Abstract: Knowledge on the dynamics and environmental controls of leaf chlorophyll fluorescence is important in understanding how plant physiological processes respond to abiotic stresses such as drought, strong radiation and extreme temperature in arid and semiarid ecosystems. Therefore, chlorophyll fluorescence measurements are an effective tool for exploring plant adaptive strategies. We conducted in situ field measurements of chlorophyll fluorescence on Artemisia ordosica in Yanchi, Northwest China from June to October in 2012. The objectives were to explore seasonal and diurnal variations of chlorophyll fluorescence parameters, and to examine the relationships between chlorophyll fluorescence parameters and environmental factors. The results showed that the photochemical efficiency (Φ) decreased with increasing photosynthetically active radiation (PAR) and air temperature (T_a), but increased with relative humidity (RH). Therefore, PAR was likely the primary factor driving the changes in chlorophyll fluorescence parameters. Both Φ and the nonphotochemical quenching (NPQ) of A. ordosica varied with PAR on a diurnal basis. The diurnal trends of both T_a and RH, however, lagged the chlorophyll fluorescence parameters by 3-4 h. Given the same PAR, Φ in the early growing season was greater than that in the late growing season, and NPQ was higher in the midgrowing season period than at the late stage of the growing season.

Key words: organic carbon storage, active organic carbon, total organic carbon, carbon pool management index, winter cover crop