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Nonstructural carbohydrates (NSCs) reflect the carbon balance in trees and play a central role in their responses to environmental stresses. However, our understanding of tree NSC storage dynamics under environmental stress is unclear. Here, we quantified the deciduous conifer Larix principis-rupprechtii at five altitudes on Luya Mountain, North-Central China. We measured NSCs in different organs and simultaneously monitored environmental variables during the growing seasons in 2018 and 2019. The results showed that temperature was the main environmental factor affecting tree NSCs. Furthermore, as the soil–atmosphere temperature gradient decreased, the concentrations of soluble sugars in the needles increased while their starch decreased, as well as the concentrations of starch in the shoots, stems, and roots increased. These results may indicate that temperature gradients may assist carbohydrate allocation within individual trees. The NSCs, especially starch, in the needles increased with lower soil moisture, and the soluble sugars and starch in the needles and shoots increased with a higher vapor pressure deficit. The soluble sugars in the stems were significantly affected by soil moisture, and the NSCs in the roots were mainly affected by temperature. These results provide new insights to improve our understanding of the environmental stress effects on future forest C balances. [ABSTRACT FROM AUTHOR]

Graphene films prepared through a self-assembly of graphene oxide and its derivatives have been recently explored for electromagnetic interference (EMI) shielding applications. However, this film preparation usually requires long-time high-temperature annealing, leading to a dramatic increase in energy and time-consumption and thus the total cost of mass production. Herein, a free-standing, highly flexible and conductive graphene film was fabricated via a simple and inexpensive method. The fabrication process starts with the chemical exfoliation of graphite in a novel binary-component system comprised of sodium peroxyborate and sulfuric acid, as a graphene suspension, which is then vacuum-filtered and mechanically pressed, not involving high-temperature post-treatment. The obtained graphene film shows excellent electrical conductivity of 1.53 × 106 S m−1. More importantly, it also exhibits an ultrahigh EMI SE of 68 dB at a frequency of 8.2–12.4 GHz, which can block 99.99999% of incident radiation. To the best of our knowledge, this is the highest EMI SE performance reported so far in such thin thickness (about 3.2 μm) of pure graphene materials. These outstanding properties make this ultrathin graphene film a promising alternative building block for electronic devices. [ABSTRACT FROM AUTHOR]

• Different periods were determined according to the pattern of the daily stem cycle. • Interspecific differences in tree water deficit declined with elevations. • Spruce showed greater daily amplitude than larch in spring rehydration rather than summer growth. • Opposite responses of stem water relations to high vapor pressure deficit between the two conifers. Internal water storage in the stem provides additional water for transpiration and photosynthesis and thus ensures tree hydraulic safety and growth under stressed conditions. Comprehensive understandings in elevation- and species-specific patterns of stem water relations and the underlying mechanism could shed light on the physiological foundation of forest conservation and management in the montane area. Here, stem radius variations of co-occurring Larix principis-rupprechtii and Picea meyeri were monitored at three sites of different elevations (2200 m, 2400 m, and 2600 m a.s.L.) in 2018 and 2019 using point dendrometers. The seasonal cycle was divided into four periods: spring rehydration, summer growth, autumn contraction, and winter dormancy. Tree water deficit-induced stem shrinkage (TWD) during the summer growth and daily stem cycles in each period were extracted and compared between species and among elevations, and their responses to environmental factors were determined. The results showed an elevational trend for averaged TWD in L. principis-rupprechtii instead of P. meyeri. TWD in both tree species had a closer relationship with vapor pressure deficit (VPD), while the TWD showed piecewise changes with species-specific differences as the VPD increased. The daily amplitude of L. principis-rupprechtii was smaller than that of P. meyeri in periods of winter dormancy and spring rehydration, however, the comparison was opposite during summer growth and autumn contraction. Furthermore, the daily amplitude of L. principis-rupprechtii and P. meyeri had different responses to the air and soil hydrothermal conditions in different periods over the year. Our study highlights interspecific water-use behaviors between larch and spruce, indicating their contrasting responses to a global increase in drought stress, especially in low elevations. [ABSTRACT FROM AUTHOR]

Transitional climate zones (TCZ) are characterized by instability due to rapid changes in climate and biological variables, and trees growing there are particularly sensitive to climate change. Therefore, knowledge about the shifted relationships of tree growth in response to climate warming will shape regional forest conservation and management strategies. China has experienced rapid warming in recent decades. However, how tree growth in semihumid to semiarid regions, such as the Guandi Mountains, responds to more sophisticated changes in the hydrothermal combination is not yet clear. In this study, we used tree-ring width data from three sites along an elevational gradient in the Guandi Mountains to present the response of Picea wilsonii Mast. radial growth to increasing temperature and elevational differences in the relationship between tree growth and climate. The results indicated that the Guandi Mountains have experienced rapid warming with a clear trend toward aridity. From 1959 to 1995, the radial growth of P. wilsonii was mainly influenced by temperature, while it was controlled by both temperature and precipitation after rapid warming in 1996. From 1959 to 2017, this species showed a generally consistent growth–climate relationship at different elevations in the Guandi Mountains. However, the radial growth of trees at higher elevations had a higher climatic correlation than at lower elevations, and it was more conditioned by higher summer temperatures and precipitation in December of the previous year. These results suggested that P. wilsonii was more susceptible to drought and high temperatures due to a warming climate and that more attention should be devoted to forest management, especially the adverse consequences of summer drought on P. wilsonii. [ABSTRACT FROM AUTHOR]

• The Weibull function was used to fit stem radius variations in cold seasons. • Stem shrinkage in Picea meyeri was greater on the forest edge after stem freeze. • The diurnal temperature range regulated the freeze-induced seasonal and diurnal variations in stem size. • Stem freeze or thaw was active when the daily minimum air temperature was around −2.5 °C. Dendrometer-derived stem radius variations (SRV) have been demonstrated as useful tools to test cold acclimation, which could reflect the tree water (ice) balance in winter and thus the frost stress. However, most previous studies focus on stem increment and water relations during growing seasons, stem radius variations in cold seasons and the underlying tree physiological information are not fully exploited, limiting our understanding of the response of mid- and high-latitudinal forests to warming winter. Hourly SRV in spruces (Picea meyeri) across an elevational transect of 700 m were observed over 6 consecutive years (2012–2017) in the present study. Elevation-specific variations in the onset of stem freeze and thaw, and the magnitude of seasonal and diurnal SRV in cold seasons were explored, and ultimately their dominant environmental factors were determined. Before stem freeze, seasonal and diurnal SRV showed linear trends with elevation, which were mainly affected by air and soil water conditions. Whereas, after stem freeze, the seasonal SRV and thus the stem dehydration was greater at the lower and upper limits of the forest belt, and the daily amplitude of freeze-thaw cycles was greater at high elevations. The diurnal air temperature range dominantly controlled the SRV on different time scales after stem freeze. Stem freeze and thaw in P. meyeri was active when the daily minimum air temperature was -2.5 °C in our study region. The onset of stem freeze and thaw advanced and delayed with elevation corresponding to a rate of 5.2 and 7.5 days/ °C when adjusted for the monitored lapse rate of 0.63 °C per 100 m, respectively. Together these findings highlight the value of high-precision variations in stem size to indicate the potential freezing stress, and trees growing at high elevations might suffer greater stress caused by frost dehydration and freeze-thaw under ongoing climate change. [ABSTRACT FROM AUTHOR]