Impacts of heat waves on food quantity and quality of soy bean/corn in the Midwest at ambient and elevated [CO2]

Siebers, Matthew

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Description

Title

Impacts of heat waves on food quantity and quality of soy bean/corn in the Midwest at ambient and elevated [CO2]

Author(s)

Siebers, Matthew

Issue Date

2014-09-16

Director of Research (if dissertation) or Advisor (if thesis)

Ort, Donald R.

Doctoral Committee Chair(s)

Ort, Donald R.

Committee Member(s)

• Bernacchi, Carl J.
• Ainsworth, Elizabeth A.
• Nelson, Randall L.

Department of Study

Plant Biology

Discipline

Plant Biology

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• heat waves
• corn
• soybean
• yield
• global change

Abstract

Heat waves have significant impacts on managed and unmanaged plant productivity. Yet, current studies of the effects of heat waves on crops are confined to post-mortem and historical analyses. There are no field based heat wave studies on major crops. In the past decade, the development of efficient infrared (IR) heating technology has made it possible to precisely control plant canopy temperatures and simulate heat waves in the field. Heat wave research was conducted at the SoyFACE research facility in Urbana, IL. Thirty years of climate data from Central Illinois were analyzed to determine the characteristics of a historically plausible, yet extreme heat wave. Heat waves were defined as 3 day long events where canopy temperatures were kept a minimum of +6 oC above the daily 30 year mean. The first two chapters of research used IR heaters to simulate heat waves in corn (Zea Mays) and soybean (Glycine Max). The principle focus of the research was on how heat waves affected: plant water status, source dynamics, sink behavior and seed yield in the field. The first chapter is composed of two years of heat wave data. In 2010 and 2011 a total of five heat waves were applied to soybean (Glycine max) in early and late reproductive periods. It was hypothesized that 1) if leaf temperatures in the heat wave plots reached supra optimal temperatures, then it would reduce rates of photosynthesis (A) and reduce yield in the short and long term. In the short term heat waves would reduce stomatal conductance (gs) and the internal carbon dioxide concentration inside the leaf (Ci) and increase photorespiration. In the long term heat waves would decrease the operating efficiency of photosystem II or alter leaf biochemical properties, i.e. the maximum rate of rubisco carboxylation (Vcmax ) or the maximum rate of electron transport (Jmax). Additionally, because soybeans flower and set pods for 25-35 days it was hypothesized that any direct reproductive damage would be negligible due to the long flowering time and high number of reproductive units. Surprisingly, even though heat waves caused significant oxidative stress to leaf tissue, there were few long term effects on the rates of A. Additionally, it appeared that in 2010 the direct effect of heat waves on reproductive structures may have been a significant cause of yield loss, since yield loss only occurred when heat waves were applied to later, sensitive reproductive periods. A follow up experiment in 2011 that tracked pod set showed that yield losses during that heat wave could be attributed to pod abortion on lower nodes of the plant. The experiment in the second chapter was performed in 2011. Two three-day long +6 oC heat waves were applied to corn (Zea mays), first to an early vegetative stage (V6) and later to a critical reproductive stage (R1, silking). Compared to the control treatment, the heat wave during R1 significantly reduced reproductive growth (seed + cob + husk tissue). Heat waves increase atmospheric vapor pressure deficit (VPD), which drives greater evapotranspiration (ET) and leads to plant water loss, decreased A, growth and yield. However, neither of the heat waves in 2011 caused lasting changes to leaf water potential or significantly increased monthly ET. It is also unclear if either of the heat wave treatments actually decreased A’: decreased midday A was not always associated with a change in nonstructural leaf carbohydrate content or specific leaf weight. Heat waves can also disrupt reproductive timing causing asynchronous flowering of male and female flowers. But, neither heat wave had an effect on the rate of reproductive or vegetative development. In corn, heat waves altered reproductive growth without long term effects on A, development or water status. The third and last chapter of this thesis is an experiment from 2012 that attempts to broaden the scope of heat wave research. Two extended five day long +6 oC heat waves were applied to soybean at an early flowering (R1) and seed fill stage (R5). Heat wave treatments were replicated at ambient CO2¬ concentrations (400 ppm, aCO2) and concentrations projected for the year 2050 (600 ppm, eCO¬2). This experiment aimed to discover whether or not eCO¬2 and heat wave treatments would interact synergistically to improve seed quality and quantity. The first hypothesis was that eCO2 will mitigate yield loss caused by heat waves. Soybean grown in eCO2 has reduced gs, which leads to lower rates of canopy ET and improved soil moisture reserves. Additionally, the temperature optimum of A is greater in eCO2 than aCO2. Theoretically, greater soil moisture availability during the heat waves and an improved tolerance to high temperature should lead to higher rates of gs and ¬A in the eCO2 heat wave plots. The second hypothesis was: if bulk flow is limiting nutrient availability in eCO2 and ET is increased by heat waves then heat waves in eCO¬2 will have improved seed quality relative to the eCO2 control. Seed quality of soybean grown in eCO2 is diminished due to decreased ET and bulk flow of water. Heat waves decreased carbon uptake during both heat waves; heat waves caused reductions in A and SLW. Although those reductions did not translate to a significant reduction in seed yield or above ground biomass during either heat wave. Seed quality was also unaffected by heat waves. There was, however, the discovery that for certain nutrients there is strong canopy position effect. For example iron concentrations were 70% greater in seeds at the bottom of the canopy.

Graduation Semester

2014-08

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Copyright 2014 Matthew Siebers

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