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Heat stress

Heat stress affects the production of ovules during bloom. Heat, in the sense of the model, is defined as exceeding a plant-specific threshold during the daylight period (photo period). For this period, the temperature is assumed as being:

\[T_{photo} = T_{max} - \frac{T_{max}-T_{min}}{4}\]

\(T_{photo}\) Temperature during the photo period \([^{\circ}C]\)
\(T_{max}\) Daily maximum temperature \([^{\circ}C]\)
\(T_{min}\) Daily minimum temperature \([^{\circ}C]\)

During a defined plant-specific phase of increased sensitivity, extreme temperatures affect the crop according to Challinor et al. (2005):

\[F_H = 1 - \left( \frac{T_{photo} - T_{critH}}{T_{limH} - T_{critH}} \right) \cdot r_F\]

\(F_H\) Heat impact on ovules \([d^{-1}]\)
\(T_{photo}\) Temperature during the photo period \([^{\circ}C]\)
\(T_{critH}\) Critical temperature for heat stress effect \([^{\circ}C]\)
\(T_{limH}\) Maximum temperature for heat stress effect \([^{\circ}C]\)
\(r_F\) Daily flower emergence rate \([d^{-1}]\)

The daily flower emergence rate during bloom is calculated following an idea of Moriondo et al. (2011):

\[r_F = p_{F,d} - p_{F, d-1}\]

\(r_F\) Daily flower emergence rate \([d^{-1}]\)
\(p_{F, d}\) Fraction of today opened flowers
\(p_{F, d-1}\) Fraction of yesterday opened flowers

where

\[p_F = \frac{1} { 1 + (\frac{1}{0.015} - 1) \cdot e^{-1.4 \cdot D_{BF}} }\]

\(p_F\) Fraction of open flowers
\(D_{BF}\) Days after begin of bloom \([d]\)

The reduction factor is derived from the smallest value of \(F_H\) during the sensitive phase:

\[\zeta_H = min(F_{H1},\, ... \,,F_{Hn} )\]

\(\zeta_H\) Reduction factor heat stress
\(F_{H1}\) Heat impact at the first day of the sensitive phase \([d^{-1}]\)
\(F_{Hn}\) Heat impact at the last day of the sensitive phase \([d^{-1}]\)

Heat stress reduces the assimilate flow to the storage organ:

\[W_s = A_g \cdot a_s \cdot \zeta_H\]

\(W_s\) Biomass of the storage organ \([kg \, TM \, ha^{-1}]\)
\(A_g\) Gross CO2 assimilation \([kg \, CO_2 \, ha^{-1} \, d^{-1}]\)
\(a_s\) Assimilate partitioning coefficient for the storage organ
\(\zeta_H\) Reduction factor heat stress

References

  • Challinor et al. (2005): Simulation of the impact of high temperature stress on annual crop yields. Agricultural and Forest Meteorology 135, 180 - 189.

  • Mirschel, W. & Wenkel, K.-O., 2007. Modelling soil-crop interactions with AGROSIM model family. In: K.C. Kersebaum, J.-M. Hecker, W. Mirschel and M. Wegehenkel (Editors), Modelling water and nutrient dynamics in soil crop systems. Springer, Stuttgart, pp. 59- 74.

  • Moriondo et al. (2011): Climate change impact assessment: the role of climate extremes in crop yield simulation. Climatic Change 104 (3-4), 679-701.