Spatiotemporal variations and determinants of stream nitrogen and phosphorus concentrations from a watershed in the Three Gorges Reservoir Area,China

Socioeconomic development induced nonpoint source (NPS) pollution has aroused an increasing concern, however, most of the previous studies were concentrated on the impacts of environmental determinants. Here, total nitrogen (TN) and total phosphorus (TP) concentrations from 13 sampling sites were collected biweekly from January 2018 to October 2021, and 26 potential factors including environmental and socioeconomic were considered in the Wangjiaqiao watershed of the Three Gorges Reservoir Area, China. Impacts of these factors on TN and TP were evaluated by partial least squares regression (PLSR) model. It showed that average TN and TP concentrations in wet seasons (TN,14.68 mg L⁻¹; TP, 0.113 mg L⁻¹) were higher than that in dry seasons (TN, 11.73 mg L⁻¹; TP, 0.087 mg L⁻¹). Additionally, the TN concentrations were greater in downstream than upstream, however, the highest TP concentrations were found in the middle of the watershed. The optimal PLSR model explained 69.6%, 73.1% and 66.1% of the variance in TN concentration, as well as 65.7%, 79.5% and 67.4% of the variance in TP concentration during the annual, dry and wet seasons, respectively. Moreover, TN was primarily influenced by topographic wetness index, planting structure, interspersion and juxtaposition index, orchard proportion, nitrogen fertilization, per capita income, and catchment area, whereas TP was mainly controlled by slope gradient, topographic wetness index, hypsometric integral, interspersion and juxtaposition index, and population density. Collectively, environmental factors had greater impacts on the TN and TP concentrations than socioeconomic factors. Raising farmers' awareness of the hazards of NPS pollution is beneficial to watershed NPS pollution control.     

Direct contribution by soil arthropods to nutrient availability through body and faecal nutrient content

Summary The direct contribution made by soil arthropods to nutrient dynamics was investigated in pine forests that differed in soil nutrient status. Nutrient concentrations (K⁺, Ca²⁺, Mg²⁺, PO ₄ ^3– , N, C) in the most abundant species and groups of arthropods in two Pinus nigra forests were compared, and distinct differences were found among taxonomic groups. In the rank order: collembolans, oribatides, isopods, diplopods, Ca²⁺ and Mg²⁺ concentrations increased, while N and C concentrations decreased. The nutrient concentrations in individuals of the same species but originating from the different forests were similar, except for the isopod Philoscia muscorum. The total and available nutrient concentrations in food and faeces of the collembolan Tomocerus minor and the isopod Philoscia muscorum were compared. The isopod faeces contained relatively less K⁺ and Mg²⁺, and more Ca²⁺, PO ₄ ^3– , and greater N availability, compared with the food material. The collembolan faeces showed a higher availability of all nutrients measured. The N species appeared to be changed by collembolans; their faeces contained high NO ₃ ^– concentrations, while their food contained relatively high concentrations of NH ₄ ⁺ . These findings were examined in relation to their significance for ecosystem functioning. It was concluded that about 12% of the total K⁺, PO ₄ ^3– , N and 2% of the Ca²⁺ in the organic layer was found in the mesofauna. It was calculated that faeces production by the collembolans resulted in a 2.4 times higher NO ₃ ^– availability in the forest floor.     

日光温室气象环境综合研究(三)——几种弧型采光屋面温室内直射光量的比较研究

本文计算了北京地区四种弧型采光屋面的温室内10～4月各月平均太阳直接辐射日总量(简称直射光总量),并进行了比较。结果表明10～4月室内直射光总量均以圆面——抛物面组合型温室最高,椭圆面最低。圆面和抛物面相比,冬季(11～2月)前者优于后者,春季(3～4月)相反。     

肥料运筹对菊苣根生产性能的影响

[目的]筛选菊苣根总糖含量最大最佳最具经济效益的施肥处理。[方法]在田间小区试验条件下,研究肥料运筹对普那菊苣根生产性能的影响。[结果]结果表明:在相同的生长条件和栽培方式下,相比对照组,每公顷追加磷肥120 kg与每公顷追加钾肥100 kg均有利于菊苣根重以及总糖含量的增加,综合考虑经济效益,追加钾肥明显优于对照组和追加磷肥组,不仅鲜根重增加、含糖量较高,其鲜草产量也最大。[结论]总糖是菊苣根营养物质含量的一个重要指标,追加磷肥和钾肥均有利于总糖含量的增加。     

自动电位滴定法在果蔬汁饮料总酸度测定中的应用

[目的]采用自动电位滴定法测定果蔬饮料总酸度。[方法]首先采用自动电位滴定法确定不同果蔬汁的滴定终点,再根据确定的滴定终点,采用自动电位滴定法测定不同果蔬汁的总酸度。[结果]该法测定果蔬汁饮料中的总酸度,操作步骤简便,测定准确度较高,可用于实际果蔬汁饮料总酸度的测定。[结论]该研究为自动电位滴定法在果蔬汁饮料总酸度测定中的应用奠定了基础。     

金盏菊总皂苷提取及其抗氧化、降血脂作用研究

通过对金盏菊总皂苷的实验室提取工艺及其抗氧化、降血脂作用研究,结果表明:金盏菊总皂苷较为理想的实验室提取工艺为:提取温度75℃,提取时间55 min,乙醇浓度75%,料液比1∶35。在此条件下,总皂苷的提取率为2.01%,总固物中总皂苷含量达到35.4%。金盏菊总皂苷对O2.、.OH皆表现出较好的清除效果,清除率分别达到47.29%和88.42%;小鼠血清中的TC、TG、LDL-C与模型组相比,均有一定程度的下降。     

Fractal features of soil particle size distribution and the implication for indicating desertification

Some of the effects of land desertification on soil properties are manifested by the coarsening of the soil particlesize distribution (PSD) and the losses in organic C and nutrients. The changes and characteristics of PSD and selected chemical properties in soils at the 0-15 cm plough layer from different degrees of desertified croplands are analyzed in the semiarid Horqin Sandy Land, northern China. The fractal dimension of the PSD is emanated to characterize the patterns of PSD. The relationships between the fractal dimension of the PSD and selected soil properties are discussed. The results show that: (1) in the transformation from potential desertified cropland to extremely desertified cropland, the sand content at the 0-15 cm soil increased from 69% to 93%, organic C and total N contents decreased by 65% and 69%, respectively; (2) the fractal dimension of PSD ranged from 2.179 to 2.611, the more the contents of sand, the lower the fractal dimension and the higher the desertified degree of farmland. In the desertification process within the studied area, the mean fractal dimension decreased from 2.555 for the potential desertified soils to 2.298 for extremely desertified soils; (3) there existed considerable linear relationships between fractal dimension and soil properties. It was shown that fractal dimensions of PSD are useful parameters able to monitor soil degradation and to estimate the degree of soil desertification.     

Solvent-extractable lipids in an acid andic forest soil; variations with depth and season

Total lipid extracts from an acid andic soil profile located on Madeira Island (Portugal) were analysed using gas chromatography (GC) and GC-mass spectrometry (GC/MS). The profile was covered mainly by grass. Bulk soil characteristics determined included soil pH (H₂O) ranging from 4.5 to 4.0 and TOC, ranging from 84 to 30 g kg⁻¹. A decrease of the contribution of lipids per TOC with depth was observed. The absence of typical bacterial markers might be an indication for reduced bacterial activity, most likely related to the low soil pH and the presence of Al and Fe (oxides). The distribution observed in the top layer with a dominant C₂₆n-alkanol, steroids and triterpenoids, reflected mainly an input by grass leaves. A strong decrease in both relative and absolute concentration of these leaf-derived compounds was observed when comparing the litter layer with the mineral soil. The presence of C₂₂-C₃₂n-alkanoic acids, C₂₂-C₂₆ ω-hydroxy acids, C₃₁n-alkane and C₂₂-C₃₂n-alkanols observed in the sub-soil is indicative of an important contribution by (grass) roots. In summer, a signal most likely reflecting the leaching of microbially derived products from the litter and/or aerial vegetation at the surface was observed.     

长期不同施肥对稻田土壤有机质和全氮的影响

通过对湖南新化、宁乡、株洲、桃江、武岗5个国家级稻田肥力长期定位试验点18年的田间定位试验,研究了不同施肥方式下0-20 cm土层土壤有机质和全N含量的演变规律。结果显示,中量和高量有机肥与化肥配合处理在提高土壤有机质和全N含量方面效果明显优于单施化肥和秸秆还田处理,且随有机肥用量的增加而增加,表明有机肥与化肥配合施用是提高土壤有机质和N素肥力的重要措施。在不同施肥方式下,稻田土壤有机质总体上呈现出上升或者下降的趋势,但在不同的年份会有波动。     

太湖地区黄泥土氮肥对水稻产量、叶片碳氮同化及不同土层氮的影响

在长期定位试验的基础上研究了太湖地区黄泥土不同施氮水平对水稻产量、碳氮同化及不同土层氮的影响。结果表明，长期施氮量（N）在161．0kg hm^-2处理和高于该施氮量处理的产量之间没有显著差异。拔节期、孕穗期和灌浆期施氮量在161．0kg hm^-2处理和高于该施氮量处理的碳氮同化水平之间几乎没有差异，但都高于施氮量在57．5kg hm^-2处理的。不同土层氮分布结果表明，长期施氮量在161．0kg hm^-2和高于该施氮量各处理中，长期施入有机肥配施NPK肥处理残留最深，其次是长期施入化肥N的处理，长期秸秆还田配施N肥处理较浅。