Effect of degradation and rebuilding of artificial grasslands on soil respiration and carbon and nitrogen pools on an alpine meadow of the Qinghai-Tibetan Plateau

The alpine meadow ecosystem on the Qinghai-Tibet Plateau has degenerated greatly in recent decades. The most effective means of restoration for severely degraded grasslands is rebuilding artificial grasslands. However, the effects of converting severely degraded grasslands to artificial grasslands on soil respiration and the relationships between soil respiration and carbon and nitrogen storage remain unclear. Therefore, we evaluated soil respiration and carbon and nitrogen storage on native grasslands with different levels of degradation (no degradation (ND), lightly degraded (LD), moderately degraded (MD) and severely degraded (SD)); the study was on a perennial artificial grassland with different restoration years (cultivated for 3 years (A3) and cultivated for 16 years (A16)) and on an annual oat grassland in an alpine meadow of the Qinghai-Tibet Plateau and applied a structural equation model to explore the relative contributions of biotic and abiotic variables in the regulation of soil respiration. Our results demonstrated that grassland degradation significantly decreased the growing season soil respiration, annual mean soil respiration, vegetation, and the soil and ecosystem carbon and nitrogen storage. Meanwhile, the establishment of annual oat grasslands significantly decreased the growing season soil respiration, annual mean soil respiration, 0-30 cm soil layer and ecosystem carbon and nitrogen storage, whereas it significantly increased the vegetation carbon and nitrogen storage. In contrast, the perennial artificial grassland had no significant effect on the growing season soil respiration or on the annual mean soil respiration but significantly increased the forage yield and ecosystem carbon and nitrogen storage. Grassland degradation and artificial grassland establishment had no significant effect on the dormant season soil respiration. Furthermore, soil moisture had a greater impact on growing season soil respiration, whereas soil temperature had a more significant effect on the dormant season soil respiration. Furthermore, a structural equation model indicated that the carbon storage in the roots and the 0-10 cm soil layer were two important biotic factors that controlled soil respiration. Considering the ecological and productive properties, establishing a perennial artificial grassland could be the best strategy for restoring the black-soil-type grasslands native to the Qinghai-Tibet Plateau.