Drought is one of the most important abiotic stresses that adversely affects plant growth and productivity worldwide. Climate change is projected to increase the frequency and intensity of drought, an outcome already experienced in many regions across the globe.
Sorghum and maize are closely related and are both adapted for warm-season grain production. Yet sorghum is more drought tolerant than maize.
Erik J. van Oosterom, Senior Research Fellow for the Queensland Alliance for Agriculture and Food Innovation (QAAFI) at The University of Queensland led a team that unraveled some aspects of why sorghum has an enhanced tolerance to water limitation than maize, but maize has greater yield potential than sorghum.
To achieve this, they dissected and modeled the comparative adaptation to water-limitation of sorghum and maize with regards to the role of transpiration efficiency, transpiration rate, and plant height.
Eight maize hybrids, 15 short sorghum genotypes (3dwarf), and 7 tall sorghum genotypes (2dwarf) were grown in lysimeters and kept well watered. The lysimeters provided daily whole plant transpiration, which was converted to daily transpiration per unit green leaf area. Plants were harvested after anthesis and total transpiration, shoot and root dry mass were measured to estimate transpiration efficiency.
The authors found that species and height had limited effect on transpiration efficiency. However, it significantly affected transpiration per unit green leaf area, which was associated with differences in biomass allocation.
To analyze the effects of species and height differences on grain yield across a range of environments, the researchers subsequently ran simulation studies using the APSIM-Sorghum (3dwarf) and APSIM-Maize crop growth simulation models. The simulations used a common transpiration efficiency for maize and 3dwarf sorghum, but different radiation use efficiency to reflect observed differences in transpiration per unit green leaf area.
The simulations predicted cross-over interactions for grain yield between species and total water use. While maize had higher yield under well-watered conditions, grain yields declined for both crops once total crop water use dropped below 300 mm. When water use fell below 250mm, sorghum was better able to maintain its yield than maize.
According to van Oosterom, “these findings highlight the fact that yield potential can come at a cost of increased water use. This can affect drought adaptation and can have adverse consequences for productivity of subsequent crops in cropping systems that rely on carry-over of water from one season to another.”
APSIM is available free of charge for non-commercial purposes, and can be downloaded here: https://www.apsim.info/