Plants thrive in a complex world by communicating, sharing resources and transforming their environments
As a species, humans are wired to collaborate. That's why lockdowns and remote work have felt difficult for many of us during the COVID-19 pandemic.
For other living organisms, social distancing comes more naturally. I am a plant scientist and have spent years studying how light cues affect plants, from the very beginning of a plant's life cycle—the germination of seeds—all the way through to leaf drop or death. In my new book, "Lessons from Plants," I explore what we can learn from the environmental tuning of plant behaviors.
One key takeaway is that plants have the ability to develop interdependence, but also to avoid it when being connected could be damaging. Generally, plants are constantly communicating and engaged with other organisms in their ecosystems. But when these ongoing connections threaten to cause more harm than good, plants can exhibit a form of social distancing.
The power of connection and interdependence
When conditions are good, most plants are networkers. The vast majority of plants have fungi that live on or within their roots. Together, the fungi and roots form structures known as mycorrhizae, which resemble a netlike web.
Mycorrhizae increase their host plants' ability to absorb water and nutrients, such as nitrogen and phosphate, through their roots. In return, the plants share sugars that they produce through photosynthesis with their fungal partners. Thus, the fungi and host plants are powerfully interconnected, and depend on one another to survive and thrive.
Mycorrhizal connections can link multiple plants in a functioning network. When plants produce more sugars than they need, they can share them via this interconnected root-fungal network. By doing so, they ensure that all plants in the community have access to the energy they need to support their growth.
Put another way, these connections extend beyond a single host plant and its fungal partner. They create communitywide relationships and interdependent networks of plants and fungi. Factors in the external environment, such as the amount of light available for photosynthesis and the composition of soil around the plants, fine-tune the connections in these networks.
Mycorrhizhae also serve as communication channels. Scientists have documented that plants pass defensive chemicals, such as substances that promote resistance against insect pests, to other plants via fungal networks. These connections also allow a plant that has been attacked by aphids or other such pests to signal to neighboring plants to preemptively activate their own defense responses.
When it's safer to keep your distance
Sharing resources or information that helps other plants ward off danger is a valuable example of the power of connectedness and interdependence in plant ecosystems. Sometimes, however, surviving requires plants to disconnect.
When environmental cues such as light or nutrients become scarce enough that a host plant can produce enough sugars through photosynthesis to support only its own growth, staying actively interconnected in a larger community network could be dangerous. Under such conditions, the host plant would lose more from sharing limited sugar supplies than it would gain from the network in water and nutrients.
At times like these, plants can limit mycorrhizal connections and development by restricting how many materials they exchange with their fungal partners and avoiding making new connections. This is a form of physical distancing that protects the plants' ability to support themselves when they have limited energy supplies so they can survive for the long term.
When conditions improve, plants can resume sharing with their fungal partners and establish additional connections and interdependence. Once again, they can benefit from sharing resources and information about the ecosystem with their extended plant and fungal communities.
Check out this amazing white #mycorrhiza on roots of a 2yo jack pine seedling! These help with nutrient uptake and forest regeneration after fires. Any ideas what it is? #FungalFriday pic.twitter.com/I90jof0u7R— Nicola J Day (@n_j_day) August 17, 2018
Recognizing kin and collaboration
Social distancing isn't the only trick plants use to make their way in the world. They also recognize related plants and tune their abilities to share or compete accordingly. When the plants that are interconnected by a fungal network are close genetic relatives, they share more sugars with the fungi in that network than they do when the other plants are more distantly related.
Prioritizing kin may feel highly familiar to us. Humans, like other biological organisms, often actively contribute to help our kin survive. People sometimes speak of this as working to ensure that the "family name" will live on. For plants, supporting relatives is a way to ensure they carry on their genes.
Plants can also transform aspects of their environment to better support their growth. Sometimes essential nutrients that are present in soil are "locked up" in a form that plants can't absorb: For example, iron can become bound up with other chemicals in forms very similar to rust. When this happens, plants can excrete compounds from their roots that essentially dissolve these nutrients into a form that the plants can readily use.
Plants can transform their environments in this way either individually or collectively. Plant roots can grow in the same direction, in a collaborative process known as swarming that is similar to bee swarms or bird flocks. Such swarming of roots enables the plants to release a lot of chemicals in a particular soil region, which frees up more nutrients for the plants' use.
Behaviors like mycorrhizal symbiosis, kin recognition and collaborative environmental transformation suggest that overall, plants are better together. By staying in tune with their external environment, plants can determine when working together and fostering interdependence is better than going it alone.
When I reflect on these tunable connections and interdependence between plants and fungi, I draw constant inspiration—especially during this pandemic year. As we make our way in a constantly changing world, plants offer all kinds of lessons for humans about independence, interdependence and supporting each other.