Plant-Soil Feedbacks, Ponderosa Pine, and SEGA -- A new study from the Bowker Lab

SEGA? Am I really talking about a video game platform on our research blog? Really? NO! Though, I am not sure which I invested more time in - crusading through the old school Sonic the Headchog video game series or prepping and launching this experiment. 

OK, OK, in all seriousness, this experiment is really stinking cool, and we finally got it launched! 

First of all, lets backup and define SEGA, acronyms are tossed around so lavishly we just assume everyone knows what they mean, but I genuinely hope everyone in the research world learns about SEGA. The Southwest Experimental Garden Array, or SEGA, is a new research tool managed by Northern Arizona University in partnership with the Bureau of Land Management, The United States Forest Service, Babbitt Ranches, The Grand Canyon Trust, University of Arizona, and Arizona State University. SEGA is effectively a series of common gardens spanning seven life zones, from high elevation Mixed Conifer to low elevation cool and warm deserts . SEGA utilizes this strong elevation gradient with a twist, soils. Soil types on the Colorado Plateau are highly variable so SEGA has two of these elevation gradients, one on predominately limestone and sedimentary derived soils, and one on basaltic soils. One of the coolest aspects of SEGA is the depth of onsite weather instrumentation - we have a live feed on virtually any weather variable you can think of across all the sites. Better yet, live irrigation that can be controlled remotely or programmed to match spikes in soil moisture at different sites - yes, that's right, we can simulate precipitation events based on real-time weather data.  

The warm desert SEGA site and its weather instrumentation. 

What is this laberous project that has been taking me away from video games and into the field? We are especially interested in plant responses to changing and dynamic climates, however, we are interested in the added complexity of soil and plant-soil organism interactions. Given any shift in a plant's environment, plants have three options for a response: 1) die 2) move 3) adapt. Most plants, like our study organism in this study - Pinus ponderosa (ponderosa pine), are highly dependent on soil organisms. Soil organisms include bacteria, nematodes, collembela, and mycorrhizal fungi (myco = fungus, rhizo = root, so mycorrhizal fungi are root fungi). These unique fungi live on or inside plant's roots and explore the soil environment for key nutrients like nitrogen and phosphorous or soil water. So we add the questions 1) If a plant migrates to a new environment, does soil type matter? 2) If a plant migrates to a new environment, is it limited by the absence of its natal, or home team, soil organisms? 3) Do different soil types change plant responses to changes in climate?

Preparring to plant in the field required deep holes to bury the pots in - better just bring in heavy equipment! 

Briefly, I just want to share a taste of the labor that went into this project. Soils are tough - most research in this field has been done in small containers in the glasshouse, because if you really want to understand the effects of soil biota and soil independently from one another, you have to start with sterile soil - and soil is far from sterile. Secondly, to grow trees for an extended time in the field requires large containers, and large containers require a lot of soil. So, firstly, we collected field soil from our three sites. All the soil was steam sterilized for 48 hours, twice. That means, field collected, shoveled into a sterilizer, shoveled back into a sterilizer, and finally shoveled into those massive pots. Then we "inoculated" with our soil organisms - how do you inoculate, you ask? In this case it's easy, we just sprinkled a single centimeter of live soil from the field on the surface of the soil. Lastly, we seeded our locally collected Ponderosa pine seed into the live soil inoculum. We then grew our seedlings into saplings for two seasons in the glasshouse. So now we have trees growing in soil from their site of origin, or in soil from a site that is two degrees centigrade warmer or a site two centigrade cooler, and soil organisms from each of the sites as well. We prepared the sites for planting by digging trenches the depth of the pots ( ~ three feet deep) and eventually plopped the pots in the ground and back filled the holes so the soil surface is flush across the site and pot. So I am one man, a fairly strong one - but none of this would have been possible without help.

I unload pots from the UHUAL trailer, excited to be getting a good work out!
Photo Courtesy of Emily Thompson

So let me ramble for a second about the importance of volunteering and all the other avenues of support we have had. The Grand Canyon Trust and their volunteer program has been quintessential to implementing this project. From the installation of fences, to the arduous effort of back-filling trenches to get the Ponderosa planted, I honestly do not know where I would be without volunteer support, well - still digging, probably. Not only do volunteers provide valuable physical assistance, but they become patrons and liaison for the science we are doing and the community. I cannot thank the dozens of volunteers that have helped with this enough. I sincerely appreciate your effort and more importantly your story. Every volunteer I have interacted with came interested in science, ready to work hard, and with a fascinating story. Most of you have been non-scientists and your engagement in our science is so important. My gratitude towards volunteers is an appreciation for our mutual relationship and the stories we share.

Grand Canyon Trust Volunteers help finish the planting of Ponderosa pine at the cool, mixed conifer site. 

The end result is 190 trees growing in the field under these different climatic conditions, and being force to grow with different soil organisms and in unique soil types.  This is really a classical plant-soil feedback experiment with a climatic twist, or a classical climate themed common garden study with a soil feedback twist. With the trees in the ground, we are excited to continually monitor our plants in terms of growth and physiology over the years to come. We expect to be able to grow the trees for several years before they out grow their containers.

100 trees happily planted on the Brow of the Kaibab Plateau at the warm Piñion Juniper site

I should note that we have a nearly identical experiment that has been in the ground for over a year, also on SEGA, using the infamous perennial grass, Boutelous gracilis (blue grama). So far, after the first year, we have observed that plants growing with their "home team" soil organisms grow the largest regardless of climate. Plants forced to grow in new climates (whether warmer or cooler) are much smaller than those growing at their home site. This reduction in size is reduced when growing with their "home team" soil organisms. Lastly, certain soil types, specifically a young basalt "cinder" soil, are seemingly nightmarish for a population of blue grama that came from much older soils. The "home team" advantage is also strongly diminished in this soil type suggesting its not just the plants that are struggling.

We hypothesize that in more stressful soil conditions, as a product of nutrient or soil limitation, the plant-soil organism mutualism will be of enhanced importance.  As soil environments become more benign, it is likely that competitive interactions or lack of dependency on soil organisms will result in a diminished importance of the "home-team". Our study system on SEGA allows us to test the many facets of plant-soil organism interactions over climate gradients through multiple growing seasons and I am extremely excited to continue to share progress with you all!

This graphic represents data from a related experiment to show how plants grown in more a mild drought (a and b) and extreme drought like conditions (c and d) are much larger when grown with their home team (a and c) soil organisms as opposed to novel soil organisms (b and d). Notice how under extreme drought, and with their home team (c) plants invested more in their mycorrhizal partners and grew just as large as plants grown under moderate drought! The soil organisms are buffering the plants from extreme stress! 

This work is important in this is important in that fe studies have examined and manipulated the role of soil organisms in facilitating plant growth and survival across a climatic gradient. Additionally, in the context of vegetation management programs, very rarely are soils and soil organisms considered in planting scenarios, whether following invasion of exotic species or in the context of restoration or post-fire rehabilitation. This work is helping us better understand the benefit of using soil organisms in vegetation management and exploring new tools that could be used as a climate solution to the often dismal outlook of widespread vegetation mortality. 

Thanks for reading! 

Michael

A scenic vista with Saddle Mountain and the Kaibab Plateau along the horizon