Jiating Li, Peng Fu, Carl J Bernacchi

Plants in natural environments often face unpredictable, co-occurring stresses, such as heatwaves and droughts, a trend that is intensifying with climate change. Reflectance spectroscopy, a valuable tool for monitoring plant health, has been widely used to detect single stress, but its potential for assessing combined stresses remains underexplored. While several reviews have explored plant molecular and physiological responses to combined stress, none has discussed the role of spectroscopy in this context. This review addresses this gap by synthesizing existing findings on plant spectral responses to two common stress combinations: drought + nitrogen deficiency and drought + heat stress. Although a limited number of studies exist, they reveal that plant spectral responses to combined stresses are often unique compared with individual stresses. These results point to three potential pathways by which spectroscopy can enhance plant resilience under combined stress: generating new hypotheses, facilitating the selection of broad-spectrum stress-tolerant genotypes, and improving stress detection for precision management. This review also suggests that spectral responses to combined stresses differ from individual stresses across spectral regions, plant species, scale of spectral sensing, and possibly other factors not yet considered here. To advance reflectance spectroscopy as a tool for studying combined stress, future research should prioritize enhanced experimental designs, standardized data presentation, integrated modeling, and sensor synergies.