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131.
132.
Battles John J. Armesto Juan J. Vann David R. Zarin Daniel J. Aravena Juan Carlos Pérez Cecilia Johnson Arthur H. 《Plant Ecology》2002,158(1):5-19
Research in pristine forests provides a necessary reference of energy and nutrient cycling in absence of anthropogenic influence. Therefore two unpolluted watersheds in the Cordillera de Piuchué of southern Chile (42 °30 S) were chosen for detailed ecosystem analysis. The goals of this study were to quantify the distribution of the living biomass in the research watershed and to document topographic gradients in the vegetation. Across a small spatial gradient from ravine bottom to ridgetop (approximately 60 m in elevation and < 300 m in length) in the Cordillera de Piuchué watersheds, there were significant shifts in vegetation composition, structure, and biomass. Based on sampling in 18, 100 m2 plots, we identified three distinct community associations: a Fitzroya forest at the bottom of the watershed, a mid-slope Pilgerodendron-Tepualia transition zone, and a ridgetop moorland community. The Fitzroya forest was dominated by a cohort of approximately 400 year-old Fitzroya cupressoides trees. Both tree basal area (138 m2/ha) and total live biomass (656 Mg ha–1) reached a maximum in this vegetation type. The Pilgerodendron-Tepualia forest consisted of smaller, shorter, and younger trees with dominance shared by Pilgerodendron uviferum, Tepualia stipularis, and to a lesser extent, F. cupressoides. Basal area and biomass were half that of the Fitzroya forest (69.5 m2 ha–1; 350 Mg ha–1) but tree density was 65% greater. The moorland can best be described as an open community of mosses and cushion plants that included low stature individuals of P. uviferum, F. cupressoides, and T. stipularis. The size and age structure of F. cupressoides in the bottomland forest suggest that the current cohort of adult trees was established following a catastrophic disturbance and that F. cupressoides is unable to regenerate under its own canopy. In contrast, the size structure of the tree populations in the Pilgerodendron-Tepualia zone indicates that all the constituent tree species, except F. cupressoides, are able to reproduce at least at some microsites in the understory. The watershed-level means for live biomass were 306 Mg ha–1 of aboveground tree biomass, 25 Mg ha–1 of large root biomass (diameter ge 1 cm), and 46 Mg ha–1 of small root biomass (diameter < 1 cm). 相似文献
133.
Carolina C. Lisboa Richard T. Conant Michelle L. Haddix Carlos Eduardo P. Cerri Carlos C. Cerri 《Ecosystems》2009,12(7):1212-1221
The effect of conversion from forest-to-pasture upon soil carbon stocks has been intensively discussed, but few studies focus
on how this land-use change affects carbon (C) distribution across soil fractions in the Amazon basin. We investigated this
in the 20 cm depth along a chronosequence of sites from native forest to three successively older pastures. We performed a
physicochemical fractionation of bulk soil samples to better understand the mechanisms by which soil C is stabilized and evaluate
the contribution of each C fraction to total soil C. Additionally, we used a two-pool model to estimate the mean residence
time (MRT) for the slow and active pool C in each fraction. Soil C increased with conversion from forest-to-pasture in the
particulate organic matter (>250 μm), microaggregate (53–250 μm), and d-clay (<2 μm) fractions. The microaggregate comprised
the highest soil C content after the conversion from forest-to-pasture. The C content of the d-silt fraction decreased with
time since conversion to pasture. Forest-derived C remained in all fractions with the highest concentration in the finest
fractions, with the largest proportion of forest-derived soil C associated with clay minerals. Results from this work indicate
that microaggregate formation is sensitive to changes in management and might serve as an indicator for management-induced
soil carbon changes, and the soil C changes in the fractions are dependent on soil texture. 相似文献
134.
135.
Little information exists on mixed-species groups between primates and other mammals in Neotropical forests. In this paper, we describe three such associations observed during an extensive large-vertebrate survey in central Amazonia, Brazil. Mixed-species groups between a primate species and another mammal were observed on seven occasions between squirrel monkeys (Saimiri cf. ustus) and either South American coatis (Nasua nasua) or tayras (Eira barbara) and between brown capuchins (Cebus apella) and coatis. All associations were restricted to floodplain forest during its dry stage. We suggest that the associations involving the coatis are connected to foraging and vigilance but may be induced by a common alternative food resource at a time of food shortage. 相似文献
136.
The N-terminus of Ciona intestinalis (Ci-VSP) is a voltage-sensing domain (VSD) controlling the activity of a phosphatase domain on the C terminus. By replacing the phosphatase domain with a tandem of fluorescent proteins, CFP and YFP, a family of fluorescence resonance energy transfer-based, genetically encoded voltage-sensing fluorescent protein (VSFP) was created. VSFP2.3, one of the latest versions of this family, showed large changes in YFP emission upon changes in membrane potential with CFP excitation when expressed in Xenopus laevis oocytes. The time course of the fluorescence has two components: the fast component correlates with the time course of sensing current produced by the charge movement, while the slow component is at least one order-of-magnitude slower than the sensing current. This suggests that the tandem of fluorescent proteins reports a secondary conformational transition of the VSD which resembles the relaxation of the VSD of Ci-VSP described in detail for the Ci-VSP. This observation indicates that the relaxation of the VSD of VSFP2.3 is a global conformational change that encompasses the entire S4 segment. 相似文献
137.
Seasonal changes in condition, nutrition, gonad maturation and energy content in barbel, Barbus sclateri, inhabiting a fluctuating river 总被引:2,自引:0,他引:2
The objective of this study was to investigate the seasonal cycle of condition, nutrition and gonad development, as well as
the magnitude of seasonal variations in energy content of somatic and gonad tissues in juveniles, males and females of Sclater's
barbel, Barbus sclateri, from the upper Guadalete River (south Spain). The influence of reproductive cycle on somatic changes
was also investigated and discussed. Measurements of condition factor (K), somatic index (SI), gonadosomatic index (GSI) and
somatic and gonad energy content (J g-1 dw) were made in individual specimens taken from the Guadalete River monthly for 12 months. This freshwater ecosystem is
characterised by strong seasonal fluctuations in water and flow level, temperature and food supply. It was found that in general
juveniles, males and females of barbel exhibited a similar condition, nutrition and somatic energy cycle throughout the year,
with the highest values in spring and the lowest in summer. Depletion of K, SI and somatic energy storage from spring until
mid-summer seems to be associated with high metabolic demands during this period, and in adult fish also with spawning-related
activity. The gonad index and energy content of the gonad were the highest in April and the lowest in summer for both sexes.
Spawning took place during late spring – early summer, with fish quiescent by mid summer. The energy required for ovarian
development (3970 J g-1 dw) was greater than the one for testes development (2763 J g-1 dw). Data on gonad energy content indicated a period (March to April) of intense energy accumulation (64% males and 37% females)
which was related to the decline in the average somatic energy content in males and females. The somatic energy content was
linearly related to K and SI. In the same way, GSI correlated positively with gonad energy. Linear trends were found between
somatic parameters (K, SI and energy content) and gonad parameters (GSI and energy content).
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
138.
Shibin Gao Carlos Martinez Debra J. Skinner Alan F. Krivanek Jonathan H. Crouch Yunbi Xu 《Molecular breeding : new strategies in plant improvement》2008,22(3):477-494
Leaf collection from the field, labeling and tracking back to the source plants after genotyping are rate limiting steps in
leaf DNA-based genotyping. In this study, an optimized genotyping method using endosperm DNA sampled from single maize seeds
was developed, which can be used to replace leaf DNA-based genotyping for both genetic studies and breeding applications.
A similar approach is likely to be suitable for all plants with relatively large seeds. Part of the endosperm was excised
from imbibed maize seeds and DNA extracted in 96-tube plates using individuals from eight F2 populations and seven inbreds. The quality of the resultant DNA was functionally comparable to DNA extracted from leaf tissue.
Extraction from 30 mg of endosperm yields 3–10 μg DNA, which is sufficient for analysis of 200–400 agarose-gel PCR-based markers,
with the potential for several million chip-based SNP marker analyses. By comparing endosperm DNA and leaf DNA for individuals
from an F2 population, genotyping errors caused by pericarp contamination and hetero-fertilization were found to average 3.8 and 0.6%,
respectively. Endosperm sampling did not affect germination rates under controlled conditions, although under normal field
conditions the germination rate, seedling establishment, and growth vigor were significantly lower than that of non-sampled
controls for some genotypes. However, careful field management can compensate for these effects. Seed DNA-based genotyping
lowered costs by 24.6% compared to leaf DNA-based genotyping due to reduced field plantings and labor costs. A substantial
advantage of this approach is that it can be used to select desirable genotypes before planting. As such it provides an opportunity
for dramatic improvements in the efficiency and selective gain of breeding systems based on optimum combinations of marker-assisted
selection and phenotypic selection within and between generations. 相似文献
139.
Sudano MJ Paschoal DM Rascado Tda S Magalhães LC Crocomo LF de Lima-Neto JF Landim-Alvarenga Fda C 《Theriogenology》2011,75(7):1211-1220
The objective was to evaluate supplementation of fetal calf serum (FCS) and phenazine ethosulfate (PES), a metabolic regulator that inhibits fatty acid synthesis, in culture media during in vitro production (IVP) of bovine embryos. Taking oocyte fertilization (n = 4,320) as Day 0, four concentrations of FCS (0, 2.5, 5, and 10%) and three periods of exposure to PES (without addition—Control; after 60 h—PES Day 2.5 of embryo culture; and after 96 h—PES Day 4) were evaluated. Increasing FCS concentration in the culture media enhanced lipid accumulation (P < 0.05), increased apoptosis in fresh (2.5%: 19.1 ± 1.8 vs 10%: 28.4 ± 2.3, P < 0.05; mean ± SEM) and vitrified (2.5%: 42.8 ± 2.7 vs 10%: 69.2 ± 3.4, P < 0.05) blastocysts, and reduced blastocoele re-expansion after vitrification (2.5%: 81.6 ± 2.5 vs 10%: 67.3 ± 3.5, P < 0.05). The addition of PES in culture media, either from Days 2.5 or 4, reduced lipid accumulation (P < 0.05) and increased blastocoele re-expansion after vitrification (Control: 72.0 ± 3.0 vs PES Day 2.5: 79.9 ± 2.8 or PES Day 4: 86.2 ± 2.4, P < 0.05). However, just the use of PES from D4 reduced apoptosis in vitrified blastocysts (Control: 52.0 ± 3.0 vs PES Day 4: 39.2 ± 2.4, P < 0.05). Independent of FCS withdrawal or PES addition to culture media, the in vivo control group had lesser lipid accumulation, a lower apoptosis rate, and greater cryotolerance (P < 0.05). The increased lipid content was moderately correlated with apoptosis in vitrified blastocysts (r = 0.64, P = 0.01). In contrast, the increased apoptosis in fresh blastocysts was strongly correlated with apoptosis in vitrified blastocysts (r = 0.94, P < 0.0001). Therefore, using only 2.5% FCS and the addition of PES from Day 4, increased the survival of IVP embryos after vitrification. Moreover, embryo quality, represented by the fresh apoptosis rate, was better than lipid content for predicting embryo survival after vitrification. 相似文献
140.
Ellen O. Martinson Edward Allen Herre Carlos A. Machado A. Elizabeth Arnold 《Microbial ecology》2012,64(4):1073-1084
The ancient association of figs (Ficus spp.) and their pollinating wasps (fig wasps; Chalcidoidea, Hymenoptera) is one of the most interdependent plant–insect mutualisms known. In addition to pollinating wasps, a diverse community of organisms develops within the microcosm of the fig inflorescence and fruit. To better understand the multipartite context of the fig–fig wasp association, we used a culture-free approach to examine fungal communities associated with syconia of six species of Ficus and their pollinating wasps in lowland Panama. Diverse fungi were recovered from surface-sterilized flowers of all Ficus species, including gall- and seed flowers at four developmental stages. Fungal communities in syconia and on pollinating wasps were similar, dominated by diverse and previously unknown Saccharomycotina, and distinct from leaf- and stem endophyte communities in the same region. Before pollination, fungal communities were similar between gall- and seed flowers and among Ficus species. However, fungal communities differed significantly in flowers after pollination vs. before pollination, and between anciently diverged lineages of Ficus with active vs. passive pollination syndromes. Within groups of relatively closely related figs, there was little evidence for strict-sense host specificity between figs and particular fungal species. Instead, mixing of fungal communities among related figs, coupled with evidence for possible transfer by pollinating wasps, is consistent with recent suggestions of pollinator mixing within syconia. In turn, changes in fungal communities during fig development and ripening suggest an unexplored role of yeasts in the context of the fig–pollinator wasp mutualism. 相似文献