Invasion by non-native species is a serious ecological threat and the susceptibility of ecosystems to invasion is often highly correlated with soil resource availability. Understanding the role of plant-soil feedbacks in invaded ecosystems could provide insight into community successional trajectories following invasion and could improve our ability to manage these systems to restore native diversity. My dissertation examined how plant-soil feedbacks and resource availability influence the success of both cheatgrass and native species with three interrelated studies. In a large-scale observational study, I evaluated plant community characteristics as well as soil and plant nutrients associated with progressive cheatgrass invasion in a broadly distributed sagebrush ecological site type. I found that although many nutrient pools did not differ among levels of invasion, soil ammonium (NH4+) was negatively affected by increases in cheatgrass cover. Also, cheatgrass nutrient content did not differ across sites indicating that cheatgrass may alter plant available soil nutrients to the detriment of competitors while maintaining its own nutritional content via high nutrient use efficiency and/or soil mining. I also conducted a field experiment to provide a more mechanistic understanding of the role of disturbance on nutrient availability and invasion and to address potential management approaches. I evaluated the effects of 4-5 years of repeated burning, in combination with litter removal and post-fire seeding, on nutrient dynamics and plant responses. Results from my field experiment indicated that repeated burning is unlikely to decrease soil N availability in cheatgrass-dominated systems due to cool fire temperatures that do not volatilize biomass N and strong effects of weather on plant growth and soil processes. Repeated burning and litter removal, however, did have negative effects on litter biomass and C and N contents which negatively influenced cheatgrass biomass, density and reproduction. In addition, post-fire seeding with common wheat decreased cheatgrass abundance, likely due to competition. Integrated restoration approaches that decrease litter biomass and seed banks and increase competitive interactions may be more effective at reducing annual grasses and establishing desirable perennial species than approaches aimed at reducing soil nutrients. Together, the observational and experimental components of my dissertation indicate that plant-soil feedbacks in arid sagebrush shrublands are complex and that understanding these feedbacks requires both spatial and temporal variability in sampling. Furthermore, the results from these studies provide valuable information on techniques that could facilitate the restoration of cheatgrass-dominated systems to more diverse plant communities.

"Fire is one of the most significant disturbances in an ecosystem, as it is capable of altering the physical, chemical, and biological properties of soil, and the fire frequency in semi-arid ecosystems is increasing. These changes can potentially alter plant-soil feedbacks that may affect post-fire recovery of the native plant and soil communities and lead to an ecosystem state change. However, there is much uncertainty about the magnitude of change as soils are exposed to more fires, because soil recovery and changes in fire severity following a first fire mediate the impact of successive fires on soil properties. To improve understanding of fire frequency effects on the soil ecology of the northern Columbia Basin sagebrush steppe ecosystem, this study assessed the physical, chemical and biological properties of soil that are critical to plant communities (e.g. soil pH, C and N, respiration and extracellular enzyme activity) from four different fire frequencies (unburned, burned once, twice, and thrice). Our study yielded three main results: 1) fire reduced the soil C concentration relative to unburned soil, but only when soil was exposed to fire once, 2) soil pH and NO3--N increased with fire frequency, whereas enzyme activity decreased, and 3) soil organic matter contents and microbial respiration were suppressed significantly in the once and thrice burned soils compared to the unburned and twice burned soils. Taken together, our findings suggest that a one-time fire in this region of the sagebrush steppe is capable of significantly changing soil properties that alter plant-soil feedbacks and hinder ecosystem resilience, thus contributing to ecosystem change particularly when fire frequency increases."--Boise State University ScholarWorks.

Bringing together ecology and management of invasive plants within natural and agricultural ecosystems, this book bridges the knowledge gap between the processes operating within ecosystems and the practices used to prevent, contain, control and eradicate invasive plant species. The book targets key processes that can be managed, the impact of invasive plants on these ecosystem processes and illustrates how adopting ecologically based principles can influence the ecosystem and lead to effective land management.

This book by soil scientists and ecologists reviews how and why plants influence soils. Topics include effects on mineral weathering, soil structure, and soil organic matter and nutrient dynamics, case studies of soil-plant interactions in specific biomes and of secondary chemicals influencing nutrient cycling, the rhizosphere, and potential evolutionary consequences of plant-induced soil changes. This is the first volume that specifically highlights the effects of plants on soils and their feedbacks to plants. By contrast, other texts on soil-plant relationships emphasize effects of soil fertility on plants, following the strongly agronomic character of most research in this area. The aspects discussed in this volume are crucial for understanding terrestrial ecosystems, biogeochemistry and soil genesis. The book is directed to terrestrial ecologists, foresters, soil scientists, environmental scientists and biogeochemists, and to students following specialist courses in these fields.

Sagebrush steppe ecosystems in the Great Basin have become increasingly threatened by the proliferation of cheatgrass (Bromus tectorum L.), an invasive annual grass. Diverse sagebrush and perennial bunchgrass landscapes can be converted to homogenous cheatgrass grasslands mainly through the effects of fire. Although the consequences of this conversion are well understood in the context of plant community dynamics, information on changes to soil communities has not been well documented. I characterized soil surface, microbial, and nematode community dynamics in sagebrush steppe and cheatgrass-invaded areas across the northern Great Basin. I also examined how restoration treatments, such as seeding with a low impact rangeland drill and applying herbicide or sugar to plots, affected soil communities. Soil community functional diversity and structure were alike at sites where soil pH and percent bare ground were similar. Rangeland drill seeding and associated human trampling decreased biological soil crust cover at sites with high proportions of cyanobacteria. Herbicide treatments had little effect on soil communities, but addition of sugar to plots increased carbohydrate utilization and fungal biomass of cheatgrass- invaded soils. In studying paired intact and cheatgrass-invaded sagebrush plots, I found that microbial functional diversity and community composition were different in sagebrush, bunchgrass, cheatgrass, and interspace soils. Fungal biomass and species richness were highest under sagebrush and decreased under cheatgrass. To examine how soil community shifts might affect ecosystem processes, I investigated the contribution of fungi to inorganic nitrogen (N) mineralization in sagebrush and cheatgrass rhizospheres. Results from a 15N pool dilution experiment modified with the fungal protein synthesis inhibitor cycloheximide showed that gross and net N cycling rates did not differ between control sagebrush and cheatgrass soils and that fungi were important for gross NH4+ production and consumption in both soil types. However, net nitrification increased in sagebrush soils after 24 h, suggesting that when organic matter decomposition by fungi ceased bacteria became carbon limited and could no longer assimilate NH4+. These studies demonstrate that cheatgrass invasion into sagebrush steppe ecosystems can bring about significant changes to soil communities and that these changes may have repercussions for ecosystem functioning in the northern Great Basin.

This book is open access under a CC BY-NC 2.5 license. This book provides an unprecedented synthesis of the current status of scientific and management knowledge regarding global rangelands and the major challenges that confront them. It has been organized around three major themes. The first summarizes the conceptual advances that have occurred in the rangeland profession. The second addresses the implications of these conceptual advances to management and policy. The third assesses several major challenges confronting global rangelands in the 21st century. This book will compliment applied range management textbooks by describing the conceptual foundation on which the rangeland profession is based. It has been written to be accessible to a broad audience, including ecosystem managers, educators, students and policy makers. The content is founded on the collective experience, knowledge and commitment of 80 authors who have worked in rangelands throughout the world. Their collective contributions indicate that a more comprehensive framework is necessary to address the complex challenges confronting global rangelands. Rangelands represent adaptive social-ecological systems, in which societal values, organizations and capacities are of equal importance to, and interact with, those of ecological processes. A more comprehensive framework for rangeland systems may enable management agencies, and educational, research and policy making organizations to more effectively assess complex problems and develop appropriate solutions.