Tag Archives: global carbon cycle

Don’t treat soil like dirt!

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Soil is a precious resource, yet most of us pay little attention to the stuff under our feet.  It is the medium in which we grow our food and the foundation on which we build our cities. Soils filter our water, detoxify our pollutants, decompose our waste and hold vast reserves of the nutrients required for life. Soils are also fragile, taking thousands to million of years to develop but destroyed in minutes by human development.

For the past three years, myself and my fellow soil enthusiast Aurora have spent our Saturdays in December showing kids how awesome soil and the microbes that inhabit it actually are. We’ve developed a number of soil and microbiology activities to teach kids of all ages what soil actually is, who lives in it, and why we should value it. The take-home message? Don’t treat soil like dirt! Human beings (and nearly ever other species on earth) depend on soil for our very survival.

Here are some highlights from the last two weeks of the workshop:

Shahada_microscope
Checking out some protozoa under the microscope!
Making a hypothesis before conducting an experiment!
Making a hypothesis before conducting an experiment!
MAKING SOIL! This is always a favorite. Want to make soil at home with your kids? Check out my homebrew recipe below...
MAKING SOIL! This is always a favorite. Want to make soil at home with your kids? Check out my homebrew recipe below…
Probably the coolest thing I've ever made in photoshop.
Probably the coolest thing I’ve ever made in photoshop.

We are even participating in an international, crowd-sourced science experiment known as the Tea Bag Index experiment to measure rates of decomposition in different soil types! This is a fun and easy experiment you can do in your backyard. All you need is a few teabags and a scale.  Decomposition, the breakdown of once-living organic matter and conversion into soil organic matter, is an important step in the global carbon cycle that is driven primarily by soil microorganisms. Ultimately, decomposed carbon is respired back to the atmosphere as carbon dioxide. Scientists are currently trying to understand how global climate change will affect decomposition and the microbial “respiration” of CO2 from soils. Projects such as the Tea Bag Index experiment provide scientists with valuable data that can be used to inform predictions about changes to the global carbon cycle. For more information on the Tea Bag Index experiment check out the website:

http://decolab.org/tbi/concept.html

Or click here to access the protocol and get involved directly!

http://decolab.org/tbi/protocol.html

Most importantly, our workshop strives to underscore the importance of soils in our everyday lives.  Kids (and parents) often come unsure of what exactly soil is or why it should matter to them, and often enjoy the experience so much that they return week after week.

Live in the Philly area and got kids? Check us out, every Saturday for the rest of the month!

And since I can’t seem to stop geeking out about this stuff, here are some more cool resources to check out on soil science education:

USDA NRCS Healthy Soil Fact Sheets

microbes improve carbon cycle models

Microorganisms are key drivers of the global carbon cycle both on the land and in the ocean. Through a diverse array of metabolic strategies, microbes decompose organic and recycle organic carbon. Just as we respire a fraction of the carbon we consume as CO2, so do microbes. Globally, vast quantities of organic carbon are funneled through many billions of microbes every year: to be decomposed, recycled, and respired into the atmosphere. In spite of this, microbial activity has historically been ignored in attempts to model the global carbon cycle and predict climate change-related feedbacks. Instead, our models rely on untested assumptions that microbes and their carbon cycle activities will respond in uniform, predictable manners to increases in temperature, and as such, can essentially be ignored.

A recent paper in Nature Geoscience paper challenges this assumption by explicitly integrating microbial physiology into a new model of the soil carbon cycle. Compared with traditional models, the new model more accurately matches current observations of carbon stocks and fluxes across ecosystems. Regarding future carbon cycling in a warming world, the model produces several widely different scenarios that vary due to the potential response of microbes to rising temperatures. In short, if microbes respond negatively to warming by decreasing their “growth efficiency”; that is, if warming slows down their growth rates, no additional carbon is released to the atmosphere as the soil warms. But if microbes are able to adapt to higher temperatures and maintain their current growth efficiencies, higher temperatures will accelerate carbon decomposition rates and lead to potentially huge additional losses of carbon dioxide from soils.

The integration of biological mechanisms into earth system models is an important step forward in our ability to forecast future climates. Future research that empirically measures microbial community responses to long-term warming is desperately needed in order to accurately model and predict this potentially huge feedback to the global carbon cycle.

http://www.nature.com/nclimate/journal/v3/n10/full/nclimate1951.html

 

Earthworms play key role in regulating carbon storage in tropical ecosystems

A principle frontier in our understanding of global carbon budgets is tropical forests, on which research is historically scarce. At temperate and high latitudes, a warmer climate is predicted to increase the rate of decomposition and soil carbon turnover, resulting in a positive feedback on atmospheric carbon as CO2 is released from soils at increasing rates. A better understanding of the mechanisms regulating tropical carbon storage is needed in order to develop a holistic picture of global carbon cycling and feedbacks due to climate change.

Earthworms are important regulators of many ecological properties of soils. Their burrowing activity increases soil pore space and contributes to soil structure and drainage. Most importantly, earthworms can digest a huge quantity of dead and partially decomposed plant material. This digestion causes chemical transformations that ultimately produce nutrient-rich soil organic matter, or SOM. SOM helps ensure soil fertility, and contributes to numerous physical and chemical soil properties such as soil structure, porosity, water retention, and the capacity of soils to buffer pH changes. SOM’s aggregate structure causes it to have high water stability. This is an essential property in tropical forests, which have the highest rainfall levels of any biome on Earth.

SOM produced by earthworms is also rich in both carbon and nitrogen. A detailed biochemical and molecular analysis of earthworm casts suggests that these creatures may in fact play a key role in controlling tropical carbon storage.

Casts are clumps of digested organic matter excreted by earthworms that aggregate into large and distinctive structures. Researchers working in the rain forest neighboring the Dong Cao village in Northeast Vietnam studied the effect of cast production by Amynthas Khami on soil C storge. A. Khami is a species of tropical earthworm that can grow up to 50 cm long and produce tower-like casts. The researchers first used a “simulated rainfall” experiment to determine the relative stability of casts versus control soils. They then measured total carbon content, lignin and mineral-bound SOM content of casts and control soils.

An earthworm cast produced by A. Khami, a large tropical species found in Northeast Vietnam.

The study found striking differences in the chemical composition of earthworm casts versus control soils that ubiquitously indicate higher carbon storage in casts. Casts are more structurally stable and can withstand at least twice as long a rainfall event as control soils without compromising their structural integrity. They are enriched in carbon compared with controls, and particularly in carbon compounds such as lignin that have a high “carbon storage” potential. Lignin, a primary constituent of woody plant tissue, is a complex and heterogeneous molecule that is both carbon-rich and difficult for microbes to decompose. Earthworms probably excrete high quantities of lignin after obtaining the more digestible carbon sources from the roots and leaves that they eat. Finally, high levels of mineral associated-SOM were found in casts. Soil minerals bind to organic matter through electrostatic interactions, and in doing so make it unavailable for decomposers.

Though it well known that earthworm digestion initially speeds up decomposition, this new study suggests that casts may in fact contribute to long-term carbon stabilization. In tropical soils, which tend to cycle carbon quite rapidly, this mechanism should not go unappreciated. Future tropical land-use decisions may want to account for the welfare of this often-unappreciated soil organism.

Hong et al. 2011. How do earthworms influence organic matter quantity and quality in tropical soils? Soil Biology and Biochemistry 43: 223-230.