不同耕作措施对黄土高原旱地土壤呼吸的影响

在甘肃省定西市李家堡镇设置不同耕作措施试验,对春小麦、豌豆双序列轮作下的土壤呼吸及其对应时间的冠层温度、土壤水分进行了测定.结果表明：春小麦和豌豆在整个生育期内的土壤呼吸都表现出不同的变化趋势,春小麦地土壤呼吸在拔节前期、灌浆期和收后分别达到高峰期;豌豆地土壤呼吸在五叶期、吐丝期、开花结荚期和收后分别达到高峰期.免耕秸秆覆盖处理和传统耕作处理下春小麦地土壤呼吸日变化明显,免耕秸秆覆盖处理明显低于传统耕作处理;而豌豆地土壤呼吸日变化不明显.春小麦和豌豆冠层温度均与土壤呼吸呈显著线性相关,春小麦孕穗期相关性最高,灌浆期次之;豌豆开花结荚期相关性最高,分枝期次之.土壤含水量与土壤呼吸间存在极显著的凸型抛物线型相关,保护性耕作下的相关性都高于传统耕作,其中免耕秸秆覆盖处理的春小麦地和豌豆地土壤含水量与土壤呼吸的相关性在各层次土壤中均为最高,10～30 cm土壤含水量对春小麦地土壤呼吸的影响最大,5～10 cm土壤含水量对豌豆地土壤呼吸的影响最大.与传统耕作相比,免耕秸秆覆盖、免耕、传统耕作秸秆还田、传统耕作结合地膜覆盖、免耕结合地膜覆盖5种保护性耕作措施都能不同程度地降低土壤呼吸,其中免耕秸秆覆盖优势最明显.     

长期保护性耕作对黄土高原旱地土壤水分及作物叶水势的影响

通过长期定位试验研究了黄土高原西部旱农区,传统耕作方式和5种保护性耕作措施对豌豆-小麦(P→W)和小麦-豌豆(W→P)轮作序列的耕层土壤水分和作物叶水势的影响。结果表明,与传统耕作(T)处理相比,保护性耕作都能不同程度地提高0—30 cm土层土壤含水量,增幅为3.29%—28.67%,其中免耕+秸秆覆盖(NTS)处理的土壤含水量在整个生育期内均为最高。豌豆和春小麦在不同生育期,叶水势的日变化趋势大致相同,均为清晨6:00最高,然后随着时间的推移而下降,大约在12:00—14:00之间达到最低,随后逐渐回升。春小麦各处理在拔节期和抽穗期的叶水势相对较高,孕穗期和开花期次之,灌浆期最低;叶片相对含水量在拔节期和抽穗期最高,开花期次之,灌浆期最低。豌豆各处理的叶水势均在出苗期和孕蕾期达到了最大值,分枝和开花期结荚期次之,灌浆成熟期相对较低;叶片相对含水量均随生育期的进程而呈下降趋势。整个生育期春小麦和豌豆各处理10:00的叶水势与0—30 cm平均土壤含水量之间显著相关,当土壤水分含量较低时,春小麦和豌豆叶水势与耕层土壤含水量的相关性达极显著水平。与传统耕作(T)相比,免耕+秸秆覆盖(NTS)、免耕+地膜覆盖(NTP)、免耕(NT)、传统耕作+秸秆还田(TS)、地膜覆盖(TP)5种保护性耕作措施能不同程度的提高作物叶水势、叶片相对含水量和作物产量,其中免耕+秸秆覆盖(NTS)的优势最明显。     

不同耕作方式对陇中旱农区春小麦和豌豆根系空间分布及产量的影响

依托陇中旱农区长期的保护性耕作定位试验,对不同耕作方式下春小麦和豌豆根系空间分布特征及作物产量进行研究,以探索耕作措施影响作物产量的机制.结果表明: 随着生育期的推进,春小麦和豌豆的总根长、根表面积呈先增后减的趋势,开花期达到最大;春小麦根系苗期以0～10 cm最多,花期、成熟期10～30 cm最多;而豌豆根系苗期和成熟期均以0～10 cm最多,花期10～30 cm最多.免耕秸秆覆盖和免耕覆膜增加了根长和根表面积,春小麦和豌豆各生育时期的根长较传统耕作增加了35.9%～92.6%,根表面积增加了43.2%～162.4%.免耕秸秆覆盖和免耕覆膜优化了春小麦和豌豆根系分布,与传统耕作相比,增加了春小麦和豌豆苗期0～10 cm土层根长和根表面积分布比例,花期和成熟期深层次根系分布也显著增加,免耕秸秆覆盖在开花期30～80 cm土层根长和根表面积的分布比例分别比传统耕作提高了3.3%和9.7%.春小麦各生育期的总根长、根表面积与产量呈显著正相关,豌豆各生育期的总根长与豌豆产量呈极显著正相关.免耕秸秆覆盖和免耕覆膜较传统耕作春小麦和豌豆产量增加23.4%～38.7%,水分利用效率提高了13.7%～28.5%.在陇中旱农区,免耕秸秆覆盖和免耕覆膜可以增加作物根长和根表面积,优化了根系在土壤中的空间分布,增强作物根层吸收能力,从而提高作物产量和水分高效利用.     

不同保护性耕作措施对旱作农田土壤水分的影响

研究了黄土高原西部旱农区传统耕作措施和五种保护性耕作措施对土壤水分垂直分布、动态变化、作物耗水量、水分利用效率及作物产量的影响。结果表明,不同保护性耕作措施对表层0~10cm土壤水分含量影响较大,免耕秸秆覆盖(NTS)在作物播种期可以显著增加播种期表层土壤含水量。0~200cm土壤剖面贮水量年变化分春夏作物旺盛生长失墒期(5月中旬~7月中旬)、夏秋雨季增墒期(7月中旬~10月下旬)和冬春稳墒期(11月~翌年5月上旬)3个阶段。尽管不同保护性耕作措施对0~200cm剖面贮水量影响不大,但作物耗水量却存在显著差异。免耕秸秆覆盖在增加作物耗水量的同时也提高了作物产量以及水分利用效率。地膜覆盖在有些年份也有利于降水的高效利用和作物产量的提高,但与秸秆覆盖相比不利于土壤肥力的持续提高。而且,如果种植小麦,出苗前若一次性降水较多时地膜覆盖将造成严重板结,影响出苗,进而降低产量和水分利用效率。因此,在黄土高原西部旱农区实施免耕 秸秆覆盖的保护性耕作措施,既有利于作物对有限降水的高效利用,提高作物产量,也可以促进农业可持续发展。     

保护性耕作对陇中旱作农田水分特征的影响

陇中旱农区生产力水平低而不稳,而保护性耕作措施是农业可持续发展的重要途径.本研究依托2001年建立在陇中旱农区的长期不同耕作措施的定位试验,研究了不同耕作措施对土壤水分入渗、蒸发、作物产量和水分利用效率的影响.该试验共设6个处理,分别为传统耕作(T)、免耕秸秆覆盖(NTS)、免耕(NT)、传统耕作+秸秆翻入(TS)、传统耕作+覆膜(TP)、免耕覆膜(NTP),春小麦和豌豆年间轮作.结果表明:与T处理相比, NTS处理的小麦地和豌豆地的土壤容重显著降低,总孔隙度显著增加.保护性耕作措施降低了豌豆地0～5 cm土壤渗吸率,NTS处理渗吸率比T处理降低56.2%.保护性耕作提高了土壤饱和导水率,无论小麦地和豌豆地,NTS均比T处理显著提高了饱和导水率,增幅为52.8%～107.1%.保护性耕作显著降低了作物生育期棵间蒸发量,NTP、TP、NTS比T处理降低了14.4%～50.8%,并减弱了雨后土壤蒸发.保护性耕作提高了作物产量和水分利用效率,NTS、TP、NTP的产量比传统耕作提高了9.5%～62.8%,水分利用效率比传统耕作提高了0.4%～50.9%.因此,在陇中旱农区,保护性耕作措施可以提高水分利用效率,增加作物产量.     

保护地蔗田对土壤优先流与根系生物量及产量品质的影响

为探明保护性耕作对蔗田土壤及甘蔗生长的影响,该研究设置2种耕作方式(常规耕作、粉垄耕作)与2种施肥水平(减量施肥20%、常规施肥),并于甘蔗苗期后在甘蔗行间近根部覆盖豆科秸秆,以第二年宿根蔗为研究对象,采用染色示踪法测定秸秆覆盖下蔗田土壤优先流特征,同时测定分析甘蔗株高、茎围、地下根系生物量、产量及品质等重要农艺性状。结果表明:(1)粉垄耕作方式下蔗田土壤优先流发生速度快且活跃,添加秸秆覆盖降低了土壤优先流发生程度,增加了土壤水分在10～25 cm土层的横向运移能力,在一定程度上提高了土壤蓄水能力。(2)粉垄保护性耕作在秸秆覆盖下提高了甘蔗根系生物量和产量,秸秆覆盖下粉垄免耕宿根蔗根系生物量提高了8.97%～25.54%,并且减量施肥处理中秸秆覆盖宿根蔗伸长期地下根系生物量显著高于无秸秆覆盖,秸秆覆盖下甘蔗株高提高了4.2%～13.1%; 在减量施肥处理中,粉垄耕作添加秸秆覆盖甘蔗产量提高了16.27%,并且添加秸秆覆盖较常规施肥中无秸秆覆盖,产量提高了5.95%。(3)粉垄保护性耕作利于提高甘蔗品质,对比无秸秆覆盖处理,粉垄耕作下秸秆覆盖后显著提高了甘蔗蔗汁视纯度,并且宿根蔗纤维分、蔗汁锤度、转光度和蔗糖分均有提升。综上认为,免耕秸秆覆盖可作为粉垄红壤坡耕地蔗田保护性生产调控方式。     

保护性耕作对农田土壤水分和冬小麦产量的影响

保护性耕作是提高土壤蓄水保墒能力并增加作物产量的重要农艺措施之一.基于河南省长期定位试验2011-2016年数据,分析不同耕作措施(传统耕作、免耕和深松处理)对土壤水分、作物产量和水分利用效率的影响.结果表明: 2011-2016年免耕和深松耕作处理下冬小麦拔节期平均相对保墒率分别为7.3%和-0.68%,且免耕较传统耕作显著提高了冬小麦拔节期0～60 cm土壤贮水量.与传统耕作相比,免耕提高了冬小麦拔节期、扬花期、灌浆期和成熟期0～100 cm土壤平均含水量,而深松耕作并未明显提高冬小麦拔节期土壤平均含水量.此外,免耕较传统耕作能够显著提高冬小麦产量和水分利用效率,尤其在较干旱年份其增产效果更优.因此,免耕的蓄水保墒及增产效果在较干旱年份明显优于深松耕作.     

黑土肥沃耕层构建效应

东北黑土区粘重的耕地土壤,经多年不合理耕作后产生了较厚的“犁底层”,成为该地区农业生产的主要限制因子.本研究利用田间试验,分析了构建肥沃耕层对作物产量、土壤物理性质、土壤含水量和微生物数量的影响.结果表明：肥沃耕层构建后,土壤形成了一个深厚的耕层,作物产量增加.与常规耕作法相比,向20～35 cm土层施用秸秆和有机肥使土壤容重分别降低了9.88%和6.20%,总孔隙度分别增加了9.58%和6.02%,饱和导水率分别增加了167.99%和73.78%,表明肥沃耕层的构建能够有效地改善土壤的通气透水性,提高大气降水的入渗能力;向“犁底层”施用秸秆和有机肥处理0～100 cm土层土壤含水量和水分利用效率均显著高于常规耕作法,该处理玉米出苗率与0～35 cm土层土壤含水量之间呈显著正相关关系.肥沃耕层的构建由于增加了土壤中的有机碳源和透气性,从而增加了土壤中的微生物数量.     

黑土肥沃耕层构建效应

东北黑土区粘重的耕地土壤,经多年不合理耕作后产生了较厚的“犁底层”,成为该地区农业生产的主要限制因子.本研究利用田间试验,分析了构建肥沃耕层对作物产量、土壤物理性质、土壤含水量和微生物数量的影响.结果表明：肥沃耕层构建后,土壤形成了一个深厚的耕层,作物产量增加.与常规耕作法相比,向20～35 cm土层施用秸秆和有机肥使土壤容重分别降低了9.88%和6.20%,总孔隙度分别增加了9.58%和6.02%,饱和导水率分别增加了167.99%和73.78%,表明肥沃耕层的构建能够有效地改善土壤的通气透水性,提高大气降水的入渗能力;向“犁底层”施用秸秆和有机肥处理0～100 cm土层土壤含水量和水分利用效率均显著高于常规耕作法,该处理玉米出苗率与0～35 cm土层土壤含水量之间呈显著正相关关系.肥沃耕层的构建由于增加了土壤中的有机碳源和透气性,从而增加了土壤中的微生物数量.     

机械化保护性耕作条件下土壤质量的数值化评价

通过9年的长期田间定位试验研究了陕西关中平原中部冬小麦 夏玉米轮作条件下深松耕（ST）、旋耕（RT）、秸秆还（SR）、免耕（NTS）等保护性耕作措施及传统耕作（TT）对土壤理化性状和作物产量的影响,并采用主成分分析方法进行土壤质量的综合评价.结果表明：与传统耕作相比,保护性耕作模式提高了土壤肥力质量,改善了土壤物理环境条件;显著提高了土壤脲酶和碱性磷酸酶的活性;除秸秆覆盖免耕处理的玉米和小麦产量低于传统耕作外,其他保护性耕作措施均不同程度地提高了作物产量,其中小麦增产13%～28%,玉米增产3%～12%.与传统耕作相比,保护性耕作土壤质量指数提高了19.8%～44.0%.综合考虑经济效应和生态效益,隔年深松、秸秆粉碎联合旋耕作业以及秸秆覆盖联合深松作业不仅能增加作物产量还可改善土壤质量,可在研究区进行推广应用.     

Race and Racism in America and in Anthropology

Race in North America: Origin and Evolution of a Worldview . Audrey Smedley
Anthropology and Race . Eugenia Shanklin     

Degradation and conversion of somatostatin in normal and diabetic rats in vivo and in vitro

Plasma somatostatin-like immunoreactivity in the portal and jugular veins of streptozotocin diabetic rats was compared with that in normal control rats. In the diabetic group, somatostatin levels in the portal (p less than 0.05) and jugular (p less than 0.01) veins were both elevated compared with those in the control group. Moreover, the degree of elevation was greater in the jugular vein than in the portal vein. To further investigate the role of the liver in the clearance of somatostatin-28 in vivo, 2 micrograms of somatostatin-28 was administered as a bolus into the external jugular vein of intact and functionally hepatectomized rats. The mean half-time of somatostatin-28 was significantly longer in intact diabetic rats than in controls (p less than 0.05). The functional hepatectomy did not cause a significant difference in the half-time in diabetic rats but made it longer in control rats. These results suggest that the longer half-time of somatostatin-28 in diabetic rats in vivo is due to its slower hepatic clearance. The hepatic clearance of somatostatin-28 and somatostatin-14 was further studied in vitro using a recirculating liver perfusion method. The hepatic clearance of 1.2 nM of either somatostatin-28 or somatostatin-14 was significantly lower in diabetic rats than in controls (p less than 0.01). This indicates that elevated plasma somatostatin levels in diabetic rats are caused at least in part by decreased hepatic clearance of somatostatin.(ABSTRACT TRUNCATED AT 250 WORDS)     

Trajectories and Constraints in Brain Evolution in Primates and Cetaceans

A negative allometric relationship between body mass (BM) and brain size (BS) can be observed for many vertebrate groups. In the past decades, researchers have proposed several hypotheses to explain this finding, but none is definitive and some are possibly not mutually exclusive. Certain species diverge markedly (positively or negatively) from the mean of the ratio BM/BS expected for a particular taxonomic group. It is possible to define encephalization quotient (EQ) as the ratio between the actual BS and the expected brain size. Several cetacean species show higher EQs compared to all primates, except modern humans. The process that led to big brains in primates and cetaceans produced different trajectories, as shown by the organizational differences observed in every encephalic district (e.g., the cortex). However, these two groups both convergently developed complex cognitive abilities. The comparative study on the trajectories through which the encephalization process has independently evolved in primates and cetaceans allows a critical appraisal of the causes, the time and the mode of quantitative and qualitative development of the brain in our species and in the hominid evolutionary lineage.     

Variation in infectivity and aggressiveness in space and time in wild host-pathogen systems: causes and consequences

Variation in host resistance and in the ability of pathogens to infect and grow (i.e. pathogenicity) is important as it provides the raw material for antagonistic (co)evolution and therefore underlies risks of disease spread, disease evolution and host shifts. Moreover, the distribution of this variation in space and time may inform us about the mode of coevolutionary selection (arms race vs. fluctuating selection dynamics) and the relative roles of G × G interactions, gene flow, selection and genetic drift in shaping coevolutionary processes. Although variation in host resistance has recently been reviewed, little is known about overall patterns in the frequency and scale of variation in pathogenicity, particularly in natural systems. Using 48 studies from 30 distinct host–pathogen systems, this review demonstrates that variation in pathogenicity is ubiquitous across multiple spatial and temporal scales. Quantitative analysis of a subset of extensively studied plant–pathogen systems shows that the magnitude of within‐population variation in pathogenicity is large relative to among‐population variation and that the distribution of pathogenicity partly mirrors the distribution of host resistance. At least part of the variation in pathogenicity found at a given spatial scale is adaptive, as evidenced by studies that have examined local adaptation at scales ranging from single hosts through metapopulations to entire continents and – to a lesser extent – by comparisons of pathogenicity with neutral genetic variation. Together, these results support coevolutionary selection through fluctuating selection dynamics. We end by outlining several promising directions for future research.     

Aminoacylation in Sulfolobus acidocaldarius and in methanogenic and halophilic archaebacteria

Abstract Phenylalanyl-tRNA synthetase (PRS) from the sulphur-metabolizing thermoacidophilic archaebacterium Sulfolobus acidocaldarius has been purified 150-fold using different chromatographic steps. The enzyme has a M _r of 270 000 and exhibits considerable thermostability in a temperature range up to 90°C with optimal activity at 70°C. Conservation of antigenic determinants could not be detected by antibodies against various PRS of all primary kingdoms. As a further means to detect traits of phylogenetic relationship, the cross-species reactivity between PRS and tRNAs of organisms from the three branches of archaebacteria and from all primary kingdoms reveals the group character of all 3 branches of the archaebacterial domain, the sulphur-metabolizing, methanogenic and halophilic archaebacteria.     

Deoxynivalenol and nivalenol in wheat and by-products in Argentina

The deoxynivalenol and nivalenol contamination in wheat and by-products obtained through milling was analized by Trucksess method slightly modified in the proportion of acetonitrile—water (3:1). Only one sample of wheat showed deoxynivalenol contamination, 1,200μg/kg. No samples obtained in different stages of the milling were contaminated with deoxynivalenol or nivalenol. In the commercial wheat flours the levels found ranged between 400 and 800μg/kg, as follows: 400μ/kg, 5 samples; 800jug/kg, 1 sample.     

Obestatin and ghrelin in obese and in pregnant women

We identified, through qPCR, receptor mRNA for a number of gut peptides in female human omental fat: the incretins, GIP and GLP-1, the orexigenic peptides PYY-Y1 and -Y2 and ghrelin, and the anorexigenic peptide obestatin. Four cohorts of women were examined: lean controls (BMI<23), obese (BMI>41), obese diabetic and term pregnant women. Human fat expressed receptor mRNAs for all six peptides. Pregnant women expressed roughly three times as much orphan GPR-39 receptor, a proposed obestatin receptor, than other women and less than half as much of the ghrelin receptor (GHSR-1a). An immunoblot probed with a GPR-39 selective antibody yielded a single band corresponding to the correct molecular weight (52 kDa) for the proposed obestatin receptor. Fluorescent immunohistochemistry of human fat employing the same antibody indicated the receptor protein was localized to the adipocyte cell membrane. The concentration of obestatin circulating in blood was measured in the same cohort of women and was significantly lower in obese and obese diabetic women compared to control.