A biophotonic sensing method for plant drought stress

Physiologically-based drought stress evaluation is very desirable for sustainable plant production, but effective measures and technologies are lacking. Drought stress limits photons utilized for photosynthetic reactions and delayed fluorescence (DF) generated by photosystem II (PSII). In this research, DF is measured as an output variable of the PSII phototransduction system and its dependence on photon utilization rate as affected by water status is modeled and analyzed. This yields an effective way to define and measure plant water status or deficiency (drought stress) according to PSII photon utilization rate. Water deficiency is determined by the deficit from the maximum photon utilization rate achievable through rehydration. The method was validated experimentally with drought-stressed plant samples. Analysis and experiments show that this drought-dependent deficit in photon utilization rate can be effectively evaluated from measured DF emissions and it varies with drought severity.