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  • Puerto Rico  (2)
  • soil organic matter  (2)
  • Animals  (1)
  • Leukemia, Experimental/genetics  (1)
  • 1990-1994  (5)
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Plant and soil 149 (1993), S. 27-41 
    ISSN: 1573-5036
    Keywords: carbon sinks ; changes in soils ; soil fertility ; soil management ; soil organic carbon ; soil organic matter ; tropical soil ; succession
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The prevailing paradigm for anticipating changes in soil organic carbon (SOC) with changes in land use postulates reductions in SOC in managed systems (agriculture and tree plantations) relative to mature tropical forests. Variations of this notion are used in carbon models to predict the role of tropical soils in the global carbon cycle. Invariably these models show tropical soils as sources of atmospheric carbon. We present data from a variety of studies that show that SOC in managed systems can be lower, the same as, or greater than mature tropical forests and that SOC can increase rapidly after the abandonment of agricultural fields. History of land use affects the comparison of SOC in managed and natural ecosystems. Our review of the literature also highlights the need for greater precautions when comparing SOC in mature tropical forests with that of managed ecosystems. Information on previous land use, bulk density, and consistency in sampling depth are some of the most common omissions in published studies. From comparable SOC data from a variety of tropical land uses we estimate that tropical soils can accumulate between 168 and 553 Tg C/yr. The greatest potential for carbon sequestration in tropical soils is in the forest fallows which cover some 250 million hectares. Increased attention to SOC by land managers can result in greater rates of carbon sequestration than predicted by current SOC models.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Plant and soil 125 (1990), S. 263-280 
    ISSN: 1573-5036
    Keywords: Anthocephalus chinensis ; Eucalyptus × patentinervis ; E. saligna ; Hernandia sonora ; Hibiscus elatus ; Khaya nyasica ; litter ; Luquillo Experimental Forest ; nutrient cycling ; Pinus caribaea var. hondurensis ; P. elliottii var. densa ; Puerto Rico ; soil fertility ; Swietenia macrophylla ; Terminalia ivorensis ; tropical tree plantations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The importance of litter to nutrient and organic matter storage and the possible influence of species selection on soil fertility in ten stands each consisting of a separate tree species were examined in this study. The plantations had been grown under similar conditions in an arboretum in the Luquillo Experimental Forest, Puerto Rico. The species involved were: Anthocephalus chinensis, Eucalyptus × patentinervis, E. saligna, Hernandia sonora, Hibiscus elatus, Khaya nyasica, Pinus caribaea var. hondurensis, P. elliottii var. densa, Swietenia macrophylla, and Terminalia ivorensis. After 26 yr, litter mass ranged from 5 mg ha-1 in the H. sonora stand to 27.2 Mg ha-1 in the P. caribaea stand. Nutrients in the litter (N, P, K, Ca, and Mg) also varied widely, but stands were ranked in different order when ranked by nutrients in the litter than then ranked according to accumulation of mass. Only E. saligna and A. chinensis stands were ranked similarly in accumulation of both nutrients and mass, and the stand of H. elatus was ranked higher with respect to nutrient accumulation than to accumulation of mass. The nutrient concentration in standing leaf litter generally increased in the order of recently fallen 〈old intact〈 fragmented. Nutrient concentration of standing leaf litter appears to increase with age and depth in the litter layer. The amount of nutrients stored in the litter compartment of these plantations was in the same order of magnitude as the quantity of available nutrients in the top 10-cm of mineral soil. Total litter mass was negatively correlated with the mass-weighted concentration of N, K, and Mg. The same relationship was found for Ca in the leaf litter and N in the fine wood litter compartments. In some stands (notably P. caribaea, P. elliottii, and E. saligna), leaf litter derived from species other than the species planted in that particular stand had higher nutrient concentration than leaf litter from the planted species. Soils of the 10 stands were classified in the same soil series and had similar texture (clay soils). However, significantly different chemical characteristics were found. Results obtained by analysis of covariance and by limiting comparisons to adjacent stands with similar soil texture, indicate that different species have had different influences on the concentration of available nutrients in soil.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1573-5036
    Keywords: forest clearing ; forest succession ; Puerto Rico ; soil carbon ; soil nitrogen ; tropics ; U.S. Virgin Islands
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Soil samples from mature and secondary forests and agricultural sites in three subtropical life zones of Puerto Rico and the US Virgin Islands were collected to determine the effects of forest conversion to agriculture and succession on soil organic carbon (C) and nitrogen (N) contents. Site characteristics that may affect soil C and N (slope, elevation, aspect, and texture) were as uniform as possible. Carbon contents (to 50 cm depth or bedrock) of cultivated sites, as a percent of corresponding mature forests, were lower in the wet (44%) and moist (31%) than in the dry (86%) life zones whereas N contents were relatively high regardless of life zone (60–130% of the mature forests). Conversion of forests to pasture resulted in less soil C and N loss than conversion to crops. The time for recovery of soil C and N during succession was approximately the same in all three life zones, about 40–50 yr for C about 15–20 yr for N. However, the rate of recovery of soil C was faster in the wet and moist life zone, whereas N appeared to recover faster in the dry life zone. Evidence for loss of soil C during cultivation and gain during succession to soil depths of 50–100 cm is presented.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1573-5036
    Keywords: biomass ; litter fall ; litter standing stock ; organic matter budget ; Pinus caribaea plantations ; root biomass ; root production ; secondary forests ; soil organic matter
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The distribution of tree biomass and the allocation of organic matter production were measured in an 11-yr-old Pinus caribaea plantation and a paired broadleaf secondary forest growing under the same climatic conditions. The pine plantation had significantly more mass aboveground than the secondary forest (94.9 vs 35.6 t ha-1 for biomass and 10.5 vs 5.0 t ha-1 for litter), whereas the secondary forest had significantly more fine roots (⩽2 mm diameter) than the pine plantation (10.5 and 1.0 t ha-1, respectively). Standing stock of dead fine roots was higher than aboveground litter in the secondary forest. In contrast, aboveground litter in pine was more than ten times higher than the dead root fraction. Both pine and secondary forests had similar total organic matter productions (19.2 and 19.4 t ha-1 yr-1, respectively) but structural allocation of that production was significantly different between the two forests; 44% of total production was allocated belowground in the secondary forest, whereas 94% was allocated aboveground in pine. The growth strategies represented by fast growth and large structural allocation aboveground, as for pine, and almost half the production allocated belowground, as for the secondary forest, illustrate equally successful, but contrasting growth strategies under the same climate, regardless of soil characteristics. The patterns of accumulation of organic matter in the soil profile indicated contrasting nutrient immobilization and mineralization sites and sources for soil organic matter formation.
    Type of Medium: Electronic Resource
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  • 5
    Publication Date: 1990-03-02
    Description: Oncogenic activation of the proto-oncogene c-abl in human leukemias occurs as a result of the addition of exons from the gene bcr and truncation of the first abl exon. Analysis of tyrosine kinase activity and quantitative measurement of transformation potency in a single-step assay indicate that variation in bcr exon contribution results in a functional difference between p210bcr-abl and p185bcr-abl proteins. Thus, foreign upstream sequences are important in the deregulation of the kinase activity of the abl product, and the extent of deregulation correlates with the pathological effects of the bcr-abl proteins.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Lugo, T G -- Pendergast, A M -- Muller, A J -- Witte, O N -- 5T32GM07185/GM/NIGMS NIH HHS/ -- IT32GM08243/GM/NIGMS NIH HHS/ -- New York, N.Y. -- Science. 1990 Mar 2;247(4946):1079-82.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Microbiology, University of California, Los Angeles 90024.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/2408149" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Blotting, Southern ; Cell Line ; *Cell Transformation, Neoplastic/genetics ; Exons ; *Gene Expression Regulation, Neoplastic ; Leukemia, Experimental/genetics ; Protein-Tyrosine Kinases/genetics/*metabolism ; Proto-Oncogene Proteins/genetics/*metabolism ; Proto-Oncogene Proteins c-abl ; Proto-Oncogene Proteins c-bcr ; Retroviridae/genetics
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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