Tallgrass prairie systems are one of the most endangered habitats worldwide, with less than 1% remaining of the original tallgrass prairie habitat across the North American Great Plains. Much of what was once prairie has been converted to agricultural fields leaving remnant prairie systems highly fragmented. Prairie restoration efforts on former agricultural fields are subjected to intense pressure from weedy species, as well as from the effects of anthropogenic nitrogen deposition in the form of fertilizers. Historically, prairie mollisols were nitrogen limited systems with high levels of black carbon as a result of naturally occurring prairie wildfires over thousands of years. Carbon soil amendments, such as sawdust, have been proposed as a tool in prairie restorations to reduce the abundance and biomass of weedy species and to promote native prairie species. Biochar, a form of black carbon produced from the pyrolysis of natural material, has recently gained interest as a carbon-rich soil amendment and has been shown to improve soil fertility and increase plant growth. Modern biochars are structurally similar to the black carbon found in prairie mollisols, yet to date there has been little work examining the effect of biochar on tallgrass prairie systems. The goal of this research was to assess the response of weed and prairie species at scales ranging from the root architecture of individual plants to community responses under field conditions as well as prairie soil fungal communities to carbon-rich soil amendments.;In our first experiment, we explored the effect of carbon-rich soil amendments on the root growth and root system architecture of native and non-native prairie forbs. Sawdust reduced native and non-native forb root productivity and root system architecture complexity but biochar affected the root system architecture of prairie forb species variably, promoting increased root system architecture complexity in the native forb Dalea purpurea and decreased root system architecture complexity in the non-native legume Lespedeza cuneata. Furthermore, while reduced nitrogen availability in carbon amended soils impacted plant species productivity similarly, the mechanism by which plant species adapted to these conditions varied. In our second experiment, we examined the effect of biochar on soil feedback loops. We found that biochar impacted plant growth inconsistently, with environmental factors (drought-like conditions) possibly playing a large role in plant species response. Furthermore, we found no evidence to suggest biochar has the potential to mitigate harmful, non-native soil legacy effects on native species, but did find the non-native legume Lespedeza cuneata benefited from biochar application in soil previously conditioned by the non-native grass Sorghum halepense , a species known to produce allelochemical compounds detrimental to leguminous species. These findings suggest there may be some potential for biochar to bind plant allelochemicals, but response may depend highly on plant species and soil conditions. In our third experiment, we examined the effect of carbon soil amendments and weed removal on prairie community diversity under field conditions and found that both sawdust and biochar had little impact on weed and prairie plant communities as a whole. Native species richness was increased after two years in biochar amended plots on a former agricultural field, but individual plant species response to biochar and sawdust was highly species-specific. Weed removal consistently resulted in increased prairie species density and richness, indicating minimal support for the use of biochar in prairie restorations, and highlighting weed removal as a critical component to improving native species growth. Finally, we explored the effect of carbon soil amendments on fungal communities of a recently restored prairie system (previously an agricultural field) two years after carbon application. Our findings suggest that two years after application, biochar and sawdust amendments have minimal effects on fungal community diversity as a whole. However, individual species response to biochar was highly variable, and an increase in ectomycorrhizal fungi in biochar amended soil was observed. Our findings suggest prairie species response to biochar, both fungal and plant, is species-specific and response to biochar application can be highly variable depending on environmental factors (soil type, climate, field, greenhouse, growth chamber). Based on our current understanding of the many factors that influence plant response to biochar, we do not recommend it as a useful tool in prairie restorations.
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