The high world population growth rate and the expansion of areas given over to crop production associated with climatic changes (longer periods of drought, irregular rainfall patterns) induced by global warming, have contributed to the acceleration of desertification.
According to World Soil Information (ISRIC) rate, in the space of 50 years, 12.8 million km2 of soils have thus experienced diminished fertility. With the aim of limiting such land impoverishment, which is hitting the intertropical and mediterranean zones particularly harshly, a range of reforestation programmes using rapid-growing forest species (such as eucalyptus, exotic pine or Australian acacias) was undertaken from the mid 1970s. Establishment of bacterial and mycorrhizal symbioses provides these trees with the adaptation ability necessary for growth on virtually barren, mineral-deficient soil.
Although no proof is needed as to their effectiveness for producing plant biomass in harsh environmental conditions and their utility as windbreaks to control erosion, there is little information on their potential impact on the genetic and functional biodiversity of the soil microorganisms. A research programme run since 2005 in Senegal and Burkina Faso by an IRD team and its partners1 yielded clues for understanding the influence of exotic plants on the structure and biodiversity of these communities of fungi and bacteria. In Burkina Faso, controlled experiments showed that the development of E. camaldulensis, the eucalyptus species most often planted in the world, outside its area of origin, significantly reduced the diversity of the mycorrhizal fungi communities essential for the healthy functioning of the ecosystem. This negative effect was also found in the soil of a Senegalese plantation of Acacia holosericea where, scarcely a few months after its introduction, the soil’s microbial characteristics had completely changed.
This quick-growing species had effectively selected certain species of mycorrhizal fungi and bacteria of the genus Rhizobium, ending in a reduction in the species diversity of these symbiotic communities. The soil sampled from areas surrounding the A. holosericea plantation had a balanced distribution of mycorrhizal fungi species, whereas the breakdown of the fungal spore content in soil from the plantation showed a predominance of one species and therefore a strong imbalance in the composition of the mycorrhizal fungi community. In the knowledge that a plant ecosystem’s productivity is closely dependent on a soil’s mycorrhizal diversity, there is a risk that the Australian acacia might create a new ecosystem whose physical, chemical and biological characteristics will not necessarily be favourable to a recolonization of the habitat by native species. The research also demonstrated that the environments generated by this species were less resistant to water and heat stress. In a context of global climate change, such habitats could therefore experience a drastic fall in their microbial activity and thus lose their ability to be the basis of proper development of the plant cover.
The conclusions of the study conducted in Senegal in a precisely defined environment cannot, however, be generalized to tropical soils as a whole. Indeed, investigations on another A. holosericea plantation, in Burkina Faso, yielded the observation of an increase in microbial functional diversity. The contradictions between these sets of results should prompt the organizations involved in natural resources management to plan for possible introductions of exotic species case by case, taking account not only of potential impacts of the plant species under consideration for introduction, but also of the nature of the soils they are to colonize. For although this practice can yield highly satisfactory results, such as increases in the species richness of severely degraded environments, such as old mining areas, it can also upset for a long time the organization of the microbial communities which guarantee the fertility of a soil.
Grégory Fléchet – DIC
1. This research work was conducted with the support of scientists from the Département de biologie végétale of the Cheikh Anta Diop University of Dakar (Senegal) and from the Laboratoire Sol-Plante-Eau of the Institut de l'Environnement et des Recherches Agricoles (Inera) of Ouagadougou (Burkina Faso)
Grégory Fléchet | alfa
Loss of habitat causes double damage to species richness
02.04.2019 | Deutsches Zentrum für integrative Biodiversitätsforschung (iDiv) Halle-Jena-Leipzig
Deep decarbonization of industry is possible with innovations
25.03.2019 | Fraunhofer-Institut für System- und Innovationsforschung (ISI)
Researchers led by Francesca Ferlaino from the University of Innsbruck and the Austrian Academy of Sciences report in Physical Review X on the observation of supersolid behavior in dipolar quantum gases of erbium and dysprosium. In the dysprosium gas these properties are unprecedentedly long-lived. This sets the stage for future investigations into the nature of this exotic phase of matter.
Supersolidity is a paradoxical state where the matter is both crystallized and superfluid. Predicted 50 years ago, such a counter-intuitive phase, featuring...
A stellar flare 10 times more powerful than anything seen on our sun has burst from an ultracool star almost the same size as Jupiter
A localization phenomenon boosts the accuracy of solving quantum many-body problems with quantum computers which are otherwise challenging for conventional computers. This brings such digital quantum simulation within reach on quantum devices available today.
Quantum computers promise to solve certain computational problems exponentially faster than any classical machine. “A particularly promising application is the...
The technology could revolutionize how information travels through data centers and artificial intelligence networks
Engineers at the University of California, Berkeley have built a new photonic switch that can control the direction of light passing through optical fibers...
Physicists observe how electron-hole pairs drift apart at ultrafast speed, but still remain strongly bound.
Modern electronics relies on ultrafast charge motion on ever shorter length scales. Physicists from Regensburg and Gothenburg have now succeeded in resolving a...
17.04.2019 | Event News
15.04.2019 | Event News
09.04.2019 | Event News
24.04.2019 | Trade Fair News
23.04.2019 | Information Technology
23.04.2019 | Earth Sciences