Seasonal climate conditions impact the effectiveness of improving photosynthesis to increase soybean yield.

CONTEXT

Photosynthetic stimulations have shown promising outcomes in improving crop photosynthesis, including soybean. However, it is still unclear to what extent these changes can impact photosynthetic assimilation and yield under long-term field climate conditions.

OBJECTIVE

In this paper, we present a systematic evaluation of the response of canopy photosynthesis and yield to two critical parameters in leaf photosynthesis: the maximum carboxylation rate of ribulose-1,5-bisphosphate carboxylase/oxygenase () and the maximum electron transport of the ribulose-1,5-bisphosphate regeneration rate ().

METHODS

Using the field-scale crop model Soybean-BioCro and ten years of observed climate data in Urbana, Illinois, U.S., we conducted sensitivity experiments to estimate the changes in canopy photosynthesis, leaf area index, and biomass due to the changes in and .

RESULTS

The results show that 1) Both the canopy photosynthetic assimilation () and pod biomass yields were more sensitive to the changes in , particularly at high atmospheric carbon-dioxide concentrations ([CO]); 2) Higher [CO] undermined the effectiveness of increasing the two parameters to improve and yield; 3) Under the same [CO], canopy light interception and canopy respiration were key factors that undermined improvements in and yield; 4) A canopy with smaller leaf area index tended to have a higher yield improvement, and 5) Increases in assimilations and yields were highly dependent on growing-season climatic conditions. The solar radiation, temperature, and relative humidity were the main climate drivers that impacted the yield improvement, and they had opposite correlations with improved yield during the vegetative phase compared to the reproductive phase.

CONCLUSIONS

In a world with elevated [CO], genetic engineering crop photosynthesis should focus more on improving . Further, long-term climate conditions and seasonal variations must be considered to determine the improvements in soybean canopy photosynthesis and yield at the field scale.

IMPLICATIONS

Quantifying the effectiveness of changing and helps understand their individual and combined contributions to potential improvements in assimilation and yield. This work provides a framework for evaluating how altering the photosynthetic rate parameters impacts soybean yield and assimilation under different seasonal climate scenarios at the field scale.