Historical change in coastal sage scrub in southern California,USA in relation to fire frequency and air pollution

Invasions resulting in the transformation of one ecosystem to another are an increasingly widespread phenomenon. While it is clear that these conversions, particularly between grassland and shrubland systems, have severe consequences, it is often less clear which factors are associated with these conversions. We resampled plots from the 1930s (Weislander VTMs) to test whether two widely assumed factors, changes in fire frequency and nitrogen deposition, are associated with the conversion of coastal sage scrublands to exotic grasslands in southern California. Over the 76-year period, coastal sage scrub cover declined by 49%, being replaced predominantly by exotic grassland species. Grassland encroachment was positively correlated with increased fire frequency and, in areas with low fire frequencies, air pollution (percent fossil carbon as indicated by ∂¹⁴C, likely correlated with nitrogen deposition). We conclude that increases in fire frequency and air pollution over the last several decades in southern California may have facilitated the conversion of coastal sage shrubland to exotic grassland systems.     

脂肪与肥胖相关基因对动物脂肪代谢的调节

脂肪与肥胖相关(fat mass and obesity associated,FTO)基因是一种与普通肥胖相关的等位基因,该基因导致的肥胖是21世纪世界各国面临的最大公共卫生挑战之一。FTO基因与机体的普通肥胖有着密切的关系,而且与脂肪沉积和脂肪代谢相关激素及基因的表达有关。本文综述了FTO基因在脂肪细胞分化和脂肪代谢中的作用,揭示了FTO基因对脂肪沉积的影响,为深入研究动物脂肪代谢的机制提供理论基础。     

大气氮沉降及其对草地生物多样性的影响

随着人类活动的加强,大气氮素沉降在逐渐增加, 已对海洋和陆地生态系统产生了明显的影响.为此总结了大气干湿沉降中氮的组成和数量变化等特点,并在此基础上,分析评述了大气氮沉降对草地生态系统中植物、动物和微生物群落发展的影响,提出了今后研究的方向.     

Analysis on Internal Stress in Polycrystalline Diamond Films Measured by Raman Spectroscopy

The divagation of the internal stress in diamond films is analyzed .It's found that due to the unknown directions of the stress and crystallographic axes , the proportional parameter to express the relationship between the stress and the shift of Raman spectrum is hard to obtain precisely , resulting in the divagation of the internal stresses which are calculated from the shift of Raman spectrum.     

The Motion Characteristics and Deposition Efficiency of Particles in the Gas -Particle Rotary Flow

Based on the motion equations of particles in the gas-particle rotary flow,the relationship among the equivalence particle diameter, characteristic time of the nonequivalence particle and their deposition efficiency is analyzed , and then the results of this study agree very well with the experimental data .     

长期施用硫酸盐肥料对土壤性质和水稻生长的影响

本文就长期施用硫酸盐肥料对土壤性质和水稻生育的影响进行了系统研究。实践证明,硫酸盐肥料能促使土壤有机质缓慢积累,能提高土壤中磷的有效性,能活化粘土矿物晶格中所固结的钾素,改善土壤钾素供应状况。土壤中速效氮、磷、钾动态变化的趋势是一致的,在早稻生育期间（5月底6月初）速效氮、磷、钾有一个高峰期。一般说,铵态氮的高峰期比较早,速效磷、钾的高峰期比铵态氮略迟。在晚稻生育期间,这些养分的动态变化与早稻生育期间不同,有效磷保持相对稳定,有效钾直线下降。其原因及其对水稻生育的影响有待进一步研究。长期施用硫酸盐肥料,对稻米蛋白质含量和氨基酸组成也有影响,优化施肥能提高稻米蛋白质含量。含硫氨基酸如蛋氨酸,胱氨酸的含量,早稻比晚稻高;碱性氨基酸的含量,晚稻比早稻高。     

New sampler for dry deposition in forest canopy

A new type of sampler for dry deposition in a forest canopy was designed and tested to confirm its usefulness. The new sampler is made of Teflon chips packed in a nylon net, and tied on a rod like a branch in the canopy. The validity and characteristics of the new sampler were checked by comparing it with the conventional bucket sampler and the foliar extraction method using hinoki (Chamaecyparis obtusa) trees. The comparison between the deposited amounts on the dummy branch and those on the bucket indicates that the dummy could trap gaseous matter more effective than the bucket. From a comparison with the foliar extracting method, it is concluded that the trapping of particulate matter by the new dummy branch is comparable to that of natural needle leaves. However, its efficiency for gaseous matter is relatively small. This disadvantage should be improved by applying other materials to the dummy. Moreover, it is found that the uptake of gas especially SO₂ through the stomata is an important point in the discussion about dry deposition. To evaluate the amounts of dry deposition in the forest canopy more precisely, combination with the additional method should be useful. This study was supported in part by a grant-in-aid for Scientific Research from the Ministry of Education, Science, Sports, and Culture, Japan.     

Dynamics and stratification of Enchytraeidae in the organic layer of a Scots pine forest

In a Dutch Scots pine forest an experiment was conducted to quantify the role of soil biota in the functioning of the soil ecosystem, and the effects of enhanced nitrogen deposition. For this, the site was sampled at 8-week intervals during 2.5 years. This paper reports on the population dynamics of enchytraeids in the field and in stratified litterbags. Mean yearly abundance of the enchytraeid community in the field was 47 600 m^–2, or 0.70 g (dry weight) m^–2. The community consisted mainly of three species: Cognettia sphagnetorum, Marionina clavata and Achaeta eiseni, of which C. sphagnetorum was dominant. The enchytraeid populations showed a marked stratification in the same sequence. Freshly fallen pine needles were colonized by C. sphagnetorum, while other species followed much later. It was found that data from the litterbags were reasonably comparable with field data, when expressed per gram of dry substrate, but less so when expressed per square metre. Multiple regression analysis of the data showed that the population dynamics in the litter layer could largely be explained by temperature and moisture fluctuations; in deeper layers other factors, such as the stage of decomposition, were probably more important. Received: 26 June 1997     

Response of protozoan and microbial communities in various coniferous forest soils after transfer to forests with different levels of atmospheric pollution

During recent decades, forest ecosystems have been exposed to high levels of atmospheric pollution, and it has been argued that this affects the composition and activity of decomposer communities and, subsequently, ecosystem functioning. To investigate the effects of atmospheric pollution on protozoa and microflora, a new experimental design was used. Undisturbed soil columns, originating from six coniferous forests across Europe and representing different stages of soil acidification, were transferred to two Scots pine forests (Fontainebleau and Wekerom) with different levels of N and S deposition (NH₄ ⁺-N=4.90 and 42.50?kg ha^–1 year^–1; SO₄ ^–S=10.90 and 30.40?kg ha^–1 year^–1, respectively). The number of protozoa, microbial biomass C and microbial activity were estimated in the organic layer (Of) of the transferred soils at the two host sites after 21 months of incubation. The experiment aimed at answering two questions: (1) Do changes in environmental conditions, studied by transferring soils from one site to another, affect protozoa and microbial communities and, if so, (2) how important are changes in both N and S deposition in explaining the effects of soil transfer on protozoa and microbial communities? The interaction between protozoa and microbial communities was addressed with regard to these changes in environmental conditions. No effect of enhanced N or S deposition on protozoan numbers and microbial biomass C, basal respiration and caloric quotient was revealed. Reciprocal transfer of various soil columns resulted in lower abundance and activity of protozoa and microbes. This reduction could not be explained by differences in N and S deposition, but by differences in microclimate and adaptation. In some cases, protozoa correlated with pH, C/N ratio, P and S content and leached mineral N.