氮素在果树成花过程中的作用

综述了氮素在果树成花过程中的作用,认为氮及含氮化合物是果树成花过程中重要的物质,其影响到果树从营养生长向生殖生长的转化,影响花粉的可育性和雌雄花的比例,影响花的质量。花芽的生理分化及形态分化期间都伴随氮素及含氮物质的波动,不同形态的含氮物质在成花过程中的作用也不同。花芽诱导措施都强烈地影响果树体内氮素及含氮化合物的水平。     

夏季运动场遮阳对舍饲小尾寒羊行为和生理指标的影响

为改善运动场的热湿环境，减少太阳辐射给舍饲小尾寒羊造成的热应激，该文作者于2004年夏季在内蒙古赤峰市某规模化羊场，采用了运动场架设遮阳棚的方式。该试验着重对遮阳棚(试验组)和露天运动场(对照组)的温热环境，以及小尾寒羊的行为和生理指标等方面进行了测试分析。试验结果表明，架设遮阳棚后，可以明显地改善舍饲运动场的热湿环境，遮阳棚内的温湿指数(THI)、辐照度和地面温度均显著小于露天运动场；遮阳棚可以使小尾寒羊比较稳定地休息与反刍，同时随着外界环境THI值的增大，选择遮阳棚的羊的数量以及羊在遮阳棚内的活动时间都随之增加；运动场遮阳有利于减缓小尾寒羊的生理应激，可以使小尾寒羊在高温时段保持正常的生理指标。     

黄土高原丘陵沟壑区农户水土保持行为研究

采取问卷调查的方式 ,对黄土高原丘陵沟壑区农户的水土保持行为进行了研究 ,结果显示农户进行水土保持的目的是追求自身利益的最大化 ,这和国家希望通过治理水土流失改善这一地区的生态环境 ,确保黄河及中下游地区的安全目标存在一定的差异。提出了协调农户和国家目标及诱导农户进行水土保持的政策措施。     

Is the reintroduced white stork (Ciconia ciconia) population in Switzerland self-sustainable?

The migratory white stork (Ciconia ciconia) became extinct in Switzerland in 1950. A reintroduction project with intensive management (translocation, prevention of migration, artificial feeding) started in 1948, and 175 pairs were breeding in 2000. For the period 1973-2000 we estimated annual survival rates and fledging success to estimate the population growth rate by a stochastic matrix projection model. Compared to other populations, adult survival rate (0.86, with 95% CI: 0.81-0.89) was very high and little variable over time, juvenile survival (0.37, CI: 0.31-0.43) was comparable to other populations whereas the average fledging success was low (1.65) but strongly variable over time. The population growth rate was positive, indicating that the population is self-sustainable at the moment. The growth of the white stork population was largely favoured by the high adult survival which more than compensates for the low fledging success. The population growth rate is particularly sensitive to changes in adult survival, but it would be very difficult to improve this further with management. However, maintenance of the high adult survival is crucial and an improvement in fledging success seems important for the long-term persistence of the white stork population in Switzerland. Fledging success depends on habitat quality, and thus restoration of breeding habitats should be the main management activity in the near future.     

A captive population in crisis: Testing hypotheses for reproductive failure in captive-born southern white rhinoceros females

The captive southern white rhinoceros (Ceratotherium simum simum) population is not self-sustaining. Many founders reproduced, but reproduction among captive-born (F₁) females has been extremely sluggish. Thus the conservation breeding program for this species faces a looming crisis. Using behavioral observations of a large captive population and a questionnaire survey circulated to facilities worldwide, several hypotheses for F₁ female reproductive failure were evaluated. Counter to predictions regarding behavioral deficiency in sociosexual behaviors, F₁ females were at least as proficient as F₀ females for all behavioral measures. Males also showed no sociosexual preferences for F₀ over F₁ females. Results indicate that most reproductive failure occurs post-copulation. The reigning root-cause hypothesis for F₁ female reproductive failure postulates that F₀ females are behaviorally dominant and suppress reproduction in F₁ females. However, no evidence for behavioral dominance was found and F₁ females housed with F₀ females were more likely to reproduce than those housed without F₀ females. Such social facilitation of reproduction is beneficial to F₁ female reproduction, but does not explain differential reproduction between F₁ and F₀ females. Because the design controlled for current conditions, these results point to development in captivity as the root cause of postcopulatory reproductive failure in F₁ females.     

Colonization of the rhizosphere, rhizoplane and endorhiza of garlic (Allium sativum L.) by strains of Trichoderma harzianum and their capacity to control allium white-rot under field conditions

Five strains (C4, C13, C17, C30, C44) of Trichoderma harzianum that efficiently antagonise Sclerotium cepivorum in vitro, were used in central México to inoculate field grown garlic (Allium sativum L.). Endorhiza, rhizosphere and soil colonization were evaluated at different times and at various root and soil depths. Experiments were conducted in both the 2000 and 2001 crop cycles to evaluate the capacity of five strains as biological control agents (BCA) against S. cepivorum. Significant differences were observed among the strains in terms of their ecological behavior. Strain C4 showed the best endorhizal and rhizosphere colonization. Strain C44, besides being a good rhizosphere colonizer, dispersed widely in the soil. In terms of all three variables, strain C30 had poor colonization ability, whereas the strains C4, C17 and C44 were best able to control white rot in the field. Of these, strain C4 showed the best performance over 2 years when it was applied as a pre-colonized substrate at planting time. High early endorhizal colonization was positively correlated with the BCA capacity of the strains. These data suggest that the ecological behavior of Trichoderma strains should be included as a criterion for strain selection for biological control purposes.     

The effect of feeding behavior on Hg accumulation in the ecophysiologically different earthworms Lumbricus terrestris and Octolaseon cyaneum: A microcosm experiment

 A soil microcosm experiment was performed to assess the uptake of Hg from various Hg-spiked food sources (soil, leaf litter and root litter of Trifolium alexandrinum) by two earthworm species, Lumbricus terrestris (anecic) and Octolaseon cyaneum (endogeic). Treatments were applied in which one of the three food sources was Hg spiked and the other two were not. Additional treatments in which all or none of the food sources were Hg spiked were used as controls. Uptake of Hg from soil into tissues of both earthworm species was significantly higher than uptake of Hg from leaf litter or root litter, indicating that soil may be the most important pool for the uptake of Hg into earthworms. In addition, the anecic L. terrestris significantly accumulated Hg from all Hg-spiked food sources (leaf litter, root litter and soil), whereas the endogeic O. cyaneum took up Hg mainly from soil particles. Interestingly, there was no further increase in Hg in L. terrestris when all food sources were Hg spiked compared to the single Hg-spiked sources. This may be attributed to the relatively high Hg content in the soil, which may have influenced the feeding behavior of the earthworms, although their biomass did not significantly decline. We suggest that, in addition to the physiological differences, feeding behavior may also play a role in the contrasting uptake of Hg by the two earthworm species.     

Designing a spatially-explicit nature reserve network based on ecological functions: An integer programming approach

An effective nature reserve network design should reflect the ecological requirements of target species, while simultaneously considering costs. In this study, we propose a design method that considers the ecological role of the spatial arrangement of reserve sites in relation to the long-term persistence of metapopulations of the target species. We apply our design method to an amphibian metapopulation, which illustrates how varying the emphasis on the importance of design factors can affect estimated metapopulation persistence. Comparisons among reserve design methods show that considering the ecological function, rather than generic spatial rules, of the spatial location of reserve sites may be more likely to support species survival. A piecemeal treatment or mechanistic application of spatial rules in reserve design may be subject to the risk of not producing the most effective reserve network, and in some cases may even compromise the conservation objective which could be achieved otherwise.     

Characterization of a USDA Kentucky Bluegrass (Poa pratensis L.) Core Collection for Reproductive Mode and DNA Content by Flow Cytometry

Kentucky bluegrass (Poa pratensis L.) is an important turf and forage grass species with a facultative apomictic breeding behavior. In this study, mature seed and leaf tissue from 38 accessions of a USDA core collection of Kentucky bluegrass were analyzed with flow cytometry to characterize the reproductive mode and DNA content for each accession. Major reproductive pathways for each accession were determined based upon the presence and the position of the peaks observed and the known methods of reproduction for Kentucky bluegrass. While the majority of the accessions exhibited facultative apomictic reproductive behavior with a combination of reduced, zygotic and unreduced, parthenogenic embryo production, obligate sexual or obligate apomictic accessions were also found to be present in this core collection. In addition, reduced, parthenogenic and unreduced zygotic embryos were also detected in several accessions. Flow cytometric analysis of somatic tissue revealed a large range of DNA variation within this core collection. We also examined the sensitivity of flow cytometry in analyzing bulked samples containing a large number of plants with varied DNA content and determined that flow cytometry can effectively detect a plant having a different DNA content within a 15-plant bulk sample. Overall the combination of mature seed and somatic tissue analysis generated important information for the Kentucky bluegrass core collection and can be an effective and affordable tool to characterize even greater numbers of Kentucky bluegrass accessions.