Andrii Zaiats, a PhD student at Boise State University, talks about his latest paper, Intraspecific variation in surface water uptake in a perennial desert shrub – his first peer-reviewed publication.

About the paper

Big sagebrush (Artemisia tridentata) in Orchard common garden, Idaho (USA). The photograph shows the spatial arrangement of plants in the  experimental site (photo by Andrii Zaiats).
Big sagebrush (Artemisia tridentata) in Orchard common garden, Idaho (USA). The photograph shows the spatial arrangement of plants in the experimental site (photo by Andrii Zaiats).

The harsh environments of arid ecosystems impose water and nutrient limitation on plants, necessitating adaptations for species to persist in these environments. Our study investigated how plant populations of big sagebrush (Artemisia tridentata) vary in their lateral root traits, which are directly relevant to overcoming water limitation. We are generally interested how individual plants interact with each other, and the role of such neighbour interactions for structuring shrub populations. In the context of semi-arid ecosystems, we hypothesized that plant neighbours would compete for water resources, where larger plants may be taking a disproportionate amount of soil water compared to smaller plants. We also anticipated that variation within the species, including genome size or adaptations to different environments, may be important for water uptake and belowground root traits.

We decided to test this hypothesis using an isotope tracer. The Hydrogen isotope, deuterium, is a natural part of water (in tiny amounts) and is widely used in ecological studies. Higher deuterium content in water does not change its physical properties, but the signature is easily detectable on the molecular level. Dr. Matt Germino of US Geological Survey proposed that we could take advantage of these deuterium properties to monitor how much water a plant takes in from the soil. The idea is to introduce deuterium-labelled water into the soil and after some time, as water moves from roots up to the leaves for photosynthesis, analyse above-ground stems for the amount of labelled water. If we introduce the tracer equidistantly among plants we can see which one up took more of the introduced water, and how water uptake changes with proximity to the plant. We decided to conduct our study in a long-term common garden experiment, established in 2010 by Dr. Bryce Richardson and colleagues, where individual plants of big sagebrush collected from across the Western US were randomly outplanted beside each other. This diversity concentrated in one place gave us the unique opportunity to test how genetically distinct individuals may share common resources, such as soil water.

            Our findings were somewhat unexpected as the relative size of the neighbours did not have a strong effect on the amount of water taken up. We found local adaptation to different environments (subspecies), in combination with genome size (ploidy level), were more important than plant size and had a stronger effect on water uptake. Specifically, tetraploid populations within a subspecies (populations with two sets of homologous chromosomes), had more lateral roots and greater effect on the surrounding soil compared to their diploid variants. These results point to the importance of within species differences in belowground traits for water uptake. Therefore, changes in climate and annual precipitation patterns may have different consequences for big sagebrush populations, depending on the degree of dependence on surface water. At the same time, the study warrants further research into the mechanisms of plant-plant interactions, which operate on longer time-frames than a single experiment.

Background

Big sagebrush (A. tridentata) is an iconic shrub of the western United States and is highly impacted by biological invasions, altering fire regime, and anthropogenic pressures. Efforts are under way to restore these populations but restoration is expensive, difficult, and unpredictable, in part, due to intraspecific variation and local adaptations. Understanding how local ecological processes operate, including interactions between plant neighbours, can give us a better sense what to expect from an intervention like restoration outplantings. Also, large restoration efforts typically involve the reintroduction of mixed populations into one place. We currently don’t have a good understanding what demographic outcomes we should expect in the long term, and what eco-evolutionary consequences may be for the species we are trying to restore. Understanding the role of variation within species for plant-plant interactions can give us a way to predict how demographic processes may play out, with consequences for both short and long-term population dynamics.

About the author

Andrii Zaiats during the experiment, Summer 2012.
Andrii Zaiats during the experiment, Summer 2012.

I became interested in the ecology of arid ecosystems and western landscapes during my Conservation and Land Management Internship with the Chicago Botanic Garden. The restoration focus came from working as an intern with Dr. Lesley DeFalco (USGS) on a few experiments to improve seed restoration and understanding the role of local adaptations for restoration efforts in the Mojave Desert. I then pursued MS Biology at Boise State University where I’m currently a PhD student in the EEB program. My current lab is working to apply theoretical demographic models to ecological restoration using satellite and UAS (drone) data. These tools will allow us make spatially-explicit predictions of population dynamics and ultimately inform management decisions and restoration planning.

What project or article are you most proud of?

This one in particular. Aside of it being my first peer-reviewed publication, I think the study demonstrates how science benefits from integrating ideas and cross-disciplinary perspectives. 

What is the best thing of being an ecologist?

Pretty much everything, but what stands out to me is the sense of community among ecologists and unity around the goal to advance science for the benefit of everyone.