土壤抑制烟草黑根腐病的机制

 能抑制植物病害的土壤称为抑病土.抑病土在世界上分布广泛,已报道了多种植物土传病害可被土壤抑制.在烟草黑根病抑病机制的研究方面也有许多报道,本文根据这些作者及自己的研究资料加以综述.     

外源轻稀土对土壤微生物数量及pH的影响

在黄刚土和马肝土上进行 3年 6季的田间试验。在稻麦轮作制中每季施用稀土制剂 0 .0 0、1 8.75、3 7.50、75.0 0、3 75.0 0 kg/hm2 ,在油豆轮作制中每季施用稀土制剂 0 .0 0、1 5.0 0、3 0 .0 0、60 .0 0、3 0 0 .0 0 kg/hm2 。试验结束时 ,测定土壤微生物数量以及土壤的 p H状况。结果表明 :在油豆轮作制中 ,施用 1 5～ 3 0 kg/hm2的稀土制剂后土壤细菌、真菌数量及微生物总量明显增加 ,而放线菌数量在这一稀土用量范围内明显减少 ;在稻麦轮作制中亦有相近趋势     

pH对汞镉与土壤脲酶活性关系的影响

以土娄土为供试土壤 ,设置不同 p H及汞、镉浓度处理 ,研究 p H对汞镉与土壤脲酶活性关系的影响。结果表明 :在供试 p H范围内 ,脲酶活性在 p H5 .5～ 6 .0和 8.0～ 9.0时最大 ;汞镉加入几乎没有改变土壤脲酶最适p H;重金属生态毒性呈现 Hg>>Cd的规律性变化。统计分析表明 ,土壤脲酶活性、最大反应速度和反应速度常数均可在一定程度上表征土壤汞镉污染的程度 ;随重金属浓度增加 ,土壤脲酶 Km 基本不变 ,Vmax降低 ,表明土壤脲酶受汞镉作用机理主要为非竞争性抑制 ;在较宽 p H范围内 ,土壤严重污染的临界汞、镉浓度分别为 2 .0 98和 30 2 .83mg/ kg。     

不同pH值对DNA提取率的影响

[目的]探索pH值与DNA提取率的关系。[方法]以新鲜猪肝为研究材料,在常规DNA提取方法的基础上设置5个不同的pH值,分析不同pH值对DNA提取率的影响。[结果]OD值与pH值有一定的关系。pH值为7.4时,OD值最大,DNA提取率最高。pH值偏离此值越远,则DNA提取率越低。pH值对DNA提取率有一定的影响。用pH=7.4的缓冲液作提取液时,DNA提取率分别为pH值为7.2、7.6、7.8和8.0时的1.09、1.03、1.06和1.11倍。DNA提取的最适pH值为7.4。[结论]该研究对于提高DNA提取率具有一定的应用价值。     

液培条件下pH和镁锌硼对莴笋的营养效应研究

液培试验表明,镁、锌、硼对莴笋生物产量的正效应以Mg(100mg/L-200mg/L),Zn(20mg/L-50mg/L),B(10mg/L-20mg/L)为最显著,增量达30．8％－125．6％。在3个pH中,以pH6生物产量最高;3关於归中硼的增产幅度最大。不同pH条件下莴笋镁、锌、硼含量与施用水平呈显著或极在相关;氮、钾养分含量与生物量变化趋势一致,磷含量变化较小。高产莴笋植株N／P比为8．70－10．05;N／K比为0．66－0．86;K／P比为11．30－14．96。     

EM用于污水灌溉对小白菜产量和土壤肥力的影响

合理的灌溉指标和方法，是污水灌溉安全高效进行的主要保证。在污水灌溉中引入EM技术，以小白菜为研究对象、盆栽试验为手段，研究了在奶牛场废水灌溉条件下，不同灌水下限条件对作物生长和土壤的影响。结果表明，奶牛场废水灌溉不会导致小白菜减产，而且能够增加土壤的速效氮和速效磷，在污水中添加EM进行灌溉，对土壤养分增加的效果更为明显。试验结果还显示70％和80％W间持水量的灌溉下限对污水灌溉较为适宜。但长期灌溉奶牛场废水是否会发生氮、磷的淋溶，污染地下水，还需进一步的研究。     

溶液pH值对水稻幼苗Cd吸收的影响

采用含10mg/L Cd的营养液培养水稻幼苗,设置pH4.0至7.5的不同处理以研究溶液pH对幼苗Cd吸收的影响。结果表明:在pH5.0时,两个水稻品种茎的Cd含量和累积量达到最高;根的Cd含量和累积则随pH值上升而增加,至pH7.5时达最大值。这两种变化趋势都能用二次方程加以描述。此外,Cd胁迫使水稻的鲜重和干重显著降低而MDA和蛋白质含量显著升高。因此,在一定Cd浓度下,溶液不同pH对水稻根和茎吸收Cd影响也不同,而10mg/L Cd抑制了水稻幼苗的生长。     

安塞县农田土壤养分现状分析

【目的】分析地处西北内陆黄土高原腹地、具有典型丘陵沟壑特征的陕西省安塞县农田土壤pH值和养分的现状及其相关性,为黄土高原丘陵沟壑区提高土地生产力和培肥土壤提供理论依据。【方法】采集安塞县12个乡镇有代表性并能充分反映土壤特性的农田耕层(0～20 cm)土样4 231个,对其pH值及有机质、全氮、碱解氮和速效磷、钾含量进行测定,分析土壤pH值与各养分含量间的相关性。【结果】安塞县农田土壤pH值为8.16,偏碱性,变异程度为弱变异。土壤有机质、全氮含量分别为8.73和0.54 g/kg,碱解氮、速效磷、速效钾含量分别为31.11,8.79和100.68 mg/kg,其中只有速效钾的含量达到了中等肥力水平,其他养分含量均处于中等以下肥力水平;各养分含量均为中等变异。土壤pH值与有机质、碱解氮、速效钾含量呈显著或极显著负相关,有机质含量与全氮、碱解氮和速效磷含量呈显著或极显著正相关。【结论】安塞县农田土壤养分含量较低,土壤有机质含量和pH值影响着土壤速效养分的含量,今后应积极推广配方施肥技术,推进退耕还林还草工程,以提高土壤肥力水平。     

Effect of dietary folate level on organ weight,digesta pH,short-chain fatty acid concentration,and intestinal microbiota of weaned piglets

Folate is increasingly thought to promote gastrointestinal health and regulate the diversity of gut microbiota to alleviate weaning stress in piglets. The present study was conducted to investigate the effects of folate on organ weight, digesta pH, short-chain fatty acids (SCFAs) concentration, and intestinal microbiota in weaned piglets. A total of 28 piglets (6.73 ± 0.62 kg) were allocated to four dietary treatments consisting of a control group, 3, 9, and 18 mg/kg of folate supplementation in a 14-d feeding trial. The results showed that piglets fed with 9 and 18 mg/kg of folate supplementation had greater (P < 0.05) average liver and spleen weight than the control group. Folate supplementation (9 and 18 mg/kg) can significantly increase (P < 0.05) the stomach pH and tend (P < 0.10) to decrease the cecum pH. Folate treatment (9 and 18 mg/kg) had a positive effect on the metabolism of SCFAs in piglets, in particular, compared with the control group, and the content of acetic acid (AA) and valeric acid was markedly increased (P < 0.05) in the cecum and colon, respectively. Moreover, isobutyric acid, butyric acid, and isovaleric acid were tended (P < 0.10) to increase in the colon. Cecum contents samples were used to determine bacterial community diversity by 16S rRNA gene amplicon sequencing. At the genus level, in the cecum, there was a higher (P < 0.05) relative abundance of Lactobacillus reuteri, Lactobacillus salivarius, and Lactobacillus mucosae in the 9 mg/kg folate supplementation group. The functional pathways analysis predicted that folate may modify nutrient metabolism by changing the gut microbiota function of weaned piglets. Furthermore, the data showed that Lactobacillus was positively correlated with AA in the cecum. Overall, these findings suggested that folate treatment could increase the organ weight and the stomach pH of weaned piglets and had beneficial effects on gut health, which might be attributed to the alteration in intestinal microbiota induced by folate and the interaction of the intestinal microbiota with SCFAs.     

Evaluation of colorimetric pH strips for wild animal meat using image analysis

Colorimetric pH strips (MColorpHast™) are very convenient to use, but the decision of pH is based on an individual's color perception and is, therefore, subjective. We developed a pH calculation program for the image of coloring strips on CIE1976 (L*a*b* color space), which slightly underestimated human judgment as the color of pH darker. This image analysis and three individuals' judgments were used for evaluating the strip's features for various qualities of meat from wild animals, and the results were compared with the assessments based on potentiometric pH. In both methods, dipping the strips in distilled water just before use improved the regression coefficient compared with that mentioned in the manual. The image analysis showed higher correlation than human judgments but slightly underestimate pH by a maximum of 0.13 unit from the regression line of the potentiometric pH. In addition, the image analysis revealed meat pigment changed pH higher on the color scale in the lower meat pH region. The strips must be used according to the manual, but dipping is effective when the meat surface is dry, and keeping the strips from touching the meat drip is important in lower pH region because the pigment affects the color of pH.