Afforestation is among the most effective means of preventing and controlling desertification. Silver poplar (Populus alba) is commonly planted tree species for afforestation of the Horqin Sandy Land of China. However, this species has exhibited some drawbacks such as top shoot dieback, premature senescence and mortality, and soil and ecosystems degradation. In contrast, Siberian elm (Ulmus pumila) rarely experiences these problems in the same regions. Ecological stoichiometry plays a vital role in exploring ecological processes and nutrient cycle relationships in plant–litter–soil systems. To explore the differences in the carbon (C), nitrogen (N), and phosphorus (P) balance, the stoichiometry characteristics and stoichiometric homeostasis in elm and poplar plantations in the Horqin Sandy Land, we measured C, N, and P concentrations in leaves, branches, roots, litter, and soils and analyzed N and P resorption efficiencies in the two plantations. The results showed that soil C and N concentrations, C:P, and N:P were greater in the elm plantation than in the poplar plantation. The leaf and root C:P and N:P during summer and litter N and P concentrations were greater, whereas N and P resorption efficiencies were lower, in the elm plantation than in the poplar plantation. Generally, elm exhibited greater N:P homeostasis than poplar. N and N:P homeostasis were greater in roots than in leaves and branches in the elm plantation, but they varied with soil N concentration and N:P in the poplar plantation. These findings indicate that poplar exhibited more developed internal nutrient conservation and allocation strategies but poor nutrient accumulation in soil, which may contribute to degradation of poplar plantation. In contrast, elm tended to return more nutrients to the soil, showing an improved nutrient cycle in the plant–litter–soil system and increased soil C and N accumulation in the elm plantation. Therefore, compared with poplar, elm may be a more suitable afforestation tree species for the Horqin Sandy Land, in terms of promoting the accumulation of soil nutrients and enhancing nutrient cycling in the plant–litter–soil system.

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Since former president Obama of America put forward the concept of 3D printing or additive manufacturing, it had been putting into use rapidly and getting acceptance widely. In particular, metal additive manufacturing machines had been successfully applied with pilot demonstration in industry. However, the present metal additive manufacturing machines cannot be directly used in medical fields such as dental restoration because of some different requirements between industry and medical fields. In this case, this paper is aimed for the development of laser fusion printing machine (LFP), also being called as selective laser melting (SLM), for ceramic teeth crown in dental restoration business. Through the reasonable design and development of key components such as machinery unit, optical unit, electrical controlling unit, and software unit, and the integration, debugging, and optimization of the entire system, the laser fusion printing apparatus for dental restoration has been successfully developed. Key technologies such as machine structure design, optical unit design, electrical controlling system design, system software and process software have been overcome, on the basis of which, a lot of process experiments of medical titanium alloy materials were deeply carried out. At last laser fusion printing technology of titanium alloy was mastered, and titanium dental crown by laser fusion printing with relative density up to 97.37% was realized. After post treatment with porcelain, it was found that the laser fusion printed porcelain teeth with titanium alloy has good metal-ceramic bonding strength, which is equivalent to the quality of traditional porcelain teeth, which showed that laser fusion printing can meet the requirements of dental restoration business and has a broad market outlook.