Browsing by Subject "Drought"
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Item Abiotic Stress Effects on Physiological, Agronomic and Molecular Parameters of 1-MCP Treated Cotton Plants(2012-02-14) Da Costa, Vladimir AzevedoAbiotic stresses impact cotton (Gossypium hirsutum L.) affecting physiological, molecular, morphological, and agronomic parameters. One of the main yield components in cotton production is the number of bolls per unit area. However, boll abortion is increased when cotton experiences various stresses during its reproductive development that can consequently reduce lint yield. Prior to abscission, a burst in ethylene is observed which may be assumed to be the signal necessary to initiate abscission of that particular structure. It is desirable to prevent fruit loss that may be induced by the peak in ethylene prior to abscission. One potential option to cope with the loss of cotton reproductive structures is the use of ethylene inhibitors. The overall objective of this research was to establish if 1-MCP would synergize, ameliorate, or overcome the effects of abiotic stresses on physiological, molecular, morphological, and agronomic parameters of cotton plants under abiotic stress conditions in field and greenhouse studies. Field and greenhouse experiments were conducted from 2007 to 2009 as a randomized complete block design with four replications in the field, and as a 2x2 factorial design in a split-block arrangement with five replications in the greenhouse. Field treatments consisted of three rates of 1-MCP (0, 25 and 50 g a.i. ha-1) in combination with a surfactant applied at mid-bloom. One day later, ethephon (synthetic ethylene) was applied as a source of abiotic stress. Greenhouse treatments were two 1-MCP rates (0 and 2.4 g a.i. L-1) during a14-h overnight incubation that were then subjected to two water regimes (control and stressed) as the source of stress. Greenhouse assessments with gas exchange analysis revealed that water deficit stress started to impact plants at a moderate water stress, 5 days after 1-MCP treatment (DAT) and a water potential (?w) of -1.4 MPa. The 1-MCP increased water use efficiency in well-watered plants at 1 DAT. Many of the yield components, plant mapping, and biomass parameters investigated were detrimentally affected by drought. However, drought increased specific leaf weight, chlorophyll content, and harvest index. The 1- MCP improved reproductive node numbers mainly during drought, but did not lead to a better harvest index, since 1-MCP caused high abscission. Ethylene synthesis and molecular investigations in greenhouse conditions showed that at 1, 5, 7, 9, 11, and 13 DAT, ethylene production of stressed plants never exceeded those of control plants. As the ?w became more negative ethylene production rate was reduced among stressed plants independent of 1-MCP treatments. However, at 1 DAT 1-MCP caused a transient climacteric stage (ethylene synthesis increase) in leaves. The two primary genes associated with ethylene synthesis, ACS6 (1-aminocyclopropane-1-carboxylic acid synthase) and ACO2 (1-aminocyclopropane-1-carboxylic acid oxidase) expression generally showed an identical trend that supported the ethylene synthesis data. The 1-MCP did not ameliorate any of the detrimental effects of water stress on gas exchange at the point where it started to impact cotton plants. 1-MCP had little or no positive effect on plant mapping, dry matter partitioning and chlorophyll content. Field investigations revealed that at harvest, fruit set in the upper portion of the canopy was influenced by 1- MCP. This portion of the canopy had a greater number of full size, yet immature bolls, which potentially could have had a positive influence on the lint yield. However, ethephon caused the highest lint yield since ethephon treated plants had more open bolls and total bolls in the lower canopy at harvest.Item Characterization of drought in Texas using NLDAS soil moisture data(2013-05) Sullivan, John R., Jr.; Maidment, David R.From June to August 2011, Texas experienced the hottest summer ever recorded in the history of the United States, and the state suffered a water shortage that made its vulnerability to drought painfully plain. This disaster sparked new interest in methods of defining drought severity, especially with regard to the variation of soil moisture levels. This thesis assesses the suitability of information from the North American Land Data Assimilation System (NLDAS), an assemblage of land surface models forced with observations data, for quantifying soil moisture levels in Texas. The potential for combining NLDAS data with the Soil Survey Geographic (SSURGO) Database’s available water capacity data is explored. It is discovered that because NLDAS is a hydrological model and SSURGO an agricultural dataset, they employ different definitions of soil moisture storage. Moreover, the temporal variation of soil moisture levels in the SSURGO polygons cannot be inferred from NLDAS data due to the vastly different spatial scales of the two datasets. A relative measure of soil saturation from 0–100% is developed instead and determined to be a more useful indicator of drought than the soil moisture level itself. Calculated solely from NLDAS data, it is used to map the severity of drought in Texas, with the results displayed at the county scale. The temporal variation in soil moisture storage across the state is compared with variations in the gravity anomaly measured by NASA’s Gravity Recovery and Climate Experiment (GRACE) satellites and variations in Texas surface water reservoir levels, both of which are physical measurements of water storage changes. This analysis suggests that the NLDAS data, which is derived from a land surface model, accurately describes subsurface moisture variations. Also, the GRACE gravity anomaly data reveals that during the 2011 drought, the total water storage in Texas was approximately 100 cubic kilometers less than normal. NLDAS data indicates that more than 50% of this deficit was due to losses from the top one meter of the state’s soils.Item Development of indices for agricultural drought monitoring using a spatially distributed hydrologic model(Texas A&M University, 2005-11-01) Narasimhan, BalajiFarming communities in the United States and around the world lose billions of dollars every year due to drought. Drought Indices such as the Palmer Drought Severity Index (PDSI) and Standardized Precipitation Index (SPI) are widely used by the government agencies to assess and respond to drought. These drought indices are currently monitored at a large spatial resolution (several thousand km2). Further, these drought indices are primarily based on precipitation deficits and are thus good indicators for monitoring large scale meteorological drought. However, agricultural drought depends on soil moisture and evapotranspiration deficits. Hence, two drought indices, the Evapotranspiration Deficit Index (ETDI) and Soil Moisture Deficit Index (SMDI), were developed in this study based on evapotranspiration and soil moisture deficits, respectively. A Geographical Information System (GIS) based approach was used to simulate the hydrology using soil and land use properties at a much finer spatial resolution (16km2) than the existing drought indices. The Soil and Water Assessment Tool (SWAT) was used to simulate the long-term hydrology of six watersheds located in various climatic zones of Texas. The simulated soil water was well-correlated with the Normalized Difference Vegetation Index NDVI (r ~ 0.6) for agriculture and pasture land use types, indicating that the model performed well in simulating the soil water. Using historical weather data from 1901-2002, long-term weekly normal soil moisture and evapotranspiration were estimated. This long-term weekly normal soil moisture and evapotranspiration data was used to calculate ETDI and SMDI at a spatial resolution of 4km ?? 4km. Analysis of the data showed that ETDI and SMDI compared well with wheat and sorghum yields (r > 0.75) suggesting that they are good indicators of agricultural drought. Rainfall is a highly variable input both spatially and temporally. Hence, the use of NEXRAD rainfall data was studied for simulating soil moisture and drought. Analysis of the data showed that raingages often miss small rainfall events that introduce considerable spatial variability among soil moisture simulated using raingage and NEXRAD rainfall data, especially during drought conditions. The study showed that the use of NEXRAD data could improve drought monitoring at a much better spatial resolution.Item Drought over the past century in Texas and New Mexico: reducing inhomogeneities in long-term climate records via statistical methods to study drought(Texas A&M University, 2008-10-10) McRoberts, Douglas BrentThis research looks at the past century of Texas and New Mexico climate in order to create datasets sufficient for documenting climatic variations. Inhomogeneities in climate records are defined as variations in climatic records caused by factors other than weather and climate. While there are indirect methodologies for inferring climate records such as tree rings and ice cores, it is the instrumental network that constitutes the most spatially and temporally complete record of land surface climate since the onset of the Industrial Revolution. A statistical method by Sun and Peterson (2005a) called Inverse Weighting of Square Distance (IWSD) will be used to reduce the inhomogeneities in climate records. The National Weather Service Cooperative Observer Program (COOP) network of stations will be used for this analysis. A subset of the extensive COOP network, called the United States Historical Climate Network (USHCN), will be used as a foundation for this study. The analysis and resulting datasets from this climatic study show precipitation trends and periods of drought and will be useful for decisions regarding future policies on drought. The result of the interpolation process was the creation of several COOP and USHCN datasets. Several of the datasets were investigated to determine the spatial characteristics of precipitation over the 20th century in Texas and New Mexico. The datasets are in good agreement that the most severe drought period of the 20th century in Texas and New Mexico was in the 1950s. The frequency of pluvial periods was higher toward the end of the 20th century, with most USHCN stations showing an increasing trend when a linear regression analysis was done on each station's precipitation data.Item The ecology of blue crab (Callinectes sapidus) megalopae in the Mission-Aransas Estuary, Texas : salinity, settlement, and transport(2013-12) Bittler, Kimberly Marie; Buskey, Edward Joseph, 1952-Blue crabs are a widely distributed estuarine species with broad economic and ecological importance. Several studies have linked blue crabs to freshwater inflows, but the precise nature of this link is still uncertain, as blue crabs have a complex life cycle that utilizes both marine and estuarine environments. One potential link between blue crabs and freshwater inflows is during recruitment, when megalopae developing offshore return to estuaries before molting into juvenile crabs. Megalopae swim during the flood tide to ensure delivery into and farther up estuaries. The behaviors regulating selective tidal stream transport (STST) on the flood tide were originally studied in North Carolina in an estuary with regular freshwater inflows and a strong salinity gradient. The model of STST was re-examined in the Mission-Aransas, an estuary with episodic freshwater inflows and salinity gradients ranging from normal estuarine conditions to hypersaline during droughts. The behavioral responses of megalopae to a range of rates of salinity increase were tested, and then modeled onto rates of salinity change observed in the field to determine the theoretical ecological consequences of STST for blue crab populations in the Mission-Aransas Estuary. To validate the ecological trends predicted by the behavioral model of STST, a simple, long-term data set reflecting changes in megalopae abundance is needed. Hog’s hair collectors are a simple and widely used method of quantifying abundance of brachyuran megalopae, including blue crabs. However, the efficiency of hog’s hair collectors in sampling for megalopae is unknown. Several studies have reported poor correlations between settlement on hog’s hair collectors, transport, and abundance of megalopae in the plankton due to disparate temporal scales and potentially turbulence-driven decoupling. Each of these issues were addressed in field and flume experiments, which were used to develop a model for interpreting settlement on hog’s hair collectors in terms of transport and planktonic abundance.Item Effect of drought conditions on the diet of insectivorous bat species: a molecular diet studyKuzdak, Kaitlin Frances; Ammerman, Loren K; Dowler, Robert; Negovetich, Nicholas; Singg, SangeetaThe effect of drought on the diets of four insectivorous bat species (Antrozous pallidus, Myotis thysanodes, M. yumanensis, and Parastrellus hesperus) was assessed using cytochrome oxidase-I mini-barcodes organized into molecular operational taxonomic units. I hypothesized that there would be a significant difference between diet diversity in the drought and non-drought years, the species would feed more opportunistically during the drought year, per optimal foraging theory, and there would be low dietary overlap between years. Fecal samples were collected in Big Bend National Park (Brewster Co., TX). Diet diversity differed between years for all species, excluding A. pallidus. Diet diversity was greater during the drought year for A. pallidus and P. hesperus. Antrozous pallidus exhibited high dietary overlap (0.608) between the years and overlap values for the other three species was low (0.027 - 0.149). Overall, no two bat species in this analysis changed their diet similarly in response to drought conditions.Item Effects of drought on climates in Texas(2016-05) Born, Katie Lynn; Maidment, David R.; McKinney, Daenne C.Drought is a growing global concern with severe ramifications for humanity. Texas is one of many places that faces recurring severe droughts, threatening the livelihood of its people. Within the bounds of Texas there are many different climates, and drought can effect these climates differently. The south east edge of the state tend to have a more humid temperate climate, whereas to the north west it becomes hot and arid. Within one state, the climate goes from subtropical to desert. This opens up the state to a lot of variability as to water supply. This Master's Report investigates the effects that drought has on the varied climates within Texas. Five areas in Texas were chosen to represent the most distinctive climatic shifts. Several hydrologic variables area accessed between regions and drought severity. The hydrologic variables examined are the 2-m above ground temperature, evapotranspiration, latent heat flux, sensible heat flux, net longwave radiation flux, net shortwave radiation flux, total hourly precipitation, and surface runoff. The scope of the analysis is limited to period of January 2000 to January 2013. Two one month periods were selected to highlight changes under dry conditions compared to normal to wet conditions; July 2007 and July 2011, respectively. In all of the areas examined, the earth was shown to be parched and dry after periods of less than average precipitation and more willing to take in water than leave it to be surface runoff. An initial investigation into the climates of the five areas showed that the temperatures in the more southeastern regions were more dramatically affected by the occurrence of drought. When drought came along to these southeastern regions, it transformed the climate into something more similar to that typically found in the northwestern regions. The more humid areas to the south east were consistently more dramatically affected by the drought than the arid regions to the north west. The more arid climates started out more similar to that of a drought ridden zone, leaving less room to change. However, all of the areas are significantly impacted by drought through a declining water supply.Item The effects of drought on predicted air quality in Texas(2015-08) Huang, Ph. D., Ling; Allen, David T.; McDonald-Buller, Elena; Hildebrandt Ruiz, Lea; Fu, Rong; Rochelle, Gary TDrought is a natural disaster that has profound and complex social, economic, and environmental impacts. As drought is predicted to occur more frequently within Texas with changes in future climate, it is critical to understand its impacts on regional air quality as the State endeavors to achieve and maintain attainment with National Ambient Air Quality Standards for ozone and fine particulate matter. Drought-induced changes in various natural systems, including emissions of biogenic hydrocarbons from vegetation and the physical removal of pollutants by vegetation via dry deposition, have the potential to effect air quality. This work characterizes land cover for eastern Texas climate regions during years with severe to exceptional drought conditions as well as years with average to above average precipitation patterns. Variability in meteorological conditions, biogenic emissions, and dry deposition rates is explored with widely applied global and regional models that have been configured specifically for multi-year analysis of eastern Texas conditions. The Comprehensive Air Quality Model with Extensions (CAMx), which has been used for air quality planning and management efforts in Texas, is used to quantify the relative contributions of various physical and chemical processes to ground-level ozone formation and changes in ground-level ozone concentrations during representative drought and wet periods. The analyses indicate that drought influences air quality in complex ways. This work suggests that the two largest drought driven changes to the physical and chemical processes that influence air quality are increased biogenic emissions due to elevated temperatures and decreased air pollutant removal through dry deposition due to changes in leaf-level processes. Both of these changes degrade air quality and their combined effect can be as large as an increase of approximately 5 ppb in ground level, 8-hour averaged ozone concentrations in parts of eastern Texas. The effects of soil moisture on biogenic emissions estimates can be as significant as temperature, but current land surface model configurations and the adequacy of the Model of Emissions of Gases and Aerosols Nature (MEGAN) algorithm to fully represent short and long-term responses to soil moisture remain highly uncertain. The characterization of soil moisture through ground and satellite-based measurement programs and validation of global and regional-scale land cover distributions should continue to be high priorities to support air quality planning in Texas.Item Evaluation of anuran persistence in an urbanized drought-affected setting in the Southern High Plains(2012-12) Ramesh, Rasika; Griffis-Kyle, Kerry; Perry, Gad; Farmer, Michael; SanFrancisco, MichaelUrbanization, due to associated habitat degradation and fragmentation, is threatening amphibian survival worldwide. Mitigating urban amphibian declines is critical for amphibian conservation and requires understanding of amphibian life-histories and their use of urban landscapes. Since amphibian monitoring is non-existent in urban centers of the Southern High Plains, I conducted amphibian surveys in 2011 and 2012 in the city of Lubbock, west Texas, to establish fundamental baseline data regarding amphibian species occurring within the city, and evaluated site-suitability at site-specific and landscape scales at 23 urban lakes. While droughts are a recurring phenomenon here, the year 2011 broke past records for drought intensity and severity. I observed greater species richness and incidence of amphibian occurrence in 2012 which was relatively wetter; Bufonids (Anaxyrus speciosus and A. cognatus) were the most widespread. Using data from the drought, I attempted to establish a simple method to base management recommendations in the event of data scarcities associated with natural climatic extremes. This was used to create a preliminary grouping of lakes in order of amphibian management priority and level of management effort, thus emphasizing the importance of data gathered under drought conditions towards amphibian management efforts in the region.Item Functional response of the soil microbial community to forecasted rainfall shifts(2010-08) Rocca, Jennifer Doyle; Hawkes, Christine V.; Jansen, Robert K., 1954-Climate models forecast lower and less frequent precipitation in the next 50 years. This is especially pronounced in the central United States, where Texas is expected to lose a week’s worth of rain every summer. Water availability is a primary driver of carbon flux in terrestrial ecosystems – controlling photosynthesis and organic matter decomposition. Thus, under proposed rainfall shifts, understanding the potential ecosystem response is key to predicting the future of terrestrial productivity. Terrestrial nutrient cycling is also driven by microbial saprotrophs, which are the chief decomposers of organic matter. Understanding the microbial response to rain shifts is key in predicting the ecosystem response. Research supports both microbial community specialization to local environment, and that the microbial communities may have the ability to rapidly acclimate to environmental change. To address this question of microbial response, we used a steep natural rainfall gradient along the Edwards Plateau in central Texas. The Edwards Plateau is an ideal field site in which to test these ideas because nearly identical grassland habitat and soils are found across its entirety, while mean annual precipitation ranges from 45 cm to 91 cm. To understand how soil microbial communities varied as a result of historical rainfall differences, we divided the gradient into four isoclines based on precipitation (46-56 cm, 56-66 cm, 66-76 cm, and 76-86 cm), and examined soil and soil microbial community characteristics at three sites in each isocline. We further used soils from the same sites for a reciprocal soil moisture experiment, where we asked how soil microbial communities responded to altered moisture conditions. Using a full factorial design, soils from each site in each isocline were exposed to one of four soil moisture treatments: soil moisture from the ‘home’ isocline and the three other ‘away’ isoclines. The moisture treatments were maintained for one year. Microbial respiration was measured at regular intervals throughout the experiment; fungal hyphal abundance and inorganic nitrogen were measured at the final harvest. The soils collected from the gradient decreased in both soil moisture and hyphal abundance from the wet to the dry end of the gradient, but there was no trend in inorganic nitrogen. In the reciprocal moisture experiment, microbial CO2 respiration was affected by both home isocline and soil moisture treatment. Drier sites had a narrower response to wetter treatments and did not achieve the same activity as wetter sites regardless of soil moisture treatment. In contrast, soils from the wettest isocline experienced severe reductions in activity with drying, with activity at the driest moisture treatment below that found in soils that were from the driest isocline. These patterns are consistent with some degree of local specialization, which may constrain the ability of microbial communities to rapidly acclimate to altered precipitation regimes. This experiment did not include immigration, however, and shifts in community composition in the presence of dispersal may be able to counteract local specialization. Given expected future increases in drought intensity microbial decomposition activity is likely to decrease and local specialization may create a lag in acclimation to the new condition. Thus, local specialization of microbial communities should be considered when predicting ecosystem responses to future climate change and their potential feedbacks to ecosystem productivity and carbon storage.Item An inconvenient thirst : a look at the 2008-2009 Texas drought(2009-12) Cheng, Christina, 1981-; Burd, Gene; Perez, DominoThe 2008-2009 Texas drought rivals the 1950s drought, known as the “drought of record,” as one of the state’s worst droughts in recent memory. Prolonged periods of little to no precipitation combined with high temperatures and the strain of population growth have created disastrous conditions especially across the southern and central regions of the state, which have been hardest and longest. At one point, more than 83 percent of the entire state was in some form of drought and the United States Department of Agriculture declared more than half the state as a primary natural disaster area due to losses from drought, above-normal temperatures and associated wildfires. More than $4 billion in agricultural losses have been predicted as a result of the drought. Even after heavy rains have lifted nearly all of Texas out of drought, there are still counties in extreme and exceptional drought. It is clear that water issues will continue to impact the state socially, economically and ecologically, so it is crucial for all Texans to have a better understanding of the myriad ramifications drought can have on various industries and communities throughout the state.Item Influence of corn hybrids and water stress on yield and nutritive value(2009-05) Montgomery, Randall; Xu, Wenwei; Thorvilson, Harlan G.; Wester, David B.; Allen, Vivien G.Silage corn (Zea mays) in Texas has increased from 16,000 ha harvested in 1985 to 53,000 ha harvested in 2005. All corn in the Texas High Plains is irrigated with water from the Ogallala Aquifer. Due to the declining water level of the Ogallala Aquifer and rising energy costs, corn silage producers need new hybrids that require less water and respond to improved crop management practices. As the dairy industry continues to grow in West Texas, producers must supply a high-quality, high-yielding corn forage that meets the nutritional demands of the dairy industry. The objective of this study was to compare the responses in regards to grain yield, forage yield and quality of five Texas Agricultural Experiment Station (TAES) corn hybrids and three widely grown commercial hybrids (Garst 8288, P31B13, and DKC66-80) under full and limited irrigation treatments. This experiment was conducted in 2005 and 2006, at Halfway, TX and Etter, TX. There were two irrigation treatments (well-watered and drought-stressed) at Etter and Halfway in both years. Drought stress was imposed by reducing the amount of irrigation water by one-half compared to well-watered plots from V10 to R3 growth stages. Plots were two-rows 5.5 m long and spaced 1 m apart at Halfway and 0.76 m apart at Etter. After planting, plots were thinned to 66,947 plants/ha at Etter and 57,383 plants/ha in Halfway. Data was collected on grain yield, silage yield, plant height, ear height, days to pollen, neutral detergent fiber (NDF), acid detergent fiber (ADF), crude protein and numerous other forage quality traits. Whole plant corn samples were collected and sub-samples were analyzed by Dairy One Forage Laboratory (Ithaca, NY) using Near Infrared Reflectance Spectroscopy (NIRS). The basic experimental design for this analysis was a randomized complete block design with two blocks (locations); irrigation treatments (100ET and 50ET) represented the main plot factor of a split-plot arrangement, and hybrid was a subplot factor. No three-way interactions were observed among year, irrigation, and hybrid for any of the variables analyzed. Additionally, interactions between irrigation and hybrid, and between irrigation and year, were not present for any of the variables analyzed. Effects of hybrids depended on the year of the experiment (year X hybrid interaction) for percentage ADF, NDF, TDN, and DM. For grain yield, per plant fresh weight (FW plant-1), DTP, PHT and EHT, differences among hybrids were independent of other factors included in this study. Thus, differences among hybrids were averaged over each yr and effects of hybrid and irrigation treatment were examined. Differences among hybrids were observed for grain yield (kg ha-1), FW plant-1, DTP, PHT, and EHT. When analyzing grain yield, the commercial check P31B13 (8703 kg ha-1) was the highest yielding hybrid with the exception of C3A654 x B110 (7800 kg ha-1) and DKC66-80 (8044 kg ha-1). In terms of FW plant-1, S1W x CML343 yielded a greater fresh weight per plant than any other hybrids except DKC66-80, while C3A654 x B110 yielded the least fresh weight per plant. Also, S1W x CML343 was the latest maturing hybrid when compared to all others and took an average of 80 d to anthesis (DTP). In terms of plant height, S2B73 x NC300 was a taller hybrid than Tx205 x B110 (230.6) and C3A654 x B110 (210.3) as it averaged 244.4 cm, while, C3A654 x B110 was statistically the shortest when compared to all other hybrids as it measured just over 210 cm on average. Drought stress (50% ET irrigation) did affect both ADF and NDF in terms of forage quality. Both cell wall (NDF) and cell wall minus hemicelluloses (ADF) were higher in hybrids subjected to water stress than hybrids irrigated at 100% ET. Irrigation level did not affect percentage CP and TDN. Grain yield was reduced about 50% by the low irrigation treatment compared with full irrigation. Surprisingly, there were no statistical differences found in the forage yield (FW plant-1) or in DTP with the imposition of drought. Effects of year and hybrid interacted with each other for ADF, NDF, TDN and DM. For DM, hybrids were similar (P > 0.1560) in 2005 and differed (P < 0.0001) in 2006. However, for ADF, NDF and TDN, hybrids differed in each year. In future studies the integration of brown mid-rib hybrids should be made a priority. Some hybrids from this study did show promise and should be considered for future studies as well. Although S1W x CML343 lacked the quality traits that some of the other hybrids, it should not be ruled out on that premise alone. It did appear to be one of the higher yielding hybrids and should be considered for future studies. While C3A654 x B110 did appear to produce higher quality forage, it also had the shortest plants and might lack the overall forage production when being considered for future studies. Also, SPG3 x B110 appeared to have quality traits that would be very desirable and at the same time may include some higher yielding traits and should be used in potential studies. A major limitation in this study was the inclusion of only two blocks, although the two locations did serve as valid blocks. More research and detailed analysis must be performed in order to select for high yielding, high producing corn forage that might potentially use less water. This study may help to serve as a reference to future researches.Item Integrated Drought Modeling For Texas Under Climate Change Impact With Implications For Water Resources Planning(2014-12-02) Rajsekhar, DeepthiDrought is a deficiency in the hydro climatic variable of interest that is experienced for an extended period of time. In many parts of the world, it is a normal, recurring feature of climate and is therefore inevitable. Adequate monitoring and planning is required for effective mitigation of droughts. The study area for this research is Texas, which has been a consistently drought prone state. There has been at least one serious drought in one part of the state or the other during every decade of the twentieth century. This trend is likely to increase in the coming years due to the effect of global warming and climate change. Taking into account the importance of water management under conditions of extreme climate, this study focuses on enhancing various aspects of drought modeling. The major goals include the development of an efficient means to quantify multiple physical forms of drought, formulation of scientifically robust drought planning regions, integrated multivariate hazard and vulnerability assessment under climate change impact, understanding the causal factors that might trigger a drought event in future, and development of an effective interface to convey the research results to decision makers. These goals were designed to bridge the gaps existing in the current drought research, which even though substantial, still fails to address some of the issues. The goals are addressed by developing a new multivariate drought index, use of copula to build the dependence structure of drought properties and subsequent plotting of multivariate risk maps, development of Drought Hazard Index (DHI) and Drought Vulnerability Index (DVI) for integrated risk analysis under climate change impact, and use of Directional Information Transfer (DIT) for grouping of homogeneous drought regions. A novel transfer entropy approach is adopted to analyze the cause-effect relationship between various hydro-climatic variables and drought properties, thus identifying the prominent future drought triggers. Finally, an efficient drought Decision Support System (DSS) is developed to convey the research results to decision makers through a number of statistical techniques and effective visualization. Ultimately, the study aims at developing a comprehensive framework for better understanding of droughts in Texas which will help decision makers to formulate a more effective adaptation and mitigation strategy in future.Item Investigation of the utility of the vegetation condition index (VCI) as an indicator of drought(2009-05-15) Ganesh, SrinivasanThe relationship between the satellite-based Vegetation Condition Index (VCI) and frequently used agricultural drought indices like Palmer Drought Severity Index, Palmer?s Z-index, Standard Precipitation Index, percent normal and deciles was evaluated using a comparative correlation analysis. These indices were compared at the county level for all 254 Texas counties for the growing-season months (March to August) using monthly data from 1982-1999. The evaluation revealed that the VCI was most strongly correlated with the 6-month SPI and the PDSI. This suggests that the VCI is most similar to drought indices that account for antecedent moisture conditions. There was also significant spatial variability in the magnitude of the correlations between the VCI and the drought indices. The reasons for this variability were explored by utilizing additional data such as irrigation, prevalent landuse/landcover, water table depth, soil moisture levels and soil hydrologic/hydraulic properties. The results demonstrated that mean annual precipitation, soil moisture, landuse/landcover, and depth of the water table accounted for a significant amount of the spatial variability (explaining more than 75% of the variance) in the relationship between the VCI and traditional drought indices.Item Mechanism of drought tolerance in cotton-response of cotton cultivars to irrigation in the Texas High Plains(2011-05) Poudel, Esha; Thompson, Thomas L.; Bednarz, Craig W.; Holaday, A. ScottMechanism of Drought Tolerance in Cotton- Response of Cotton cultivars to Irrigation in the Texas High Plains (2011) Esha Poudel Chair of Advisory Committee: Dr. T.L.Thompson Cotton is the most profitable crop produced in the Texas High Plains but water deficiency is a crucial factor affecting both the yield and fiber quality in the region. Increasing cotton tolerance to water stress will be of even greater importance in the future. We tested the hypothesis that different cotton phenotypes, with okra and normal-leaf morphology, will have similar values for physiological responses related to water stress, such as, stomatal conductance, photosynthetic rate, vapor pressure deficit levels, internal CO2 concentration, and transpiration rate, under varying water availability and that these responses will similarly related to yield. A two year field study was conducted to determine the effects and interactions of irrigation amounts and cultivars on yield and quality of cotton and analyze and identify the physiological traits associated with drought tolerance in Lubbock County, Texas in 2008 and 2009. The experiment consisted of three irrigation amounts and two cultivars in each year. An important objective of the study was to see whether the yield and fiber quality will be independent of the phenotypes and the irrigation treatments. In both the years the yield was significantly different between the phenotypically different cultivars. Yields were also not independent of the irrigation in 2009. Fiber quality parameters showed varying response to irrigation amounts in both years. Stomatal conductance, photosynthetic rate and the internal CO2 concentration increased with increase in irrigation in 2009. The normal leaf phenotype was more responsive to irrigation than the okra leaf cultivar and also achieved higher yield. In both cultivars, stomatal conductance and photosynthesis were positively correlated with water availability. As expected, vapor pressure deficit was negatively correlated with water availability. Because the normal leaf cultivar was more responsive to water availability we reject our hypothesis.Item Phenotyping Drought Tolerance in Cotton (Gossypium hirsutum, L.)(2014-04-30) Terhune, Austin CatesCotton plant breeders need well-defined phenotypic parameters by which they can select drought tolerant lines as well as correlate phenotypes to allelic polymorphisms in the cotton genome. Soil-moisture availability is usually the most limiting factor for cotton crop productivity, especially in Texas. Characteristics of roots logically play an important role in determining the response of plants to limited soil moisture. The objectives of this study were to develop and refine techniques that could be used by plant breeders to phenotype plants? drought tolerance. Approaches include using a Trimble GreenSeeker?, to identify individual and progeny rows with enhanced photosynthetic capabilities in the presence of drought, leaf canopy temperatures under drought conditions, and measurement of root parameters in growth tubes in a greenhouse. Results from these experiments were related to yield performance in field trials at three locations in 2013. Several conclusions can be drawn from this study. First, Normalized Difference Vegetative Index and leaf temperature are rapid and reliable tools to evaluate plant health. The utility of these tools hinges upon timing of data collection, but they clearly demonstrated the propensity to differentiate phenotypic differences. Secondly, evaluation of root systems in growing tubes in a greenhouse is probably an ineffective method of characterizing drought tolerance potential since the growing conditions are radically different from what a plant would encounter in a field environment. Examining roots with this system would likely yield significant differences among plant species, but within upland cotton, it would be difficult to determine differences among genotypes. Ultimately the best determinant of drought tolerance is performance testing in droughty conditions because it encompasses most of the contributing factors that induce drought stress and measures the cotton plant?s inherent ability to recover and compensate in response to rainfall through the course of a growing season.Item Physical and geochemical response in cave drip waters to recent drought, central Texas, USA : implications for drought reconstruction using speleothems(2015-08) Hulewicz, Michelle; Banner, Jay L.; Breecker, Dan; Musgrove, MaryLynnA five-year study (2009-2014) of eight drip sites in Inner Space Cavern (IS), a cave on the Edwards Plateau in central Texas, was undertaken to assess the physical and geochemical response of cave drip waters to extreme drought. Drip rate, calcite growth rate, and dripwater geochemistry were monitored before, during, and after the peak of a record-breaking drought in central Texas that began and peaked in 2011, and which continued through to early 2015. Three groups of drip sites are identified based on average drip rate (slow sites, 0.2 -- 0.4 mL/min; intermediate sites, 1.2 -- 4.4 mL/min; fast sites, 6.7 -- 18 mL/min) and similarities in geochemical variation. Drip rates of slow sites have the lowest rate and magnitude of response to changes in hydrological conditions, while fast sites have the largest rate and magnitude of response. In contrast, the geochemical response to drought of the three groups does not correspond to the drip rate response. Slow and fast sites exhibit limited geochemical responses to changes in hydrologic conditions, including dripwater Mg/Ca, Sr/Ca, and Ba/Ca ratios, Sr isotope values, Ca concentrations, and oxygen isotope values. This lack of response indicates limited water-rock interaction (WRI) and/or prior calcite precipitation (PCP) affects these dripwaters. Intermediate drip sites exhibit the greatest geochemical response to changes in hydrologic conditions, including extreme drought, expressed by a decrease in Sr isotope values and an increase in Mg/Ca ratios during drier periods. Quantitative modeling indicates that both WRI and PCP can account for trace-element and Sr isotope variations at intermediate sites. The peak of the drought in 2011 coincides with high cave-air CO₂ and slow calcite growth rates, yet PCP may be an important process at two intermediate drip sites during drought. Geochemistry of intermediate drip waters at IS is likely controlled by water supplied by conduit and matrix flow and may provide the preferred speleothem record for reconstructing past droughts in central Texas using trace-elements ratios. Flow-route characteristics of drip sites at other caves that may be expected to show drought response in terms of trace elements include drip rate response to changes in moisture conditions but relatively low drip rate coefficient of variation and sub-equal matrix- and conduit-flow contributions. The monitoring of key geochemical and physical parameters at a range of sites in a given cave may allow for the identification of speleothems that are most likely to be geochemically responsive to changes in climate, making the speleothem sampling process more informed and less destructive.Item Physiological and genetic control of water stress tolerance in zoysiagrass(Texas A&M University, 2006-04-12) Dewey, Daniel WadeSignificant cultivar difference in many water stress responses of zoysiagrass (Zoysia japonica (Steud.) and Zoysia matrella (L.) Merr.) are shown in this study. Of the four cultivars, Palisades was the most water stress tolerant, had the most negative turgor loss point, and leaf rolled after loss of full turgor pressure. On the other end of the spectrum, Diamond was the least water stress tolerant, had the lowest full turgor pressure, the least negative turgor loss point, and leaf rolled at full turgor. Differences between Diamond, Cavalier, Palisades, and DALZ 8504 in leaf rolling, loss of full turgor, water release curve parameters, root characteristics and gene expression make zoysiagrass a prime candidate for further investigation into the mechanisms of water stress avoidance/tolerance. Enhanced antioxidant activity and stomatal control, along with root characteristics, most likely explain the cultivar difference in water stress tolerance of zoysiagrass. Palisades and DALZ 8504 maintained full turgor for significantly longer than Diamond and Cavalier, which may be associated with root characteristics and/or enhanced stomatal control as only those two cultivars showed enhanced expression of a stomatal control gene (phospholipase D). The apparent response (most apparent in turgid weight/dry weight ratios (TWDW)) of well watered plants to water stressed neighbor plants will likely be the most novel finding of this study. Well watered zoysiagrass and Kentucky bluegrass responded to water stressed neighbors by reducing TWDW. Significant increases in gene expression of a systemin degrading enzyme and of an integral membrane protein (signal receptor) were also observed in well watered plants. Results from this study indicate that this phenomenon is occurring and expose a dearth in scientific understanding that must be filled. Improving water stress tolerance through breeding for parameters like those discussed in this paper (delayed leaf rolling or loss of full turgor, enhanced stomatal control, enhanced antioxidant activity, deep rooting characteristics, etc.) may very likely produce turfgrasses that can survive and maintain desired aesthetic qualities using significantly less water.Item Quantitative Trait Locus (QTL) Mapping of Transpiration Efficiency Related to Pre-flower Drought Tolerance in Sorghum [Sorghum bicolor (L.) Moench](2012-07-16) Heraganahally Kapanigowda, MohankumarThere is an increasing need to improve crop water-use efficiency (WUE) (ratio of whole-plant biomass to cumulative transpiration) due to decreased water availability and increased food and energy demands throughout the world. The objective of the study was to estimate the genetic variation and genetic basis for transpiration efficiency A:E (CO2 assimilation rate (A) divided by transpiration rate (E)) trait and its relationship to WUE related to pre-flower drought tolerance in recombinant inbred lines (RILs) of sorghum and associated QTLs. A greenhouse study was conducted at Bushland, TX, 2008, using 71 RILs derived from cross of Tx430 x Tx7078. A randomized complete block experimental design was used, with both genotype and water regime (40 and 80 percent water regime) as experimental factors, and four replications. Genotype had a significant effect on A, E and A:E under both the environments. Among the RILs, entry means for A:E ranged from 1.58 to 3.07 mmol CO2 mol^-1 H2O and 1.18 to 4.36 mmol CO2 mol^-1 H2O under 80 percent and 40 percent water regime, respectively. Heritability estimates based on individual environments for A:E , A and E were 0.77, 0.45 and 0.37 under 80 percent water regime and 0.90, 0.33 and 0.71 under 40 percent water regime, respectively. A genetic map was constructed by digital genotyping method using Illumina GAII sequencer with 261 informative indel/ single-nucleotide polymorphism (SNP's) markers distributed over 10 linkage groups. Three significant QTLs associated with transpiration efficiency were identified; two on SBI-09 and one on SBI-10 with one logarithmic of odds (LOD) interval length ranging from 5.3 to 5.7 cM and accounting for 17 percent - 21 percent of the phenotypic variation. In field and greenhouse evaluation of agronomic of traits at College Station and Halfway, TX, 91 QTL that control variation in six major agronomic traits such as plant height, flowering, biomass, leaf area, leaf greenness and stomatal density were identified. Co-localization of transpiration efficiency QTLs with agronomic traits such as leaf area, biomass, leaf width and stomatal density indicated that these agronomically important QTLs can be used for further improving the sorghum performance through marker assisted selection (MAS) under pre-flowering drought stress conditions.Item Seasonal dynamics of nutritional quality during a drought of four browse species preferred by white-tailed deer (Odocoileus viginianus) in the Rolling Plains of Texas.(2012-08) Mitchell, Scott; Villalobos, Carlos; Dabbert, Charles B.; Wester, David B.; Galyean, Michael L.Woody plant encroachment is a constant issue that must be addressed by ranchers and landowners on the Rolling Plains of Texas. While many consider any type of woody vegetation on rangeland to be noxious, certain species provide a valuable and dependable source of quality forage for wildlife such as white-tailed deer. The purpose of this research was to identify four species of browse preferred by white-tailed deer and test certain nutritional parameters throughout each season during a drought. Application of fertilizer was added as one of the treatments to evaluate forage quality. The four browse species selected for evaluation were: fourwing saltbush [Atriplex canescens (Pursh.) Nutt.], ephedra (Ephedra antisyphilitica Berl. ex.C.A. Mey.), netleaf hackberry (Celtis reticulata) and redberry juniper (Juniperus pinchotii Sudw.). Each species were divided into a control or fertilizer treatment group. Crude protein and in vitro dry matter digestibility were evaluated for forage quality. Netleaf hackberry and redberry juniper were analyzed for condensed tannins. Fourwing saltbush and redberry juniper did not show a response to the addition of fertilizer. The response from ephedra between control and fertilizer was significant in all seasons for crude protein content (spring +1.66%, summer +3.14%, fall +2.09% and winter +1.63%). Netleaf hackberry showed a statistically significant increase in crude protein for summer (+1.05%) and fall (+0.35%). Dry matter digestibility was generally the same between control and treatment for all species. There was no significant difference between control and treatment for condensed tannin concentrations. Redberry juniper exhibited high levels concentrations of condensed tannins throughout the year (spring 36.20 mg CE/gDM, summer 50.59 mg CE/gDM, fall 61.27 mg CE/gDM and winter 60.36 mg CE/gDM). Netleaf hackberry contained smaller amounts of condensed tannins (spring 6.06 mg CE/gDM, summer 15.31 mg CE/gDM and fall 3.51 mg CE/gDM).