Seasonal Dynamics And Mechanism Of Photosynthetic Nitrogen Use Efficiency Of Artemisia Ordosica Leafactors

Photosynthetic nitrogen use efficiency?PNUE?,the ratio of maximum net photosynthetic rate?Pmax?of leaf to the nitrogen content per unit area?Narea?,has been considered as an important leaf trait in relation to leaf economics,physiology,and survival strategy.In this study,we aimed at revealing the seasonal variation of leaf PNUE in a typical sandy plant Artemisia ordosica in the Mu Us Sandland and its biophysical control using continuous observation in situ.The main results and conclusions were as follows:?1?The seasonal variation of PNUE was the result of a combination of soil water content?VWC?and leaf nitrogen content per unit mass?Nmass?.VWC was the main factor driving the seasonal variation of PNUE.The trend of PNUE in the whole growing season was similar to that of VWC,increasing with the increase of the latter.In addition,PNUE would also have corresponding fluctuations when Nmass changed largely.?2?The leaf nitrogen allocation of photosynthetic apparatus?PP?refers to the nitrogen content that is allocated to the photosynthetic system as a percentage of the total leaf nitrogen content.There was a positive linear correlation between PP and PNUE throughout the growing season.Nmas also affected PNUE through its effect on PP.However,there was a Nmass threshold of PNUE.PP and PNUE increased with the increase of Nmass when Nmass was below the threshold?25g kg-1?,otherwise,PP and PNUE decreased significantly..?3?VWC was the only abiotic factor that was significantly associated with PNUE.VWC at the depth of 10 cm?VWC₁0?and 30 cm?VWC₃0?was positively correlated with Pmax and PNUE,and negatively correlated with Narca,with higher correlation coefficient for VWC 30 than for VWC 10.And there was a positive liner correlation between PP and VWC 30.VWC also affected PNUE through its effect on PP.We studied the seasonal dynamics of photosynthetic nitrogen use efficiency in Artemisia ordosica and its biophysical control.It was conlcluded that the seasonal variation of PNUE was the result of a combination of VWC and Nmass,and the former was the main driving factor.VWC and Nmass affected PNUE by PP,which is the essential factor affecting PNUE...