# Altered Trends in Light Use Efficiency of Grassland Ecosystem in Northern China
Zhongbin Yao  
College of Grassland Agriculture, Northwest A&F University, Xianyang 712100, China; [EMAIL_ADDRESS] (T.Z. ); [EMAIL_ADDRESS] (H.Y. ); [EMAIL_ADDRESS] (C.Z.) Zhongbin Yao  
College of Grassland Agriculture, Northwest A&F University, Xianyang 712100, China; [EMAIL_ADDRESS] (T.Z. ); [EMAIL_ADDRESS] (H.Y. ); [EMAIL_ADDRESS] (C.Z.) Zhongbin Yao  
College of Grassland Agriculture, Northwest A&F University, Xianyang 712100, China; [EMAIL_ADDRESS] (T.Z. ); [EMAIL_ADDRESS] (H.Y. ); [EMAIL_ADDRESS] (C.Z.) Zhongbin Yao  
College of Grassland Agriculture, Northwest A&F University, Xianyang 712100, China; [EMAIL_ADDRESS] (T.Z. ); [EMAIL_ADDRESS] (H.Y. ); [EMAIL_ADDRESS] (C.Z.) Zhongbin Yao  
College of Grassland Agriculture, Northwest A&F University, Xianyang 712100, China; [EMAIL_ADDRESS] (T.Z. ); [EMAIL_ADDRESS] (H.Y. ); [EMAIL_ADDRESS] (C.Z.) Zhongbin Yao  
College of Grassland Agriculture, Northwest A&F University, Xianyang 712100, China; t_yourhang@nwafu. The LUE calculation methods are often diverse [13]. LUE is generally defined as the ratio of carbon flux (such as Gross Primary Production (GPP) and Net Primary Production (NPP), etc.) to light energy (such as Incoming Shortwave Radiation (SW), Photosynthetically Active Radiation (PAR), Absorbed Photosynthetically Active Radiation (APAR), etc.). LUE can indicate the ability of plants to use PAR absorbed by vegetation during photosynthesis and define the efficiency of carbon sequestration at the ecosystem level. As a key parameter regulating the absorption of carbon from the atmosphere into the biosphere [9; 12], revealing the interannual dynamics of LUE and its driving factors is crucial [8; 14]. Previous studies on LUE concentrated on the estimation model of productivity at the leaf and canopy scales, based on a limited amount of site data. Nevertheless, in these studies, little attention is devoted to the interannual variability and long-term trends of LUE. On different time scales, LUE has exhibited diverse trends (significant increase, significant decrease, and no significance) in various terrestrial ecosystems around the world. For instance, the LUE trend in the central African forest varied between 2% and 5% every decade from 1982 to 2010, whereas the LUE trend in the African northern savannahs stayed consistent [15]. LUE demonstrated significant year-to-year variation in a peatland pasture in Canada during 2014-2015 [16]. LUE increased and decreased in the opposite direction on two different grassland types in Inner Mongolia, China [17]. Temperature, precipitation, radiation, soil moisture, and nutrients are key factors limiting the photosynthetic processes of grassland ecosystems in different regions [14; 15; 17; 18; 19; 20]. According to global studies, temperature and light are the major limits to LUE in alpine regions, whereas water stress is the main factor affecting the interannual dynamics of LUE in arid and semi-arid regions. In the Tibetan Plateau, Inner Mongolia, and Loess Plateau grasslands in northern China, temperature, light conditions, precipitation, and soil nutrients are limiting variables for plant growth [21; 22; 23; 24]. However, while most studies on spatial and temporal variation in LUE have focused on seasonal variation at the station scale [8; 17; 25], there have been relatively few studies on long-term and large-scale LUE and its influencing factors. Our study sought to develop a dataset of LUE for grasslands in northern China from 1982 to 2018 based on Global Land Surface Satellite (GLASS) products GPP data, GLASS Fraction of Photosynthetically Active Radiation (FPAR) data, and Climate Research Unit (CRU) SW data. The study's main objectives were to (1) clarify the interannual dynamics of LUE in grasslands and different grassland types in northern China; (2) reveal the contributions of different climate factors to the interannual LUE variability in grasslands in northern China; and (3) clarify the main driving factors of the interannual dynamics of LUE in grasslands in northern China.