A comparison of the effects of sward improvement on invertebrates, sward establishment and herbage yield

Field experiments were done at two widely separated sites in England (Tadcaster, North Yorkshire and North Wyke, Devon). In each case an old permanent sward was re-seeded after ploughing or by direct drilling, or was left intact and fertilised. The carbamate pesticide aldicarb was applied to half of each experimental plot. The effects of sward improvement and pesticide on various soil invertebrate groups were assessed. Soil-dwelling macrofauna arthropods were scarce at both sites. Stem-boring dipterous larvae, however, were numerous at both sites. At Tadcaster, Oscinella vastator was the only species present in the original sward, but 0. frit was by far the most prevalent species in re-seeded areas. These can only have arisen from direct oviposition of eggs by adults on or near the emerging seedlings and not by migration of larvae from buried turf or the desiccated old pasture.
Mites and Collembola were abundant. Their numbers were reduced initially by cultivation and pesticide usage, but the effects of these practices were transient and their numbers recovered to previous levels usually within 10 wk.
Earthworms were present at both sites. Deep burrowing species, e.g. Lumbricus terrestris and Allolobophora longa were less affected by the treatments imposed than species such as A. chlorotica and L. rubelius which usually live close to the soil surface. Effects on their numbers were in any case, short-lived.
No improvement method consistently provided the greatest herbage dry matter yield. Pesticide application, however, greatly increased seedling stand and/or herbage yield at both sites and showed the benefits of using crop protectants, especially on direct-drilled re-seeds.     

Field evaluation of symbiotic nitrogen fixation by rhizobial strains using15N methodology

Summary Small differences in N₂ fixation by nodulated soybeans (Glycine max. (L.) Merr.), inoculated with various strains ofRhizobium japonicum, were assessed in field experiments using¹⁵N methodology, and compared with yields of plant dry matter and total N. Percentage of plant-N derived from atmospheric N₂ and from fertilizer, and values of %¹⁵N atom excess had lower coefficients of variation than did total N and dry matter yield. Nevertheless the precision of estimates of kg N/ha fixed were sufficient to differentiate only the extremes of the range of strains tested, and there were discrepancies between ranking of strains based on % N derived from fertilizer and on total N yield.     

Fluorescence Transients as Indicator for the Existence of Regulatory Mechanisms in Photosynthetic Electron Transport

In green algae several characteristic differences in the slope of the fast 685 nm fluorescence transient indicate the existence of different mechanisms for the regulation of the photosynthetic electron transport in vivo with respect to the requirements for ATP and NADPH. Autotrophically cultivated Chlamydobotrys stellata exhibits a normal time curve of the fluorescence yield. Anaerobiosis and C0₂-deficiency raise the O-, I- and S-level, whereas the P- level is lowered and the I-D-decay disappears. The readdition of oxygen increases the fluorescence significantly. Supplementation of aerobic cells with CO₂ restores the normal fluorescence transients. The replacement of carbon dioxide by acetate as a carbon source in the light lowers the overall fluorescence emission and abolishes the D-P-increase and the P-S-decline. The presence of DCMU increases fluorescence only at high intensities of incedent light. Anaerobiosis in these photoheterotrophic algae lowers the fluorescence emission. In this case DCMU increases fluorescence even at low light intensities. In Gonium multicoccum, which shows a normal fluorescence transient when cultivated autotrophically, CO₂-deficiency abolishes the O-level and increases the I- and S-niveau. Additional anaerobiosis in CO₂-deficient cells raises the steady state emission. Readdition of oxygen to these cells raises the I- and S-level even more and prevents the build up of the P-level. In Gonium     

Energy conservation during nitrate respiration in Paracoccus denitrificans

P/2e ratios were calculated from anaerobic chemostat cultures of Paracoccus denitrificans with nitrogenous oxides as electron acceptor. P/2e ratios were calculated, using the Y _ATP ^max values determined for aerobic cultures. When succinate was the carbon and energy source the average P/2e values of the sulphate-and succinate-limited cultures with nitrate as electron acceptor were 0.5 and 0.7, respectively, and of the nitrite-limited culture 0.9. With gluconate as carbon and energy source the average P/2e values of the gluconate-limited with nitrate as electron acceptor and nitrate limited cultures were 0.9 and 1.1, respectively.H⁺/O ratios measured in cells obtained from sulphate-, succinate, nitrite-, gluconate-and nitratelimited cultures yielded respective average values of 3.4, 4.5, 3.5, 4.8 and 6.2 for endogenous substrates. From our data we conclude that sulphate-and nitritelimitation causes the loss of site I phosphorylation. Nitrite has no influence on the maximum growth yield on ATP. We propose that metabolism in heterotrophically grown cells of Paracoccus dentrificans is regulated on the level of phosphorylation in the site I region of the electron transport chain.     

Quantum yield and energy dependence for photooxidation of chlorophyllide in greening wheat

Dark grown leaves of wheat were irradiated with red light of different intensities, at a temperature close to 0°C. The rate of photoreduction of the protochlorophyllide 650-form into chlorophyllide 684-form was measured. On continued irradiation the chlorophyllide 684-form was photodecomposed. By comparing the rates of the two processes the quantum yield for photooxidation of the chlorophyllide 684-form was calculated. The quantum yield was 2°10^-5 at an intensity of 2200 W m^-2, and increased with decreasing light intensity to 3.2°10^-5 at an intensity of 170 W m^-2.     

Growth yields and the efficiency of oxidative phosphorylation of Paracoccus denitrificans during two- (carbon) substrate-limited growth

Paracoccus denitrificans was grown aerobically during two-(carbon)substrate-limitation on mannitol and methanol in chemostat cultures. Theoretical growth parameters were calculated based on the presence of 2 or 3 sites in the electron-transport chain of Paracoccus denitrificans. Experimental growth parameters determined during two-(carbon)substrate growth were conform to the presence of 3 sites of oxidative phosphorylation, while cells grown only on mannitol possessed 2 sites. The maximum growth yield on adenosine triphosphate (ATP), corrected for maintenance requirements, determined in chemostat experiments in which the methanol concentration is less than 2.11 times the mannitol concentration was 8.6 g of biomass. When the methanol concentration was more than 2.11 times the mannitol concentration the maximum growth yield on adenosine triphosphate decreased due to the more energy consuming process of CO₂-assimilation. Cells use methanol only as energy source to increase the amount of mannitol used for assimilation purposes. When the methanol concentration in chemostat experiments was more than 2.11 times the mannitol concentration, all mannitol was used for assimilation and excess energy derived from methanol was used for CO₂-assimilation via the ribulose-bisphosphate cycle. The synthesis of ribulosebisphosphate carboxylase was repressed when the methanol concentration in chemostat experiments was less than 2.11 times the mannitol concentration or when Paracoccus denitrificans was grown in batch culture on both methanol and mannitol. When in chemostat experiments the methanol concentration was more than 2.11 times the mannitol concentration ribulose-bisphosphate carboxylase activity could be demonstrated and CO₂-assimilation will occur. It is proposed that energy produced in excess activates or derepresses the synthesis of the necessary enzymes of the ribulose-bisphosphate cycle in Paracoccus denitrificans. Consequently growth on any substrate will be carbonas well as energy-limited. When methanol is present in the nutrient cells of Paracoccus denitrificans synthesize a CO-binding type of cytochrome c, which is essential for methanol oxidase activity.The reason for the increase in efficiency of oxidative phosphorylation from 2 to 3 sites is most probably the occurrence of this CO-binding type of cytochrome c in which presence electrons preferentially pass through the a-type cytochrome region of the electron-transport chain.Non Standard Abbreviations X prosthetic group of methanol dehydrogenase - q _substrate specific rate of consumption of substrate (mol/g biomass. h.) - Y _substrate, Y _substrate ^MAX are respectively the growth yield and the maximum growth yield corrected for maintenance requirements (g biomass/mol) - m _substrate maintenance requirement (mol substrate/g biomass) - specific growth rate (h^-1) - M [methanol]/[mannitol] ratio in the nutrient - N part of mannitol that is assimilated when M=o - R _m amount of methanol-equivalents that has the same energy content as 1 mannitol-equivalent - P/O _N , P/O _F , P/O _X is the amount of ATP produced during electron-transport of two electrons from respectively NADH+H⁺, FADH₂ and XH₂ to oxygen     

长期不同养分投入对土壤养分和水稻生产持续性的影响

以中国科学院桃源农业生态试验站15a长期田间定位试验为研究对象,分析了不同养分投入对稻田土壤养分和水稻产量可持续性的影响.结果表明,化肥与系统内循环的有机物料循环的肥力效力和产量效应基本一致,有机物料循环更有利于土壤有机质和氮素的积累;在不同养分投入下,土壤耕层有机质和全氮均呈上升趋势,年均增长率分别为1.5%～5.8%和2.5%～9.4%;与试验前相比,不同养分投入耕层磷素变动幅度在-18.3%到30%之间,钾素养分有所亏缺,下降幅度在8.1%～22.6%之间;通过可持续性指数的分析得出,土壤N素养分的可持续性对化肥的依赖性较大,而P、K养分的可持续性则对有机肥的依赖性更高.稻田生态系统具有良好的自维持能力,系统内有机物循环有利于提高稻谷产量的稳定性和可持续性.     

Leaf traits of natural populations of <Emphasis Type="Italic">Adiantum reniforme</Emphasis> var. <Emphasis Type="Italic">sinensis</Emphasis>, endemic to the Three Gorges region in China

Leaf mass per unit area (LMA), carbon and nitrogen contents, leaf construction cost, and photosynthetic capacity (P _max) of Adiantum reniforme var. sinensis, an endangered fern endemic to the Three Gorges region in southwest China, were compared in five populations differing in habitat such as soil moisture and irradiance. The low soil moisture and high irradiance habitat population exhibited significantly higher LMA, area-based leaf construction (CC_A), and carbon content (C_A), but lower leaf nitrogen content per unit dry mass (N_M) than the other habitat populations. The high soil moisture and low irradiance habitat populations had the lowest CC_A, but their cost/benefic ratios of CCA/P _max were similar to the medium soil moisture and irradiance habitat population due to their lower leaf P _max. Hence A. reniforme var. sinensis prefers partially shaded, moist but well-drained, slope habitats. Due to human activities, however, its main habitats now are cliffs or steeply sloped bare rocks with poor and thin soil. The relatively high energy requirements and low photosynthetic capacity in these habitats could limit the capability of the species in extending population or interspecific competition and hence increase its endangerment.     

临泽绿洲边缘区棉花群体光合速率、蒸腾速率及水分利用效率

在甘肃河西走廊中部黑河中游绿洲边缘区,于6月下旬和8月上旬,利用Li-8100土壤碳通量测定系统与改进的同化箱联合对田间条件下早熟陆地棉(Gossypium hirsutum)品种新陆早8号的群体光合特性进行了研究.结果表明：试验地6月下旬的土壤呼吸速率和土壤蒸发速率显著高于8月上旬（P＜0.01）;棉花群体光合速率日变化均呈“单峰型”,6月下旬的群体光合速率显著高于8月上旬,其日平均值分别为（43.11±1.26）和（24.53±0.60）μmol CO₂·m^-2·s^-1, 差异极显著（P＜0.01）;群体蒸腾速率日变化也呈“单峰型”,6月下旬和8月上旬的日平均值分别为（3.10±0.34）和（1.60±0.26）mmol H₂O·m^-2·s^-1,两者存在极显著差异（P＜0.01）;6月下旬和8月上旬的群体水分利用效率日平均值分别为（15.67±1.77）和（23.08±5.54） mmol CO₂·mol^-1 H₂O,但差异不显著（P＞0.05）.两生育时期棉花群体光合速率与温度、光合有效辐射及土壤含水量均呈正相关关系.表明棉花群体光合速率在6月下旬和8月上旬均没有出现中午光合下调,8月由于土壤水分降低和植物叶片衰老,棉花群体光合速率和蒸腾速率显著降低,但水分利用效率并无显著下降.     

Atomic Layer Deposition of CdS Quantum Dots for Solid‐State Quantum Dot Sensitized Solar Cells

Functioning quantum dot (QD) sensitized solar cells have been fabricated using the vacuum deposition technique atomic layer deposition (ALD). Utilizing the incubation period of CdS growth by ALD on TiO₂, we are able to grow QDs of adjustable size which act as sensitizers for solid‐state QD‐sensitized solar cells (ssQDSSC). The size of QDs, studied with transmission electron microscopy (TEM), varied with the number of ALD cycles from 1‐10 nm. Photovoltaic devices with the QDs were fabricated and characterized using a ssQDSSC device architecture with 2,2',7,7'‐tetrakis‐(N,N‐di‐p methoxyphenylamine) 9,9'‐spirobifluorene (spiro‐OMeTAD) as the solid‐state hole conductor. The ALD approach described here can be applied to fabrication of quantum‐confined structures for a variety of applications, including solar electricity and solar fuels. Because ALD provides the ability to deposit many materials in very high aspect ratio substrates, this work introduces a strategy by which material and optical properties of QD sensitizers may be adjusted not only by the size of the particles but also in the future by the composition.