Coupled hydraulics and carbon economy underlie age-related growth decline and revitalisation of sand-fixing shrubs after crown removal.

Crown removal revitalises sand-fixing shrubs that show declining vigour with age in drought-prone environments; however, the underlying mechanisms are poorly understood. Here, we addressed this knowledge gap by comparing the growth performance, xylem hydraulics and plant carbon economy across different plant ages (10, 21 and 33 years) and treatments (control and crown removal) using a representative sand-fixing shrub (Caragana microphylla Lam.) in northern China. We found that growth decline with plant age was accompanied by simultaneous decreases in soil moisture, plant hydraulic efficiency and photosynthetic capacity, suggesting that these interconnected changes in plant water relations and carbon economy were responsible for this decline. Following crown removal, quick resprouting, involving remobilisation of root nonstructural carbohydrate reserves, contributed to the reconstruction of an efficient hydraulic system and improved plant carbon status, but this became less effective in older shrubs. These age-dependent effects of carbon economy and hydraulics on plant growth vigour provide a mechanistic explanation for the age-related decline and revitalisation of sand-fixing shrubs. This understanding is crucial for the development of suitable management strategies for shrub plantations constructed with species having the resprouting ability and contributes to the sustainability of ecological restoration projects in water-limited sandy lands.

[Plasticity and coordination of branch and leaf traits in Ulmus pumila along a precipitation gradient]. / 沿降水梯度白榆的枝叶性状可塑性与协同变异.

We compared branch and leaf functional traits of Ulmus pumila trees inhabiting different climatic zones (sub-humid, dry sub-humid and semi-arid zones), aiming to investigate the role of trait plasticity and coordination in tree acclimation to different water conditions. The results showed that leaf drought stress of U. pumila increased significantly from sub-humid to semi-arid climatic zones, as indicated by a 66.5% reduction in leaf midday water potential. In the sub-humid zone with less severe drought stress, U. pumila had higher stomatal density, thinner leaves, larger average vessel diameter, pit aperture area and membrane area, which could ensure the higher potential water acquisition. With the increases of drought stress in dry sub-humid and semi-arid zones, leaf mass per area and tissue density increased, and the pit aperture area and membrane area decreased, indicating stronger drought tolerance. Across different climatic zones, the vessel and pit structural characteristics were strongly coordinated, while a trade-off between xylem theoretical hydraulic conductivity and safety index was found. The plastic adjustment and coordinated variation of anatomical, structural and physiological traits may be an important mechanism contributing to the success of U. pumila in different climate zones with contrasting water environments.

Xylem hydraulics strongly influence the niche differentiation of tree species along the slope of a river valley in a water-limited area.

Xylem hydraulic characteristics govern plant water transport, affecting both drought resistance and photosynthetic gas exchange. Therefore, they play critical roles in determining the adaptation of different species to environments with various water regimes. Here, we tested the hypothesis that variation in xylem traits associated with a trade-off between hydraulic efficiency and safety against drought-induced embolism contributes to niche differentiation of tree species along a sharp water availability gradient on the slope of a unique river valley located in a semi-humid area. We found that tree species showed clear niche differentiation with decreasing water availability from the bottom towards the top of the valley. Tree species occupying different positions, in terms of vertical distribution distance from the bottom of the valley, showed a strong trade-off between xylem water transport efficiency and safety, as evidenced by variations in xylem structural traits at both the tissue and pit levels. This optimized their xylem hydraulics in their respective water regimes. Thus, the trade-off between hydraulic efficiency and safety contributes to clear niche differentiation and, thereby, to the coexistence of tree species in the valley with heterogeneous water availability.

Graphene Reinforced Anticorrosion Transparent Conductive Composite Film Based on Ultra-Thin Ag Nanofilm.

Transparent conductive films are widely used in electronic products and industrial fields. Ultra-thin Ag conductive nanofilm (ACF) was prepared on a soda lime silica glass (ordinary architectural glass) substrate with industrial magnetron sputtering equipment with AZO (Al2O3 doped ZnO) as the crystal bed and wetting layer. In order to improve the corrosion resistance and conductivity of the ACF, graphene nanosheets were modified on the surface of the ACF by electrospraying for the first time. The results show that this graphene modification could be carried out continuously on a meter scale. With the modification of the graphene layer, the corrosion rate of graphene-decorated ACF (G/ACF) can be reduced by 74.56%, and after 72 h of salt spray test, the conductivity of ACF samples without modification of graphene can be reduced by 34.1%, while the conductivity of G/ACF samples with modification of graphene can be reduced by only 6.5%. This work proves the potential of graphene modified ACF to prepare robust large-area transparent conductive film.

[Hydraulics and non-structural carbohydrate contents of Ginkgo biloba under different environmental conditions in Shenyang City, China.] / 沈阳市区不同环境下银杏水力特征和非结构性碳水化合物含量.

Ginkgo biloba is an important urban ornamental tree species, but poor growth and damages often occur in urban environments. As a street tree species, the decline and death of G. biloba is particularly frequent, with the relevant physiological mechanism being unclear. In this study, we compared hydraulic characteristics, non-structural carbohydrate (NSC) contents and health status between G. biloba trees growing along the streets and those in parks in Shenyang City. The results showed that G. biloba growing along the streets showed higher degrees of branch and leaf mortality than those growing in the parks. Branches of G. biloba growing in both conditions showed lower degrees of xylem embolism. Branch hydraulic vulnerable curves of G. biloba under the two growing conditions also showed no significant difference, with the average P50 being lower than -2.8 MPa. G. biloba growing along the streets had lower leaf area specific conductivity, smaller tracheid diameter, smaller hydraulic diameter, lower soluble sugar content and total NSC than those growing in parks. Hydraulic failure was not the direct reason for the decline and mortality of G. biloba growing along streets. Under the more stressed growth conditions along the streets, G. biloba had smaller tracheid diameters in stems and lower Huber values, which limited the ability of water transport and photosynthetic carbon assimilation at the whole branch level. In addition, in order to deal with more serious stress such as greater heat and drought stresses, G. biloba might need to invest more NSC to repair damage, which further decreaded NSC contents in branches and increased the risk of carbon imbalance. At the same habitat (street or park), xylem hydraulics and NSC contents of G. biloba also showed relatively large difference among sampling sites, which reflected large heterogeneity of urban environment for tree growth.

Greater hydraulic safety contributes to higher growth resilience to drought across seven pine species in a semi-arid environment.

Quantifying inter-specific variations of tree resilience to drought and revealing the underlying mechanisms are of great importance to the understanding of forest functionality, particularly in water-limited regions. So far, comprehensive studies incorporating investigations in inter-specific variations of long-term growth patterns of trees and the underlying physiological mechanisms are very limited. Here, in a semi-arid site of northern China, tree radial growth rate, inter-annual tree-ring growth responses to climate variability, as well as physiological characteristics pertinent to xylem hydraulics, carbon assimilation and drought tolerance were analyzed in seven pine species growing in a common environment. Considerable inter-specific variations in radial growth rate, growth response to drought and physiological characteristics were observed among the studied species. Differently, the studied species exhibited similar degrees of resistance to drought-induced branch xylem embolism, with water potential corresponding to 50% loss hydraulic conductivity ranging from -2.31 to -2.96 MPa. We found that higher branch hydraulic efficiency is related to greater leaf photosynthetic capacity, smaller hydraulic safety margin and lower woody density (P < 0.05, linear regressions), but not related to higher tree radial growth rate (P > 0.05). Rather, species with higher hydraulic conductivity and photosynthetic capacity were more sensitive to drought stress and tended to show weaker growth resistance to extreme drought events as quantified by tree-ring analyses, which is at least partially due to a trade-off between hydraulic efficiency and safety across species. This study thus demonstrates the importance of drought resilience rather than instantaneous water and carbon flux capacity in determining tree growth in water-limited environments.

Tailorable Metal-Ceramic (Cu-TiC0.5) Layered Electrode with High Mechanical Property and Conductivity.

Two-dimensional materials have been extensively investigated in the fields of electrochemical sensors, field-effect transistors, and other electronic devices due to their large surface areas, high compatibility with device integration, and so on. Conventional electrodes, such as precious metal layers that are deposited on polymer or silicon wafers, have gradually revealed increasing difficulties in adapting to various device structures, especially for two-dimensional materials, which prefer high exposure of surface atoms. Here, we demonstrate a tailorable metal-ceramic (Cu-TiC0.5) layered structure as novel electrodes with high mechanical property and conductivity and fabricate a highly sensitive gas sensor with graphene lying on this proposed electrodes. The Cu-TiC0.5 layered structure exhibits remarkably high tensile yield strength and compressive yield strength, which increase 7 and 8 times than those of the pure copper, respectively. Meanwhile, excellent flexibility and conductivity could also be obtained with the further thinning of the Cu-TiC0.5 layered composite, which shows its potential applications in flexible electronics. Finally, we demonstrated that a graphene-based gas sensor fabricated on tailored metal-ceramic electrodes was ultrasensitive and robust, which benefits from the good thermal conductivity and peculiar gas channels etched on the surface of copper alloy electrodes.

The diameter-dependent photoelectrochemical performance of silicon nanowires.

We demonstrate the first systematic study of the diameter-dependent photoelectrochemical performance of single silicon nanowires within a broad size range from 200 to 2000 nm. SiNWs with a diameter of 1415 nm exhibit the highest solar energy conversion efficiency, which can be mainly traced to their diameter-dependent light absorption properties.

The role of MoS2 as an interfacial layer in graphene/silicon solar cells.

The role of MoS2 as an effective interfacial layer in graphene/silicon solar cells is systematically investigated by varying MoS2 film annealing temperature and thickness. It is found that the power conversion efficiency (PCE) is increased by ∼100% from ∼2.3% to ∼4.4% with 80 °C annealed MoS2 film whereas it drops significantly to ∼0.6% with 200 °C annealed MoS2 film. The results are well explained based on the device energy band diagram. That is, the incorporation of MoS2(80) films leads to the formation of type II structure, facilitating hole transport; while valence band mismatch is formed with MoS2(200) films due to the increase in the work function of MoS2. Besides, the PCE increases gradually with decreasing MoS2 film thickness, and "saturates" at about 2 nm. The PCE can be further enhanced to ∼6.6% with the aid of silicon surface passivation. Our work demonstrates that MoS2 is an excellent interfacial layer to improve the PCE with low-temperature annealing (80 °C in air), which may be helpful in developing efficient and low-cost G/Si solar cells.

Novel ALD-assisted growth of ZnO nanorods on graphene and its Cu2ZnSn(S(x)Se(1-x))4 solar cell application.

The hydrothermal growth of ZnO nanorods on graphene draws a specific interest for the advantages of low-temperature processability over a large area and low cost, but challenges still remain in directly growing uniform ZnO seed layers on pristine graphene without impairing its beneficial properties. In this work, the direct growth of ZnO seed layers on graphene via H2O-based atomic layer deposition (ALD) has been investigated. It is found that uniform ZnO thin films can be deposited on graphene via ALD using a combination of single-layer graphene/Cu stacks as substrates and a facile pre-H2O treatment process. After growing ZnO nanorods on graphene, its photovoltaic application in a Cu2ZnSn(SxSe1-x)4 (CZTSSe) solar cell is demonstrated. The performance of graphene-based cells approaches that of ITO-based cells with similar architectures, highlighting that graphene is a potential replacement for ITO in optoelectronic devices. The method reported herein for fabricating ZnO nanorods on graphene using ALD-ZnO as seed layers preserves its properties, and is thus applicable to a wide variety of graphene-based nanoelectronic devices.

Quantitative analysis of photons' decaying pathways in Si nanowire arrays for highly efficient photoelectrochemical solar hydrogen generation.

We quantitatively investigated excitons' decaying pathways of photon-excited SiNW arrays to determine the reason for their low performances. It is demonstrated that excitons decay through both carriers' separation and energy transfer due to Si's indirect-band-gap feature, and these two pathways could be regulated through surface modification.

Efficient visible light photocatalyst fabricated by depositing plasmonic Ag nanoparticles on conductive polymer-protected Si nanowire arrays for photoelectrochemical hydrogen generation.

Photoelectrochemical (PEC) water splitting to produce H2 is a renewable method for addressing the worldwide energy consumption increasing and fossil fuels storage shrinking. In order to achieve sustainable PEC H2 production, the semiconductor electrodes should have good photo-absorption ability, proper band positions, and chemical stability in aqueous condition. Different from the large-band-gap semiconductors such as TiO2, which can work efficiently under UV light, Si is an narrow-band-gap semiconductor that can efficiently absorb visible light; however, Si is indirect semiconductor and susceptible to photocorrosion in aqueous solution. In this paper, we demonstrate a new strategy of first protecting and then activating to develop a stable visible light photoanode for photoelectrochemical hydrogen production. This AgNPs/PEDOT/SiNW arrays show an encouraging solar-to-chemical energy conversion efficiency of 2.86 % and a pronounced incident photo-to-current conversion efficiency (IPCE) across the whole visible region. Our strategy proposed here contributes to further improvement of corrosion protection and solar energy harvesting for narrow-band-gap semiconductors that employed in visible light photoelectrochemical and photoelectric conversion applications.