Flying duck(weed)s

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

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”.

For details about ISCDRA see

a mallard covered in duckweed (Lemna)
Figure1: A male mallard duck (Anas platyrhynchos), which has just left a Lemna-covered pond, takes some “hitch-hiking” duckweed across land on a foraging trip (image © Roy Battell).


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.

Dessication tolerance

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.

Practical considerations

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 Biology 17, 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 Invasions 19, 625-634.




New edition “Plant Stress Physiology”, edited by Sergey Shabala

Cover of book "Plant Stress Physiology"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”

Plant UV-responses

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

Freshwater Biology Article Published

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

One of the article’s accompanying figures was selected for the cover of this issue of Freshwater Biology:

mallard covered in duckweed Continue reading Freshwater Biology Article Published

Wood ash in Ireland, compositional variation and hazards – PhD Study

On January 20, 2017 Lucas Jagodzinski successfully defended his PhD thesis entitled “Compositional variation and hazards of wood ash in Ireland”.

Supervisors and examiners in the presence of PhD candidate Lucas Jagodzinski
Left to right; supervisors Dr Frank van Pelt, Prof John O’Halloran , Prof Marcel Jansen, PhD candidate Lucas Jagodzinski, examiners Prof Roeland Samson, Dr Fidelma Butler

Continue reading Wood ash in Ireland, compositional variation and hazards – PhD Study

Comparative study of Lemna minuta and Lemna minor – PhD study

On November 11, 2016 Ms. Simona Paolacci successfully defended her PhD thesis entitled “A comparative study of the invasive species Lemna minuta and the co-generic native Lemna minor”.

Dr Simona Paolacci with on the right Prof Klaus Appenroth and on the left Prof Marcel Jansen.
Smiles all around after the successful PhD defence. Dr. Simona Paolacci with examiner Prof. Klaus Appenroth (right) and supervisor Prof. Marcel Jansen (left).

Continue reading Comparative study of Lemna minuta and Lemna minor – PhD study

Congratulations: Simona Paolacci submits PhD thesis

Congratulations to Simona Paolacci who submitted her PhD thesis on October 7, 2016. Simona’s research focused on the question why some aquatic plants become highly invasive outside their natural distribution area. This is an important question as alien aquatic plants are a major threat to biodiversity and a considerable amount of money is spend on their management and control. Being able to recognise potentially invasive species before they are widely distributed in their new environment may facilitate management, and reduce management costs.Simona presents her PhD thesis Continue reading Congratulations: Simona Paolacci submits PhD thesis

Panel discussion at the National Ploughing Championship

panel discussion at the National Ploughing Championship 2016
Dr Marcel Jansen, Dr. Klara Finkele, and host Nuala Carey at the panel discussion

At the recent National Ploughing Championships, RTÉ hosted panel discussions with a different meteorologist and agri scientist each day. Dr. Marcel Jansen (Plant Stress group, UCC)  took part in one of these open panel discussions, together with Dr. Klara Finkele, a meteorologist from MetEireann.  The event was hosted by Nuala Carey of RTÉ (Raidió Teilifís Éireann, the national broadcaster), and organised by SFI (Science Foundation Ireland).

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Phosphates affect invasiveness of Lemna minuta

Aquatic Botany paper by Simona Paolacci

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).

Lemna minuta (left) and Lemna minor (right)
Lemna minuta (right) and Lemna minor (left)

Continue reading Phosphates affect invasiveness of Lemna minuta