Soil carbon and nitrogen pools and their relationship to plant and soil dynamics of degraded and artificially restored grasslands of the Qinghai–Tibetan Plateau

Land disturbances and management approaches can significantly alter the restoration of degraded grasslands. Therefore, understanding the carbon and nitrogen storage accompanying plant and soil physical and chemical properties due to anthropogenic disturbance and different management strategies is important, as it can help us understand not only how ecosystem responds to its dynamics but also the restoration effects of restoration methods. In our study, we investigated carbon, nitrogen storage, plant community alterations and other soil chemical and physical properties regarding artificial grasslands with different restoration years and native grasslands with different degradation levels. We found that artificial grassland establishment significantly increased above- and belowground biomass, but the richness, diversity and evenness indexes had a decreasing trend compared with extremely degraded grasslands. Grazing also had a negative effect on plant communities and diversity indexes. The soil organic carbon (SOC) was highest in non-degraded grasslands (ND). The SOC content had decreased 21.89%, 38.30% and 43.15% with the increase of the grassland degradation compared with ND. The total nitrogen (TN) content was also higher in the ND (0.955kg·m−2) than in either degraded grasslands (0.908kg·m−2, 0.786kg·m−2, and 0.769kg·m−2 for moderately, heavily and extremely degraded, respectively). The total carbon, SOC and TN content were concentrated on the 0–4cm depth, accounting for more than 50% of the total content. We also found that the soil nutrients substantially decreased with increasing restoration years. Furthermore, soil nutrients had a close relationship with plant and soil factors, as reflected by a correlation index. The above-mentioned results indicated that artificial grasslands can be used as an effective method to restore “black-beach” soil grassland. In the long term, however, management interventions should be implemented to prevent the degradation of artificial grasslands.