Impact Of Elevated Carbon Dioxide On The Viability And Nitrogen Content Of Spring Wheat

Author : Laura Elizabeth Emberson
Publisher :
ISBN 13 : 9780355460940
Total Pages : pages
Book Rating : 4.4/5 (69 download)

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Download or read book Long-term Effects of Climate and Nitrogen on Wheat (Triticum Aestivum) Carbon-water Relations in California written by Laura Elizabeth Emberson and published by . This book was released on 2017 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The tracking of crop yields as affected by climate variability and rising carbon dioxide (CO2) levels is essential in creating a framework for sustainable agricultural management decisions in the future (Izaurralde et al. 2003; Rosenberg et al. 2003; Asseng et al. 2015). In this research, winter wheat grown in an arid climate is used as a model system to understand climate and atmospheric changes on crop yield potential. (Idso et al. 1979; Smit et al. 1988; Daniel et al. 2002; Asseng et al. 2015; Stratonovitch and Semenov 2015). Wheat is the third most commonly produced crop in the world (kg/ha) (Field to Market 2012). The following study investigates 16 years of field data (1998-2013) collected from the Century Experiment at Russell Ranch Sustainable Agricultural Facility at Davis, California. The climate at Russell Ranch covers a range of conditions from severe drought to unusually moist, representing total rainfall from 221.1 mm to 735 mm. However, results indicate that the water stress metrics used to describe seasonal water status do not have significant effects on yield outcomes. Analyses also indicate that there is no effect of carbon dioxide on yield within the range from 360-400 ppm during the study period. Results show a strong correlation between nitrogen availability and yields, when controlling for yearly variability and variability within plots of replicated treatments. Results also show that the physiological indicator of stress, represented by carbon-13 discrimination in the grain, improves the modelled description of yield. Other findings indicate that nitrogen limitations have caused much greater stress on yields than climate variability since 1998. The anisohydric adaptation of wheat is hypothesized to be a mechanism to cope with water stress. This plant strategy maintains photosynthetic capacity under stress, by favoring stomatal conductance over turgor pressure. An abiotic explanation of these results suggests climatic conditions have not reached threshold conditions to cause yield changes. Carbon dioxide levels, for instance are currently near 400 ppm, while carbon enrichment experiments only show growth effects above 550 ppm in elevated CO2 experiments. Likely, both explanations are partly responsible for the result. These findings suggest that wheat culture will remain resilient to future climate change and atmospheric change. Chapter 2: Consideration of [delta]13C and [delta]18O in wheat to understand physiological stress and weather reconstruction in a Mediterranean climate Stable isotope signatures of carbon and oxygen in wheat reflect an integrated measure of stomatal aperture throughout the season due to the interface between carbon dioxide being assimilated and water being transpired at the stomatal pore. Stomata close when available water is scare and evapotranspiration rates are high (Barbour et al. 2000; Ainsworth and Long 2005; Farooq et al. 2014). This connection between stomatal conductance and water status is reflected in the strong negative trend of [delta]13C and the strong positive trend of 18O in wheat with increasing vapor pressure deficit (Roden et al. 2000; Fry 2006).This investigation examines the relationship between 13C discrimination ([delta]13C), 18O enrichment ([delta]18O), and weather factors in three plant materials. Wheat bulk straw, straw cellulose, and bulk grain samples archived during a long-term agricultural field experiment. The field experiments original design also has three soil nitrogen treatments (Torbert et al. 2016). This archival data provided two decades worth of samples grown under natural weather conditions, rather than imposed water and carbon dioxide levels. The four major climate factors of interest were seasonal precipitation, the Palmer Drought Severity Index (PDSI), potential evapotranspiration (ETo), and atmospheric carbon dioxide concentration.Changes in stable isotope signatures indicate wheat is experiencing a physiological stress and is responding by stomatal closure. Carbon-13 discrimination had a negative correlation to evapotranspiration as expected, but had no relation to any other weather metric. Oxygen-18 enrichment values had a strong positive correlation with evapotranspiration in all sample types. Grain [delta]18O and cellulose [delta]13C had the most sensitive signals to changes in ETo. Straw cellulose [delta]18O was also strongly correlated to drought severity. The significant negative correlation between carbon and oxygen verifies that the changes in carbon signatures are due to water stress and not other factors. The disparity between [delta]18O responding to both ETo and PDSI, while [delta]13C only responded to ETo illuminates two points. It is evidence that oxygen isotopes are better proxies, in general, for climate conditions than carbon isotopes and that carbon isotope data, paired with [delta]18O data is better for accurately identifying stomatal response to external climate conditions. All the findings above indicate that wheat is under physiological stress throughout the field conditions experienced (Farquhar et al. 1989; Condon et al. 1992; Cabrera-Bosquet et al. 2009a). However, the results also reveal that precipitation conditions over the past two decades of experimentation was not driving the stomatal closure response. Rather, wheat stomata are responsive to the vapor pressure deficit increases and rising temperatures captured in higher ETo values. This study highlights the fact that although the utilization of isotope signatures as proxies has blossomed over the past 40 years, it is essential to understand the isotopes in context of the study to avoid incorrect water stress conclusions.