Spatial Variability of 13C Isotopic Discrimination in Corn

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Water stress influences photosynthesis induced isotopic 13C discrimination (Δ) in C3 and C4 plants. In C4 plants, Δ increases with increasing water stress, while in C3 plants the opposite is true. The amount of Δ that occurs is a function of plant type, interactions between climatic conditions, plant available water, water stress, photosynthesis capacity, plant water demand, and yield. The objective of this study was to determine if Δ measured in corn (Zea mays) tissue collected from summit, shoulder, backslope, and toeslope areas contains spatial structure. Corn grain or fodder samples collected from grid points located at five sites were analyzed for total nitrogen (N) and Δ on a Europa 20:20 ratio mass spectrometer. At sites where crop growth was not N limited, Δ spatial dependence was described using linear models. Spatial dependence most likely was generated by environmental and physical factors that interacted to influence plant available water. Spatial dependence indicates that the basic physiological response of corn to water stress, i.e., stomatal closure, can be measured at the plant and integrated to the landscape scale. A relationship between relative yields and Δ suggests that Δ provides an index for water stress under non nutrient limiting conditions. However, because Δ can be influenced by many factors, Δ as a direct measure of water stress must be used with caution.

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Communications in Soil Science and Plant Analysis





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