The effect of Al stress on leaf pigment contents, chlorophyll (Chl) a fluorescence transient, and leaf gas exchange of Citrus sinensis and Citrus grandis were investigated in sandy culture with nutrient solution (control) or supplemented by 0.5 mM AlCl3·6H2O (Al toxic) for 54 weeks. We found a significant decline of Chl a, carotenoids (Car), Ch a/b, and Car/Chl (a+b) in C. grandis caused by Al stress. Except the significant increase of Car/Chl (a+b), no remarkable difference was found in C.

more »

... nsis. The Al-induced downregulation of CO2 assimilation was related to the imbalance of reduction and oxidation of primary quinone acceptor of PSII in two Citrus species. Compared to C. grandis, increasing ratio of Car/Chl (a+b) for photooxidation protection and decreasing inhibition of electron transfer contributed to electron conversion efficiency maintenance of PSII under Al stress in C. sinensis, a relatively Al-tolerant species. efficiency of Rubisco (= PN/Ci); Chl -chlorophyll; Ci -intercellular CO2 concentration; E -transpiration rate; ET0 -energy flux beyond QA; F0 -minimal fluorescence of dark-adapted state; Fm -maximal fluorescence; Fv -variable fluorescence (= Fm -F0); Fv/F0 -the ratio of variable fluorescence to initial fluorescence; Fv/Fm -maximum photochemical efficiency of PSII; gs -stomatal conductance; PIabs -performance index of absorption; PN -net photosynthetic rate; RC -reaction center; TR0 -energy trapping flux by PSII center; WUE -water-use efficiency (= PN/E); Ψ0 -efficiency that an electron moves further than QA -.