Effects of Soil Moisture Availability On Sunflower Stomatal Conductance and Root Development.

Drought stress is a significant limiting factor in crop growth and development in Colorado. Drought is expected to affect crops differently in coarse and fine textured soils because water percolates quickly through coarse soils resulting in rapid drying, and slowly through fine textured soils resulting in gradual drying. This difference potentially allows for root-shoot reallocation to ameliorate plant response to drought in fine textured soils. The objective of this research was to test the effects of root development and soil texture on plant stress in sunflower, Helianthus annuus L., under two levels of soil moisture availability. Soil electrical conductivity (EC, an indicator of soil texture), root growth and distribution in the soil profile, whole plant leaf area, and stomatal conductance were measured on field plants under two irrigation treatments (full and x % ET) that spanned the range of soil texture present at our field site. Effects of irrigation treatment on stomatal conductance were tested with a repeated measures statistical design defining EC and root:shoot ratio as covariates. The factor explaining the greatest variation in stomatal conductance was irrigation treatment. Shallow EC, down to 30 cm soil depth, also explained significant variation. Root:shoot ratio was marginally significant in determining stomatal conductance under water deficit. A potential explanation for the marginal significance of root:shoot ratio is that sunflower is particularly efficient at mining available water from the soil profile in all soil types in a deficit environment.