Browsing by Author "Cotrufo, Francesca, committee member"

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Open Access
A binary approach to the analysis of prehistoric bison distribution and paleoecology in northern Colorado and southern Wyoming
(Colorado State University. Libraries, 2014) McKetta, Suzanne B., author; LaBelle, Jason M., advisor; Glantz, Mica, committee member; Cotrufo, Francesca, committee member
Bison exploitation is at the heart of prehistoric hunter-gatherer subsistence on the Great Plains and can reveal robust information regarding patterns of migration, chronology, and variability in paleoclimate. However, despite association with human subsistence practices, bison population and distribution patterns across time and space are unclear. This thesis presents a study of prehistoric bison distribution and population ecology in archaeological and natural contexts in northern Colorado and southern Wyoming. Two methods are used here to reconstruct the diet and distributions of prehistoric bison populations. The first method involves identifying the known distribution of bison in archaeological and natural settings in the study area through an analysis of archival documentation. Cultural chronologies based on archaeological associations have long been valuable in regional research, but can be imprecise and of insufficient resolution for constructing detailed sequences of prehistoric events. Therefore, to expand knowledge of the regional archaeological distribution of bison, this research utilized a total of 272 archaeological sites containing faunal remains. In addition, 291 calibrated radiocarbon dates were used to compile and analyze bison presence and absence through sum probability distributions and statistical analyses. The second method explores the paleoecology of bison through the use of carbon (13C/12C) and nitrogen (15N/14N) stable isotopes analysis of bone collagen from 35 prehistoric bison specimens. Stable isotopes analysis helps to characterize bison distribution and ecology through reconstruction of bison dietary forage and is compared with paleoclimate data in order to identify trends in bison migration and population patterns. This study adds significant chronological information to the regional record of bison presence in northern Colorado and southern Wyoming and helps to correlate bison distribution patterns with the paleoclimate record.
Open Access
Addressing nitrogen and water availability challenges in semi-arid maize cropping systems
(Colorado State University. Libraries, 2025) Donovan, Tyler, author; Schipanski, Meagan, advisor; Comas, Louise, advisor; Cotrufo, Francesca, committee member; Conant, Richard, committee member
In many parts of the world, access to irrigation is threatened as competition for water resources increases and water availability decreases. This includes the Great Plains Region of the U.S. where roughly 25% of U.S. irrigated cropland is located. Loss of irrigation threatens global food security as irrigated lands are highly productive; accounting for just 20% of cropland but responsible for 40% of agricultural production. Thus, there is urgent need for achieving high yields with less water. Many studies have been conducted to increase crop productivity with limited water, but the interactive effect of nitrogen (N) and water availability on crop response has received limited attention with variable conclusions. Additionally, the effect of varying N availability under different water levels on soil N mineralization (Nmin), contribution of Nmin to crop N uptake, and the recovery and fate of N fertilizer has been largely unexplored. Soil Nmin is an important source of N for crops therefore, quantifying Nmin rates and contribution to crop N uptake is important for N management. Additionally, minimizing N losses is an important goal for agroecosystems as N losses come with an economic and environmental cost. The general aim of my dissertation was to explore the effects of N availability on soil N cycling and crop response within maize cropping systems, an important irrigated crop in the Great Plains Region, under contrasting water availability. Examining field data from 2021 – 2023, I found that maize grain yield response to N was dependent on water. When water was limited, maize grain yield was maximized with ~ 200 kg N ha-1, with excess N being detrimental for all three growing seasons. This was true even during 2023, which was an extremely wet year, and had reduced N fertilizer rates due to higher pre-plant soil residual N. Maize N uptake continued to increase with N availability beyond 200 kg N ha-1, showing maize was not co-limited by N when water was limited water. Rather, excess N and subsequent N uptake had negative effects on root and shoot growth, potentially via effects on stomatal conductance and photosynthesis, leading to yield declines. Soil net Nmin surrounding peak maize N uptake exhibited an N × water interaction where increased N fertilization rate decreased net Nmin with full water but increased with N rate when water was limited. Soil N-acquiring enzyme activity, a proxy for gross Nmin, had a different response where it increased with N regardless of water. This could suggest N fertilizer increased plant available N through increased microbial mediated depolymerization of N containing compounds in the soil. The different responses were likely due to the exclusion of living maize plants and maize N uptake in the net Nmin incubation tubes. Across the entire season, both net Nmin and enzyme activity tended to be higher during maize vegetative stages than during early reproductive stages when N demands are the highest. A 15N tracer study revealed that recovery was high, and losses low and unaffected by N and water treatments. This suggests that lower N rates should have lower N losses. Maize N uptake increased with N rate, but primarily from 15N fertilizer, rather than non-N fertilizer sources such as soil Nmin. This could be due to the asynchrony between soil N supply and maize N demand. Additionally, microbial biomass N at the end of the season suggests that immobilization occurred, but primarily for non-N fertilizer sources. Immobilization of non-N fertilizer sources later in the season when soil Nmin rates are low and maize N demands are high likely led to maize acquiring N from N fertilizer to meet its N requirements. The wet growing season during 2023 made the water treatments negligible. Future studies with treatment differences in water availability could reveal how water availability affects fate and recovery of N fertilizer, as well as contribution of non-N fertilizer sources, such as soil Nmin, to crop N uptake with different N fertilizer rates. Overall, my findings show that water limited maize is not co-limited by N, and that excess N is detrimental to maize growth and yield. For limited water, reducing N fertilizer rate should reduce N losses while still maximizing yields and resource use efficiency. Reducing N fertilizer rate when water is fully available and maize N demands are high may be challenging. Higher N fertilizer rates appeared to increase bioavailable N through increased soil enzyme activity, however maize was not able to significantly increase uptake of N from sources other than the 15N fertilizer applied, such as soil Nmin, regardless of treatment. Maize was more reliant on N fertilizer rather than non-N fertilizer sources when supplied with high N fertilizer rates, while more reliant on non-N fertilizer sources when supplied with low N fertilizer rates. Management practices that increase internal N cycling, especially later in the season when maize N demands are greater, may help reduce the reliance on synthetic N fertilizer inputs thus reducing N losses without sacrificing productivity. Using field experiments from 2021 – 2023 I found that maize grain yield response to N was dependent on water. When water was limited, maize grain yield was maximized with ~ 200 kg N ha-1, with excess N being detrimental for all three growing seasons. This was true even during 2023, which was an extremely wet year, and had reduced N fertilizer rates due to higher pre-plant soil residual N. With limited water, maize N uptake continued to increase with N availability beyond 200 kg N ha-1, showing maize was not co-limited by N. Rather excess N and subsequent N uptake had negative effects on root growth, and potentially stomatal conductance and photosynthesis leading to yield declines. Soil net Nmin surrounding peak maize N uptake exhibited an N × water interaction where increased N fertilization rate decreased net Nmin with full water but increased with N rate when water was limited. Soil N-acquiring enzyme activity, a proxy for gross Nmin, had a different response where it increased with N regardless of water. This could suggest N fertilizer increased plant available N through increased microbial mediated depolymerization of N containing compounds in the soil. The different responses were likely due to the exclusion of living maize plants and maize N uptake in the net Nmin incubation tubes. For the entire season both net Nmin and enzyme activity tended to be higher during maize vegetative stages as opposed to early reproductive stages when N demands are the highest. A 15N tracer study revealed that recovery was high, and losses were low and unaffected by the N and water treatments. This suggests that lower N rates should have lower N losses. Maize N uptake increased with N rate, but primarily from 15N fertilizer, rather than non-N fertilizer sources such as soil Nmin. This could be due to the asynchrony between soil N supply and maize N demand. Additionally, microbial biomass N at the end of the season suggests that immobilization occurred and primarily occurred for non-N fertilizer sources. Immobilization of non-N fertilizer sources later in the season when soil Nmin rates are lower, and maize N demands are high, likely led to maize acquiring N from N fertilizer to meet its N requirements. The wet growing season during 2023 made the water treatments negligible. Future studies with more extreme water differences will help reveal how water availability affects fate and recovery of N fertilizer, as well as contribution of non-N fertilizer sources, such as soil Nmin, to crop N uptake with different N fertilizer rates. Overall, my findings show that water limited maize is not co-limited by N, and that excess N is detrimental to maize growth and yield. For limited water, reducing N fertilizer rate should reduce N losses while still maximizing yields and resource use efficiency. Reducing N fertilizer rate when water is fully available and maize N demands are high may be challenging. Higher N fertilizer rates appeared to increase bioavailable N through increased soil enzyme activity, however maize was not able to significantly increase uptake of N from sources other than the 15N fertilizer applied, such as soil Nmin, regardless of treatment. Maize was more reliant on N fertilizer rather than non-N fertilizer sources at the higher N fertilizer rate, while the lower N fertilizer rates were more reliant on non-N fertilizer sources. Management practices that increase internal N cycling, especially later in the season when maize N demands are greater, may help reduce the reliance on synthetic N fertilizer inputs thus reducing N losses without sacrificing productivity.
Open Access
Conservation management practice impacts on rangelands in California
(Colorado State University. Libraries, 2025) Banuelos, Ashley, author; Paustian, Keith, advisor; Cotrufo, Francesca, committee member; Havrilla, Caroline, committee member
Rangelands hold potential for mitigating climate change through soil organic carbon (SOC) storage. SOC plays a critical role in plant growth, soil structure and water retention, yet significant degradation of the world's soils poses major risks to forage production and water quality. To address this, California has promoted the adoption of conservation practices to restore SOC storage. Given California's diverse climatic zones, climate-specific conservation strategies are necessary, as climate influences the effectiveness of different practices. These practices not only affect overall SOC stocks but also influence how SOC is stabilized in the soil, particularly through the formation of SOC fractions - particulate organic carbon (POC) and mineral-associated organic carbon (MAOC). POC generally contributes to the short-term carbon pool due to its rapid turnover however, when microbial activity is limited, its decomposition slows, allowing it to persist in the long-term carbon pool. In contrast, MAOC is more inherently stable and primarily associated with long-term carbon storage. This thesis investigated the effects of three conservation management practices - riparian restoration, tree plantings, and perennial seeding - on SOC storage in California rangelands. We used a retrospective paired-site analysis, comparing 'restored' (i.e., locations where a conservation practice was adopted) and 'unrestored' sites (i.e., a nearby similar location but lacking adoption of a conservation practice). Restored sites varied by the time since conservation practices were adopted, providing a chronosequence approach to estimate SOC and SOC fractions (POC and MAOC) change over time. While overall SOC differences between restored and unrestored sites were inconclusive, clear trends between practice types emerged within the restored sites. In drier regions, perennial seeding had higher POC stock compared to riparian restoration and tree plantings. Climate significantly influenced apparent SOC accrual in tree plantings, with a rate of 3.1 Mg C ha-1 yr-1 observed in moist climates, while in drier climates, SOC stocks were lower in tree planting sites compared to the unrestored sites. However, soil under tree canopies had 9% higher SOC content compared with soil sampled between trees, outside the tree canopy. Canopy cover appeared to promote proportional contributions to both POC and MAOC, highlighting the potential of tree plantings to increase SOC stocks, in relatively cooler, wetter regions. These findings underscore the importance of climate-specific conservation strategies for maximizing carbon storage in rangelands, particularly given the challenges inherent in managing these dynamic ecosystems. The variability in the apparent response to conservation practice adoption from the retrospective paired-site analysis raised questions about potential confounding factors. While this approach offers an alternative to long-term experiments by leveraging existing conservation practices, it introduces inherent uncertainties, particularly concerning prior disturbances that may influence SOC storage. A key assumption of the paired analysis is that vegetation and soils were approximately the same on both sites within a pair before the adoption of conservation practice. However, even when controlling for factors such as soil type, topography, and current vegetation, differences in past land use - such as disturbance events occurring at one site but not the other - could have led to SOC stock differences prior to when conservation practices were implemented. These historical land-use differences may obscure or exaggerate the measurement inferred impacts of conservation practices, highlighting the need to account for site history when interpreting SOC dynamics in retrospective studies. To address this, we analyzed remote sensing imagery to evaluate site conditions, prior to conservation practice adoption, identifying disturbance events and assessing vegetation cover and soil exposure from historical observations dating back to 1984. Our analysis revealed that 12 out of 36 paired sites experienced a disturbance event, on only one of the sites within a pair, including mastication, tillage, and burn events, potentially confounding the assumption of similar SOC stocks prior to the time of conservation practice adoption. Additionally, restored sites with significant pre-treatment differences in vegetation cover and bare soil exposure often originated from more degraded conditions compared to the unrestored site in the pair. This suggests a potential selection bias toward implementing conservation practices on more degraded lands, emphasizing the need to account for pre-existing site conditions in retrospective studies. Integrating remote sensing into paired-site analyses enhances the accuracy of assessments of conservation practice effectiveness assessments on SOC dynamics. This study underscores the importance of both climate considerations in conservation management and the value of remote sensing tools for improving SOC research methodologies.
Open Access
Drought tolerance and implications for vegetation-climate interactions in the Amazon forest
(Colorado State University. Libraries, 2012) Harper, Anna Biagi, author; Denning, Alan Scott, advisor; Randall, David, committee member; Kummerow, Christian, committee member; Cotrufo, Francesca, committee member
On seasonal and annual timescales, the Amazon forest is resistant to drought, but more severe droughts can have profound effects on ecosystem productivity and tree mortality. The majority of climate models predict decreased rainfall in tropical South America over this century. Until recently, land surface models have not included mechanisms of forest resistance to seasonal drought. In some coupled climate models, the inability of tropical forest to withstand warming and drying leads to replacement of forest by savanna by 2050. The main questions of this research are: What factors affect forest drought tolerance, and what are the implications of drought tolerance mechanisms for climate? Forest adaptations to drought, such as development of deep roots, enable Amazon forests to withstand seasonal droughts, and the maintenance of transpiration during dry periods can affect regional climate. At high levels of water stress, such as those imposed during a multiyear rainfall exclusion experiment or during interannual drought, trees prevent water loss by closing their stomata. We examine forest response to drought in an ecosystem model (SiB3 - the Simple Biosphere model) compared to two rainfall exclusion experiments in the Amazon. SiB3 best reproduces the observed drought response using realistic soil parameters and annual LAI, and by adjusting soil depth. SiB3's optimal soil depth at each site serves as a proxy for forest drought resistance. Based on the results at the exclusion sites, we form the hypothesis that forests with periodic dry conditions are more adapted to drought. We parameterize stress resistance as a function of precipitation climatology, soil texture, and percent forest cover. The parameterization impacts carbon and moisture fluxes during extreme drought events. The loss of productivity is of similar magnitude as plot-based measurements of biomass loss during the 2005 drought. Changing stress resistance in SiB3 also affects surface evapotranspiration during dry periods, which has the potential to affect climate through changing sensible and latent heat fluxes. We examine the effects of forest stress resistance on climate through coupled experiments of SiB3 in a GCM. In a single column model, we find evidence for a more active hydrologic cycle due to increased stress resistance. The boundary layer responds through changes in its depth, relative humidity, and turbulent kinetic energy, and the changes feed back to influence wet season onset and intensity. In a full global GCM, increased stress resistance often decreases drought intensity through enhanced ET and changes to circulation. The circulation responds to changes in atmospheric latent heating and can affect precipitation in the South Atlantic Convergence Zone.
Open Access
Integrated assessment of agricultural ecosystems using simulation-optimization and machine learning
(Colorado State University. Libraries, 2018) Nguyen, Trung H., author; Paustian, Keith, advisor; Cotrufo, Francesca, committee member; Kelly, Eugene, committee member; Leisz, Stephen, committee member; Davies, Christian, committee member
Agriculture provides many ecosystem services to human society but is also a major cause of environmental degradation. The key challenge of modern agricultural production is to meet projected increases in global demands for food, water, and energy in sustainable ways. Sustainable agricultural production requires integrated decision-support tools and rigorous assessment methods to improve the efficiency of natural resource management while minimizing its impacts to society and long-term ecosystem health. This dissertation focuses on developing methodology and modeling tools to support decision-making for sustainable agricultural resource management. The Millennium Ecosystem Assessment is used as a guiding framework for all the model development. The dissertation balances between the communication of the integrated assessment methodology and the presentation of the modeling techniques through four independent case studies. The first study links biogeochemical models with life cycle assessment (LCA) to explore the impact of regionally-specific ecosystem carbon stock changes associated with cassava cultivation for ethanol production in Vietnam. The second study couples biogeochemical models with GIS and optimization algorithms to conduct a high-resolution, spatially-explicit trade-off analysis of ecosystem services for irrigated corn production systems in the South Platte River Basin, Colorado, USA. The derived modeling platform is named the "Agricultural Ecosystem Service Optimization" (Ag-EcoSOpt). The third study integrates LCA into the Ag-EcoSOpt for a life-cycle-based optimization of feedstock landscape design for a hybrid corn grain- and stover-based ethanol production system at Front Range Energy biorefinery, Windsor, Colorado, USA. The last study develops a surrogate-based optimization framework for Ag-EcoSOpt to reduce the computational burden of large-scale landscape analyses. The study explores the trade-offs among seven management objectives of the irrigated corn production systems in Colorado, USA at different spatial scales.
Embargo
Regenerative agriculture and soil carbon storage in the Upper Corn Belt
(Colorado State University. Libraries, 2025) Ellis, Elizabeth M., author; Paustian, Keith, advisor; Cotrufo, Francesca, committee member; Schipanski, Meagan, committee member; Manning, Dale, committee member
Land use conversion, agricultural mismanagement, and topsoil erosion have depleted global soil organic carbon (SOC) stocks in the top two meters of soil by an estimated 133 petagrams (Pg), resulting in a significant SOC debt. Regenerative cropping practices, such as no-till and cover cropping, are recognized for their potential to enhance soil organic carbon (SOC) stocks and bolster soil health, all while allowing producers to maintain commodity crop production systems. Evaluations of these practices are typically conducted through agricultural experiments with randomized and replicated statistical designs. While these experiments are essential for understanding the mechanisms behind changes in soil properties as a function of management, they often fail to capture the complexities of diverse agricultural settings and management choices. Through an interdisciplinary, system-level study of commercial farms in the Upper Corn Belt region, I evaluated how regenerative management affects SOC storage, erosion processes, and microbial community structure. Factors such as topography, time since adoption of regenerative practices, climate, and soil texture significantly influenced SOC stocks and microbial community structure. Slope and historical erosion emerged as a key control on SOC stocks, which is largely overlooked in current process-based models. I present a method for coupling estimated soil erosion with the DayCent model to improve simulations of SOC stocks on farmland with slight slopes. I also discuss the unique challenges of simulating commercial farm scenarios using data collected from real-world farmers. The dissertation concludes with a collaborative, social science chapter on the impact of social networks on the adoption of regenerative practices in Iowa agricultural communities. In summary, this dissertation contributes to our knowledge of regenerative agriculture and its impacts on SOC storage, soil microbial diversity, and social connections in agricultural communities, including unique methods to measure, evaluate, and model these impacts.
Open Access
Temperature sensitivity as a microbial trait
(Colorado State University. Libraries, 2017) Alster, Charlotte J., author; von Fischer, Joseph, advisor; Cotrufo, Francesca, committee member; Smith, Melinda, committee member; Wallenstein, Matthew, committee member
Reaction rates in biological systems are strongly controlled by temperature, yet the degree to which temperature sensitivity varies for different enzymes and microorganisms is being largely reformulated. The Arrhenius equation is the most commonly used model over the last century that predicts reaction rate response with temperature. However, the Arrhenius equation does not account for large heat capacities associated with enzymes in biological reactions, thus creating significant deviations from predicted reaction rates. A relatively new model, Macromolecular Rate Theory (MMRT), modifies the Arrhenius equation by accounting for the temperature dependence of these large heat capacities found in biological reactions. Using the MMRT model I have developed a novel framework to assess temperature sensitivity as a biological trait through a series of experiments. This work provides evidence that microbes and enzymes can have distinct heat capacities, and thus distinct temperature sensitivities, independent of their external environment. I first assessed temperature sensitivity of soil CO2 production from different soil microbial communities and then worked with pure cultures to examine temperature sensitivity of enzyme activities from soil microbial isolates. From these experiments I determined that temperature sensitivity varies based on genetic variation of the microbe and substrate type as well as examined the importance of using MMRT over the Arrhenius equation. Finally, I used a meta-analysis to analyze the distribution of temperature sensitivity traits to look across a variety of biological systems (e.g., the food industry, wastewater treatment, soils). I found that temperature sensitivity traits vary with organism type, environment, process type, and biodiversity. Exploring temperature sensitivity as a trait allows for new insights of soil microbes from an ecological perspective as well has the potential to inform ecosystem climate models.
Open Access
The effects of temperature and moisture on alpine microbial processes across a gradient of soil development
(Colorado State University. Libraries, 2012) Osborne, Brooke Bossert, author; Baron, Jill, advisor; Cotrufo, Francesca, committee member; von Fischer, Joseph, committee member; Wallenstein, Matthew, committee member
Alpine ecosystems are being transformed by global change. Climate change and atmospheric nitrogen deposition are exposing soils to novel temperature regimes, melting alpine glaciers, altering precipitation patterns, and directly introducing bioavailable nutrients. Because microbial communities are important drivers of nutrient cycling and ecosystem function in the alpine, and because temperature, moisture and nutrient availability are primary controls of microbial abundance and activity, it is likely that microbial linkages exist between global change and ecosystem-level consequences of global change in alpine regions. Deglaciation in high-elevation regions incrementally exposes soils to primary succession, which creates a wide range of soil environments. Yet, little is understood about these unusual environments' respective microbial communities or how they respond to the influence of global change. This research studied the effects of changing temperature and moisture controls on microbial carbon and nitrate (NO3-) processing in a range of alpine soils. The soils were collected from a watershed that exhibits characteristics of nitrogen saturation as a result of atmospheric nitrogen deposition. Glacial outwash, talus, and meadow soils were characterized by physical, chemical and biological properties. Soil temperature regimes were highly variable in the field, with some soils experiencing great diurnal fluctuations, while others remained consistently cold. The response of microbial community size, structure, activity and behavior to warming and changing soil moisture was addressed with laboratory incubations. Microbial community size and nutrient availability increased with increasing soil organic carbon. Microbial activity in all soils increased with temperature and moisture, as evidenced by total and microbial biomass-specific rates of respiration. However changes in microbial biomass carbon and parameters of community structure and behavior differed among the soils. This indicated that the soils responded using individual mechanisms to changing microclimate conditions during the incubations. The net production of NO3- occurred in all soils under all experimental conditions, however the rate at which NO3- was produced responded differently to temperature and moisture treatments. This suggests that global change may affect biological controls of NO3- availability in the alpine.
Open Access
Utilizing plant genetic resources for pre-breeding of water-efficient sorghum: genetics of the limited transpiration trait
(Colorado State University. Libraries, 2022) Cerimele, Gina, author; Morris, Geoffrey, advisor; Cotrufo, Francesca, committee member; McKay, John, committee member
Shifting precipitation patterns driven by the changing climate threaten productivity of dryland agricultural systems. Increasing the efficiency of water use by crops grown in dryland regions, such as sorghum (Sorghum bicolor), is a target for plant breeding to address this issue. c variants conferring efficient water use in sorghum may be found within collections of plant genetic resources (PGR). However, tropical sorghum PGR require adaptation to the target temperate environment to begin the pre-breeding trait discovery process. The landmark Sorghum Conversion Program unlocked diverse sorghum genetics for temperate breeding by adapting tropical African lines to temperate height and maturity standards. In the U.S. Sorghum Belt, spanning South Dakota to central Texas, the limited transpiration (LT) trait could provide growers a 5% yield increase in water-limited conditions with high vapor pressure deficit (VPD) according to crop modeling. To transfer the LT trait into commercial breeding programs, an elite donor line must be developed. Characterizing the genetic architecture of LT informs markers and breeding strategy for development of an elite donor. To characterize the genetic architecture of LT, two biparental recombinant inbred line (RIL) mapping families were developed from crossing putative LT parents SC979 and BTx2752 by putative non-LT parent RTx430. For this study, the families were grown together as a mapping population in three locations (continental-humid eastern Kansas, semi-arid western Kansas, and semi-arid Colorado) in one year. The families were phenotyped for the LT trait using UAS- collected thermal imaging and canopy temperature as a proxy. The families were initially designed with the goal of controlling phenotypic covariates of canopy temperature associated with height and flowering time, like neighbor-shading and artifactual temperature inflation related to panicle imaging. To test whether the family design controlled for height and flowering time covariates, the populations were phenotyped for both traits. High broad-sense heritability (H2) > 0.86 for all traits and families across locations indicates that the traits are not fixed. However, phenotypic distributions reveal that most lines are within an agronomically-relevant range that limits confounding covariates. Using DArTseq-LD genotyping data, GWAS analyses of height and flowering time reveal putatively significant marker-trait associations (MTA) with known loci underlying height and maturity in sorghum. These results collectively indicate that, while genetic variation for height and flowering exist in the LT mapping families, the resulting phenotypes are homogeneous enough to be suitable for LT genetic mapping. To test hypotheses on the monogenic, oligogenic, or polygenic architecture of the LT trait, canopy temperature data collected by the UAS-thermal imaging missions was used. Non-zero H2 of canopy temperature in most location-timepoints indicates genetic variation is present for LT in the population. Continuous phenotypic distributions imply a quantitative architecture. GWAS analyses revealed moderate marker-trait association peaks visible within timepoints and across locations, indicating oligogenic architecture of LT. Some of those peaks also colocalize with sorghum homologs of aquaporin genes in Arabidopsis thaliana, suggesting that aquaporin variation could be a molecular basis underlying the trait. These results provide a basis for marker-assisted selection in developing an LT donor line.