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Warming-induced drought stress leads to convergent and negative growth responses to temperature between sympatric tree species, implying an increasing interspecific competition for soil moisture. In mixed forests, sympatric tree species avoid competition by partitioning their niches according to available environment resources. We raise the hypothesis that climate warming leads to a convergence in growth responses to climate, thus increasing the competition among sympatric species in drought-prone forests. In this study, we selected a mixed forest located at ca. 3600 m a.s.l in the Baima Snow Mountains, an inner dry valley of the southeastern Tibetan Plateau. We measured width of the tree rings produced during 1910–2016 in 60 trees belonging to three sympatric species: Abies georgei, Picea likiangensis, and Betula delavayi. We analyzed the changes in radial growth and their responses to climate. We detected shifts in the responses to climate after the 1990s. The radial growth of all species was positively correlated with precipitation from 1964 to 1990, but negatively correlated with March–June temperature from 1991 to 2016. Compared to the period 1964–1990, convergent and negative growth responses to warmer temperatures in the period 1991–2016 probably reflect less available soil moisture for growing in this mixed forest. We conclude that climate warming will affect the niches of sympatric species in mixed forests subjected to seasonal drought, thus increasing competition and altering structure and composition of the stands in dry regions.

Forest ecosystems provide environmental services that benefit human communities. Despite their importance, forests have experienced deforestation and land-use changes that are particularly severe in the tropics and subtropics. Increasing concern about forest sustainability management and conservation supports the need for studies on forest recovery after deforestation. Many studies have estimated that recovery of forest structure, species composition and richness takes more than 50 years to reach a state similar to that of adjacent undisturbed forests. To date, most of these studies were carried out in the tropics and at high latitudes. However, less is known about the recovery process of sub-alpine forest after deforestation. The natural sub-alpine forest on the southeastern Tibetan Plateau is an important ecosystem, which ranges from 3000 to 4400 m above the sea level (a.s.l.), and these forests were disturbed by human before 1998. In the forests near the town of Lulang, Smith fir ( Abies georgei var. smithii ) is the dominant tree species above 3500 m a.s. l. The climate is mainly influenced by the Indian monsoon and westerlies. In summer, the Indian monsoon brings abundant precipitation to our study area. The winter climate is controlled by the westerlies producing cold and dry conditions. According to the instrumental record from the Nyingchi meteorological station, mean annual temperature and total annual precipitation are 8.9°C and 672.7 mm, respectively. This area has experienced a significant warming trend during the past five decades. Our study focused on logged and burnt sites of Smith fir forests (3460–3865 m a.s. l.) near Lulang in Nyingchi. Three and five rectangular plots (30 m ´ 30 m) were established in the logged (azimuth angle: 326°–328°) and fire-affected (azimuth angle: 243°–260°) gaps, respectively. Global Positioning System (GPS) was used to record the locations of the 8 plots. For each plot, the upper and lower sides were perpendicular to the direction of slope aspect. The lower-left side of each plot was regarded as the origin for each sampling grid. To assess the regeneration in each plot, we tagged all of the trees and measured their position coordinates ( x and y ). The tree species were also recorded. The ages of the gaps were estimated by taking increment cores from nearby adult trees surrounding the gap and examining the synchronous and abrupt growth release events. These cores were then air dried, carefully sanded, and crossdated in the lab. The ring-width series were measured under the Lintab 6 system (Rinntech, Heidelberg, Germany). We used several methods to estimate the age of each tree. For the seedlings and saplings, we estimated their age by counting the number of bud scars along the main stem. For the adult trees, we used the increment borer to get a core (close to the pith) at the base of the trunk. The ages of these samples were obtained by counting the number of rings under the stereomicroscope. The date of the burnt gap formation was estimated as 1942 and the logging gap formed in 1991, both based on abrupt growth release of nearby adult trees surrounding the gaps after fire and logging. According to the surveyed data and tree age, we obtained the decadal recruitment series for each tree species. In the burnt gaps (southwestern facing slope), we found that the regenerated tree species mainly consist of spruce ( Picea likiangensis var . linzhiensis ), juniper ( Sabina squamata ) and oak ( Quercus aquifolides ). In the logged site (northwestern facing slope), the regenerated tree species is mainly Smith fir. Compared with the natural Smith fir forest, the tree density is lower in the burnt and logged sites. In summary, once the forest on the southeastern Tibetan Plateau is logged or burnt, it will take longer time to recover to undisturbed Smith fir forest.

Engineered nanomaterials (ENMs) have been widely used in various fields due to their novel physicochemical properties. However, the use of ENMs has led to an increased exposure in humans, and the safety of ENMs has attracted much attention. It is universally acknowledged that ENMs could enter the human body via different routes, eg, inhalation, skin contact, and intravenous injection. Studies have proven that ENMs can cross or bypass the blood-brain barrier and then access the central nervous system and cause neurotoxicity. Until now, diverse in vivo and in vitro models have been developed to evaluate the neurotoxicity of ENMs, and oxidative stress, inflammation, DNA damage, and cell death have been identified as being involved. However, due to various physicochemical properties of ENMs and diverse study models in existing studies, it remains challenging to establish the structure-activity relationship of nanomaterials in neurotoxicity. In this paper, we aimed to review current studies on ENM-induced neurotoxicity, with an emphasis on the molecular and cellular mechanisms involved. We hope to provide a rational material design strategy for ENMs when they are applied in biomedical or other engineering applications.

Physicochemical properties of nanomaterials play important roles in determining their toxicological profiles during nano-biointeraction. Among them, surface modification is one of the most effective manners to tune the cytotoxicity induced by nanomaterials. However, currently, there is no consistency in surface modification including moiety types and quantities considering the conflicting toxicological profiles of particles across different studies. In this study, in order to systematically investigate how the moiety density affects cytotoxicity of NPs, we chose three different types of functional groups, that is, -NH2, -COOH, and -PEG, and further controlled their densities on modified Stober silica nanoparticles (NPs). We demonstrated that densities of functional groups could significantly affect the cytotoxicities of Stober silica NPs. Regardless of the types of functional groups, high grafting densities could ameliorate the cytotoxicities induced by Stober silica NPs in macrophages, for example, J774A.1 and N9 cells. When equal amounts of functional groups were present, the cell viability increased in the order of -COOH < -NH2 < -PEG. Furthermore, it was shown that surface modification could significantly affect the quantities of the surface silanol, which is the determining factor that affects their cytotoxicity. These results show that it is critical to control the surface moiety both quantitatively and qualitatively, which can tune the interaction outcomes at the nano-bio interface. The results found in this article provide useful guidance to adjust nanomaterial cytotoxicity for safer biomedical applications.

With the wide application of Stober silica nanoparticles and their ability to access the brain, it is crucial to evaluate their neurotoxicity. In this study, we used three in vitro model cells, i.e., N9, bEnd.3 and HT22 cells, representing microglia, microendothelial cells and neurons, respectively, to assess the neurotoxicity of Stober silica nanoparticles with different sizes. We found that Stober silica nanoparticles almost had no effect on the viability of bEnd.3 and HT22 cells. In contrast, they induced size-dependent toxicity in N9 cells, which represent the residential macrophages of the central nervous system. Further mechanistic study demonstrated that the toxicity in N9 cells was related to their surface silanol display. In addition, we demonstrated that Stober silica nanoparticles induced the production of mitochondrial ROS, release of IL-1β, cleavage of GSDMD, and occurrence of pyroptosis in N9 cells. Features of pyroptosis were also observed in primary microglia and macrophage J774A.1. In conclusion, these findings were helpful for the safety consideration of Stober silica nanoparticles considering their wide applications in our daily life.