Canopy Architecture and Transpiration Efficiency In Sorghum.

Increasing crop transpiration efficiency (TE), the amount of biomass produced per unit water transpired, can enhance crop productivity and yield potential. The objective of this study was to evaluate the factors affecting TE and radiation use efficiency (RUE) among eight sorghum (Sorghum bicolor L. Moench) lines, including crop canopy architecture. RUE is the amount of dry matter produced per unit of intercepted or absorbed solar radiation that is suitable for photosynthesis (PAR). Canopy architecture is the distribution of area, shape and orientation of leaves, stems and reproductive structures. This study hypothesized that increased TE and RUE could increase the dry matter production in sorghum; and that increased TE and RUE could be associated with differences in canopy architecture. Destructive harvests at boot, post-anthesis, and late grain filling stages quantified above-ground biomass of the selected sorghum lines. Crop water use was calculated from changes in stored soil water, precipitation and irrigation. TE was calculated by the ratio of above-ground biomass accumulation to water use for specified sampling intervals. RUE was calculated as the ratio of above-ground biomass to cumulative intercepted PAR (IPAR). Canopy architecture was characterized by internode length, leaf area index, leaf dimensions and leaf angle. Sorghum lines showed significant differences in apparent TE, RUE and canopy architecture when grown under field conditions. The correlation between TE and biomass (0.89) was greater than the correlation between TE and water use (0.24). RUE was positively correlated to TE and tended to increase with internode length (ratio of stem height, calculated as the distance between soil and flag leaf ligule, to leaf number at maturity). Lines with greater TE also exhibited greater RUE; the similarity among lines in IPAR indicated the increased productivity exhibited by these lines was due to increased utilization of radiation rather than radiation capture.