Document Type

Dissertation - Open Access

Award Date

2025

Degree Name

Doctor of Philosophy (PhD)

Department / School

Natural Resource Management

First Advisor

Lora Perkins

Abstract

Plant-soil feedbacks (PSFs) describe how plants change their soil environment in ways that can either negatively or positively affect subsequent plant growth. In doing so, they offer an opportunity to connect ecological processes with agricultural practice. My dissertation examines PSFs created by native perennial monocultures, commonly used for native seed production, across time and space, and through soil legacies. Specifically, I focus on how plant species identity shapes both soil nutrient and soil microbial community responses. To address these questions, I conducted field experiments with monocultures of five forb species native to South Dakota and established plots with these species adjacent to annual crop plots. I measured soil nutrient pools, soil microbial activity, and community composition across multiple growing seasons, along edges between crops and perennial plots, and in bioassays with phytometers grown in soils conditioned by each species. This design allowed me to evaluate how PSFs form over time, extend across space, and endure as soil legacies. Through time, PSFs were more pronounced in soil nutrient dynamics as compared to soil soil microbial communities. Agastache nepetoides reduced nitrate availability, mobilized potassium, and increased β-glucosidase activity, whereas Liatris ligulistylis increased calcium and cation exchange capacity. Legumes such as Dalea candida and Glycyrrhiza lepidota slightly influenced phosphorus and micronutrients, and Tradescantia occidentalis showed little effect. These results show that nutrient dynamics may drive PFS processes. Soil microbial changes were less consistent, with enzyme activity being the only soil microbial indicator where shifts were observed. Across space, PSFs were driven by shifts in microbial soil communities. G. lepidota created a microbial soil transition zone extending roughly 0.5 m into neighboring corn plots, coinciding with reduced relative leaf chlorophyll levels in adjacent corn rows. Conversely, A. nepetoides exhibited soil microbial shifts inward from the boundary. Soil nutrient concentrations remained consistent across space, indicating that soil microbial groups, rather than chemistry, drive short-range spillover of the plant effects across plot edges. Subsequent phytometer performance was impacted by the species of the previous native perennial crop, however the mechanisms that influenced subsequent plant growth remain unclear. The influences I observed could have happened through shifts in nutrient availability, or changes in soil microbial associations, or both. Soils conditioned by L. ligulistylis improved phytometer (Raphanus sativus) performance despite lower nitrate availability, suggesting beneficial soil microbial associations. Conversely, A. nepetoides soils suppressed both phytometer and dicot weed development, reflecting negative PSFs, although the underlying mechanisms, whether soil microbial pathogens, allelopathy, or other soil mediated processes, remain uncertain. These divergent results illustrate how soil legacy can either promote or constrain subsequent plant productivity. Together, these findings show that PSFs in native perennial monoculture systems are dynamic and species-specific. Temporal PSFs were mostly shaped by shifts in nutrient chemistry, whereas spatial PSFs were driven by soil microbial communities. Soil legacies reflected their integration which was observed in subsequent plant growth outcomes. By linking species identity with space and time, this work advances PSF theory and provides applied insight into how native perennials can be managed to enhance soil health, reduce inputs, and balance agricultural production with restoration goals.

Publisher

South Dakota State University

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Rights Statement

In Copyright