Graduate Defense: Ashley Leavell

Thesis Information

Title: Biochar Impacts On Soil And Sagebrush Seedling Establishment Across A Natural Recovery Gradient In The Sagebrush Steppe

Program: Master of Science in Biology

Advisor: Dr. Marie-Anne de Graaff, Biological Sciences

Committee Members: Dr. Marcelo Serpe, Biological Sciences; Dr. Leonora Bittleston, Biological Sciences; and Dr. Deborah S. Page-Dumroese, Biological Sciences

Abstract

Large areas of the sagebrush steppe are lost to fire, which catalyzes invasive species growth, increases soil nitrogen availability, reduces soil water retention, and disrupts soil symbiont-plant interactions. These changes in biogeochemical properties may explain why restoration success remains limited. Biochar is a soil amendment created from pyrolyzed plant biomass that may reduce soil N availability and increase water retention. Our study aims to evaluate whether changing soil properties using biochar may enhance the survival of sagebrush seedlings. We installed an experiment south of Boise, Idaho at a site that burned in 1983. Nursery-grown sagebrush seedlings were hand-planted in November 2021, and were amended with three biochar types that vary in particle size and chemical composition and a no biochar control. Biochar treatments were applied in two areas, one with partial recruitment of sagebrush near the boundary of the fire (hereafter: “recovering”) and one with no sagebrush recruitment further into the burned area (hereafter: “not recovered”). We analyzed planted seedling survival, biomass, and fitness as well as soil biogeochemical properties for two and a half years, to include three winters post-planting. The recovering zone exhibited greater seedling survival compared to the not recovered zone and was characterized by higher soil organic matter (SOM) and pH, and lower N. Biochar application decreased plant growth and volume, as well as increased the root-to-shoot ratio, but as expected did not consistently impact soil properties. One type of biochar used increased survival, but reduced NO3 concentrations in soil, whereas another biochar type reduced plant growth and increased soil pH. Biochar was found to only impact survival after the third winter survival was calculated. In addition, many of the interactions were zone dependent, highlighting the differences in soil properties within the two zones. Overall, this experiment showed that a recovering sagebrush community aided in planted sagebrush survival, and biochar may have long term impacts that contribute to sagebrush survival, but further research is needed to elucidate these mechanisms.