Drought sensitivity of solar-induced chlorophyll fluorescence in maize (Zea mays L.)

Solar-induced chlorophyll fluorescence (SIF), derived from satellite remote-sensing observations, is closely related to photosynthetic activity in plants. Here, to evaluate the effectiveness of SIF as an indicator for drought stress monitoring in agricultural crops, specifically in maize, we analyzed the relationship between SIF and the standardized precipitation evapotranspiration index (SPEI) during the rain-fed maize growing season (May–September) in Liaoning Province, China, in 2001–2020. Comparing monthly averages of SIF anomalies (relatively to the 20-year average) with the SPEI, we determined proportions of positive correlations of 77% between negative SIF anomalies and negative SPEI (drought events) and of 67% between positive SIF anomalies and positive SPEI (no-drought periods), indicating a higher SIF sensitivity to SPEI under drought conditions. Sorting years into four categories related to drought properties (length, severity) and crop yield loss, we also analyzed SIF sensitivity to drought for representative years. SIF was sensitive to both concurrent and earlier drought events; its response, affected by a temporal lag of 8–64 days explained by drought length, severity, and previous drought conditions, was more rapid for increasingly severer droughts. Moreover, correlations were highly significant between SIF anomalies and SPEI values from earlier (8–24 days) severe drought events. Finally, maize SIF recovery from drought stress was more complicated when drought events occurred during critical reproductive growth stages (e.g., silking and milk stages), causing substantial yield loss. Over the study period, correlations between average SIF anomalies and maize yield were highest in August, demonstrating the usefulness of SIF for early drought warning and yield loss forecast.