Allie Igwe

Plant root bacteria change with soil type and impact seedling survival

Contributed by Ash Zemenick @mtn_ash & Allie Igwe @an_igwe


Bacteria, Black, Community ecology, Ecology, Experimental, Field, Fundamental research, Lab, Mental health, Natural history, North America, Plants, Race/ethnicity, Terrestrial, Woman



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Alexandria Igwe and Rachel Vannette. 2019. Bacterial communities differ between plant species and soil type, and differentially influence seedling establishment on serpentine soils. Plant and Soil 441: 423–437 link



Slide 1: Researcher’s Background

Allie is a microbial ecologist who studies the how microbial communities impact plant phenotypes. She is currently a PhD candidate in the Microbiology Graduate Group at UC Davis. She completed her Masters Degree at Texas A&M where she researched the role of plant root exudates and soil microbial community dynamics in hydrocarbon-contaminated soils. Allie also works to support and mentor students – she is the Program Director of the UC Davis Student Recruitment and Retention Center (SRRC), and worked as a Success Coach at the UC Davis Office of Educational Opportunity and Enrichment Services (OEOES). 


PB: Why did you become a biologist?

AI: There were two reasons I became a biologist: interest and money. First, I enjoyed science. I grew up participating in science fairs and most of my topics dealt with nature: surveying insects, growing plants, growing crystals, etc. I was all set to become a medical doctor when I was introduced to research as a career which led to my second reason I became a biologist: money. Although I learned about research as a career later in life, I was excited about exploring a career where I could, essentially, get paid to learn and explore topics of interest.


PB: What is your favorite part about your job?

AI: I love coming up with research questions and experiments. I also enjoy problem-solving and the validation I get when other people are interested in my research topic.


PB: What obstacles have you overcome to get where you are?

AI: I had to overcome my own self-doubt and family expectations to get where I am. I am still working on feeling confident in myself and capabilities, but I am happy to report my family is fully supportive of my career choice now.


PB: What advice do you have for aspiring biologists?

AI: My advice for everyone is take time to consider your values, interests, personality, and skills. My current career honors the autonomy I value, my interest in nature, my introverted and curious personality, and I am constantly learning new skills. What do you value? What are your interests? How would you describe your personality (i.e., competitive vs. collaborative, introverted vs. extroverted, etc.)? What skills do you already have or are willing to learn?


PB: Do you feel that any dimension of your identity is invisible or under-represented/marginalized in STEM?

AI: Yes. I am a Black woman in STEM and that comes with its own assumptions and barriers. However, I find the labs and environments I join are very supportive although I have had interesting experiences with micro-aggressions related to those identities (i.e., being spoken over, questioned, tokenized). More invisible struggles are related to mental health. I can be high-performing so some mental health issues can come as a surprise to others and sometimes to myself.


Slide 2: Research Overview

Take home message of study

In this study, Allie Igwe sought to understand whether the bacterial communities associated with plant roots change depending on the type of soil the plant is found in, and if so, whether differences in root-associated microbial communities differences had impacts on seedling survival and growth. To do this, Allie collected soil from plant species that grow in serpentine and non-serpentine soil types and surveyed the root bacterial communities. She found that bacterial communities were different in serpentine and non-serpentine soils, and that the different bacterial communities were associated with different levels of seedling survivorship.


Study system

Hopland Research and Extension Center showing nonserpentine (top portion of picture) and serpentine soil (bottom portion of picture). The change from nonserpentine to serpentine is often stark and clearly delimited. Serpentine soils are created from volcanic rocks tend to be harsh living conditions for plants because they have high concentrations of heavy metals (e.g. chromium, iron, cobalt, and nickel) and low concentrations of important nutrients (e.g. calcium, nitrogen, phosphorus, and potassium). 


Slide 3: Key Research Points

Main figure

Top panel: a portion of Figure 2 from Igwe and Vannette 2019 shows that microbial species were differentially abundant in serpentine and non-serpentine soils. The plots show the abundance of microbes (y-axis) isolated from serpentine soils (yellow bars) or non-serpentine soils (dark blue bars). The 5 different panels show the abundance data of the microbe species that were most important in defining the different microbial communities found in the different soil types. Bars indicate the mean value +/- standard error of the mean.

Bottom panel: a portion of Figure 3 from Igwe and Vannette 2019 shows the “hazard ratio for seedling establishment” for plants grown in different soil types. Values on the left of the dash line indicate plants with lower survival compared to autoclaved soil (with no living microbes), and values on the right of the dash line indicate that plants had higher survival rates compared to autoclaved soil. The results show that plants grown in soil with non-serpentine microbes (“NSS”) had significantly lower survival than plants grown in soil that was sterile (“Autoclaved”), had microbes from serpentine soil (“SS”) or soil collected from serpentine areas (“Serpentine”).

Societal Relevance

Plants are incredibly important – we grow them for food, fiber, medicine, and they play many roles in natural ecosystems. Therefore, understanding what impacts plant survivorship and growth is incredibly important as it can inform conservation, restoration, and sustainable agricultural practices. 

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