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81.
Marney E. Isaac Jean-Michel HarmandDidier Lesueur Joseph Lelon 《Forest Ecology and Management》2011,261(3):582-588
Acacia senegal, an important leguminous tree in arid and semi-arid environments, has shown promise as a multipurpose species, including gum production and soil fertility improvement, linked with N2-fixation capabilities. Of particular interest are ontogenetic and edaphic effects on A. senegal performance in natural populations. Our research objectives were to investigate the effect of tree age and site phosphorus conditions on (1) tree N2-fixation and (2) soil N and C dynamics in natural stands of A. senegal var. senegal, Baringo District, in the Rift Valley, Kenya. Sites consisted of A. senegal saplings (9 months) and mature A. senegal trees (7 years) along an edaphic gradient of soil P availability. A single-tree neighborhood approach was employed using a two by two factorial design: site conditions [high and low soil P contents] and tree age class [juvenile and mature]. Soil (N and C pools and fluxes) and plant metrics were quantified. A soil transfer experiment was also employed to confirm age and site effects on soil N mineralization. On the high soil P site, A. senegal had significantly lower foliar (15N levels than neighboring non-leguminous species (Balanites aegyptiaca), while foliar δ15N values in A. senegal on the low P site exhibited no significant difference with our reference plant, B. aegyptiaca. Across P sites, B. aegyptiaca had similar foliar δ15N values. These results indicate that the rate of N2-fixation of A. senegal trees, as determined with foliar 15N natural abundance methodology, increased with increasing soil P availability in these natural populations. However, N2-fixation rates declined with age. Although soil texture and soil CO2 efflux did not differ between sites or across ages, soils under mature A. senegal at the high P site exhibited significantly greater total N content and total C content in comparison to soils at the low P site and under juvenile plants. Furthermore, under mature A. senegal trees, soil N mineralization rates were significantly greater as compared to under saplings. Soil transplants confirmed that soil microbial activity may be stimulated under mature trees as N mineralization rates were 2-3 fold greater compared to under A. senegal saplings. Our findings suggest that tree age and soil P availability are important factors in the nitrogen budget of natural populations of A. senegal, determining N2-fixation rates, and potentially influencing soil total N and C pools and soil mineral N. This study provides information regarding the adaptation of A. senegal under differing edaphic conditions thus increasing accuracy of management support for A. senegal populations as productive agroforests. 相似文献
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Isaac Middle Peta Dzidic Amma Buckley Dawn Bennett Marian Tye Roy Jones 《Urban Forestry & Urban Greening》2014,13(4):638-645
When planned coherently, urban green spaces have the potential to provide cities with a range of unique ecosystem services that support ecosystem and human health. This paper draws on existing green space planning literature to argue that the integration of community gardens into standardised and previously under-utilised public park landscapes represents an innovative approach to providing ecosystem services. Particular focus is given to the challenges facing green space planning in Perth, Western Australia. At an individual level, community gardens provide a venue for an alternative and more accessible form of physical activity – gardening – and a restorative park environment that is a more attractive destination for neighbourhood walking. At the community level, gardens can facilitate bridging interactions between different social groups, whilst providing opportunities for local residents to participate actively in green space planning processes. Perhaps most importantly, community gardens can provide unique opportunities for environmental education that lead to enhanced local ecological outcomes. The paper concludes with a brief overview of the main challenges likely to be faced with this integration, and some strategies that may allow them to be overcome. It is hoped this paper will provide a background for future case studies, and a catalyst for increasing integration between formal green space planning and community garden development. 相似文献
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Dehal P Satou Y Campbell RK Chapman J Degnan B De Tomaso A Davidson B Di Gregorio A Gelpke M Goodstein DM Harafuji N Hastings KE Ho I Hotta K Huang W Kawashima T Lemaire P Martinez D Meinertzhagen IA Necula S Nonaka M Putnam N Rash S Saiga H Satake M Terry A Yamada L Wang HG Awazu S Azumi K Boore J Branno M Chin-Bow S DeSantis R Doyle S Francino P Keys DN Haga S Hayashi H Hino K Imai KS Inaba K Kano S Kobayashi K Kobayashi M Lee BI Makabe KW Manohar C Matassi G Medina M Mochizuki Y Mount S 《Science (New York, N.Y.)》2002,298(5601):2157-2167
The first chordates appear in the fossil record at the time of the Cambrian explosion, nearly 550 million years ago. The modern ascidian tadpole represents a plausible approximation to these ancestral chordates. To illuminate the origins of chordate and vertebrates, we generated a draft of the protein-coding portion of the genome of the most studied ascidian, Ciona intestinalis. The Ciona genome contains approximately 16,000 protein-coding genes, similar to the number in other invertebrates, but only half that found in vertebrates. Vertebrate gene families are typically found in simplified form in Ciona, suggesting that ascidians contain the basic ancestral complement of genes involved in cell signaling and development. The ascidian genome has also acquired a number of lineage-specific innovations, including a group of genes engaged in cellulose metabolism that are related to those in bacteria and fungi. 相似文献
87.
Aparicio S Chapman J Stupka E Putnam N Chia JM Dehal P Christoffels A Rash S Hoon S Smit A Gelpke MD Roach J Oh T Ho IY Wong M Detter C Verhoef F Predki P Tay A Lucas S Richardson P Smith SF Clark MS Edwards YJ Doggett N Zharkikh A Tavtigian SV Pruss D Barnstead M Evans C Baden H Powell J Glusman G Rowen L Hood L Tan YH Elgar G Hawkins T Venkatesh B Rokhsar D Brenner S 《Science (New York, N.Y.)》2002,297(5585):1301-1310
The compact genome of Fugu rubripes has been sequenced to over 95% coverage, and more than 80% of the assembly is in multigene-sized scaffolds. In this 365-megabase vertebrate genome, repetitive DNA accounts for less than one-sixth of the sequence, and gene loci occupy about one-third of the genome. As with the human genome, gene loci are not evenly distributed, but are clustered into sparse and dense regions. Some "giant" genes were observed that had average coding sequence sizes but were spread over genomic lengths significantly larger than those of their human orthologs. Although three-quarters of predicted human proteins have a strong match to Fugu, approximately a quarter of the human proteins had highly diverged from or had no pufferfish homologs, highlighting the extent of protein evolution in the 450 million years since teleosts and mammals diverged. Conserved linkages between Fugu and human genes indicate the preservation of chromosomal segments from the common vertebrate ancestor, but with considerable scrambling of gene order. 相似文献
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Tobias O. Okeno Isaac S. Kosgey Alexander K. Kahi 《Tropical animal health and production》2010,42(6):1073-1079
Cost-benefit analysis using net present value (NPV) as the economic evaluation criterion was used to investigate the economic
merits of four breeding strategies used for genetic improvement of dairy cattle in Kenya. The breeding strategies were evaluated
over a 25-year period. The costs involved in setting up and running each strategy were obtained from large-scale dairy cattle
farms, and government and private institutions involved in genetic improvement of dairy cattle. Only benefits from genetic
improvement were considered. The impact on NPV due to changes in genetic and economic parameters was investigated. The ranking
of the breeding strategies greatly differed with genetic ranking. Among the local selection programs, a strategy utilizing
young bulls, sons of local bulls, was more profitable than one utilizing old progeny tested bulls. Continuous semen importation
was not an economically viable alternative. The strategy utilizing young bulls progeny of imported bulls (PIB) was only viable
if imports were from countries which are >2.00 SD in genetic merit above the local dairy cattle population. The ranking of
strategies was not sensitive to changes in genetic parameters but to economic parameters. The use of local semen from young
bulls progeny of local proven bulls is recommended. Alternatively, PIB can be utilized but the semen will have to be imported
from countries which are >2.00 SD above the local dairy cattle population or the cost of imported semen should be ≤ US$40
per straw. 相似文献