金沙江干热河谷不同海拔土壤碳氮磷化学计量和酶活性研究

【目的】金沙江干热河谷生态环境恶劣,植被生长发育差,探明该区域内土壤碳、氮、磷化学计量和酶活性特征,对金沙江干热河谷植被恢复及生态治理具有重要意义。【方法】选取金沙江干热河谷上、中、下游海拔800~2000 m内的土壤为研究对象,通过野外调查、土壤采集和室内分析,对该区域土壤的基本理化性质、碳氮磷元素含量及土壤酶活性进行测定。【结果】在金沙江干热河谷不同海拔气候、土壤、植被等环境因子影响下,上、中、下游的土壤有机碳、全氮、全磷含量均随海拔升高而显著增加(P<0.05);金沙江干热河谷环境因子恶劣,导致土壤C/N、C/P、N/P值均小于全国平均水平。在金沙江干热河谷不同海拔气候、土壤、植被等环境因子影响下,上、中、下游的土壤脲酶、β⁃葡萄糖苷酶和酸性磷酸酶的活性均随海拔升高而显著增加(P<0.05)。金沙江干热河谷不同海拔的土壤碳、氮、磷元素含量与土壤脲酶、β⁃葡萄糖苷酶和酸性磷酸酶的活性之间呈极显著正相关(P<0.01),两者相互联系能更客观地反映金沙江干热河谷土壤质量及变化特征。【结论】金沙江干热河谷上、中、下游800~2000 m海拔内土壤碳、氮、磷化学计量和土壤酶活性特征具有高度空间异质性,海拔越高,土壤碳、氮、磷元素含量和酶活性越高。

PEG-6000模拟干旱胁迫和温度对岩柿种子发芽的影响

为了解干旱胁迫和不同温度处理对岩柿种子萌发的影响,明确岩柿种子萌发适宜温度和耐旱程度,探讨岩柿种子萌发期的抗旱能力。以岩柿种子为材料,在10℃、15℃、20℃、25℃、30℃等不同温度下开展PEG-6000溶液(0%、5%、10%、15%、20%、25%)模拟干旱胁迫试验。试验结果表明:(1)低温(0℃、10℃)种子不能萌发,重度干旱胁迫(25%PEG)种子不萌发。(2)岩柿种子能在温度为15℃、20℃、25℃、30℃和PEG轻度干旱(5%PEG)、中度干旱(10%、15%PEG)和重度干旱(20%PEG)下萌发,超过10%PEG浓度种子萌发指标受到不同程度的抑制。(3)随着PEG浓度的增加,种子受胁迫程度越高,种子各项发芽指标均呈现先增加后减少的趋势。结论:岩柿种子萌发受温度和干旱胁迫的影响较大,种子萌发适宜温度为20℃~30℃,PEG耐旱范围是0~25%PEG的干旱条件。发芽率与PEG浓度有着显著的负相关(P<0.05),发芽指数、活力指数与PEG浓度有着极显著的负相关(P<0.01)。抗旱指数与PEG浓度呈负相关,两者相关性不显著(P>0.05)。

Ultralight pyrolytic carbon foam reinforced with amorphous carbon nanotubes for broadband electromagnetic absorption

For electromagnetic wave-absorbing materials,maximizing absorption at a specific frequency has been constantly achieved,but enhancing the absorption properties in the entire band remains a challenge.In this work,a 3D porous pyrolytic carbon(PyC)foam matrix was synthesized by a template method.Amorphous carbon nanotubes(CNTs)were then in-situ grown on the matrix surface to obtain ultralight CNTs/Py C foam.These in-situ grown amorphous CNTs were distributed uniformly and controlled by the catalytic growth time and can enhance the interface polarization and conduction loss of composites.When the electromagnetic wave enters the internal holes,the electromagnetic energy can be completely attenuated under the combined action of polarization,conductivity loss,and multiple reflections.The ultralight CNTs/Py C foam had a density of 22.0 mg·cm^(-3)and a reflection coefficient lower than-13.3 d B in the whole X-band(8.2-12.4 GHz),which is better than the conventional standard of effective absorption bandwidth(≤-10 dB).The results provide ideas for researching ultralight and strong electromagnetic wave absorbing materials in the X-band.

PEG-6000模拟干旱胁迫对毛叶柿种子萌发及生长量的影响

为了解干旱胁迫下毛叶柿(Diospyros dumetorum)种子萌发情况,探究干旱对毛叶柿种子萌发期生长量的影响。以毛叶柿种子为材料,用PEG-6000溶液(0、5%、10%、15%、20%、25%)处理种子以此来模拟不同程度的干旱胁迫。结果表明:1)轻度干旱(5%~10%PEG)能促进种子相对发芽率和相对发芽势的增长,超过10%PEG浓度,种子萌发指标与对照组相比均受到不同程度的抑制。2)随着PEG浓度的增加,幼苗生长指标均值有所下降,与对照组(0PEG)相比,轻中度干旱(PEG0~10%)的胚根长和胚芽长有所增加,胚根长对干旱胁迫的响应更敏感。3)随着PEG浓度的增加,种子受胁迫程度越高,种子地下生长量呈现增加趋势,PEG浓度与根干质量和鲜质量呈极显著相关(P<0.01)。结论:干旱胁迫下毛叶柿种子通过降低相对萌发率、增加胚根鲜质量、干质量和根冠比的生长适应干旱胁迫。

Porous hybrid scaffold strategy for the realization of lightweight,highly efficient microwave absorbing materials

Exploring an advanced and efficient electromagnetic(EM) wave absorbing material by improving dielectric loss capacity and adjusting impendence matching is crucial yet challenging. Herein, the bacterial cellulose(BC) derived carbon aerogel(CA) with a robust nanofibrous network was used as a conductive loss scaffold to dissipate EM waves effectively, and the Zn O microparticles with excellent dielectric properties and low electrical conductivity were decorated on the scaffold to adjust dielectric parameters and impedance matching adequately. By using different zinc precursors, the tunable size and morphologies of Zn O crystals were obtained due to the growth rate of different crystallographic, including flowerlike, nanorod like, and cauliflower-like morphologies, which is beneficial to strong multiple reflections,intensive interfacial polarization, better impendence matching, as well as excellent maintenance of the hierarchical structure. Owing to the appropriate impendence matching and the considerable EM wave dissipation, the CA@ZnO composites achieve a superior EM absorbing performance with a broad effective absorbing bandwidth(whole X band) and a minimum reflection coefficient(-53.3 d B). This work paves a new way for developing lightweight and highly efficient EM absorbing materials comprising the carbon scaffold and semiconductor microparticles.

Structure,dielectric properties of low-temperature-sintering BaTiO3-based glass–ceramics for energy storage

The 0.85BaTiO3–0.15Bi(Mg_(2/3)Nb_(1/3))O_(3)(BTBMN)ceramics with low-melting-temperature B_(2)O_(3)–Na_(2)B_(4)O_(7)–Na_(2)SiO_(3)(BNN)glass addition were prepared by the solid state method.The composition of the glass–ceramics was BTBMN–x wt.%BNN(x=0,1,3,5,7,9,12,15;abbreviated as BG).The sintering characteristics,phase structure,microstructure,dielectric properties and energy storage properties were systematically investigated.The sintering temperature of BTBMN ceramics was greatly reduced by the addition of BNN glass.The second-phase BaTi(BO_(3)T_(2)was observed in the BG system until the glass content reached 15 wt.%.The addition of BNN glass significantly reduces the grain size of BTBMN ceramics.With the increase of BNN glass content,dielectric constant of BG glass–ceramics at 1 kHz gradually decreased,the maximum dielectric constant("mT of BG glass–ceramics gradually decreased,while the temperature corresponding to the maximum dielectric constant(T_(m)T increased,the ferroelectric relaxation behavior decreased and the temperature stability of the dielectric constant gradually improved.As the BNN glass content increased,the breakdown electric field strength(BDS)of BG glass–ceramics increased first and then decreased,and the polarization values reduced gradually,while the trend of energy storage performance is similar to BDS.When the BNN glass content was 3 wt.%,the energy storage properties of the BG glass–ceramics were optimal,and a recoverable energy storage density(Wrec)of 1.26 J/cm^(3)and an energy storage efficiency(η)of 80.9%were obtained at the electric field strength of 220 kV/cm.The results showed that BG glass–ceramics were promising for energy storage capacitors.