Photosynthetic response to different irradiances of undergrowth plants in tree-herb plantation

Photosynthetic characteristics of Illicium henryi and Farfugium japonicum herbs were determined, with Cinnamomum camphora seedling as the control, under low, medium and high canopy densities of C. camphora forest in Songjiang, Shanghai. Results showed that I. henryi and F. japonicum had higher apparent quantum efficiency (AQE) and lower light compensation point (LCP). On the other hand, C. camphora seedling exhibited higher maximum photosynthetic rate (P_max) and light saturation point (LSP). AQE of three plant species increased with increasing canopy density, and with significant differences among different canopy densities. For I. henryi and F. japonicum, P_max initially increased and then eventually decreased, but that for C. camphora seedling decreased right throughout with increasing canopy density. While dark respiration (R_d) initially decreased and then increased for C. camphora seedling, that for undergrowth I. henryi and F. japonicum steadily decreased. There was an obvious adaptation of C. camphora seedling to low irradiance, due to decreasing LCP and LSP. But its stressed photosynthesis under high canopy density was observed. While P_max in I. henryi and F. japonicum occurred under medium canopy density, low irradiance was accommodated by not only low LCP and LSP, but also low energy consumption. This showed that I. henryi and F. japonicum were highly tolerant to shade.