Research PaperModelling the effects of post-heading heat stress on biomass growth of winter wheat

- Heat stress accelerated leaf chlorophyll degradation and reduced leaf photosynthesis.
- Both, lower leaf chlorophyll and smaller leaf area index contributed to reduced biomass growth.
- Quantified relationship between leaf photosynthesis, LAI and heat stress.
- New heat stress routines significantly improved the simulation of biomass growth.

Climate change scenarios project an increase in the frequency of heat stress events, making it critical to quantify adverse heat stress effects on wheat production. Biomass growth determines much of grain yield in winter wheat, but it is substantially reduced under heat stress during the reproductive phase. In this study, leaf photosynthesis, biomass production, and leaf area index (LAI) dynamics were measured under various heat stress treatments in a 4-year phytotron experiment with two winter wheat cultivars. Heat stress at anthesis and during grain filling accelerated the measured degradation of leaf chlorophyll (SPAD) and resulted in a lower leaf photosynthesis rate with decreased final biomass growth. The observed relationships between leaf photosynthesis, LAI, and high temperatures were integrated into the WheatGrow model. In this study, we introduced a new cultivar parameter into the model to simulate cultivar difference in the sensitivity of biomass growth to heat stress. The new heat stress routines in the WheatGrow model significantly improved the simulated growth dynamics and the root mean square error (RMSE) with an independent validation data set for LAI and final aboveground biomass by 40% and 57% under heat stress treatments, respectively. This improvement in the crop model WheatGrow enables more reliable studies on climate change impacts and reduces uncertainties in simulations, particularly the impacts of extreme temperature events on crop growth and yields.