Photochemical reflectance index and solar-induced fluorescence for assessing cotton photosynthesis under water-deficit stress
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2018, The Institute of Experimental Botany. Rapid and non-destructive assessment of water status is essential to enhance crop performance. This study aimed to evaluate photosynthetic performance and to monitor water status in cotton under field conditions. A two-year experiment was conducted with three irrigation regimes to measure the following parameters: photochemical reflectance index (PRI), structural independent pigment index (SIPI), water index (WI), solar-induced fluorescence (SIF; retrieved from reflectance by using Fraunhofer line-depth method), gas exchange, and chlorophyll fluorescence (CF). The results showed that PRI decreased > 30 % in moderate drought (MD) and >50 % in severe drought (SD), compared with control. PRI was found to be positively correlated with net photosynthetic rate (P N ), stomatal conductance, transpiration rate, actual quantum yield of photosystem II photochemistry ( PSII ), but a negatively correlated with nonphotochemical quenching (NPQ). Solar-induced fluorescence around 761 nm (SIF 761 ) had significant correlations with P N , PSII , and NPQ, but not with maximal quantum yield of PS II photochemistry (F v /F m ). The relationship between PRI and P N was stronger at the beginning of water stress (R 2 = 0.86) than for the all stress stages (R 2 = 0.54), indicating that PRI could be more effective for assessing P N of cotton at early water stress. PRI was better correlated with relative water content and photosynthetic parameters than SIPI and WI and so it could also be a good indicator to evaluate cotton water status.
