Plant Science students (60% success rate for three families; 55 students) were less plant blind than Life on Earth students (less than 44% success rate in any of the four families; 200 students). Students engaged well with the activity with all groups submitting sensible attempts at the responses. Most students reported that the activity increased links to lecture material and all but one student reported positive experiences. Our students found the treasure hunt learning environment is a fun way to engage with the plant topics covered in lectures. In future iterations, we will more explicitly explain the links to potential careers and will address some of the logistical challenges faced in this first cohort.

Adventitious root formation is essential for cutting propagation of diverse species; however, until recently little was known about its regulation. Strigolactones and ethylene have both been shown to inhibit adventitious roots and it has been suggested that ethylene interacts with strigolactones in root hair elongation. We have investigated the interaction between strigolactones and ethylene in regulating adventitious root formation in intact seedlings of Arabidopsis thaliana. We used strigolactone mutants together with 1-aminocyclopropane-1-carboxylic acid (ACC) (ethylene precursor) treatments and ethylene mutants together with GR24 (strigolactone agonist) treatments. Importantly, we conducted a detailed mapping of adventitious root initiation along the hypocotyl and measured ethylene production in strigolactone mutants. ACC treatments resulted in a slight increase in adventitious root formation at low doses and a decrease at higher doses, in both wild-type and strigolactone mutants. Furthermore, the distribution of adventitious roots dramatically changed to the top third of the hypocotyl in a dose-dependent manner with ACC treatments in both wild-type and strigolactone mutants. The ethylene mutants all responded to treatments with GR24. Wild type and max4 (strigolactone-deficient mutant) produced the same amount of ethylene, while emanation from max2 (strigolactone-insensitive mutant) was lower. We conclude that strigolactones and ethylene act largely independently in regulating adventitious root formation with ethylene controlling the distribution of root initiation sites. This role for ethylene may have implications for flood response because both ethylene and adventitious root development are crucial for flood tolerance.