Mountain Scholar :: Browsing by Author "Fonte, Steven, committee member"

Browsing by Author "Fonte, Steven, committee member"

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Open Access
Analysis of land use change and greenhouse gas emissions in Kalasin Province, Thailand
(Colorado State University. Libraries, 2018) Chailangka, Preeyarat, author; Paustian, Keith, advisor; Fonte, Steven, committee member; Leisz, Stephen, committee member
Growing global population causes many stresses on the environment, perhaps the most serious is global warming due to Greenhouse Gas (GHG) emissions. Major contributors to GHG emissions include agricultural production and land use change. Southeast Asia is one of the world's fastest growing regions and provides many crops for export, so the land use changes are rapid and not always made in an environmentally conscious manner. The province chosen for this study, Kalasin, is located in a major economic development region with the multi-country East-West Economic Corridor (EWEC) running through it. The EWEC has brought many changes to this province such as expansion of the manufacturing sector, more urban growth to support new factories, and new roads to reach areas which were previously not developed. The largest single land use in Thailand and the Kalasin province is cropland. There have been many changes in farming practices in the province as well, from the types of crops grown to the increasing numbers of commercial farms. These shifts in land use are leading to changes in the amount of GHG emissions and are also leading to land degradation in parts of the province as well. The largest GHGs emissions in agricultural sector come from rice cultivation (45%), followed by biomass carbon stock losses (40%). Some government policies have led to crops being grown on unsuitable lands, which is often associated with greater use of fertilizers and intensive tillage practices applied. Other practices involve draining wetlands, creating rice paddies on unsuitable soils, or clearing forests to farm the area. In this study we look at land use and land use changes throughout the province and use that data to estimate a GHG emissions inventory in the agricultural sector in order to better understand the effects that growth, land use and land use changes in the Kalasin province have on the environment.
Open Access
Bridging the gap between regenerative agriculture and the biological mechanisms controlling soil organic matter dynamics
(Colorado State University. Libraries, 2024) Prairie, Aaron, author; Cotrufo, M. Francesca, advisor; Fonte, Steven, committee member; Rosenzweig, Steven, committee member; Hall, Edward, committee member
This dissertation investigates the complex impacts of regenerative agriculture on soil organic matter (SOM) dynamics and soil fauna biodiversity, addressing a broad range of objectives from uncovering global patterns and policy needs to mechanistic understanding. Through global meta-analyses, policy evaluations, field studies, and mechanistic experiments, this research provides a comprehensive understanding of how regenerative practices influence soil health, carbon sequestration, and biodiversity. Chapter 2 aimed to understand global patterns through a meta-analysis quantifying the effects no-till (NT) and cropping system intensification significantly increase SOM, via impacts on both particulate organic matter (POM) and mineral-associated organic matter (MAOM). The analysis reveals that NT and cropping intensification synergize with integrated crop-livestock (ICL) systems to greatly enhance soil organic carbon (SOC) stocks, highlighting the potential of regenerative practices to mitigate climate change and promote soil health. Chapter 3 sought to evaluate the impacts of diversified agricultural systems on SOC, soil health, and yield across the United States. The findings indicate that diversified systems consistently show higher levels of SOC, improved soil health, and improved agronomic outcomes. The policy recommendations include increasing funding for soil health practices, supporting longer participation of producers in conservation programs, and tailoring these programs regionally to maximize their effectiveness. Chapter 4 focused on field-level impacts by examining the effects of varying degrees of regenerative practice adoption on SOM dynamics and soil fauna biodiversity in 22 farms within the Cheney Watershed, of central Kansas. By developing a Regenerative Farming Index (RFI), the study clearly links regenerative practices to increased carbon and nitrogen stocks in both POM and MAOM, and indicates a positive correlation between regenerative practices and soil biodiversity. Path analysis suggests that soil fauna indirectly influence SOM through their role in enhancing regenerative practices. Chapter 5 aimed to provide a mechanistic understanding of SOM dynamics by exploring the interactions between predatory mites and bacterivorous nematodes. The study highlights how these interactions shape microbial necromass accrual and MAOM formation. The findings underscore the importance of considering the entire soil food web in ecological studies to fully understand SOM formation and stabilization mechanisms. Overall, this dissertation advances the understanding of SOC dynamics under regenerative agriculture, providing valuable insights for sustainable soil management and climate change mitigation. By integrating global and local scales, it offers a holistic view of how regenerative practices can restore soil health and contribute to more resilient and productive agricultural systems.
Open Access
Effect of phosphorus fertilization on rhizosphere microbiome of crops
(Colorado State University. Libraries, 2019) Pantigoso Guevara, Hugo A., author; Vivanco, Jorge M., advisor; Manter, Daniel, committee member; Minas, Ioannis, committee member; Fonte, Steven, committee member
Recent studies in plant-microbe interactions have revealed the importance of the rhizosphere microbiome in agriculture. However, little is known about the impact of fertilization on the rhizosphere and its associated microbial communities. This thesis investigates whether phosphorus (P) fertilizer has led to a shift in bacterial community composition and functions in both cultivated and non-cultivated plants. Two independent greenhouse experiments were conducted to evaluate P impacts. The first study explored the effects of low (0 and 50 kg ha-1) and higher P levels (101 and 192 kg ha-1) of triple super phosphate (0-45-0) amendments on soil microbial community composition associated with the rhizosphere of blueberry plants. The abundance of soil bacteria with phosphatase genes was also tested. The second experiment used a gradient of domesticated potato plants (modern cultivars, landrace and wild) to evaluate the effect of P addition on plant biomass and bacterial communities associated with the potato rhizosphere. Further, the study aimed to detect the most abundant microbial taxa, shared and unique, across six genotypes of Solanum genera. Four tuber-bearing and two non-tuber bearing potatoes were used in this study. Tuber-bearing included Solanum tuberosum subsp. tuberosum (a direct progenitor of modern potatoes) and the potato cultivars 'Red Norland', 'Yukon Gold' and 'Russet Burbank'. The non-tuber bearing potatoes included Solanum bulbocastanum and Solanum tuberosum subsp. tuberosum. Plants were grown in soils collected from an agricultural field where cover crops were previously cultivated. Three levels of phosphorus were applied (0, 67, 133 kg ha-1) during the experiment. Rhizosphere soil was collected and analyzed by amplicon sequencing targeting 16S rRNA gene. Our results showed that potato genotype is the main driver of microbial community composition, followed by fertilizer level. Non-tuber bearing potatoes were different from tuber-bearing potatoes and showed a higher degree of dissimilarity in microbial taxa compared to others. Additionally, a shift in bacterial abundance within the community was observed in response to high P levels. Xanthomonadacea and Alteromonadacea were the two families consistently increase or decrease (respectively) in response to incremental P levels. Interestingly, the latter was only present in non-cultivated potato plants, this family could be an important microbial member that has been lost with cultivation.
Open Access
Evaluation of cyanobacterial biofertilizer as a supplemental or solitary fertilizer on peach yields, leaf tissue nutrient concentration, and trunk growth
(Colorado State University. Libraries, 2016) Sterle, David, author; Davis, Jessica G., advisor; Caspari, Horst, committee member; Fonte, Steven, committee member
Nitrogen (N) is the nutrient applied in the greatest quantities to peach trees and is a necessary component of proteins. As a result, carbon assimilation is dependent upon adequate levels of N in leaf tissue. Cyanobacteria are a type of bacteria which can fix gaseous N from the atmosphere enzymatically. This N fixation can be exploited in a cyanobacterial biofertilizer (cyano-fertilizer) production raceway, which allows farmers to grow their own source of N with relatively small energy inputs. Cyano-fertilizer was grown on three peach farms in Western Colorado, and applied to peach orchards in combination with a chicken feather meal (mixed with meat and bone meal), a dried chicken manure, and separately in comparison to a conventional foliar fertilizer, fish emulsion fertilizer foliarly applied, and a soil application of fish emulsion fertilizer. Treatments were assigned to experimental units across three separate farms (Farms A, B, and C) and arranged using Randomized Complete Block Designs. Peach fruit yield, trunk cross sectional area, leaf tissue nutrient concentrations, soil nutrient concentrations, SPAD and fruit juice quality characteristics were measured. A significant fruit yield increase was seen on Farm B in treatments which included cyano-fertilizer and manure (Cyano-Manure), versus manure alone (No-Cyano). Trunk cross sectional area showed less growth in treatments including cyanobacteria on Farm B. Significantly higher leaf tissue S, P, and Cu concentrations were found in Cyano-Manure treatments on Farm B; however, significantly greater Ca concentrations were found in the No-Cyano treatment. Chlorosis was present throughout Farm B and so relative leaf chlorophyll content was estimated by measuring Soil Plant Analysis Development (SPAD). SPAD readings were positively correlated with leaf Fe concentration. In the 2015 fertilization section, SPAD readings were higher in Cyano-Manure treatments despite the relatively low amount of Fe present in the cyano-fertilizer, suggesting that cyano-fertilizer may have increased Fe uptake by the trees. Significant differences in leaf micronutrient concentrations were found among treatments in Farm C. Across all farms, treatment effects were masked by three unforeseen events. First, a large infestation of aphids on Farm A caused the death of young vegetative tissue and also killed young peach fruit. Second, a freezing event during bloom, killed most of the fruit on two of the farms. Lastly, there were prior fertilizations earlier in the season on Farm C which lowered the impact additional fertilizer had on the trees.
Open Access
Impacts of conservation tillage on water quality and soil health characteristics under furrow irrigation
(Colorado State University. Libraries, 2017) Deleon, Emmanuel, author; Bauder, Troy, advisor; Fonte, Steven, committee member; Arabi, Mazdak, committee member
Furrow irrigation-induced sediment and nutrient loss continues to be a serious problem in the Western States of the US. Sediment and nutrients in runoff can eventually be discharged into streams and rivers impairing water quality, causing adverse effects on the environment and reducing soil productivity over time. Continuous intensive tillage along with excessive sediment and nutrient loss ultimately lead to the degradation of soil quality. We hypothesize that conservation tillage under furrow irrigation can reduce the sediment and nutrient losses in surface runoff as well as improve soil quality parameters. The objectives of this research are to compare two conservation tillage treatments, minimum tillage (MT) and strip tillage (ST), to a traditional conventional tillage (CT) system under furrow irrigation and understand the impacts of these practices on annual sediment and nutrient concentrations and loads from irrigation and storm events. We quantified total suspended solids (TSS), total Kejdahl nitrogen (TKN), nitrate (NO3), ammonium (NH4), total nitrogen in aqueous solution (TNa), total phosphorus (TP), dissolved reactive phosphorus (DRP), and total soluble phosphorus (TSP) loads from irrigation runoff over two growing seasons for the three treatments. Relative to CT, conservation tillage reduced TSS loads by 84% and 88% in 2015 and by 98% and 87% in 2016 for MT and ST, respectively. In 2015, TKN was reduced by 80% and 86% in MT and ST respectively when compared to CT. Total P was significantly higher in CT, with an 87% load reduction under MT and ST in 2015 and an 85% load reduction under MT in 2016. Total P concentration (mg L-1) correlated well with TSS concentrations (g L-1) (R2 = 0.72, P < 0.001). Total soluble P loads were significantly higher in the CT treatment when compared to the conservation treatments in the 2015 season. Reduced tillage and residue management in the conservation treatments improved irrigation flow parameters such as reduced runoff. The conservation treatments had a greater impact on sediment-bound than soluble nutrients largely due to surface residue reducing erosion in the furrows. Results show that reduced tillage and residue management are an effective best management practices (BMPs) in sediment and nutrient abatement in irrigation and storm runoff. Furrow irrigation is still practiced in 40% of all irrigated lands in Colorado and it is expected to continue across much of the State. Under furrow-irrigated systems, CT practices are common, but such practices can degrade soil quality. The project sought to examine the effects of conservation tillage on soil health at a production scale, understand relationships between soil parameters, and to evaluate the economic feasibility of conservation practices. Soil biological, physical, and chemical parameters were evaluated during the fifth and sixth years of a study (2015 and 2016) comparing two different management systems, MT and ST, verses CT (the control). Measurements included Active C (POXC), macrofauna diversity and abundance, aggregate stability, infiltration, and residue cover. POXC was significantly higher for MT when compared to CT and ST. Results from both years suggest that conservation treatments increased macrofauna abundance, especially earthworms, and diversity (richness) relative to the control. Aggregate stability was significantly higher in the conservation treatments for 2015, but not in 2016. Infiltration rates in the ST treatment was 18% higher when compared to CT. Residue cover was positively correlated with earthworm abundance while earthworm abundance was positively correlated with aggregated stability and infiltration. When comparing economic cost, and returns among systems, ST and MT treatments had a 39% and 32% greater net return when compared to CT plots. These preliminary results show potential for conservation tillage under furrow-irrigation to improve soil quality parameters as well as increasing net income.
Embargo
Integrated weed management: insights from a weed resistance survey and non-chemical weed seed control in the Central Great Plains
(Colorado State University. Libraries, 2023) Simões Araujo, André Lucas, author; Gaines, Todd, advisor; Dayan, Franck, committee member; Fonte, Steven, committee member
With the impending release of genetically engineered sugar beet varieties with resistance to glyphosate, dicamba, and glufosinate, significant changes are expected in weed management practices, particularly with regards to in-crop weed control. Glyphosate is used during fallow and in-crop periods, while dicamba is commonly employed in fallow applications, specifically targeting glyphosate-resistant weed species. This study provides insights into the resistance status and frequency of resistance in problematic weed species to the three active ingredients in sugar beet systems across Colorado, Nebraska, and Wyoming. While numerous studies have highlighted the widespread prevalence of glyphosate-resistant kochia and Palmer amaranth across the United States, there is limited research focusing on these species within the context of a sugar beet system. Additionally, our findings reveal the first occurrence of glyphosate-resistant and dicamba-resistant Palmer amaranth populations in Colorado, and dicamba-resistant kochia populations within a sugar beet system. Furthermore, we report that all dicamba-resistant kochia populations tested in Colorado lack a known target-site resistance mechanism, suggesting the involvement of a novel resistance mechanism. Surveys assessing glufosinate resistance in the sugar beet system have not been conducted until now, and we provide valuable baseline information on the resistance frequency for this herbicide prior to an anticipated increase in glufosinate use. To address the widespread issue of herbicide resistance in various crop systems, it is crucial to adopt alternative strategies that mitigate resistance evolution and maintain the long-term effectiveness of available herbicides. One promising approach is chaff lining, a harvest weed seed control method that has gained popularity in Australia due to its effectiveness in reducing populations of herbicide-resistant ryegrass, especially when combined with other weed control methods. However, the efficacy of chaff lining may be influenced by several factors, including crop and environmental factors, as reported in Australian literature. Scientific studies assessing the applicability and effectiveness of chaff lining in the United States are limited. Recognizing this research gap and aiming to explore the potential of chaff lining, our study investigated its applicability in field settings within the Central Great Plains region of the United States. Through our research, we provide insights into chaff lining efficacy of and highlight the potential inconsistencies that may arise in suppressing weed seeds using this method. Notably, we demonstrate that various factors, including location and environmental conditions, may be involved and impact the effectiveness of chaff lining as a weed management strategy. These findings underscore the importance of integrating chaff lining with other weed management methods to achieve effective and sustainable weed control. Chaff lining, like any other weed management strategy, should not be solely relied upon. Instead, it should be implemented as part of an integrated approach to ensure its long-term effectiveness.
Open Access
Muddy state development in Ghana’s upper east region: one village, one dam, and its effects on smallholder farmers in a study community
(Colorado State University. Libraries, 2023) Roan, Patrick, author; Hausermann, Heidi, advisor; Leisz, Stephen, committee member; Fonte, Steven, committee member; Nyantakyi-Frimpong, Hanson, committee member
Warming trends and drought conditions across northern Ghana portend major implications for water access critical to the future of smallholder farming, food security, and human health. To mediate the impacts of future water resource concerns, the Ghanaian government launched the One Village, One Dam initiative (1V1D) in 2017 which aimed to construct or repair approximately 570 small-scale dams on ephemeral streams in northern communities. Hundreds of dams have been constructed or overhauled to develop northern regions and provide communities with access to water, particularly for dry season farming. This thesis examines the implications of the 1V1D intervention in one study community in Ghana's Upper East Region including social-ecological relationships between smallholders and their farming practices, land-use changes, gold mining, climate data, and farmer perceptions of climate change. My findings reveal that while the government attempted a community-based approach with 1V1D, local insight was marginalized and implementation relied more on outside engineering expertise and State preferences. Most participants contend the dam embankment was poorly designed, improperly located for adequate water capture, and heavy sedimentation including from gold mining is decreasing its capacity. The dam is insufficient for dry season farming, forcing farmers and livestock to depend on wells and boreholes for water, and regional markets for supplemental food supply. Issues of food, water, and economic insecurity are therefore not well addressed by this State development project. A comparative analysis of participant perceptions on climate change is explored and this thesis ends with insights on community ideas for more sustainable climate adaptation interventions.
Open Access
Nitrogen fertilizer impacts on soil microbiome and tomato plant development
(Colorado State University. Libraries, 2023) Rohrbaugh, Carley, author; Vivanco, Jorge, advisor; Delgado, Jorge, committee member; Fonte, Steven, committee member; Manter, Daniel, committee member
Nitrogen (N) fertilization largely supports agricultural production. Urea is a common N amendment used in agriculture and when overapplied it has negative consequences in the environment due to its highly labile and reactive form. Alternative fertilizers, such as controlled release fertilizers (CRF) have been designed to diminish the harmful effects of applied N. This thesis investigates and makes comparisons regarding N fertilizer types and their effects on microbial community composition and plant development. Both research questions were addressed by growing tomato (Solanum lycopersicum 'Rutgers') plants as the test crop, which serve as a good model crop for indoor greenhouse production and were grown to the vegetative stage in both studies covered in this thesis. The fertilizer types considered are urea, a quick releasing form of N fertilizer and Environmentally Smart Nitrogen (ESN), a controlled release fertilizer. The soil used in these studies was from a low N plot (5.2 mg/L NO3) from the Agricultural Research, Development and Education Center (ARDEC) in Fort Collins, Colorado. The first research question addressed in Chapter 2 examines how different types of N fertilizers compare under different soil conditions and fertilizer rates. Altering the soil microbiome through sterilization (via autoclave processing) allows us to understand how urea and a controlled release fertilizer compare in their impact on microbial community composition and N assimilation by a tomato crop. It was found in this study that the use of ESN promoted plant performance and enhanced soil nitrate concentration. The soil microbiome findings from this first experiment showed that high rates of nitrogen fertilization led to higher relative abundances of nitrifying bacteria species. The second research question addressed in Chapter 3 follows a developmental study to track how N fertilizer impacts tomato plant performance, rhizosphere microbiome assembly, and plant nutrient uptake by sampling weekly for eight weeks. It was found in this study that ESN enhanced nitrogen use efficiency and plant nitrogen uptake. The soil microbiome results indicated a shift in community structure at the middle stage of the rhizosphere development. By studying the plant growth and rhizosphere microbiome response to urea and a controlled release fertilizer applied soil, we can improve our understanding on N release rates and bacteria that are responsive to these agents. This is the first research to our knowledge examining N fertilization's impact on rhizosphere development during early to vegetative growth using, especially using a weekly sampling resolution.
Open Access
Pathways of soil organic matter formation in agroecosystems as influenced by litter chemistry, root depth and aggregation
(Colorado State University. Libraries, 2024) Fulton-Smith, Sarah E., author; Cotrufo, M. Francesca, advisor; Paustian, Keith, committee member; Ojima, Dennis, committee member; Fonte, Steven, committee member
Soils contain more carbon (C) than any other terrestrial reservoir, and the increase of these C stocks has been targeted as a potential climate solution globally. Agroecosystems play a critical role in our ability to provide these climate solutions through increasing soil organic matter (SOM). There is significant potential for SOM accrual in agroecosystems due to the degradation of SOM typically observed in these systems. One promising approach to increasing soil C sequestration is through the selection of deep-rooted crops, such as Sorghum bicolor. However, significant questions remain about root inputs' ability to contribute to SOM in order to balance the greenhouse gas (GHG) lifecycle of a bioenergy feedstock. My dissertation aims to answer some of these questions as well as to propose a framework to integrate the study of SOM formation from crop inputs with soil aggregate structure. Bioenergy has the potential to emit fewer GHGs than other fuel sources, such as fossil fuels, yet there are some emissions during the transportation production of bioenergy feedstocks and fuels that could be offset by soil C sequestration. However, in annual bioenergy systems, aboveground biomass is typically removed from the system, meaning roots are the primary source of OM available to return to the soil. However, roots and shoots may differ significantly in their ability to contribute to SOM due to differences in litter chemistry. In Chapter 2, I conducted a field incubation to understand how sorghum root versus leaf litter, as influenced by their contrasting chemistry, affect the formation and stabilization of SOM. Using unique soil-biomass microcosms to incubate root or leaf litter in topsoil (0-30 cm) for 19 months in the field, I traced the fate of litter decomposition products by combining stable 13C and 15N isotope labeling with extensive separation of physical soil fractions, free or within different aggregate structures. I found that roots, which were lower quality than leaves, decomposed more slowly but contributed more efficiently to total SOM formation than leaves. However, leaves contributed more to the stable SOM pool (i.e. associated to minerals) while roots contributed more to less stable fractions (i.e. light particulate organic matter). Additionally, sorghum is known to produce roots to a depth of 2 meters. There is limited understanding of how roots deeper in the soil (e.g., below 30 cm) lead to SOM formation and stabilization. In Chapter 3, I used the same microcosm approach as in Chapter 2, with roots that were incubated up to a 90 cm depth to better understand how depth influences the ability of roots to contribute to the formation of SOM and what role aggregates play in this process. Results of this study showed that differences in root decomposition dynamics with depth resulted in greater accrual of root litter C in more stable mineral associated SOM pools in the surface depth while there was slower decomposition and greater accrual in the less stable particulate organic matter fractions in the deep soil. Interestingly, most of the stable fraction was recovered within soil aggregates, particularly microaggregates. The results of these experiments emphasized the important role of microaggregates in modulating SOM dynamics. In Chapter 4, I used the information gleaned from Chapters 2 and 3 as well as advances in the SOM research community to speculate on the role of aggregation, specifically microaggregates, in moderating SOM formation by presenting a conceptual framework that integrates aggregates within our current understanding of particulate and mineral associate SOM dynamics. Overall, my dissertation addresses fundamental questions about our ability to increase SOM levels and resulting soil C accrual through the production of a deep-rooted crop through a field incubation. At the same time, I have connected these relevant results to the broader SOM research community by presenting a novel conceptual model that advances our current SOM framework. My hope is that this will be a valuable contribution to the field and spark discussion and future research.
Open Access
Reforestation practices and microsite effects on the performance of contrasting sympatric tree species: a case-study for adaptive silviculture
(Colorado State University. Libraries, 2019) Hill, Edward, author; Ex, Seth, advisor; Nagel, Linda, committee member; Fonte, Steven, committee member
In the central-southern Rocky Mountain region, warming climate in low-elevation Engelmann spruce forests may limit future viability of spruce but favor sympatric species like ponderosa pine, prompting consideration of both species in adaptive reforestation efforts. We used a planting experiment to systematically evaluate survival and root growth of these contrasting species to microsite conditions resulting from silvicultural regeneration treatments in a spruce forest on the Uncompahgre Plateau, Colorado. Our assessment targeted the effects of varying levels of canopy cover generated by different regeneration treatments, paired with and without microsite shelter from coarse woody debris. For explaining survival, we also considered the potential for covarying microsite influences of vegetation, soil, or litter cover, soil moisture and depth, surrounding natural tree regeneration, and seedling size. Survival of pine was twice that of spruce, but the relative effects of microsite variables were similar, possibly due to the severe drought during our study and the stress of first-season establishment. Coarse woody debris shelter benefitted survival of both species, likely from shading of succulent stem tissue and improved soil moisture retention. Influences of canopy cover were comparatively indistinct overall, which may reflect reduced capacity for temperature and moisture buffering on extremely dry sites. Survival was also strongly negatively affected by seedling height, suggesting a potential benefit of lower above-to-belowground biomass ratios for establishment in stressful environments. Root growth was seemingly limited by light for both species in the most dense, unharvested canopy environments, and for pine in coarse woody debris shelter. Our results imply that adaptive reforestation efforts in similar environments should consider more drought-adapted, sympatric species as viable alternatives or supplements to moisture-dependent species at their current lower range limits. Additionally, our results show that first-season seedling survivorship is strongly dependent on facilitating influences of adjacent, non-living shelter, especially compared to canopy cover effects, and seedling development prior to outplanting, favoring lower shoot-to-root ratios.
Open Access
Role of rhizosphere bacteria and root exudates on the assimilation of phosphorus
(Colorado State University. Libraries, 2022) Pantigoso Guevara, Hugo A., author; Vivanco, Jorge M., advisor; Fonte, Steven, committee member; Davis, Jessica, committee member; Manter, Daniel, committee member
Deficient phosphorus (P) bioavailability in soils is a major challenge for sustainable food production as effective strategies to access unavailable P are limited. Solubilizing-bacteria and root exudate metabolites that solubilize P are promising approaches to increase available P for plants. We hypothesized that compounds in root exudates could elicit the P-solubilization activity of bacteria. To test this hypothesis, the root exudates of Arabidopsis grown in vitro under sufficient and deficient P conditions were characterized using GC-MS. We tested the ability of previously screened root exudates to solubilize plant-unavailable P in vitro. In parallel, potential P-solubilizing bacteria were isolated from the rhizosphere of wild potatoes using conventional microbiology techniques. The bacteria strains were tested, both individually and in consortia, for their ability to solubilize organic (phytin) and inorganic (calcium) P sources in vitro and in planta. Lastly, selected root exudate compounds were incubated together with P-solubilizing bacteria, and bacterial growth, P solubilization activity, and plant growth were evaluated. Our results demonstrate that malic, nicotinic, and 3-hydroxypropionic acids improved solubilization of P as compared to a control. Likewise, the bacterial strains E. cloacae, P. pseudoalcaligenes, and B. thuringiensis enhanced plant growth and P content with additions of plant-unavailable P. Furthermore, we found that threonine and 4-hydroxybutyric acid elicit P solubilization in all bacteria, under both organic and inorganic sources, independent of bacterial growth. Subsequent exogenous application of threonine to soils improved plant root growth, enhanced nitrogen and phosphorus content in roots and increased available levels of potassium, calcium, and magnesium in soils. Altogether, our findings expand on the function of exuded specialized compounds and suggest approaches to effectively recover residual P from soil, improving crop growth and nutrition.
Open Access
Soil nematode community response to climate change and associated alterations to precipitation and vegetation
(Colorado State University. Libraries, 2021) Ankrom, Katharine Elizabeth, author; Wall, Diana, advisor; Fonte, Steven, committee member; Knapp, Alan, committee member; Lockwood, Dale, committee member
Understanding of the belowground grassland response to climate change is much more limited than aboveground responses. This disparity in knowledge is partially due to the vast diversity in species in belowground ecosystems and the overwhelming task of identifying the roles and processes associated with each. Soil nematodes represent the most abundant soil fauna on earth and are exceptional in that they occupy every trophic level, contain multiple life history strategies, and are relatively easy to extract and identify from soil. Moreover, nematode activity (e.g. feeding) directly regulates the size and function of fungal and bacterial populations thus indirectly impacting the rates of carbon and nitrogen turnover. Determining the abundance of each nematode genera in a soil sample can allow for calculation of ecological indices that can further explore the trophic complexity, energy pathways, and both the sensitivity and resilience of soil nematode communities to stress and disturbance. Therefore studying soil nematode communities provides a means for gaining important insights about poorly understood belowground responses to altered environments. The aim of this dissertation is to expand our knowledge of soil community dynamics in grasslands in the face of extreme precipitation changes and possible vegetation shifts. In the first chapter of this dissertation, I introduce the importance of grassland ecosystems and the challenges looming from climate change. Next I highlight the two scenarios in which my research is based and give the details on how utilizing nematode data can answer these questions. The second chapter of this dissertation addresses the question: Can nematode trophic analysis reveal associations between vegetation cover types? This study revealed striking differences in the abundances of fungivores and the combined omnivore/predator trophic groups found under the dominant grass compared to both an invasive forb and bare soil cover types. In the third chapter a focus on the most well-studied nematode trophic group; plant parasitic nematodes (PPN) sought to determine if different feeding strategies lead to distinct responses in precipitation treatments across three grassland sites. This research aimed to understand if host plants will have an increased burden harboring greater PPN populations along with increased water stress. Our results showed that the response of PPN feeding type abundance, functional guild, and herbivory index to precipitation was site dependent, a finding not previously studied. Building on the findings of Chapter 3, Chapter 4 utilized the entire soil nematode community and calculated indices to see how the different grassland types; arid, semiarid, and mesic would respond to the same precipitation treatments. Specifically, I tested if nematodes would be effective indicators of the soil community to changes in rainfall events. The results of this study showed the importance of genera level resolution and suggests that the sensitivity of these indices allows for ecological interpretation of belowground function and status in a natural setting. A finding that is especially pertinent, as these grasslands will not respond to precipitation alterations similarly and will therefore require unique mitigation strategies. In summary, with both field and laboratory work my PhD project has: 1) found associations between nematode trophic group abundance and vegetation cover types; 2) revealed the different response of grassland ecto-and endoparasitic nematodes to manipulated rainfall across a precipitation gradient; 3) quantified the herbivory index of a PPN population in response to precipitation treatments across three grassland sites; and 4) demonstrated the sensitivity of nematode ecological indices and found indicator genera in three grassland sites with manipulated precipitation treatments. Together these results bolster our knowledge of how soil nematode communities will respond to climate change and highlight their potential role for monitoring and influencing grassland ecosystem dynamics into the future.

Browsing by Author "Fonte, Steven, committee member"

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