Effects of size,neighbors, and site condition on tree growth in a subtropical evergreen and deciduous broad‐leaved mixed forest,China

Successful growth of a tree is the result of combined effects of biotic and abiotic factors. It is important to understand how biotic and abiotic factors affect changes in forest structure and dynamics under environmental fluctuations. In this study, we explored the effects of initial size [diameter at breast height (DBH)], neighborhood competition, and site condition on tree growth, based on a 3‐year monitoring of tree growth rate in a permanent plot (120 × 80 m) of montane Fagus engleriana–Cyclobalanopsis multiervis mixed forest on Mt. Shennongjia, China. We measured DBH increments every 6 months from October 2011 to October 2014 by field‐made dendrometers and calculated the mean annual growth rate over the 3 years for each individual tree. We also measured and calculated twelve soil properties and five topographic variables for 384 grids of 5 × 5 m. We defined two distance‐dependent neighborhood competition indices with and without considerations of phylogenetic relatedness between trees and tested for significant differences in growth rates among functional groups. On average, trees in this mixed montane forest grew 0.07 cm year^?1 in DBH. Deciduous, canopy, and early‐successional species grew faster than evergreen, small‐statured, and late‐successional species, respectively. Growth rates increased with initial DBH, but were not significantly related to neighborhood competition and site condition for overall trees. Phylogenetic relatedness between trees did not influence the neighborhood competition. Different factors were found to influence tree growth rates of different functional groups: Initial DBH was the dominant factor for all tree groups; neighborhood competition within 5 m radius decreased growth rates of evergreen trees; and site condition tended to be more related to growth rates of fast‐growing trees (deciduous, canopy, pioneer, and early‐successional species) than the slow‐growing trees (evergreen, understory, and late‐successional species).     

四步法消除SYBR GreenⅠ实时定量RT-PCR中引物二聚体的影响

为建立一种新的SYBRgreenⅠ实时定量RT PCR方法 ,使之能够有效消除引物二聚体 (PDs)对实时定量结果的影响 .对RT PCR特异性扩增产物和PDs分别进行了凝胶电泳检测和熔解曲线分析 .依据PDs和扩增产物的熔解温度 (Tm)特点 ,在通用的三步法的延伸步骤之后 ,增加一个短暂的 (5s)恒温和荧光检测步骤 ,使这个步骤的温度高于PDs的Tm,但低于扩增产物的Tm,简称该法为四步法 .PDs的Tm 通常高于 72℃ ,但低于扩增产物的Tm .将四步法第四步的温度设置在高于PDs的Tm ,但低于扩增产物的Tm 时 ,四步法能够有效地消除PDs的影响 .对三步法和四步法SYBRgreenⅠ实时定量RT PCR进行了比较 ,发现三步法根本不能用于RNA的实时定量 ,而四步法能够实现包括低丰度RNA在内的RNA的定量 .选择Tm 值尽可能小的引物 ,使PDs与扩增产物Tm 值之间有足够的差距 ,将更有利于四步法的应用 ,并可成功地用于低丰度RNA的准确定量     

β-Galactosidase production by the psychrotolerant yeast Guehomyces pullulans 17-1 isolated from sea sediment in Antarctica and lactose hydrolysis

A psychrotolerant yeast Guehomyces pullulans 17-1 was isolated from sea sediment in Antarctica. It was found that it could yield both extracellular and cell-bound β-galactosidase. After optimization of the medium and cultivation conditions, it was found that the yeast strain produced over 17.2 U mL⁻¹ of β-galactosidase activity within 120 h at the flask level while the yeast strain produced over 25.3 U mL⁻¹ of β-galactosidase activity within 144 h during the 2-L fermentation. This is the highest β-galactosidase activity produced by the wild type yeast strains reported so far. However, the optimal pH and temperature for the crude β-galactosidase were 4.0 and 50 °C, respectively. Lactose could be converted into glucose and galactose and a large amount of reducing sugar could be released from milk under catalysis of the yeast culture.     

南宁地区唐氏综合征患者的细胞遗传学研究

为了探讨中国南宁地区唐氏综合征患者染色体核型分布及其特点, 对广西壮族自治区妇幼保健院1994年以来的500例疑似唐氏综合征(Down syndrome, DS)患者进行外周血染色体核型分析, 130例确诊为DS患者。其中, 单纯型21-三体为86.15%(112/130); 易位型为8.46%(11/130); 嵌合型为5.39%(7/130)。在单纯型21-三体中性别比为女∶男=1∶1.8; 93.08% 的唐氏综合征患儿由年轻母亲(<35岁)所生, 另有6.92% 由高龄产妇所生。结果表明, 南宁地区86% 以上唐氏综合征患者的染色体核型是单纯型21-三体, 男性唐氏综合征患儿明显高于女性患儿。     

中药渣蚓粪对玉米生长及土壤肥力特性的影响

采用盆栽试验,研究了中药渣蚓粪对玉米生长及土壤肥力的影响.结果表明: 随着蚓粪施用量的增加,玉米的株高、茎粗、叶面积、叶绿素含量均显著增加;生长60 d收获时,多数蚓粪处理的土壤容重显著降低;蚓粪处理的土壤pH显著高于对照和相应的化肥处理.蚓粪处理的土壤全氮、有机质含量也明显高于化肥处理,且随蚓粪施用量的增加,效果越趋显著.中药渣蚓粪可作为一种高效有机肥,其合理施用有助于改善土壤物理结构,缓解土壤的酸化进程,提高土壤有机质和氮素含量,有效促进作物生长.     

长双歧杆菌TTF菌株增强机体免疫活性研究

通过长双岐杆菌TTF活菌、菌体破碎物和发酵上清液3种处理物灌胃正常小鼠和免疫功能低下小鼠试验发现,长双歧杆菌TTF的3种受试物对环磷酰胺（Cy）造成的免疫功能低下小鼠模型（IDMM）3项免疫指标均有显著（P〈0．05）或极显著（P〈0．01）影响,且在本试验选取的3个剂量范围内基本呈量效关系。B．longum TTF的3种受试物对IDMM的非特异性免疫功能的影响普遍大于对小鼠的细胞免疫和体液免疫的影响;对正常小鼠免疫功能影响的水平低于其对IDMM各项免疫指标的影响,且无论活菌、菌体破碎物、发酵上清液均不会改变小鼠自身正常的免疫功能。急性毒性试验表明,B．longum,TTF3种处理物对健康小鼠无急性毒性。就3种处理物来讲,发酵上清液组的效果高于菌体破碎物和活菌。     

刈割强度对冷蒿可溶性碳水化合物的影响

通过对播种、移植于大小不同花盆的1年龄和多年龄冷蒿进行刈割实验。探讨冷蒿在不同刈割强度下可溶性碳水化合物含量和库的变化。结果表明。在不同的刈割强度下。冷蒿可溶性碳水化合物含量表现为：刈割1／4和刈割2／4比不进行刈割和刈割3／4高。可溶性碳水化合物库表现为：刈割1／4＞对照＞刈割2/4＞刈割3／4;刈割后在不同的资源与空间。冷蒿体内可溶性碳水化合物含量和可溶性碳水化合物库均表现为：大盆＞小盆＞移栽盆;在不同的刈割强度下生物量发生明显的变化,刈割1／4冷蒿生物量比对照增加,出现超补偿生长。别割3／4生物量降低。出现欠补偿生长。说明适度的干扰有利于冷蒿碳水化合物、生物量的积累;可利用资源、空间越多。可溶性碳水化合物含量越高。可溶性碳水化合物库的变化趋势与再生生长的趋势一致。说明可溶性碳水化合物库可以表征再生生长能力。     

太湖湖滨生态修复区大型底栖动物群落结构及梯度分布

2010—2011年对太湖贡湖湾湖滨带生态修复区滨岸挺水植物带(Ⅰ)、湾相沉水植物带(Ⅱ)和堰外开敞水体(Ⅲ)3个滨岸生境梯度带的水质状况和底栖动物群落特征进行了研究。结果表明:调查共发现底栖动物13科18种,其中仅出现于1个生境梯度带的物种7个;在其余的11个物种中,有5个种群的密度在生境梯度带间存在显著差异;比较发现,按底栖动物摄食功能类群的相对比例,刮食者相对丰度在带Ⅰ最高,收集者在带Ⅱ最高,滤食者在带Ⅲ最高,不同生境梯度带间底栖动物的摄食功能类群构成存在显著差异。对底栖动物相对丰度和水环境参数的冗余分析显示,环节动物和昆虫与DO、NO3--N和PO43--P浓度正相关,软体动物则与NO3--N和PO43--P负相关,一些腹足类对低DO耐受能力较强,与NH4+-N和COD正相关。修复区3个梯度带水动力条件、水质状况和底质类型的差异性对底栖动物的分布有重要影响,形成了生活习性、摄食特征等显著不同的3个底栖动物群落。     

生淀粉高浓度酒精发酵的研究

本研究利用国内常用的糖化酶制剂糖化生玉米面中的淀粉,同时接种酵母菌,在30℃下,探讨了玉米淀粉的高浓度酒精发酵工艺。选择到了一株产高浓度酒精酵母菌,H0菌株。发酵温度为30℃、pH4一s、加糖化酶量为每克原料300单位、酵母接种量3％(v／v)和原料加量为33．0％(w／v)时,这株酵母菌在70小时内可产生17．5％(v／v)的乙醇。如果原料加量为36．0％(w／v)时,该菌株在96小时内可以产生18．O％(v／v)的乙醇。在前一种加料情况下,成熟发酵醪中的pH为5、残还原糖为O．19％、残总糖为3．5“。在后一种加料情况下,成熟发酵醪中的pH为5、残还原糖为0．81％、残总糖为5．1％。