Don't be Ranunculus... Little known plant behaviours

Guest post by Agneta Szabo, MEnvSci Candidate in the Professional Masters of Environmental Science program at the University of Toronto-Scarborough

Through the scientific study of plant behaviour, we continue to discover new ways in which plants interact with their environment in animal-like ways. Words like “listening”, “foraging”, and “parenting” may seem odd to associate with plants, and yet plants show evidence of all of these behaviours. Here are some of the many ways in which plants behave.

Listening

As it turns out, plants are listening! A study by Heidi Appel and Rex Cocroft published in 2014 describes their discovery that plants can detect their predators acoustically and ramp up their defenses as a response. Appel and Cocroft recorded the sound vibrations of caterpillars chewing on Mouse‑ear Cress leaves, and played these recorded vibrations to previously unaffected Mouse-ear Cress plants over several hours before allowing caterpillars to attack the plants. The researchers found that, compared to plants that were primed with recordings of silence, those who were primed with recordings of chewing produced much higher levels of the oils glucosinolate and anthocyanin, which are toxic to caterpillars. Furthermore, Appel and Cocroft found that the plants were able to distinguish the sound vibrations caused by chewing from recordings of wind or other insect noises.

In addition to listening for their predators, plants can also listen for water. In 2017, Monica Gagliano and her colleagues published a paper showing that the Garden Pea was able to locate water by sensing the vibrations generated by water moving inside pipes. Garden Pea seedlings were planted in pots shaped like an upside-down Y, and each arm of the pot was treated with different experimental conditions. When one arm was placed in a tray of water and the other was dry, plant roots grew towards the arm with water. Seems obvious enough. However, when one arm was placed above a tube with flowing water and the other was dry, the plant roots still grew towards the water, even though there was no moisture. When given a choice between a tray of water and the tube with flowing water, the Garden Pea seedlings chose the tray of water. This led Gagliano to hypothesize that plants may use sound vibrations to detect water at a distance, but that moisture gradients allow the plants to reach their target at close proximity.

Garden Pea water acoustics experimental set-up (Gagliano et al., 2017)

Foraging

Plant roots forage for food in a similar way to animals. In his 2011 review, James Cahill explores plant root responses to varying nutrient cues in the soil. Cahill explains that plant roots are responsive to both spatial and temporal nutrient availability. For example, when a nutrient patch is placed in the soil at a distance from the plant, there is a substantial acceleration in root growth in the following days. This growth is directed precisely towards the nutrient patch, and as the root approaches its target, the rate of growth slows as the nutrient patch is consumed. Furthermore, plants develop greater root biomass in richer nutrient patches, and they allocate more root biomass to patches with increasing nutrient levels.

Other foraging plants include the parasitic Dodder vine. This plant has no roots and lives off a host plant. In 2006, Consuelo De Moraes and her team published a study demonstrating that the Dodder plant uses scent, or volatile chemical cues, to locate and select its host plant. De Moraes experimentally planted Dodder seedlings between a Tomato and Common Wheat plant, the Tomato being its preferred host. Using a time lapse camera, De Moraes captured the circling movement of the Dodder plant as it approached both host options repeatedly, before settling on the Tomato plant 90% of the time. Through further experimentation by giving the Dodder seedlings a choice between the condensed chemical odour of the Tomato plant and a live Tomato that has been covered to prevent giving off odour, it was determined that the Dodder uses the chemical signals to select its host. Without being able to “smell” the live Tomato plant, the Dodder chose to attach to the vile containing the condensed chemical odour. 

Dodder vine attaching to a Tomato plant

(PBS, 2014: https://www-tc.pbs.org/wnet/nature/files/2014/09/Mezzanine_485.jpg)

Parenting

One of the most fascinating aspects of plant behaviour is parental care and kin recognition. Suzanne Simard’s work studying forests as a complex, interconnected organism has been featured on several popular media outlets including the TED Talk series and the Radiolab podcast. Through her research, Simard discovered that through a network of mycorrhizal fungi, adult trees were nurturing their young with a targeted exchange of nutrients such as carbon and nitrogen, as well as defense signals and hormones. Through experimental plantings of Douglas Fir seedlings that were directly related to the adult trees and unrelated Douglas Fir seedlings, she found that the “mother trees” recognized and colonized their kin with larger networks of mycorrhizal fungi, and sent more carbon to these seedlings. Furthermore, there was a reduction in root competition with the related seedlings. When injured, the adult trees sent large amounts of carbon and defense signals to their young, which increased the seedlings’ stress resistance.

Tree mycorrhizal network schematic 

(Medium, 2017: https://medium.com/ideo-colab/fungal-networks-connected-businesses-b38025ca7171)

Similar recognition of kin was observed by Susan Dudley and Amanda File in a 2007 paper. In this study, Dudley and File planted related “sibling” Sea Rocket plants together in pots, as well as unrelated “stranger” Sea Rocket plants together in pots. After several weeks, the roots were cleaned and assessed. The study found that kin groups allocated less biomass to their fine roots, while stranger groups grew larger roots in order to compete for resources. The same responses were not observed when kin and stranger groups were grown in isolated pots, which suggests that the mechanism for kin recognition was through root interactions.

Although we still don’t fully understand the mechanism by which plants process information, it is clear that the way plants interact with their environment is far more complicated than we previously thought. The concept of plants as inanimate organisms, blindly competing for resources is now outdated. Continued discoveries in plant behaviour demonstrate, once again, how little we understand about the natural environment—a humbling thought in an age when humankind thinks itself superior to our fellow species.

Bibliography

Appel, H.M. & Cocroft, R.B. (2014). Plants respond to leaf vibrations caused by insect herbivore chewing. Oecologia, (2014)175: 1257–1266.

Cahill, J.F. & McNickle, G.G. (2011). The behavioral ecology of nutrient foraging by plants. Annual Review of Ecology, Evolution, and Systematics, 2011(42): 289–311.

Dudley, S.A. & File, A.L. (2007). Kin recognition in an annual plant. Biology Letters (2007)3: 435–438.

Gagliano, M., Grimonprez, M., Depczynski, M. & Renton, M. (2017). Tuned in: plant roots use sound to locate water. Oecologia (2017)184: 151–160.

Runyon, J.B., Mescher, M.C. & De Moraes, C. (2006). Volatile chemical cues guide host location and host selection by parasitic plants. Science, 313(5795): 1964–1967.

Simard, S. (2016). Suzanne Simard: How trees talk to each other [Video file]. Retrieved from https://www.ted.com/talks/suzanne_simard_how_trees_talk_to_each_other#t-18444

Gained in translation: translational ecology for the Anthropocene

A recent evaluation of the state of science around the world run by 3M found that 86% of the 14,000 people surveyed believed that they knew 'little to nothing' about science. 1/3 of all respondents also said they were skeptical of science and 20% went farther, saying that they mistrust scientists and their claims.

Those attitudes wouldn't surprise anyone following US politics these days. But they're still troubling statistics for ecologists. Perhaps more than most scientific disciplines, ecologists feel that their work needs to be communicated, shared, and acted on. That's because modern ecology can't help but explicitly or implicitly include humans – we are keystone species and powerful ecosystem engineers. And in a time where the effects of global warming are more impactful than ever, and where habitat loss and degradation underlie an age of human-caused extinction, ecology is more relevant than ever.

The difficulties in converting primary ecological literature into applications are often construed as being caused (at least in part) by the poor communication abilities of professional scientists. Typically, there is a call for ecologists to provide better science education and improve their communication skills. But perhaps this is an 'eco-centric' viewpoint – one that defaults to the assumption that ecologists have all the knowledge and just need to communicate it better. A more holistic approach must recognize that the gap between science and policy can only be bridged by meaningful two-way communication between scientists and stakeholders, and this communication must be iterative and focused on relevance for end-users.

William H. Schlessinger first proposed this practice - called Translational Ecology (TE) - nearly 8 years ago. More recently an entire special issue in Frontiers in Ecology and the Environment was devoted to the topic of translational ecology in 2017. [The introduction by F. Stuart Chapin is well worth a read, and I'm jealous of the brilliant use of Dickens in the epigraph: “It was the best of times, it was the worst of times, it was the age of wisdom, it was the age of foolishness, it was the epoch of belief, it was the epoch of incredulity.”]

Although applied ecology also is focused on producing and applying ecological knowledge for human problems, translational ecology can be distinguished by its necessary involvement of the end user and policy. Enquist et al. (2017, TE special issue) note: "Ecologists who specialize in translational ecology (TE) seek to link ecological knowledge to decision making by integrating ecological science with the full complement of social dimensions that underlie today's complex environmental issues."

From Hallet et al. (2017, TE special issue)

The essential component of translational ecology is a reliance on people or groups known as boundary spanners, which are the key to (effectively) bridging the chasm between research and application. These people or organizations have particular expertise and skill sets to straddle the divide between "information producers and users". Boundary spanners are accountable to the science and the user, and generally enable communication between those two groups.

Boundary spanners likely have interdisciplinary backgrounds, and integrate knowledge and skills from ecology and biology, as well as disciplines such as anthropology, human geography, sociology, law, or politics. The key issue in that boundary spanners can overcome is the lack of trust between information users and producers. Translational ecology – through communication, translation, and mediation – is especially focused on developing relationships with stakeholders and boundary spanners are meant to be particularly skilled at this. 

For example, academics publish papers, and then the transmission of information to potential users is usually allowed to occur passively. At best, this can be slow and inefficient. At worst, potential end users lack access, time, and awareness of the work. Boundary spanners (including academics) can ensure this knowledge is accessibly by producing synthetic articles, policy briefs and white papers, by creating web-based decision-support tools, or by communicating directly with end users in other ways. A great example of existing boundary spanners are Coop extension offices hosted at US land grant universities. Coops are extensions of government offices (e.g. USDA) whose mission is to span the knowledge produced by research and to bring it to users through informal education and communication. 

For working academics, it may feel difficult to jump into translational ecology. There can be strong institutional or time constraints, and for those without tenure, fear that translational activities will interfere with other requirements. Institutions interested in working with ecologists also often face limitations of time and funding, and variable funding cycles can mean that boundary-spanning activities lack continuity.

But what's hopeful about the discussion of translational ecology in this issue is that it doesn't have an individualistic viewpoint: translational ecology requires teams and communities to be successful, and everyone can contribute. I think there is sometimes a very simplistic expectation that individual scientists can and must be exceptional generalists able to do excellent research, write and give talks for peers, teach and lecture, mentor, and also communicate effectively with the general public (in addition to taking care of administration, human resources, ordering and receiving, and laboratory management). We can all contribute, especially by training boundary spanners in our departments and labs. As F.S. Chapin says, "The key role of context in translational ecology also means that there are roles that fit the interests, passions, and skills of almost any ecologist, from theoreticians and disciplinarians to people more focused on spanning boundaries between disciplines or between theory and practice. We don't need to choose between translational ecology and other scientific approaches; we just need to provide space, respect, and rigorous training for those who decide to make translational ecology a component of their science." 

From Enquist et al. (2017, TE special issue).

References:
Special Issue: Translational ecology. Volume 15, Issue 10. December 2017. Frontiers in Ecology and the Environment