Quantifying Water Use Efficiency at Leaf and Field-Scales for Soybean, Miscanthus and Switchgrass

Apurupa Gorthi, Purdue University

Abstract

Understanding the complex relationship between plant carbon assimilation and water loss as a function of environmental factors is critically important for improving managed agricultural systems. Water use efficiency (WUE) measures the carbon uptake of a plant relative to the water used by the plant. Over the years, it has been described at several spatial and temporal scales depending on methods available for carbon and water flux quantification. One approach for developing crop cultivars that are well adapted to water-limited conditions has been to use leaf-level measurements of carbon isotope ratios to identify those individuals that best conserve water. How this leaf-level water conservation translates to agronomic-scale water use has not been thoroughly demonstrated. This work investigated the leaf-scale and field-scale WUE of three crops, namely, soybean (Glycine max), Miscanthus (Miscanthus giganteus) and switchgrass (Panicum virgatum) for the years 2010 to 2014. Plant biomass harvested at the end each growing season was used for carbon isotopic analysis, a metric used to estimate leaf-level WUE. Further, grain and biomass yields, tile drainage and climate data (precipitation, vapor pressure deficit, air temperature) were used to calculate field-scale WUE and related metrics. Based on analysis of WUE at leaf and field scales for soybean at this study site, a 1% increase in leaf-scale WUE showed ~10% increment in field-scale WUE at the lower end of this relationship. Further, the leaf-level WUE explained 90% of the annual variability in field-scale WUE perhaps showing that leaf-scale WUE is an effective breeding tool to improve field-scale WUE in soybean under these conditions. For Miscanthus and switchgrass, we observed that Miscanthus consistently outperformed switchgrass both in terms of biomass yield and field-scale WUE. Five-year averages of agronomic WUE for Miscanthus and switchgrass were 19 kg dry matter ha-1 mm-1 and 7 kg dry matter ha-1 mm-1. The difference in performance of Miscanthus and switchgrass at the study site, both under drought and non-drought conditions was due to subtle differences in the C4 pathway between these crops.

Degree

M.S.

Advisors

Welp, Purdue University.

Subject Area

Hydrologic sciences|Biogeochemistry|Agriculture

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