TAIPEI (Taiwan News) — Planting more trees seems like a logical way of counteracting climate change, as forests facilitate carbon sequestration, the process of capturing and storing atmospheric carbon dioxide (CO2), but as efforts to remove CO2 from the atmosphere intensify, organisms from another kingdom — fungi — are showing they have an indispensable role to play in this process.
"Almost all plant life coexists with fungi during a certain period, if not the entire life cycle of a plant, but the reasons for this coexistence and its effects have not yet been fully deciphered," said Ko-Hsuan "Koko" Chen, an assistant research fellow at Academia Sinica's Biodiversity Research Center. Her lab studies plant-fungal symbiosis, especially between fungi and early photosynthetic organisms such as mosses.
Funguses are commonly used as ingredients in food and in medicines. However, their dynamic relationship with plants is not so well known and is significantly tied to the prosperity of plant species and element cycles, which are defined as the biogeochemical pathways in which elements are transformed by natural processes.
Just as human bodies are hubs for microbes, a myriad of fungi co-exist with plants. The ones that determine whether plants can thrive in their habitat are mycorrhizal fungi, which live among plants' roots.
One study investigating the successful colonization of pine species in the southern hemisphere concluded that the trees are strongly associated with symbiotic ectomycorrhizal (EM) fungi, which "cannot flourish on land without their fungal partner."
"Even in the savanna of Ecuador, where shrubs originally dominated, the pine trees introduced by European colonizers from the northern hemisphere grew vigorously with the EM fungi," Chen explained.
EM fungi typically form mantles on plant roots but do not penetrate their cell walls. They help plants absorb nutrients and water from the soil and increase their resistance to disease and drought.
They might not be familiar to many, but some EM fungi do enjoy worldwide recognition, including tasty truffles and fly agarics — the red-capped mushroom in "Super Mario."
Truffles (top) and the fly agaric are examples of EM fungi. (Wikimedia Commons photos)
Most importantly, EM fungi are believed to be climate change warriors. One study found that despite the worldwide loss of mycorrhizal symbiosis, ecosystems containing mycorrhizal vegetation store 350 gigatons of carbon globally compared to just 29 gigatons where it is absent.
EM fungi contribute to carbon sequestration because they help plants grow larger and better, leading to robust photosynthesis that absorbs more CO2. In addition, as these fungi are capable of degrading organic matter in the soil, they outcompete the saprobic fungi that play the role of decomposers, feeding on dead organic matter by breaking it down with enzymes.
Because of the competition, the overall decomposition in ecosystems slows down. More carbon is locked in organic matter instead of returning to the air — imagine piles of un-decomposed leaves and pine cones on the forest floor as a massive reservoir of carbon.
Nevertheless, scientists recently found that nitrogen pollution results from burning fossil fuels, which along with fertilizer used on farms is paring back EM fungi's contribution to carbon sequestration.
These findings suggest forests exposed to high levels of nitrogen pollution have far fewer trees harboring EM fungi. This phenomenon could be universal, especially in developing countries that rely particularly heavily on fossil fuels for power generation.
Understanding the symbiosis between plants and fungi can not only help combat climate change but also advance agriculture. For example, people can harness toxic fungi growing on leaves or stems as natural pest control to prevent crops from being eaten.
Nevertheless, the war on crop-afflicting fungi, especially the notorious ergot, will continue. This fungus ravaged Europe in the Middle Ages and is still a threat in some impoverished African nations.
Ergot suspected of being behind witch trials in medieval Europe. (Flickr, On a Need to Grow Basis photo)
As an island nation with varying elevations, Taiwan is home to a diversity of plant species. Chen's lab focuses on the peat moss that thrives in Taiwan's cloud forests.
"Across the lineage of plant species, moss is the group where we do not find typical mycorrhizal fungi. However, these plants have a host of other fungi in their bodies," she said.
Chen's goal is to figure out what exactly these fungi did to these non-vascular plants that helped them conquer the terrestrial world several million years ago.
Cloud forests in Taiwan are full of mosses. (Ko-Hsuan Chen photo)
Chen in her lab at Academia Sinica. (Taiwan News photo)