UC Davis

The steady increase in atmospheric CO2 since the industrial revolution is well established as the major driver of global climate change but its direct impacts on biochemical processes like photosynthesis are also of major concern. Some crop plant species have been shown to be less effective at assimilating nitrate, the most abundant form of nitrogen available to plants in most agricultural soils, when grown under elevated CO2. This indicates that rising CO2 concentrations could negatively impact the nitrogen use efficiency of many important crop species and may explain why protein content in some plant species decreases with CO2 enrichment. Improved techniques to measure nitrogen metabolism in plants are needed to further study the underlying cause of this phenomenon and mitigate the impact of rising atmospheric CO2 on our food supply. The three projects described here are a part of this effort. Chapter 1 describes a rosette area measurement tool that was developed as part of a larger study investigating the genetic basis of plant response to different nitrogen forms and concentrations. This tool was able to accurately estimate rosette area from photographs of Arabidopsis seedlings grown on agar plates even when the photographs did not provide a scale. We present a general-purpose ultra-high-resolution data acquisition system in chapter 2. The system interfaces a 32-bit analog to digital converter with a Raspberry Pi single board computer. We provide a simple open-source hardware design and easy to use software libraries enabling this system to be easily built and adapted for any purpose. Finally, we demonstrate the high performance of the system by making precise temperature measurements. Many elements of this data acquisition system were used in the Oxygen analyzer described in chapter 3. Chapter 3 documents the design and characterization of a novel high-resolution oxygen analyzer designed to measure small O2 fluxes against the large ambient background. The original motivation for this instrument was to estimate nitrate assimilation in plants through the ratio of CO2 assimilated to O2 evolved. The design is based around a zirconia O2 sensor that has not traditionally been used for high precision applications. The O2 measurement repeatability of the analyzer was better than 70 ppm, nearly 2 orders of magnitude better than what had previously been reported for an analyzer using this type of sensor. Further improvements to temperature control may yield even higher precision enabling measurements of photosynthetic O2 fluxes.