Hydraulic Conductivity and Transpiration Rates of Soybean Plants Differing in Leaflet Orientation and Root Morphology.

The objective of this study was to evaluate effects of leaflet orientation and root morphology on water use characteristics in soybeans.  Nine lines and the parental varieties were selected for this experiment from the population USG 5601T x PI 416.937 based on their leaflet orientation and root morphology characteristics.  Hydraulic conductance and whole plant transpiration were measured with the Dynamax High Pressure Flow Meter (HPFM) and the Dynamax Flow 32 Sap Flow system, respectively.  Four plants of each line were measured when the plants were in the active pod filling stage of growth (R4,R5,R6).  Leaflet orientation, yield, agronomic characteristics, leaf area, and biomass were recorded in four replications. Differences in the root morphology allowed characterization of three distinct root classes (prolific, intermediate, and normal).  Hydraulic conductivities will be discussed and compared to whole plant transpiration measurements.  High leaflet orientation plants tended to transpire more water in a 24 hour period and use more water per unit yield relative to lower leaflet orientation plants.  The dry weight biomass of prolific rooted plants was significantly greater than normal rooted plants.  Prolific rooted plants had significantly lower transpiration rates than the other two root classes.  Although not significant (p=0.15), prolific rooted plants also tended to have better water use efficiencies, using less water per unit seed yield.  The data from this study indicated a trend that lower leaflet orientation and prolific rooting morphology may result in lower transpiration rates and increased water use efficiencies.  Additional data analysis on larger population sets are planned to further address the effects of the two traits on water use and yield in soybeans.