Dynamics Of Leaf Water Use Efficiency In Artemisia Ordosica In Response To Environmental Factors

We aimed to understand the dynamics in leaf water use efficiency?WUE?in a typical desert plant Artemisia ordosica in the semi-arid region of northwestern China and its responses to environmental factors.The leaf stomatal conductance?g_c?,net photosynthetic rate?P_n?and transpiration?Tr?of Artemisia ordosica were measured using Li-6400 portable photosynthetic analyzer in the growing season of 2018-2019.We analyzed the relationship between WUE and environmental factors over the two-year growing seasons.There are the main results and conclusions:?1?During the whole growing season,the seasonal variation in leaf WUE in Artemisia ordosica was mainly controlled by soil water content?SWC?.There was a SWC threshold value of 0.1 m³/m³for WUE.When SWC?0.1 m³/m³,WUE increased with increasing SWC,and when SWC>0.1 m³/m³,WUE decreased with increasing SWC.?2?The controlling factors of WUE differed with phenophases.Photosynthetically active radiation?PAR?was dominant factor controlling leaf WUE during leaf expanding period,SWC during leaf expanded period,and air temperature?T_a?during leaf coloration period.WUE was lowest at expanded leaf phase and highest at the leaf coloration phase.The daily change of WUE showed an asymmetric trend around 12:00,and the highest value mostly appeared in the morning,and the WUE in the morning was generally higher than the WUE in the afternoon.On a daily scale,the dominant factor affecting the WUE was vapor pressure deficit?VPD?,and there was a negative correlation between them.?3?Soil water content modified the response of WUE to environmental factors.The WUE were more sensitive to VPD when SWC?0.08 m³/m³.When SWC>0.08 m³/m³,the WUE was more sensitive to PAR,T_aand leaf nitrogen content per unit mass(N_mass).When soil moisture was deficient,the leaf WUE was higher than that in water sufficiency,indicating that under drought or water limited conditions,Artemisia ordosica perform a conservative strategy using soil moisture efficiently.This strategy is beneficial to surviving frequent dry conditions in arid and semi-arid area.The research results are an important addition to better understanding the adaptation mechanism of desert plants to environmental changes and making management strategies for desert ecosystems.