Improving the accuracy of predictions regarding how plants respond to climate change is crucial to protecting biodiversity. However, little is known about the effects of seed source and elevation on ...the response of mountain plant species to reductions in precipitation. Here, we collected seeds of a tree species (
Euptelea pleiospermum
) from three seed sources and carried out a two-growing-season reciprocal transplant experiment with precipitation manipulation at three sites along an elevation gradient in the Shennongjia Mountains, central China. Variations in whole-plant traits, leaf traits, and root traits were investigated. We found that most plant traits of
E. pleiospermum
seedlings were affected by reductions in precipitation, and responses varied among different elevations and seed sources. Whole-plant traits, root biomass, and leaf traits related to photosynthesis capacity decreased under reduced precipitation treatments at mid and high elevation sites. Thus, climate change induced drought will likely have a negative influence on seedling growth at mid and high elevation regions. In addition, a home-site advantage in whole-plant traits and root traits was observed. However, the responses of leaf traits in most cases were not affected by seed source because of higher phenotypic plasticity. Our results suggested that both local adaptation and phenotypic plasticity were important in seedling growth responses to reduced precipitation. We also highlight the importance of taking intraspecific variation into account when studying the response of plants to changes in climate.
• This study aimed to reveal species–genetic diversity correlations (SGDCs) and their underlying mechanisms in natural and disturbed forests. • A community survey and molecular analyses were carried ...out to compare species diversity (SD), the genetic diversity of the dominant tree species Euptelea pleiospermum (GD), the altitudinal patterns of SD and GD, SGDC, genetic differentiation (FST), community divergence (FST‐C), effective population size (Ne), and recent migration rate between mountain riparian forests along the Yandu (natural) and Nan (disturbed) rivers. • In natural forests, both SD and GD showed a unimodal altitudinal pattern and GD was positively correlated with SD, whereas a unimodal pattern and positive SGDC were not found in the disturbed forests. SD and FST at the natural sites were higher than those at the disturbed sites. However, there were no significant differences in GD, FST‐C, Ne or recent migration rate between the natural and disturbed sites. • A correlation between the patterns of SD and GD along a geographical gradient (e.g. altitude) is an important driver of positive SGDC. The absence of positive SGDC in the disturbed forests may result from reduced SD but unaffected GD, indicating nonparallel changes in SD and GD. This study furthermore cautions against generalizations about changes in SD and GD following disturbance.
Aim: This study tests predictions of the central-marginal (C-M) hypothesis using geographical patterns of genetic variation in a Cenozoic relict tree species Euptelea pleiospermum. Additionally, we ...explore the extent to which post-glacial recolonization and landscape barriers created by topographical heterogeneity shape spatial genetic variation. Location: South-west and central subtropical China. Methods: Using microsatellite data of 678 individuals from 21 populations, we documented geographical patterns of genetic diversity and population genetic structure, supplemented with current and past (Last Glacial Maximum, LGM) distributions based on species distribution models (SDMs). Genetic structure was determined by non-spatial and spatially sensitive Bayesian clustering, analysis of molecular variance, barrier analysis and a multivariate population graphing approach. We also examined both historical and contemporary gene flow. Results: Genetic diversity significantly declined with distance from centre and showed unimodal patterns along both latitude and longitude. The C-M pattern of genetic diversity along latitudinal gradient is high-latitude-skewed, with the peak at higher portion of the species' latitudinal extent. The Sichuan Basin divided individuals into south and north clusters, whereas the Qinba Mountains did not. The general shape of the predicted distribution during the LGM is strongly similar with that of current distribution, except the Sichuan Basin. Main conclusions: Our study provides genetic evidence for the C-M hypothesis in a Cenozoic relict tree species across its distribution in China. The Sichuan Basin, rather than the Qinba Mountains, acts as dispersal barrier for a mountain tree species. Our results suggest that in situ refugia were maintained across southwest and central China during the LGM. The slight post-glacial northward expansion and asymmetrical south—north historical-gene flow did not result in a low-latitude-skewed C-M pattern of genetic diversity. Instead, complex topography in combination with the C-M dispersal dynamics shaped the latitudinal pattern of genetic diversity.
Aim: Most studies on latitudinal gradients of biodiversity have focused on gradients of species richness. Here we aim to test whether, on top of these strong diversity gradients, processes of ...community assembly vary along a latitudinal gradient of more than 33°. Location: China, latitude 18.67-51.86° N. Methods: We used species abundance distribution (SAD) data collected in 32 forest tree plots, and fitted a non-neutral model of community assembly to these SADs. We then calculated the fitted deviation from neutrality, δ, and looked for correlations between δ and geographical and environmental data. Results: The fitted parameter δ was positive in most plots, and was furthermore positively correlated with latitude and negatively with temperature, indicating a less even abundance distribution and a likely increase in the strength of environmental filtering in regions further from the tropics and with decreasing temperatures. These results imply that on top of reducing the species richness, cold temperature may impact community assembly processes by strengthening local environmental filtering. Main conclusions: Our results suggest a latitudinal gradient in tree community assembly process in Chinese forests, in which deviations from neutrality increase with latitude, probably because of an increase in environmental harshness.
Dendroecological techniques were employed to explore the growth response of subalpine fir (
Abies fargesii
) to climatic conditions across its altitudinal range in both the north and south aspects in ...the Shennongjia Mountains, central China. Correlation function analyses indicated that temperatures in current summer were significantly negatively correlated with fir radial growth at the lower limits, while temperatures in previous autumn and in current spring showed significantly positive correlations with fir radial growth at the mid- and high-elevations in both aspects. Radial growth of the subalpine fir was significantly and positively influenced by precipitation in previous autumn and in current spring at the lower elevations and by precipitation in current spring at the mid-elevations, while precipitation had no significant effects on its radial growth at the upper elevations. Moving correlation functions showed that temperatures in early spring of the current year (i.e., February-April) had a relatively stable effect on tree growth over time at the mid- and upper-elevations in both aspects. Thus, the growth of the subalpine fir responded differently to climatic conditions along the altitudinal gradient, showing that the importance of temperatures for the fir radial growth increased while the importance of precipitation decreased with increasing altitude in both aspects in the Shennongjia Mountains, central China.
We used landscape genetics and statistical models to test how landscape features influence connectivity or create barriers to dispersal for a mountain riparian tree species, Euptelea pleiospermum. ...Young leaves from 1078 individuals belonging to 36 populations at elevations of 900-2000 m along upper reaches of four rivers were genotyped using eight nuclear microsatellite markers. We found no evidence for the unidirectional dispersal hypothesis in E. pleiospermum within each river. The linear dispersal pattern along each river valley is mostly consistent with the "classical metapopulaton" model. Mountain ridges separating rivers were genetic barriers for this wind-pollinated tree species with anemochorous seeds, whereas river valleys provided important corridors for dispersal. Gene flow among populations along elevational gradients within each river prevails over gene flow among populations at similar elevations but from different rivers. This pattern of gene flow is likely to promote elevational range shifts of plant populations and to hinder local adaptation along elevational gradients. This study provides a paradigm to determine which of the two strategies (migration or adaptation) will be adopted by mountain riparian plants under climate warming.
•We studied regeneration dynamics of a tree species along latitude and altitude.•Our results provided evidence for northward migration along the latitudinal gradient.•We found disparity in ...altitudinal shifts of a tree species along different mountains.•Sprouting is an important strategy to buffer range contraction at the trailing edge.
Poleward and upward range shifts are important strategies for range-restricted tree species in the face of climate warming, but empirical studies of both latitudinal and altitudinal shifts are scarce. We investigated regeneration dynamics of an endemic Tertiary-relict tree (Euptelea pleiospermum) along (i) a latitudinal gradient across its range in China and (ii) altitudinal gradients along three mountains at low, middle and high latitudes. Sprouting ratio and relative seedling density present contrasting latitudinal patterns, with more seedlings at the leading edges and more sprouts at the trailing edges. We detected no apparent shift, a downslope shift and an upward shift along mountains located at low, middle and high latitudes, respectively. Sprouting ratio and relative seedling density also show contrasting altitudinal patterns. Our results suggested (i) northward migration along the latitudinal gradient and (ii) disparity in altitudinal shifts of the same tree species along different mountains. Furthermore, we emphasize that sprouting is an important strategy for sprouting tree species to buffer range contraction at the trailing edges in the face of climate warming.
The bonding joints of 2219 aluminum alloy with different deformations of 30%, 45% and 55% were fabricated using hot-compression bonding, and subsequent subjected to homogenization treatment. The ...interfacial microstructure and interfacial oxide evolution of the bonding joints were systematically investigated. The results showed that increasing deformation can effectively reduce the formation of interfacial voids and promote the interfacial grain boundary migration (IGBM). As the deformation increased from 30% to 55%, the flat bonding interface transformed into curved grain boundaries, and ultimately being occupied by dynamically recrystallized (DRXed) grains. The development of IGBM and interfacial DRXed grains is crucial for ensuring high-quality bonding joints. At 55% deformation, the interface bonding strength reached 156.2 MPa, corresponding to 98.1% of the matrix bonding strength. In addition, the residual interfacial oxide film Al2O3 reacted with MgO and transformed into MgAl2O4 spinel. The final evolution products at the bonding interface were the mixture of MgO, Al2Cu, Al2O3, and MgAl2O4. The bonding interface at 55% deformation successfully achieved relatively clean atomic bonding after homogenization. Based on interfacial void closure, interfacial oxide film fragmentation and evolution, and interfacial recrystallization, the bonding mechanism of 2219 aluminum alloy joints was proposed. These findings contribute to our understanding of the interfacial bonding process in metal solid bonding.
From supporting wood production to mitigating climate change, forest ecosystem services are crucial to the well-being of humans. Understanding the mechanisms that drive forest dynamics can help us ...infer how to maintain forest ecosystem services and how to improve predictions of forest dynamics under climate change. Despite the growing number of studies exploring above ground biomass (AGB) dynamics, questions of dynamics in biodiversity and in number of individuals still remain unclear. Here, we first explored the patterns of community dynamics in different aspects (i.e., AGB, density and biodiversity) based on short-term (five years) data from a 25-ha permanent plot in a subtropical forest in central China. Second, we examined the relationships between community dynamics and biodiversity and functional traits. Third, we identified the key factors affecting different aspects of community dynamics and quantified their relative contributions. We found that in the short term (five years), net above ground biomass change (ΔAGB) and biodiversity increased, while the number of individuals decreased. Resource-conservation traits enhanced the ΔAGB and reduced the loss in individuals, while the resource-acquisition traits had the opposite effect. Furthermore, the community structure contributed the most to ΔAGB; topographic variables and soil nutrients contributed the most to the number of individuals; demographic process contributed the most to biodiversity. Our results indicate that biotic factors mostly affected the community dynamics of ΔAGB and biodiversity, while the number of individuals was mainly shaped by abiotic factors. Our work highlighted that the factors influencing different aspects of community dynamics vary. Therefore, forest management practices should be formulated according to a specific protective purpose.
Electromagnetic continuous casting technology serves as a significant means for enhancing the casting performance of 2219 aluminum alloy. Investigating the influence of electromagnetic field ...variations on the solidification process is crucial for studying the microstructure and mechanical properties of electromagnetic cast billets. Through experimental research, variations in the microstructure and mechanical properties were examined for ordinary direct chill casting, as well as three different electromagnetic power casting ingots. The COMSOL software (COMSOL Multiphysics 6.0) was utilized to simulate the temperature and flow field, enabling an explanation of the resulting performance changes. The results showed the effect on electromagnetic continuous casting technology by the electromagnetic field generated by the Lorentz force and melt stirring, improving the melt flow and temperature distribution so that the melt center and the edge of the melt forcible convection were enhanced, thus realizing the tissue refinement, mechanical properties, and Cu element segregation of the improvement. With an increase in electromagnetic power, the distribution of the temperature field was more homogeneous, the segregation phenomenon was more alleviated, and the improvement in mechanical properties was more significant. The optimal microstructure and mechanical properties were achieved at a power of 20.0 kW, with a 74.7% improvement in grain refinement in the center and a tensile strength increase of 30.8%. Additionally, significant improvements were observed in segregation phenomena.
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