National Autonomous University of Mexico

About: National Autonomous University of Mexico is a education organization based out in Mexico City, Distrito Federal, Mexico. It is known for research contribution in the topics: Population & Galaxy. The organization has 72868 authors who have published 127797 publications receiving 2285543 citations. The organization is also known as: UNAM & Universidad Nacional Autónoma de México.

The effect of canopy gaps on growth and morphology of seedlings of rain forest species.

Abstract: Growth and morphology of seedlings of ten tropical rain forest species were studied at Los Tuxtlas, Mexico. Seedlings were grown in three environmental conditions: the shaded forest understorey (FU, receiving 0.9-2.3% of the daily photosynthetic photon flux, PF, above the canopy), a small canopy gap of approx. 50 m2 (SG, receiving 2.1-6.1% of daily PF), and a large canopy gap of approx. 500 m2 (LG, receiving 38.6-53.4% of daily PF). The growth of all species was enhanced in gaps, and in LG the effect was stronger than in SG. Plants grown in LG had a sunplant morphology, with a high root-shoot ratio (R/S), a high specific leaf weight (SLW) and a low leaf area ratio (LAR). Plants grown in SG or FU showed a shade-plant morphology, with a low R/S, a low SLW and a high LAR. Growth responses varied from species unable to grow in the shade but with strong growth in the sun, to species with relatively high growth rates in both shade and sun conditions. Shade tolerant species were able to grow in the shade because of a relatively high unit leaf rate. The pioneerCecropia had a high growth rate in LG because of a high LAR. Most species showed a complex growth response in which they resembled the shade intolerant extreme in some aspects of the response, and the shade tolerant extreme in other aspects.

Impact of Forest Fragmentation on Understory Plant Species Richness in Amazonia

Abstract: Forest fragmentation in the tropics severely affects large trees, but its effect on other life stages and plant life forms is poorly understood. In Central Amazonia, 9 to 19 years after fragmentation, we recorded species richness and net seedling recruitment rate in forest fragments of 1, 10, and 100 ha and in continuous forest. In 1991 all seedlings 5–100 cm tall within permanent 1-m2 plots in fragments and continuous forest were counted and grouped into tree, liana, palm, and herb life-form classes. In 1993 we manually removed all seedlings that were <1 m tall from the permanent plots. Six years and 5 months later ( 1999 ), all new seedlings recruited into the plots were counted, grouped into different life forms, and classified into distinct morphospecies. The species richness of recruited tree, liana, herb, and palm seedlings was lower in forest fragments than in continuous forest, with the 1-ha fragment having the poorest species richness. The total number of recruited individuals was 40% less than that previously present for all life forms, except lianas. Liana recruitment was 7% to 500% higher than the original abundance in the forest fragments and continuous forest. In general, species similarity was higher among fragments than between fragments and continuous forest, with the 1-ha fragment being less similar. Species rank/abundance curves showed that continuous forest species in all life forms tended to disappear in forest fragments, whereas common species in forest fragments were absent from continuous forest. Overall, our results suggest that the life-form composition and structure of the regenerative plant pool in fragments were shifting toward a species-poor seedling community. Losses of understory species diversity, but especially of tree seedlings, threaten the maintenance of rainforest biodiversity and compromise future forest regeneration. Resumen: La fragmentacion de las selvas tropicales afecta severamente a a los arboles de gran porte, sin embargo, su efecto sobre otros estadios y formas de vida de las plantas es poco conocido. En la Amazonia central, de 9 a 19 anos despues de la fragmentacion, se registro la riqueza de especies y la tasa neta de reclutamiento de plantulas en fragmentos de selva de 1, 10, y 100 ha y en selva continua. En 1991, todas las plantulas de 5–100 cm de altura dentro de cuadrantes permanentes de 1-m2 en los fragmentos y en la selva continua, fueron contadas y agrupadas en diferentes formas de vida: arboles, lianas, palmas y hierbas. En 1993 se removieron manualmente todas las plantulas <1 m de altura dentro de los cuadrantes. Seis anos y cinco meses mas tarde (1999) se contaron todas las plantulas reclutadas dentro de los cuadrantes, se agruparon en diferentes formas de vida v se clasificaron en morfoespecies distintivas. La riqueza de especies de plantulas reclutadas en todas las formas de vida fue menor en los fragmentos que en la selva continua, con el fragmento de 1 ha presentando la menor riqueza de especies. El numero total de individuos reclutados fue 40% menor que los previamente presentes para todas las formas de vida, excepto lianas. El reclutamiento de lianas fue de 7 a 500% mayor que la abundancia original en los fragmentos y en la selva continua. En general la similitud de especies fue mayor entre fragmentos que entre fragmentos y selva continua, con el fragmento de 1-ha siendo el menos similar. Las curvas de rango/abundancia de especies, mostraron que las especies de selva continua en todas las formas de vida tendieron a desaparecer de los fragmentos, mientras que las especies comunes en los fragmentos estuvieron ausentes en la selva continua. En general, nuestros resultados sugieren que la composicion de formas de vida y la estructura del banco regenerativo en fragmentos tienden a convertirse en una comunidad de plantulas pobre en especies. La perdida de diversidad de especies del sotobosque, pero especialmente de plantulas de arboles, amenaza el mantenimiento de la biodiversidad y pone en peligro la regeneracion futura de la selva.

Mechanisms of Pb(II) sorption on a biogenic manganese oxide.

Abstract: Macroscopic Pb(II) uptake experiments and Pb L3-edge extended X-ray absorption fine structure (EXAFS) spectroscopy were combined to examine the mechanisms of Pb(II) sequestration by a biogenic mang...

An artificial reef improves coastal protection and provides a base for coral recovery

Abstract: Silva, R.; Mendoza, E., Marino-Tapia, I.; Martinez, M.L., and Escalante, E. 2016. An artificial reef improves coastal protection and provides a base for coral recovery. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 467-471. Coconut Creek (Florida), ISSN 0749-0208. In 2007, Hurricane Dean caused extensive damage along the coast of Riviera Maya, exceptionally large mass of wind-transported sand was deposited on the beach front and gardens of the former NH Hotel in Puerto Morelos. Due to the chaotic sea state and the debris carried by the storm, the sand was contaminated with various pollutants, including terrigenous materials and biogenic matter. As an emergency measure, this sand was used to create an artificial dune in the grounds of the hotel. Given the high probability of future storms of such magnitude, it was decided that some form ...

Signaling versus punching hole: How do Bacillus thuringiensis toxins kill insect midgut cells?

Abstract: Cry proteins, produced by Bacillus thuringiensis (Bt), are widely used for the control of insect pests in agriculture as spray products or expressed in transgenic crops, such as maize and cotton. Little was known regarding the mechanism of action of these toxins when the first commercial Bt product was introduced fifty years ago. However, research on the mechanism of action over the last two decades has enhanced our knowledge of toxin interaction with membrane receptors and their effects in insect midgut cells. All this information allowed for the rational design of improved toxins with higher toxicity or toxins that overcome insect resistance, which could compromise Bt use and effectiveness in the field. In this review we discuss and evaluate the different models of the mode of action of Cry toxins, including a discussion about the role of various receptors in toxin action.