Under environment with various water contents, the variations in the mixing state and particle size of coated black carbon (BC) aerosols cause changes in optical and radiative effects. In this study, fractal models for thinly, partially, and thickly coated BC under six relative humidities (RHs 1/4 0-95%) are constructed and optically simulated at 1064 and 532 nm. Differential scattering cross-sections are selected to retrieve the mixing state (Dp/Dc) of BC to investigate the possible retrieval errors caused by the nonspherical morphology when using the single-particle soot photometer (SP2). Furthermore, the radiative forcing of BC aerosols at different RHs are analyzed. Results showed that the retrieval errors (REs) of Dp/Dc are negative for coated particles with BC volume fraction smaller than 0.10, indicating that the mixing states of coated fractal BC are underestimated during the hygroscopic growth. The partiallycoated BC has the best retrieval accuracy of the mixing state, followed by the closed-cell and coatedaggregate model, judging from averaged REs. Radiative forcing enhancements for partially-coated aerosols with different BC volume fractions exponentially increase to opposite values, resulting in a warming or cooling effect. This study helps understand the uncertainties in Dp/Dcof BC aerosols retrieved by SP2 and their radiative forcing at different RHs. (c) 2025 Chinese Society of Particuology and Institute of Process Engineering, Chinese Academy of Sciences. Published by Elsevier B.V. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

Global warming has caused the gradual degradation of permafrost, which may affect the vegetation water uptake from different depths. However, the water utilization strategies of different vegetation species during the thawing stages of permafrost regions need further study. To elucidate these differences, we selected the permafrost region in Northeast China as study area. We analyzed the water uptake from different depths of Larix gmelinii, a deciduous coniferous tree, Pinus sylvestris var. mongolica, an evergreen tree, and Betula platyphylla, a deciduous broadleaf tree, using stable isotopes of xylem water, soil water, and precipitation from June to October 2019. The results showed that L. gmelinii primarily used shallow soil water (0-40 cm) with the highest proportion at 64.1%, B. platyphylla generally used middle soil water (40-110 cm) with the highest proportion at 55.7%, and P. sylvestris mainly used middle (40-110cm) and deep soil water (110-150 cm) with the highest proportion at 40.4% and 56.9%. The water sources from different depths exhibited more frequent changes in P. sylvestris, indicating a higher water uptake capacity from different soil depths. L. gmelinii mainly uptakes water from shallow soils, suggesting that the water uptake of this species is sensitive to permafrost degradation. This study revealed the water uptake strategies from different depths of three tree species in a permafrost region, and the results suggested that water uptake capacity of different tree species should be considered in the prediction of vegetation changes in permafrost regions under a warming climate.

Ecosystems at the southern edge of the permafrost distribution are highly sensitive to global warming. Changes in soil freeze-thaw cycles can influence vegetation growth in permafrost regions. Extant studies mainly focused on analyzing the differences of vegetation dynamics in different permafrost regions. However, the intrinsic drivers of permafrost degradation on vegetation growth remain elusive yet. Based on the top temperature of permafrost (TTOP) model, we simulated the spatial distribution of permafrost in Northeast China (NEC) from 2001 to 2020. Using the data of the vegetation Net Primary Productivity (NPP), vegetation phenology, climate and permafrost phenology, and analytical methods including partial correlation, multiple linear regression, and path analysis, we explored the response of vegetation growth and phenology to soil freeze-thaw changes and climate change under different degrees of permafrost degradation. Overall, the start date of the growing season (SOS) was very sensitive to the start date of soil thaw (SOT) changes, and multiple regression analyses showed that SOT was the main factor influencing SOS in 41.8% of the NEC region. Climatic factors remain the main factors affecting vegetation NPP in NEC, and the results of partial correlation analysis showed that only 9.7% of the regional duration of soil thaw (DOT) had a strong correlation with vegetation NPP. Therefore, we determined the mechanism responsible for the soil freeze-thaw changes and vegetation growth relationship using the path analysis. The results indicated that there is a potential inhibitory effect of persistent permafrost degradation on vegetation growth. Our findings would contribute to the improvement of process-based models of forest dynamics in the boreal region, which would help to plan sustainable development and conservation strategies in permafrost areas.

The growth resilience of forests to extreme drought event has become an urgent topic in global change ecology because of exacerbated water constraints upon trees' growth over the last few decades. Yet, surprisingly little is empirically known about the contribution of stand age, a key factor influencing forest structure and ecological processes, to variation in growth resilience among stands. This study revealed discrepancies in the drought resilience of forests of different stand ages by analyzing an extensive tree-ring dataset from Qinghai spruce (Picea crassifolia Kom.), a typical moisture-sensitive tree species in northwestern China. We found that older growth Qinghai spruce forest stands have higher resistance to droughts than do younger growth ones. Conversely, however, the post-drought recoveries of these older growth forest stands are lower than those of the younger growth stands. Patterns in the variation of resilience indices were consistent between two contrasting hydrological niche regions, whereas the stand age-related discrepancies in drought resilience became significantly smaller going from the wetter region to the drier region. These findings imply that, instead of a one-size-fits-all strategy, more meticulous and more targeted strategies are needed to enhance forest management and strengthen forest conservation given the experienced and projected climate trends, which feature increasing precipitation but higher extreme-drought frequency across this spruce tree's habitat and distribution in northwestern China.

Understanding the impact of management upon post-drought tree growth recovery and drought legacy effects is among the fundamental challenges hindering the improvement of forest conservation strategies in the face of increasingly frequent, longer, and intensified extreme droughts under ongoing climate change. Yet surprisingly little is known to date about how management practices can influence drought legacy effects; and previous studies of management impacts on forest resilience to drought have reached inconsistent and contentious conclusions. This study sought to tackle these pressing questions and gain insight by analyzing tree-ring datasets from non-managed and managed Qinghai spruce forests in northwestern China. The results show improved growth resilience to drought of those trees under management practices. Moreover, Qinghai spruce radial growth in non-managed forest exhibited significant legacy effects of extreme drought, whereas such legacy effects were mitigated in managed forest. Nevertheless, both the resilience augmentation and the mitigation of drought legacy effects by management were much weaker in the face of a three-year persistent drought than a single-year event. Hence, we may conclude that current management practices are advantageous and necessary for forest conservation under exacerbated drought conditions, for which strategies and measures should be better thought out and tailored to specific situations, rather than being one-size-fits-all, to better serve the goals of forest managers and conservationists.

The dendroecology of larch (Larix gmelinii Rupr.) in the world's northernmost forest provided insight into the complex relationship of tree growth, forest stand establishment, and changing eco-climatic factors. The Ary-Mas forest in the northern Siberia (72 & DEG; + NL) is an ecological island, surrounded by tundra. We hypothesized that the environmental constraints that limit larch growth in this harsh habitat include soil moisture and winter winds as well as low air temperature. We constructed and analyzed the larch growth index (GI) chronology from the eighteenth century until 2019. We found that the larch GI depended on the air temperature, soil moisture anomalies, and winter wind speed, and that dependence was significantly different before and after the 2000s. Larch GI responded to the onset of climatic warming in the 1970s by a minor GI increase followed by a GI decrease until the end of 1990. Increased air temperature early in the growing season favored increased GI, whereas elevated winter wind speed negatively influenced larch growth. After warming in the 2000s, the length of the growing season increased by 15 days, and larch GI was sensitive to air temperature both early and late in the growing season. The adverse influence of winter winds has gradually decreased since the 1970s, becoming a minor factor in the 2000s. Soil moisture in wet, cold soils negatively influenced larch growth. Meanwhile, decreased soil moisture in the northern lowlands favored increased larch growth. We found that larch growth increases were strongly correlated with GPP and NPP (gross and net primary productivity) within the Ary-Mas site and for the central Siberian Arctic. We infer that this Arctic region continues to be a carbon sink.

It is widely accepted that global warming is affecting forests near the tree line by increasing tree growth in these cold-limited environments. However, since about 1970, a reduction in tree growth near the tree line has been observed in response to warming and increased drought stress. This reduction in tree growth has been mainly reported in forests of the northern hemisphere but less studied in southern forests. In this study, we investigated tree populations of Nothofagus pumilio located near the arboreal altitudinal limit in the central Patagonian Andes (45-47 degrees S, Aysen region, Chile). In this region, warming has been accompanied by increased drought conditions since the 2000s. We explored whether this climatic variability has promoted or reduced tree growth at the regional scale in tree lines of these broadleaved temperate forests of central Patagonia. We constructed tree-ring chronologies and determined common growth patterns and trends, and then analyzed the influence of recent climate. We detected a significant change in the slope of regional growth trends between the periods 1955-1985 and 1985-2015. We found that positive growth trends in the period 1955-1985 were associated with warmer and drier springs. However, after 1985, we found a stabilization in N. pumilio growth associated with a steady increase in temperature in autumn. Our results support the idea that more frequent warm autumns, with very thin or no snow cover, have stabilized tree growth due to water deficit at the end of the growing season of N. pumilio. The predicted climate change scenario of increasing temperatures and drought in central Patagonia may increase competition among trees for water, particularly at the end of the growing season. Consequently, we could expect a decreasing forest growth trend in central Patagonia, potentially impacting forest dynamics of these southern forests.

Rising atmospheric carbon dioxide (CO2) may enhance tree growth and mitigate drought impacts through CO2 fertilization. However, multiple studies globally have found that rising CO2 has not translated into greater tree growth despite increases in intrinsic water-use efficiency (iWUE). The underlying mechanism discriminating between these two general responses to CO2 fertilization remains unclear. We used two species with contrasting stomatal regulation, the relatively anisohydric Qilian juniper (Sabina przewalskii) and the relatively isohydric Qinghai spruce (Picea crassifolia), to investigate the long-term tree growth and iWUE responses to climate change and elevated CO2 using tree ring widths and the associated cellulose stable carbon isotope ratios (delta C-13). We observed a contrasting growth trend of juniper and spruce with juniper growth increasing while the spruce growth declined. The iWUE of both species increased significantly and with similar amplitude throughout the trees' lifespan, though the relatively anisohydric juniper had higher iWUE than the relatively isohydric spruce throughout the period. Additionally, with rising CO2, the anisohydric juniper became less sensitive to drought, while the relatively isohydric spruce became more sensitive to drought. We hypothesized that rising CO2 benefits relatively anisohydric species more than relatively isohydric species due to greater opportunity to acquire carbon through photosynthesis despite warming and droughts. Our findings suggest the CO2 fertilization effect depends on the isohydric degree, which could be considered in future terrestrial ecosystem models.

Ice and snow tourism has yielded considerable socioeconomic benefits, especially for the countries and regions that are rich in ice and snow resources. Boosted by the Beijing Winter Olympics, China's ice and snow tourism economy is likely to usher in a period of high-quality development. This study utilized Hailuogou Glacier Forest Park, a relatively well-developed glacier tourism area in China, as the study area. We used data on the regional GDP of Ganzi Prefecture and the comprehensive tourism revenue of Hailuogou scenic area from the period of 1990-2021 to quantitatively analyze the reciprocal feedback relationships between the regional economic growth of Ganzi Prefecture and the development of Hailuogou glacier tourism. The analyses were performed through the construction of a VAR model and through conducting robustness tests using the instrumental variable method. The results show that there is a long-term equilibrium cointegration relationship between regional economic growth in Ganzi Prefecture and tourism development in the Hailuogou scenic area, with each 1% increase in the former driving a corresponding growth of 2.01% in the latter. There is an asymmetric reciprocal feedback relationship between the economic growth of Ganzi Prefecture and the development of tourism in the Hailuogou scenic area. Economic growth in Ganzi Prefecture significantly contributes to the development of glacier tourism in Hailuogou over a longer period of time, with a contribution rate of 49%; meanwhile, the development of tourism in the Hailuogou scenic area has a limited effect on the quality and acceleration of economic development in Ganzi Prefecture, with a contribution rate of 16%. Based on the above results, relevant policy recommendations are proposed to provide a theoretical basis and decision-making reference for the high-quality development of the Hailuogou scenic area in the post-COVID-19 and post-Winter Olympics era.

Arctic-alpine ecosystems are considered hot-spots of environmental change, with rapidly warming conditions causing massive alterations in vegetational structure. These changes and their environmental controls are highly complex and variable across spatial and temporal scales. Yet, despite their numerous implications for the global climate system, the underlying physiological processes and mechanisms at the individual plant scale are still little explored. Using hourly recordings of shrub stem diameter change provided by dendrometers, paired with on-site environmental conditions, enabled us to shed light on these processes. In this way, growth patterns in three widely distributed shrub species were assessed and linked to thermal and hygric conditions. We started our analysis with a close examination of one evergreen species under extreme environmental conditions, followed by a comparison of evergreen and deciduous species, and, finally, a comparative look at growth patterns across local micro-habitats. The results revealed distinct growth strategies, closely linked to species-specific water-use dynamics and cambial rhythms. Within the heterogenous alpine landscape these conditions were mainly attributed to the variation in local micro-habitats, defined by fine-scale topography and consequent variation in snow conditions and exposure. Thus, the overall growth success was mainly controlled by complex seasonal dynamics of soil moisture availability, snow conditions, and associated freeze-thaw cycles. It was therefore in many cases decoupled from governing regional climate signals. At the same time, exceedingly high summer temperatures were limiting shrub growth during the main growing season, resulting in more or less pronounced bimodal growth patterns, indicating potential growth limitation with on-going summer warming. While shrubs are currently able to maximize their growth success through a high level of adaptation to local micro-site conditions, their continued growth under rapidly changing environmental conditions is uncertain. However, our results suggest a high level of heterogeneity across spatial and temporal scales. Thus, broad-scale vegetational shifts can not be explained by a singular driver or uniform response pattern. Instead, fine-scale physiological processes and on-site near-ground environmental conditions have to be incorporated into our understanding of these changes.