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Vegetation is one of the most important components of the land ecosystem. Human activity and climate change are the two main factors that control the changes in regional vegetation distribution. The past vegetation changes have been extensively studied all over the world, while few had focused on the relative contributions of human activities and climate change on vegetation change. Due to its key geographic position, the Qinghai Lake basin (QLB), located on northeastern Qinghai-Tibetan Plateau, is an ideal locality to carry out such study as its vegetation dynamics are more sensitive to any natural and anthropogenic disturbances. In this study, we analyzed the chain length distribution and concentration of n -alkanes of a 3.6 m thick loess profile (QH-18) in the QLB to infer the information about past vegetation change and its controlling factors. The proxy for aquatic macrophytes (P aq) and carbon preference index (CPI) values have been applied to distinguish the relative contributions from aquatic or terrestrial higher plants to the n -alkanes. Combining with luminescence-based chronology and magnetic susceptibility data of the QH-18 section, the resulted showed that the n -alkane distribution was characterized with two remarkable variations at ∼11.5 ka and ∼2 ka, respectively. The first major variation in n -alkanes was considered to be correlate to the gradual climate warming and humidification during the last deglaciation period, suggesting the response of loess n -alkanes to natural environmental changes over the orbital scales. The second markedly change at ∼2 ka was mainly controlled by the enhanced human activities. We concluded that the hydroclimate has played the dominant role before 2 ka, but human impacts have overwhelmed the natural variabilities thereafter and become the major controlling factor of n -alkane variations and vegetation change in QLB. • The n -alkanes in the loess from QLB can be used as an indicator for the past vegetation change. • The hydroclimate condition played the dominant role in n -alkane variations and vegetation change in QLB before 2 ka. • The n -alkane variations responded to hydroclimate change on both the orbital and millennial time scales. • Human activity became the main controlling factor of the n -alkane accumulation in loess in QLB since ∼2 ka. [ABSTRACT FROM AUTHOR]

Background: Current and historical events have both affected the current distribution patterns and intraspecific divergence of plants. While numerous studies have focused on the Qinghai-Tibetan Plateau (QTP), the impacts of such events on the flora of subtropical China remain poorly understood. Subtropical China is famous for its highly complex topography and the limited impact from glaciation during the Pleistocene; this may have resulted in a different genetic legacy for species in this region compared to fully glaciated areas. Methodology/Principal Findings: We used plastid and nuclear DNA sequence data and distribution modeling to analyze the divergence patterns and demographic history of Primula obconica Hance, a widespread herbaceous montane species in subtropical China. The phylogenetic analysis revealed two major lineages (lineage A and lineage B), representing a west-east split into the Yunnan and Eastern groups, and the Sichuan and Central groups, respectively. The Eastern and Central groups comprised relatively new derived haplotypes. Nested Clade Analysis and Bayesian Skyline Plot analyses both indicated that P. obconica mainly experienced a gradual expansion of populations. In addition, the simulated distribution of P. obconica during the Last Glacial Maximum was slightly larger than its present-day distribution. Conclusion/Significance: Our results are the first to identify a west-east migration of P. obconica. The gradual expansion pattern and a larger potential distribution range in cold periods detected for P. obconica indicate that the population expansion of this species is consistent with the phalanx model. In addition, the current patterns of genetic differentiation have persisted as a result of the extensive environmental heterogeneity that exists in subtropical China. [ABSTRACT FROM AUTHOR]

• Closely spaced (10 cm) OSL dating was applied to a 360 cm thick loess-palaeosol sequence to establish its high-resolution chronology; • The end-member analysis of sediment grain-size distribution was for tracing the sources of loess and aeolian activities; • Holocene aeolian accumulation history around Qinghai Lake basin was inferred, and then compared with other paleoenvironmental records; • Regional hydroclimates and the lake-levels of Qinghai Lake may regulate the Holocene aeolian accumulation processes. Aeolian sediments are widely distributed in the Qinghai Lake basin on the northeastern Tibetan Plateau (TP), and have been extensively investigated for the palaeoclimate reconstruction. However, due to the relatively scanty of dating materials and applicable techniques, and also the commonly existed hiatus in aeolian sequences, the details of the Holocene aeolian activities in the Qinghai Lake basin remain unclear. In this study, we applied the optically stimulated luminescence (OSL) dating technique to a 3.6 m thick loess-palaeosol sequence (QH-18) located on the southern bank of the Qinghai Lake to establish a high-resolution chronology of the aeolian accumulation history. The quartz OSL chronology demonstrated that the loess accumulation commenced since the last deglaciation and continued during the Holocene (∼14.6–0.5 ka), characterized with a remarkably low sedimentation rate period from 6 ka to 2 ka. Similar phenomenon has been recorded in previously investigated aeolian sequences not only in the Qinghai Lake basin but also across the northeastern TP, which was likely owing to the optimal environment conditions that have suppressed the dust emission from the source areas in the extensive arid and semiarid areas. The end-member (EM) analysis of grain-size distribution in QH-18 yielded an optimal model with three EMs, i.e., EM1 (6 μm, background dust), EM2 (56 μm, fraction of medium or long-distance transportation) and EM3 (447 μm, fraction from proximal or local source). The EM3 fraction can only be transported with saltation process in short distances that derived from proximal or local sources. In addition to the regional climatic conditions, according to the variation and contribution of the EMs, we consider that the Holocene aeolian activity in the Lake Qinghai basin was also modulated by the lake-level fluctuations of Lake Qinghai, in the way of changing the supply of sandy materials. [ABSTRACT FROM AUTHOR]