δ¹³C as a tool for iron and phosphorus deficiency prediction in crops

Many studies proposed the use of stable carbon isotope ratio (δ13C) as a predictor of abiotic stresses in plants, considering only drought and nitrogen deficiency without further investigating the impact of other nutrient deficiencies, that is, phosphorus (P) and/or iron (Fe) deficiencies. To fill this knowledge gap, we assessed the δ13C of barley (Hordeum vulgare L.), cucumber (Cucumis sativus L.), maize (Zea mays L.), and tomato (Solanum lycopersicon L.) plants suffering from P, Fe, and combined P/Fe deficiencies during a two-week period using an isotope-ratio mass spectrometer. Simultaneously, plant physiological status was monitored with an infra-red gas analyzer. Results show clear contrasting time-, treatment-, species-, and tissue-specific variations. Furthermore, physiological parameters showed limited correlation with δ13C shifts, highlighting that the plants' δ13C, does not depend solely on photosynthetic carbon isotope fractionation/discrimination (Δ). Hence, the use of δ13C as a predictor is highly discouraged due to its inability to detect and discern different nutrient stresses, especially when combined stresses are present.