Modeling impacts of climate change and grazing effects on plant biomass and soil organic carbon in the Qinghai–Tibetan grasslands

Abstract

Abstract. The Qinghai Province supports over 40 % of the human population of the Qinghai-Tibetan Plateau (QTP) but occupies about 29 % of its land area, and thus it plays an important role in the plateau. The dominant land cover is grassland, which has been severely degraded over the last decade due to a combination of increased human activities and climate change. Numerous studies indicate that the plateau is sensitive to recent global climate change, but the drivers and consequences of grassland ecosystem change are controversial, especially the effects of climate change and grazing patterns on the grassland biomass and soil organic carbon (SOC) storage in this region. In this study, we used the DeNitrification-DeComposition (DNDC) model and two climate change scenarios (representative concentration pathways: RCP4.5 and RCP8.5) to understand how the grassland biomass and SOC pools might respond to different grazing intensities under future climate change scenarios. More than 1400 grassland biomass sampling points and 46 SOC points were used to validate the simulated results. The simulated above-ground biomass and SOC concentrations were in good agreement with the measured data (R 2 0.71 and 0.73 for above-ground biomass and SOC, respectively). The results showed that climate change may be the major factor that leads to fluctuations in the grassland biomass and SOC, and it explained 26.4 and 47.7 % of biomass and SOC variation, respectively. Meanwhile, the grazing intensity explained 6.4 and 2.3 % variation in biomass and SOC, respectively. The project average biomass and SOC between 2015 and 2044 was significantly smaller than past 30 years , and it was 191.17 g C m −2 , 63.44 g C kg −1 and 183.62 g C m −2 , 63.37 g C kg −1 for biomass and SOC under RCP4.5 and RCP8.5, respectively. The RCP8.5 showed the more negative effect on the biomass and SOC compared with RCP4.5. Grazing intensity had a negative relationship with biomass and positive relationship with SOC. Compared with the baseline, the biomass and SOC changed by 12.56 and −0.19 % for G 0 , 7.23 and 0.23 for G −50 , and −5.17 and 1.19 % for G +50 . In the future, more human activity and management practices should be coupled into the model simulation.

Response of Carbon Dynamics to Climate Change Varied among Different Vegetation Types in Central Asia

“…Therefore, shrubs are insensitive to changes in temperature and moisture. On the other hand, grasslands, most of which are annual herbs, are more sensitive to climate variability and human activity [14,15]. Forest is more obviously influenced by nitrogen deposition compared with other vegetation types [63,64], yet the effects of nitrogen deposition are opposite to rising temperature [65]; therefore, the results would be improved if nitrogen deposition effects were considered.…”

“…Degradation of grassland is a predominant issue for Central Asia, and this can be attributed to climate change and grazing. Grazing alters grassland carbon stocks by stimulating regrowth of plant or just reducing above-ground biomass [14,15]. Therefore, grassland carbon cycling is not only affected by climate variation, but also by human activity.…”

Effects of grazing on the allocation of mass of soil aggregates and aggregate-associated organic carbon in an alpine meadow

“…The dynamic changes in the soil carbon pool of alpine ecosystems are considered a typical representative of terrestrial ecosystems responding to the global carbon cycle [6][7][8]. Over the past few decades, the alpine grassland on the Qinghai-Tibet Plateau has experienced severe degradation, but the driving factors of grassland ecosystem degradation and their impacts have not been determined [9][10][11]. Some researchers believe that grazing may be the main factor that has led to changes in the productivity, soil structure and soil organic carbon in these alpine grasslands relative to the impact of climate change [12].…”

Aboveground Biomass Dynamics in the Low-Mountain Dry Grasslands of the Tianshan Mountains

“…Therefore, identifying the dynamics of grassland biomass is vital for maintaining ecological and economic functions when managing grasslands, particularly in arid and semi-arid areas [5]. As a result, this issue has been receiving increasing levels of research focus [6].…”

“…However, these studies focused on estimating the total values of annual AB, rather than detailing AB dynamics at different growing stages [4,6]. In addition, direct records of biomass from field observations remain limited in this region.…”