Effect of continuous cropping on Angelica sinensis diurnal photosynthetic dynamics

Diurnal dynamics of photosynthesis under three rotation systems (potato-wheat-A. sinensis, A. sinensis-wheat-A. sinensis, and wheat-A. sinensis-A. sinensis rotation system over a three-year period) were monitored by using portable CI-310 Photosynthetic Gadget. Based on the results, diurnal variations in A. sinensis Pn, Tr, Gs and Ci exhibited di-peak curves, with obvious midday (12:00) depressions. However, difference existed in the time and value of diurnal variation curve peaks and troughs for Pn, Tr, Gs and Ci. The diurnal tendencies of Pn, Ci and Gs suggested that the midday depression was caused by stomatal conditions. Wheat-A. sinensis-A. sinensis and A. sinensis-wheat-A. sinensis rotation systems significantly decreased leaf chlorophyll content in A. sinensis. Diurnal average values of Pn, Tr, Gs and Ci under potato-wheat-A. sinensis rotation system were significantly higher than those under wheat-A. sinensis-A. sinensis rotation system. Continuous cropping significantly decreased A. sinensis leaf chlorophyll content and Gs, Ci, Pn and Tr, which resulted in decreased A. sinensis yield.