Desert adaptations are fascinating to me. I love learning about plant and animal adaptations that help organisms survive the arid conditions deserts sustain. To be honest, I know much more about plant and animal adaptations in desert ecosystems compared to my fungal knowledge. This is why I decided to do some research and write this article. Fungi from the genus Montagnea are interesting desert adapted species that have evolved several adaptations helping them to survive these demanding environmental conditions. Today, I’ll share with you what I learned about these organisms.
Up until the early ‘90s, ecologists thought that the fungal kingdom was not important to desert ecosystem functioning. Studies quantifying fungal spore densities in the ‘70s and ‘80s found very few spores compared to other fungal rich habitats. Also, a preconceived notion was that areas with little rainfall had very few fungi. With few fungi, there must be limited fungal interactions. Though some researchers simply refused to believe fungi had no place in dessert ecosystems.
In 1995, Katherine Jacobson wanted to better understand fungal ecology in these arid ecosystems. She set off to Namibia, the driest country in southern Africa to get a more comprehensive look at desert adapted fungi. Here, only 10% of the country receives more than 55 cm of rain. Where I reside in Western NY, we easily get double that amount annually. The ephemeral streams and rivers that seasonally flow from the Namibian highlands to the ocean drive much of the ecology here, causing the migration of large mammals, and providing plants with enough water to reproduce and withstand the driest parts of the year. These river and stream beds also provide a proper substrate for fungi too.
On her intense dry season forays, many fungal species Katherine found occurred beneath Acacia trees endemic to the area (Acacia erioloba). She soon realized the several reasons why these areas are fungal hotspots. The first obvious reason is that these trees shade the sandy substrate, reducing the amount of water loss. With more water available, more fungi can persist. An interaction that promotes fungal fruiting not brought up in the original publication has to do with hydraulic lift. Hydraulic lift occurs as the deep tap roots of the Acacia tree access water from the water table. As water travels up the roots, some of that water, following water potential gradients leaves the roots near the surface, essentially bringing water up to the dryer portions of the substrate. But possibly the most fascinating ecological interaction she described deals with large herbivorous mammals.
Desert adapted mammals not only have specialized physiological responses to reduce water loss, but behavioral responses as well. Katherine soon realized that a desert adapted, elk-sized ungulate known as oryxes also escape the intense rays of the sun by taking refuge beneath these same Acacia trees. Upon closer investigation, she realized that not only were some of these fungi breaking down the woody debris falling from these trees, but many of the fungi present were actually coprophilous; consuming the fecal material from these same ungulates.
As these large mammals move from Acacia tree to Acacia tree, they dig up patches of soil and sand to reveal a cooler substrate to lay on. In doing so, they excavate fungal spores and essentially become fungal dispersers as they vector spores between different trees. Montagnea species can be found fruiting from these nutrient rich piles of oryx dung beneath Acacia trees across Namibia. Although the fungus eludes much of the nutrient and water limitations present in desert ecosystems with its coprophilic ecology associated with Acacia trees, it has still over time evolved some fitness enhancing physiological adaptations.
Unlike other agarics, Montagne sp. require less available water to release their spores. Most gilled mushrooms release their spores actively as two separate water droplets form on the microscopic spores. When these two droplets come together the center of gravity shifts dramatically, dislodging the spore from the club shaped basidia allowing it to enter the surrounding air current. In Montagnea, the spores are not forcibly discharged. Instead, a plug forms within the sterigmata, the branch attaching the spore to the basidia. That plug becomes a weak point as the fungus dries out. Strong enough winds will eventually dislodge the spore passively. This mechanism of spore release works extremely well in these desert habitats.
In addition to its spore release mechanism, the fungal tissue itself is woodier compared to the tissue of species within temperate ecosystems. Because of this, the fruiting body can better withstand desiccation. Additionally, these hardy structures containing spores that do get toppled over by strong desert winds are structurally sound and can still release spores as they tumble across the desert floor.
To be honest, I was planning on learning about a lot more physiological adaptations desert adapted fungi have. Instead, I learned more about their specific ecology that allows them to exist in some of the most demanding environments on the planet. By utilizing the microhabitats Acacia erioloba provides, and shifting to a coprophilous ecology, Montagnea species do just fine in areas you and I would only last 3 hours in.