Search

• SOC higher in the permafrost region than in the non-permafrost region. • Regression-kriging method was the best upscaling approach for the prediction of SOC. • 317 Tg SOC was stored in the entire soil profile of Qinghai Lake watershed. Soil organic carbon (SOC) on the Qinghai-Tibet plateau is of global significance, due to the high carbon density and potential positive feedbacks to climate warming. Qinghai Lake watershed is an important soil pool in Qinghai-Tibet plateau, but the magnitude and characteristics of SOC stock in the high-altitude basin were not clear. To understand better how much SOC was stored and its spatial patterns in the watershed, this study analyzed the vertical variation of SOC content, quantified its influence by varied environmental factors, and further predict its storage in the entire basin. Results showed that, the SOC content decreased with the increasing depth, and was the highest in the alpine meadow in all depths, following by the alpine steppe and temperate steppe, respectively. It was generally higher in the permafrost region than that in the non-permafrost region at all depths. Soil profile depth, soil water content and NDVI could together explain about 72.6% of total variation in SOC density. The regression-kriging method was the best upscaling approach for the prediction of SOC in the study area. Approximately 317 Tg organic carbon was stored in the entire soil profile of Qinghai Lake watershed, in which 136, 140, and 41 Tg were at 0–30 cm, 30–100 cm, and below 100 cm, respectively. The higher SOC density mainly appeared on the northeast and southern region of Qinghai Lake, while the high-altitude area in the northwest of the watershed had the lower values. Moreover, it increased firstly and then decreased with the increase of altitude, with the maximum values at 3350–3400 m, which was dominated by the elevational variation of soil profile depth and NDVI. Overall, the comprehensive assessment of SOC demonstrated high storage and strong heterogenicity of soil carbon in the Qinghai Lake watershed, and it is critical for the sustainability of regional terrestrial ecosystem with future climate change. [ABSTRACT FROM AUTHOR]

• We selected Tibetan Plateau to examine net primary production during 2000–2018. • The NPP in permafrost region had a steadier and faster increasing rate. • Soil water and temperature were the main reasons for NPP changes. • The NPP values will show greater interannual changes in the future. Permafrost affects soil water and soil temperature regimes; however, its effects on net primary production (NPP) remain unknown. Here, we examined temporal-spatial changes in grassland NPP during 2000–2018 in permafrost and permafrost-free areas on the Qinghai–Tibetan Plateau using the random forest (RF) and radial basis function artificial neural network (RBF-ANN). Our results indicated that the areas that showed increasing, decreasing, and non-significant trends for NPP accounted for 13.88%, 1.90%, and 84.22% of the permafrost area, respectively. For the permafrost-free areas, these NPP trends accounted for 22.25%, 2.68%, and 75.07% of the permafrost-free area, respectively. The mean NPP in the permafrost regions showed a faster and steadier (1.520 g C/m2/yr, p < 0.05) increase than in non-permafrost regions (1.224 g C/m2/yr, p < 0.05). The Biome-BGC model confirmed that these spatial NPP patterns could be attributed to differences in soil water and soil temperature between permafrost and permafrost-free areas. Both the soil temperature and soil water content in permafrost sites exhibited relatively lower variance than in permafrost-free sites. Although many factors may be attributed to these patterns, our results suggest that there is a possibility that the relatively stable change in permafrost NPP can be explained by the fact that permafrost can regulate soil water and temperature regimes. Therefore, climate warming can increase NPP in cold regions, and permafrost degradation may destabilize the grassland ecosystem, which may cause NPP values to exhibit greater interannual changes in the future. [ABSTRACT FROM AUTHOR]

[Display omitted] • A. splendens dominates areas of degraded grasslands in China. • A. splendens reduces grassland productivity and changes soil microbial characteristics. • The growth age of A. splendens significantly decreased the plant biomass. • The relative abundances of Firmicutes and Gemmatimonadetes decreased significantly as the age increased. • Effective measures should be taken to eliminate the growth of A. splendens. Achnatherum splendens (Trinius) Nevskia dominates areas of degraded grasslands in China. However, the spatio-chronological patterns of A. splendens and its soil properties remain unknown. We conducted a field study comprising four tussock diameter classes (i.e., an age series) of A. splendens in three degraded grasslands of China (HB: Hebei Province; IM: Inner Mongolia, and QH: Qinghai Province) to determine the soil bacterial community and diversity in the root-associated soil of A. splendens by high-throughput sequencing technology. Achnatherum splendens exhibited strong adaptability and could survive under a low soil water content in the region of IM and in highly alkaline soil in the region of HB. Our findings demonstrated that the biomass of the degraded A. splendens grasslands had a significantly different spatio-chronological distribution, and the plant biomass decreased significantly as the diameter increased. The main bacteria in the root-associated soil of A. splendens showed a significant difference at the spatial scale. Based on the Calinski–Harabasz index, HB belonged to the Actinobacteria enterotype, and IM and QH belonged to the Proteobacteria enterotype, implying that the bacterial structure in root-associated soil of A. splendens had significant spatial differences that were mainly affected by climate factors. The relative abundances of Firmicutes and Gemmatimonadetes decreased significantly as the plant tussock diameter increased. The plant C/N ratio, plant biomass, and soil pH had a positive impact on bacterialβ-diversity between the three habitats, but negatively influenced the bacterial Shannon diversity (α-diversity) in the A. splendens root-associated soil. Our findings highlight that A. splendens not only reduces plant productivity as the diameter increased, but also changes the soil microbial characteristics. Therefore, the spatio-chronological preventive treatment of A. splendens , especially for the older age classes, is very important for improving the productivity of degraded grasslands in China. [ABSTRACT FROM AUTHOR]

[Display omitted] • A. splendens dominates areas of degraded grasslands in China. • A. splendens reduces grassland productivity and changes soil microbial characteristics. • The growth age of A. splendens significantly decreased the plant biomass. • The relative abundances of Firmicutes and Gemmatimonadetes decreased significantly as the age increased. • Effective measures should be taken to eliminate the growth of A. splendens. Achnatherum splendens (Trinius) Nevskia dominates areas of degraded grasslands in China. However, the spatio-chronological patterns of A. splendens and its soil properties remain unknown. We conducted a field study comprising four tussock diameter classes (i.e., an age series) of A. splendens in three degraded grasslands of China (HB: Hebei Province; IM: Inner Mongolia, and QH: Qinghai Province) to determine the soil bacterial community and diversity in the root-associated soil of A. splendens by high-throughput sequencing technology. Achnatherum splendens exhibited strong adaptability and could survive under a low soil water content in the region of IM and in highly alkaline soil in the region of HB. Our findings demonstrated that the biomass of the degraded A. splendens grasslands had a significantly different spatio-chronological distribution, and the plant biomass decreased significantly as the diameter increased. The main bacteria in the root-associated soil of A. splendens showed a significant difference at the spatial scale. Based on the Calinski–Harabasz index, HB belonged to the Actinobacteria enterotype, and IM and QH belonged to the Proteobacteria enterotype, implying that the bacterial structure in root-associated soil of A. splendens had significant spatial differences that were mainly affected by climate factors. The relative abundances of Firmicutes and Gemmatimonadetes decreased significantly as the plant tussock diameter increased. The plant C/N ratio, plant biomass, and soil pH had a positive impact on bacterialβ-diversity between the three habitats, but negatively influenced the bacterial Shannon diversity (α-diversity) in the A. splendens root-associated soil. Our findings highlight that A. splendens not only reduces plant productivity as the diameter increased, but also changes the soil microbial characteristics. Therefore, the spatio-chronological preventive treatment of A. splendens , especially for the older age classes, is very important for improving the productivity of degraded grasslands in China. [ABSTRACT FROM AUTHOR]

[Display omitted] • Soil water contents on the Tibetan Plateau during 1986–2016 were analyzed. • Soil water in permafrost areas had smaller changes than non-permafrost areas. • Climate factors could not explain the different soil water content patterns. • Permafrost favors the stability of soil water regimes. Permafrost is an important factor affecting soil hydrology in cold regions, while the effects of permafrost on temporal changes in soil water content largely remain unknown. Here, based on the calibrated Climate Change Initiative (CCI) soil moisture products using field observation soil water data at 5 cm depth from 8 representative sites, we examined changing trends of climate conditions and soil water contents during 1986–2016 between the permafrost and permafrost-free sites on the Qinghai-Tibetan Plateau (QTP). We found that all the sites have been experienced continuous warming during this period. Soil water contents showed significant increasing or decreasing trends at three of the four permafrost-free sites, but there were no significant increasing or decreasing changes at all the four permafrost sites. In addition, the Mann-Kendall (M−K) test showed that there were 2 change-points in soil water content for the sites with the active layer thickness was about 2 m, while the sites with active layer thickness larger than 3 m and permafrost-free sites showed 3–5 change-points, indicating that the soil water contents in areas with shallower active layer showed smaller changes. The different changing trends and change-points between permafrost and permafrost-free sites were associated with the existence of permafrost and active layer thickness. Although soil water contents can be affected by many factors, our results suggested that permafrost existence can affect interannual changes in soil water contents, and permafrost degradation including increasing active layer thickness and disappearance of permafrost may decrease ecosystem resilience in the face of climate change. [ABSTRACT FROM AUTHOR]