Erick de la Barrera

Stem water relations and net CO2 uptake for a hemiepiphytic cactus during short-term drought

Abstract Hylocereus undatus is widely distributed naturally and is currently cultivated in 19 countries for fruit. Because of its relatively thin stems, H . undatus was hypothesized to respond to drought more rapidly than other cacti. Stem water potential, water content and thickness were monitored during drought to provide easily measured parameters to be correlated with net CO 2 uptake ability, allowing the development of irrigation schedules to optimize water-use efficiency. H. undatus exhibited Crassulacean acid metabolism, as maximal stomatal opening and net CO 2 uptake occurred at night. Although the soil water potential decreased to −4.2 MPa during 12 days without watering, the stem water status parameters remained near their values under wet conditions ( Ψ stem of −0.67 MPa, water content of 90.8%, thickness of 4.48 mm). The drought was accompanied by a 63% decrease in the maximal water vapor conductance and a 57% decrease in the maximal net CO 2 uptake rate, but when the roots were excised for plants under wet conditions, neither parameter decreased appreciably over a comparable time period. Injection of 100 μM abscisic acid into attached stems and placing cut ends of detached stems in such a solution substantially reduced gas exchange 1 day later; at 2 days after injecting the hormone, the maximal water vapor conductance was similar to the minimal daytime values under wet conditions and the net CO 2 uptake rate was inhibited by 97%. Abscisic acid produced in the roots apparently leads to stomatal closure for this hemiepiphyte—whose roots can occur in very limited soil volumes—as soon as the water supply starts to deplete rather than after a large fraction of its stem water is transpired.

Wind effects on leaf morphology for the mangrove Conocarpus erecta at an oceanic island from the Mexican Pacific Ocean

Se midio la morfologia foliar y se calcularon atributos aerodinamicos ademas de tasas potenciales de transpiracion del mangle Conocarpus erecta en sitios naturalmente protegidos y expuestos al viento oceanico en la Isla Socorro, Mexico, y de C. erecta, Laguncularia racemosa y Rhizophora mangle en un estuario continental cerca de La Manzanilla, Jalisco, Mexico. Se realizaron comparaciones entre especies y sitios. Las hojas de C. erecta, de 5,98 cm de longitud y 2,03 de ancho, fueron las mas pequenas y aerodinamicas de los mangles del continente. Mas aun, ambas dimensiones foliares fueron 32 % mas pequenas para los arboles de los sitios expuestos en la Isla Socorro que en el continente. Para cualquier velocidad del viento, el numero de Reynolds fue 10 a 33 % menor en Isla Socorro que para las hojas de C. erecta en el continente, por lo que el viento ejerce una fuerza de arrastre 17 a 45 % menor para las primeras. El numero de Reynolds caracteriza la turbulencia de un fluido que se mueve adyacente a una superficie; aqui se utilizo dicho numero adimensional como medida del revoloteo de las hojas. La tasa de transpiracion de C. erecta en Isla Socorro fue 25 % menor para las plantas de sitios expuestos que para aquellas de sitios protegidos, cuya transpiracion promedio 4 mmol m_2 s_1 al medio dia. Conocarpus erecta presento mejores caracteristicas para ambientes con viento debido a que sus hojas son mas pequenas y aerodinamicas. La poblacion de Isla Socorro presento mayores cambios morfologicos en respuesta al viento en sitios expuestos, explicando, en parte, la presencia de esta especie y no de otros manglares en esta isla oceanica

Responses to simulated nitrogen deposition by the neotropical epiphytic orchid Laelia speciosa

Potential ecophysiological responses to nitrogen deposition, which is considered to be one of the leading causes for global biodiversity loss, were studied for the endangered endemic Mexican epiphytic orchid, Laelia speciosa, via a shadehouse dose-response experiment (doses were 2.5, 5, 10, 20, 40, and 80 kg N ha−1 yr−1) in order to assess the potential risk facing this orchid given impending scenarios of nitrogen deposition. Lower doses of nitrogen of up to 20 kg N ha yr−1, the dose that led to optimal plant performance, acted as fertilizer. For instance, the production of leaves and pseudobulbs were respectively 35% and 36% greater for plants receiving 20 kg N ha yr−1 than under any other dose. Also, the chlorophyll content and quantum yield peaked at 0.66 ± 0.03 g m−2 and 0.85 ± 0.01, respectively, for plants growing under the optimum dose. In contrast, toxic effects were observed at the higher doses of 40 and 80 kg N ha yr−1. The δ13C for leaves averaged −14.7 ± 0.2‰ regardless of the nitrogen dose. In turn, δ15N decreased as the nitrogen dose increased from 0.9 ± 0.1‰ under 2.5 kg N ha−1yr−1 to −3.1 ± 0.2‰ under 80 kg N ha−1yr−1, indicating that orchids preferentially assimilate NH4+ rather than NO3− of the solution under higher doses of nitrogen. Laelia speciosa showed a clear response to inputs of nitrogen, thus, increasing rates of atmospheric nitrogen deposition can pose an important threat for this species.

Potassium enhances frost tolerance in young individuals of three tropical dry forest species from Mexico

Movement of species outside their range of distribution could be a strategy for conservation purposes, but before implementation, it is necessary to evaluate plants responses to the conditions that they will experience in new locations. We evaluated the effect of potassium fertilisation to enhance the frost tolerance of young individuals of Albizia plurijuga (Standley) Britton & Rose, Cedrela dugesii S.Watson and Ceiba aesculifolia (Kunth) Britten & Baker f., which are all common species from tropical dry forests in Mexico. Plants were propagated in a shade-house and fertilised during 9 months with different concentrations of potassium (39, 189 and 528ppm). In frost simulations, plants were exposed to temperatures below 0°C during different time periods and frost injury was assessed by electrolyte leakage of leaf discs from young and old leaves. We observed that potassium fertilisation enhanced frost tolerance by reducing electrolyte leakage mainly in young leaves. We recorded plant re-sprouting ability after exposure to subzero temperatures over 45 days, finding notable differences among species: all individuals of C. dugesii sprouted, followed by some of A. plurijuga and finally just one of C. aesculifolia. Also, high potassium levels increased re-sprouting response. These species have a low frost tolerance, but potassium fertilisation seemed to be effective to enhance it for young individuals, increasing the probability of survival if plants are moved to colder areas than current habitats.

In vitro germination and development of two endangered endemic Colombian orchids Cattleya mendelii and Cattleya quadricolor

Cattleya mendelii y C. quadricolor son dos orquideas endemicas de Colombia que han sido sujetas a extraccion de sus ambientes naturales para la venta, esto ha conducido a estas plantas a estar criticamente amenazadas. En la actualidad, no existe una practica sustentable para el manejo de estas especies. El objetivo de este estudio fue establecer un protocolo de cultivo in vitro para ambas especies. El efecto de diferentes combinaciones de medios de cultivo MS y KC modificados con AG3 y ANA fueron evaluados para la germinacion y desarrollo in vitro. El desarrollo fue evaluado cada 30 dias, durante 120 dias. La mayor produccion de explantes para ambas especies fue observada con MS. Mayor proporcion de AG3 de 1.5 μM resulto en el aumento de la germinacion, asimismo mayores concentraciones de ANA de 1.5 μM favorecen los estadios tardios del desarrollo vegetal in vitro. El numero y la longitud de los brotes y las raices fueron mayores cuando las plantas de ambas especies se cultivaron en medio MS. La germinacion y desarrollo in vitro de C. mendelii and C. quadricolor en este estudio fue una aproximacion exitosa para la propagacion y puede ser considerada para programas de conservacion de estas orquideas.

Evaluation of three organic fertilizers for growing the widely cultivated crop Cucurbita pepo L.

As a result of an increase in the urban demand for organic horticultural products, locally available soil amendments need to be evaluated. Here, the effects on growth and reproductive output of Cucurbita pepo , were assessed for the aquatic invasive Eichornia crassipes , a commercially produced vermicompost, and chicken manure. In addition, their effects were contrasted with those of a Nitrogen (N) dose-response experiment that was used for standardization of plant responses. In general, higher N doses yielded a greater reproductive output. For instance, the high N concentrations of 3.2 and 8 mM yielded over 50% more flowers that were also about three times larger than those from the lower doses. While chicken manure inhibited seed germination for C. pepo , transplanted individuals treated with this soil amendment were the only ones to produce female flowers. In addition, a greater number of male flowers (4-fold greater) that were substantially (3.3-fold by dry mass) heavier than the control resulted from this amendment. Plants fertilized with vermicompost produced twice as many flowers than the control, and were 43% heavier. In turn, the plants fertilized with E. crassipes tended to be similar to the control. Key words: Chicken manure, invasive species control, organic fertilizer, vermicompost, water hyacinth. INTRODUCTION The use of organic soil amendments for crop production has become increasingly important around the world (Altieri, 1987; Gliessman, 1997). For the case of Mexico such an organic agriculture has two main drivers. First, a majority of agricultural operations are of self sustenance and receive low agrochemical inputs, owing to their ever increasing prices. In this case, many farmers resort to the use of organic soil amendments, usually derived from farm and domestic residues. The second driver for the use of organic soil amendments is the fact that an import-ant portion of the country’s commercial agriculture caters to international markets that exert an increasing pressure to implement more sustainable agricultural practices. In

Biomonitors of atmospheric nitrogen deposition: potential uses and limitations

Atmospheric nitrogen deposition resulting from anthropic activities is a major threat to global biodiversity. Given high costs of deploying automated monitoring networks, this paper makes the case for the use of plant biomonitors, such as mosses, grasses, trees and epiphytes to characterize atmospheric nitrogen pollution.

Characterization of nitrogen deposition in a megalopolis by means of atmospheric biomonitors

An increase of nitrogen deposition resulting from human activities is not only a major threat for global biodiversity, but also for human health, especially in highly populated regions. It is thus important and in some instances legally mandated to monitor reactive nitrogen species in the atmosphere. The utilization of widely distributed biological species suitable for biomonitoring may be a good alternative. We assessed the suitability of an ensemble of atmospheric biomonitors of nitrogen deposition by means of an extensive sampling of a lichen, two mosses, and a bromeliad throughout the Valley of Mexico, whose population reaches 30 million, and subsequent measurements of nitrogen metabolism parameters. In all cases we found significant responses of nitrogen content, C:N ratio and the δ15N to season and site. In turn, the δ15N for the mosses responded linearly to the wet deposition. Also, the nitrogen content (R2 = 0.7), the C:N ratio (R2 = 0.6), and δ15N (R2 = 0.5) for the bromeliad had a linear response to NOx. However, the bromeliad was not found in sites with NOx concentrations exceeding 80 ppb, apparently of as a consequence of excess nitrogen. These biomonitors can be utilized in tandem to determine the status of atmospheric nitrogenous pollution in regions without monitoring networks for avoiding health problems for ecosystems and humans.

High resilience to extreme climatic changes in the CAM epiphyte Tillandsia utriculata L. (Bromeliaceae)

Climate change is expected to increase the frequency of extreme climatic events, yet few studies have addressed the capacity of plant species to deal with such events. Species that are widespread are predicted to be highly plastic and able to acclimate to highly changing conditions. To study the plasticity in physiological responses of the widely distributed epiphyte Tillandsia utriculata, we transplanted individuals from a coastal scrub and broadleaf evergreen forest to a similar coastal scrub site and forest. After a 45-day acclimation, the plants were moved to a semi-controlled greenhouse at each site, and then subjected to a 20-day drought. Physiological variables were measured during the acclimation and the drought. The individuals of scrub and forest populations had similar relative water content and carbon assimilation in the contrasting conditions of the two transplantation sites despite the high discrepancy between the environments at their original site. Electron transport rates were higher in individuals from the scrub population. Electron transport rates were also higher than estimated from carbon assimilation, suggesting that photorespiration was present. The individuals of the coastal scrub population had a higher capacity to dissipate excess energy this way. The relative distance index of plasticity was high overall, indicating that some traits are highly plastic (titratable acidity, carbon assimilation) in order to maintain the stability of others (maximum quantum yield Fv /Fm and relative water content). We conclude that T. utriculata is a highly plastic species with a high capacity to tolerate extreme environmental changes over a short time.

Mapping pollution in a megalopolis: the case for atmospheric biomonitors of nitrogen deposition

An increase of nitrogen deposition resulting from human activities is not only a major threat for global biodiversity, but also for human health, especially in highly populated regions. It is thus important and in some instances legally mandated to monitor reactive nitrogen species in the atmosphere. However, deployment of automated networks can be excessively costly for most cities so the utilization of widely distributed biological species suitable for biomonitoring may be a good alternative. The aim of this work was thus to assess the suitability of different atmospheric organisms as biomonitors of nitrogen deposition, by means of an extensive sampling of a lichen, two mosses, and one bromeliad throughout the Valley of Mexico, the basin where the megalopolis of Mexico City (population 20 million) is located, and subsequent measurements of nitrogen metabolism parameters. In all cases significant responses of nitrogen content, C:N ratio and δ15N were found for the lichen Anaptychia sp. the mosses Grimmia sp. and Fabronia sp., and the bromeliad Tillandsia recurvata in response to season and collected site. In turn, δ15N for the mosses responded linearly to the wet deposition (R2 = 0.7 for Grimmia sp. and R2 = 0.2 for Fabronia sp.). Also, the nitrogen content (R2 = 0.7), the C:N ratio (R2 = 0.6), and δ15N (R2 = 0.5) for the bromeliad had a linear response to NOx. However, latter species was not found in sites with NOx concentrations above 212 ppm. These biomonitors can be utilized in tandem to determine the status of nitrogenous pollution in regions without monitoring networks. Capsule An ensamble of atmospheric biomonitors of nitrogen deposition can be usefull for determining pollution in urban areas. In particular, tissue nitrogen content, C:N ratio, and δ15N of mosses responded to wet deposition, while those of Tillandsia recurvata were able to track NOx.An increase of nitrogen deposition resulting from human activities is not only a major threat for global biodiversity, but also for human health, especially in highly populated regions. It is thus important and in some instances legally mandated to monitor reactive nitrogen species in the atmosphere. The utilization of widely distributed biological species suitable for biomonitoring may be a good alternative. We assessed the suitability of an ensemble of atmospheric biomonitors of nitrogen deposition by means of an extensive sampling of a lichen, two mosses, and a bromeliad throughout the Valley of Mexico, whose population reaches 30 million, and subsequent measurements of nitrogen metabolism parameters. In all cases we found significant responses of nitrogen content, C:N ratio and the δ 15 N to season and site. In turn, the δ 15 N for the mosses responded linearly to the wet deposition. Also, the nitrogen content (R 2 = 0.7), the C:N ratio (R 2 = 0.6), and δ15N (R 2 = 0.5) for the bromeliad had a linear response to NOx. However, the bromeliad was not found in sites with NOx concentrations exceeding 80 ppb, apparently of as a consequence of exceeding nitrogen. These biomonitors can be utilized in tandem to determine the status of atmospheric nitrogenous pollution in regions without monitoring networks for avoiding health problems for ecosystems and humans.