Gross Biomass and Root/Shoot Ratio Mediated Drought Sensitivities of Ecosystem Carbon Exchange in a Meadow Steppe

According to IPCC’s Report (2007), global precipitation regimes will change largely in the future, with more annual precipitation at the mid-latitude regions. Simultaneously, due to the accelerating industrialization and use of nitrogen (N) fertilizer, significant increase in nitrogen deposition has been widely documented (Liu et al., 2013). Water and nitrogen are the two most important limiting factors for the ecological processes of arid and semi-arid grassland ecosystems; therefore, altered precipitation regimes and enhanced nitrogen deposition are likely to change vegetation composition, ecosystem productivity, and aboveground vs belowground biomass distribution. In addition to these long-term changes, short-term climate extremes, such as drought, are projected to increase in frequency and intensity in the future, and thus there is a clear need to understand how they will impact ecosystem carbon exchange, especially after the vegetation structure has been modified by altered precipitation regimes and nitrogen deposition (Reichstein et al., 2013). However, not much information is available in the literature about the sensitivity of ecosystem carbon exchange to extreme drought, particularly when the ecosystem productivity and biomass distribution were altered by nitrogen deposition and changed precipitation regimes