No abstract

With an increase in growth irradiance (from 15 to 100 % of full sunlight, I 15 to I 100 ), the maximum net photosynthetic rate (P max ), compensation (CI) and saturation irradiances of A. annua increased. At full sunlight, A. annua had a high capacity of photosynthesis, while at low irradiance it maintained a relatively high P max with a low CI. The height and diameter growth, total and leaf biomass, and artemisinin content of A. annua decreased with the decrease in irradiance, which might be connected with lower photosynthesis at lower than at higher irradiance. Irradiances changed biomass allocations of A. annua. The leaf/total mass ratio of A. annua increased with decreasing irradiance, but the root/total mass ratio and root/above-ground mass generally increased with increasing irradiance. Thus A. annua can grow in both weak and full sunlight. However, high yield of biomass and artemisinin require cultivation in an open habitat with adequate sunshine.

Saturation (SI) and compensation (CI) irradiances [μmol(photon) m -2 s -1 ] were 383.00±18.40 and 12.95±0.42 for wild C. nitidissima (in mid-July) and 691.00±47.39 and 21.91±1.28 for wild C. sinensis, respectively. C. nitidissima is a shade tolerant species, whereas C. sinensis has a wide ecological range of adaptability to irradiance. Both wild and cultivated C. nitidissima demonstrated low maximum net photosynthetic rate, maximum carboxylation rate, maximum electron transfer rate, and SI, which indicated low photosynthesis ability of leaves that were unable to adapt to strong irradiance environment. Both C. nitidissima and C. sinensis demonstrated strong photosynthetic adaptabilty in new environments. Hence proper shading may raise photosynthetic efficiency of cultivated C. nitidissima and promote its growth.Additional key words: compensation irradiance; net photosynthetic rate; saturation irradiance.--