| The growth of plants in arid and semi-arid regions of China was frequently affected by high temperature,high radiation and drought.In order to explore the dynamics of typical sandy speices in this area and its response mechanism to environmental fluctuations,this study conducted a long-term in-situ continuous monitoring of chlorophyll fluorescence parameters in Artemisia ordosica in May-September from 2018 to 2019.Meteorological factors and biological factors were measured simultaneously.And statistical regression analysis was used to examine the variations in chlorophyll fluorescence parameters at different time scales in response to biotic and abiotic factors.The main research results were as follows:(1)Diuranlly,the variation in actual photochemical efficiency(?PSII)was"U"-shaped,reaching the minimum at noon.The pattern of diuranl variation in photosynthetic electron transfer rate(ETR)was opposite to that of?PSII,being inverted"U"-shaped and reaching maximum at 13-14 O'clock.Diurnally,?PSIIand ETR were mainly affected by photosynthetically active radiation(PAR),air temperature(Ta)and relative humidity(RH).?PSIIhad a nonlinear quadratic correlation with PAR and Ta.When PAR>1500?mol·m-1s-2or Ta>15?,?PSIIdecreased.?PSIIhad a linear correlation with RH,and it increased with the increasing of RH.ETR had a linear positive correlation with PAR diurally,and a nonlinear quadratic correlation with Taand RH.When Ta>20?or RH>57%,the ETR value decreased.The light intensity and temperature threshold of ETR were both greater than those of?PSII,indicating that when Artemisia ordosica is under environmental stress in a day,the photoreaction center can adjust and transfer excess light energy timely to avoid permanent damage to PSII.(2)Seasonally,?PSIIfluctuated slightly with environmental factors over the growing season.The average value of?PSIIin the growing season from 2018 to 2019 was 0.62±0.04 and 0.66±0.09,respectively.ETR fluctuated greatly on a seasonal scale,and generally presented a trend of firstly increasing and then falling,and it droped rapidly at the end of the growth.The average ETR during the growing season were 72.31±8.43 and 66.35±10.16,respectively.On a seasonal scale,?PSIIand ETR were mainly affected by PAR,Ta,relative chlorophyll content(SPAD)and leaf nitrogen content(Nmass).The sensitivity of?PSIIand ETR to environmental variations differed in different phenological periods,being largere to weak light than to strong light.There is no significant difference in the fitting slope of?PSIIin strong and weak light during the leaf development stage and the mature stage,and the fitting slope increased during deciduous stage.When Ta<10?,the fitting slope of?PSIIand ETR to Tawas small.When 10??Ta<20?,the fitting slope reached the maximum during the deciduous period,followed by the development and maturity periods,while the trend of ETR was opposite.The fitting slope of ETR to high temperature gradually decreased from leaf expanding to defoliation.The sensitivity of?PSIIto SPAD gradually increased from leaf expanding to defoliation.The fitting slope of?PSIIto Nmas was the largest in the mature period.In conclusion,the chlorophyll fluorescence parameters in Artemisia ordosica in Mu Us Sandy Land had obvious seasonal variability.The controlling factors differed with time scales for both?PSIIand ETR,being dominantly controlled by biotic factors at diurnal scale,and by biotic and abiotic factors at seasonal scale.The results of this study are helpful to better understand the photosynthetic adaptation mechanism of desert vegetation and provide scientific support for desert ecosystem management. |
PDF Full Text Request