Abstract: Gas exchange of Capsicum annuum L. under shading and greenhouse conditions was measured by LI6400 Portable Photosynthetic System. The lightresponse curves of photosynthesis and instantaneous wateruse efficiency were fitted by lightresponse models. The change tendency of the net photosynthetic rate and instantaneous wateruse efficiency of leaves were measured under different light conditions. The results showed that the maximum net photosynthetic rate (P_nmax) and transpiration rate (T_r) ofC. annuum leaves in greenhouse were lower than that under shading, whereas the maximum instantaneous wateruse efficiency (WUE_instmax) of C. annuum in greenhouse was higher than that under shading, and the corresponding saturating lightintensity (I_instsat) was lower than that under shading. There was no significant difference of WUE_instmax and I_instsat between the conditions in greenhouse and in shading (P>0.05). Furthermore, there was significant difference between I_sat(corresponding to P_nmax) and I_instsat(corresponding to WUE_instmax) (P<0.05), and the values of I_sat  were greater than the values of I_instsat. Our results indicate that both photosynthesis and instantaneous wateruse efficiency of C. annuum leaves are not synchronized for each of two different light conditions.

Key words: Hurst index, spatiotemporal dynamics, NPP, CASA, Loess Plateau., human activity