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831.
Sánchez Dávila F Bernal H Colín J Olivares E del Bosque AS Ledezma R Ungerfeld R 《Tropical animal health and production》2011,43(4):887-891
The objective of this study was to determine whether season and total rainfall during the breeding season, sheep parity, and/or
litter size affect the interval from the introduction of rams to estrus (IRE) in hair Saint Croix sheep in northeastern Mexico.
An analysis was made of 874 services performed during 9 years, introducing the rams into the sheep flock after an isolation
period of 60 days during the postpartum period. Estrus was recorded twice daily during 35 days. Year and season influenced
significantly on the interval between ram introduction and estrus length (P < 0.01). Winter IRE length (7.9 ± 0.1 days) was shorter than in the other three seasons (11.1 ± 0.2, 11.1 ± 0.1, and 16.2 ± 0.2 days
in summer, autumn, and spring, respectively) (P < 0.01). An interaction was observed between rainfall and season, then by rainfall between 0 and 100 mm, IRE was shorter
(P < 0.05) in winter (6.8 ± 0.3 days), and by rainfall between 100 and 199 mm, IRE was shorter (P < 0.05) in autumn (10.2 ± 0.5 days); however, when rainfall was beyond 200 mm, IRE length was shorter (P < 0.01) in summer (4.8 ± 0.5 days) than in autumn (14.5 ± 0.3 days). The IRE length was also longer in first lambing ewes
(P < 0.05) and was not affected by litter size. In the present study, several factors, including the breeding season, rainfall
and parity, directly influenced the interval between the male introduction and the onset of estrus by Saint Croix hair sheep. 相似文献
832.
Roxana Yanira Parada Serafina Castro Reina de Serrano Blanca Estela Castillo Jaime Ayala Eduardo Vides Javier Romero 《Journal of General Plant Pathology》2006,72(1):40-42
A new disease of the fruit tree Jocote de Corona (Spondias purpurea L.) was observed in El Salvador, Central America. The symptoms included small chlorotic leaves, highly proliferating shoots,
and shortened internodes. Absence of sweet pulp in fruits made them inedible, causing considerable yield losses for farmers.
The disease etiology was investigated using polymerase chain reaction with phytoplasma-specific primers, sequencing, and phylogenetic
analysis. We obtained no amplification products from symptomless plants, whereas all tests were positive from plants with
symptoms. Phylogenetic analysis indicated that this phytoplasma clustered in the 16S rIII group, the type member of which
is X-disease phytoplasma. This is the first report of a phytoplasma associated with Jocote de Corona disease in El Salvador
and Central America.
The nucleotide sequence data reported are available in the DDBJ/EMBL/GenBank databases under the accession number AJ888471 相似文献
833.
Liu L Castillo-Olivares J Davis-Poynter NJ Baule C Xia H Belák S 《Veterinary microbiology》2008,129(3-4):262-268
Samples from horses experimentally infected with the “large plaque variant (LP3A+)” of equine arteritis virus were analysed. These included 182 nasal swabs collected from day 1 to 14 post-infection (p.i.), and 21 virus isolates obtained from white blood cells of animals that showed a prolonged viraemia between days 30 to 72 p.i. In order to determine the genetic stability of the virus and particularly to characterise the genetic variants found during the prolonged viraemia, partial sequences of open reading frame 5 (ORF5) encoding glycoprotein 5 (GP5) were generated. Viruses with amino acid substitutions in GP5 were used for further amplification and sequencing of a fragment encompassing ORFs 2b, 3, and 4. The ORF5 nucleotide sequences of the virus present in 65 out of 66 nasal swabs were identical to that of the inoculated virus, suggesting that the ORF5 gene of LP3A+ was genetically stable during the first 2 weeks p.i. Contrary to this, a number of mutations were found in the ORF5 of virus isolates obtained from day 30 p.i. The mutations mainly clustered in antigenic neutralization site C within variable region 1 of the GP5 ectodomain. Sequence variability was also identified in ORFs 2b, 3 and 4, with ORF 4 having the highest proportion of non-synonymous changes (4/6). 相似文献
834.
Héctor Viveros-Viveros Cuauhtémoc Sáenz-Romero J. Jesús Vargas-Hernández Javier López-Upton Gustavo Ramírez-Valverde Amalio Santacruz-Varela 《Forest Ecology and Management》2009
The altitudinal pattern of genetic variation in Pinus hartwegii Lindl. populations was explored for seedling height growth, frost damage, grass-stage, and phenological stage of the terminal shoot. A provenance test was conducted with open-pollinated seed from 13 populations collected along an altitudinal transect (3000–3600 m) at the National Park Pico de Tancítaro, Michoacán, center-west Mexico. Height growth of seedlings in a nursery was assessed at seven and 18 months of age. Frost damage at −15 °C was evaluated in laboratory at 18 months of age; proportion of plants that had left grass-stage and stage of shoot development was assessed at the age of 22 months. Significant differences among provenances (P < 0.0001) were detected for all of the evaluated characters. The variation among populations was structured as a moderate altitudinal cline, with populations from lower altitudes showing larger height growth in seedlings, larger proportion of frost damages, fewer seedlings in grass-stage and more seedlings with developed shoot, whereas in populations from higher altitudes, seedlings exhibiting shorter plant height, lower percentages of frost damage, more seedlings with unbroken grass-stage, and fewer seedlings with advanced shoot development were displayed. Options for seed and seedling movement along the altitudinal gradient are discussed under the scope of reforestation, aiming at ecological restoration, conservation of forest genetic resources, and assisted migration considering global warming. We suggest delineation of two altitudinal seed zones (Zone I: 3000–3350 m; Zone II: 3350–3700 m). 相似文献
835.
Shade acclimation in the forage grass Festuca Pallescens: biomass allocation and foliage orientation
Plants can acclimate to shade through different processes. In particular, they can modify their biomass allocation and the
architecture in order to increase light interception. The objective of this study was to evaluate the shade acclimation capacity
of Festuca pallescens (St. Ives) Parodi, as part of research concerning the use of this species in silvopastoral systems in Patagonia, Argentina.
Biomass allocation was estimated from the leaf and root dry weights of plants growing in an open pasture and forested plots.
Crown architecture of plants growing in the open and in two shade treatments was studied dividing each plant in three concentric
cylinders, within which leaf angles and leaf area were measured. Light interception of plants in each treatment was estimated
from the projected leaf areas and the relative amount of radiation reaching each location. Biomass allocation changed significantly
in plants growing under shade conditions, increasing the proportion of leaves relative to the roots (Leaf Mass Fraction =
0.29 (SD: 0.12) and 0.40 (SD: 0.09) in plants in the open and under shade, respectively). Also, mean leaf inclination angles
changed in plants growing under shade conditions, allowing an increase in light interception of approximately 35% compared
to plants with the crown architecture typical of the open treatment. Previous studies have shown that F. pallescens does not change its photosynthetic response to light under shade conditions. Therefore, we conclude that the reported changes
in biomass allocation and crown architecture, in addition to the increment in specific leaf area explain the relatively high
shade tolerance of this species.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
836.
Javier Puntieri Javier Grosfeld Luis Tejera Víctor Mondino Leonardo Gallo 《Annals of Forest Science》2013,70(5):471-479
? Context
There is evidence that Nothofagus nervosa (= N. alpina) is suitable for timber production in temperate regions due to its wood quality and fast growth. However, high intra-specific variability in the architectural traits of this species limits its usefulness.? Aims
This study was aimed at evaluating intra-specific variability in the architecture of N. nervosa trees at the population level, with emphasis on traits related to the suitability of trees for timber production.? Methods
The size of 13-year-old trees installed in an experimental field population and the extent of differentiation between trunk and branches were compared among families (trees derived from different mother trees).? Results
The large majority of trees exhibited architectural features indicative of high suitability for timber production: clear differentiation between trunk and main branches and few occurrences of permanent trunk forks, apex deaths, and sylleptic branching. Trees belonging to different families differed in height and trunk diameter. Micro-environmental conditions had a very significant effect on most architectural traits, including the trunk differentiation.? Conclusions
N. nervosa emerges as a suitable option for timber production in temperate regions. Trunk growth seems to be under both environmental and genetic control in this species. 相似文献837.
Ana Navas Javier Machín Santiago Beguería Manuel López-Vicente Leticia Gaspar 《Agroforestry Systems》2008,72(3):173-185
Large changes in land use have occurred in the Central Spanish Pyrenees during the twentieth century. This mountain area supported
an intense human use since the Middle Ages, that greatly transformed the natural landscape. The land uses changed dramatically
during the first half of the twentieth century, due to major socioeconomic forces which lead to depopulation and land abandonment.
Since then, a process of natural vegetation recovery has taken place. The anthropogenic impact during centuries deteriorated
the soil quality, threatening the sustainability of agroecosystems and the natural vegetation re-growth. In this study, a
soil survey was performed to identify the soil types and the physico-chemical properties of the soil that are relevant for
maintaining the soil function for the recovery of vegetation after land abandonment. The study was conducted in the Arnás
River catchment, which is representative of the region. The highest cation exchange capacity (CEC), nutrients, water retention,
water availability and infiltration rates, as well as the lowest pH and carbonates, occurred in Lithic Hapludolls and Calcic
Haploxerolls at the shady aspect, under a forest cover. Lithic Ustochrepts and Lithic Xerorthents on the sunny aspect, which
were covered by shrubs, were of lesser quality than were the deeper and better-developed soils on the shady aspect. This is
seen as an evidence of different patterns of soil degradation, which conditioned the re-growth of natural vegetation after
land abandonment. The results provide insights into the main soil factors that have affected the re-establishment of natural
vegetation in recent years. Recommendations are given for designing effective strategies for soil conservation after land
abandonment in similar mountain environments. 相似文献
838.
Differences in soil properties between forests and pastures have been well documented in the literature, especially under
coniferous forests. However, since nearly all of these reports have been time-point comparisons, utilizing long-term paired-sites,
properties of transitional states and time of their appearance can only be inferred at present. In this study, a deciduous
forest ecosystem was converted to a silvopasture ecosystem by tree thinning, fertilization, and sheep incorporation of seed
and forest litter. After 2 years, topsoil (0–15 cm) physico-chemical properties, particularly P fractions, and phosphatases
were monitored over the growing season in these ecosystems, and a nearby pasture ecosystem. Initially, before spring vegetative
growth, differences were found for pH, exchangeable cations and soil moisture, most of which could be explained by management
history. Compared to forest, organic-C (Co) and organic-N (No) concentrations were reduced in silvopasture by 17 and 9%, respectively, indicative of substantial litter decomposition.
Most values for all these physico-chemical properties for silvopasture were intermediate between forest and pasture, and generally
remained so throughout the growing season. Initial total P (TPt), organic-P (TPo) and inorganic-P (TPi) concentrations were generally as anticipated for the forest and pasture. Silvopasture, however, had 36 and 23% greater TPo than forest and pasture, respectively, presumably due to fertilizer-P immobilization induced by incorporation of forest litter.
Total P components remained essentially constant over the growing season in all ecosystems, with the exception of pasture,
likely due to high forage TPi uptake. Bray I-extractable-organic-P (BrPo) and bicarbonate-extractable-organic-P (BiPo) concentrations, although consistently highest in the forest and silvopasture soils, were not reflective of the increase
in TPo under silvopasture. Acid phosphatase (PMEac) activities were highest in spring in all the ecosystems, then gradually declined
to typically 25–50% initial activities. Alkaline phosphatase (PMEal) activities showed a broadly-similar pattern, with exception
of forest and silvopasture soils, which exhibited low activities throughout the season. For the entire data set, PMEac and
PMEal activities were poorly correlated with TPi, BrPi, and BiPi. These results demonstrate that conversion of forest to silvopasture results in soil changes indicative of its rapid transition
to pasture and that an increased Po reservoir results that should be taken into account in fertilizer-P recommendations for temperate silvopastures. 相似文献
839.
Sonia Mediavilla Montserrat Martínez-Ortega Santiago Andrés Javier Bobo Alfonso Escudero 《林业研究》2022,33(1):39-50
Implications of the differences in leaf life span are still subject to debate in the field of ecophysiology. Since leaf traits associated with these differences may be decisive for determining the distribution of tree species, this topic is particularly relevant in the context of climate change. This study analyzes the effects of the differences in leaf life span on premature losses of leaf area owing to insect herbivory and to abiotic stress. Loss of leaf area may be an important determinant of... 相似文献
840.
Juan Estefanell Javier Roo Marisol Izquierdo Juan Socorro Rafael Guirao 《Journal of the World Aquaculture Society》2013,44(1):66-75
Octopus vulgaris is a potential candidate to diversify marine aquaculture. Even though mortality under rearing conditions has been related to reproductive processes, the benefit of sex segregation remains unclear. In order to clarify this, wild octopuses (862 ± 101 g) were reared in floating cages under three proportions of male : female sex ratio: 1:1, 1:0, and 4:1 (n = 30 per treatment). The experimental period lasted 2 mo and octopuses were fed on bogue, Boops boops (aquaculture by‐product). Higher growth rates were observed in octopuses reared under 1:1 and 1:0 (1.8%/d) in comparison with those reared under 4:1 conditions (1.6%/d). Regarding sexes, a lower growth was detected in females reared under 4:1 (1.1%/d) in comparison with females (1.8%/d) and males (1.7–1.9%/d) reared under 1:1 conditions. Survival was 97, 97, and 90% in sex ratio 1:1, 1:0, and 4:1, respectively. Sexual maturity data showed that males were all mature, while most females were still maturing (60–84%) at the end of the rearing period. High lipid content in bogue (44% dw) did not reflect on octopus muscle. This tissue showed a similar biochemical composition irrespective of the sex ratio condition, with a high protein (87% dw), a low lipid (5% dw), and a high n‐3 HUFA content (42%). 相似文献