# The Net Influence of Drought on Grassland Productivity over the Past 50 Years
## 3 Results and Discussion
### The Net Influence on Regional Grassland Productivity of Drought over the Past Five Decades
The desert steppe can resist the interference of severe drought, without resulting in serious degradation of the desert steppe ecosystem or ecosystem collapse. Based on the analysis of the influence on the desert steppe of different degraded droughs, severe and moderate droughs had less influence on the desert steppe NPP, while the water-use efficiency of vegetation increased, and therefore did not cause a serious influence on the desert grassland NPP [49; 50; 51]. Due to the increased precipitation in the western desert steppe, we know that the interference of appropriate drought in the west region had promoted the NPP increased instead. It was shown that the interference of drought, to a certain extent, had promoted increased grassland ecosystem water-use efficiency, and even increased productivity. Figure 14: Total NPP changes for different grassland types caused by droughs over the past 50 years: **(a)** Inner Mongolia grassland; **(b)** meadow steppe; **(c)** typical steppe; **(d)** desert steppe. A positive value indicates that NPP decreases, and a negative value indicates that NPP increases. Climate change intensifies the uncertainty of the influence of drought on grass productivity at some level. The further intensification of climate change increases the uncertainty of the impact of drought on grassland, and also increases the vulnerability of the grassland ecosystems [33; 52; 53]. Climate change affects grassland ecosystems in different ways, while its impact is not equal to the sum of the impact of every single factor [54]. This study also suggests that the influences on the ecological system of drought, precipitation, and temperature changes are not equal to the sum of their single impacts, but the complex interactions. In the temperate grassland of Inner Mongolia, the precipitation increase can raise the variation of NPP significantly. The response amplitudes of precipitation change have been shown to be different in the meadow, typical, and desert steppes in northern China, which is similar to the results of this study [43]. Moderate drought and warming did not enhance the resistance and resilience of the grassland ecosystem to subsequent extreme drought. However, warming and extreme drought can strongly stimulate the decomposition of soil organic carbon in grasslands, enhancing soil respiration mainly by stimulating soil microbial activity, root activity, and nitrogen mineralization rates, further reducing the ecosystem carbon sequestration function. At the same time, researchers have found that drought did not lead to a decrease in NPP of an ecosystem, which may be caused by the fact that the temperature promotes vegetation photosynthesis and offsets the negative influence of drought on NPP [55]. Climate warming and elevated CO\({}_{2}\) concentration can increase soil moisture content and productivity of semi-arid grasslands to a certain extent [22]. This study supported this conclusion because it was found that the NPP increased in the desert and meadow steppe areas. A temperature increase of 2 \({}^{\circ}\)C can decrease C3 grassland carbon sequestration ability, and enhance C3-C4 and C4 grass carbon sequestration ability [56]. In this study, there is a large difference in different grassland ecosystem responses to drought, precipitation, and temperature change. Nevertheless, precipitation variation in Inner Mongolia is the main driving factor of grassland productivity annual fluctuation [57; 58]. In the Inner Mongolia grassland, the serious water deficit in the ecosystem caused by decreased precipitation and increased temperature, cause a serious drop in the NPP [59]. The results of this study also show that the influence of drought on grassland productivity in Inner Mongolia is mainly caused by the precipitation deficit variation.