2023-09-12 11:31:43
The idea of this program, crucial for SNCF Réseau, is to develop ecological methods to contain the development of invasive species using local plants. It brings together several academic research partners, including the LAE laboratories (Joint UL-INRAE research unit), LSE (UMR UL-INRAE) and the LIEC (UMR UL-CNRS) for the Grand Est Region, where sixteen experimentation stations have been set up by SNCF Réseau, mainly in Champagne and Ardennes.
The growth of invasive species near the tracks poses both maintenance and safety problems for the SNCF, which in its fight once morest the development of these plants, seeks to no longer use phytosanitary products. On the one hand, the SNCF faces a technical impasse, especially since the problem is amplified due to the sometimes phenomenal growth and development potential of invasive species (example of Japanese knotweed). On the other hand, the fight once morest the spread of invasive species is a major issue for the preservation of biodiversity. The consortium which was structured around the Reeves program is betting that ecological restoration might make it possible to provide concrete solutions to the SNCF that have little impact on biodiversity.
Three years of observations, measurements and analyzes have made it possible to update certain mechanisms of ecological restoration and to consider initial management options, in the light of rather promising results.
Field experiments associated with fundamental research
Credits: Valentin Morin (SNCF Réseau)
Two levels of study were associated in the project: the search for practical experimental methodologies and fundamental research aimed at understanding the mechanisms at work, with the aim of designing an ecological method for managing invasive plants.
Three invasive species are targeted for the Grand Est region: black locust, ailantum and Japanese knotweed. These species have high growth potential, they destabilize the local ecosystem. They adapt to many soils and climates and they have no antagonists (predators or diseases) locally.
Different methods are traditionally used to try to contain them, such as pruning or mowing, but with very mixed success and significant costs accumulating each year.
On the ground, the idea is to develop a relevant management method by replanting invaded areas. After cutting out invasive species, the establishment of local so-called “restoration” species aims to slow down their installation and development over several years. A large community of restoration plants was used in the Grand Est region, such as sapwood viburnum, dogwood, hawthorn (around ten species), etc.
The first results show, in the presence of these restoration plants, downward trends in the growth of invasive species, particularly for knotweed, which gives hope for better control. Some of the species used in the restorative plant community establish and survive very well in the harsh conditions of railway embankments. However, it is too early to conclude: monitoring must continue in the field and other tests/trials must be conducted.
Competition and allelopathy
between species at stake Fundamental research has made it possible to study the processes involved, such as allelopathy or mycorrhization (whether by restoration plants or invasive plants), processes that would be difficult to evaluate directly.on site
. One of the experiments carried out at the LAE (Agronomy and Environment Laboratory) consisted of putting a mixture of restoration plants with rhizomes ofknotweed
. The mixture included meadow grasses, a variety of perennial and covering comfrey as well as shrubs adapted to these types of environments. :
The results show that barberry reduced by 40%
the exit of knotweed stem by competition and allelopathy. Furthermore, the biomass of knotweed is reduced by 50 to 75% by the presence of companion plants: this is mainly a “competition” effect, because it is maintained in the presence of activated carbon (which traps allelochemical substances ). This “competition” effect also reduces leaf surface area (and therefore photosynthetic capacity). We also observe a reduced density of knotweed stems of 2 thirds in the presence of restorative plants.
Thus, the overall performance of knotweed as a function of restorative plants is reduced by 30 to 50%. In this regard, beyond laboratory models, we can say that poaceae, comfrey and elderberry seem to be good candidates for the ecological restoration of railway embankments: they are also easy to install plants. For theblack locust
, the tests are less advanced but the germination process has already been studied. In the presence of a macerate of barberry, elderberry and comfrey, the germination potential of black locust is affected. The mixture of different macerates appears to be the most effective. We are now seeking to target which molecules are responsible for this effect. A next step will be to work on young black locust false acacia plants.
Boost restorative plants?
The different natural symbioses with microorganisms or mycorrhizal fungi can improve the growth and resistance of plants to stress.The potentially negative effect of knotweed ( via
molecules from the plant) was therefore tested on microbial communities and mycorrhization (reciprocal benefit association between a fungus and the roots of a plant). Indeed, railway embankment conditions are not ideal for plant growth and it might be interesting to inoculate candidate restorative plants for better establishment.
Tests were carried out with alfalfa, a plant that establishes symbiotic associations with both nitrogen-fixing bacteria and mycorrhizal fungi. The results show that the germination of fungal spores is inhibited by a knotweed extract, but that it does not affect nodulation (formation of tissue expansions at the roots in which nitrogen-fixing microorganisms lodge). The inhibitory effect of this same extract is also observed during the establishment of mycorrhizae. On the other hand, this effect is less marked on already established symbioses.
These first results suggest ensuring the good state of mycorrhization of restoration plants before their establishment in the field.
Better assess the risk of dispersion by lots of backfill soil
At the same time, the soils of railway embankments and railway wastelands were characterized according to pedological protocols, with the aim of knowing their properties, particularly in terms of fertility. This knowledge of the functioning of these soils will thus make it possible to have a diagnosis of the quality of the sites. They have fairly high levels of various organic and metallic contaminants and physicochemical properties close to highly anthropized soils. A first work was to look for indicators of the presence of invasive plants, making it possible to assess the risk of their dispersion and to evaluate the quality of soil used for the embankments. The lots of soil used actually come from various sources and it may be important to eliminate some of them. A methodology has been constructed to help decide whether or not to accept these batches. From a fundamental point of view, the results acquired made it possible on the one hand to place these railway embankment soils within anthropized soil gradients and therefore to predict their evolution, and on the other hand to obtain information on the localization of potentially allelochemical substances within Japanese knotweed rhizomes with a view to understanding competition mechanisms between species.
An important parallel question would be to try to understand whether contamination can play a role in favor of invasive species. This might be assessed on the former Fonteno railway site within the Nancy metropolitan area, for which correlations between the progression of knotweed and contaminant levels will be established.
In view of these results, new avenues of research and experimentation are opening up: further investigating the nature of the allelochemical compounds at work, studying the effect of pollutants (common in these environments), better understanding when and how to provide inoculum for restorative plants, optimize associations of restorative plants, continue to develop management methods… This first 3-year stage of the Reeves project has kept its promises and the project should begin in the summer a second phase.
Allelopathy:
biological phenomenon by which an organism produces and releases into its environment one or more substances called allelochemicals which positively or negatively influence the germination, growth, survival and reproduction of other organisms.
1694520850
#Limit #development #invasive #species #railway #embankments #native #species
