Sensitivity of sun-induced chlorophyll fluorescence (SIF) and hyperspectral reflectance to drought response in soybean genotypes with contrasting affinities for arbuscular mycorrhizal fungi

Abstract

Increasing frequency and severity of drought events impact global and domestic agricultural productivity. Monitoring drought in agricultural fields with remote sensing can provide faster, lower-cost decision management support for critical field management activities. We evaluated the application of sun-induced chlorophyll fluorescence (SIF) emitted at red (SIF_Red) and far-red (SIF_FarRed) wavelengths in comparison with chlorophyll- and xanthophyll-sensitive reflectance-based remote sensing indices (NDVI, NIR_V, NIR_VP and PRI) for drought stress monitoring at the canopy scale. To do so, we evaluated impacts of drought stress on two soybean varieties with similar phenology but contrasting affinities for arbuscular mycorrhizal fungi (AMF), which can provide host plants with extended access to water and nutrients in exchange for carbohydrates. Drought response physiology of the two genotypes was further explored using leaf level photosynthetic gas exchange, chlorophyll fluorescence, water potential and phenology. We observed distinct responses, with the low-affinity genotype exhibiting lower SIF_Red and more negative midday leaf water potential, as well as reduced growth and development rate compared with the high-affinity genotype. SIF_FarRed and NIR_VP exhibited the strongest correlation with canopy photosynthesis followed by NIR_V. We also observed different timing of drought response parameters associated with different remote sensing signals. Our findings demonstrate the particular sensitivity of SIF to physiological drought responses, conferred here through AMF associations in the soil, and provide insight to the physiological drought responses tracked by different remote sensing signals.