Impact of altering the water table height of an acidic fen on N2O and NO fluxes and soil concentrations

The impact of experimentally intensified summer drought and precipitation on N₂O and NO turnover and fluxes was investigated in a minerotrophic fen over a 2‐year period. On three treatment plots, drought was induced for 6 and 10 weeks by means of roofs and drainage and decreased water table levels by 0.1–0.3 m compared with three nonmanipulated control plots. When averaged over the three treatment plots, both N₂O and NO emission showed only little response to the drought. On the single plot scale, however, a clear impact of the treatment on N₂O and NO fluxes could be identified. On the plot with the weakest water table reduction hardly any response could be observed, while on the plot with the greatest drainage effect, N₂O and NO fluxes increased by 530% and 270%, respectively. Rewetting reduced NO emissions to background levels (0.05–0.15 μmol m^?2 h^?1), but heavily enhanced N₂O emission (18–36 μmol m^?2 h^?1) for several days in the plots with largest water table reduction. These peaks contributed up to 40% to the cumulative N₂O fluxes and were caused by rapid N₂O production according to isotope abundance data. According to N₂O concentrations and isotope abundance analysis N₂O was mostly produced at depths between 0.3 and 0.5 m. During water table reduction net N₂O production in 0.1 m depth steadily increased in the most effectively dried plot from 2 up to 44 pmol cm^?3 day^?1. Rewetting immediately increased net N₂O production in the topsoil of the drought plots, showing rates of 18–174 pmol cm^?3 day^?1. This study demonstrates that drought and rewetting can temporarily increase N₂O emission to levels that have to date only been reported from nutrient rich and degraded fens that have been drained for agricultural purposes.     

播种时期与密度对关中灌区夏玉米群体生理指标的影响

采用二次饱和D最优试验设计,运用作物群体生理学方法,研究了关中灌区玉米密度、播期与群体生理指标的关系及其影响效应.结果表明,关中灌区夏播条件下,在6月13日—7月22日,播期与玉米籽粒产量、干物质积累量(DMA)、吐丝期叶面积指数(LAImax)、总光合势(LAD)、群体净同化率(NAR)、作物生长率(CGR)呈负相关,播期对CGR、LAD的影响较大,对LAImax和NAR的影响较小;在45000～65918株·hm-2范围内,密度与玉米籽粒产量、DMA、LAImax、LAD、CGR呈正相关,而与NAR呈负相关,密度对CGR、LAImax和LAD的影响较大,而对NAR的影响较小.播期对玉米群体生理指标的总影响效应显著大于密度,实际生产中应力争早播.对密度和播期与玉米群体生理指标建立的回归模型表明,陕单8806玉米在关中灌区夏播中实现高产的适宜播期为6月10—20日,密度应控制在57767～71706株·hm-2.     

夏玉米叶片水分变化与光合作用和土壤水分的关系

叶片是光合作用的重要器官,其含水量的变化必将影响光合作用,但关于叶片水分变化对光合作用的影响报道较少。以华北夏玉米为研究对象,利用三叶期不同水分梯度的持续干旱模拟试验资料,分析夏玉米叶片水分变化及其与叶片净光合速率和土壤水分的关系。结果表明:夏玉米叶片净光合速率对叶片水分变化的响应显著且呈二次曲线关系,叶片含水量约为70.30%时,叶片净光合速率为零;叶片含水量与土壤相对湿度呈非直角双曲线关系,叶片最大含水量约为85.14%。研究结果可为准确描述叶片水分变化对光合作用的影响及客观辨识夏玉米干旱的发生发展及监测预警提供参考。     

Summer mastitis experimentally induced by Hydrotaea irritans exposed to bacteria

Abstract. Summer mastitis is an acute suppurative bacterial infection of the udder in heifers and dry cows. To ascertain the possible role of flies in the transmission of the disease, experimental exposures of recipient heifers to Hydrotaea irritans previously exposed to bacteria were carried out. Flies were allowed to feed on secretions from clinical cases of summer mastitis. The pathogens present were the bacteria Staphylococcus aureus, Streptococcus dysgalactiae, Actinomyces pyogenes , Stuart-Schwan cocci, Peptococcus indolicus, Fusobacterium necrophorum and Bacterioides species. The teats of eight heifers were exposed to flies with verified pathogen content. Two teats of each animal were deliberately damaged before fly exposure. One teat was cut, another pricked with insect needles to mimic insect bites. Two of the heifers developed summer mastitis in the quarters where teats had been cut. The bacterial species isolated from these quarters corresponded to those that had previously been fed to the flies. For the first time, it is now demonstrated that H.irritans is capable of transmitting summer mastitis pathogens and so causing summer mastitis in recipient heifers. Lesions on the teat orifice may be a predisposing factor in the development of the disease.     

Feeding, Ichthyophonus sp. infection, distribution and growth history of Norwegian spring-spawning herring in summer

After its collapse in the late 1960s, 1991 was the first year of systematic herring investigations after the Norwegian Sea stock returned to the traditional summer-feeding areas. Of 11 prey groups three dominated the diet; Calanus finmarchicus, Parathemisto spp. and Sebastes spp. There was a high prevalence of Ichthyophonus sp. at stations in the central and western parts of the Norwegian Sea where the cpue was low. This suggests that infected individuals were unable to return from the feeding to the wintering area of the Norwegian fjords. Highest cpue were recorded between 68–73° N and 5–15° E. Age groups 2, 3 and 8 were most frequently caught and age group 8 (the 1983 year class) dominated the samples. Herring occurred in dense concentrations where C. finmarchicus dominated diet. 0-group fish dominated diet at stations along the coast from 66–73° N and out to c . 300 km off the coast. Mature herring overlapped in distribution with 0-group fish and Sebastes spp. contributed largely to herring diet in this area. The first rich year-class after the collapse, the 1983 year class, had a faster growth than rich year classes from past herring periods, but slower than poor ones.     

In sito galanthamine extraction during the cultivation of Leucojum aestivum L. shoot culture in two‐phase bubble column cultivation system

Two‐phase bioreactor cultivation system was developed and applied for in sito recovery of extracellular galanthamine during the cultivation of Leucojum aestivum L. shoot culture in a modified column bioreactor system. The inclusion of an external circulation column with adsorbent resin Amberlite XAD‐4 as a second phase, on the 21st day of the beginning of cultivation resulted in 1.25 folds increase in biomass accumulation and maximal amounts of accumulated galanthamine of 6 mg/L (3.1 mg/L intracellular and 2.9 mg/L extracellular). It was demonstrated that the inclusion of a second phase at the cultivation of the L. aestivum shoot culture in a bubble column bioreactor with internal sections redirected the alkaloid metabolism to galanthamine synthesis and inhibits the synthesis of hemanthamine and lycorine type alkaloids. Our research demonstrated that the application of the two‐phase cultivation systems could be an important tool to increase the yields of valuable secondary metabolites in plant tissue culture‐based bioprocess.