北京山区典型植被土壤水分对次降雨的响应

为了揭示北京山区不同植被类型土壤水分对不同强度降雨的响应过程,选取北京山区内侧柏、荆条灌丛、荒草地为研究对象,基于2022年6—10月降雨和土壤水分的连续观测数据,分析土壤水分对不同降雨事件的响应特征。结果表明：(1)观测期内研究区降雨事件主要由小雨构成,小雨事件的总降雨量占总降雨量的14.78%,小雨事件对土壤水分的响应深度可达到40—60 cm土层;中雨、大雨、暴雨事件的总降雨量占总降雨量的85.52%,中雨、大雨、暴雨事件对土壤水分的响应深度均可达到60—80 cm土层;大降雨事件对土壤水分的补给作用更明显,降雨量越大,降雨能补给的土层深度越深,土壤水分补给效果越好。(2)三种植被平均土壤水分补给速率大小依次为荒草地>侧柏>荆条灌丛,说明降雨对荒草地的补给效果最好;土层活跃程度对植被土壤水分有影响,土层越活跃,土壤水分波动越大,三种植被平均土壤水分变异系数大小依次为荒草地>荆条灌丛>侧柏,而三种植被平均土壤储水量大小则依次为侧柏>荒草地>荆条灌丛,说明侧柏的土壤水分最为稳定。(3)荒草地、荆条灌丛剖面上各层土壤水分逐渐减少,侧柏则增加,说明土壤...     

黄土丘陵区坡耕地与撂荒地土壤水分对降雨的响应特征

为了揭示黄土丘陵区不同土地覆被方式下土壤含水量对不同强度降雨的响应过程,选取山西省冯家沟小流域农耕地和撂荒地为研究对象,基于2019年4—10月降雨和土壤含水量以小时为单位的观测数据,分析了土壤含水量对不同强度降雨的响应规律。结果表明:(1)小雨、中雨、大雨和暴雨对土层的影响深度分别为20、20、60 cm和60 cm,研究区降雨最主要的形式—小雨对土壤水分的补给作用较小。(2)各强度降雨过程中,除0—10 cm土层外,农耕地土壤含水量均大于撂荒地,且大雨条件下农耕地各土层土壤含水量变化较显著,而撂荒地仅0—10 cm和10—20 cm土层土壤含水量有所增加。(3)不同土层土壤含水量对降雨的响应不同,表层响应相对明显而深层相对减弱;农耕地土壤平均含水量最大值出现在50—60 cm土层,而撂荒地出现在30—40 cm土层。(4)本地区农耕地土壤含水量高于撂荒地,表明在该地区适当的作物种植有较好的储存土壤水分的作用。本研究的结果对地区水资源的高效利用和水土流失防控提供了一定的科学依据。     

贵州中部喀斯特山地不同植被生态系统细根生态特征及养分储量

为了解喀斯特生态系统退化过程中树木细根生物量和土壤养分的变化,选择贵州中部喀斯特山地乔木林、灌木林和灌草丛3种植被生态系统,比较分析不同深度(0～5 cm、5～10 cm和10～15 cm)土壤细根数量及其养分情况.结果表明:树木细根主要分布在0～10 cm土层,并随土层加深而减少.在0～10 cm土层中,乔木林、灌木林和灌草丛的活细根生物量分别占0～15 cm总细根生物量的42.78%、56.75%和53.38%,总活细根生物量的83.36%、86.91%和93.79%.不同植被下优势种植物细根生物量存在差异.0～5 cm土层乔木林活细根氮素和磷素储量均显著高于灌草丛和灌木林(P0.05),但灌木林和灌草丛间没有差异;5～10 cm土层乔木林活细根氮和磷储量显著高于灌草丛和灌木林(P0.05),灌木林下又显著高于灌草丛下(P0.05).0～10 cm土层的活细根生物量与植株地上部分生物量呈正相关,植物叶片氮、磷养分含量与细根比根长呈显著的负相关,说明细根的养分储量对地上生物量的建成和生态系统功能的发挥具有重要作用.     

黄土高原不同演替阶段草地植被细根垂直分布特征与土壤环境的关系

研究了黄土区不同演替阶段草地植被细根垂直分布特征与土壤环境的关系,结果表明不同演替阶段草地植被细根生物量、根长密度、表面积、直径和比根长均具有明显的垂直分布特征。细根生物量、根长密度和细根表面积一般随土层加深而逐渐减少,且集中分布于0-40cm土层;随着演替的进行,除20a弃耕地外,0—80cm土层细根生物量、根长密度和细根表面积逐渐增加;除25a弃耕地外,细根直径随演替进行逐渐减小。0～100cm土层土壤含水量随演替进行而增加,不同演替阶段深层土壤水分较表层稳定。土壤容重的变化趋势为9〈4〈15〈20〈25a弃耕地,根系对表层土壤水分和容重的影响较大,而对深层土壤水分与容重影响较少。不同演替阶段细根各参数和土壤水分、容重差异均达到显著水平。各弃耕地细根参数之间,细根参数和土壤环境因子之间存在不同程度的相关关系,土壤含水量在草本植被的不同演替阶段均是影响其细根垂直分布的关键因素。土壤容重在演替早期对草本植被根系的影响较小,随着演替进行其影响作用进一步增强。     

科尔沁沙地人工小叶锦鸡儿植被水分入渗动态研究

通过对科尔沁沙地不同年龄人工小叶锦鸡儿固沙植被降雨入渗的研究 ,阐明植被对沙地水分入渗的影响。结果表明 ,在降雨量 4 3 4mm ,降雨强度 3 9mm·h-1时 ,降雨后 12 0h内流动沙丘和 5年生人工小叶锦鸡儿植被的水分入渗深度分别为 180cm和 15 0cm ,15年生人工小叶锦鸡儿植被降雨入渗深度为 10 0cm。流动沙丘降雨后土壤水分变化剧烈 ;有植被沙地降雨后土壤水分变化平缓 ,水分下渗浅 .随着植被年龄的增加 ,浅层土壤截留降雨能力不断加强 ,最终形成不透水土层。降雨后短期内流动沙丘浅层土壤中含水量高 ,后期有植被沙丘深层土壤含水量高     

金沙江干热河谷人工植被土壤水环境

金沙江干热河谷异常干热的气候特点,普遍存在水分亏缺问题,人工植被土壤水环境问题比其它干旱、半干旱地区更加突出．在干热河谷典型地段——元谋的试验观测表明,现有的乔木林明显表现出“土壤干化”的特点,土壤水分持续长时间亏缺,雨季结束之后的11月份。2m土层内的土壤含水量只有15％(相当于田间持水量的35％)左右,之后持续下降,直到5月份达到最低点(9％左右),几乎接近林木的凋萎湿度(元谋表蚀燥红壤的凋萎湿度为9．O％)．由此而导致林木生长缓慢．车桑子(Radonaea wiscosa)灌木林同层土壤含水率相对比乔木林高42．68％,自然草坡的土壤水分明显优于乔木和灌木林,分别比乔木林和灌木林高34．36％和22．22％．这种人工乔木林的“土壤干化”问题在干热河谷地区的植被恢复中还没有引起重视,将极大地制约人工植被的可持续发展．     

覆被对桔园旱季土壤水分变化和利用的影响

稻草覆盖和自然覆被是解决红壤丘陵区季节性干旱的有效措施.2005～2006年在桃源农业生态试验站进行了稻草覆盖和自然覆被对桔园降雨入渗、土壤蒸发、土壤水分调控和利用结构影响的研究,结果表明:稻草覆盖和自然覆被更有利于雨水的储存和向深层入渗,雨后48h分别比裸地土壤储水增量多3.33mm和1.33mm,降雨入渗深度分别为40cm和80cm.此外,稻草覆盖和自然覆被分别抑制了69.10%和36.53%的土壤蒸发,其蒸发抑制作用在午间高温时段表现尤为明显,使得更多的水分以植物蒸腾(稻草覆盖15.71%、自然覆被7.30%)和土壤蓄留的方式支出,并且分别降低了20.55mm(稻草覆盖)和14.33mm(自然覆被)的水分支出.覆被下土壤水分结构发生明显改变,0～20cm土层受外界条件影响较大,土壤水分变异系数较大,自然覆被由于覆盖的植被消耗表层水分,水分亏缺较大,平均含水量为稻草覆盖>裸地>自然覆被;20～80cm土壤水分变异减小,平均含水量稻草覆盖>自然覆被>裸地;120～160cm深土层中,自然覆被下土壤水分得不到补给,变异系数增大,稻草覆盖和裸地水分变化稳定,平均含水量稻草覆盖>裸地>自然覆被.     

三峡库区典型茶园土壤水分对不同降雨模式的响应

土壤水分是坡面产流和生物地球化学过程的关键控制因素。降水事件可以通过引起土壤剖面不同深度的土壤水分响应,从而影响流域中的径流路径、产流机制和土壤侵蚀过程等。基于三峡库区典型分布的茶园为对象,通过长期定点、高频的气象和水分数据观测,研究不同降雨模式下茶园不同土层深度(0—10、10—20、20—30、30—40cm)土壤水分的时空变化特征,分析茶园不同深度土壤在雨季的水分动态变化规律和对不同降雨模式的响应特征。结果表明：(1)研究区内的降雨和土壤水分含量均表现出明显的季节性特征。降雨在7月达到最大值,土壤水分含量则在8月达到峰值。表明降雨是影响土壤水分含量变化的重要因子,土壤水分对降雨有着明显的响应过程。(2)在相同降雨条件下,土壤含水量具有明显的垂直梯度变化。随着土层深度的增加,土壤水分对降雨的响应逐渐呈现出滞后现象。表层土壤(0—20cm)对降雨的响应较为迅速且幅度更加明显,深层土壤(30—40cm)水分含量变化相对稳定,并且对降雨的响应时间更加滞缓。随着土层深度的增加,土壤水分含量的变化幅度逐渐趋于平稳。(3)土壤水分含量对不同的降雨模式表现出显著差异。在较大雨强条件下,土壤水分变...     

水蚀风蚀交错区典型植被土壤水分消耗和补充深度对比研究

研究了黄土高原水蚀风蚀交错区六道沟小流域8种植被类型条件下植物消耗土壤水分深度与降水对应的补充深度。结果表明:裸地、农地、撂荒地、人工草(灌)地(苜蓿地、柠条地、沙打旺地)、当地典型草地(荒草地、长芒草地)在平水年及干旱年,土壤水分均表现为负平衡;丰水年部分样地土壤水分得到补充。平水年以及干旱年(2010—2011年)植物耗水深度依次为:柠条地撂荒地沙打旺地苜蓿地≈长芒草地≈荒草地农地裸地,降水补充深度为农地裸地撂荒地荒草地长芒草地沙打旺地苜蓿地柠条地。丰水年(2012年)裸地、苜蓿地、荒草地与沙打旺地土壤水分并未显示出明显负平衡过程,但柠条地耗水深度依然达到260 cm,其它样地依次为撂荒地农地长芒草地;降水入渗深度排序:农地裸地撂荒地=柠条地荒草地=苜蓿地长芒草地沙打旺地。水蚀风蚀交错区土壤蒸发(裸地蒸发)以及降水补充深度一般为0—120 cm范围内,丰水年土壤水分能得到恢复。农地的土壤水分消耗与补充深度略有增加。农地撂荒后耗水深度与撂荒地植被类型有密切联系,随植被盖度与丰度的增加,耗水有进一步加深的趋势,撂荒地土壤水分补充深度小于等于消耗深度。农地退耕还草所种植的深根性植被(苜蓿、沙打旺、柠条等)不仅会迅速消耗当季降水,同时会进一步消耗土壤深层储水,致使120 cm以下观测土层土壤含水量较低,造成土壤水分消耗深度较浅的假象。除撂荒地外,高生物产量的人工草(灌)耗水量高,耗水深度也深,因此在退耕还林(草)过程中,应该充分考虑不同植被类型的年度水分交换深度,采取措施降低消耗深度,增加入渗深度。     

猫儿山荷木林不同层次土壤含水量的降雨响应

以漓江上游猫儿山林区典型荷木林(Schima superba)为研究对象, 对0-20 cm, 20-40 cm, 40-60 cm, 60-80 cm等4 个层次的土壤进行土壤含水量定位监测, 分析各层次土壤含水量的降雨响应。结果表明: (1)0-20 cm、20-40 cm、40-60 cm、60-80 cm 4 个层次土壤土壤含水量差异显著, 年均值分别为: 50.66%, 41.71%, 47.23%, 34.92%, 垂直变化复杂, 降雨与各层次土壤含水量呈极显著正相关; (2)4 个层次土壤含水量上升拐点出现的时间依次滞后, 随着深度的增加, 土壤含水量对降雨的响应变慢; (3)在前期土壤含水量较低的情况下, 土壤含水量都会出现一个“平台”期, 然后迅速升高, 达到最高值; (4)深层土壤对降雨的响应与产生饱和界面, 地下水位抬高有关; (5)在大雨和暴雨条件下, 60-80 cm 深层土壤由于初始含水量低, 随降雨增速很快; 降雨结束后, 该层次的土壤含水量下降最快。为揭示漓江上游森林植被对降水径流的调节作用, 客观评估漓江上游水资源潜力、加强流域水资源管理和森林经营提供科学依据。     

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)     

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.     

Electroejaculation in chimpanzees and gorillas and artificial insemination in chimpanzees

Electroejaculation was performed in 3 chimpanzees, 1 pygmy chimpanzee, and 2 gorillas with an instrument that delivers a modified sine wave current with a frequency of 24 Hz. The current stimuli were applied by a rectal probe with longitudinal electrodes. The electrical parameters varied from 6 to 12 V and from 30 to 40 mA for response of erection and lay between 8 and 18 V and between 40 and 145 mA during semen emission. Eleven chimpanzee semen samples showed the following data (x ± SD): total volume 1.9 ± 1.3 ml, volume of the liquid fraction 0.3 ± 0.2 ml, spermatozoa per ejaculate 743 ± 376 × 10⁶, sperm motility 52.7 ± 9.6%, morphologically abnormal spermatozoa 12.2 ± 7.5%. From an adult gorilla, three semen samples were collected, in each case without spermatozoa. The electrostimulation of a 6-year-old gorilla led to an erection, but not to semen emission. Three female chimpanzees were inseminated with fresh or frozen semen, each of them within three different estrous cycles. None of these inseminations led to a pregnancy.     

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.     

Advances in purine and pyrimidine metabolism in health and diseases

ABSTRACT

In June, 2015, the Purine and Pyrimidine Society organized the 16th biennial symposium on Purine and Pyrimidine metabolism at the Faculty House of Columbia University, New York City. This exciting meeting focused on these important molecules, new developments in inborn errors of metabolism; therapeutic analogs. In addition, the biochemistry of mammalian and non-mammalian systems were discussed. Due to significant advances in molecular medicine, the boundaries between clinical and basic sciences have merged into exciting translational research, of which a small portion was highlighted in the presymposium.     

MPD and DNA Bending in Crystals and in Solution

Bending of 15 to 24° is observed within crystal structures ofB-DNA duplexes, is strongly sequence-dependent, and exhibits no correlation with the concentration of MPD (2-methyl-2,4-pentanediol) in the crystallizing solution. Two types of bends are observed: facultative bends or flexible hinges at junctions between regions of G·C and A·T base-pairs, and a persistent and almost obligatory bend at the center of the sequence R-G-C-Y. Only A-tracts are characteristically straight and unbent in every crystal structure examined to date. A detailed examination of normal vector plots for individual strands of a double helix provides an explanation, in terms of the stacking properties of guanine and adenine bases. The effect of high MPD concentrations, in both solution and crystal, is to decrease local bending somewhat without removing it altogether. MPD gel retardation experiments provide no basis for choosing among the three models that seek to explain macroscopic curvature of DNA by means of microscopic bending: junction bending, bent A-tracts, or bent general- sequence DNA. Crystallographic data on the straightness of A-tracts, the bendability of non-A sequences, and the identity of inclination angles in A-tract and non-A-tractB-DNA support only the general-sequence bending model. The pre-melting transition observed in A-tract DNA probably represents a relaxation of stiff adenine stacks to a flexible conformation more typical of general-sequence DNA.