The latest UNEP-report on the effects of stratospheric ozone depletion has now been published.
The “Montreal Protocol on Substances that Deplete the Ozone Layer” is a global agreement to protect the Earth’s ozone layer by phasing out the production and consumption of ozone-depleting substances, such as CFC’s. The global agreement was signed in 1987 and is an example of a highly successful international effort to protect the biosphere. In fact, the Montreal Protocol has helped to avoid large, and potentially catastrophic, increases of solar UV‑B radiation in the biosphere. As part of the Montreal Protocol, the Environmental Effects Assessment Panel assesses impacts of ozone layer depletion and changes in UV-radiation. The panel is made up of scientists from throughout the world, and especially experts in photobiology and photochemistry. Prof. Marcel Jansen is the Irish co-author of the report.
The 2018 report, “Environmental Effects and Interactions of Stratospheric Ozone Depletion, UV Radiation, and Climate Change: 2018 Assessment Report”, also known as the “ninth Quadrennial Assessment”, has now been published. The full report can be downloaded directly from the UNEP website (https://ozone.unep.org/science/assessment/eeap). The 381-pages report captures the latest scientific understanding on impacts of ozone layer depletion. The ninth Quadrennial Assessment places strong emphasis on the novel challenge of interactive effects of ozone depletion and climate change on human health and the environment.
Chapter 3, entitled “Linkages between stratospheric ozone, UV radiation and climate change: Implications for terrestrial ecosystems”, assesses the effects of stratospheric ozone depletion and associated changes in ultraviolet-B radiation (UV‑B, 280-315 nm) on terrestrial biota, and especially the role of climate change in mediating effects of UV‑B radiation on organisms and ecosystems. The report states that “in some regions ozone depletion is itself contributing to climate change such that ecosystems are being affected by the consequent ozone-driven changes in temperature, precipitation and UV‑B radiation”. In other cases interactive effects of ozone depletion, UV‑B radiation and climate change impact directly on terrestrial organisms and ecosystems, including agricultural systems. Thus, co-exposure to UV‑B and drought, heat or elevated CO2 levels result in new challenges for living organisms, and for the scientists studying these interactive effects.
In the most recent issue of the Duckweed Forum, Marcel Jansen, with co-workers Neil Coughlan, Simona Paolacci, Ronan Bonfield, and Tom Kelly summarised some of their recent work on duckweed dispersal (ISCDRA Duckweed Forum issue #17, 2017-04). The paper “Flying duck(weed)s” can be downloaded as part of this issue of Duckweed Forum from http://lemnapedia.org/wiki/Duckweed_Forum#2017-04.
Duckweed Forum is a very attractive bulletin, published by ISCDRA. The “International Steering Committee on Duckweed Research and Applications” (ISCDRA) is an organisation of duckweed researchers and users, and its aim is to strengthen and synergistically connect duckweed academic research with the application communities, and to educate and increase public awareness about the importance and potential of duckweeds for a more sustainable future. As part of its activities, ISCDRA regulates the international registration of duckweed clones, and publishes the “Duckweed Forum”.
Marked differences in physiological and morphological traits have been found between different species of Lemnaceae, and between different clones of species. Traits like relative growth rates, salt tolerance, and starch content can vary a lot. This makes different clones and/or species more suitable for some applications than others. This also triggers the question, how to prevent the mixing of “undesirable” species or clones with selected Lemnaceae when these are grown under outdoor conditions for applications such water remediation. Perhaps more fundamentally it triggers the question, how do duckweeds disperse?
In the case of Lemnaceae, it has been argued that rapid drying out of fronds will limit the distance of dispersal, and that the frequency of transport will be low. However, the reality appears different. Neil Coughlan developed a simple system to quantify dispersal of L. minor. Quite surprisingly, Neil observed a total of 67 separate dispersal events (transfer of at least one frond) over a period of 20 weeks, and across 6 replicate stake and bowl structures. In total 156 colonies comprising 317 fronds were found to be transferred to receiving bowls in a relatively short period (full details see Coughlan et al., 2017), and this was attributed to birds. The question remains, however, over what distances Lemnaceae can be dispersed, a question that focusses heavily on desiccation tolerance of the plants.
Lemna minuta taken out of the aquatic medium was found to have lost viability after just 90 minutes at a Relative Humidity (RH) of 44% and a temperature of 21˚C (Coughlan et al., 2015). At a slightly higher RH of 58% (T = 23˚C) Lemna minuta still displayed some viability after 4 hours out of the aquatic medium (Coughlan et al., 2015). Neil Coughlan’s research showed that between the feathers near the posterior neck of a mallard duck, the RH is around 65% and the temperature 23˚C. Near the inner crural (upper part of the leg), the RH is even higher at around 77% with a temperature of 24˚C. Interestingly, the downy feathers of the inner crural were also found to retain entangled Lemnaceae fronds more effectively than areas of less downy plumage, such as the back of the neck. All in all, we reckon that Lemna minuta can be entangled between feathers, and survive flights of up to four hour’s duration. Given an average speed for mallards of 65 km/h-1, we argue that duckweed dispersal over distances of up to 250km is realistic, although much shorter distances (< 50km) are likely more common. This underlines the mobility of Lemnaceae.
So where does that leave the duckweed industry? There are two practical considerations for Lemnaceae cultivation systems:
(1) preventive steps need to be taken if one wants to avoid bird-mediated contamination of an outdoor Lemnaceae culture (e.g. dilution of a selected clone by non-selected, native clones)
(2) preventive steps need to be taken to avoid introduction of selected alien species or clones into the local environment.
At present, substantial efforts are involved in control of Landoltia punctata in Florida USA, where this is an alien, invasive species. Similarly, Lemna minuta is the focus of management efforts in various European countries. There is absolutely no evidence that the introduction of L. punctata in Florida, or L. minuta in Europe is associated with cultivation of these species by the Lemnaceae industry. Nevertheless, the industry needs to adopt a responsible approach when cultivating alien species of Lemnaceae, and prevent their spread in to the surrounding environment in order to maintain the positive public perception of duckweed applications as being eco-friendly and sustainable.
Coughlan N.E., Kelly T.C., Jansen M.A.K., 2015. Mallard duck (Anas platyrhynchos)-mediated dispersal of Lemnaceae: a contributing factor in the spread of invasive Lemna minuta? Plant Biology17, 108–114.
Coughlan, N.E., Kelly, T.C. and Jansen, M.A.K., 2017. “Step by step”: high frequency short-distance epizoochorous dispersal of aquatic macrophytes. Biological Invasions19, 625-634.
A second edition has been published of Sergey Shabala’s popular book on plant stress physiology. The revised text contains, amongst others, chapters on heavy metal toxicity (White & Pongrac), salinity stress (Shabala and Munns), flooding stress (Pucciariello & Perata), drought stress (Manavalan & Nguyen), chilling stress (Ruelland) and reactive oxygen species (Demidchik).
Plant stress terminology
Prof Marcel Jansen and Dr Geert Potters contributed an introductory chapter on the terminology of plant stress response, citing Hans Selye who stated “everybody knows what stress is and nobody knows what it is”. The authors state that “there is too much variation in the way in which plant stress researchers use and understand terminology such as stress, stressor, acclimation and adaptation. This causes ambiguity, and impedes scientific progress.
Moreover, there is a lack of recognition that plant stress responses comprise a mixture of eustress and distress, and that this mixture depends on the dose of the stressor, as well as on exposure kinetics. Thus, without appropriate calibration of stress-conditions, contradictory data can be produced that are of limited use for the understanding of plant stress responses. Selye, Levitt, Lichtenthaler and Tsimilli-Michael have provided theoretical frameworks defining stress, and these frameworks can be used to place molecular, biochemical or physiological data in the appropriate context. The theoretical stress frameworks have demonstrated that in the plant-world stress is more than just a clinical condition. Rather, stress-conditions are important drivers that help a plant to perceive the outside environment, to harmonise itself with it and thus to optimise growth and development”
Prof Jansen contributed a further chapter on plant UV-responses, summarising how “following the discovery of ozone layer depletion in the late 1980s, large numbers of studies investigated the effects of ambient and/or enhanced levels of ultraviolet-B (UV-B) radiation on plants, animals, humans and micro-organisms.
Initial studies reported severe, inhibitory UV effects on plant growth and development, and these were associated with damage to genetic material and the photosynthetic machinery. This led to a strong perception that UV-radiation is harmful for plants. Since that time, a conceptual U-turn has taken place in the way that UV-B effects are perceived. Under realistic UV-B exposure conditions, accumulation of UV-mediated damage is a relatively rare event.
Instead, it is now recognized that UV-B is predominantly an environmental regulator that controls cellular, metabolic, developmental and stress-protection processes in plants through a dedicated UV-B photoreceptor. UV-B regulated signalling pathways control, amongst others, expression of 100’s of genes, the biochemical make-up and the morphology of plants and this, in turn, can alter the nutritional value, pest and disease tolerance, sexual reproduction, and hardiness of plants and plant tissues. As a consequence, UV-B radiation can impact on trophic relationships and ecosystem function, but is also a potentially valuable tool for sustainable agriculture”.
Plant Stress Physiology, 2017, Edited by S Shabala, CABI publishers; ISBN-13:978 1 78064 729 6
Congratulations to Neil Coughlan on his latest article, published in Freshwater Biology. The title of the review paper is “Up, up and away: bird-mediated ectozoochorous dispersal between aquatic environments”. The paper can be freely accessed at http://onlinelibrary.wiley.com/doi/10.1111/fwb.12894/full.
One of the article’s accompanying figures was selected for the cover of this issue of Freshwater Biology:
PhD student Simona Paolacci has published a paper entitled “A comparative study of the nutrient responses of the invasive duckweed Lemna minuta and the native, co-generic species Lemna minor” in the journal “Aquatic Botany” (Paolacci, S., Harrison, S. and Jansen, M.A.K, 2016. Aquatic Botany, 134, pp.47-53).
Dr. Xiaolin Chen has a first paper on her PhD research in plant toxicology accepted for publication in the journal “Aquatic Toxicology”. The title of Xiaolin’s paper is “The toxicity of Zinc-Oxide nanoparticles to Lemna minor (L.) is predominantly caused by dissolved Zinc”.