Seasonal Dynamics Of Light And CO₂ Response Curves Of Photosynthesis In Artemisia Ordosica In Relation To Environment Factors

Understanding the photosynthetic characteristics of plants and their relationship with environmental factors is of great significance for the accurate simulation of carbon cycle in ecosystems.However,the photosynthetic parameters involved in model fitting are often affected by seasonal changes and interannual differences in environmental factors,leading to large uncertainty in estimate of photosynthetic production.In this study,we used the Li-6400 portable photosynthesis system to measure the diurnal and seasonal changes in light and CO2 response curves in A.ordosica in situ during the growing season from 2012 to 2014.Environmental factors and biological factors were measured simutaneously.We examined the diurnal and seasonal variations in photosynthetic parameters and their year-to-year differences,as well as the main factors affecting photosynthetic parameters.The main results and conclusions were as follows:(1)Diurnally,net photosynthetic rate(Pn)showed a trend of one-peak curves and two-peak curves.(2)Seasonally,the variations of Pn was significant in 2012 and 2013,and not significant in 2014,the results showed that the seasonal dynamics of Pn was significantly different in years.(3)The response of Pn to light and CO2 were different in different years and in different phenoloeical periods,the maximum net photosynthetic rate(Pnmax),maximum carboxylation rate(Vcmax),maximum electron transportation rate(Jmax)of the main parameters representing the photosynthetic characteristics of A.ordosica were varied significantly with seasons,ranges of Pnmmax,Vcmax and Jmax being 11.43-45.55 ?molCO2·m-2·s-1,31.1-93.29?mol·m-2·s-1,23.1-74.44?molCO2·m-2·s-1,respectively.(4)Analysis of seasonal variations of photosynthetic parameters of A.ordosica showed that the seasonsal trends of Pnmax,Vcmax and Jmax were consistent over years,but the trend was not fixed.Pnmax and light saturation point(LSP)in 2012 was "W" type change trend.The trends of other parameters were different in the same year,and the trends of the same parameters were inconsistent over years.(5)The daily variation of Pn was mainly affected by photosynthetically active radiation(PAR).The main factors affecting Pnmax were specific leaf area(SLA),leaf nitrogen content(Nmass),the main factors affecting Vcmax were SLA,temperature(Ta),and the main factors affecting Jmax were Nmass,Ta,SLA.In addition,dark respiration in light(Rp)was significantly positively correlated with Nmass in 2012,the dark respiration at night(Rd)was significantly positively correlated with Nmass,and the light compensation point(LCP)was significantly negatively correlated with saturated vapor pressure(VPD)in 2013.There were significantly negative correlations between and VPD,and between LCP and SLA.The apparent quantum yield(a)was positively correlated with Nmass.The results above showed that the seasonal dynamics of photosynthetic parameters and physiological parameters were different in years,and the variation of Pn was mainly affected by PAR.The factors affecting photosynthetically physiological parameters were various among different years.The results of this study can provide some data support for vegetation restoration in arid and semi arid areas,and provide some important physiological and ecological parameters for modeling biomass productivity.