Photosynthetic characteristics changes and evaluation on shade tolerance of three kinds of Lamiaceae wild flowers under shading

【Objective】 This study explored the effects of shading on morphology, photosynthetic indexes and chlorophyll fluorescence parameters of Lamiaceae flowers, in order to provide theoretical basis for Lamiaceae flowers' development and utilization.【Method】 Leonurus japonicus, Glechoma longituba, Ajuga nipponensis of potted flowers as tested materials were subjected to 30%, 50%, 70% and 90% shading treatment, with unshading ones as control(CK). Their photosynthetic indexes and chlorophyll fluorescence parameters were studied, and the shade tolerance was evaluated by principal component analysis and membership function.【Result】 The leaf length, leaf width and plant height of the three kinds of Lamiaceae flowers treated with shading were higher than those of CK. Leaf water content was positively correlated with shading intensity, while leaf weight was negatively correlated with shading intensity. The photosynthetic pigment contents of L. japonicus and G. longituba under shading treatment continued to increase with the increase of shading intensity. A. nipponensis showed a change trend of rising first and then falling. The chlorophyll a/b(Chla/b) of G. longituba and A. nipponensis were both significantly lower than those of CK(P<0.05). With the increase of shading intensity, the apparent quantum yield(AQY) of the three kinds of Lamiaceae flowers increased first and then decreased. and the light saturation point(LSP), light compensation point(LCP) and dark respiration rate(R_d) decreased. The maximum net photosynthetic rate(P_nmax) of L. japonicus increased first and then decreased, while the P_nmax of G. longituba and A. nipponensis decreased all the time. Except for chlorophyll fluorescence parameters of initial fluorescence(F_o), absorbed light energy per unit area(ABS/RC) and dissipated energy(DI_o/RC), the values of the remaining parameters of the three kinds of Lamiaceae flowers increased to different degrees under shading compared with CK. Using principal component analysis and membership function to comprehensively evaluate above indexes, the results showed that the shade tolerance of G. longituba and A. nipponensis was better than that of L. japonicus.【Conclusion】 With the decrease of light intensity, the morphology, photosynthetic characteristics and chlorophyll fluorescence parameters of L. japonicus, G. longituba and A. nipponensis are affected differently, and show different shade tolerance. The suitable shading environment for L. japonicus is 30% shading, while the growth of G. longituba and A. nipponensis is better under 50% shading.