## 3 Results and Discussion
### The Variation Coefficient of Climate Effect on NDVI  
The variation coefficient of the AMT effect on NDVI showed no significant change in trend (Figure 4A). This result indicated that the NDVI was not sensitive to the significant increase in temperature during 1982-2010 (\(R^{2}\) = 0.39, \(p\) < 0.0005, Figure 4C). In contrast, the variation coefficient of the AMP on NDVI exhibited a highly significant increasing trend (\(R^{2}\) = 0.27, \(p\) < 0.005, Figure 4B). From this result, it can be concluded that the NDVI was sensitive to the significant decrease in precipitation during 1982-2010 (\(R^{2}\) = 0.10, \(p\) < 0.05, Figure 4D). Similar to our results, previous studies also found that the grasses during 1982-1999 in North China were strongly affected by the change in precipitation, but the sensitivity of grass growth to increasing temperature declined [17]. For temperate grassland, water is the key factor of plant growth [28]. For example, in the arid sub-humid area of northern China, precipitation has a positive impact on NDVI [38]. Precipitation is also the main influencing factor of NDVI in the growing season in Northeast China [39]. However, the effect of precipitation on NDVI had significantly decreased from 1982 to 2010 (\(R^{2}\) = 0.11, \(p\) < 0.05, Figure 3B). The precipitation is unevenly distributed during the vegetation growing season. The high variation effect of precipitation on NDVI (Figure 4B) was due to the significant decrease in precipitation from 1980 to 2010 (Figure 4D). Previous studies also found that grasslands in the Tibetan Plateau [18] and the US Great Plains [40] were sensitive to the dynamic of precipitation. In Konza, both the drought and high temperature reduced grass productivity [41]. Generally, on a global scale, the grasses in alpine zones worldwide, Central Asia, southeast of South America, and eastern areas of Australia were sensitive to the variability of precipitation. However, the plants in the  
Figure 3: The dynamic effects of temperature (**A**) and precipitation (**B**) on NDVI in Inner Mongolia from 1982 to 2010. In addition, the dynamic effects of temperature (**C**) and precipitation (**D**) on NDVI across climatic gradients in Inner Mongolia. AMT, AMP, and NDVI represent the annual mean temperature, annual mean precipitation, and the normalized difference vegetation index, respectively. Quantitative analysis demonstrated that 39.01%, 35.47%, and 0.56% of the dynamic of NDVI from 1982 to 2010 was accounted for by the factors of AMT and AMP, AMP, and AMT, respectively (Figure 5). Water shortage caused by the decreasing precipitation from 1982 to 2010 is an important environmental factor that affects the photosynthetic physiological process and NDVI of grasslands [29; 43; 44]. The negative effect of water deficit on plants is greater when the decreasing precipitation is coupled with the increasing temperature [28], because water and heat availability are the key factors that mediated the growth of grasslands [21; 44]. After sensing water stress, plants resist and adapt to stress through a series of physiological and ecological changes to reduce stress damage, such as stomatal closure, reduction in photosynthesis and transpiration water consumption rate, growth restriction, and so on [43; 45]. In order to survive, plants will evolve to be more and more drought resistant [6; 42; 46]. That is to say, plants need to reduce the impact of precipitation changes on them, so plants are less affected by the precipitation in 2010 than that in 1982 (Figure 3B). Figure 4: The variation coefficient of the climate effect on NDVI from 1982 to 2010 (variation coefficient of the AMT effect on NDVI (**A**) and variation coefficient of the AMP effect on NDVI (**B**)); and the dynamic of AMT (**C**) and AMP (**D**) from 1982 to 2010. AMT, AMP, and NDVI represent the annual mean temperature, annual mean precipitation, and the normalized difference vegetation index, respectively.