Kalahari sands and scientific curiosity — Global Soil Biodiversity Initiative

Adam B. Cobb

Postdoctoral Research Fellow

Oklahoma State University, USA.

My favorite part of studying soil ecology is the complexity. Regardless of my deficiencies as a scientist, I have an abundance of curiosity. On every continent, in every ecosystem, there are countless unanswered questions about how plants and microbes interact with soils and each other.

Curiosity compelled a group of researchers from Oklahoma State University (OSU) and Kansas State University (KSU) to fly >15 hours from the USA to southern Africa. We rented a van that barely fit the nine of us and our luggage, and we spent two weeks experiencing and examining the ecology of Botswana, from rhinos to grasses to soil microbes.

In these dry sandy soils, we wanted to uncover mechanisms of drought-tolerance in grasses. Hypothesizing the formation of rhizosheaths can protect roots from desiccation, we sampled and assessed sites on both Botswana’s wetter east and drier west. Despite being a global phenomenon in dry sandy soils, the amount of peer-reviewed data on rhizosheaths is remarkably thin.

We have numerous questions, including: why do some grass species form rhizosheaths while others do not? What proportion of rhizosheath development can we attribute to plant exudates, and how much is built by microbial communities? How do edaphic and climate conditions influence rhizosheaths? Perhaps we will be able to answer some of these questions by comparing characteristics such as moisture dynamics and microbial functional groups between rhizosheath soil and bulk soil, across environmental conditions and between grass species.

When Dr. Dave Hartnett (KSU) and Dr. Gail Wilson (OSU) envisioned this trip, they drew upon extensive past experience. Dave lived in Botswana twice during sabbaticals. Gail took every opportunity to visit and facilitate student trips over the years. After gathering data in Botswana in 2009, they published an article on rhizosheath formation across a suite of warm-season grasses (Hartnett et al., 2013; DOI: 10.1111/j.1442-9993.2012.02422.x). This research served as the foundation of our current objectives.

In addition to plant and soil ecology, Dave and Gail are interested in getting the next generation of scientists excited about intercontinental research. Most of us are early career, and some of us had never traveled outside the USA. Seeing Africa’s megafauna, experiencing the Okavango Delta, and witnessing the hospitality and culture of Botswana got us hooked.

Eric Duell (left), Seton Bachle (middle), Gail Wilson (middle), and Dave Hartnett (right) sampling grasses in Western Botswana. Photo credit, Adam Cobb.

This is my other favorite part about studying soil ecology—community. Spending two weeks in a cramped van has the potential to be horrible. However, the right people can make the experience fun. In one minute, our group was excited to know the scientific name of a bird we spotted; in the next minute, we were recalling lines from Disney movies, circa 1990. There was also an informal population study on termite mounds for one day: 527 total.

When you get a group of passionate scientists together in a new place, amazing things can happen. Toward the end of the trip, a few of us started planning our next experiment. There is so much to discover about rhizosheaths. Our field collections made us ask new questions about the plant-soil-microbial mechanisms, so we planned to tease those relationships apart with a series of greenhouse experiments.

Who knows what might come of these experiments and this new community of researchers? I have spoken to senior scientists who explained that a random opportunity to team up with another researcher in their early careers turned into 20+ years of friendship along with at least a dozen coauthored publications and hundreds of thousands of dollars of collaborative grant funding across their careers. Perhaps this group will keep exploring rhizosheath questions together for years.

The answers to those questions could improve conservation of semi-arid ecosystems around the planet—ecosystems supporting substantial biodiversity. The implications also reach further into the future. I do most of my research in managed grasslands and agroecosystems; in a warmer and drier world, the capacity of productive plant species to withstand drought is critical for global nutrition security. Perhaps understanding rhizosheath development in the Kalahari sands of Botswana will help us improve the resilience and sustainability of our food systems in a changing world.

I for one also want to know for the sake of knowing. On our trip, we dug up a lot of grasses. When we set the roots of Pogonarthria squarrosa (Herringbone Grass) that form extensive rhizosheaths, next to the roots of Digitaria eriantha (Pangola Grass) that do not, I was amazed. Why would these species, growing a few feet apart, display such a difference? Finding the answer to that question is a good enough reason to come back to Botswana.