Net Carbon Fluxes Over Burned and Unburned Native Tallgrass Prairie

Prescribed burning of aboveground biomass in tallgrass prairie is common and may influence dynamics and magnitudes of carbon (C) movement between the surface and atmosphere. Carbon dioxide (CO₂) fluxes were measured for 2 yr using conditional sampling systems on two adjacent watersheds in an ungrazed tallgrass prairie near Manhattan, Kansas. One watershed was burned annually (BA) and the other biennially (BB). Leaf and soil CO₂ fluxes were measured in the source area. Net ecosystem exchange (NEE) of CO₂ reached a maximum daily gain of 26.4 g CO₂·m^?2·d^?1 (flux toward surface is positive) in July 1998 (year when both sites were burned and precipitation was above normal); gains were similar between sites in 1998. The maximum daily NEE loss of CO₂ was ?21.8 g CO₂·m^?2·d^?1 from BA in September 1997 (year when only BA was burned and precipitation was below normal). When data were integrated over the two years, both sites were net sources of atmospheric CO₂; NEE was ?389 g C·m^?2·2 yr^?1 on BA and ?195 g C·m^?2·2 yr^?1 on BB. Burning increased canopy size and photosynthesis, but the greater photosynthesis was offset by corresponding increases in respiration (from canopy and soil). Carbon losses from fire represented 6–10% of annual CO₂ emissions (bulk came from soil and canopy respiration). Data suggest that annual burning promotes C loss compared to less-frequently burned tallgrass prairie where prairie is not grazed by ungulates. Greater precipitation in 1998 caused large increases in biomass and a more positive growing season NEE, indicating that C sequestration appears more likely when precipitation is high. Because C inputs (photosynthesis) and losses (canopy and soil respiration) were large, small measurement or modeling errors could confound attempts to determine if the ecosystems are long-term CO₂ sources or sinks.     

不同日龄混合柄瘤蚜茧蜂对寄主虫龄的选择及子代蜂发育表现

对同一头混合柄瘤蚜茧蜂雌蜂连续观察5 d,比较其对蚕豆蚜若蚜和成蚜的选择,并观察了子代蜂的发育特性。结果表明:5日龄蜂对不同虫龄蚜虫的寄生率无显著差异,子代蜂羽化率和雌性比亦无显著差异,但寄生2、3龄若蚜的子代雌蜂体型显著大于寄生其他蚜虫的子代雌蜂,寄生3龄若蚜的子代雄蜂显著大于寄生成蚜的子代雄蜂。在其他日龄(1～4)蜂中,1、4日龄蜂对不同龄若蚜的寄生率无显著差异,但均高于对成蚜的寄生,2、3日龄蜂对2龄若蚜的寄生偏好显著高于对更高虫龄的寄生;3日龄蜂的子代蜂羽化率在各虫龄蚜虫之间无显著差异,其他日龄蜂寄生低龄若蚜的子代羽化率高于寄生较高虫龄蚜虫;寄生中间龄期若蚜(3、4龄)的子代蜂雌性比显著高于寄生1龄或成蚜的子代蜂;1日龄蜂子代雌蜂体型在不同虫龄蚜虫间无显著差异,但2～4日龄蜂寄生2、3龄若蚜的子代雌性体型大于寄生1龄、4龄或成蚜的子代雌蜂;1、2日龄蜂的子代雄蜂体型在各虫龄蚜虫间无显著差异,3、4日龄蜂寄生中间龄期若蚜的子代雄性体型大于寄生1龄若蚜或成蚜。根据本研究结果推测,与低龄蜂相比高龄蜂对寄主品质要求更高,其幼虫对寄主的调节能力更强。     

Development of Y‐chromosome‐Specific SCAR Markers Conserved in Taurine,Zebu and Bubaline Cattle

Sex pre‐selection of bovine offsprings has commercial relevance for cattle breeders and several methods have been used for embryo sex determination. Polymerase chain reaction (PCR) has proven to be a reliable procedure for accomplishing embryo sexing. To date, most of the PCR‐specific primers are derived from the few single‐copy Y‐chromosome‐specific gene sequences already identified in bovines. Their detection demands higher amounts of embryonic genomic material or a nested amplification reaction. In order to circumvent this, limitation we searched for new male‐specific sequences potentially useful in embryo sexing using random amplified polymorphic DNA (RAPD) analysis. Random amplified polymorphic DNA (RAPD) assay reproducibility problems can be overcome by its conversion into Sequence Characterized Amplified Region (SCAR) markers. In this work, we describe the identification of two bovine male‐specific markers (OPC16₃₂₃ and OPF10₁₁₆₈) by means of RAPD. These markers were successfully converted into SCARs (OPC16₇₂₆ and OPF10₉₈₄) using two pairs of specific primers.Furthermore, inverse PCR (iPCR) methodology was successfully applied to elongate OPC16₃₂₃ marker in 159% (from 323 to 837 bp). Both markers are shown to be highly conserved (similarity ≥95%) among bovine zebu and taurine cattle; OPC16₃₂₃ is also highly similar to a bubaline Y‐chromosome‐specific sequence. The primers derived from the two Y‐chromosome‐specific conserved sequences described in this article showed 100% accuracy when used for identifying male and female bovine genomic DNA, thereby proving their potential usefulness for bovine embryo sexing.     

Effect of Recombinant Bovine Somatotropin on Plasma Concentrations of Insulin‐like Growth Factor I,Insulin and Membrane Integrity of Bull Spermatozoa

This study aimed to evaluate the effect of the exogenous recombinant bovine somatotropin (rbST) on plasma concentrations of insulin‐like growth factor I (IGF‐I), insulin and semen quality of bulls. Twenty bulls (Aberdeen Angus and Brangus) were divided by breed into two groups. Placebo group was injected with NaCl 0.9% (s.c.) and treatment group with rbST (s.c., 500 mg) at days 0 and 14 of the experiment. Immediately after semen collection, blood samples were taken on days 0, 14, 28, 42 and 56 of the experiment. Semen was also collected on day 70 of the experiment. Evaluation of sperm motility was performed at pre‐freezing and post‐thawing stage, whereas assessment of sperm membrane integrity was performed after freezing and thawing. Analysis of data revealed that the effect of treatment and treatment‐by‐collection day on plasma concentrations of IGF‐I and insulin was not significant. However, mean plasma concentrations of IGF‐I and insulin were affected (p < 0.0001) by days of blood sampling. Effect of treatment and treatment‐by‐collection day on motility of spermatozoa was similar (p > 0.05) at pre‐freezing and post‐thawing stage. Intactness of plasmalemma and tail membrane of spermatozoa at post‐thawing stage was higher (p < 0.05) in rbST‐treated group than in control. In conclusion, rbST did not affect plasma concentrations of IGF‐I and insulin, however, it did improve post‐thaw sperm membrane integrity.     

Spray-Dried Yerba Mate Extract Capsules: Clinical Evaluation and Antioxidant Potential in Healthy Individuals

Plant Foods for Human Nutrition - The aim of the present study was to evaluate the clinical effects and antioxidant potential of spray-dried yerba mate extract (SDME) capsules in healthy...     

绥化市北林区农机化发展经验探讨

绥化市北林区农机事业在黑龙江省起步比较早,与全省其他市县一道,通过近两代农机人的共同努力,积累了丰富的工作经验。为此,对改革开放以来北林区农机工作进行较系统的总结,旨在为今后优化农机化发展决策提供参考.     

Methods used for producing polyploid agricultural plants

Samenvatting Methoden ter verkrijging van polyploide landbouwgewassen Verschillende methoden ter verkrijging van polyploiden bij granen en andere gewassen worden beschreven en met elkaar vergeleken.Aanvankelijk gaf een verkorting van de behandelingsduur van drie op anderhalve dag bij de methode vanNavashin Gerassimova voor rogge reeds een belangrijke verbetering, waardoor het aantal tetraploiden, dat per winterseizoen verkregen is, van ongeveer 50 tot ruim 250 werd verhoogd.De beste werkwijze bleek tenslotte een kortdurende behandeling van jonge kiemplanten met colchicine oplossingen van zwakke concentratie tijdens een periode van actieve groei, begunstigd door een iets verhoogde temperatuur. Het aantal tetraploiden, dat op deze wijze verkregen is, bedroeg meer dan 2500 resp. meer dan 1500 per seizoen, het tienvoudige van het volgens de verbeterde methodeNavashin Gerassimova verkregen aantal.Voor rogge en ook voor bieten voldeed het best een behandeling met 0.1 % colchicine gedurende 3 uur bij 27°C.Ook van andere gewassen als gerst, kanariezaad, vlas en boekweit werden volgens de nieuwe methode van colchicinebehandeling grote aantallen tetraploiden verkregen.Een methode werd beschreven voor het onderzoek van cytologische preparaten met behulp van de phase-contrast microscoop.Dit instrument maakt het mogelijk in ongekleurde preparaten van rogge, bieten en andere landbouwgewassen, waarbij colchicinebehandeling is toegepast, na te gaan of het chromosomenaantal verdubbeld is.Bij rogge wordt dit onderzocht aan worteltopcellen van kiemplanten opgekweekt uit het zaad van de met colchicine behandelde planten.Bij bieten komen kerndelingen vooral voor in de zeer jonge blaadjes uit het hart der planten. Zowel blaadjes van de behandelde bietenplanten zelf werden onderzocht, als blaadjes van planten ontstaan uit het zaad van de behandelde planten.Voor het onderzoek van de weefsels worden deze in N. HCl bij 60°C gemacereerd, waardoor zij zacht worden en op een objectglas in een druppel 45 % azijnzuur onder een dekglas uitwrijfbaar zijn, waarbij de celstructuur aanwezig blijft. Is dit geschied, dan is het preparaat klaar voor onderzoek.In bietenpreparaten steken de chromosomen diep zwart tegen het doorzichtige plasma af. In worteltoppreparaten van rogge, waarin de cellen groter zijn en een vrij dicht plasma hebben, is het contrast minder sterk. De chromosomen krijgen hier een donker grijze tint.Bij rogge kan één persoon per dag met de phase-contrast microscoop 150 à 200 planten onderzoeken. Bij bieten, waarvan ook mixoploide planten onderzocht moeten worden, waarbij in één preparaat diploide naast tetraploide cellen voorkomen, kunnen hoogstens 80 à 100 planten per dag onderzocht worden.     

长沙市1997～2010年土地利用总体规划实施可持续利用评价

以长沙市为例,运用生态足迹的方法对长沙市上轮土地利用总体规划的可持续利用情况进行了全面评价,为更好地修编新一轮土地利用总体规划提供依据,同时提出保持土地可持续利用应采取的措施。     

Dietary amino acids fed in free form and as protein components do not differently affect postprandial plasma insulin, glucagon, growth hormone and corticosterone responses in rats

This study examined, whether the postprandial fate of dietary amino acids from different amino acid sources is regulated by the responses of insulin, glucagon, corticosterone and growth hormone (GH). Male Wistar rats were cannulated in the vena jugularis and assigned to dietary groups. The diets contained 21% casein or the same amino acids in free form. In the free amino acid diets, methionine level was varied between the groups. The feed was supplied in two distinct meals. In previous experiments it was established that oxidative amino acid losses of the free amino acid diets and protein diets were different. After 3 weeks on those diets, it appeared that the differences in postprandial oxidative losses had been diminished. GH was measured every 12 min, from 144 min before the start of the experimental meal over the following 144 min. Insulin and corticosterone were measured six times from the start of the meal until 270 min after the meal. No differences have been observed between the hormonal responses to both meals at day 5 and at day 26. In conclusion, it has been found that the differences in the oxidative losses between protein and free amino acid meals are not mediated by the combined action of the insulin, glucagon, corticosterone and GH. Postprandial catabolism of amino acids is most probably regulated by substrate induction.