The impact of the photosynthetic traits’ downregulation on the leaf nutrient composition
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The atmospheric CO2 concentration determines to a large extent how plants perform their photosynthesis. The photosynthetic parameters, Vcmax and Jmax, explain respectively the maximum rate of RuBisCo carboxylase activity and the maximum rate of photosynthetic electron transport. Prior research evidenced a positive relation between these photosynthetic traits and leaf nitrogen (Smith et al., 2019). This research aims to analyse the relationship between the photosynthetic parameters, nitrogen and phosphorus and the micronutrient content (zinc, iron and calcium) of four plant species. The plant material has been derived from a field study in the Ebro basin (north-eastern Spain). The photosynthetic parameters have been measured by using a leaf gas exchange machine. Input from the experience during the internship at the nutrition company DSM has been used to determine which micronutrients (iron, zinc and calcium) should be focused on to increase the relevance of this research. For the elemental analysis of the leaf material, two machines have been used: the CN-analyser and the Picofox TXRF spectrometer. The created dataset contains data from 34 samples, including five groups (comprising four species: alfalfa, almond, grape, and apple; the latter including irrigated and nonirrigated samples), analysed on photosynthetic activity and elemental content. The results of the research have been derived by using analysis of (co)variance (ANOVA and ANCOVA) statistical tests and by analysing the variance for the absolute values for micronutrients compared to the variance with the ratios with nitrogen (N) and phosphorus (P). The results of the F-test indicate a decrease in variance with the ratios with N and P compared to the absolute values of micronutrients, which gives insights in the stoichiometry of the leaf. The ANOVA tests reveal a significant difference in nutrient content per plant species. When performing the ANCOVA tests, it became clear that a significant correlation exists between Jmax and Vcmax and the P concentration. Also, the P concentration is a significant determinant for the absolute zinc (Zn) concentration and the Zn:N and Zn:P ratio in the plant, this is a positive correlation. To conclude, the results of this research indicate that an increase in CO2 leads to a downregulation of the photosynthetic traits, resulting in a lower concentration of leaf P, and a significantly lower concentration of Zn in the leaf. Further research is needed to perform this analysis on a larger sample size and to analyse other plant material besides the leaf, such as fruits and grains.