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991.
通过对长沙市园林地被植物应用情况的实地调查,发现目前长沙市园林常用的地被植物约40种,分析了长沙市园林中宽阔地域、小面积地域、人工湖及人工溪流旁、坡和角以及林下等4种不同的地被植物的配置应用形式及目前存在的问题,并提出了发展对策. 相似文献
992.
三倍体杨树具有突出的营养生长优势,研究造林密度对三倍体毛白杨杂种无性系径向生长的影响规律,可为三倍体毛白杨工业用材林营建和经营管理提供理论指导。以定植于河北威县的11年生三倍体白杨杂种无性系(B301、B331和S86)以及二倍体毛白杨对照无性系1316密度试验林为研究对象,研究造林密度(2 490、1 665、1 110、825、615、495株/hm2和405株/hm2)对三倍体白杨杂种无性系胸径和树皮厚度的影响。结果表明,造林密度和无性系以及造林密度与无性系间的交互效应均对三倍体白杨杂种无性系的胸径生长具有极显著的影响,以495株/hm2造林密度条件下三倍体白杨杂种无性系S86的胸径生长量最大,平均胸径达25.1 cm;三倍体白杨杂种无性系B301、S86的胸径生长量显著大于无性系B331和二倍体对照毛白杨无性系1316;无性系对11年生三倍体白杨杂种无性系的树皮厚度具有极显著的影响,造林密度对11年生三倍体白杨杂种无性系的树皮厚度具有显著的影响。三倍体白杨杂种无性系B301、B331、S86以及二倍体对照毛白杨无性系1316内部个体间胸径与树皮厚度均呈现正相关,说明树皮厚度随着胸径生长量的增大而增厚。研究结果对于认识造林密度对杨树径向生长的影响和指导三倍体白杨良种无性系的推广具有重要意义。 相似文献
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Michael Dannenmann Judy Simon Rainer Gasche Jutta Holst Ingrid Kögel-Knabner Helmut Mayer Rodica Pena Heinz Rennenberg 《Soil biology & biochemistry》2009,41(8):1622-1631
Nitrogen (N) cycling in terrestrial ecosystems is complex since it involves the closely interwoven processes of both N uptake by plants and microbial turnover of a variety of N metabolites. Major interactions between plants and microorganisms involve competition for the same N species, provision of plant nutrients by microorganisms and labile carbon (C) supply to microorganisms by plants via root exudation. Despite these close links between microbial N metabolism and plant N uptake, only a few studies have tried to overcome isolated views of plant N acquisition or microbial N fluxes. In this study we studied competitive patterns of N fluxes in a mountainous beech forest ecosystem between both plants and microorganisms by reducing rhizodeposition by tree girdling. Besides labile C and N pools in soil, we investigated total microbial biomass in soil, microbial N turnover (N mineralization, nitrification, denitrification, microbial immobilization) as well as microbial community structure using denitrifiers and mycorrhizal fungi as model organisms for important functional groups. Furthermore, plant uptake of organic and inorganic N and N metabolite profiles in roots were determined.Surprisingly plants preferred organic N over inorganic N and nitrate (NO3−) over ammonium (NH4+) in all treatments. Microbial N turnover and microbial biomass were in general negatively correlated to plant N acquisition and plant N pools, thus indicating strong competition for N between plants and free living microorganisms. The abundance of the dominant mycorrhizal fungi Cenococcum geophilum was negatively correlated to total soil microbial biomass but positively correlated to glutamine uptake by beech and amino acid concentration in fine roots indicating a significant role of this mycorrhizal fungus in the acquisition of organic N by beech. Tree girdling in general resulted in a decrease of dissolved organic carbon and total microbial biomass in soil while the abundance of C. geophilum remained unaffected, and N uptake by plants was increased. Overall, the girdling-induced decline of rhizodeposition altered the competitive balance of N partitioning in favour of beech and its most abundant mycorrhizal symbiont and at the expense of heterotrophic N turnover by free living microorganisms in soil. Similar to tree girdling, drought periods followed by intensive drying/rewetting events seemed to have favoured N acquisition by plants at the expense of free living microorganisms. 相似文献
996.
The dynamics of inorganic N in soil following the application of plant residues depends on their composition. We assumed that all plant materials are composed of similar components, each decomposing at a specific rate, but differ in the proportions of the various components. The NCSOIL model that simulates C and N turnover in soil was used to link the rates of residue decomposition to their composition, defined as soluble, cellulose-like and lignin-like C and N, and thereby integrate short and long-term effects of residues on available N dynamics in soil. Five plant residues in a wide range of C:N ratios were incubated in soil for 24 weeks at 30 °C, during which C and N mineralization were measured. The materials with large C:N ratios (corn, rice hulls and wheat straw) were also incubated with NH4+-N to avoid N deficiency. The residues were analyzed for total and soluble C and N. The partitioning of insoluble C and N between cellulose- and lignin-like pools was optimized by best fit of simulated C and N mineralization to measured results. The decomposition rate constants of the soluble and lignin-like pools were assumed to be 1.0 and 10−5 d−1, respectively, and that of the cellulose-like pool, obtained by model optimization against mineralization of cellulose with NH4+-N in soil, was 0.051 d−1. The optimized, kinetically defined lignin-like pool of all residues was considerably larger than lignin contents normally found in plant residues by the Van Soest procedure. Gross N mineralization of tobacco and rape residues was similar, but N recovery from tobacco was larger, because a larger fraction of its C was in the lignin-like pool. N in rice hulls, corn and wheat residues was mostly recalcitrant, yet rice hulls did not cause N deficiency, because most of its C was recalcitrant too. The soluble components of the residues had strong short-term effects on available N in soil, but the cellulose-like pool was equally important for short and medium-term effects. Soluble and cellulose-like C were 29 and 42% of total C, respectively, in corn and 7 and 50% in wheat. Maximal net inorganic N losses, measured in both residue treatments after 2 weeks, were 42 mg g−1 C applied as corn and 31 mg g−1 C applied as wheat, or 84 and 110 mg g−1 decomposed C of corn and wheat, respectively. Rice hulls immobilized N slowly, but by the end of 24 weeks all three residues immobilized 26-27 mg N kg−1 C applied. The different dynamics of N immobilization demonstrated the need to determine the decomposability of C and N rather than their total contents in plant residues. 相似文献
997.
As the world becomes more urbanized, urban cemeteries may become increasingly valuable for biodiversity conservation as cemeteries are ubiquitous elements of the green infrastructure in cities worldwide. By implementing a multi-taxon approach at different spatial extents, we analyzed habitat functions of a large urban cemetery in Berlin (Weiÿensee Jewish Cemetery) and explored related environmental variables. This cemetery is an outstanding cultural heritage site but it also stands for old urban cemeteries that have progressed to urban woodland, an ecosystem type that exists in many regional and religious contexts. The cemetery provided a habitat for 604 species; species of conservation concern comprised 1.6100% of total species among different groups of taxa (in decreasing order: bats, birds, lichens, bryophytes, carabids, vascular plants, spiders). Species richness and species composition at the plot level were significantly related to differences in management intensity and resulting vegetation structures but differed among taxonomic groups. In vascular plants, carabids and spiders, the species composition varied significantly with habitat age, and there was a set of characteristic species for different age classes in each species group. Our results thus support the use of differentiated management approaches to maintain habitat heterogeneity by allowing wilderness development in some parts of a cemetery while keeping others more open. Since these aims can be combined with efforts to preserve outstanding grave architectures and allow access to visitors, our study indicates ways of reconciling conflicting aims of heritage preservation and biodiversity conservation, a promising perspective for biodiversity conservation in culturally shaped urban landscapes. We conclude that cemeteries provide important cultural ecosystem services within the urban green infrastructure. 相似文献
998.
鸭嘴式旱作多功能精密穴播轮的试验研究 总被引:1,自引:0,他引:1
在室内试验台架上进行了穴播轮容种量、转速、成穴投种器和翼板的几何安装尺寸对播种性能影响的试验 ,并在此基础上进行了相应的正交寻优试验。试验结果表明 ,穴播轮可靠工作速度为 0 .18~ 0 .2 7m/s,容种高度为 2 0~ 170mm ;当固定管后倾角为 10° ,翼板长度为 80mm ,翼板位置角为 12 0°时 ,播种质量最佳 相似文献
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