Subjects: Agriculture, Forestry,Livestock & Aquatic Products Science >> Soil Science submitted time 2023-03-13 Cooperative journals: 《干旱区研究》
Abstract： A grazing and enclosed Pinus sylvestris var. mongolica forests in sandy land was selected to explore the effects of grazing on soil nutrients and microbial communities. The microbial community composition and diversity between grazing and enclosed soil was determined using high-throughput sequencing technology. Soil chemical indexes were determined for estimating variation in the nutrients. The results showed that total phosphorus content decreased significantly after grazing (P < 0.05). Soil organic carbon and total nitrogen content also decreased, while ammonium nitrogen, nitrate nitrogen, and available phosphorus increased, but the change was not significant (P > 0.05). The grazing and enclosed plots showed 17.1%-24.6% similarity in the soil microbial community composition and the OTUs of fungi and bacteria were lower in grazing than enclosed plots. At each classification level, the number of fungi and bacteria in grazing plots was less than that in enclosed plots. Results showed grazing significantly reduced the number of bacteria at the genus level(P < 0.05). The proportion of basidiomycetes in grazing was significantly lower than that in enclosure (P < 0.05). No significant indigenous effect on bacterial phylum level (P > 0.05) was observed. In terms of soil microbial diversity, grazing significantly reduced the Chao1 index and Shannon index of bacteria (P < 0.01), and had no significant effect on fungal community diversity (P > 0.05). The effect of grazing on soil bacterial diversity index was greater than that of fungi. In summary, grazing in the Pinus sylvestris var. mongolica forest in sandy land has different degrees of negative impacts on soil nutrients and soil microorganisms. Therefore, the grazing should be moderately reduced in this region to alleviate land pressure and ensure the sustainable utilization of the Pinus sylvestris var. mongolica plantation.
Subjects: Astronomy >> Astrophysical processes submitted time 2019-05-07 Cooperative journals: 《天文研究与技术》
Abstract：近地天体数量多且撞击危害大，对其进行预警防御是有效应对其撞击威胁的基本手段，具体的预警防御技术已成为国际研究热点。中国现已加入专门负责近地天体预警防御的国际组织，但具体研究多处于起步阶段。详细阐述了发展近地天体预警防御技术的必要性及基本的应对流程，阐述了搜索监测、国际组织及其技术研究、深空探测项目等各方面的国际研究进展情况，简要分析了轨道偏转防御的基本策略和核爆、动能撞击、引力牵引、改变太阳光压及激光剥蚀等5种主要防御手段的原理及优缺点，总结了近地天体预警防御领域未来工作的四个重点方向。最后针对我国的研究现状提出几点建议和思考。
Hits
Hits
Downloads
Comment