CAREER: Root Herbivory and Symbiotic Associations Mediate Responses of Root Productivity to Precipitation Extremes and Nitrogen Addition

Plants obtain all water and nutrients through roots. Across grasslands, plants store most of the carbon that they consume from the atmosphere in their roots and the substances that roots secrete. Despite their critical role, plant roots are understudied.

This NSF-CAREER grant will explore the effect of extreme precipitation and nutrient deposition on root growth, and the consequences of root expansion in the context of a changing environment. The project will involve an interdisciplinary team that includes graduate students and postdoctoral researchers, in addition to the principal investigator and his collaborators.

The team will test the novel hypothesis that the response of root productivity to precipitation extremes depends on the nature of the response of root productivity to water availability. Mechanisms to be tested include root-system expansion through partnership with fungi, and root-system contraction when eaten by soil nematode worms. The team will use multiple approaches including greenhouse and lab experiments, as well as large-scale field experiments.

This research will be of broad societal value because it will enable a better understanding of grassland ecosystems and their role in the carbon cycle.

This CAREER grant builds upon previous work on aboveground responses to precipitation and nutrient availability manipulations by turning previous concepts, hypotheses, and mechanisms upside down and centering empirical tests on belowground processes in three hierarchical steps. First, it explores mechanisms behind the effect of precipitation variability on root productivity related to the shape of the relationship between root growth and water availability as stated by the Jensen inequality.

Second, it incorporates nitrogen availability and tests for interactions that change the shape of such relationships altering the net root productivity response to precipitation variability. And third, it considers the effect of symbiotic associations between root and soil fungi that may enhance root fitness and nutrient uptake in contrast to root herbivory by nematodes that reduces the capacity of roots to uptake water and nutrients.

In addition, the project considers structural differences among grassland ecosystems by testing the applicability of experimental findings across grassland types globally. This work will integrate a comprehensive education plan using multiple approaches from undergraduate courses to student mentoring at all levels (high school through graduate students) and dissemination of results to land managers and scientists.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.