Dynamic Changes In Leaf-level Resource Use Efficiencies And Its Regulatory Mechanisms In Artemisia Ordosica In The Mu Us Desert

Resource use efficiencies（RUEs）of a plant,especially light use efficiency（LUE）,water use efficiency（WUE）and nitrogen use efficiency（NUE）are key indicators of its acclimation to climate change and extremes.Understanding the variation and regulatory mechanisms of RUEs of dominant desert plants is critical to address the adaptability and stability of desert ecosystems under climate change.However,at present,trade-offs and regulatory mechanisms of RUEs in desert plants are not yet clear.This study was based on season-long in-situ observations,lab analysis and continuous measurements of leaf photosynthesis and leaf traits of the dominant desert subshrub species,Artemisia ordosica,and environmental factors in the Mu Us Desert from 2014 to 2019.It was aiming to analyze the temporal and relative changes in RUEs,and their biophysical controls,to examine the resource use strategy and acclimation mechanism to environmental stress and to further clarify regulatory mechanism of resources（light,nitrogen and water）in RUEs of A.ordosica.The key findings are as follows.（1）There was obvious interannual variation in RUEs during the growing season from 2014 to 2019（P<0.01）.Among the RUEs,the seasonal variation was largest in WUE（CV=76%）and the lowest in LUE（CV=48%）.The mean annual LUE,WUE,and NUE in growing season over years 2014–2019 was0.056±0.003 mol mol^-1,112.94±86.59μmol mol^-1,and 7.62±3.98μmol g^-1 s^-1,respectively.NUE was positively correlated with LUE and WUE（P<0.01）,while LUE and WUE being negatively correlated on seasonal scale（P<0.05）.This trade-off among RUEs was most significant in leaf-expanded period and weakest in leaf-coloring period.（2）Specific leaf area（SLA）was the key biotic factor,and soil total nitrogen（Nsoil）and soil water content（SWC）were the main abiotic factors to regulate RUEs in A.ordosica at both seasonal and interannual scales.At seasonal scale,WUE was more sensitive to environmental changes than LUE and NUE.The sensitivity of RUEs to biophysical factors differed with phenological periods,being mainly sensitive to biotic factor in leaf-expanding period and most sensitive to abiotic factor in leaf-coloring period.（3）A higher resource use efficiency in corresponding resource stress status indicated a conservative strategy of A.ordosica to acclimate to the corresponding stressed condition.WUE and NUE in drought period(SWC≤0.10 m³ m^-3)and nitrogen-deficient period(Nsoil≤0.11 g kg^-1)became higher,respectively.Furthermore,the WUE in dry years was higher than wet years.The NUE in nitrogen-deficient years was higher than nitrogen-rich years.Thus,our result support the ecological economic theory,in which plant can reduce the constraints by maximizing the use efficiency of the most limiting resource in response to resource stress.The response patterns of RUEs to SLA were same under different soil water and soil nitrogen conditions.And the response sensitivities of RUEs to SLA decreased in drought and nitrogen-deficiency period.The response patterns and sensitivities of RUEs to abiotic factors（Nsoil,SWC and T）in drought period and nitrogen-deficiency period were significantly different from wet period and nitrogen-rich period,respectively.（4）Leaf-level multiple-resource use efficiency（m RUE）decreased with the increase of availability of Nsoil and SWC,being coincided with the law of“declining marginal returns”that implies decreasing levels of RUEs with increasing resources supply,and indicating that RUEs were mainly limited by availability of resources.LUE decreased with the increase of availability of PAR and Nsoil,and WUE decreased with the increase of availability of Nsoil and SWC.Nsoil and SWC were the main resources limiting m RUE,confirmed that Nsoil and SWC were the dominant abiotic factors of seasonal and annual variations in RUEs.In summary,soil water and nitrogen were the main abiotic factors limiting RUEs.SLA was the main biotic determinant of variations in RUEs.A.ordosica selected the resource-conservation strategy to acclimate to environment stress.Our findings are important addition to the understandings of response and acclimation strategies of desert plants to climate change and helpful to understand the functional adaptation strategies of desert ecosystem to environmental change.It could provide theoretical support for improving scientific management of desert and stability of desert ecosystems.