Grain Sorghum Transpiration Efficiency at Different Growth Stages As Affected By Growing Period Vapor Pressure Deficit.

Transpiration efficiency (TE) is an important physiological trait for producing high yield with limited water supply. In contrast to other major food crops, little is known about the sorghum (Sorghum bicolor L.) TE and its dynamics in relation to vapor pressure deficit (VPD). Two studies in both greenhouse and plant growth chamber facilities were conducted simultaneously to assess grain sorghum TE at four different growth stages, and to determine the effect of VPD on TE. Plants were grown in lid-covered boxes and harvested at six-leaf stage (S1), flag leaf stage (S2), grain filling stage (S3), and maturity stage (S4). For all studies, shoot biomass increased linearly with cumulative water used for transpiration. From seedling emergence to four harvesting or growth stages, root biomass increased up to S3 and declined thereafter, but shoot biomass and shoot:root (S:R) ratio increased continuously from S1 through S4. Under constant VPD, shoot transpiration efficiency (TE_shoot) values from seedling emergence to different growth stages were similar for each study. VPDs were different from one study to the other. When data from all four studies were combined, ET_shoot showed linear decrease as the crop growing period VPD increased.