The occurrence and sources of PAHs, oxygenated PAHs (OPAHs), and nitrated PAHs (NPAHs) in soil and vegetation from the Antarctic, Arctic, and Tibetan Plateau.

Although the fate of PAHs in the three polar regions (Antarctic, Arctic, and Tibetan Plateau) has been investigated, the occurrence and contamination profiles of PAH derivatives such as oxygenated PAHs (OPAHs) and nitrated PAHs (NPAHs) remain unclear. Some of them are more toxic and can be transformed from PAHs in environment. This study explored and compared the concentrations composition profiles and potential sources of PAHs, OPAHs, and NPAHs in soil and vegetation samples from the three polar regions. The total PAH, OPAH, and NPAH concentrations were 3.55-519, n.d.-101, and n.d.-1.10 ng/g dry weight (dw), respectively. The compounds were dominated by three-ring PAHs, and the most abundant individual PAH and OPAH were phenanthrene (PHE) and 9-fluorenone (9-FO), respectively. The sources of PAHs and their derivatives were qualitatively analyzed by the diagnostic ratios and quantified using the positive matrix factorization (PMF) model. The ratios of PAH derivatives to parent PAHs (9-FO/fluorene and 9,10-anthraquinone/anthracene) were significantly higher in the Antarctic samples than in the Arctic and TP samples, implying a higher occurrence of secondary OPAH and NPAH formation in the Antarctic region. To our knowledge, this is the first comparative study that simultaneously investigated the contamination profiles of PAHs and their derivatives in the three polar regions. The findings of this study provide a scientific basis for the development of risk assessment and pollution control strategies in these fragile regions.

Asymmetric warming reduces the strength of selection pressure of moderate grazing on reproductive phenology in alpine plants.

Both warming and grazing already affect the reproductive phenology of alpine plants. However, their effects have mostly been studied in isolation, and their interaction is still unclear. In this study, an asymmetric warming (average + 1.2 °C during daytime and + 1.7 °C during nighttime and + 1.5 °C during summer and + 2.0 °C during winter) with moderate grazing experiment was conducted for four years to determine their individual and interactive effects on the onsets and durations of reproductive phenophases for fifteen alpine plant species on the Qinghai-Tibetan Plateau. Individual warming and grazing simultaneously advanced the average start dates and ending dates of budding, flowering and fruiting by 5.3-6.2 days, and further resulted in smaller effects on their durations for most plant species. The interactions between warming and grazing on them varied with plant species and year, which advanced by average 12.1 days for all plant species. The effects of grazing on the temperature sensitivity of the start dates of reproductive phenophases (average by -8.5 days °C-1) were greater than that of warming alone (average by -3.4 days °C-1) and warming with grazing (average by -5.5 days °C-1) for most of the alpine plant species. There were significant effects of the previous phenological events on subsequent reproductive phenophases. Therefore, our results suggested that both warming and grazing advanced reproductive phenophases through altered soil temperature and soil moisture and carry-over effects of previous phenological events on subsequent phenological events. Warming reduced the temperature sensitivity of the start dates of reproductive phenophases to grazing, suggesting that it depressed strength of selection pressure of grazing on the onsets of reproductive phenology in alpine plants.

Warming delays but grazing advances leaf senescence of five plant species in an alpine meadow.

Leaf senescence is the final stage in the life cycle of leaves and is critical to plants' fitness as well as to ecosystem carbon and nutrient cycling. To date, most understanding about the responses of leaf senescence to environmental changes has derived from research in forests, but the topic has been relatively neglected, especially under grazing conditions, in natural grasslands. We conducted a 3-year manipulative asymmetric warming with moderate grazing experiment to explore the responses of leaf senescence of five main species in an alpine meadow on the Qinghai-Tibetan Plateau. We found that warming prolonged leaf longevity through earlier leaf-out and later leaf senescence, and grazing prolonged it through a greater advance in leaf-out than first leaf coloration for all plants. Warming did not affect leaf nitrogen (N) content or N resorption efficiency (NRE), but grazing increased N content in coloring leaves for P. anserine and P. nivea and decreased NRE for K. humilis, P. anserine under no-warming, and for P. nivea under warming. The interactive effects of warming and grazing on leaf phenology and leaf traits depended on species identity and year. There were positive relationships between leaf-out and leaf senescence mainly derived from grazing, and positive relationships between NRE from old leaves and leaf senescence for three out of five plant species. Therefore, our results indicated that earlier leaf-out could result in earlier leaf senescence only under grazing, but depending on plant species. Delayed leaf coloring increased NRE from old leaves for some plant species measured under warming and grazing. Our results suggested that alpine plants may develop strategies to adapt to warming and grazing to assimilate more carbon through prolonged leaf longevity rather than increased NRE through earlier leaf coloring in the alpine meadow.

Novel brominated flame retardants (NBFRs) in soil and moss in Mt. Shergyla, southeast Tibetan Plateau: Occurrence, distribution and influencing factors.

Research on the environmental fate and behavior of novel brominated flame retardants (NBFRs) remains limited, especially in the remote alpine regions. In this study, the concentrations and distributions of NBFRs were investigated in soils and mosses collected from two slopes of Shergyla in the southeast of the Tibetan Plateau (TP), to unravel the environmental behaviors of NBFRs in this background area. The total NBFR concentrations (∑7NBFRs) ranged from 34.2 to 879 pg/g dw in soil and from 72.8 to 2505 pg/g dw in moss. ∑7NBFRs in soil samples collected in 2019 were significantly higher than those in 2012 (p < 0.05). Decabromodiphenyl ethane (DBDPE) was the predominant NBFR, accounting for 90% of ∑7NBFRs on average. The ratio of the concentrations in moss and soil showed significantly positive correlations with LogKOA except for DBDPE (p < 0.05), indicating that the role of mosses as accumulators compared to soils are more pronounced for more volatile NBFRs. In addition, the concentrations of NBFRs generally decreased with increasing altitude on the south-facing slope, whereas on the north-facing slope some NBFRs exhibited different trends, suggesting concurrent local and long-range transport sources. Normalization based on total organic carbon/lipid concentrations strengthened the correlation with altitude, implying that the altitude gradient of the mountain slope and forest cover could jointly affect the distribution of NBFRs in the TP. Furthermore, principal components analysis (PCA) with multiple linear regression analysis (MLRA) showed that the average contribution of the mountain cold trapping effect (MCTE) accounted for the major (77%) contribution and forest filter effect (FFE) has only a modest contribution to the deposition of NBFRs in soil.