基于REE示踪的土壤团聚体破碎转化路径定量表征

土壤团聚体破碎转化路径是坡面侵蚀过程研究的难点问题之一。目前团聚体破碎转化路径的定量表征仍不明晰,一定程度上限制了土壤侵蚀过程中泥沙分选搬运机制的深入研究。基于大样带调查选取6种不同质地的典型农耕地土壤为研究对象,结合稀土元素(Rare Earth Elements,REE)示踪方法,综合分析不同粒径土壤团聚体(5~2,2~1,1~0.5,0.5~0.25,<0.25 mm)和不同径流扰动周期(24 h,7天)对REE吸附和解吸能力的影响,探究REE示踪不同粒径土壤团聚体破碎转化的可行性,定量表征了土壤团聚体破碎转化路径。结果表明:REE与土壤团聚体的实际吸附浓度低于施放浓度,2~1,1~0.5,0.5~0.25,<0.25 mm土壤团聚体的REE吸附浓度与黏粒含量呈显著正相关(P<0.05);径流扰动影响对吸附于土壤团聚体的REE解吸作用十分微弱,解吸浓度仅占REE实际吸附浓度的0.001%~0.139%。5~2,2~1,1~0.5,05~0.25,<0.25 mm土壤团聚体经过湿筛后向各粒径转化的路径基本相同,向<0.25 mm微团聚体转化为土壤团聚体破碎的主要路径。相较于粉粒、黏粒含量较高的土壤团聚体,砂粒含量较高的土壤团聚体向1~0.5,0.5~0.25 mm粒径的转化贡献率整体偏低。基于REE示踪得到的>0.25 mm各粒径团聚体质量整体被低估,低估范围为-27.96%^-11.08%;而<0.25 mm团聚体质量则被高估,高估范围为3.65%~22.73%。基于各粒径土壤团聚体的REE量化值建立了校正关系,可将计算相对误差降低至0.04%~16.24%。     

Phosphorus fractions and dynamics as affected by land-use changes in the Central Mexican highlands

Land-use change from forest to agriculture in the volcanic ash-derived soils of Mexico has increased over recent decades. It is likely that land uses and management practices, particularly fertilizer use have affected phosphorus (P) distribution and availability. The objective of this study was to evaluate the effects of land-use types (native forest and maize mono-cropping), and the related P addition, on the forms and distribution of soil P and their isotopic exchangeability. An Andisol, sampled from a cropping site, along with the contiguous area under native forest was treated with ³²P-labelled potassium phosphate (KH₂³²PO₄). The soil samples were extracted after incubation times of 7, 21, 35 and 49 days. Phosphorus content and ³²P recovery in fractions sequentially extracted were assessed for each incubation time. Total soil P was dominated by inorganic fractions (79 to 86%) in both land-use types. Resin-Pi, bicarbonate extractable inorganic P (Bic-Pi) and sodium hydroxide extractable inorganic P (NaOH_0.1-Pi) were all raised with P addition. However, the proportion of organic P fraction was reduced under cropped soil. The recovery of ³²P in soils with P addition indicates that resin-Pi, Bic-Pi and NaOH_0.1-Pi comprised nearly all the exchangeable P. In native soils with no P addition, more than 19% of the ³²P was recovered in Bic-Po and NaOH_0.1-Po forms. This finding indicates that organic P cycling is crucial when soil Pi reserves are presented in an inadequate amount. Ecologically based management has to be designed for replenishment and succeeding maintenance of soil organic P compounds to increase sustainable agricultural production.     

基于多指标评价和分形维数的坡耕地优先流定量分析

以重庆紫色砂岩区坡耕地田间染色示踪试验为基础,采用形态学和统计学方法,对3种坡耕地土壤剖面染色图像进行指标提取,运用多指标评价法确定了优先流指数PFI,并结合几何学中的分形理论,定量评价了土壤优先流的发育程度。结果表明:6个优先流特征指标(优先流区染色面积比、基质入渗深度、优先流分数、长度指数、峰值指数和变异系数)均表现出南瓜地和柑橘地的优先流程度高于玉米地;优先流指数PFI由大到小为南瓜地(0.88)、柑橘地(0.77)、玉米地(0);通过Fractal Fox 2.0软件计算得到的优先流湿润峰迹线分形维数由大到小为南瓜地、柑橘地、玉米地。与土壤优先流指数PFI进行比较,所得结果基本一致,说明利用分形维数来评价土壤优先流发育程度是准确可行的。     

基于15N示踪技术的干旱区滴灌葡萄氮素利用分析

为研究水氮调控对干旱区滴灌葡萄氮素吸收利用的影响,以新疆鲜食葡萄弗雷为试验材料,利用¹⁵N 示踪技术,设置2种灌水处理(灌水量为4 950、5 400 m³·hm^-2,分别记作W1、W2),3种施氮处理(施氮量为177、235、292 kg·hm^-2,分别记作F1、F2、F3)进行大田试验。结果表明,各处理土壤全氮含量和¹⁵N丰度差异极显著(P<0.01),并且在0~20 cm土层出现富集现象。各器官征调氮素能力随水氮投入加大极显著增强(P<0.01)。根系、茎秆、叶片器官的生物量随着吸氮量的增加极显著提高(P<0.01),而较高施氮量(F3)不利于果实器官生物量的积累。果树吸收的肥料氮量随水氮投入的加大逐渐增加,受水氮调控影响极显著(P<0.01),果树吸收的土壤氮量大于肥料氮量。W2F1的¹⁵N标记氮肥利用率和¹⁵N标记氮肥偏生产力最高,分别为38.36%和114.20 kg·kg^-1,W2F2的产量最高,为20 253 kg·hm^-2,但与W2F1差异不显著。表明水氮投入过多会引起茎秆和叶片器官徒长且不利于提高¹⁵N标记氮肥利用率。综上所述,灌水量5 400 m³·hm^-2、施氮量177 kg·hm^-2(W2F1)是兼顾经济效益与生态效应的可行水氮运筹模式。本研究结果为干旱区滴灌葡萄高产高效种植提供了参考。     

菌株Bacillus sp.CLb芽孢漆酶对染料、模拟染料废水脱色的研究

[目的]研究芽孢杆菌菌株CLb的芽孢漆酶在介体的互作下对不同类型的染料及模拟染料废水的脱色效果。[方法]制备芽孢粗酶液,在介体的互作下,测定具有漆酶活性的粗酶液对活性亮蓝、活性黑、靛红和结晶紫的脱色效果,筛选出对染料脱色有促进作用的漆酶介体,并且研究芽孢漆酶在不同pH条件下对染料和模拟染料废水脱色的影响。[结果]菌株CLb的芽孢漆酶在无介体参与下只能使活性亮蓝和结晶紫脱色。在介体乙酰丁香酮（ACE）的作用下,芽孢漆酶对4种染料的脱色率均超过70%。在pH 7.0条件下,芽孢漆酶浓度为44.74 U/L和介体ACE浓度为1 mmol/L时对模拟染料废水的脱色效果最好,6 h脱色率超过80%。在介体乙酰丁香酮存在,pH 7.0的条件下,菌株CLb的芽孢漆酶对合成染料脱色效率高于pH 9.0时的脱色率。[结论]在介体乙酰丁香酮的存在下,芽孢漆酶对染料和模拟染料废水均具有较好的脱色效果。     

Analysis of the structure of lignin-carbohydrate complexes by the specific13C tracer method

In the present study the specifically¹³C-enriched lignin precursors of biosynthesis (i.e., coniferin-[side chain–¹³C], coniferin-[side chain-–¹³C] and coniferin-[side chain-–¹³C]) were synthesized and administered exogeneously to ginkgo shoots (Ginkgo biloba L.) to obtain¹³C-enriched lignin-carbohydrate complexes (LCCs). The specifically¹³C-enriched LCCs were isolated from the newly formed xylem of ginkgo shoots administered with the¹³C-enriched precursors and degraded by enzymes. Lignin-rich fractions, so called enzyme-degraded LCCs (EDLCCs), were obtained. By determining their¹³C-NMR spectra, information related to the chemical structure of lignin building units and linkages between phenylpropane units of lignin and carbohydrates were obtained. It was found that these precursors were incorporated in natural lignin successfully. Three lignin-carbohydrates linkages (i.e., ether type, ester type, ketal type) were found at the C -position of the side chain of phenylpropane units in ginkgo LCC. No lignin-carbohydrate bond at the C- or C-position of the lignin side chain was observed in the¹³C-NMR spectra of the¹³C-enriched LCCs. This fact indicates that a specific¹³C tracer technique can be useful in NMR study of the chemical structure of LCCs.Part of this paper was presented at the 5th Pacific Polymer Conference, Kyongju, Korea, October 1997     

根际注射施肥对黄土高原苹果氮素吸收利用及产量和品质的影响

【目的】在西北黄土高原地区,春季干旱少雨和肥料利用率低限制着生产优质苹果。国外通常应用水肥一体化技术来克服水肥利用率低的问题,但由于其硬件设施要求高,投资大,短期内在我国难以推广。近年来我国采用的根际注射施肥可利用施肥枪将肥料溶液直接注入根际土壤中,施肥成本低且技术简单。本研究利用同位素15N示踪技术,研究根际注射施肥对苹果氮素吸收利用及产量品质的影响,可为黄土高原果园水肥高效利用提供依据。【方法】以9年生富士/M26/新疆野苹果为试验材料,利用15N尿素标记肥料去向,最后通过MAT-251质谱计测15N丰度,得出果树各器官和土壤的肥料利用率。同时利用叶绿素仪(SPAD-502)测定标记叶片的SPAD值,用浸以磷酸甘油溶液的海绵进行田间原位测定,得到土壤氨挥发的量,用静态箱—气相色谱法测定土壤的N2O逸失量。综合对比分析黄土高原传统环状开沟撒施肥与根际注射施肥对苹果吸收利用氮素、肥料氮在土壤中残留及果实产量和品质的影响。【结果】黄土高原苹果园根际注射施肥的优越性体现在:1)施肥后一个月内,果园土壤的气态氮素损失发生变化,根际注射施肥比传统环状开沟施肥的氨挥发总量低54.9%,同时N2O的排放通量低5.0%。2)根际注射施肥后,促进了肥料在土壤中的扩散范围,扩大了根系肥水吸收容积,叶片和果实吸收的肥料氮比例(Ndff%)在整个生长季始终处于较高水平。生长季末期,根际注射施肥的整株氮素当季吸收率为53.04%,比环状开沟施肥提高12.25个百分点,表明根际注射施肥有利于氮素更快地被吸收利用,显著提高苹果树的氮素当季利用率。3)生长季末,在0—60 cm土层内,根际注射施肥的土壤氮素残留率为36.55%,而环状开沟施肥为43.13%,前者显著低于后者。4)在整个生长季内,根际注射施肥处理下的树体新梢叶片内叶绿素含量(SPAD)值一直高于环状开沟施肥。根际注射施肥能提高苹果单株产量和单果重,其单果重和单株产量分别比环状开沟施肥处理提高了3.8%和19.7%。【结论】黄土高原地区推广的果树根际注射施肥技术可以有效提高苹果树体氮素的利用率,降低了土壤中的氮素残留。此外注射施肥的深度、注射量、密度和时间均可根据不同时期的养分需要随时调整,使水肥在土壤中均匀分布,达到节水节肥的目的。同时可避免传统施肥时挖坑作业对浅土层吸收根的损伤,降低劳动力成本。综合来看,根际注射施肥是提高黄土高原区旱地苹果树肥水利用率、产量和品质的有效方式之一。     

天然染料大黄对纳米TiO2改性丝素膜染色的研究

以溶胶-凝胶法制备纳米TiO2改性丝素复合膜,用原子力显微镜(AFM)观察,发现纳米TiO2均匀地分散在丝素中,粒子之间有明显的连续相,没有出现明显的相分离现象,其粒径约为80 nm。改性后的丝素膜,其上染率和色牢度均比纯丝素膜大大提高。     

同位素示踪法在磺酰脲类除草剂残留分析中的应用

除草剂的同位素残留分析技术日益受到人们的重视,并取得了长足的发展。本文综述了利用同位素示踪技术对4种磺酰脲类除草剂的残留分析进展。     

Effect of subcritical hydrophobicity in a sandy soil on water infiltration and mobile water content

Recent research shows that most soils are more or less water repellent. Already subcritical water repellency may cause incomplete soil wetting and preferential flow. Both processes potentially reduce the residence time of water and solutes in the vadose zone, resulting in an enhanced risk of groundwater contamination. The objective of the present paper is, therefore, to evaluate the impact of reduced soil wettability on the soil water infiltration rate and to investigate the tendency towards preferential flow with the analysis of the immobile water content in the infiltration zone. In november 2002, a field experiment was done in a coniferous forest, 30 km N of Hannover, Germany. Soil hydrophobicity was quantified by measuring the contact angles. The hydraulic conductivity of the podsolic sandy soil was measured depth‐dependent with a double‐ring tension infiltrometer in three soil horizons. To quantify possible preferential‐flow effects, a LiBr‐Tracer was added to the infiltrating water to evaluate the mobile water‐content fraction after infiltration. Additionally, infiltration rates of water were compared with infiltration rates of ethanol which were determined after water infiltration at the same locations. Results show that the actual water repellency of field‐moist soil was mainly subcritical (contact angle <90°). Water infiltration rates were reduced due to subcritical repellency by a factor of 3–170 compared with ethanol infiltration rates (exclusion of wetting effects). This spatially variable infiltration behavior was not clearly reflected neither by the small‐scale contact‐angle measurements nor by the analysis of the average immobile soil water content in the infiltration zone. We conclude that this specific infiltration behavior of water caused by small‐scale wettability effects may temporarily reduce the local connectivity of water‐flow pathways.