Unravelling the impacts of phosphorus deficiency on the photosynthetic machinery to determine the phosphorus status of plants
PhD defence by Andreas Carstensen
Phosphorus (P) is an essential plant nutrient with a structural role in nucleic acids, ATP, NADPH, and phospholipids. Phosphorus deficiency is a major limiting factor in global plant production, and the main source of P fertilizer (rock phosphate) is a finite and non-renewable resource, predicted to become limited in the future. Estimating plant available P in the soil is usually associated with many uncertainties, and the correlation between extracted P and true plant P uptake is often poor when using the classic soil P extraction analyses. Consequently, there is an urgent need for better real-time estimations of P status in plants.
This PhD study investigated chlorophyll a fluorescence as a new analytical approach to reveal the P status of plants directly in the field. The chlorophyll a fluorescence fingerprint is a reliable probe of photochemistry, and the sensitive signal is a powerful tool for detecting multiple plant stresses.
The work demonstrated that P deficiency caused specific changes in the chlorophyll a fluorescence transient, which was correlated with the current plant P status. Furthermore, a prediction model was developed to estimate the P status of plants using chlorophyll a fluorescence measurements. The mechanisms behind the discovery were further described by presenting a comprehensive biological model for how P deficiency affects the photosynthetic machinery. Finally, a new handheld device for detecting P deficiency was developed, which was shown to provide a unique opportunity for a timely correction of P deficiency under field conditions.
The PhD thesis concludes that chlorophyll a fluorescence is a promising method for revealing P status of plants, thereby providing a unique opportunity for timely detection of P deficiency in agriculture, with the potential to increase P use efficiency in global plant production.
Martin Broadley, Professor, University of Nottingham, United Kingdom
Gitte Rubæk, Associate professor, Aarhus University, Denmark
Poul Erik Jensen, (Chairman) Professor, University of Copenhagen, Denmark
Søren Husted, Professor, University of Copenhagen, Denmark