Search for: All records

Abstract Global changes such as nitrogen (N) enrichment and elevated carbon dioxide (CO₂) are known to exacerbate biodiversity loss in grassland ecosystems. They do so by modifying processes whose strength may vary at different spatial scales. Yet, whether and how global changes impact plant diversity at different spatial scales remains elusive.We collected data on species presence and cover at a high resolution in the third decade of a long‐term temperate grassland biodiversity—global change experiment. Based on the data, we constructed species—area relationships across three spatial orders of magnitude (from 0.01 to 3.24 m²) and compared them for the different global change treatments.We found that N enrichment, both under ambient and elevated CO₂levels, decreased species richness across almost all spatial scales, with proportional decreases being largest at the smallest spatial scales. Elevated CO₂also reduced richness at both ambient and enriched N supply rates but did so proportionally across all spatial scales. Suppression of diversity was stronger at all scales for diversity indices that include relative abundances than for species richness. Taken together, these results suggest that CO₂and N are re‐organizing this grassland system by increasingly favouring, at fine scales, a small subset of dominant species.Synthesis: Our results highlight the role of spatial scales in influencing biodiversity loss, especially when it is driven by anthropogenic resource changes that might influence species interactions differently across spatial scales. 

The McMurdo Dry Valleys (MDVs) of Antarctica are a mosaic of extreme habitats which are dominated by microbial life. The MDVs include glacial melt holes, streams, lakes, and soils, which are interconnected through the transfer of energy and flux of inorganic and organic material via wind and hydrology. For the first time, we provide new data on the viral community structure and function in the MDVs through metagenomics of the planktonic and benthic mat communities of Lakes Bonney and Fryxell. Viral taxonomic diversity was compared across lakes and ecological function was investigated by characterizing auxiliary metabolic genes (AMGs) and predicting viral hosts. Our data suggest that viral communities differed between the lakes and among sites: these differences were connected to microbial host communities. AMGs were associated with the potential augmentation of multiple biogeochemical processes in host, most notably with phosphorus acquisition, organic nitrogen acquisition, sulfur oxidation, and photosynthesis. Viral genome abundances containing AMGs differed between the lakes and microbial mats, indicating site specialization. Using procrustes analysis, we also identified significant coupling between viral and bacterial communities (p = 0.001). Finally, host predictions indicate viral host preference among the assembled viromes. Collectively, our data show that: (i) viruses are uniquely distributed through the McMurdo Dry Valley lakes, (ii) their AMGs can contribute to overcoming host nutrient limitation and, (iii) viral and bacterial MDV communities are tightly coupled. 

ABSTRACT Elements are the basic substances that make up living organisms, and the element composition in plants quantitatively reflect the adaptation of plants to environment. However, the drivers that constitute the species‐specific plant elementome, as well as the bivariate bioelemental correlations in determining the stability of different bioelements are yet unclear. Based on 1058 leaf observations of 84 plant species from 232 wetlands across large environmental gradients, we found that bioelements with higher concentration were more stable and evolutionary constrained. We proposed a stability of well‐coordinated elements hypothesis, suggesting that bioelements that coordinate well in driving certain physiological functions constrain each other, thus maintaining relatively stable ratios in plants. In contrast, those functionally independent bioelements fluctuate greatly with environmental nutrient availability. Cold and saline stresses decreased plant stoichiometric network connectivity, complexity, and stability. Our research filled the gap in study of wetland plant elementome, and provided new evidences of plant–environment interactions in regions sensitive to climate change. 

Strong, tough, and lightweight composites are increasingly needed for diverse applications, from wind turbines to cars and aircraft. These composites typically contain sheets of strong and high-modulus fibers in a matrix that are joined with other materials to resist fracture. Coupling these dissimilar materials together is challenging to enhance delamination properties at their interface. We herein investigate using a trace amount of carbon nanotube sheets to improve the coupling between composite skins and core in a composite sandwich. Ultra-thin (~100 nm) forest-drawn multi-walled carbon nanotube (MWNT) sheets are interleaved within the skin/core interphase, with MWNTs aligned in the longitudinal direction. The mechanical behavior is characterized by end notched flexural testing (ENF). With two MWNT sheets placed in the skin/core interphase, the following performance enhancements are achieved: 36.8 % increase in flexural strength; 127.3 % and 125.7 % increases in mode I & II fracture toughness values, respectively; and 152.8 % increase in interfacial shear strength (IFSS). These are achieved with negligible weight gain of the composite sandwich (0.084 wt% increase over the baseline sandwich without MWNT sheets). The finite element simulation results show that MWNT sheets enhance the skin/core coupling by reducing stress concentration, enabling the transition from catastrophic brittle failure to a stable ductile failure mode. The MWNT sheets interleaved sandwich composites are thus demonstrated to be stronger and tougher while providing electrical conductivity (4.3 × 104 S/m) at the skin/core interface for potential de-icing, electromagnetic interference shielding, and structural health monitoring. 

Spread tow carbon fiber composites are receiving increased attention for diverse applications in space and sports gear due to their thin form, which is suitable for deployable structures, and high tensile strength. Their compressive strength, however, is much lower than their tensile strength due to low interlaminar strength. Herein we report a facile technique to enhance their performance through interlaminar insertion of aligned carbon nanotube (CNT) sheets. The inserted CNT sheets also provide electrical conductivity in the composites even at a low CNT loading below the electrical percolation threshold established for CNT-filled composites. Mechanical and electrical characterization was conducted on the CNT sheet-inserted composites and the baseline composites. Results show that the CNT sheets increase the compressive strength by 14.7% compared with the baseline. Such an increase is attributed to the increased adhesion provided by the inserted CNT sheets at the interface between neighboring plies, which also increases the interlaminar shear strength by 33.0% and the interfacial mode-II fracture toughness by 34.6% compared with the baseline composites without inserting CNT sheets. The well-aligned CNT sheet structure maintained between the neighboring plies contributed to a 64.7% increase in electrical conductivity compared with the baseline composites. The findings indicate that the insertion of well-aligned ultrathin CNT sheets in the interlaminar region of a spread tow carbon fiber composite provides significant enhancement in mechanical and electrical performance, paving the path toward applications where both mechanical and electrical performances are crucial, such as for structural health monitoring, lightning protection, and de-icing in aircraft and wind blades. 

Portevin–Le Chatelier effect, associated with dynamic strain aging, is widely found in various alloys, and the maximum serration magnitude from the tensile stress–strain curve can be considered as the point closest to the failure threshold. Due to the difficulty to define solute and solvent atoms in multicomponent alloys, it is a great challenge to explore the serration mechanism. In this study, the atoms that play the role of pinning are defined as solute atoms. Aided by mean-field theory, an in situ pinning model coupled with the twinning effect in a CoNiV alloy with low stacking fault energies is successfully established, which can well predict the failure threshold, i.e., the maximum serration magnitude. The present study paves a new way to correlate the serration dynamics and in situ pinning, and further predicts the failure threshold upon loading for multicomponent high- and medium-entropy alloys.