QScience.com | Exposure To Desert Cyanobacteria May Pose A Risk To Human Health

QScience.com | Exposure To Desert Cyanobacteria May Pose A Risk To Human Health

Revenge of the crust. Interesting emerging ideas about ubiquitous BMAA production in many cyanobacteria and its connection to Lou Gehrig's disease. Lots of gulf war vets may have been exposed when their vehicles disrupted crusts and allowed emission of dust containing cyanos. There's a life lesson here....

Score one for the little guys: cryptogam contributions to global carbon and nitrogen cycles

A recent paper by Elbert et al. in Nature Geoscience estimates the global contribution of "cryptogamic covers" to nitrogen fixation and net primary productivity. One of the authors, Bettina Weber, recently presented this work at the Ecological Society of America meeting. The discussion about how carbon can be sequestered almost always revolves around carbon intense ecosystems, those which store a lot of carbon per unit area, or ecosystems which can produce a lot of biomass very quickly. Cryptogams -- a catchall referring to bryophytes, lichens, and cyanobacteria-- are small and have a reputation for being slow growers (sometimes they are, sometimes they aren't). Because they are small and because they are perceived as slow-growing, they get little attention as carbon repositories or players in the carbon cycle. This study investigates the global impacts of cryptogamic communities such as soil biocrusts, rock biocrusts, boreal moss & lichen "carpets", and epiphytic mosses and lichens growing in tree canopies (Figure 1). 

Figure 1 (Elbert et al. 2012). a, Ground cover in the Namib lichen fields (Teloschistes capensis, Xanthoparmelia walteri, Ramalina spp.), Alexander Bay, South Africa. b, Soil crust with cyanobacteria (black) and chlorolichen (Psora decipiens), Nama Karoo semi-desert, Northern Cape, South Africa. c, Rock crust with chlorolichen (Rhizocarpon geographicum aggr.), Sadnig, Eastern Alps, Austria. d, Rock crust with chlorolichens (Chrysothrix chlorina, yellow, Leproloma membranaceum, whitish-grey) and mosses (Dicranum scoparium, Hypnum cupressiforme var. filiforme), Spessart, Germany. e, Plant cover with cyanolichen (Physma byrsaeum) on rainforest tree, northeast Queensland, Australia. f, Plant cover with chlorolichens (Evernia prunastri, Parmelia sulcata, P. subrudecta and others) and a bryophyte (Orthotrichum affine) on maple tree, Trier, Germany.


The very first terrestrial communities were likely communities of cryptogams. Today, to a large degree, these communities occupy the leftovers -- habitat not occupied by the vascular plants, or in some cases the actual surfaces of vascular plants. In some places it seems that the Earth is wearing a fuzzy cryptogram sweater....have you ever seem a temperate rainforest? If so you know what I mean. Can these forgotten botanical panhandlers, vagabonds and mendicants have any role to play in something so grand and large as the carbon and nitrogen cycles of Planet Earth? Yeah, of course (and stop calling them "lower" plants, it's just plain offensive).

Carbon-wise, it is the ground covers in temperate and boreal forests that are taking up the most carbon. Again, if you've ever been to one, you'll understand. A black spruce taiga up in Alaska might have half a meter of water-logged moss and lichen tissue accumulated on the ground.  I notice in Figure 3 from the paper, that the deserts are showing some modest values due to soil and rock covers. Across the planet the authors estimate cryptogamic communities are comprising about 7% of the primary productivity.

Nitrogen-wise, the most intense fixation rate estimates are in desert cryptogamic soil and rock covers...a.k.a. biocrusts. Cryptogamic plant covers in extratropical forests are a distant second place. Across the planet the authors estimate cryptogamic communities are conducting almost half of the biological nitrogen fixation.

There are 2 reasons why we should take these communities seriously as part of the carbon sequestration equation. First, comprising 7% of the global NPP may not seem like a lot, but its actually similar in magnitude to the flux we generate by burning fossil fuels according to the authors. The second reason is that primary production in most ecosystems is limited by nitrogen. Most of the Earth's nitrogen is in the atmosphere in a form that's useless to primary producers. A small minority of organisms have the ability to convert this atmospheres nitrogen to essentially a plant fertilizer (nitrogen fixation). This study suggests that nearly half of the biologically fixed nitrogen in terrestrial ecosystems is fixed by these cryptogamic communities. So, in other words cryptogams are largely in charge of the key missing ingredient that would allow for greater plant production and carbon sinking.

In figure 3 from the paper, the authors map where on earth these cryptogam-mediated porcesses are most intense. For carbon (left side), note the importance of the boreal forest. Because we have so little land in the southern hemisphere at similar latitudes, this is primarily a northern hemisphere phenomenon. For nitrogen (right side), look at the drylands coming into play.

Figure 3 (Elbert et al. 2012) Geographic distribution of CO2 uptake and N2 fixation by cryptogamic covers. a–f, The colour coding indicates the flux intensity of carbon net uptake (a,c,e) and nitrogen fixation (b,d,f) by CGC (a,b), CPC (c,d) and their sum (CGC + CPC, e,f). The flux units are g m−2 yr−1 ; note that the scale bars for carbon (e) and nitrogen (f) differ by two orders of magnitude. White areas indicate ecosystems for which no data are available; hashed areas were excluded from global budget calculations (annual mean precipitation <75 mm yr−1 and desert areas designated as dune sand/shifting sands and rock outcrops). 

 

 

One observation I have is that the authors seem to be trying to estimate current rates of carbon and nitrogen fixation, not the potential. Since I am so used to seeing soil biocrusts compromised by disturbance, I wonder how much higher these rates would be without such disturbances...twice as high, three times? How much C could we sink worldwide if we stopped chronically disturbing soil biocrusts?

Wolfgang Elbert,, Bettina Weber,, Susannah Burrows,, Jörg Steinkamp,, Burkhard Büdel,, Meinrat O. Andreae, & Ulrich Pöschl (2012). Contribution of cryptogamic covers to the global cycles of carbon and nitrogen Nature Geoscience DOI: 10.1038/ngeo1486

Moss Tumbleweeds

Moss Tumbleweeds

This is too cool. Racomitrium mosses, some of the same guys that are early post-glacial colonizers form mobile balls that rool around on glaciers with microfauna hitching a ride.

KLCC Eugene Oregon NPR-Scientists Step Lightly To Study Northwest's Desert Crust

link to a transcript of a local radio show in Oregon from a couple years back

KLCC Eugene Oregon NPR-Scientists Step Lightly To Study Northwest's Desert Crust

Biological soil crust is on Facebook....

.....didn't even know he/she/it could type.

check it out here

Key to life in the desert: What new research reveals about the importance of soil crusts

Key to life in the desert: What new research reveals about the importance of soil crusts


A Science Daily piece about an upcoming paper by Williams et al. in the Soil Science Society of America Journal

Maestre Lab: The Maestre lab starts to publish and share databa...

 A biocrust data resource to watch for.....


Maestre Lab: The Maestre lab starts to publish and share databa...: With the aim to foster the use and public impact of the research carried out at the Maestre lab, we are starting to share all the rese...

Ecological Society of America meeting encrusted

On the way to dinner. Pictured are Nichole Barger, Bettina Weber, Yunge Zhao, Yuanming Zhang, Matthew Bowker, Jayne Belnap, Burkhard Budel, James Meadow, Mingxiang Xu, Lea Condon, and two young family members. Elisabeth Huber-Sannwald must be taking the photo. I picked the photo with the fewest closed eyes, but we are looking into the sun. Also I was standing on the highest steps and am not actually 8 feet tall.

The last time there was a crust session at ESA (also in Portland, several years ago), I recall good talks but the funny thing was that everyone (me too!) did the same crust 101 introduction......even lifting the same photo from the web. Another notable thing was that by and large the audience was made up of speakers in the session. This one, organized by Bettina Weber and Jayne Belnap, drew more people (speakers were perhaps 25% of the audience...despite it being the last day), and we basically assumed that if you're attending a session about biological crusts you know what they are and went without much introductory material. Finally, I believe that last time, all speakers were from the US. This time around we had representation from Germany and Mexico, and three of our Chinese colleagues made the long trip. If you take into account all coauthors, we add Australia, Spain, and Colombia. I think all are signs that both awareness of and interest in biocrusts are increasing....we are less and less fringe lunatics. Next year we have the second international crust conference in Madrid to keep up the momentum.

Hugo Beraldi-Campesi spoke about how he believes we should rewrite the story of the colonization of land by living organisms. It is difficult to make inferences about this time because most rocks of the crucial age have been recycled by the Earth's grand conveyor belt. But the idea that plant communities were the first land communities ought to rightfully be viewed with scrutiny, since we know cyanobacteria were around and they had the entire toolbox (desiccation tolerance, n-fixation, UV- protective pigments) to colonize land. James Meadow introduced us to a fascinating community of biocrusts with a labyrinthine physical structure (apparently initially created by goose footprints), growing near hot springs in Yellowstone. I propose the term "Sharpei-oid" for this structure. He presented some of the lessons of molecular characterization of this community which was cool, but I think he had already amazed us when he told us that most of the soil particles are in fact discarded frustules of diatoms. What a weird community. Check out his photos below.

Rebecca Hernandez spoke about a gradient of California study sites sampled for biocrust moss and lichen diversity. She identified over 80 species, which is a pretty high number. She had a look at other studies and proposed that not only are Meditterranean ecosystems hotspots for plant biodiversity, but also for biocrust diversity. I think its an intriguing idea that I'd like to see developed further in a formal metanalysis at a global scale. Perhaps due to my experience with gypsiferous soils (rich in crust species, poor in plant species), I'd often thought there was a negative correlation between biocrust and plant diversity....but maybe not. Burkhard Budel took us on a world tour of his crust study sites including Africa, Australia, and Antarctica. He spoke about the diversity of photosynthetic behavior of crust organisms. For example green algal lichens can photosynthesize when humidity is high, whereas cyanobacterial lichens require liquid water. Different species of lichens exhibit different response surfaces to light, moisture, and temperature gradients; for, example they can have markedly different degrees of photosynthetic depression due to oversaturation. This really struck me as an example of how species diversity can promote productivity. In a plot with many species with complementary photosynthetic patterns, photosynthesis will be active in portions of the crust throughout a wider parameter space of light-moisture-temperature. Nicole Pietrasiak advanced a model of landscape development in the Mojave desert. There are 2 pathways in her model, an abiotic and a biotic one. Along the abiotic paths vegetation becomes sparse a desert pavements from. If, however there is bioturbation from rodent burrowing activity shrub density increases, the pavement never develops and biocrusts are happiest. Yuanming Zhang presented one of the best studies I've seen on the recurrent but never quite answered question: are crusts good or bad for plants? Our problem is that we usually want to study only one facet of this interaction, like germination success, which is not at all the entire picture. The answer isn't simple, it depends on the phenology and identity of the plant and the type of crust. Reduced seedbank and germination effects of biocrusts occurred, but herbs which do germinate on crusts grow faster and their reproductive period is altered. Bruce McCune, on about 12 hours of notice, filled in a vacany in the schedule. He presented some work of his student, Heather Root, modeling the distributions of rare lichens and determining the footprint of human land use on the potential niche of these species. It turns out that Texosporum Sancti-jacobi prefers to grow (perhaps I should say did grow, once) where we prefer to grow crops and install wind farms.Yunge Zhao presented some of her work restoring mosses to eroding landscapes of the Loess Plateau. Using ground moss tissue she is able to field inoculate and reduce erosion rates by about 30% in one year. Bettina Weber estimated the contributions of cryptogamic communities on soil, rock and trees to global C and N fixation. The majority of the planet's N-fixation was attributed to these communities, as well as 7% of the C-fixation which is more than the human C-flux from fossil fuels. Finally I did a review of the utility of biocrusts as a model system for learning about ecology. We've been invited to do a special issue for the journal Ecological Processes, a new open access journal from Springer.

Increasing frequency of Phoenix dust storms

A video plucked from the web from a Phoenix NBS Channel 12 news program... They mention increasing frequency of dust storms. Also at one point there is a mention of at least one dust source north of Tuscon. What they don't mention is that there is considerable agriculture and abandoned agriculture in that area(spurred by wartime cotton demand. I don't know if Phoenix's dust comes from these areas but it seems like a likely candidate. The news program seems to lay the blame for increasing dust storms at the feet of drought, which is one key driver, but never suggests that there is a human land use component to this phenomenon.

Why mosses can grow in the desert, and why their future is uncertain

Readers of this blog won't be so surprised, but most people are unaware that mosses grow in deserts and semiarid zones. The reason they can do so is that desert mosses are dessication tolerators, meaning they are capable of drying without dying. While dry, they are in a state of suspended animation, simply waiting for the next hydration period so that biological activity - and hopefully - net photosynthesis can occur. They rehydrate literally in seconds, and are immediately active. You could measure their respiration right away, for example. I always tell people that this is somewhat like spilling a glass of water on Tutankhamun, resulting in him coming back to life. A pretty cool party trick in my opinion. Biocrust organisms in general do this, but it is perhaps most dramatic in the mosses. Here's a video posted by Casey Allen of a simulated rain event.

And another from a class led by Larry Macafee at Badlands National Park. Focus is a little fuzzy, but you can see individual plants hydrating.

Neat trick for sure, but it does come with costs. Biocrust organisms do not regulate water loss with stomates (pores which a plant can open and close to regulate the rate of carbon coming in and water going out), so they lose that water they gained passively due to simply evaporation. They hang onto water very similarly to a piece of a paper towel - soaking it up via contact and losing it to evaporation. Every dry down event is thought to damage membrane integrity a little bit, so that the first order of business when rehydrating is maintenance. Many researchers have shown that upon rehydration there is a period of net respiration, and that after the photosynthetic rate may exceed the respiration rate, resulting in positive carbon uptake. If that happens growth is possible. But if that net photosynthetic threshold is not reached, the hydration event has resulted in carbon loss, and therefore dry mass loss. In other words the mosses would be shrinking a tiny bit rather than growing....bad news. So you can imagine that short hydration events due to small rain events or just high temperature driving fast evaporation, could damage mosses. Further, many such events could even kill them. So nature's tough guys have an Achilles heel, and seem to straddle a knife edge of survival. The climate is changing: what if increased temperatures or altered frequency or magnitude of rain events decrease hydration times? These mosses seem vulnerable to catastrophe.

Recent papers, including an awesome one by Reed et al. in Nature Climate Change, have induced rapid changes in biocrust community composition as a function of experimental climate change manipulations in a 5 year experiment. They induced a 2 degree C warming using infrared lamps in the field in Utah. This is a modest warming effect compared to multi-GCM projections for the area. They crossed this warming effect with a watering treatment which doubled the frequency of rain events but only slightly increased the total amount of rainfall. It's not surprising to me that this had an effect....but what is surprising is that the authors induced a 90% moss mortality in only 1 year!.

Moss dieback in response to increased frequency of small summer rainfall events (Zelikova et al. 2012)

Mosses fail to attain net photosynthesis when experiencing 1.25 mm rain events, contrasting with a 5 mm rain event (Reed et al. 2012).

This effect was essentially exclusively driven by the watering frequency treatment. The group also tracked effects rippling through the entire community. Under the high frequency summer rain treatment, cyanobacterial cover apparently expanded filling the gap left by the mosses, but pigment concentrations suggest that biomass was declining (Zelikova et al. 2012). Meanwhile bacteria and fungi were in decline (Zelikova et al. 2012), and enzyme signatures suggested that decomposition rates were faster under the frequent watering regime. In addition, changes were induced to nitrogen cycling, including increased nitrfication and a shift from an ammonium to a possibly leakier nitrate dominated regime.

Unlike temperature projections, precipitation projections from climate models are notoriously variable. Therefore, we don't know if climate changes will induce this utter tanking of biocrusts and their function. It is a plausible scenario, however,  that the summer monsoon in the Colorado Plateau region would bring a higher frequency of storms. This is exactly what we don't want. Not only would we lose soil fertility, but biocrusts would be less able to aggregate soils and prevent dust emissions which could go on to affect Western US water supplies (see previous post).

I should point out that this simulated climate change scenario is not necessarily the most plausible in all drylands, and the apparent indifference of biocrusts to warming may also not be universal. These studies from Utah, contrast nicely with another study which shows a clear negative effect of 2 - 4 degree C warming on lichen-dominated biocrusts in Spain (Escolar et al. in press).

Escolar C, Maestre FT, Martínez, I, Bowke, MA 2012. Warming reduces the growth and diversity of lichen dominated biological soil crusts in a semi-arid environment: implications for ecosystem structure and function. Proceedings of the Royal Society B: in press.

Zelikova TJ, Houseman DC, Grote EE, Neher DA, Belnap J. 2012. Warming and increased precipitation frequency on the Colorado Plateau: implications for biological soil crusts and soil processes. Plant & Soil DOI 10.1007/s11104-011-1097-z

Reed SC, Coe KK, Sparks JP, Houseman DC, Zelikova, TJ, Belnap J (2012). Changes to dryland rainfall result in rapid moss mortality and altered soil fertility. Nature Climate Change DOI: 10.1038/nclimate1596

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Asian dust storms crossing oceans

A dust storm can be seen over Turkmenistan, Central Asia, in this photograph from the International Space Station in 2009.
NASA/Earth Observatory

Dust storms made it to science daily today, based on a new paper in Science. According to Science Daily article, half of North American dust is coming from Asia, and the large majority of aerosols are desert dust.

I'll have to go read the original paper now, but I've got to say this quote stuck in my craw:

Satellite images also showed that the majority of high-flying aerosols were made up of desert dust, which can affect climate patterns in a number of ways. And while experts continue to debate the effects of climate change and development on the conversion of fertile lands to deserts in many parts of the world, most of the dust in the atmosphere probably comes from the natural lifting of desert sands, said Daniel Jacob, an atmospheric chemist at Harvard University in Cambridge, Mass.

"In terms of the effect of aerosols on climate, we tend to be fixated on human activity," Jacob said. "But we have this big dust haze layer that's several miles over our heads. This study nicely reminded us of that." 

Its true that many dust sources contribute with little influence of humans, but someone should tell the author that human activity increases dust emissions. I mean grazing, burning and biomass harvest. Sure, climate is a a major inter actor, but there is a big human component. Take away the plants and crusts, you get dust.


Check out the Science Daily article here:
http://news.discovery.com/earth/asia-dust-weather-climate-patterns-120802.html#mkcpgn=rssnws1