不同品种空心菜对重污染土壤砷的吸收累积及其亚细胞分布

采用水泥池小区试验研究了土壤As污染(66.4 mg·kg-1)胁迫对19种空心菜生长、As累积以及As的亚细胞分布的影响。结果表明,各品种空心菜均能生长,但不同品种空心菜生物量及As累积量存在显著差异(P0.05),地上部As含量范围为0.73~191.12 mg·kg-1,均超出食品中污染限量的标准(0.5 mg·kg-1)。台湾白骨柳叶空心菜、泰国白梗柳叶空心菜、油青空心菜3个品种为相对低累积品种;台湾大叶白骨空心菜、菜农D-95空心菜、港种青绿梗叶空心菜、泰国竹叶空心菜4个品种为相对高累积品种。19个品种空心菜亚细胞中固持As含量大小顺序为胞质(49.06%~77.44%)细胞器(19.90%~46.82%)细胞壁(2.22%~16.73%)。     

长期施用畜禽养殖废弃物下潮土重金属的累积特征

通过田间试验研究了畜禽养殖废弃物长期施用(2001—2013年)对重金属(Cr、Cu、Zn、Pb、Cd、As)在潮土中累积、形态转化及迁移行为的影响。试验设置畜禽养殖废弃物(猪粪,OM)和化肥氮磷钾(NPK)两个处理,每处理设置3个重复。结果显示,畜禽养殖废弃物的长期施用造成Cu、Zn在OM处理土壤中的含量明显高于NPK处理,并主要累积于耕层土壤(0~20 cm),但总体含量(Cu:38.71 mg/kg;Zn:83.26 mg/kg)较低,对农田生态安全的影响较小。形态分析结果显示,OM处理土壤中DTPA络合态、弱酸结合态和铁锰结合态Cu、Zn、As的含量均显著高于NPK处理,但不同形态Cr、Pb、Cd在两种处理土壤中的差异相对较小。其中,Cr主要以非提取态的形式存在(Cr95%)。外源性Cu易累积于非提取态(52%),而Zn则以弱酸溶解态(40%)和铁锰结合态(60%)为主。畜禽养殖废弃物的农田施用不仅是土壤重金属的重要来源,也是土壤重金属活性提高的重要原因,并造成部分重金属在剖面土壤中发生明显迁移行为,累积于更深层土壤中。     

潮褐土上蔬菜产量和土壤各形态磷变化对长期过量施磷的响应

【目的】研究长期连续过量施用磷肥下蔬菜的产量响应、磷肥去向及土壤各形态磷库的动态变化。 【方法】在太行山山前平原典型潮褐土上,连续进行11年21茬露地蔬菜的长期定位肥料试验,P₂O₅年施用量设0 (P0)、360 (P1)、720 (P2)、1080 (P3)、1440 (P4) kg/hm2共5个处理,分别测定每茬蔬菜产量及各年土壤不同形态磷素含量。 【结果】与不施磷肥处理比较,单季P₂O₅用量180、360、540、720 kg/hm2均显著增加大白菜、菜豆产量,不同磷肥用量间蔬菜产量均无显著差异。P₂O₅年用量为360、720、1080、1440 kg/hm2,土壤年盈余磷为41.2～478.7 kg/hm2,积累率为26.2%～76.1%。与基础土比较,随着磷肥用量的增加,土壤有效磷、全磷、无机磷总量及无机磷中的Ca₂-P、Ca₈-P、Al-P、Fe-P含量均呈显著增加趋势,无机磷中的O-P、Ca₁₀-P含量无显著变化。P₂O₅年用量为720、1080、1440 kg/hm2处理土壤的有效磷年均增加量为2.3、4.2、5.0 mg/kg;土壤有效磷增加量与磷盈余量呈显著直线正相关关系,土壤磷素每盈余100 kg/hm2,有效磷、Ca₂-P、Ca₈-P、Al-P、Fe-P 含量分别增加1.13、2.41、15.27、4.14、1.37 mg/kg。随着土壤磷盈余量和施肥年限的增加,有效磷占全磷比重、Ca₂-P、Ca₈-P、Al-P占无机磷比重逐渐增加。 【结论】施用磷肥显著增加大白菜和菜豆产量,过量施用磷肥蔬菜产量无显著变化;土壤磷素处于盈余状态下,随着磷肥用量的增加或种植年限的增加,土壤积累磷的有效性随之增加。基于蔬菜对磷肥产量响应和土壤磷素收支表观平衡状况,露地大白菜P₂O₅推荐用量180 kg/hm2,菜豆270 kg/hm2。     

华南花岗岩风化土体粒度成分的分形特征

根据花岗岩风化土体机械分析数据计算不同层位风化土体的粒度分维值,结果表明,华南花岗岩风化土体粒度分布表现出良好的分形特征,整个风化壳剖面自上而下粒度分维值逐渐在减小,平均值约为2.74.分维值是定量表征土体粒度分布特征的有效参数,其值大小反映了风化壳的风化强弱.     

姬松茸子实体多糖分离纯化研究

采用分级醇沉和凝胶过滤法(Sepharose 6 FastFlow,Sephacryl S-300凝胶柱)从姬松茸子实体热水浸提多糖中分离出三个均一多糖组分,分别命名为ABM-Ⅰ、ABM-Ⅱ和ABM-Ⅲ,理化性质研究表明,三个组分的分子量分别为>2.0×106、1.4×106和3.8×105,旋光度分别为+62.5、+44.3和+5.5。通过完全酸水解和光谱法初步研究了组分ABM-Ⅰ的结构,结果表明ABM-Ⅰ的主链为α-(1→6)-D-吡喃型葡聚糖。     

关于环Zn上RSA型公钥密码体制的小解密指数d攻击

讨论了对环Zn上的RSA型公钥密码体制及Zn上广义圆锥曲线上的RSA型公钥密码体制的小解密指数d的Wiener的连分数攻击,指出了某些研究成果中的错误.     

一类负极值指数Pickands型估计量的渐近展开及平滑参数的最优选取

在二阶正规变化条件下,研究了一类负极值指数Picands型估计量的渐近展式.并在均方误差意义下,讨论了平滑参数的最优选择.     

Postoperative oxygenation in healthy dogs following mechanical ventilation with fractions of inspired oxygen of 0.4 or >0.9

ObjectiveTo evaluate arterial oxygenation during the first 4 postoperative hours in dogs administered different fractions of inspired oxygen (FiO₂) during general anesthesia with mechanical ventilation.Study designProspective, randomized clinical trial.AnimalsA total of 20 healthy female dogs, weighing >15 kg and body condition scores 3–7/9, admitted for ovariohysterectomy.MethodsDogs were randomized to breathe an FiO₂ >0.9 or 0.4 during isoflurane anesthesia with intermittent positive pressure ventilation. The intraoperative PaO₂:FiO₂ ratio was recorded during closure of the linea alba. Arterial blood was obtained 5, 60 and 240 minutes after extubation for measurement of PaO₂ and PaCO₂ (FiO₂ = 0.21). Demographic characteristics, duration of anesthesia, PaO₂:FiO₂ ratio and anesthetic agents were compared between groups with Wilcoxon tests. The postoperative PaO₂, PaCO₂, rectal temperature, a visual sedation score and events of hypoxemia (PaO₂ < 80 mmHg) were compared between groups with mixed-effects models or generalized linear mixed models.ResultsGroups were indistinguishable by demographic characteristics, duration of anesthesia, anesthetic agents administered and intraoperative PaO₂:FiO₂ ratio (all p > 0.08). Postoperative PaO₂, PaCO₂, rectal temperature or sedation score were not different between groups (all p > 0.07). During the first 4 postoperative hours, hypoxemia occurred in three and seven dogs that breathed FiO₂ >0.9 or 0.4 during anesthesia, respectively (p = 0.04).Conclusions and clinical relevanceThe results identified no advantage to decreasing FiO₂ to 0.4 during anesthesia with mechanical ventilation with respect to postoperative oxygenation. Moreover, the incidence of hypoxemia in the first 4 hours after anesthesia was higher in these dogs than in dogs breathing FiO₂ >0.9.     

Effect of different starch sources in a raw meat-based diet on fecal microbiome in dogs housed in a shelter

A dietary intervention study was assessed to determine if different sources of starch in homemade diets could significantly modify fecal microbiome of dogs. Twenty-seven adult dogs were enrolled and fed a diet based on a mixture of rice and pasta with fresh raw meat (CD). After 90 d, 8 dogs continued to receive CD diet, 10 dogs received a diet made of a raw meat and a complementary food with rice as the main source of starch (B1), and 9 dogs were fed a diet with the same raw meat and a complementary food with potato as the main source of starch (B2). Samples of feces were collected from each dog in the mornings at the beginning of the study and after 15 d and analyzed for pH, ammonia N (N–NH₃) and total N, short chain fatty acids (SCFA) and lactic acid. Relative abundance of fecal microbiota was assessed by sequencing and annotating the V3–V4 regions of the 16S rRNA. Total starch intake was similar between diets but differed in the in vitro rate digestion and in the resistant starch, which was higher in B2 than in B1 and CD diets. Dogs fed B2 diet showed lower (P < 0.05) N–NH₃ and pH but higher (P < 0.05) molar proportion of lactic acid. Linear discriminant analysis of the genera relative abundances indicated a significant (P < 0.01) increase of SMB53 genus at the end of the study in B1 diet and of Megamonas genus in B1 and B2 diets in comparison to CD diet. These results suggest that changes of starch source in a raw meat-based diet have limited effects on fecal microbiome in healthy dogs, but underline a high variability of microbiota among dogs.     

Leaching requirement for soil salinity control: Steady-state versus transient models

Water scarcity and increased frequency of drought conditions, resulting from erratic weather attributable to climatic change or alterations in historical weather patterns, have caused greater scrutiny of irrigated agriculture's demand on water resources. The traditional guidelines for the calculation of the crop-specific leaching requirement (LR) of irrigated soils have fallen under the microscope of scrutiny and criticism because the commonly used traditional method is believed to erroneously estimate LR due to its assumption of steady-state flow and disregard for processes such as salt precipitation and preferential flow. An over-estimation of the LR would result in the application of excessive amounts of irrigation water and increased salt loads in drainage systems, which can detrimentally impact the environment and reduce water supplies. The objectives of this study are (i) to evaluate the appropriateness of the traditional steady-state method for estimating LR in comparison to the transient method and (ii) to discuss the implications these findings could have on irrigation guidelines and recommendations, particularly with respect to California's Imperial Valley. Steady-state models for calculating LR including the traditional model, which is an extension of the original U.S. Salinity Laboratory LR model, WATSUIT model, and water-production-function model were compared to transient models including TETrans and UNSATCHEM. The calculated LR was lower when determined using a transient approach than when using a steady-state approach. Transient conditions and the influence of preferential flow did not have as significant an effect on lowering the LR as salt precipitation for a representative study of the Imperial Valley using Colorado River water (EC = 1.23 dS/m) for irrigation. A valley-wide LR of 0.08 for a crop rotation of alfalfa/alfalfa/alfalfa/alfalfa/wheat/lettuce, as calculated by both WATSUIT and UNSATCHEM, was concluded to be the most reasonable estimate for the entire Imperial Valley as compared to a LR of 0.13 by the commonly used traditional method. The reduced LR for the Imperial Valley would result in a diminished drainage volume of approximately 1.23 × 10⁸ m³ (i.e., 100,000 ac-ft). The most significant conclusion derived from the comparison is that the use of the traditional steady-state model for estimating LR needs to be reevaluated.