地下水位对黄河三角洲柽柳根系生长的影响

为揭示黄河三角洲柽柳根系生长特征对地下水位的响应规律,明确柽柳生长适宜的地下水位,在咸水矿化度（6 g/L）下,模拟设置0、0.3、0.6、0.9、1.2、1.5、1.8 m共7个地下水位。测定分析栽植柽柳土柱的水盐参数与根系生长指标。结果表明：在咸水矿化度下,地下水位可显著影响土壤水盐变化,从而影响柽柳根系的生长。随地下水位的降低,土壤含水量、含盐量和土壤溶液绝对浓度显著降低。在高水位（≤0.6 m）下,柽柳根系生长受水盐胁迫影响显著,柽柳根长、根径、侧根数、总生物量、侧根生物量、根系连接长度均较低,拓扑结构呈叉状分支;中水位（0.9 m）时,土壤水盐条件适宜,柽柳侧根数、根径、二级侧根和毛细根生物量达到最大值,拓扑结构由叉状分支向鱼尾形分支过渡;低水位（≥1.2 m）下,土壤水盐含量低,柽柳根系总生物量、主根生物量、一级侧根生物量和根系平均连接长度在1.2 m水位达到最大值后降低,拓扑结构呈鱼尾形分支。柽柳根系生长与地下水位密切相关,柽柳通过改变根系生长和调整构型来适应不同土壤水盐和地下水位条件。高水位（≤0.6 m）下柽柳以降低根系生长深度,增加分叉,调配各组织器官的生物量来适应水盐胁迫;中水位0.9 m下土壤水盐条件最适宜柽柳生长;低水位（≥1.2 m）下柽柳主要受土壤干旱胁迫而使根系向下生长,增加根系连接长度,以此扩大资源获取效率。柽柳根系生长及根系构型对咸水矿化度下不同地下水位表现出较强的适应性和可塑性。     

鸡粪有机肥对设施菜地土壤重金属和微生物群落结构的影响

通过田间试验,研究在设施菜地上施用不同剂量的鸡粪有机肥对土壤-植物系统中重金属的累积、重金属有效性和土壤微生物群落结构的影响,进一步探讨土壤微生物群落结构与土壤重金属之间的相关关系。结果表明,与对照相比,施用有机肥可提高小白菜地上部生物量,其中施肥量为60 t/hm²时值最大,增幅为59.92%;小白菜地上部Cd、Cr、Cu、Zn和As含量均大幅增加,但Pb含量无明显变化。土壤重金属Cd、Cr、Cu、Zn和As的全量均随鸡粪有机肥施加量的增加而增大,最高增幅分别为21.30%、21.58%、17.40%、19.40%和17.43%,出现明显的累积现象;施用有机肥均增加了土壤Cd、Cr、Cu、Zn和As的有效态含量,而Pb的全量和有效态含量无显著变化;除重金属Pb外,不同重金属元素全量与有效态含量均显著正相关,其中元素Zn的全量与有效态含量相关性最强。磷脂脂肪酸（PLFA）分析结果表明,土壤中含量较高的PLFA为16：0、18：1ω7c、10Me16：0和18：1ω9c,土壤微生物总PLFA和各类群PLFA含量均呈现M0.5 > M1 > CK > M2 > M4;相关性分析结果表明,土壤Cu、As全量和Cd、Cr、Cu、As有效态含量与微生物总PLFA和各类群PLFA含量均呈现显著负相关关系,其中有效态Cr和Cu含量对微生物群落结构的影响最为显著。     

土壤氮素异质性分布和马先蒿寄生对长芒棒头草生长发育及根系分布的影响

无论在农田还是自然生态系统中,土壤养分异质性普遍存在。植物具有感知土壤养分异质性的能力,并通过调节根系生物量分配及空间分布以获取更多资源。了解寄生胁迫在不同养分条件下对寄主生长发育及根系空间分布的影响,对解析寄主应对寄生胁迫和养分胁迫的适应策略,进而指导寄生性杂草防控具有重要的指导意义。该文采用分根试验,通过对寄主分根,并控制根室两侧氮供应水平及寄生胁迫程度,考察了氮胁迫及两种寄主依赖程度不同的马先蒿的寄生对寄主长芒棒头草生长发育及根系空间分布的影响。结果表明:(1)土壤氮水平与马先蒿寄生均可显著影响长芒棒头草生物量及根冠比,并且两者之间存在显著交互作用,其中土壤氮水平为主要影响因子。(2)两种马先蒿对长芒棒头草的危害程度不同。在NPK和2NPK处理时,三色马先蒿的寄生显著降低长芒棒头草生物量(茎叶:37. 1%、51. 5%;根系:35. 6%、63.6%);在NPK处理时,大王马先蒿的寄生显著增加长芒棒头草生物量(茎叶:29.9%,根系:61.2%)。(3)长芒棒头草的根系生长和空间分布受氮营养的异质分布和寄生的影响,具有明显的感知养分空间分布及调节根系生长能力。     

A Temporary Local Energy Pool Coupled to Neuronal Activity: Fluctuations of Extracellular Lactate Levels in Rat Brain Monitored with Rapid-Response Enzyme-Based Sensor

Abstract: A successfully developed enzyme-based lactate microsensor with rapid response time allows the direct and continuous in vivo measurement of lactic acid concentration with high temporal resolution in brain extracellular fluid. The fluctuations coupled to neuronal activity in extracellular lactate concentration were explored in the dentate gyrus of the hippocampus of the rat brain after electrical stimulation of the perforant pathway. Extracellular glucose and oxygen levels were also detected simultaneously by coimplantation of a fast-response glucose sensor and an oxygen electrode, to provide novel information of trafficking of energy substances in real time related to local neuronal activity. The results first give a comprehensive picture of complementary energy supply and use of lactate and glucose in the intact brain tissue. In response to acute neuronal activation, the brain tissue shifts immediately to significant energy supply by lactate. A local temporary fuel "reservoir" is established behind the blood-brain barrier, evidenced by increased extracellular lactate concentration. The pool can be depleted rapidly, up to 28% in 10–12 s, by massive, acute neuronal use after stimulation and can be replenished in ∼20 s. Glutamate-stimulated astrocytic glycolysis and the increase of regional blood flow may regulate the lactate concentration of the pool in different time scales to maintain local energy homeostasis.     

Nutritive value of peas for nonruminant diets

Peas, the seeds of Pisum sativum, are produced usually in temperate regions but are accepted as a food source worldwide. Traditionally, nonruminant diets utilized peas which had been rejected by the food industry but specific cultivars of feed (or field) peas also have been developed for livestock use. In view of the diversity of varieties, seeding times (spring or winter-sown) and agronomic conditions during the growing season, there is a considerable range in the composition and nutritive value of peas. The seed coat (hull) represents 70 to 140 g kg⁻¹ of the total weight and consists mainly of non-starch polysaccharides, while the major components of the dehulled pea are starch ( 450 g kg⁻¹) and protein ( 250 g kg⁻¹). Published energy values for the whole seed range from 12.2 to 16.6 MJ ME kg⁻¹ DM for pigs and 10.1 to 12.8 MJ TME_N kg⁻¹ DM for poultry. Reported analyses for crude protein vary from 156 to 325 g kg⁻¹ DM, while content and availability of the constituent amino acids vary also with cultivar, seed type and analytical methods. Most concerns about low digestibilities relate to the sulphur amino acids and tryptophan. Potentially detrimental constituents in raw peas include anti-proteases, haemagglutinins, phytic acid and tannins although these appear negligible in Canadian peas. When analytical data are lacking, the following limits to use of peas are suggested: 100, 200 and 350 g kg⁻¹, respectively, in pig starter, grower and finisher diets; 200 g kg⁻¹ in broiler, 250 g kg⁻¹ in turkey and 300 g kg⁻¹ in layer diets.     

Diversity and specificity of host‐natural enemy interactions in an urban‐rural interface

1. Urbanisation and agricultural intensification cause the replacement of natural ecosystems but might also create novel habitats in urban and rural ecosystems promoting some insect communities by providing food and nesting resources. 2. This study investigated how host–natural enemy communities change in urban and rural landscapes and their transitional zone, the urban–rural interface, by using trap nests for cavity‐nesting Hymenoptera in gardens and rapeseed fields that were either isolated or paired in the urban–rural interface. 3. Host dynamics were important for natural enemy occurrence, species richness and parasitism rates, and landscape effects were evident for natural enemy variables except for the richness of bee natural enemies. The number of parasitised brood cells was at its highest in the urban–rural interface, but the highest parasitism rates of bees were observed in isolated gardens. Parasitism rates of bees were negatively affected by host abundance, while parasitism rates of wasps were positively affected. 4. Higher specialisation and lower connectivity of host–natural enemy interactions were found in paired habitats than in isolated habitats. This indicates that paired habitats comprise more specific natural enemies and vulnerable interactions, while isolated habitats comprise more generalist natural enemies, and thus interactions appear more stable. 5. These results confirm that host dynamics play an essential role in the abundance and richness of natural enemies and drive parasitism. However, high habitat heterogeneity found in the urban–rural interface can also have an effect on host–natural enemy communities. This highlights that the provisioning of resources in the urban–rural interface can benefit insect communities in these areas.     

Using Fecal Glucocorticoids to Assess Stress Levels in Captive River Otters

Abstract Reintroduction projects often expose animals to a series of acute stressors that may cause chronic stress and lead to the stress response. The stress response results in the release of glucocorticoids that, when excessive, can cause detrimental effects to the animal. Glucocorticoids can be extracted from feces and quantified as an effective method for assessing stress levels. We collected scats from 10 river otters (Lontra canadensis; 3 from MD and 7 from NY, USA) held captive for the Pennsylvania River Otter Reintroduction Project (PRORP). We used these scats to verify the use of the Correlate-EIA^TM Corticosterone Enzyme Immunoassay Kit (Assay Designs, Inc., Ann Arbor, MI) to evaluate stress levels in otters. We also determined trends in stress levels during the initial 10–12 days otters were in PRORP captivity, and compared glucocorticoid levels for 5 of the New York otters the morning before, the morning of, and the morning after veterinary examinations to determine if associated procedures (e.g., physical and chemical restraint) caused increased stress levels. Glucocorticoid concentrations declined from time 1 to time 2 for the 3 otters from Maryland (an average decline of about 6-fold) and for 5 of 7 otters from New York. Among otters evaluated for stress associated with veterinary examinations, average glucocorticoid concentrations were increased the morning of and the morning after veterinary examinations from the day before the veterinary examinations. We demonstrated that fecal glucocorticoids are an effective method for assessing stress levels in otters and that PRORP's captive management program did not contribute to increasing stress during the 10–12-day evaluation period. Fecal glucocorticoid assays could be used to evaluate stress levels of zoo or permanently captive otters, determine the most effective husbandry techniques for housing otters, and evaluate effects of both management practices and environmental conditions in the wild and in captivity.     

Pregnancy rates relative to recipient plasma progesterone levels on the day of nonsurgical transfer of frozen/thawed bovine embryos

A total of 71 synchronized dairy heifers (Holstein Friesian x German Black Pied) were used as recipients of seven-day old frozen/thawed bovine embryos. Plasma progesterone concentrations and corpus luteum quality on the day of nonsurgical transfer (= day 7) were determined and related to pregnancy rates or estrus intervals in nonpregnant recipients. A total of 32 recipients (45.1 %) maintained pregnancy; 39 recipients (54.9 %) did not. No significant differences could be detected between progesterone levels in recipients that remained pregnant (3.14 +/- 0.24 ng/ml; x +/- SEM ) and those that did not maintain pregnancy (3.23 +/- 0.28 ng/ml). Optimal progesterone levels were between 2 and 5 ng/ml coinciding with a pregnancy rate of 51.1 % (24 47 ). Pregnancy rates apparently were decreased when progesterone levels were below 2 ng/ml (35.3 %; 6 17 ) or above 5 ng/ml (28.6 %; 2 7 ). Hence, optimal progesterone levels were identical to those for freshly collected embryos reported previously by Remsen et al. (1). Bovine corpus luteum quality graded by rectal palpation was related to some extent to progesterone levels but not to pregnancy rates. Out of 39 nonpregnant recipients seven animals (17.9 %) with a mean plasma progesterone level of 3.76 +/- 0.72 ng/ml showed an extended estrus interval of more than 55 days, probably indicating early embryonic mortality. Progesterone levels did not significantly differ between nonpregnant recipients with estrus intervals of various length. Plasma progesterone levels at the time of transfer are of limited diagnostic value for screening recipients prior to transfer of frozen/thawed embryos.     

Rapid variations in the content of the RNA of the small subunit of ribulose-1,5-bisphosphate carboxylase of mature tobacco leaves in response to localized changes in light quantity. Relationships between the activity and quantity of the enzyme

Mature green leaves from tobacco (Nicotiana tabacum L.) plants were submitted to contrasting light conditions; half of each leaf was shaded (changed from 60 to 25 mol photons· m^-2 ·s^-1=LL) and the other half was exposed to higher light (changed from 60 to 360 mol·m^-2· s^-1=HL) for 24 h. The activity and quantity of ribulose-1,5-bisphosphate carboxylase (RuBPCase) were measured during the first 24 h in each leaf region and the variation was compared with that of small subunit (SSU)-and large subunit (LSU)-mRNA contents determined by a hybridot technique. Each leaf half responded separately to the actual light received. The activity of RuBPCase increased progressively in the HL zones and decreased in the LL zones. The RuBPCase-protein content was not significantly modified during the first 24 h but SSU-mRNA content responded very rapidly to the treatment. Within 2 h a significant difference in SSU mRNA appeared between LL and HL zones: at the end of the photoperiod the content in LL zones was approx. 25% of the initial value. The increase in the exposed zone, however, was not significant, indicating that there was a dissymmetry of the response to variation in incident white light. The LSU-mRNA contents from the same leaf extracts were totally unaffected by the light treatment. No day-night variations were noted in either SSU or LSU mRNAs in control plants.Abbreviation HL high-light irradiance - LL lower-ligh irradiance - LSU large subunit of RuBPCase - RuBPCase ribulose-1,5-bisphosphate carboxylase - SSU small subunit of RuBPCase