Desert Mosses That Live Under Rocks

Syntrichia caninervis growing in both soil surface and milky quartz. [SOURCE]

To be accused of living under a rock is generally not a good thing in today’s society. That is, unless you are a moss living in the Mojave Desert. By setting up residency under milky quartz, a few Mojave mosses are able to find much more favorable growing conditions than they would in the surrounding desert environment.

Microclimates are extremely important, especially in harsh environments like the Mojave. By providing conditions that are ever so slightly better than ambient conditions, microclimates can increase the amount of habitat available, which can lead to greater biodiversity overall. That is exactly what is going on beneath milky quartz in high elevation habitats of the Mojave Desert.

Tortula inermis (white arrow) and S. caninervis (black arrow) growing in a milky quartz. [SOURCE]

While dabbling in a bit of mineral appreciation, bryologists from the University and Jepson Herbaria at UC Berkeley discovered bright green moss growing under some chunks of quartz. Whereas moss growing on the surface of soil and rocks throughout the region were dark, dry, and dormant, the moss growing under quartz was green, lush, and growing. This observation launched a series of experiments to better understand how milky quartz may be providing more favorable microclimates for some desert mosses.

By measuring the conditions under chunks of milky quartz and comparing it to that of the surrounding landscape, researchers found that these minerals do indeed provide mosses with much more favorable conditions. Moreover, the benefits to living under milky quartz are numerous, offering many advantages to resident mosses.

For starters, milky quartz serves as a buffer against large swings in temperature. Deserts are known for being extremely hot but they can also be extremely cold. Sandy soils may heat up very quickly when the sun is out but, by the same logic, they also cool extremely quickly as soon as the sun sets. Rapid swings in temperature can be very harmful to plants so anything that can buffer such swings is generally a good thing. That is exactly what milky quartz does. As the sun rises in the sky, it takes milky quartz longer to heat up than the surrounding landscape, which means the environment directly underneath stays cooler for longer. Similarly, once warmed by the sun, milky quartz takes longer to cool down as the sun sets. As such, the environment directly underneath doesn’t cool down as quickly. By monitoring temperatures over the course of a year, it was found that temperature swings under the quartz were buffered by an average of 4°C (7°F) compared to that of the surrounding environment.

Tortula inermis was more likely to be found growing under quartz at high elevations. [SOURCE]

Though widespread in the Mojave, Syntrichia caninervis nonetheless grows better under quartz. Photo by John Game licensed under CC BY 2.0

Another benefit to living under quartz involves humidity. Not only are deserts hot, they can also be very dry. The Mojave is certainly no exception to this rule as it is considered the driest desert in North America. A lack of water can be troublesome for mosses. Because they lack roots and a vascular system, mosses rely on osmosis for obtaining the water they need to grow and reproduce. They also lose water and dehydrate quickly. For individuals growing exposed to the elements, this means drying up and going dormant. Mosses simply can’t grow when water isn’t around. By monitoring the relative humidity under milky quarts, researchers found that the undersides of milky quartz were twice as humid as the surrounding landscape.

Thanks to this increased humidity, mosses living under milky quartz are able to hold onto water for much longer than mosses growing on exposed soil. This has both short and long-term consequences for moss growing seasons in this harsh desert ecosystem. Increased humidity under milk quartz prolongs the moss growing season much longer than that of their exposed neighbors. In support of this, the researchers found that mosses growing under milky quartz also grew longer shoots. Longer shoots also means more water storing capabilities, which very well could lead to a positive feedback loop between humidity, growing season, and moss health.

(A) Box plot of hypolithic and soil surface S. caninervis shoot length. (B) An S. caninervis shoot fromunder quartz. (C) An S. caninervis shoot from the soil surface. [SOURCE]

Finally, milky quartz may actually protect resident mosses from the blistering rays of the sun. Growing at high elevation means much more exposure to the power of the sun. When fully exposed, desert mosses will often pump their tissues full of pigments like carotenoids, anthocyanins, and flavonoids, which act as sunscreens, protecting their sensitive tissues from UV damage. Even so, exposed mosses can suffer greatly from sun damage and, while dormant, have no means of repairing said damage.

By monitoring the light environment directly under milky quarts, researchers found that, depending on the size of the rock, light transmittance is reduced down to anywhere between 4% and 0.04% of full exposure. Moreover, the crystalline structure of milky quartz is such that it may actually filter out both UV-A and UV-B radiation, thus further reducing the harmful effects of the sun. In fact, mosses growing under milky quartz were found to produce far less sunscreen pigments than their exposed neighbors. If they don’t have to protect themselves from the blistering sun, it appears they don’t waste the energy on such pigments. While a reduction in light may sound bad for a photosynthetic organism, it would appear that the mosses in this study are well adapted to photosynthesizing at lower light levels.

In effect, milky quartz acts like parasols for desert mosses. Just as we like to sit under umbrellas at the beach, these desert mosses find much more favorable growing conditions under milky quartz. While none of the mosses in the study are restricted to growing under quartz, those that do experience multiple measurable benefits that increase their growing season in this largely unforgiving desert ecosystem.

Photo Credits: [1] [2] [3] [4] [5]

Further Reading: [1]

Himalayan snowball plants and their fashionably functional coats

Credit to CGTN Nature film crew

Hairy plants are both fun and functional. Hairs or trichomes on the leaves of plants can serve a variety of functions. If the plant is growing in a region prone to cold temperatures, it is thought that a dense layer of hairs can function like a wool coat, keeping the plant warm when temperatures drop. This is such a popular idea that it is often assumed rather than tested. For a strange group commonly referred to as Himalayan snowball plants, the truth is a bit more complicated.

Himalayan snowball plants are members of the genus Saussurea, which hails from the family Asteraceae. Though the genus is widespread, the Himalayan snowball plants are confined to high elevation, alpine habitats in central Asia. As you can imagine, life at such altitudes is defined by extremes. Temperatures during the day can skyrocket due to the lack of atmospheric insulation. Conversely, temperatures can take a dive as weather changes and/or the sun goes down. One look at the Himalayan snowball plants tells you that these plants are wonderfully adapted to such habitats. But what kind of advantages does that this coat of hair provide?

Credit to CGTN Nature film crew

Well, research has revealed a bit more nuance to the whole “winter coat” idea. Indeed, it does appear that the furry coat does in fact provide some insulation to the plant. However, most of the warmth appears to come from the dark color of the inflorescence rather than by pure insulation alone. After all, the vast majority of plants do not produce any heat. The flower heads or capitula of these daisy relatives is low in stature. This keeps it out of the way of the coldest winds. Also, they are so deeply violet in color that they can appear black. This is no accident. As anyone can tell you, darker colors absorb more heat and that is exactly what happens with the Himalayan snowball plants.

Another interesting thing to consider is that most of the growth and reproduction in these plants occurs during frost-free periods of the year. Though temperature swings are frequent, it rarely gets cold enough to severely damage plant tissues until long after the plants have flowered and set seed. Moreover, there is some evidence to suggest that the dense coat of hairs may have a cooling effect during periods of intense exposure to sunlight. Their light color may reflect a lot of the incoming radiation, sparing the plant from overheating. Therefore, it appears that the benefit of such a thick coat of hairs has more to do with avoiding temperature swings than it does ensuring constant warmth. By buffering the plant against huge swings in ambient temperature, the hairs are able to maintain more favorable conditions for plant growth and reproduction.

Credit to CGTN Nature film crew

Also, because this area experiences a monsoon season during growth and flowering of Himalayan snowball plants, these hairs may also serve to repel water, keeping the plants from becoming completely saturated. If water were to stick around for too long, it could open the plant up to pathogens like fungi and bacteria. It could also be that by insulating the plant against temperature swings, the hairs also provide a more favorable microclimate for pollinators. Bumblebees are thought to be the main pollinators of Himalayan snowball plants and despite their ability to maintain higher internal temperatures relative to their surroundings, anything that can buffer them as they feed would be beneficial to both the bees and whatever plant they may be pollinating as a result.

Photo Credit: [1]

Further Reading: [1] [2]

Burrowing Birds, Biocrust, and Biodiversity: A Microclimate Story

Nolana humifusa (Solanaceae) Photo by Michael Wolf licensed by GNU Free Documentation License

Peru’s coastal deserts are some of the driest places on Earth. Most of the water they receive comes not from rain but rather fog rolling in off the ocean. These fog-fed habitats are known as Lomas and they support a surprising diversity of plant species. Still, life in the Lomas is no treat so plants growing there need a bit more than a tough disposition to get by. Many components of the Lomas flora rely on favorable microclimates to survive long enough to reproduce. Recently it has been found that a few species of burrowing birds are responsible for creating some of these favorable microclimates.

The beneficial effects of burrowing or “fossorial” animals on plant diversity has many examples in nature. This is especially true in harsh climates. The act of burrowing disturbs the surrounding soil and can expose nutrient-rich soils as well as increase hydrology. However, more than just mammals burrow. As such, researchers wanted to investigate the role of burrowing birds on Lomas plant diversity.

A pair of burrowing owls (Athene cunicularia) Photo by Ron Knight licensed by CC BY 2.0

The birds in this study consist of one owl - the burrowing owl (Athene cunicularia), and two species of miner birds (Geositta peruviana & G. maritima). Instead of nesting in trees, which are few and far between in such arid habitats, these birds nest in the ground. To do so, they excavate burrows. As they excavate, these birds break up the thin biocrust of cyanobacteria that carpets undisturbed stretches of sand. This biocrust is an immensely important component of the local ecology. It stabilizes sandy soils and increases their fertility. It also has a considerable impact on water infiltration, runoff, albedo, and temperature of the soil.

The greyish miner (Geositta maritima)

The coastal miner (Geositta peruviana) Photo by Berichard licensed by CC BY-SA 2.0

Taken together, it is easy to see how large patches of biocrust can either promote or inhibit plant germination and growth. Some species perform well under such conditions while others do not. This is why researchers were so interested in burrowing birds. By breaking up the biocrust and constructing mounds outside of their burrows, these birds are changing the microclimates of the surrounding area. This creates a heterogeneous patchwork of soil types that in turn influence the plant species that can grow and survive.

It turns out, burrowing birds on the Peruvian coast are having considerable effects on local plant diversity. By studying the soil properties around burrows and comparing it to undisturbed soil patches nearby, researchers were able to show that the plant communities living in these areas are in fact different. For starters, despite undisturbed soils having far more seeds in the soil seed bank than burrow mound soils, far more plants germinated and grew on the mounds than in the biocrusts. Also, though the seed bank of the mounds was largely comprised of similar species to that of the undisturbed soils, the seeds of species that produce bird-dispersed berries such as Solanum montanum were more abundant in the mound soil.

Fuertesimalva peruviana (Malvaceae) Photo by Jose Roque licensed by CC BY-SA 3.0

In terms of seedlings, mound soils not only exhibited higher seedling emergence, they also exhibited a higher species richness than the undisturbed biocrust soils nearby. The benefits of growing in the mound soils were most apparent for three plant species in particular: Cistanthe paniculata (Montiaceae), S. montanum (Solanaceae), and Fuertesimalva peruviana (Malvaceae). It appears that these species are much more likely to germinate and survive in and around the burrows than they are in the surrounding landscape. Such a boost to growth and survival, however marginal, means a lot in such a harsh, uninviting landscape.

Even more incredible is how specific burrow microclimates can be. Plants growing on the mounds didn’t do so in a uniform way. Instead, tiny variations in the soil of the burrow mound appeared to make a huge difference for plants. Soils near the entrance of an active burrow are disturbed far more often than soils on the backside of the mound. As such, more plants were found growing on the backside of the mound, demonstrating yet again how slight improvements in favorable microclimates can have astounding impacts on plant survival and diversity.

A. Soil profiles of the studied treatments. B. Landscape of the study area. The lower site of the hills is covered in biocrust except where it is disturbed by birds' burrows (Bioperturbation labeled in the picture). C. Dark cyanobacterial biological soil crust that covers the study site. D. Burrowing owl Athene cunicularia standing on its bioperturbation. [SOURCE}

The reason some plants do much better in disturbed soils over those covered in cyanobacteria biocrust are still not entirely clear. It is likely that some plants simply can’t break through the biocrust as they germinate. It is also possible that the seeds of some of these species simply can’t break through the biocrust to even make it into the soil seedbank. Not only would this cause them to blow around, it also means that they aren’t contacting the soil enough to imbibe water and germinate. Despite containing fewer seeds, the act of digging a burrow may loosen up the soil enough so that seeds are properly buried and thus can maintain good soil to seed contact for long enough to promote germination and growth.

All in all it appears that these three bird species are important ecosystem engineers across the Lomas of the Peruvian coast. By creating a patchwork of different soil properties, these birds are essentially creating a patchwork of different habitats that support different plant species. Take the birds away and it is reasonable to assume that plant diversity would decline. This is yet another important reminder of how interconnected the natural world truly is. It is also an important reminder of why habitat, rather than species-specific conservation efforts should be a much higher priority than it is today. Please, support a land conservation agency today!

Photo Credits: [1] [2] [3] [4] [5] [6]

Further Reading: [1]

Tropical Ferns in Temperate North America

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All plants undergo some form of alternation of generations. It is the process in which, through reproduction, they cycle between a haploid gametophyte stage and a diploid sporophyte stage. In ferns and lycophytes, this alternation of generations has been taken to the extreme. Instead of the sporophyte relying on the gametophyte for sustenance, the two generations are physically independent and thus separated from one another. In a handful of fern genera here in North America, this has led to some intriguing and, dare I say, downright puzzling distributions.

The presence of a small handful of tropical fern genera in temperate North America has generated multiple scientific investigations since the early 1900's. However, as is constantly happening in science, as soon as we answer one question, seemingly infinite more questions arise. At the very least, the presence of these ferns in temperate regions offers us a tantalizing window into North America’s ancient past.

To say any of these ferns offer the casual observer much to look at would be a bit of an exaggeration. They do not play out their lives in typical fern fashion. These out-of-place tropical ferns exists entirely as asexual colonies of gametophytes, reproducing solely by tiny bundles of cells called gemmae. What's more, you will only find them tucked away in the damp, sheltered nooks and crannies of rocky overhangs and waterfalls. Buffered by unique microclimates, it is very likely that these fern species have existed in these far away corners for a very, very long time. The last time their respective habitats approached anything resembling a tropical climate was over 60 million years ago. Some have suggested that they have been able to hang on in their reduced form for unthinkable lengths of time in these sheltered habitats. Warm, wet air gets funneled into the crevices and canyons where they grow, protecting them from the deep freezes so common in these temperate regions. Others have suggested that their spores blew in from other regions around the world and, through chance, a few landed in the right spots for the persistence of their gametophyte stages.

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The type of habitat you can expect to find these gametophytes.

Aside from their mysterious origins, there is also the matter of why we never find a mature sporophyte of any of these ferns. At least 4 species in North America are known to exist this way - Grammitis nimbata, Hymenophyllum tunbridgense, Vittaria appalachiana, and a member of the genus Trichomanes, most of which are restricted to a small region of southern Appalachia. In the early 1980's, an attempt at coaxing sporophyte production from V. appalachiana was made. Researchers at the University of Tennessee brought a few batches of gametophytes into cultivation. In the confines of the lab, under strictly controlled conditions, they were able to convince some of the gametophytes to produce sporophytes. As these tiny sporophytes developed, they were afforded a brief look at what this fern was all about. It confirmed earlier suspicions that it was indeed a member of the genus Vittaria, or as they are commonly known, the shoestring ferns. The closest living relative of this genus can be found growing in Florida, which hints at a more localized source for these odd gametophytes. However, both physiology and subsequent genetic analyses have revealed the Appalachian Vittaria to be a distinct species of its own. Thus, the mystery of its origin remains elusive.

[SOURCE]

In order to see them for yourself, you have to be willing to cram yourself into some interesting situations. They really put the emphasis on the "micro" part of the microclimate phenomenon. Also, you really have to know what you are looking for. Finding gametophytes is rarely an easy task and when you consider the myriad other bryophytes and ferns they share their sheltered habitats with, picking them out of a lineup gets all the more tricky. Your best bet is to find someone that knows exactly where they are. Once you see them for the first time, locating other populations gets a bit easier. The casual observer may not understand the resulting excitement but once you know what you are looking at, it is kind of hard not to get some goosebumps. These gametophyte colonies are a truly bizarre and wonderful component of North American flora.

Photo Credit: [1] [2]

Further Reading: [1] [2] [3] [4]