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PhD Defense

ESS Oral Defense: Aria Hamann Duncan "Unveiling Alternate Wetting and Drying Effects on Rice Production Under Future Climate Conditions"

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Stanford University

*** Ph.D. Thesis/ Oral Defense ***

Sterol Biosynthesis in Methylococcales and Myxococcota

Aria Hamann Duncan

Friday, July 5, 9:00am

Green Earth Sciences 365

Department of Earth System Science

Advisor: Dr. Scott Fendorf

Rice is an important staple crop—essential for global food security. However, climate change threatens future rice production. Rising temperatures cause heat stress and alter soil biogeochemical processes exacerbating the toxic effects of widespread endemic soil arsenic and challenging future rice production. Alternate wetting and drying irrigation (AWD) has the potential to decrease grain arsenic, water use, and methane emissions, thus helping to mitigate the impacts of a changing climate. This dissertation experimentally explores the combined effects of AWD and climate change (rising temperatures and atmospheric CO2) on the soil-rice system. I assess the temporal dynamics of arsenic bioavailability in the rice root zone and find decreases in dissolved arsenic following drainage events. Differences in rice root arsenic exposure due to irrigation management led to a 32% decrease (p = 9.1 x 10-5) in grain total arsenic with AWD under current climate conditions (daily high of 33 ºC and 420 ppmv CO2). Under a severe warming scenario (+5 ºC and 850 ppmv CO2), grain arsenic decreased by 22% (p = 0.025) with AWD. I illustrate that AWD can partially compensate for climate-induced yield losses, despite evidence of abiotic stress. With conventional, continuously flooded irrigation, severe warming led to a 55% yield loss (p = 0.04); whereas, with AWD, warming led to a 9% yield loss (p = 0.70), which was not statistically significant. The combination of AWD and elevated CO2 also enhanced root system growth. Finally, I explore the spatial distribution of arsenic in and around rice roots using X-ray fluorescence mapping. Our findings reveal that both climate and irrigation strongly influence arsenic distribution in the root zone. Continuously flooded irrigation encourages arsenic enrichment on root surfaces, and AWD results in more uniformly distributed arsenic. This dissertation indicates that from rice yield to grain arsenic, AWD appears advantageous for rice production and consumption even under severe warming.

 

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