Location: Global Change and Photosynthesis Research
2023 Annual Report
Objectives
Objective 1: Develop, test, and quantify the benefits of specific strategies for agricultural greenhouse gas mitigation, including enhanced rock weathering, overwintering corn and soybean, expanded use of cover crops, and genetic manipulations to increase photosynthetic efficiency.
Sub-objective 1.A: Apply micrometeorological techniques to quantify ecosystem-scale fluxes of greenhouse gases, energy, and water in response to environmental variability, land-use change, and variable management practices.
Sub-objective 1.B: Test the effect of basalt application on maize and soybean leaf and seed nutrient content.
Objective 2: Adapt crops to future atmospheric conditions through identifying key genes and loci associated with CO2 response, N use efficiency, crop quality and ozone tolerance.
Sub-Objective 2.A: Identify the genetic factors that coordinate photosynthesis with N availability and characterize how manipulation of these factors impacts plant traits.
Sub-objective 2.B: Test whether the ability to obtain biologically fixed N provides an advantage to how plants acclimate to elevated CO2 and characterize the factors that signal C/N status between source and sink tissues.
Sub-objective 2.C: Test soybean response to elevated ozone and drought stress.
Sub-objective 2.D: Design an experiment to disentangle the relative contributions of high temperature and increased vapor pressure deficit on the physiology, growth, and yields of soybean.
Objective 3: Develop and apply tools using a field-based high-throughput phenotyping platform to quantify growth, physiology, yield quantity, yield quality, and scalability of crop adaptations to current and future environmental conditions.
Sub-objective 3.A: Develop multi- and hyper- spectral techniques for high-throughput phenotyping of leaf, plant, and canopy growth, physiological, and nutritional properties to associate genotype to phenotype and to quantify physiological responses to genetic manipulations to increased photosynthetic efficiency.
Sub-objective 3.B: Develop and test hyperspectral methods to measure soil characteristics, including water content, and iron and zinc concentrations.
Objective 4: Develop, train, and validate computer models of crop nutrient uptake and growth in order to identify traits and genes that will improve crop quality and yield.
Sub-objective 4.A: Develop models of yield for key crops that include effects of CO2 concentration, temperature, soil characteristics and vapor pressure.
Sub-objective 4.B: Develop soil and root nutrient uptake and distribution models.
Approach
Research aims to understand and reduce the negative impacts of agriculture by quantifying greenhouse gas fluxes using Eddy covariance techniques, investigating the effectiveness of soil amendments to store carbon, and developing state-of-the-art high-throughput techniques for fast and accurate measurements of crop traits. Experiments will test how elevated carbon dioxide impacts enhanced rock weathering in corn and soybean ecosystems and will monitor carbon dioxide, water and ozone fluxes in long-term experimental facilities. Research will test how interrelated metabolic and stress response pathways are coordinated at the genetic scale, generate crop models that identify trait and gene targets for crop improvement, and develop novel high throughput phenotyping techniques to measure plant and canopy traits and efficiently process immense data streams from sensors. Experimental approaches scale from the molecular to the ecosystem level, combining biophysics, physiology, molecular biology, genetics, and genomics. Research will take advantage of unique field and greenhouse experimental and monitoring facilities, along with integrated collaborations with other ARS and university researchers and commercial farmers.
Progress Report
This is the first report for project 5012-21000-032-000D, which began in June 2023, and continues from the previous project 5012-21000-030-000D “Optimizing Photosynthesis for Global Change and Improved Yield.” Research has been initiated for all milestones.
In support of Objective 1, maize was grown with and without crushed basalt rock at ambient and elevated carbon dioxide concentration (CO2) at the Free Air Concentration Enrichment (FACE) facility. The experiment tests the potential for elevated CO2 to interact with enhanced rock weathering (ERW) to improve CO2 sequestration in agricultural ecosystems. ERW is the biogeochemical improvement of cropland soils with crushed basalt, an abundant natural silicate rock, for carbon sequestration. ERW involves the acceleration of silicate mineral dissolution that occurs when rock grains react with rainfall and CO2 in soil to sequester CO2. Measurements of crop development, photosynthesis, stomatal conductance, soil respiration, soil nitrous oxide emissions, soil moisture, water chemistry, soil pH and cation exchange capacity and rates of in situ rock weathering were made throughout the season. Samples for leaf and grain quality and nutritional status are being analyzed currently.
In support of Objective 2, alfalfa lines with and without nitrogen fixation capabilities were grown in different nitrogen and CO2 concentrations. Specifically, these experiments test the hypothesis that legumes will have an advantage at elevated CO2 as they can exchange excess carbon from greater photosynthesis with nitrogen-fixing bacteria. The nitrogen-fixing bacteria could provide a greater sink for carbohydrate and in return exchange nitrogen to the plant at elevated CO2. The experiments showed that symbiosis with nitrogen fixing bacteria provided a significant advantage to the plant, especially at elevated CO2. Gene regulatory networks identified important genetic regulators that integrated nitrogen and carbon signaling.
In support of Objective 3, field experiments at the SoyFACE experimental facility were built to test the interactive effects of drought and ozone stress, and high temperature and vapor pressure deficit. A rainfall exclusion awning was constructed within each elevated and control ozone plot and capture ~40% of seasonal rainfall and decreased soil moisture by up to 25% in the shallow soil layers. There was an interactive effect of elevated ozone and reduced soil moisture on yields, with reduced soil moisture causing greater yield losses in ambient ozone compared to elevated ozone conditions. This research is among the first to provide field-level experimental evidence of the interactive effects of drought and ozone pollution on soybean growth and productivity and is important for modeling crop responses to global climate change.
In support of Objective 3, hyperspectral reflectance of sand substrate with known quantities of zinc and iron were measured and statistical models were used to predict concentration from reflectance data. These experiments are testing the potential for high throughput phenotyping of soil nutrient status and are an important first proof of concept. Partial least squares regression models could accurately predict iron content in the substrate and less accurately predict zinc content. Current research is extending the methods to scan soils in two dimensions, potentially providing the ability to use spatially resolved models to understand root-soil interactions.
In support of Objective 4, soybean plants were grown in hydroponics to investigate nitrogen uptake from the medium and transport to shoots and seeds. Measurements made from plants were paired with a nitrogen distribution model to test which processes potentially limit the content of nitrogen in seeds. The modeling suggested that transport to seeds was the major limiting factor, identifying a key process for future improvement. This work is important for maintain high soybean protein content, which has been declining over recent decades as a result of breeding for higher yields.
Accomplishments
1. Determined gene regulatory networks integrate nitrogen assimilation and photosynthesis in nodulating and non-nodulating alfalfa. Understanding how plants sense, signal, and integrate nitrogen and carbon status will be critical to improving nitrogen use efficiency and yields in future climates. Due to their ability to form symbiotic association with nitrogen-fixing bacteria, it has been proposed that legumes such as alfalfa will have an advantage at elevated carbon dioxide levels as they can exchange excess sugars made from carbon dioxide obtained from increased photosynthesis for additional nitrogen. To test this hypothesis, ARS researchers in Urbana, Illinois, grew alfalfa lines capable of obtaining fixed nitrogen alongside mutant lines that could not fix nitrogen in different nitrogen and carbon dioxide conditions. The symbiotic relationship with nitrogen-fixing bacteria provided a significant advantage, particularly at elevated carbon dioxide, based on measurements of biomass, photosynthetic rate, and nitrogen content. Gene expression measured on the same plants enable the elucidation of gene regulatory networks that integrate nitrogen and carbon availability. This work provides breeders and biotechnologists a set of gene targets for optimizing nitrogen-photosynthesis interactions and improving nitrogen use efficiency in alfalfa in future higher carbon dioxide climate conditions.
