The duckweeds feature global distributions and diverse applications in phytoremediation and nutrition, as well as use in fundamental studies of development. Existing collections have minimal environmental data linked to natural habitats. Thus, there is a lack of understanding of natural variation in the context of native habitats. Here, a novel collection of 124 duckweed accessions from 115 sites across the United Kingdom was characterized by genome sequencing and ionomics. In common nutrient-replete experimental conditions, all accessions hyperaccumulated P, K, Mg and Ca. Local but not large-scale associations were revealed between elemental composition of duckweed in common, replete conditions and native water profiles. Lemna minor was the most prevalent species in the UK, with a closely related hybrid L. japonica frequently found in waters with higher micronutrient concentrations. Invasive L. minuta was common in the southern and midland regions, but restricted in Scotland. Lemna accessions accumulated heavy metal contaminants typically together with macronutrients, suggesting phytoremediation potential, but some limitations as food. Furthermore, monitoring the ecological interactions between native, hybrid and invasive Lemna species should be ongoing in the interest of biodiversity.

Duckweeds (water lentils) are a nutritious human food source, with Wolffia species consumed traditionally in Eastern Asia. Duckweed contain up to 45% protein by dry weight, high macronutrients, minerals and carotenoids. However, duckweed are not cultivated at scale and there are circa 35 other species to consider for food potential in other global regions. Here, we measured the suitability of four Lemna species and Spirodela polyrhiza for nutritional assessment, by scaling up growth of 25 ecotypes from the United Kingdom in a glasshouse. Here we showed intra- and inter-species variation of aromatic and metabolic profiles, together with biomass obtained from production. The dominant volatile organic compounds (VOCs) in duckweed are hexanal, 1-penten-3-one, 1-penten-3-ol, cis-2-pentanol and pentadecanal, with variations in amounts of 22 other compounds between species. In comparison with other leafy herbs, duckweed aroma profiles were most similar to spinach and dandelion with high 'green' and 'fresh' aroma compounds. Spirodela polyrhiza contained high flavonoids including apigenin and luteolin, offering potential benefits for health. Our results demonstrate that Lemna and Spirodela species have suitable flavonoid and amino acid profiles for nutrition. VOCs found here had positive aroma descriptors and can be used as biomarkers of freshness during storage of duckweed foodstuffs.

Duckweeds span 36 species of free-floating aquatic organisms with body sizes ranging from 2 mm to 10 mm, where each plant body plan is reduced to a largely leaf-like structure. As an emerging crop, their fast growth rates offer potential for cultivation in closed systems. We describe a novel UK collection derived from low light (dLL) or high light (dHL) habitats, profiled for growth, photosynthesis, and photoprotection (non-photochemical quenching, NPQ) responses. Twenty-three accessions of three Lemna species and one Spirodela polyrhiza were grown under relatively low light (LL: 100 mu mol m-2 s-1) and high light (HL: 350 mu mol m-2 s-1) intensities. We observed broad within- and between-species level variation in photosynthesis acclimation. Duckweeds grown under HL exhibited a lower growth rate, biomass, chlorophyll, and quantum yield of photosynthesis. In HL compared with LL, carotenoid de-epoxidation state and NPQ were higher, whilst PSII efficiency (phi PSII) and Chl a:b ratios were unchanged. The dLL plants showed relatively stronger acclimation to HL compared with dHL plants, especially Lemna japonica accessions. These achieved faster growth in HL with concurrent higher carotenoid levels and NPQ, and less degradation of chlorophyll. We conclude that these data support local adaptation to the light environment in duckweed affecting acclimation in controlled conditions. Adaptation to high light levels in duckweed is characterized by growth and pigment alterations, with accessions from low light environments showing stronger acclimation than accessions from high light environments.

BACKGROUND AND AIMS:The duckweeds (Lemnaceae) consist of 36 species exhibiting impressive phenotypic variation, including the progressive evolutionary loss of a fundamental plant organ, the root. Loss of roots and reduction of vascular tissues in recently derived taxa occur in concert with genome expansions of ≤14-fold. Given the paired loss of roots and reduction in structural complexity in derived taxa, we focus on the evolution of the ionome (whole-plant elemental contents) in the context of these fundamental changes in body plan. We expect that progressive vestigiality and eventual loss of roots might have both adaptive and maladaptive consequences that are hitherto unknown. METHODS:We quantified the ionomes of 34 accessions in 21 species across all duckweed genera, spanning 70 Myr in this rapidly cycling plant (doubling times are as rapid as ~24 h). We related both micro- and macroevolutionary ionome contrasts to body plan remodelling and showed nimble microevolutionary shifts in elemental accumulation and exclusion in novel accessions. KEY RESULTS:We observed a robust directional trend in calcium and magnesium levels, decreasing from the ancestral representative Spirodela genus towards the derived rootless Wolffia, with the latter also accumulating cadmium. We also identified abundant within-species variation and hyperaccumulators of specific elements, with this extensive variation at the fine (as opposed to broad) scale. CONCLUSIONS:These data underscore the impact of root loss and reveal the very fine scale of microevolutionary variation in hyperaccumulation and exclusion of a wide range of elements. Broadly, they might point to trade-offs not well recognized in ionomes.

Duckweeds are free-floating aquatic organisms with species ranging from 2 mm-10 mm, where each plant is a single leaflike structure. Recognized as an emerging food crop, their fast growth rates offer potential for cultivation in closed systemsHowever the majority of available duckweed clones lack information regarding habitat origin and physiology. We describe a novel UK collection derived from low light (dLL) or high light (dHL) habitats and profiled for growth, photosynthesis and photoprotection (Non Photochemical Quenching, NPQ) responses. Multiple ecotypes of three Lemna species and one ecotype of Spirodela polyrhiza , were grown under low light (LL:100 μmol m -2 s-1) and high light (HL:350 μmol m -2 s-1). We found species and ecotypic variation in photosynthesis acclimation. Duckweeds grown under HL exhibited lower growth rate, biomass, chlorophyll and quantum yield of photosynthesis. In HL-compared to LL, carotenoid de-epoxidation state and NPQ were higher whilst photosystem II efficiency (ϕPSII) and chla:b ratios were unchanged. Interestingly dLL plants showed relatively stronger acclimation to HL compared to dHL plants: These ecotypes achieved faster growth in HL: by area and colony gain, higher carotenoid levels and less degradation of chlorophyll. We conclude that adaptation to local habitat among ecotypes strongly affects performance under controlled conditions.

Organ loss occurs frequently during plant and animal evolution. Sometimes, non-functional organs are retained through evolution. Vestigial organs are defined as genetically determined structures that have lost their ancestral (or salient) function.1,2,3 Duckweeds, an aquatic monocot family, exhibit both these characteristics. They possess a uniquely simple body plan, variably across five genera, two of which are rootless. Due to the existence of closely related species with a wide diversity in rooting strategies, duckweed roots represent a powerful system for investigating vestigiality. To explore this, we employed a panel of physiological, ionomic, and transcriptomic analyses, with the main goal of elucidating the extent of vestigiality in duckweed roots. We uncovered a progressive reduction in root anatomy as genera diverge and revealed that the root has lost its salient ancestral function as an organ required for supplying nutrients to the plant. Accompanying this, nutrient transporter expression patterns have lost the stereotypical root biased localization observed in other plant species. While other examples of organ loss such as limbs in reptiles4 or eyes in cavefish5 frequently display a binary of presence/absence, duckweeds provide a unique snapshot of an organ with varying degrees of vestigialization in closely related neighbors and thus provide a unique resource for exploration of how organs behave at different stages along the process of loss.

Duckweeds are morphologically simplified, free floating aquatic monocots comprising both rooted and rootless genera. This has led to the idea that roots in these species may be vestigial, but empirical evidence supporting this is lacking. Here we show that duckweed roots are no longer required for their ancestral role of nutrient uptake. Comparative analyses of nearly all rooted duckweed species revealed a highly reduced anatomy, with greater simplification in the more recently diverged genus Lemna . A series of root excision experiments demonstrated that roots are dispensable for normal growth in Spirodela polyrhiza and Lemna minor . Furthermore, ionomic analyses of fronds in these two species showed little difference in the elemental composition of plants in rooted versus root-excised samples. In comparison, another free-floating member of the Araceae, Pistia stratiotes , which colonized the aquatic environment independently of duckweeds, has retained a more complex root anatomy. Whilst Pistia roots were not absolutely required for growth, their removal inhibited plant growth and resulted in a broad change in the mineral profile of aerial tissues. Collectively, these observations suggest that duckweeds and Pistia may be different stages along a trajectory towards root vestigialization Given this, along with the striking diversity of root phenotypes, culminating in total loss in the most derived species, we propose that duckweed roots are a powerful system with which to understand organ loss and vestigiality.One sentence summary Through their adaption to the aquatic environment, duckweed roots have progressively become structurally reduced making them an ideal plant model with which to study vestigiality.

Nocturnal stomatal conductance (g(sn)) represents a significant source of water loss, with implications for metabolism, thermal regulation and water-use efficiency. With increasing nocturnal temperatures due to climate change, it is vital to identify and understand variation in the magnitude and responses of g(sn) in major crops. We assessed interspecific variation in g(sn) and daytime stomatal conductance (g(s)) in a wild relative and modern spring wheat genotype. To investigate intraspecific variation, we grew six modern wheat genotypes and two landraces under well watered, simulated field conditions. For the diurnal data, higher g(sn) in the wild relative was associated with significantly lower nocturnal respiration and higher daytime CO2 assimilation while both species exhibited declines in g(sn) post-dusk and pre-dawn. Lifetime g(sn) achieved rates of 5.7-18.9% of g(s). Magnitude of g(sn) was genotype specific 'and positively correlated with g(s). g(sn) and g(s) were significantly higher on the adaxial surface. No relationship was determined between harvest characteristics, stomatal morphology and g(sn), while cuticular conductance was genotype specific. Finally, for the majority of genotypes, g(sn) declined with age. Here we present the discovery that variation in g(sn) occurs across developmental, morphological and temporal scales in nonstressed wheat, presenting opportunities for exploiting intrinsic variation under heat or water stressed conditions.

SUMMARYA key target for the improvement of Oryza sativa (rice) is the development of heat‐tolerant varieties. This necessitates the development of high‐throughput methodologies for the screening of heat tolerance. Progress has been made to this end via visual scoring and chlorophyll fluorescence; however, these approaches demand large infrastructural investments to expose large populations of adult plants to heat stress. To address this bottleneck, we investigated the response of the maximum quantum efficiency of photosystem II (PSII) to rapidly increasing temperatures in excised leaf segments of juvenile rice plants. Segmented models explained the majority of the observed variation in response. Coefficients from these models, i.e. critical temperature (Tcrit) and the initial response (m1), were evaluated for their usability for forecasting adult heat tolerance, measured as the vegetative heat tolerance of adult rice plants through visual (stay‐green) and chlorophyll fluorescence (ɸPSII) approaches. We detected substantial variation in heat tolerance of a randomly selected set of indica rice varieties. Both Tcrit and m1 were associated with measured heat tolerance in adult plants, highlighting their usability as high‐throughput proxies. Variation in heat tolerance was associated with daytime respiration but not with photosynthetic capacity, highlighting a role for the non‐photorespiratory release of CO2 in heat tolerance. To date, this represents the first published instance of genetic variation in these key gas‐exchange traits being quantified in response to heat stress in a diverse set of rice accessions. These results outline an efficient strategy for screening heat tolerance and accentuate the need to focus on reduced rates of respiration to improve heat tolerance in rice.

Gas pipeline leaks occur regularly. It is essential that such leaks are discovered quickly to avoid environmental pollution and waste of resources. When pipelines are buried in the soil, it can be difficult to find the leaks, especially if leakage rates are low. One method to locate gas leaks is to use vegetation as an indicator. Satellite remote sensing might be a tool for monitoring the vegetation growing along the pipelines continuously, providing gas companies with information about possible leaks. Although research has been done the influence of gas leakage on vegetation reflectance, it is not known exactly how gas in the soil affects plant health and reflectance. In this research, we tried to understand how natural gas and two of its components (methane and ethane) affect the development and reflectance of maize plants. Two experiments were done in which plants were exposed to gas in the soil. In the first (greenhouse) experiment, the focus was on the influence of natural gas, methane, and ethane on plant development and leaf reflectance. The second experiment focused on the influence of natural gas on canopy reflectance. During one growth season, weekly measurements were done on the development and the reflectance of the plants and canopy. The results show that natural gas hampers the development of plants, even in small concentrations. Ethane, which is a component of natural gas, seems to be the most stressful component. Although the development of the plants was affected by low gas concentrations, the red edge position and several NIR/VIS ratios show that small amounts of the gases hardly affect the reflectance of the plants. However, high gas concentrations do have an effect on plant reflectance. The combination of plant development and reflectance characteristics will be a key to find gas leaks in pipelines.