Investigating plant-soil feedbacks as a mechanism driving competition and coexistence dynamics
Plants are known to cultivate species-specific rhizosphere microbial communities which then feedback to affect the fitness of their plant associates. Previous work have shown that these plant-soil feedbacks (PSF) are a potential mechanism that promotes self-limitation in associated plants, leading to increased opportunities for coexistence. But does it work? Is it important relative to all the other biotic and abiotic variables that control population dynamics of plants? For my dissertation, I tested this idea in the greenhouse and in the field.
Part 1: Can microbe-mediated plant-soil feedbacks alter competition and negative frequency dependence between desert grasses?
To get at this question, I set up a greenhouse experiment which provided the first test of PSF altering the relative strengths of intra- and interspecific competition, using blue and black grama plants (Bouteloua gracilis and B. eriopoda; pictured in banner above). I found that negative PSF increased intraspecific competitive responses of the superior competitor (blue grama) compared to interspecific competition, potentially promoting coexistence between the two species. Check out the paper here.
Part 2: So okay, it works. But do plant-soil feedbacks matter in the field over time scales that determine perennial plant coexistence?
After the greenhouse test provided evidence that PSF exist and could matter in this desert grassland ecosystem, the next step was to take this concept out into the field. At the Sevilleta LTER, 25+ year records of vegetation dynamics show spatial variability in the coexistence dynamics between blue and black grama. Along a 400m transect, patches are recorded to have higher/lower rates of turnover between blue and black grama (Fig. 3 below). Are differing strengths of PSF driving this spatial variability in temporal coexistence patterns? To test this question, I set up experimental transplants in plots along the transect adjacent to areas identified as having high or low species turnover rates according to the long term data in 2014. I found that patches that are more stable in dominant plant composition through time are associated with negative PSFs, and patches with higher rates of composition change are associated with positive/neutral PSFs.
Part 3: What are the belowground drivers of plant-soil feedbacks?
I was awarded an NSF-DDIG in 2016 to unravel the belowground changes in fungal community composition that drive the aboveground plant responses seen in my other work. I used a combination of microscopy, next-generation sequencing, culturing, and inoculation trials to open up the “black box” of soil microbial communities. Early results show that root-associated fungal communities differ widely among study types and between host plants. In addition, patches that exhibit higher plant community change and turnover in the field are associated with increased root fungal diversity.