# Drought and Carbon Cycling of Grassland Ecosystems under Global Change: A Review
## 2 Drought and Grassland \(C\) Cycling under Global Change
### Grassland Ecosystem Properties  
To a certain extent, the effects of drought on an ecosystem are related to the traits of the dominant species, as well as plant functional diversity [139]. The ecosystem functions and species composition of grasslands are likely to be impacted by droughts [140]. Drought may have pronounced effects on functional performance, such as C-fixation as well as fluxes and pools [36; 56]. However, a grassland's plant diversity provides a buffer against environmental fluctuations because different species respond differently to these fluctuations, triggering functional compensations among species [11; 141]. Plant diversity has a stronger effect on soil microbial functions and enzymes [142]. Plant diversity is a major determinant of soil microbial biomass in a changing environment [143]. Specifically the ability for a community to maintain ecosystem functions during a stressful event (resistance) or to recover rapidly from it (resilience) is a component of stability [144]. Likewise, a grassland may withstand moderate drought in areas with rich biodiversity [104; 145]. In particular, greater ecological diversity means higher resistance to drought because of the complementary use of available water and other resources when compared to communities with low ecological diversity [146]. Accordingly, at the species level, the individual may not respond to drought, but the ecosystem significantly responds [147]. Because of high diversity, the ecosystem exhibits greater stability and ensures species persistence and ecosystem functions [71; 148]. Post-drought recovery of an ecosystem is much more rapid where greater levels of biodiversity are conserved than in less diverse areas [149]. On the other hand, droughts are not buffered by increased biodiversity richness. Intriguingly, frequent mild droughts did not change the productivity patterns and point to a higher resistance to severe droughts, with increasing richness levels not necessarily enhancing resistance [91]. Similarly, higher drought stress with increased biodiversity richness led to greater mortality, yet all communities are able to recover similar green cover post-drought [150]. In fact, another threat to \(C\) sequestration in grassland stems from the rapid loss of plant diversity, which is projected under climate change [151].  
In a grassland, soil plays an important role in buffering the impacts from drought. Plant-soil interaction plays an important role in regulating \(C\) cycling [152]. The adaptive strategies of plant-soil interactions play a key role in the short-term stability of \(C\) cycling to extreme drought events [49]. To better withstand times of drought, increased amounts of \(C\) sequestered as SOM into soil enhance rainfall effectiveness through increased infiltration, water-holding capacity, and water source replenishment. Moreover, grasslands may be most likely missing \(C\)-sinks [3; 113], owing to grasslands potential capacity to sequester and store \(C\) in soils [5; 153]. Higher soil \(C\) levels can reduce the impacts of droughts [154; 155]. The relative extent of drought impacts on soil respiration depends on the level of belowground biomass and soil \(C\)[156]. Sequestering \(C\) in grassland soils brings about a number of positive environmental outcomes, or co-benefits, beyond offsetting GHG emissions [157]. SOM plays an important role in determining soil chemical properties, including pH, nutrient availability and cycling, and buffer capacity [158]. Thus, increasing SOM is an effective method for increasing drought resistance in arid and semiarid areas.