Competition and propagule density affect sexual and clonal propagation of a weed.

Atwater, Kim, Tekiela, Barney


This study was pioneered by Wonjae Kim, an undergraduate student at Virginia Tech who designed and executed it on a grant from the Fralin Life Sciences Institute.

Wonjae confirmed that Johnsongrass establishes readily both from seed and from buried rhizome fragments, although these two modes of reproduction differed in their sensitivity to competition and soil quality. In fact, a single plant produces enough seeds and rhizomes to establish over more than a hectare (if spread out evenly)!

Wonjae’s results show that effective management of Johnsongrass must limit spread from both seeds and underground rhizomes.

A great way to ring in the new year!

Ecotypic diversity of a dominant grassland species resists exotic invasion

Yang, Callaway, Atwater

In this study, Lixue Yang showed that bluebunch wheatgrass (Pseudorogneria spicata) populations with greater within species diversity were pound-for-pound more resistant to invasion by spotted knapweed (Centaurea stoebe) than populations with less species diversity, by an order of magnitude.

Dr. Yang attributed this to two processes: 1) as seen in our previous study,  more diverse bluebunch populations had greater yield, and 2) even accounting for their increased yield, diverse populations were more resistant to invasion than suspected.

The causes of this phenomenon remain mysterious, but they may have something to do with root recognition among related bluebunch or with activity of soil communities.

This paper takes an important step towards demonstrating the extreme–yet cryptic–effects that within-species diversity has on plant communities.

Evidence for fine-scale habitat specialization in an invasive weed

Atwater, Fletcher, Dickinson, Paterson, Barney (pdf)

In previous studies, we found evidence for striking genetic and phenotypic differentiation in Johnsongrass (Sorghum halepense) populations collected throughout the United States. Here, we report that Johnsongrass may be adapting to local habitat variation.

Johnsongrass from non-agricultural populations competed better in a field community than Johnsongrass from agricultural populations. Agricultural and non-agricultural populations were separated by less than a kilometer, suggesting that this species may be adapting to habitat variation at extremely fine spatial scales.

These results contribute to a growing list of studies revealing the importance of fine-scale habitat specialization in invasive species, with possible ecological and management implications.

Multi-phase US spread and habitat switching of a post-Columbian invasive, Sorghum halepense

Sezen, Barney, Atwater, Pederson, Pederson, Chandler, Cox, Cox, Dotray, Kopec, Smith, Schroeder, Wright, Jiao, Kong, Goff, Auckland, Rainville, Pierce, Compton, Lemke, Philips, Kerr, Mettler, Paterson (pdf)

I’m happy to announce that PLoS One has accepted Uzay Sezen’s paper documenting the population genetics of colonizing Johnsongrass (Sorghum halepense).

Using a panel of almost 500 Johnsongrass accessions from 70 sites throughout the US, Dr. Sezen showed that Johnsongrass was introduced to the US at two locations. It has subsequently colonized much of North America, demonstrating surprising genetic variation even at range margins.

Johnsongrass populations have also differentiated strikingly along habitat boundaries, with genetic clusters segregating strongly between crop populations and those found in roadsides and other disturbed environments.

The mechanisms and consequences of interspecific interactions among plants

Aschehoug, Brooker, Atwater, Maron & Callaway (pdf)

I’m very pleased to announce that Annual Reviews of Ecology, Evolution and Systematics has accepted our review article documenting recent advances in our understanding of interspecific plant interactions.

I am proud to have been a part of this group. Erik spearheaded this effort and has worked very hard to bring the finished product together. I look forward to the publication of our review in November!

Intraspecific diversity buffers the inhibitory effects of soil biota

Luo, Callaway & Atwater (link)(pdf)


In sterilized soil, bluebunch grew the same regardless of the soil that was used. In unsterilized soil, bluebunch did not grow well in soil from the low-richness plots.

Congratulations to Wenbo Luo for recently having a paper accepted to Ecology! In this paper, Wenbo shows that soil microbes inhibit the growth of related bluebunch wheatgrass plants (Pseudoroegneria spicata).

To do this, he collected soil from bluebunch populations varying in their genetic diversity. He then grew bluebunch seedlings in that soil and compared their growth.

Seedlings did not grow well in soil from populations with low genetic diversity. This effect went away when the soil was sterilized, suggesting that soil microorganisms were responsible.

Soil feedbacks such as these are thought to result from adaptation by soil pathogens. Wenbo’s results suggest that soil pathogens specialize not only on species but on related individuals. This also provides a mechanism affecting the high productivity we see in genetically diverse bluebunch wheatgrass populations.

I presented the results of my environmental niche modeling work at the 2016 Weed Science Society of America Meeting in San Juan, Puerto Rico. I attended the meeting with my advisor, Jacob Barney, and Dan Tekiela, a graduate student in Jacob’s lab.

The weather was lovely and we had an excellent time escaping winter’s grip to enjoy some sunshine and sea air! We also had a fantastic conference, meeting new people and learning about the exciting work that WSSA members are doing.

Congratulations to Jacob for winning the Outstanding Early Career Weed Scientist award!

An exotic invasive plant selects for increased competitive tolerance, but not competitive suppression, in a native grass

Fletcher, Callaway & Atwater (pdf)


At each of four sites, bluebunch from knapweed invaded plots (I) had much better ability to tolerate knapweed than those from uninvaded plots (U). However they were not better at suppressing knapweed.

Many congratulations to Rebecca Fletcher, who just had a paper accepted into Oecologia. Her paper shows that spotted knapweed, an invasive plant, selects for bluebunch wheatgrass plants that are tolerant of knapweed competition, but not for ones that are better at competitively suppressing knapweed.

This is the first direct test of the hypothesis that neighbor suppression does not provide fitness benefits to competing plants. Her finding is important because it challenges long-held notions of what makes a plant a good competitor. Becky performed this research as an undergraduate student at the University of Montana, on a grant she wrote for the Montana Integrative Research Experience for Students (MILES) program.



Propagule pressure alone cannot always overcome biotic resistance: The role of density-dependent establishment in four invasive species

Barney, Ho & Atwater (link)
I am very pleased to announce that we have just had a paper accepted for publication into Weed Research. This paper documents Master’s Student Matt Ho’s research into the role of propagule pressure in invasion. He found that negative density-dependent germination probability causes diminishing returns for species that broadcast a large number of seeds. His results suggest that site conditions and species interactions play an important role in determining invasion probability even when propagule pressure is intense.


Invasion probability increases as the number of seeds (aka propagule size) increases. When germination is density dependent (solid line), invasion probability increases much more gradually than when it is not (dashed line). This means that site conditions play a very important role in determining invasion probability, even when propagule pressure is high.

Pictured, left to right: Big Dan, Morgan, Little Dan (top); Jacob and Benjamin Franklin (bottom)

I recently presented the results of my niche modeling work at the 2016 Northeastern Plant Pest and Soils Conference in Philadelphia. I went the the conference along with most of the rest of my postdoc advisor’s (Jacob Barney’s) lab and we had a great time. I met a lot of people, including the First American, Benjamin Franklin, who looked great despite being only a week away from his 310th birthday.

At the conference, I presented the results of our study of climatic niche shifts in introduced species. Jacob and I have found that species experience major niche shifts as they cross continents. This work is in preparation for submission.

Also, congratulations are in order for “Little” Dan Tekiela, who won the Robert D. Sweet Outstanding Graduate Student Award and placed first in the Student Paper Contest. Virginia Tech also won the NEPPSC quiz bowl, besting teams from Cornell, Penn State, UMass, Maine, NC State, and Delaware, as well as the EB-ESA Linnaean Games. Graduate students Morgan Franke and Dan Tekiela both gave excellent presentations of their research.