Dynamics Of Canopy Structure And Its Effect On Gross Primary Productivity For Artemisia Ordosica Community In The Mu Us Desert

Canopy structure greatly influences plant material accumulation and growth through adjusting and redistributing the spatial allocation of natural resources such as water and sunlight,thus affecting microclimate of plant community.Therefore,studying dynamics of canopy structure is of vital importance to understand the relationship between ecosystem processes and environmental changes.This study measured leaf area index(LAI),Normalized Difference Vegetation Index(NDVI)and gross primary productivity(GPP)of Artemisia ordosica community in Mu Us Desert by in situ continuous monitoring and field experiment during the growing seasons from 2012 to 2014.Our objective was to examine the dynamics of canopy structure and its effecs on GPP ofArtemisia ordosica community.The results suggest that:(1)The canopy structure of Artemisia ordosica community showed obviously seasonal and interannual variation.Both LAI and NDVI showed a hump-shaped seasonal patterns.The interannual variation of canopy structure was significant.NDVI showed a increasing trend over years 2012-2014.(2)NDVI had strong influences on LAI during the growing season,accounting for 54%,76%and 92%of the variation in LAI from 2012 to 2014,respectively.The optimal LAI model with NDVI being input variable is LAI=1.071n(NDVI)+1.83.These modle can be used to acquire continuous LAI estimates for Artemisia ordosica communities in the Mu Us Desert using continuous NDVI measurements.(3)NDVI showed significant correlation with air temperature(Ta),soil water content(VWC),photosynthetically active radiation(PAR),accumulated air temperature(?D)and relative air humidity(RH).Among these factors,?D and VWC affect NDVI more.(4)GPP for Artemisia ordosica ecosystem showed "n" pattern throughout the growing season,with the lowest GPP value at the beginning and end of the growing season and the highest GPP value in summer.The interannual variation of GPP was significant.(5)GPP showed significant positive correlation with LAI and NDVI,and the sensitivity and correlation to canopy structure was significantly different from month to month.The comprehensive effect of LAI and NDVI on GPP suggested that NDVI had stronger effect on GPP.This study revealed the dynamics of the canopy structure for Artemisia ordosica community in the Mu Us Desert and its influence on GPP.The results have important contribution to understanding the ecosystem process of Artemisia ordosica community and the carbon cycle process of desert ecosystems.