Fungi as Fixers

The plants in this restored prairie at Elm Creek Park Reserve are mostly mycorrhizal. Fungi live with their roots in a mutually beneficial relationship.

The last post introduced mycorrhizae, the fungus-root associations that benefit both partners. The fungus transports nutrients and water to the plant, while the plant gives sugars and other carbon-containing molecules to the fungus. Most plants are mycorrhizal and are dependent on this symbiosis for their best growth.

On a larger scale, mycorrhizae are also important in ecological restoration, the practice of regenerating native plant communities after they’ve been degraded or destroyed. They may also help with carbon sequestration, in this case the storage of carbon in fungal mycelia, the underground bodies of fungi.

Mycorrhizae and Ecological Restoration

In a 2023 review article, a team of scientists led by Lisa Markovchick wrote about a gap between the science and practice of using mycorrhizae in restoration projects. Although research supports such use, practice lags, in part because of negative views of fungi as only pathogens.

To counter this perception, Markovchick and her collaborators offer insights from research and tips for both protecting mycorrhizal fungi and deploying them during restoration projects. A few of those insights and tips are below. Links to Markovchick’s full paper and a webinar summarizing her work follow the list.

According to Markovchick and her collaborators:

• Mycorrhizae perform many functions, such as promoting water infiltration and retention, preventing erosion, and boosting plant nutrition, survival, and resilience.
• Mycorrhizal fungi also have roles in providing ecosystem services, such as responding to disturbance and providing habitat for other organisms, thereby enhancing biodiversity.
• Change in land use, drought, invasive plants, and other disturbances can deplete mycorrhizal fungi or change the fungal species present. Even some necessary practices, such as applying herbicides to invasive plants, can affect mycorrhizae.
• The benefits of mycorrhizal fungi are clear from many studies. For example, they can significantly increase species richness (the number of different plant species in a community), and plant biomass, and their effects tend to grow with time.
• There must be a good match between plants and mycorrhizal fungi when both are used to restore a community. Mass-produced mycorrhizal fungi may not provide that important pairing, leading to neutral or negative results. Introducing fungi from a native community near the restoration site has proven most beneficial.

References

The Gap Between Mycorrhizal Science and Application. Wild Earth Guardians YouTube video featuring Lisa Markovchick. 53:46.

The gap between mycorrhizal science and application: existence, origins, and relevance during the United Naton’s Decade on Ecosystem Restoration. Lisa M. Markovchick, Vanessa Carrasco-Denney, Jyotsna Sharma, and others. Restoration Ecology Vol. 31, No. 4. May 2023.

 

Mycorrhizae and Carbon Sequestration

Potential solutions to a warming climate include nature-based options such as protecting forests, grasslands and wetlands. Protecting and enhancing mycorrhizal growth could be another solution, because plants transfer carbon-containing compounds such as sugars to below-ground fungal bodies (mycelia) and the roots they support.

The carbon that builds those compounds comes from atmospheric carbon dioxide captured during photosynthesis, and it can be a significant amount. In a 2023 review article, Heidi-Jayne Hawkins and others estimate that, globally, about 13 gigatons of carbon dioxide equivalents are transferred to the mycelia of mycorrhizal fungi each year. That amounts to about 36 percent of the carbon dioxide emissions from fossil fuels in 2021.

Living mycelia can also promote long-term carbon storage by releasing sugars and acids from their hyphae (the fungal strands that constitute the mycelium). These compounds eventually lead to the formation of mineral-associated organic matter, or MAOM. In this type of soil organic matter, carbon compounds are bound to clay, silt, or other mineral particles in soils. MAOM is slower to decompose, in part because it’s protected inside mineral aggregates that are harder for decomposers to access.

Even after fungal mycelia die, they can support carbon storage. Their organic matter is added to the soil, where it can attract soil particles and form the enlarging aggregates that stabilize carbon as MAOM.

The authors emphasize that there is more to understand about the flow of carbon into and through mycorrhizae and its effects on carbon sequestration. Still, they consider mycorrhizal fungi “a major carbon pool.”

Reference

Mycorrhizal mycelium as a global carbon pool. Heidi-Jayne Hawkins, Rachael I.M. Cargill, Michael E. Van Nuland, and others. Current Biology, Volume 33, Issue 11. June 5, 2023.

How can we support mycorrhizal fungi?

 Lisa Markovchick’s article recommends several actions and tips to improve the diversity and function of mycorrhizae, specifically in natural areas. A few of them are below. For a full list, see the link above.

• Protect source populations of mycorrhizae. Native communities with little or no history of disturbance are refuges for these fungi.
• When restorations are planned, include steps for soil conservation.
• Choose mycorrhizal fungi that are appropriate for the plant species being restored. This could be accomplished by introducing the “full diversity” of fungi from nearby native communities like the one being regenerated.
• Plants and their mycorrhizal fungi won’t associate unless both are alive and come into direct contact. Timing and placement are important, as is the source of fungi. Commercial mycorrhizal products may be a poor choice.

Plant Profile: Starflower

Starflower blooming in late May in a mixed coniferous-deciduous forest in north-central Minnesota.

Starflower (Trientalis borealis, aka Lysimachia borealis) is a spring-blooming, perennial wildflower of coniferous and deciduous forests. In early spring, stems emerge from overwintering tubers and grow 4–8 inches tall, their slender stems bearing six to eight lance-shaped leaves of unequal size. In May and June, one, two, or rarely three flowers grow from the leaf axils. Each flower is about ½ inch wide and typically has seven white, pointed petals and orange anthers that later turn brown.

The flowers are self-incompatible, so they can’t pollinate themselves. To form seeds, they must receive pollen from another patch of starflowers, delivered primarily by native mining bees (andrenid bees), sweat bees (halictid bees) and hover flies (syrphid flies). If the bees are present, if the patches are close enough for the bees to transit, and if pollination is successful, small seed capsules eventually form at the tips of the stems.

That’s a lot of ifs and little assurance of a next generation. Starflower doesn’t depend only on seeds for reproduction, however. In fact, very little of its energy is dedicated to flowering and seed set. Most of its reproductive effort is spent on rhizomes, underground stems that extend the plant’s reach and give rise to new plants. It’s a faster way of reproducing, and in a stable environment, it’s more reliable. The downside is that the parent plant and its vegetative offspring are genetically identical, so if the environment changes, the plants may not have what it takes for a population to survive.

If conditions remain favorable, though, the rhizomes grow and form patches of new plants. By midsummer, tubers begin forming at their tips. Aided by the cool nights of late summer and fall, they fill with starch to fuel next year’s growth. Rhizome connections then wither and the leaves yellow and fall. Bare stems topped with capsules are all that remain above ground, while tubers below ground carry their incipient roots and shoots through winter, ready to resume growth in spring. Starflower seeds also overwinter, but they don’t germinate until fall of the second year.

Starflower range in North America (left ) and the Upper Midwest (right). Maps from USDA Plants Database.

As with many plants, Starflower is facing challenges brought by climate change. The cool nights needed for maximum tuber development are warmer now, and researchers have found that flowering and seed set lessen toward the southern edge of the plant’s range. These changes raise questions and concerns about whether the species can adapt, because in some places, it isn't. Starflower is state-listed as endangered in Georgia and state-listed as threatened in Illinois.

Populations in Minnesota and other northern locations are responding to warmer May temperatures by flowering earlier. That may or may not be beneficial, but so far, starflower seems to be holding its own here. The species name borealis, meaning “of the north,” may be truer than ever.

References

Minnesota Wildflowers

Illinois Wildflowers

USDA, NRCS. 2023. The PLANTS Database (http://plants.usda.gov, 06/03/2023). National Plant Data Team, Greensboro, NC USA.

Roger C. Anderson. June 1970. The role of daylength and temperature in tuber formation and rhizome growth of Trientalis borealis Raf. Botanical Gazette, Volume 131, Number 2, pp. 122-128.

Roger C. Anderson and Orie L. Loucks. July 1973. Aspects of the biology of Trientalis borealis Raf. Ecology, Volume 54, Issue 4, pp. 798-808.

Roger C. Anderson and Michael H. Beare. March 1983. Breeding system and pollination ecology of Trientalis borealis (Primulaceae). American Journal of Botany, Volume 70, Issue 3, pp. 408-415.

Emily Dangremond. No date. Climate change and starflower in the Midwest. Illinois Native Plant Society.

Emily Dangremond, Christopher H. Hill, Shahd Louaibi, and Ivette Muñoz. 2021. Phenological responsiveness and fecundity decline near the southern range limit of Trientalis borealis (Primulaceae). Plant Ecology, Volume 223, pp. 41-51.  

Linda G. Chafin. 2020. Trientalis borealis Raf. Georgia Biodiversity Portal, Georgia Department of Natural Resources/Wildlife Resources Division.

City Trees Green Up Earlier

 A recent study found that trees in cities leaf out in earlier in spring than those in rural areas.  This post explains what happens as deciduous (leaf-shedding) plants enter and leave dormancy, and how a shift in timing could have ripple effects.

It is December, and the trees are, in their way, asleep. They are dormant, quieted by the declining temperatures and longer nights that signal a time of harsh conditions.

They will have a long nap. Last summer many deciduous trees began covering their buds – next year’s hope of growth – in protective scales. In autumn the leaves gave it up. The chlorophyll, proteins and sugars in their blades broke down or withdrew into branches, trunks and roots to be stored over winter.

As their substance retreats, leaves become liabilities. Through stomates, small pores on the surfaces of their blades, leaves continue to lose water that can’t be replaced from frozen soil. To prevent desiccation, the leaves are cut off.  Invisible lines of cells, called abscission layers, form on the leaves’ petioles, like tear-off lines that mark where they will separate from the trees. Some leaves offered a colorful sendoff and fell. Others, those with abscission layers not quite complete, are still hanging on, rattling in the winter wind.

Although they are dormant now, the trees are primed to renew their growth in spring. After enough cold days have accumulated and as days grow longer, they will begin to stir. As in all aspects of plant growth, timing is everything. If buds break too early, say in an unusually warm February, new growth would likely be damaged by a returning freeze. To avoid this, day length acts as a check. Even if buds have been adequately winter-chilled and temperatures then rise, short days (long nights) are a sign that winter isn’t over, and growth will not resume.

Timing is important not only to avoid freezing, but also to attract pollinators. Insect-pollinated trees and shrubs, especially those that are native here, have long relationships with native insects. Time of flowering may coincide with time of insect emergence and vice versa, each benefiting from the presence of the other. If plants flower earlier than normal, their pollinators may not yet have emerged, or if it's too cold, they may not be active. 

If timing of life events -- phenology -- depends on external cues, what happens when temperature and light are altered? Does a tree’s phenology change when environmental indications change, such as in warmer and artificially brighter cities?

Yes, according to a recent study that looked at satellite and phenological data around the globe (1). According to the study, on average, spring green-up occurs six days earlier in cities compared to rural areas, due mostly to warmer urban temperatures.  When photoperiod – daylength– is factored in, the effect is greater. Urban trees exposed not only to warmer temperatures but also to lights on streets, parking lots, billboards and other artificial sources leafed out an average nine days earlier than rural trees. It's thought that night length, normally a check on early leaf-out, is shortened by city light, and the trees are “tricked” into resuming growth in artificially warmer and brighter conditions. 

The study raises several questions, especially about climate change.  If a warming climate causes trees to green up earlier even in the countryside, would rural darkness limit how much earlier they resume growth? In other words, without city lights, would winter's long nights continue to serve as a check on how early the trees leaf out?

Also, could warm urban winters, made even warmer by climate change, prevent city trees from accumulating enough cold exposure to leaf out early, even if nights are artificially short and spring-like? 

If trees do leaf out and flower early, will allergy season also start earlier? How will insects adapt to the change? Will their phenology shift, too?

These questions can be answered by part by continuing to observe the phenology of plants and animals. Both citizens and scientists are important in that effort. By recording when trees, shrubs and other plants leaf out, flower and form seeds, they contribute to an understanding of what triggers these life events and how their timing might be shifted by environmental changes. 

To learn more about phenology and how to help observe seasonal changes, open the Phenology tab.  

References

(1) Meng, Lin. 2021. “Green with phenology.” Science Vol. 374, Issue 6571 (November 25, 2021): 1065-1066. DOI: 10.1126/science.abm8136

Dr. Meng’s study is also discussed in a National Public Radio interview at https://www.npr.org/2021/11/29/1059861862/climate-change-and-city-lights-are-tricking-trees-into-growing-leaves-too-soon