不同钙浓度对烤烟生长及镁吸收的影响

为研究钙浓度对烤烟生长及镁吸收的影响,以烤烟K326为试验材料,采用营养液培养方式,测定不同Ca²⁺浓度下,烤烟各生育时期的农艺性状、生物量、团棵期及现蕾期烟叶钙和镁含量及钙镁比,并对Ca²⁺浓度与烟叶钙镁含量和农艺性状进行相关性分析。结果表明：上、下部叶片镁含量与培养液Ca²⁺浓度呈显著负相关;中部叶片镁含量与烟叶钙含量呈显著负相关。Ca²⁺浓度为12.25mmol/L时烤烟的长势最佳,为11.22mmol/L时最有利于烤烟叶片生物量的积累。烤烟生长的最佳根际Ca²⁺浓度为11.22~12.25mmol/L。     

Experimental establishment of a declining dry-grassland flagship species in relation to seed origin and target environment

Supporting species persistence may involve (re)connecting suitable habitats. However, for many declining species habitat suitability and drivers of establishment are poorly known. We addressed this experimentally for a declining flagship species of dry grasslands in Germany, Armeria maritima subsp. elongata. In three regions, we sowed seeds from each of eight source populations back to their origin and to eight apparently suitable, but currently unoccupied, habitats close to the source populations. Overall, seeds germinated and seedlings established equally well in occupied and potential sites indicating that suitable habitats are available, but lack seed input. Germination and establishment varied among sowing sites. Moreover, seeds from populations of lower current connectivity established less well in new sites, and establishment was more variable among seeds from smaller than from larger populations, possibly reflecting genetic consequences of habitat fragmentation. Further, establishment across different new environments differed between seeds from different populations. As this was neither related to a home-away contrast nor to geographic or environmental distance between sites it could not clearly be attributed to local adaptation. To promote long-term persistence within this dry-grassland meta-population context we suggest increasing the density of suitable habitats and supporting dispersal connecting multiple sites, e.g. by promoting sheep transhumance, to increase current populations and their connectivity, and to colonise suitable habitats with material from different sources. We suggest that sowing experiments with characteristic species, including multiple source populations and multiple recipient sites, should be used regularly to inform connecting efforts in plant conservation.     

松嫩平原不同旱地生境芦苇的光合特性研究

芦苇是世界广布植物。在松嫩平原不同旱地生境，芦苇叶片的净光合速率日变化均为双峰曲线，有明显的光合“午休”现象。在草甸、沙地和碱斑生境，芦苇光合“午休”现象是气孔限制因素所致，低洼生境则由叶肉光合能力下降所致。芦苇叶片的净光合速率以碱斑生境最高，以长期受到林荫影响的沙地生境最低。4个旱地生境芦苇的光响应曲线具有相同的规律性变化，均可用二次方程定量刻画。芦苇的光补偿点和光饱和点与生境土壤条件无关，只与光照条件有关。在长期林荫影响下的沙地生境，芦苇的光补偿点和光饱和点均较低。     

红壤丘陵茶园镁营养调控研究

对湘南红壤丘陵茶园土壤及茶叶中镁素含量进行了测定,结果得到土壤有效镁含量在6.29-25.98 mg/kg,平均为13.02 mg/kg,显示缺镁症叶片的有效镁含量为264.10 mg/kg。在缺镁茶园施用水溶性硫酸镁肥料后,缺镁症逐渐消失,产量比对照平均增长9.8％—13.6％。喷施含镁叶肥试验结果平均增产20.8％。施镁还能显著改善茶叶品质,氨基酸、咖啡碱及水浸出物含量分别比对照提高5.8％,9.2％、2.3％。文章还讨论了我国南方红壤丘陵茶园镁营养的现状及今后镁肥开发的思路。     

Pollination requirements for seed set in ulluco (Ullucus tuberosus)

Summary Pollination experiments were carried out on ulluco (Ullucus tuberosus), known as a very poor seed producer. All the clones used were diploids. The effect of self-vs. cross-pollination was studied in Experiment 1. Caged selfpollinated flowers produced no seeds. Different clones produced seeds in 0–8% of caged cross-pollinated flowers and in 5–19% of cross-pollinated non-caged flowers. Ulluco is thus basically an outbreeder.Experiment 2 studied whether seed set is limited by pollen availability. Total seed number per inflorescence number did not differ between plants treated with supplemental pollen and control plants; pollen availability thus did not limit seed set. The treated plants, however, produced more seeds in cross-pollinated than in other flowers on the plant, and the control flowers on treated plants produced fewer seeds than those on the control plants. In the treated plants, resources may have been allocated to artificially cross-pollinated flowers at the expense of other flowers. In some clones, seed set after artificial cross-pollination was at a level practicable for breeding work.     

小四轮拖拉机配套农具纵垂面内悬挂参数和重量限度的计算机辅助设计

本文针对小四轮拖拉机悬挂机构的提升行程和提升能力,研究了确定其配套农机具在纵垂面内悬挂参数及重量限度的计算机辅助设计方法;提出了小四轮拖拉机配套农具的瞬心π₁点的合理设计区域。计算结果说明提高农具的设计重量限度和重力入土力矩与提高其运输间隙是矛盾的,结合设计优化目标能迅速的设计出最佳方案。     

Pollen-limited production of viable seeds in an endemic dwarf birch, Betula apoiensis, and incomplete reproductive barriers to a sympatric congener, B. ermanii

An endemic dwarf birch, Betula apoiensis, is critically endangered, and two populations of this species are restricted to the ridges of Mt. Apoi in Hokkaido, Japan. We observed the flowering phenology, pollen dispersal, and viable seed production and conducted pollination experiments in order to examine pollen limitation and hybridization with a sympatric congener, B. ermanii. B. apoiensis flowered earlier than B. ermanii but had a more variable flowering time among trees than B. ermanii. The female flowering of B. apoiensis temporally overlapped with the male flowering of B. ermanii as well as with that of B. apoiensis. Pollination experiments demonstrated that seed set and seed germination were higher in female flowers outcrossed than in those that were non-pollinated, selfed, hybridized with B. ermanii pollen, or pollinated naturally. A few selfed or hybrid seeds were filled and germinated, which indicates that self-incompatibility and reproductive barriers are not complete. Logistic regressions of local density of conspecific trees on natural seed set and seed germination were significantly positive. These results suggest that B. apoiensis is pollen-limited.     

Population decline in the epiphytic orchid Aspasia principissa

The population dynamics of the epiphytic orchid Aspasia principissa, growing in the moist tropical forest of Barro Colorado Island, Panama, were studied from 1997 until 2004. Using growth analysis, projection matrix analysis, elasticity analysis, and different types of simulations, we identified the components of the life cycle with the strongest effect on population growth rate (λ), and related differences in vital rates to environmental variation, mainly in precipitation. Such information, which is almost completely lacking for tropical orchids, is essential for the efficient conservation of these frequently rare and endangered plants. Elasticity analysis indicated that the population growth rate (λ), which averaged 0.92, was primarily affected by survival, and much less affected by growth or by sexual reproduction. Simulations, which included different levels of pollinator limitation, showed that complete pollination would raise λ to such an extent as to allow long-term persistence of the population. Pollinator limitation per se, however, is presumably not responsible for the currently observed population decline. Instead, we discuss a possible link between low λ and (a) a long-term decline in precipitation and (b) recent increases in forest dynamics: variation in annual rainfall significantly affected both recruitment and growth rates of smaller orchid individuals, while the hypothesised increase in the rates of branch and tree falls would increase mortality rates in this epiphyte.     

The mycorrhizal fungus (Glomus intraradices) affects microbial activity in the rhizosphere of pea plants (Pisum sativum)

Pea plants were grown in γ-irradiated soil in pots with and without addition of the AM fungus Glomus intraradices at sufficient N and limiting P. Depending on the growth phase of the plant presence of AM had negative or positive effect on rhizosphere activity. Before flowering during nutrient acquisition AM decreased rhizosphere respiration and number of protozoa but did not affect bacterial number suggesting top-down regulation of bacterial number by protozoan grazing. In contrast, during flowering and pod formation AM stimulated rhizosphere respiration and the negative effect on protozoa decreased. AM also affected the composition of the rhizosphere bacterial community as revealed from DNA analysis (DGGE). With or without mycorrhiza, rhizosphere respiration was P-limited on very young roots, not nutrient limited at more mature roots and C-limited at withering. This suggests changes in the rhizosphere community during plant growth also supported by changes in the bacteria (DGGE).