Interface engineering of MXene towards super-tough and strong polymer nanocomposites with high ductility and excellent fire safety

The integration of high strength, high toughness, and excellent flame retardancy in polymer materials is highly desirable for their practical applications in the industry. However, existing material design strategies often fail to realize such a performance portfolio because of mutually exclusive mechanisms between strength and toughness, and low flame retardancy efficiency of nanofillers in polymers. Here, we reported the preparation of a multifunctional nanohybrid, Ti3C2Tx@MCA, by engineering the surface of titanium carbide nanosheets (Ti3C2Tx, MXene) with melamine cyanurate (MCA) via hydrogen bonding interactions, and subsequent thermoplastic polyurethane (TPU)/Ti3C2Tx@MCA nanocomposites. The resultant TPU nanocomposite containing 3.0 wt% of Ti3C2Tx@MCA shows a high tensile strength of 61.5 MPa, a toughness as high as 175.4 ± 7.9 MJ m−3 and a high strain at failure of 588%, and 40% reduction in the peak of heat release rate. Such extraordinary mechanical and fire retardant performances are superior to those of its previous counterparts. Interfacial hydrogen bonding in combination with the “labyrinth” effect and catalytic action of 2D Ti3C2Tx nanosheets are responsible for the outstanding mechanical and fire retardancy properties of TPU nanocomposites. This work provides a new paradigm for integral design of high-performance polymeric materials with excellent mechanical and fire-safe performances portfolio

Whole soil acidification and base cation reduction across subtropical China

International audienc

Litter decomposition and nutrient release are faster under secondary forests than under Chinese fir plantations with forest development

Abstract In terrestrial ecosystems, leaf litter is the main source of nutrients returning to the soil. Understanding how litter decomposition responds to stand age is critical for improving predictions of the effects of forest age structure on nutrient availability and cycling in ecosystems. However, the changes in this critical process with stand age remain poorly understood due to the complexity and diversity of litter decomposition patterns and drivers among different stand ages. In this study, we examined the effects of stand age on litter decomposition with two well-replicated age sequences of naturally occurring secondary forests and Chinese fir (Cunninghamia lanceolata) plantations in southern China. Our results showed that the litter decomposition rates in the secondary forests were significantly higher than those in the Chinese fir plantations of the same age, except for 40-year-old forests. The litter decomposition rate of the Chinese fir initially increased and then decreased with stand age, while that of secondary forests gradually decreased. The results of a structural equation model indicated that stand age, litter quality and microbial community were the primary factors driving nutrient litter loss. Overall, these findings are helpful for understanding the effects of stand age on the litter decomposition process and nutrient cycling in plantation and secondary forest ecosystems

Temporal changes in soil C‐N‐P stoichiometry over the past 60 years across subtropical China

Controlled experiments have shown that global changes decouple the biogeochemical cycles of carbon (C), nitrogen (N), and phosphorus (P), resulting in shifting stoichiometry that lies at the core of ecosystem functioning. However, the response of soil stoichiometry to global changes in natural ecosystems with different soil depths, vegetation types, and climate gradients remains poorly understood. Based on 2,736 observations along soil profiles of 0–150 cm depth from 1955 to 2016, we evaluated the temporal changes in soil C‐N‐P stoichiometry across subtropical China, where soils are P‐impoverished, with diverse vegetation, soil, and parent material types and a wide range of climate gradients. We found a significant overall increase in soil total C concentration and a decrease in soil total P concentration, resulting in increasing soil C:P and N:P ratios during the past 60 years across all soil depths. Although average soil N concentration did not change, soil C:N increased in topsoil while decreasing in deeper soil. The temporal trends in soil C‐N‐P stoichiometry differed among vegetation, soil, parent material types, and spatial climate variations, with significantly increased C:P and N:P ratios for evergreen broadleaf forest and highly weathered Ultisols, and more pronounced temporal changes in soil C:N, N:P, and C:P ratios at low elevations. Our sensitivity analysis suggests that the temporal changes in soil stoichiometry resulted from elevated N deposition, rising atmospheric CO2 concentration and regional warming. Our findings revealed that the responses of soil C‐N‐P and stoichiometry to long‐term global changes have occurred across the whole soil depth in subtropical China and the magnitudes of the changes in soil stoichiometry are dependent on vegetation types, soil types, and spatial climate variations

Tree mycorrhizal type mediates the responses of foliar stoichiometry and tree growth to functionally dissimilar neighbours in a subtropical forest experiment

Plant nutrient stoichiometry is of critical importance to productivity and nutrient cycling in terrestrial ecosystems. The impacts of tree species diversity on productivity have been well studied at the stand level. However, it is unclear how neighbourhood interactions impact the foliar nutrient stoichiometry of trees at the neighbourhood scale and how plant mycorrhizal associations can mediate such effects. - We randomly selected eight tree species from a large-scale biodiversity experiment with mixtures up to 32 tree species in subtropical China to assess the effects of species richness, phylogenetic and trait dissimilarities and competition on the foliar nutrient stoichiometry of focal trees associated with either arbuscular mycorrhizal (AM) or ectomycorrhizal (EM) fungi. We further investigated whether neighbourhood diversity can alter focal tree growth by regulating C:N:P stoichiometry. - Neighbourhood species richness had no significant impact on the foliar C:N, N:P or C:P for both AM and EM trees. Increased neighbourhood phylogenetic dissimilarity significantly decreased the foliar N:P and C:P of AM trees but did not affect those of EM tree species. Foliar C:N, N:P and C:P of AM trees decreased with increasing neighbour trait (specific leaf area, root diameter, wood density dissimilarity, total trait) dissimilarities, while those of EM trees increased or remained unchanged. The increase of the neighbourhood competition index resulted in an increase in the foliar C:N of AM tree species but not EM tree species. The structural equation model analysis revealed that the increase of neighbourhood phylogenetic dissimilarity and functional trait dissimilarity indirectly enhanced tree growth of AM trees by decreasing foliar C:N. Conversely, the increase of neighbourhood-specific root length and wood density dissimilarity indirectly reduced the growth of EM trees by increasing foliar N:P. - Synthesis. Our results indicate that neighbourhood trait dissimilarity regulated tree foliar stoichiometry and growth performance, but the effects depended on the mycorrhizal type of trees. Our findings highlight the importance of tree mycorrhizal associations for better understanding the relationship between plant diversity and ecosystem functions

FE-<b>Tree mycorrhizal type mediates the responses of </b><b>foliar </b><b>stoichiometry </b><b>and tree growth to functionally dissimilar neighbours in a subtropical forest experiment</b>

Tree mycorrhizal type mediates the responses of foliar stoichiometry and tree growth to functionally dissimilar neighbours in a subtropical forest experiment</p