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Beijing Forestry University (2020)

A Study on Dynamics of Light Use Efficiency of A Desert Steppe Ecosystem in Yanchi, Ningxia

李成;

Titre : A Study on Dynamics of Light Use Efficiency of A Desert Steppe Ecosystem in Yanchi, Ningxia

Auteur : 李成;

Grade : Doctoral Dissertation 2020

Université : Beijing Forestry University

Résumé partiel
Light use efficiency(LUE)refers to the efficiency of vegetation photosynthesis transforming absorbed energy into organic dry matter,being a key indicator for evaluation of the ecosystem productivity.However,the understandings of the characteristics of light use efficiency in desert steppe ecosystem at different time scales and its controlling mechanism are still limited.Moreover,the studies examined how LUE responds to different sky conditions as climate model has predicted a year-by-year decrease in radiation quantity,which may significantly impact the photosynthetic characteristics of the desert steppe ecosystem.Here,we made a continuous in situ measurments of carbon flux in a desert steppe ecosystem using the eddy-covariance techniques.The specific objectives are to(1)analyze the dynamics of light use efficiency(LUE,a ratio of gross ecosystem productivity(GEP)to absorbed photosynthetically active radiation(APAR))at different time scales in relation to environmental and biological factors,as compared with the apparent quantum yield(α)derived from rectaular hyperbolic curve,(2)examine the effects of diffuse radiation on the photosynthetic characteristics of desert steppe ecosystem under different sky conditions.Main results and conclusions were as follows.(1)Theαand LUE of the desert steppe ecosystem showed similar seasonal variation in both years2014-2015.The seasonal changes ofαin 2014 and 2015 are consistent,and they gradually increased in early growing season and reached a maximum at the mid-growing season,and then gradually decreased.The seasonal changes of LUE in 2014 is similar to the seasonal change trend ofα ;The seasonal changes of LUE in 2015 with the start of the change of the growing season is gradually increased and a small trough appears in July and then continues to increase.It peaks in September and then declines with the end of the growing season.The average values ofαin 2014 and 2015 were 0.0075μmol CO2μmol-1 PAR and 0.0098μmol CO2μmol-1 PAR,respectively ;And the average values of LUE were 0.0019 g C MJ-1and 0.0017 g C MJ-1,respectively.LUE had obvious daily variations.LUE decreased and reached the lowest at around 13:00-14:00 every day,and then increased gradually.This change trend of LUE is mainly because the photosynthetically active radiation reaches its maximum at about 13:00 every day,and the change rate of APAR is greater than the change rate of GEP.(2)The seasonal variation ofαis mainly affected by:Ta,Ts,VPD,andαincreases with the increase of temperature(Ta and Ts)and VPD.αgradually decreased with the increase of REW in 2014,but there was no obvious correlation between the changes in REW andαin 2015.With the increase of temperature(Ta and Ts),LUE increased first and then decreased.The LUE gradually decreases with the increase of VPD,and increases with the increase of REW.The light use efficiency(αand LUE)rapidly increases with the increase of NDVI.When gs is within a certain range,the light use efficiency increases with the increase of gs

Mots clés : apparent quantum yield; light use efficiency; clearness index; diffuse photosynthetically active radiation; desert steppe ecosystem;

Présentation (CNKI)

Page publiée le 16 juin 2021, mise à jour le 21 octobre 2021