Do cover crops change the lability of phosphorus in a clayey subtropical soil under different phosphate fertilizers?

Plants have developed different mechanisms to absorb and solubilize phosphorus (P) in the soil, especially in environments with low P availability. This study evaluated the effects of different winter cover crops on soil P availability in a clayey subtropical (Hapludox) soil receiving soluble P fertilizer and a rock phosphate applied to the summer crop, under no‐tillage. The experiment was carried out over 3 yrs (2009–2011) with five different cover crop species: common vetch, fodder radish, ryegrass, black oat, white clover and fallow as control. The soil was sampled after the third year of cover crop cultivation and analysed for inorganic and organic P forms according to the well‐established Hedley fractionation procedure. Phosphate fertilizers promoted accumulation of both labile and nonlabile P pools in soil in the near surface layer, especially under rock phosphate. Fertilizer applications were not able to change P fractions in deeper layers, emphasizing that the Brazilian clayey soils are a sink of P from fertilizer and its mobility is almost nil. Although the cover crops recycled a great amount of P in tissue, in a short‐term evaluation (3 yrs) they only changed the content of moderately labile P in soil, indicating that long‐term studies are needed for more conclusive results.     

大花君子兰叶绿体基因组及其特征

采用Illumina MiSeq测序平台对大花君子兰（Clivia miniata）叶片总DNA进行测序，通过组装获得了其叶绿体基因组（cpDNA）全长序列（158 114 bp）。对其cpDNA注释得到135个基因，包含87个蛋白编码基因、40个tRNA基因和8个rRNA基因。采用生物信息学方法对获得的cpDNA进行简单序列重复（SSR）分析和密码子偏好性分析。结果显示：①大花君子兰cpDNA中共有61个SSR位点，其中单核苷酸、二核苷酸、三核苷酸、四核苷酸、五核苷酸和六核苷酸重复数分别为38、9、2、8、3和1个，多数SSR分布在基因间隔区；②大花君子兰cpDNA密码子偏爱以A或U（T）结尾，亮氨酸使用频率最高，半胱氨酸使用频率最低。基于24种植物的cpDNA全长和23种植物的叶绿体ycf2基因序列进行系统发育分析，结果显示大花君子兰与石蒜科植物在同一分支，显示最近的亲缘关系，支持大花君子兰属于石蒜科。基于叶绿体ycf2的系统发育分析结果与基于cpDNA全长的系统发育分析研究结果大部分相同，支持ycf2基因可以代替cpDNA全长用于植物系统发育分析。     

Oxygen isotope ratios of plant available phosphate in lowland tropical forest soils

Phosphorus (P) cycles rapidly in lowland tropical forest soils, but the process have been proven difficult to quantify. Recently it was demonstrated that valuable data on soil P transformations can be derived from the natural abundance of stable oxygen isotopes in phosphate (δ¹⁸O_P). Here, we measured the δ¹⁸O_P of soils that had received long-term nutrient additions (P, nitrogen, and potassium) or litter manipulations in lowland tropical forest in Panama and performed controlled incubations of fresh soils amended with a single pulse of P. To detect whether δ¹⁸O_P values measured in the incubations apply also for soils in the field, we examined the δ¹⁸O_P values after rewetting dry soils. In the incubations, resin-P δ¹⁸O_P values converged to ∼3.5‰ above the expected isotopic equilibrium with soil water. This contrasts with extra-tropical soils in which the δ¹⁸O_P of resin-P matches the expected equilibrium with soil water. Identical above-equilibrium resin-P δ¹⁸O_P values were also found in field soils that did not receive P additions or extra litter. We suggest that the 3.5‰ above-equilibrium δ¹⁸O_P values reflect a steady state between microbial uptake of phosphate (which enriches the remaining phosphate with the heavier isotopologues) and the release of isotopically equilibrated cell internal phosphate back to the soil. We also found that soil nutrient status affected the microbial turnover rate because in soils that had received chronic P addition, the original δ¹⁸O_P signature of the fertilizer was preserved for at least eight weeks, indicating that the off-equilibrium δ¹⁸O_P values produced during microbial phosphate turnover was not imprinted in these soils. Overall, our results demonstrate that ongoing microbial turnover of phosphate mediates its biological availability in lowland tropical soils.     

氨氮胁迫对四鼻须鲤鱼肝脏GST酶活力的影响

实验采用生态毒理学方法,以NH4Cl为实验药物,设置0、50、150和250mg/L实验浓度。通过对野生和养殖群体的四鼻须鲤鱼氨氮对肝脏谷胱甘肽巯基转移酶（GST）活力的影响,比较两个群体抗氨氮能力。结果表明：在相同的氨氮浓度和胁迫时间下,四鼻须鲤鱼养殖群体GST酶活力的变化趋势与野生群体大致相同。除250mg/L浓度组在胁迫5d和10d时,野生群体酶活性略低于养殖群体外,在其余时间点的野生群体酶活性均高于养殖群体,而且,在高浓度氨氮胁迫下,野生群体肝脏的GST酶活性达到峰值的时间比养殖群体更短,显示出较强的抗氨氮能力。     

苦瓜对8种蔬菜的化感作用

以8种海南主要栽培的蔬菜为受体,采用室内生测法研究苦瓜(Momordica charantiaL.)茎叶水浸提液对其化感作用。结果表明:苦瓜茎叶水浸提液对8种受体植物的种子萌发和幼苗生长均有一定的化感效应,且化感作用方式和强度在受体间及指标间存在显著差异;化感作用综合效应的平均值大小顺序为:辣椒黄瓜豇豆菜豆萝卜樱桃番茄胡萝卜番茄。试验结果为建立合理的栽培制度提供了理论和试验依据。     

论卓越人才教育培养计划与素质教育的契合

卓越人才教育培养计划是我国高等教育现有条件下的素质教育,它立足专业开展素质教育,让素质教育通过具体的培养标准渗透到专业教育的各门课程和教学环节之中,是对素质教育内容和形式的拓展和创新。厘清卓越人才培养模式改革的深刻内涵,全面贯彻素质教育思想,使卓越人才培养与素质教育有效契合,是实施卓越人才教育培养计划的关键所在。     

甘蓝型油菜耐低温生长生理生化响应机制

为提高甘蓝型油菜耐寒育种过程中的筛选效率，研究甘蓝型油菜耐低温机理，以8个不同抗寒性的甘蓝型油菜为材料，对低温条件下各材料的生物量、叶绿素、脯氨酸和相对电导率进行测定，发现在室外平均气温2.75℃时，抗性材料的生物量、叶绿素和脯氨酸的累积量都显著高于敏感材料，相对电导率没有显著差异；当平均气温7.52℃回升至12.39℃，抗性材料和敏感材料生物量的累积量无显著差异；在恒定低温10℃/4℃处理下抗性材料和敏感材料在处理前3周生物量均持续累积，但从第4周开始敏感材料新叶出现白斑，生物量减少，抗性材料老叶出现白斑，生物量维持不变。结果表明，耐低温材料在低温条件下叶绿素含量受到的影响较小，脯氨酸的积累量持续上升，具有较强的快速适应能力，在低温下具有显著的持续生长优势。     

应用Excel软件分析敌敌畏农药对两广二号家蚕的安全间隔期

应用Excel软件中的曲线方程分析判断敌敌畏农药对两广二号家蚕的安全间隔期。结果表明：敌敌畏1000倍液的安全间隔期是6d多，其数学模型为幂函数曲线方：y=88．0653x-1834本方法克服以往家蚕的农药安全期无数学模型可循或使用的BASIC方法陈旧繁杂的缺点，也避免英文统计软件SPSS难以在农村普及的不足，是一种计...     

科技英语疑问句的信息功能探析

句子的功能所实现的交际任务是传递信息。根据话语信息传递和语言交际功能理论原则,通过甄选科技英语相关例证作为分析语料,从英语的科技文体视角探析了疑问句在科技英语信息推进中的五大作用,同时指出了解这些相关作用的必要性。