Growing up and dying, in constant and repeated cycles, is a key strategy for the success of the plant Carpobrotus edulis -an exotic and invasive species in lots of countries around the world- to invade new territories without leaving any other vegetal plants left.
This is the innovative hypotheses given by the scientific magazine Trends in Plant Science in a project led by Sergi Munné Bosch, tenured lecturer at the Department of Evolutionary Biology, Ecology and Environmental Sciences of the UB, together with Erola Fenollosa -first author of the work and also member of the mentioned Department of the University of Barcelona -- and Deborah A. Roach, from the University of Virginia (USA).
The plant Carpobrotus edulis, originally from South Africa, is an exotic and invasive species which is nowadays distributed around several continents. In the Iberian Peninsula, it is provoking a big environmental impact on dunes, sandy areas and cliffs in the Cantabrian coast (Asturias, the Basquelands, and Galicia), the Mediterranean sea (Costa Brava, Delta de l'Ebre, Menorca) and the South-Atlantic. This plant, which multiplies itself in a fast way if not controlled, makes it difficult for the native species to regenerate and it eases the progress of other invasive species.
Why are some exotic species invasive?
Not all the exotic species become invasive when they are accidentally or intentionally placed into new geographic areas. There are currently a lot of open doubts about the implied mechanisms in the plant world biological invasions.
Some invasive species as aggressive as Carpobrotus edulis show clonal growth, which means there is a reproduction which doesn't imply seeds and can contribute to the invasive ability of the plants. Clonal reproduction, expanded in plant taxonomy, creates a series of ramets which are genetically identical and can survive both independently and connected.
According to Professor Sergi Munné Bosch, who was given the ICREA Academy Award in 2008 and 2014, "no wonder the growth ability, reproduction (both sexual and asexual or clonal), spreading and establishment of new seedings are main factors of the plant eco-physiology -which help some exotic species to have invasive abilities."
"Actually -he continues- the clonal propagation allows colonizing new places in a fast way, competing efficiently for the light and occupying other native species' places. And if, moreover, the invasive plants are well adapted to the new environment they occupy, they can become a great threat for the native plants. The clonal growth makes this process much easier."
The clonal plants are shown as cooperative biological systems with a high ability of colonizing new environments. They control lots of vegetal communities and are frequent in habitats where there is a lot of competence or under extreme environmental conditions. "From an evolutionary perspective, cloning is less efficient than sexual reproduction. However, when sexual and asexual reproduction combine, the invasive species can cause, like in C. edulis's case, a great environmental impact on the natural habit" says Munné Bosch.
Clones and biological invasions: an evolutionary success
The repetitive "grow and die" strategy would be a decisive factor for the success of the clonal invasive plants like C. edulis, say the authors. "While some clones grow and asexually reproduce themselves to gain space, others die in a controlled way (after reproducing) and allow the growth of the same species but not like others, in a process known as auto-facilitation. As a result of this process, the conditions of the ground are altered and other species cannot grow in there" say the authors of this study.
"The senescence, which is a kind of programmed cell death, is also part of the process. In a controlled way, the reproductive sprouts die. Therefore, the same death is an active process and a key factor for the invasive process. Moreover, the clonal reproduction can generate variability, and therefore, a greater adaptive potential thanks to the epigenetic changes, which ease a fast adaptation of these species in the new place they occupy."
A threatening future for the plant biodiversity
In this threatened context for the global environment, it will be essential to know the biological mechanisms that promote the invasive attitude of lots of plant species. "Some of these species, such as Carpobrotus edulis or Aptenia cordifolia, are found in our gardens. Without any doubt, these organisms can contribute to an important loss of the current biodiversity and are a threat if we want to keep our natural ecosystem as they are now" warns Munné.
In order to face future challenges protecting biodiversity, Professor Sergi Munné Bosch leads a team in the UB which promotes research projects on eco-physiology and agrobiotechnology, with special emphasis on the antioxidants (vitamin E and C, and flavonoids), plant aging and senescence, and resistance mechanisms against external factors (water stress, salinity, etc.) and photo-protection.
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