Chlorophyll fluorescence imaging as a tool to understand the impact of iron deficiency and resupply on photosynthetic performance of strawberry plants

- Chl fluorescence imaging could be used to evaluate Fe problems and fertilization management.
- Fe-stressed leaves displayed spatio-temporal heterogeneity in fluorescence response.
- ϕII, measured in interveinal mesophyll areas is the best indicator of Fe deficiency.

Bare-root transplants of strawberry (Fragaria × ananassa Duch. cv 'Diamond') were grown in a Hoagland's nutrient solution with or without Fe. Forty two days after Fe deprivation, recovery was induced by addition of 10 μM of Fe (Fe-EDDHA) to the Fe(−) nutrient solution. Total leaf chlorophyll concentration in young leaves decreased progressively with time in Fe-deprived plants, and before Fe resupply it was only 6% of that of Fe(+) control plants. Spatio-temporal changes on photosynthetic efficiency were monitored by imaging chlorophyll a fluorescence in four areas of interest (AOIs) located on the midrib and on interveinal mesophyll areas of leaf blades. Chlorophyll fluorescence images (Fv/Fm, ϕII, NPQ, qp) showed a large spatial variation, particularly at day 42, with greater values in midrib areas. Temporal changes were also observed in all measured parameters along the experimental period, but the onset and intensity of impact was clearly different between parameters. Maximal efficiency of PSII (Fv/Fm) was the last parameter to be affected, being the effects visible only in plants that had lost over 90% of their chlorophyll (day 42). In contrast, actual efficiency of PSII (ϕII) and photochemical quenching (qp) were affected earlier on, showing noticeable changes by day 20, when chlorophyll concentration had declined by 38%. Decreases in ϕII were balanced by increases in quantum yield of non-regulated energy dissipation (ϕNO). Fluorescence parameters, with the exception of ϕII and Fe content, recovered within eight days following Fe resupply to values found in Fe(+) plants. The results of this study indicate that: (i) Chl fluorescence imaging is a useful technique to evaluate Fe deficiency (ii) Fe stress generates spatio-temporal heterogeneity in fluorescence response (iii) ϕII measured in interveinal mesophyll areas could be used as an early and fast indicator of Fe deficiency and could be applied for fertilization management.