Plants, Life, Riverside is an ongoing interpretive project about plants in the bustling urban landscape of Riverside, CA.
Soil is alive.
It may look like dirt and in need of human intervention to become productive and worthwhile, but this is not the case.
Soil is alive with nutrients, minerals, animals and plants. While we collectively spend most of our time contemplating how to explain why people need plants, the truth is that there wouldn’t be plants if there wasn’t soil. So today we take a moment to address “plant blindness” by addressing another invisible element of our environment — soil.
Pedology is the study of soil. Soil scientists contribute their expertise to many disciplines. They conduct research, manage crop production, advise land managers, design hydrologic plants in urban areas, evaluate water availability, assess environmental hazards, regulate land use, and teach (Soil Science Society of America).
Today we have the opportunity to learn from a botanist at the University of California Riverside who is also a soil scientist.
Camille Wendlandt is currently researching nitrogen deposition in soil and the relationship between legumes and nitrogen-fixing bacteria.
Please join me in welcoming Camille Wendlandt!
Cami, thank you for taking time out of your busy schedule to discuss your research with us. You study the relationship between pollution, legumes and nitrogen-fixing bacteria. Tell us about your work.
I am a second year PhD student in the Department of Botany and Plant Sciences, and I study how air pollution affects the relationship between legumes and nitrogen-fixing bacteria, which are called rhizobia. Rhizobia convert nitrogen gas, which is an inert chemical, to a water-soluble form that plants can use for growth. Many legume species support colonies of rhizobia in their roots, which allows them to pass sugar directly to the rhizobia in exchange for fixed nitrogen.
This intimate relationship is called a “symbiosis,” and many researchers have been interested in the strategies legumes use to keep rhizobia from cheating — that is, from stealing sugar from their host without providing nitrogen in return. Many legume species are able to screen potential rhizobial partners before they infect and to police them after they infect, denying them sugar if they fail to produce nitrogen. Air pollution enters the story because nitrogen-rich chemicals emitted from car exhaust can settle into the soil in urban areas, providing legumes with a very cheap source of nitrogen. I am studying how nitrogen deposition affects the ability of legumes to police their rhizobial partners. On the one hand, legumes with access to a lot of free nitrogen might enforce rhizobial cooperation even more, to ensure that only the best strain make it into their roots. On the other hand, these legumes might stop policing rhizobia at all, if it requires more energy to police rhizobia than they gain from selecting the best strains. We just don’t know.
How did you come to study this relationship?
I was interested in plant biology and environmental science during college, and after working for a few years I knew I wanted to research climate change so that, as a society, we can make better management decisions. The legume-rhizobia symbiosis is also an exciting system because it is extremely important in agriculture (legumes are grown for food and fodder all over the world) but also wide-spread in nature, so research in this area can be very broadly applied.
California is known for its smog and Riverside has had some of the worst smog in the area. Is this a contributing factor to your study of pollution?
Yes, indeed. Nitrogen oxides from car emissions react to form ozone, which is the primary constituent of smog, and these nitrogen oxides are the same compounds that settle into the soil and become available to plants. Because smog (and therefore nitrogen deposition) is restricted to specific areas by mountain ranges and prevailing wind patterns, I am also interested in how regional differences in air pollution might lead to parallel regional differences in legume policing mechanisms.
What are legumes, exactly? What types of legumes are commonly grown in urban areas?
Legumes are an incredibly diverse family of plants. The most familiar examples are crops like beans, peas, lentils, peanuts, and soybeans, but there are also shrubs and trees in the legume family. Outside my lab there is a legume tree called the Hong Kong orchid tree (Bauhinia blakeana) that puts out gorgeous purple flowers all summer. You can tell that it’s a legume because of its fruits, which look more or less like beans, although they are much woodier. Another legume tree that you’ll see in Riverside are Eastern or Oklahoma redbuds, which stay pretty short and work well as street trees under power lines.
What types of legumes might Riverside residents encounter in natural areas such as Sycamore Canyon Wilderness Park?
You’ll see plenty of herb and shrub legumes out there. My study species is a tiny herb called Lotus strigosus (the common name is “strigose lotus,” which isn’t very helpful, is it?). A larger and prettier species from that genus is Lotus scoparius, commonly called deer weed. It is a perennial shrub with long spires of small yellow flowers. I have seen both Lotus species in Sycamore Canyon Wilderness Park. Another common legume is arroyo lupine (Lupinus succulentus), which has bright blue flowers. One of my favorite legume shrubs, even though it’s not native, is the bird of paradise (Caesalpinia gilliesii), which I have seen in the Box Springs Mountain Park; you can spot it by its yellow flowers with long, red stamens. If you head east beyond Palm Springs, you’ll start to see native woody desert legumes like palo verde (Parkinsonia) and ironwood (Olneya tesota).
Back when I was a very active gardener, I used to rotate my backyard crops and I even planted a cover crop one year. In your research, have you come across resources that may be of particular interest to the urban gardener?
The University of California Cooperative Extension runs Master Gardener programs on a county-by-county basis, and I think this is a great resource for anyone wanting region-specific gardening advice. Since moving to California, I have also become a huge fan of Calflora.org, which is a continuously updated public record of all the plants out in the wild in our state, whether they are native or introduced. It is a little technical, but if you are a plant nerd already, it’s a lot of fun! If you’re interested in landscaping with native plants, for example, it’s a great tool for figuring out what species grow in your area.
In your research so far, have you discovered anything you weren’t expecting?
I can tell you what surprised me most as I embarked on this work. I knew that pollution put nitrogenous greenhouse gases into the atmosphere, where they contribute to global warming, but it never occurred to me that these pollutants settled into the soil (by “dry deposition”) and were directly available to plants as a form of fertilizer. I thought the only sources of reactive nitrogen in the soil were biological nitrogen fixation, lightning strikes, synthetic fertilizers, and manure. I was shocked that even natural areas protected from agricultural runoff could still be indiscriminately fertilized as a result of human activity.
Camille’s interesting research brings attention to our ongoing relationship with soil. It is a relationship that the Soil Science Society of America (SSSA) wants to bring attention to as well. This year the SSSA has named 2015 as the International Year of Soils. In commemoration of this year-long outreach event to enhance soil science education, the SSSA created the 2015 International Year of Soils Educator Kit. This kit includes:
- SOIL! Get the Inside Scoop, a 36-page book written for students in grades 4-5 that explores how soil is a part of our lives.
- An activity list highlighting SSSA event for 2015.
- A coloring and activity book for grades K-2.
- A soil taxonomy poster
- An overview of how soils sustain life.
- A poster about careers in soil science
- I “Heart” Soils ruler
- A “Know Soil, Know Life” pencil
- Information about becoming a Friend of Soil Science
- Information about how educators can receive a free trial membership with SSSA.
This kit of educational materials was sent to teachers earlier this year. Most of these materials are now available as downloads on the SSSA website. Limited quantities of the Careers posters and Soil Taxonomy poster remain. Go to the website of the International Year of Soils to view the resources for teachers.
I would like to send special thanks to Cami for her time and for introducing us to her fascinating research linking botany and soil science with our urban lives.
Soil Science Society of America. Careers Poster in 2015 International Year of Soils Educator Kit.
Wood, Phyllis. 1994. Scientific Illustration: A Guide to Biological, Zoological, and Medical Rendering Techniques, Design, Printing, and Display. New York, NY: John Wiley & Sons
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