Nitrogen deposition has a considerable impact on biogeochemical cycling in terrestrial ecosystems.However,how litter production and element return respond to N addition remains poorly understood in nitrogen-rich subtr...Nitrogen deposition has a considerable impact on biogeochemical cycling in terrestrial ecosystems.However,how litter production and element return respond to N addition remains poorly understood in nitrogen-rich subtropical regions.In this study,a 4-year nitrogen addition experiment explored its eff ects on foliar litter production and carbon,nitrogen and phosphorus in a subtropical Michelia wilsonii forest.A clear seasonal pattern in foliar litterfall was observed,regardless of nitrogen treatments,with a peak in spring and a smaller one in autumn.Foliar litter increased with increasing nitrogen but did not aff ect litter carbon concentrations and often decreased nitrogen and phosphorous concentrations.The eff ect of nitrogen addition was dependent on time(month/year).Carbon,nitrogen and phosphorous return showed similar bimodal seasonal patterns.Nitrogen addition increased carbon and nitrogen return but did not aff ect phosphorous.Our results suggest that the addition of nitrogen stimulates carbon and nutrient return via litterfall.展开更多
Ever increasing pressures on tropical forests worldwide due to anthropogenic disturbances have greatly affected both above-and belowground functioning of these forests.While fine roots play major ecological roles in f...Ever increasing pressures on tropical forests worldwide due to anthropogenic disturbances have greatly affected both above-and belowground functioning of these forests.While fine roots play major ecological roles in forests through assisting in nutrient and water uptake and returning elements to the soil environment,coarse roots play an important role in C sequestration.We studied changes in fine and coarse root biomass,production,turnover and carbon and nitrogen return to the soil in two regenerating forest stands(RFs)following stonemining that were 5 years(RF-5)and 15 years(RF-15)post-disturbance compared with a natural forest stand(NF)in Mizoram,North-east India.Fine(<2mm)and coarse root(2-10 mm)biomass differed significantly among the forest stands and ranged from239(RF-5)to 415(NF)and 230(RF-5)to 436(NF)g m 2,respectively.Total root(fine+coarse)biomass increased during stand development but the proportion of very fine root(<0.5 mm)to total root production decreased.Fine root biomass decreased with increasing soil depth.Fine and total root biomass showed strong seasonal correlations with soil moisture,more so than for rainfall and temperature,whereas these relationships were less clear for the coarse root biomass.The amount of N(25-55 kg ha-1)and C(1.9-3.6t ha-1)stored in root biomass increased with stand age with a corresponding increase in production and turnover of C and N to the soil.Disturbance to these tropical forests negatively affected root dynamics,influenced their spatiotemporal patterns,and reduced the production,amount and availability of nutrients returned to the soil along with a strong reduction in the root biomass carbon pool and sequestration in carbon residence time.We observed that root growth,especially fine roots,is dependent on abiotic variables,and plays a significant role in early stages of secondary succession by adding organic matter and nutrients through high turnover rates in these forests.展开更多
本文以斗式提升机为模型,采用DEM(Discrete Element Method)算法对粉料在提升机内运动过程进行离散元模拟仿真,分析粉料颗粒在其内部的运动轨迹,得出粉料粒径以及料斗数对提升机回料率的影响规律,为提升机的结构优化提出理论性的指导。...本文以斗式提升机为模型,采用DEM(Discrete Element Method)算法对粉料在提升机内运动过程进行离散元模拟仿真,分析粉料颗粒在其内部的运动轨迹,得出粉料粒径以及料斗数对提升机回料率的影响规律,为提升机的结构优化提出理论性的指导。结果表明:(1)均匀粉料粒径越小,机尾回料越严重,并得到回料量与粒径之间的关系式;(2)斗数增加可以提高提升机输送效率,降低粉料回料量;(3)随着粉料粒径的增大,料斗填充率呈现先增大后降低的趋势,并在4 mm粉料粒径时得到峰值,填充率达到69%。展开更多
为明确电能计量装置自身误差受电磁场影响程度,对特高压用计量电流互感器(CT)开展一次绕组偏心及返回导体对误差影响的定量分析。首先根据磁路平衡原理建立在圆柱坐标内CT误差数学模型,推导出不同位置的外加磁场点对CT误差影响计算公式...为明确电能计量装置自身误差受电磁场影响程度,对特高压用计量电流互感器(CT)开展一次绕组偏心及返回导体对误差影响的定量分析。首先根据磁路平衡原理建立在圆柱坐标内CT误差数学模型,推导出不同位置的外加磁场点对CT误差影响计算公式,并结合实例得到有限元与解析解结果一致,证明推导公式的正确性;然后在二维电场中对1 000 k V工程中典型CT尺寸及一次电流进行磁场分布仿真,定量的得到对于特高压用计量CT,一次绕组偏心大于1/8的CT半径后会铁心内部会产生局部饱和,导致误差产生突变进而导致超差可能;此外,仿真结果指出外部返回导体距离CT中心应大于3倍CT半径后,返回导体引起的磁场对CT误差的干扰才能被忽略;最后搭建实际特高压误差测试平台对一次绕组偏心开展试验,测试数据与仿真结果趋势一致。展开更多
基金supported by the National Natural Science Foundation of China(grants 32071745,32001165,31901295 and 31800519)the Program of Sichuan Excellent Youth Sci-Tech Foundation(2020JDJQ0052)+1 种基金the Applied Basic Research Program of Sichuan of China(2021YJ0340)the National Key Research and Development Program of China(2016YFC0502505 and 2017YFC0505003).
文摘Nitrogen deposition has a considerable impact on biogeochemical cycling in terrestrial ecosystems.However,how litter production and element return respond to N addition remains poorly understood in nitrogen-rich subtropical regions.In this study,a 4-year nitrogen addition experiment explored its eff ects on foliar litter production and carbon,nitrogen and phosphorus in a subtropical Michelia wilsonii forest.A clear seasonal pattern in foliar litterfall was observed,regardless of nitrogen treatments,with a peak in spring and a smaller one in autumn.Foliar litter increased with increasing nitrogen but did not aff ect litter carbon concentrations and often decreased nitrogen and phosphorous concentrations.The eff ect of nitrogen addition was dependent on time(month/year).Carbon,nitrogen and phosphorous return showed similar bimodal seasonal patterns.Nitrogen addition increased carbon and nitrogen return but did not aff ect phosphorous.Our results suggest that the addition of nitrogen stimulates carbon and nutrient return via litterfall.
基金University Grants Commission, New Delhi for financial support
文摘Ever increasing pressures on tropical forests worldwide due to anthropogenic disturbances have greatly affected both above-and belowground functioning of these forests.While fine roots play major ecological roles in forests through assisting in nutrient and water uptake and returning elements to the soil environment,coarse roots play an important role in C sequestration.We studied changes in fine and coarse root biomass,production,turnover and carbon and nitrogen return to the soil in two regenerating forest stands(RFs)following stonemining that were 5 years(RF-5)and 15 years(RF-15)post-disturbance compared with a natural forest stand(NF)in Mizoram,North-east India.Fine(<2mm)and coarse root(2-10 mm)biomass differed significantly among the forest stands and ranged from239(RF-5)to 415(NF)and 230(RF-5)to 436(NF)g m 2,respectively.Total root(fine+coarse)biomass increased during stand development but the proportion of very fine root(<0.5 mm)to total root production decreased.Fine root biomass decreased with increasing soil depth.Fine and total root biomass showed strong seasonal correlations with soil moisture,more so than for rainfall and temperature,whereas these relationships were less clear for the coarse root biomass.The amount of N(25-55 kg ha-1)and C(1.9-3.6t ha-1)stored in root biomass increased with stand age with a corresponding increase in production and turnover of C and N to the soil.Disturbance to these tropical forests negatively affected root dynamics,influenced their spatiotemporal patterns,and reduced the production,amount and availability of nutrients returned to the soil along with a strong reduction in the root biomass carbon pool and sequestration in carbon residence time.We observed that root growth,especially fine roots,is dependent on abiotic variables,and plays a significant role in early stages of secondary succession by adding organic matter and nutrients through high turnover rates in these forests.
文摘本文以斗式提升机为模型,采用DEM(Discrete Element Method)算法对粉料在提升机内运动过程进行离散元模拟仿真,分析粉料颗粒在其内部的运动轨迹,得出粉料粒径以及料斗数对提升机回料率的影响规律,为提升机的结构优化提出理论性的指导。结果表明:(1)均匀粉料粒径越小,机尾回料越严重,并得到回料量与粒径之间的关系式;(2)斗数增加可以提高提升机输送效率,降低粉料回料量;(3)随着粉料粒径的增大,料斗填充率呈现先增大后降低的趋势,并在4 mm粉料粒径时得到峰值,填充率达到69%。
文摘为明确电能计量装置自身误差受电磁场影响程度,对特高压用计量电流互感器(CT)开展一次绕组偏心及返回导体对误差影响的定量分析。首先根据磁路平衡原理建立在圆柱坐标内CT误差数学模型,推导出不同位置的外加磁场点对CT误差影响计算公式,并结合实例得到有限元与解析解结果一致,证明推导公式的正确性;然后在二维电场中对1 000 k V工程中典型CT尺寸及一次电流进行磁场分布仿真,定量的得到对于特高压用计量CT,一次绕组偏心大于1/8的CT半径后会铁心内部会产生局部饱和,导致误差产生突变进而导致超差可能;此外,仿真结果指出外部返回导体距离CT中心应大于3倍CT半径后,返回导体引起的磁场对CT误差的干扰才能被忽略;最后搭建实际特高压误差测试平台对一次绕组偏心开展试验,测试数据与仿真结果趋势一致。
