Representing persistent stress effects in LPJmL through sink limitation and tissue damage

Global crop models such as LPJmL typically represent environmental stress through reductions in photosynthesis and leaf area development. Such predominantly source-limited approaches allow for strong post-stress compensation and exhibit little persistence of stress effects. This results in a weak dependence of yield losses on stress timing and an underestimation of impacts during sensitive developmental phases.

We present an enhancement of the LPJmL crop module that explicitly represents persistent stress effects through sink limitation and tissue damage. The main novelty is the introduction of sink limitation, which constrains growth during vegetative development and yield formation during grain filling. Specifically, the number and potential size of harvest organs are determined during flowering, a phenological phase that is highly sensitive to stress. Stress during this period leads to a persistent reduction in sink capacity, limits subsequent growth, and reduces harvest index. Sink limitation leads to a dynamic downregulation of photosynthesis, a process currently absent from the LPJmL crop module.

In addition, we introduce tissue damage as a distinct and partially irreversible pathway to represent impacts of conditions such as waterlogging and frost, which are poorly captured by existing stress formulations.

The model is initially implemented and evaluated for wheat, focusing on nitrogen and water limitation as well as newly introduced waterlogging and frost stress. Heat stress is addressed in complementary work. By representing persistence, this development improves LPJmL’s sensitivity to stress timing and severity and strengthens its mechanistic basis for climate impact assessments.