轻小型移动式喷灌机组现状及其与国外的差距   总被引：5，自引：3，他引：5  

潘中永  刘建瑞  施卫东  刘厚林  金树德 《排灌机械》2003,21(1):25-28

节水灌溉是农业现代化的重要组成部分，发展节水灌溉、提高水的利用率是实现农业现代化的必由之路。通过对国内相关厂家的调研，初步分析了我国轻小型移动式喷灌机组的现状及其与国外先进水平之间存在的差距。在此基础上，提出了今后研究工作的具体目标。  相似文献   

中国基本养老保险制度财务平衡与可持续性研究——基于国发［2005］38号文件形成的城镇基本养老保险制度     

刘昌平  殷宝明 《湖南农业大学学报(自然科学版)》2011,(1):19-24

采用“到期债务”定义，按照国发［2005］38号文件形成的制度模式，通过构造公式测算了基本养老保险制度的隐性债务、转制成本理论值以及基金缺口的期限结构。结论表明：做实个人账户真正实现了“统账结合、分账管理、实账运行”；社会统筹账户基金缺口规模被有效降低，偿债周期可以接受；社会统筹账户是一个精算盈余的制度安排，缴费率存在下降空间；参保率和缴费基数对基金缺口规模的影响很大，应进一步提高参保率和严格规范缴费基数。  相似文献   

Simulating responses of Northeastern China forests to potential climate change   总被引：5，自引：0，他引：5  

赵士洞  延晓冬  杨思河  陶大立  代力民 《林业研究》1998,9(3):166-172

IntroductionItissurethatpresentelevatiollsofCO2a11dotllergrcc11-housegasesinducedbyhumanactivitiesaren1akli1gglobalclimategothroughinexperielICedcl1anges(Scl1le-subgerl987).Thecurrentquasi-equilibriulllstatesofbio-sphereecosystCm,esPeciallyterrestrialecosystems,wouldbebrokenbecausetl1estructure,fu11ction,distributio11andtlledynamicsofanyexistedecosystemsareIberesultsoflongtermadaptationofbio-systemtocurrentclin1ate.Theec()systemsdistributedinhighlatitlldeareawouldhavemuchbiggerchai1ge(Bona…  相似文献   

Canopy recruitment in the beech (<Emphasis Type="Italic">Fagus engleriana</Emphasis>) forest of Mt. Shennongjia,Central China     

Quanfa Zhang  Mingxi Jiang  Feng Chen 《Journal of Forest Research》2007,12(1):63-67

A dendrochronological technique was used to investigate canopy recruitment of beech (Fagus engleriana Seem.) trees in western Hubei Province of Central China by identifying growth releases through gap formation. The results indicated that 83% and 17% of the canopy trees regenerate in gaps and the understory, respectively. Radial growth analyses demonstrated that there are three modes for beech regeneration and canopy recruitment: (1) gap origin without suppression; (2) gap origin with period(s) of suppression; and (3) understory origin. Multiple periods of release and suppression imply that beech regeneration and canopy recruitment are very sensitive to gap formation.  相似文献   

Spatial pattern and regeneration dynamics in a temperate Abies–Tsuga forest in southwestern Japan     

Yasuhiro Kubota 《Journal of Forest Research》2006,11(3):191-201

This article reports the regeneration dynamics of a temperate Abies–Tsuga forest in Kirishima Yaku National Park, southwestern Japan, and examines the influence of species coexistence mediated by gap disturbances on biomass production. All trees taller than 2 m in a 1-ha plot were monitored over four growing seasons. Three growth-form groups occupied different vertical layers. Evergreen conifers and deciduous broad-leaved trees tended to be spatially segregated from evergreen broad-leaved trees, which formed thickets in the understorey. The regeneration of understorey evergreen broad-leaved trees was affected by canopy gaps. The recruitment of conifers and deciduous broad-leaved species was not observed during the four growing seasons. This suggests that regeneration is sporadic and the present environmental conditions are not favorable for these canopy species. The mortality and unsuccessful recruitment of conifers and deciduous trees appeared to cause fluctuations in the productivity of the stand. However, an abundance of canopy gaps accelerates the regrowth of shorter species, and the fluctuation of productivity resulting from the population dynamics of canopy species would be partly mitigated by the regeneration of evergreen understorey species. The horizontal and vertical heterogeneity of the temperate mixed forest was a result of the patch structures of the three growth-form groups. The different regeneration patterns among the three groups, which were driven by interactions of species-specific regeneration niches and disturbance regimes, might be an important factor in maintaining the aboveground productivity in a transitional mixed forest between warm-temperate and cool-temperate zones.  相似文献   

Effects of light and microsite conditions on tree size of 6-year-old Cryptomeria japonica planted in a group selection opening     

Toru Kohama  Nobuya Mizoue  Satoshi Ito  Akio Inoue  Kotaro Sakuta  Hiroyuki Okada 《Journal of Forest Research》2006,11(4):235-242

We examined the extent to which direct and indirect measures of light and microsite conditions could explain variation in tree height and diameter at the base of 6-year-old Cryptomeria japonica trees planted in a group selection opening of about 0.32 ha on a steep slope at Shiiba, Miyazaki Prefecture, southern Japan. We first used the gap light index (GLI) and soil thickness (ST) as directly measured indices. For an indirect measure of light, we used a between-cohort competition index (BCI) estimated from the position and total height of residual trees. For indirect measures of microsite, we examined topographic indices (slope, plan and profile curvature, average slope gradient, and relative elevation) derived from digital elevation models (DEMs) with different resolutions ranging from 2 to 10 m. The multiple linear regression using GLI and ST explained about 45% of variation in tree size, while simple regression using only GLI explained about 35%. The contribution of ST was about half of GLI. The multiple regressions using BCI and the topographic indices did not explain any more variation than using BCI alone (R ² of about 0.26). We conclude that microsite conditions with shallower soil and steeper slope have negative effects on tree growth in group selection openings, although the relative importance is smaller than light conditions. More comprehensive studies considering several openings with more heterogeneous topography including different species are needed to generalize our growth prediction using the indirect measures, which are useful for practical forest management.  相似文献   

Overstory and shrub effects on natural regeneration processes in native Pinus radiata stands     

Michael J. O&#x;Brien  Kevin L. O&#x;Hara  Nadir Erbilgin  David L. Wood 《Forest Ecology and Management》2007,240(1-3):178-185

Native Monterey pine (Pinus radiata D. Don) stands on the Monterey peninsula have been significantly modified by natural and anthropogenic disturbances. The exclusion of fire and the introduction of pitch canker (caused by Fusarium circinatum Nirenberg & O’Donnell) created a need for the examination of these changing ecosystems with respect to regeneration, especially as these stands reach mature ages. We established 210 plots on 35 transects distributed throughout five stands in order to describe the current stand structure and quantify the extent and condition of regeneration. The results indicated that Monterey pine seedling establishment varies throughout the peninsula depending on percent canopy cover, duff and litter depth, and percent shrub cover while seedling growth is influenced by percent shrub cover. Canopy cover was also found to inversely influence shrub cover. Our study highlights the importance of understory removal to increase Monterey pine regeneration and seedling growth as canopy cover decreases, especially in areas where coast live oak (Quercus agrifolia Nee) and poison-oak (Toxicodendron diversilobum E. Greene) are abundant.  相似文献   

林隙(GAP)干扰研究进展   总被引：76，自引：3，他引：76  

臧润国  徐化成 《林业科学》1998,34(1):90-98

本文系统地介绍了森林循环的理论、自然干扰的概念、林隙的一般特征和林隙干扰的时空格局。干扰是森林循环的驱动力,干扰形成的林隙是森林循环的起点。林隙的大小、形成年龄、形成方式以及形成木的特征是研究林隙特征的重要参数,虽然不同森林群落中,林隙干扰的频率和程度及其时空变化规律不同,但大多数森林的年平均干扰率是在１％左右。不同的森林类型中,大、小型干扰的比例不同。小型林隙干扰与大型灾难性干扰在不同时空条件下的组合,就形成了不同森林景观的时空变化格局。  相似文献   

Effects of synthetic kainic acid on microfilament expression and gap junction in astrocytes     

ZHANG Jie  XU Hua 《园艺学报》2014,30(5):937-941

AIM：To study the effects of synthetic kainic acid (SKA) and 1-heptanol (1-Hep), a gap junction blocker, on the cytoskeletal filament expression in the astrocytes. METHODS：The neonatal rat brain was obtained from the Wistar rats (1 day old) and primary purified astrocytes were obtained by differential attachment for removing filamentoblasts and orbital shaker for removing the oligodendrocytes. The effects of SKA and other interventions on the morphologic changes and expression levels of skeleton protein filamentous actin (F-actin) were observed in the astrocytes after 24 h of the exposures by laser scanning confocal microscopy. The effect of 1-Hep on the expression of F-actin was also explored. RESULTS：Compared with control group, the fluorescence intensities in KCl group and KCl+SKA group were increased, and highly increased in KCl+SKA group. The F-actin filaments in the above 2 groups were more intensive, thickened and concentrated than those in control group, and more obvious in KCl+SKA group. l-Hep significantly decreased the expression of F-actin in KCl group and KCl+SKA group as compared with control group, and parts of the filamentous fracture were seen in the astrocytes in all 1-Hep-treated groups, in which some of the filamentous lines were crosscut. CONCLUSION：Increase in the expression of F-actin in the astrocytes affects the structure and function of the intercellular gap junctions, which may be involved in the mechanism of SKA-induced epilepsy.  相似文献   

闽楠林窗更新的立地因子效应研究     

欧建德 《安徽农业科学》2014,(21):7057-7058

该研究应用数理化理论模型Ⅰ的方法,对福建明溪闽楠林窗更新培育基地进行样地调查与数据收集,分析探讨不同立地因子对林下闽楠生长效应的影响。结果表明,影响林窗更新闽楠生长的主要因素依次是坡位、坡向、坡度,且对闽楠生长影响均达到极显著。在闽楠林窗更新过程中,进行坡位、坡向和坡度选择十分必要。  相似文献