Partitioning of evapotranspiration and the influencing factors of evapotranspiration components in a shrub ecosystem dominated by Artemisia ordosica and Hedysarum fruticosum var. mongolicum in the Mu Us Desert, Northwest China.

Evapotranspiration (ET) is an important part of water cycle and energy flow in ecosystem. Accurate estimation of ET and its components is critical for understanding the impacts of ecophysiological processes on ecosystem water balance and plant water use strategy. Using the eddy-covariance technique and the micro-lysimeter, we measured ET, evaporation (E), transpiration (T) of the Artemisia ordosica-Hedysarum fruticosum var. mongolicum shrubland in the Mu Us Desert during May 20 to September 15, 2019, quantified the ET components, and analyzed the seasonal characteristics and influencing factors of ET and its components. The results showed that T was the main component of ET in the growing season, with a T/ET of 53.1%. T/ET increased and E/ET decreased as precipitation decreased. The partitioning of evapotranspiration was regulated by precipi-tation. At the seasonal scale, the value of E was positively correlated with soil water content at 10 cm depth (SWC10) and net radiation (Rn), while SWC10 was the main factor influencing E. The value of T increased with the increases of Rn and leaf area index (LAI), and increased first and then decreased with the increases of soil water content at 30 cm layer (SWC30). T was affected by SWC30, Rn and LAI. Moisture was the main influencing factor of ET. The ET/P in the growing season was 109.2% and was 250.5% in May, indicating that the water consumption of ET in early growing season was partly from the precipitation in non-growing season.

[Simulation on photosynthetic-CO2 response of Quercus variabilis and Robinia pseudoacacia in the southern foot of the Taihang Mountain, China.] / å¤ªè¡Œå±±å—éº“æ “çš®æ Žå’Œåˆºæ§å ‰åˆä½œç”¨-CO2响应模拟.

In this study, leaf photosynthetic CO2-response curves of Quercus variabilis and Robinia pseudoacacia were measured using a Li-6400XT photosynthetic measurement system in the southern foot of the Taihang Mountain, China. The rectangular hyperbola model (RH), nonrectangular hyperbola model (NRH) andYe model (YZP) were used to fit photosynthetic-CO2 response curves and compare photosynthetic parameters, including the maximum net photosynthetic rate (Amax), the initial carboxylation rate (η), light respiration rate (Rp), CO2 compensation point (CCP) and CO2 saturation point (CSP). Compared with the NRH and YZP models, Amax, η, Rp and CCP obtained by the RH model were higher, and were 59.8%, 128.6%, 133.4% and 19.8% higher than the measured values. The accuracy of the RH model was lower and its relative error was higher than that of the NRH and YZP models.Compared with the RH and YZP models, Amax fitted by the NRH model was higher, and was 11.1% higher than the measured value. η, Rp and CCP fitted by the NRH model were closer to the measured values. CO2 saturation phenomenon of photosynthesis could be simulated by the YZP model, and Amax and CSP were fitted well. Amax, Rp and CCP in the shaded leaves of Q. variabilis were 31.3%, 5.2% and 14.3% lower than those in the sunlit leaves. Amax, Rp and CCP in shaded leaves of R. pseudoacacia were 23.5%, 11.0% and 5.4% more than those in the sunlit leaves. η in the shaded leaves of Q. variabilis and R. pseudoacacia were 6.9% and 7.0% higher than those in the sunlit leaves, respectively. Rp and CCP of R. pseudoacacia leaves had linear relationships with temperature (T) and photosynthetic active radiation (PAR), and η had a significant relationship with stomatal conductance (gs). η of Q. variabilis leaves was linearly correlated with PAR and gs, and CCP was affected by T and relative humidity. Amax of Q. variabilis leaves had significant positive linear relationships with RH and gs.