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Table 1 Mann–Whitney U test statistics for significant differences at the 0.05 probability level (marked with asterisks sign) in OJIP parameters between X-ray exposed and non-exposed adjacent area (the same size and bordering the exposed area) of pepper leaves (n = 4)

From: Analysis of trace metal distribution in plants with lab-based microscopic X-ray fluorescence imaging

Chl fluorescence parameters N Median U Z Asymp. Prob > |U|
ΦPo  
 Area under X-ray 4 0.985 3 − 1.29904 0.19393
 Adjacent area 4 0.993    
ΦRE1o  
 Area under X-ray 4 1.23 12 1.01036 0.31232
 Adjacent area 4 1.1    
ΦET2o  
 Area under X-ray 4 0.951 0 − 2.16506 0.03038*
 Adjacent area 4 0.991    
ΦPSII
 Area under X-ray 4 0.823 4 − 1.01036 0.31232
 Adjacent area 4 0.883    
  1. The Z value represents standardized value corrected for the presence of ties in case of similar values which are assigned to the same rank. Asymp. Prob > |U| indicates the asymptotic significance; when it is lower than the statistical threshold, the alternative hypothesis that the two distributions are different, is accepted. ΦPo—maximum quantum yield of primary PSII photochemistry, ΦET2o—quantum yield of the electron transport flux from QA to QB, and ΦRE1o—quantum yield of the electron transport flux until PSI electron acceptors according to Stirbet and Govindjee [33]. ΦPSII- operating PSII efficiency according to Küpper et al. [25]