Research

Texas sand dunes: Testing community and ecosystem responses to soil microbial amendments during restoration

Recently, we were funded by Texas Sea Grant to test how plant diversity and microbial amendments influence restoration of Texas sand dunes.  Texas dunes provide important ecosystem services, such as flood prevention and eco-tourism.  However, many dunes have been lost over the years to human development and natural degradation during storm events.  When dunes are restored, many land managers have noted that the restorations aren’t very successful.  We are testing whether increasing the diversity of plantings and/or incorporating microbial amendments will help increase restoration success.  We are especially interested in the long-term effects of our treatments, as an increase in some desired outcome (like soil stability) may come at a cost to other desired outcomes (like natural colonization of native plant species).

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Our project site at the University of Houston Coastal Center

For more information on this project, Gulf Coast sand dunes, and dune restoration please visit sanddunerestoration.wordpress.com !

Effects of plants and soil microbes on ecosystem development

Terrestrial soils play a key role in many critical ecosystem processes, such as primary productivity, nutrient cycling, and the sequestration of atmospheric carbon dioxide. Therefore, understanding the factors that control the soil’s ability to fulfill these functions is imperative. Plants and their associated soil microbial communities can influence soil development by altering soil nutrient cycling, soil aggregate stability, and soil organic matter.  Despite this, few studies have examined soil development in a community context.  We are working in a primary successional system with preserved chronosequences, the Great Lakes sand dunes, to address how plants and microbes influence soil development.  By pairing experiments with data collected from independent chronosequences, we will be able to examine how these effects scale-up in space and time.

Chronosequence at Sleeping Bear Dunes National Lakeshore

Indirect microbially-mediated effects of invasives on native community structure

Invasive plant species play a key role in the worldwide decline of native biodiversity.  While much work has been devoted to understanding their effects on natives via direct effects such as competition, less is known about how invasives may affect natives via indirect effects such the modification of abiotic and biotic soil properties.  Understanding how invasives influence native plant communities through soil-mediated effects will provide important insights into the forces underlying plant community assembly and enlighten efforts to control invasives and restore native habitats.  We are currently conducting experimental studies and meta-analyses to determine whether and to what extent invasive species influence native community structure through changes in soil microbial properties.

Lespedeza cuneata  grown in sterile (left) and unsterilized (right) soil conditioned by natives (top) or itself (bottom)

Independent and interactive effects of genetic diversity and species diversity

Separate studies have shown that plant species diversity and genetic diversity within a plant species can influence community properties and ecosystem processes.  However, these studies have been conducted in different systems and at different times.  In nature, it is likely that species diversity and genetic diversity interact to structure ecosystems.  To clarify the relative importance of species diversity and genetic diversity and to test if the two levels of diversity interact to influence community and ecosystem responses, we established long-term community garden experiments at Sleeping Bear Dunes National Lakeshore.  The experiment 1) independently manipulated plant species diversity, 2) independently manipulated genetic diversity within the dominant species, Ammophila breviligulata, and 3) simultaneously manipulated species diversity and genetic diversity within A. breviligulata.  Even though neither species diversity or genetic diversity independently influenced primary productivity, species diversity and genetic diversity interacted to influence primary productivity.  In the common gardens, we also measured the response of the arthropod community, soil microbial community structure and function, and soil properties.  Check back soon for more results!

Photograph of the experiments at Sleeping Bear Dunes National Lakeshore

Consequences of genetic diversity

In response to global declines in biodiversity, much work has focused on the consequences of species loss for communities and ecosystems and found that decreasing plant species diversity leads to decreases in primary productivity, overall community diversity, and nutrient cycling.  These effects are driven by variation among species’ traits. However, individuals within a species can also vary widely in their traits.  Therefore, it might be predicted that genetic diversity within a species may mimic the effect of species diversity.  To address this hypothesis, we tested the consequences of genetic diversity within plant populations in two separate systems.  We found that increasing genetic diversity within populations of Arabidopsis thaliana increased population-level germination, biomass, flowering duration, and fruit number.  These findings suggest that genetic diversity may be a predictor of colonization success.  We also found that increasing genetic diversity in populations of Solidago altissima increased rates of parasitism by the goldenrod bunch gall midge, which indirectly increased arthropod diversity by providing new habitat.  This was among the first studies to show an indirect effect of genetic diversity on community diversity.

Arabidopsis thaliana in the greenhouse at Rice University

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