# Altered Trends in Light Use Efficiency of Grassland Ecosystem in Northern China
## 3 Results
### Impact of Climate Factors on the Interannual Dynamic of LUE  
The results of partial correlation analyses between LUE and the four climate factors show the following: From 1982 to 2018, the positive correlation between temperature and LUE accounted for 31%, and the negative correlation accounted for 1% of the grassland area in northern China, while AS and AM were the most representative. The positive correlation between precipitation and LUE accounted for 26%, and the negative correlation accounted for 4% of the grassland area in northern China. TS's LUE was greatly affected by precipitation, and the positive correlation area accounted for 62% of TS. The correlation between VPD and solar radiation and LUE was weak, except for in TS which had a large area of negative correlation with solar radiation (Figure 6).  
From 1982 to 1997, the LUE in most grassland areas of northern China was positively correlated with temperature and precipitation, while it was negatively correlated with  
Figure 6: Partial correlation coefficients between LUE and climate factors. Partial correlation coefficients between LUE and temperature (**a**,**e**,**i**), precipitation (**b**,**f**,**j**), VPD (**c**,**g**,**k**), and solar radiation (**d**,**h**,**l**) during 1982–2018 (first column), 1982–1997 (second column), and 1998–2018 (third column). The insets represent the percentages of significantly correlated (\(p<0.05\)) areas in the grasslands of northern China and the six grassland types, while blue and pink represent positive and negative correlations, respectively. Gross, grasslands of northern China; AM, alpine meadow; AS, alpine steppe; TM, temperate meadow; TS, temperate steppe; SG, sparse grassland; SS, sparse shrubland.  
VPD and solar radiation. Of all grassland types, TS and SS were greatly affected by climate factors. For 1998 to 2018, the results of the partial correlation analysis between LUE and climate factors in the grasslands of northern China was relatively complex. LUE in the eastern study area, where TS was distributed, was positively correlated with precipitation and negatively correlated with VPD. The southwestern study area was shown to be negatively correlated with VPD. Furthermore, our results show that temperature and solar radiation had a weak correlation with LUE from 1998 to 2018 (Figure 6).  
We further demonstrate the relative contributions of different driving factors to interannual dynamic changes in LUE in the grasslands of northern China. As shown in Figure 7a, temperature changes had the greatest impact on interannual LUE variability in the past 40 years, accounting for 41% of the study area, followed by precipitation (36%), VPD (13%), and solar radiation (11%). The main climate factors driving LUE dynamics in the grasslands of northern China are spatially heterogeneous. The interannual dynamics of LUE in the western study area are mainly driven by temperature, while the eastern study area is mainly affected by precipitation (Figure 7a). Additionally, this study found that most of the significant trends in LUE between 1982 and 1997 were predominantly caused by temperature (38%) (Figure 7b). However, the driving factor of interannual LUE variability changed to precipitation (39%) and VPD (26%) after 1998 (Figure 7c).