Temperature for Wheat

Temperature affects wheat growth and development throughout the APSIM wheat model. The main pathways represented in Wheat.json are listed below.

Temperature

  • Drives phenological development through Phenology.ThermalTime.
  • Controls phase progression rates and duration (thermal time accumulation).
  • Controls leaf appearance rate through the Haun stage relationship:
    • HaunStage Delta = ThermalTime / Phyllochron.
  • Influences phyllochron-based leaf development via thermal-time driven processes.
  • Influences potential organ processes which reference thermal time (for example, leaf growth and structure dynamics).

High temperature

  • Reduces thermal-time response above the optimum range:
    • ThermalTime.Response: 0 at 0 degrees C, peak at 26 degrees C, and back to 0 at 37 degrees C.
  • Reduces leaf photosynthesis (RUE model) at hot temperatures:
    • Leaf.Photosynthesis.FT: 1.0 between 15 and 25 degrees C, declining to 0 by 35 degrees C.
  • Reduces leaf growth rate factor at hot temperatures:
    • Leaf.FRGRFunction.FT uses the same temperature response shape as photosynthesis.
  • Can delay vernalisation progress in sensitive genotypes during warm conditions:
    • In the vernalising phase memo, warm temperatures (>18 degrees C) are associated with slower apparent Vrn1 progression in vernalisation-sensitive types.

Low temperature

  • Slows or stops thermal-time accumulation near very low temperatures:
    • ThermalTime.Response is 0 at 0 degrees C.
  • Reduces leaf photosynthesis and leaf growth at low temperatures:
    • Leaf.Photosynthesis.FT and Leaf.FRGRFunction.FT are 0 at 0 degrees C.
  • Can accelerate vernalisation in vernalisation-sensitive wheat:
    • During LeavesInitiating (vernalising phase), cooler temperatures increase Vrn1 expression relative to Haun stage, shortening vernalisation duration.

Note

  • In this base wheat resource, Leaf.FrostFraction is set to 0.0.
  • Explicit frost and heat damage to yield is described separately in Frost and Heat Combined Stress.