New research reveals that the quintral, a Chilean native mistletoe, could act as a natural biological control agent in disturbed ecosystems.
A team of scientists has revealed the unexpected and crucial role of the quintral (Tristerix corymbosus), a native hemiparasitic plant, in containing invasive tree species in central Chile. Traditionally viewed as forest pests, parasitic plants may be playing a key role in the conservation of native biodiversity by limiting the growth of exotic species such as poplars, willows, and acacias.
The research offers a new ecological perspective, as the quintral could act as a natural biological control agent, negatively affecting invasive species while strengthening the resilience of altered ecosystems by attracting native fauna, enriching the soil, and increasing plant diversity.
“This study provides a model example of how parasitic plants might help resist invasions in general and help ecosystems recover,” conclude authors Alex Fajardo, Claudia Reyes-Bahamonde, Francisco Fontúrbel, Frida Piper, and Ragan Callaway in their article Shining a new light on parasitic plants: resistance to invasion, recently published in New Phytologist.
What are parasitic plants?
Parasitic plants obtain vital resources such as water and nutrients from other plants. Within this group, two types are distinguished: hemiparasites and holoparasites. The quintral belongs to the first type, since although it extracts water and nutrients from its hosts, it also photosynthesizes through its leaves. “There are hemiparasitic plants, to which the quintral belongs, which are those that acquire both water and nutrients from their host plant and are capable of photosynthesis, hence they are ‘half’ (hemi) parasites. And there are holoparasites, which acquire all types of resources from their hosts,” explains Alex Fajardo, a researcher at the Institute of Ecology and Biodiversity (IEB) and professor at the University of Talca.
For his part, Francisco Fontúrbel, a researcher at the Millennium Nucleus of Patagonian Limit-of-Life (LiLi) and the Catholic University of Valparaiso, and co-author of the paper, points out that “some parasitic plants can cause harm, although most have non-lethal effects on their hosts. Contrary to popular belief, they can have direct positive impacts on the plant they grow on, and even indirect positive effects on uninfected neighboring plants, which can make them key species for the structure and diversity of ecosystems.”
Currently, there are more than 4,500 known species of parasitic plants distributed across most of the planet's biomes, from dense tropical forests to arid deserts. Some infect only one plant species, while others are generalists, although they tend to show certain preferences.
The effects of quintral in Chilean cities
In Chile, quintral is distributed across more than 10 degrees of latitude, inhabiting biomes as varied as the Mediterranean scrubland in the center of the country and the temperate rainforest of southern Chile and Argentina. It is found parasitizing more than 30 species of trees, shrubs, and even lianas, including native species such as maqui (Aristotelia chilensis), corcolén (Azara integrifolia), and maitén (Maytenus boaria). It is the only hemiparasitic plant species found in urban areas.
Fajardo emphasizes that “the quintral rarely kills its native hosts, suggesting that both the hemiparasite and the host have coexisted and co-evolved for many thousands of years.” Fontúrbel adds that “many animal species depend on it for food. During the winter, the nectar from its flowers is the main food of the green-backed firecrown hummingbird (Sephanoides sephaniodes), and in summer, its fruits are key for the tiny monito del monte marsupial (Dromiciops gliroides)”.
In addition, quintral provides nutrient-rich leaf litter, which is key in nitrogen-poor ecosystems. “Mistletoes don't need to conserve nutrients, as they obtain them relatively easily. Therefore, they have a low efficiency in nutrient reabsorption, meaning they don't recover many nutrients from their leaves before they fall,” Fajardo points out. This leaf litter improves soil quality, boosting nutrient cycling.
An ecological reckoning?
Chile’s Central Valley’s native vegetation has been severely altered by centuries of human activity, being replaced by exotic species such as black poplar (Populus nigra), weeping willow (Salix babylonica), and acacia trees (Acacia dealbata and A. melanoxylon), the latter recognized as invasive and potential causes of forest fires.
The massive presence of quintral in exotic species motivated researchers to investigate their behavior. “This phenomenon represents an ecological pattern that needs to be explained. It is a good example of how ecological research is done: observations of natural systems, establishment of a pattern, establishment of hypotheses that explain the pattern, and evaluation of those hypotheses,” Fajardo explained.
The study found that quintral grows more and is more abundant in large, fast-growing non-native species, such as poplars, willows, and acacias. “Larger sizes mean more resources. Poplars, willows, and acacias are fast-growing species, capable of rapidly acquiring resources; therefore, they constitute ideal hosts for the proliferation of quintral,” the researcher states.
They also found that species with a higher degree of quintral infection tend to die. This has led the authors to propose quintral as a biological controller of exotic tree species.
“It is possible that quintral does not deplete the resources of native species at the rate it does in exotic species, and that this explains the successful coexistence between quintral and native species. We are also studying whether it is possible that quintral provides carbohydrates produced by its own photosynthesis to native species,” adds Frida Piper, a researcher at the IEB, LiLi, and the University of Talca.
“This has led to it being viewed as an intensely damaging tree pest. However, even if it affects these trees, it is likely to increase community diversity, especially in altered systems, attracting pollinating and seed-dispersing animals and increasing soil nutrients, thus having multiple direct and indirect positive effects on modified communities and landscapes,” Fajardo notes.
"The quintral is causing what I've called a 'territorial recovery,' by recolonizing the Central Valley, which was once full of native species," he adds. "In the case of the quintral-exotic host relationship, we believe that a 'settling of scores' may be taking place between both parties; that is, natural selection is occurring, with some exotic individuals not being easy hosts for the quintral, and, on the other hand, the quintral may evolve to meet these new challenges."
New trophic interactions
The expansion of quintral is also generating new ecological relationships. Its seeds are dispersed by the monito del monte in the southern temperate forests, and by the Chilean mockingbird (Mimus thenca), a frugivorous bird common in urban and rural environments in the center of the country. In both cases, the quintral contributes to the persistence of these species.
Exotic trees provide perches for the Chilean mockingbird, which defecate quintral seeds upon landing, facilitating their spread. Thus, the quintral not only affects its hosts but also maintains ecological networks of pollination and dispersal in altered environments. Finally, it should be noted that there are several hemiparasitic species in Chile, but so far only the quintral has been reported proliferating in exotic and invasive species.
MSc. Javiera Diaz, Millennium Nucleus of Patagonian Limit-of-Life
Dr. Xuksa Kramcsak, Institute of Ecology and Biodiversity, Chile
Photo credit: Cesar Muñoz
Shining a new light on parasitic plants: resistance to invasion
Alex Fajardo, Claudia Reyes‐Bahamonde, Francisco E. Fontúrbel, Frida I. Piper, Ragan M. Callaway