Eficiencia de reabsorción de nitrógeno y fósforo y sus relaciones estequiométricas durante la senescencia en especies del Desierto Sonorense

Antecedentes: Nitrógeno (N) y Fósforo (P) son los nutrientes más limitantes en plantas y su eficiencia de reabsorción sugiere estrategias de conservación. La reabsorción además afecta los cocientes estequiométricos en la hojarasca, modificando las interacciones ecológicas y los ciclos biogeoquímicos en gradientes de aridez. Hipótesis: Existirá mayor eficiencia de reabsorción de nutrientes en especies de sitios con mayor aridez, por lo que esperamos que los cocientes estequiométricos de C:N y C:P sean mayores en hojas senescentes. Especies de estudio: Ipomoea arborescens, Fouquieria macdougalii, Cercidium microphyllum, Encelia farinosa, Mimosa laxiflora, Jatropha cardiophylla, Cenchrus ciliaris, Olneya tesota, Prosopis velutina, Cercidium floridum, Fouquieria splendens, Brongniartia minutifolia, Jatropha cordata, Colubrina viridis, Larrea tridentata y Cercidium praecox. Sitio de estudio y fechas: Tres sitios en un gradiente de aridez del Desierto Sonorense, en la región central de Sonora. Agosto - noviembre 2017 y 2018. Métodos: Se obtuvieron la eficiencia de reabsorción de N y P, y cocientes estequiométricos C:N, C:P y N:P en hojas verdes y senescentes de especies, comparando tipos funcionales y sitios. Resultados: La eficiencia de reabsorción disminuyó con el incremento de aridez así como los cocientes estequiométricos C:N y C:P en hojas senescentes y N:P en leguminosas. Conclusiones: La eficiencia de reabsorción no sugiere una estrategia de conservación de recursos, sin embargo, las diferencias entre tipos funcionales permitieron diferenciar estrategias ecológicas y estequiométricas, en particular las leguminosas, que ayudan a resaltar su influencia en la biogeoquímica de las zonas áridas Sonorenses y posiblemente del país.

Prosopis velutina (velvet mesquite).

P. velutina was widely introduced around the world intentionally, due to its value as a fuel/fodder species and also an ornamental in some regions. It was widely used by native Amerindians as a source of poles and fuels, and the pods were a valuable source of human and animal nutrition. The month of the year when pods were harvested was commonly named after the tree, indicating its importance. However, its has also spread, both in its native range and where introduced, and its infamy as an invasive species has lead to several governments banning further importation of planting stock, and the risk of introduction is perceived as low. P. velutina is a declared noxious weed in Australia and South Africa, and the genus as a whole is regulated in several other countries. Losses to the livestock industry from P. velutina invasion in its native range, although much less than that caused by the invasion of P. glandulosa, are still considerable. The thorns can also cause injury to livestock, and consumption of the pods, when they may up the bulk of the animal's diet, can lead to ill health and even death. A similar situation to that of the south-western USA exists in Australia and South Africa, where P. velutina is a major weed of rangelands.

Effects of Prosopis velutina Invasion on Soil Characteristics along the Riverine System of the Molopo River in North-West Province, South Africa

Invasive alien plants are one of the major threats to ecosystems. Many invasive plant species, such as Prosopis species, have been introduced around the world and can alter the soil properties of invaded ecosystems. It is one of the most aggressive invasive plant invaders in the North-West Province of South Africa, but little information is available about their influence on soil properties. This study was conducted to investigate the effect of Prosopis velutina invasion on selected soil properties at five different sites along the riverine system of the Molopo River in North West Province. At each study site, soil characteristics were measured from soil samples taken under P. velutina canopies, between canopies and in the benchmark stands free of Prosopis species. The effect on selected soil properties of P. velutina invasion varied between the three stands and between sites. In all the sites, almost all soils collected from under the canopies had a significantly higher soil exchangeable Ca, K, Mg, and Na, organic matter (OM), total nitrogen (TN), available phosphorus (P), Electrical conductivity (EC), and cation exchange capacity (CEC) than the other sample positions, except for the pH which had the high value in intercanopies. Significantly higher ( p < 0.05 ) values of almost all soil properties were found on the densely invaded sites (Tshidilamolomo I and Tshidilamolomo II) compared to lightly invaded sites (Mabule, Black Heat Farm, and Bray). However, it was difficult to generalise as the effects often appear to be site-specific. In addition, the findings also indicated that soils textural classes ranged between sand, silt, and clay in all study sites with a higher proportion of sand in the benchmark than in the soil under the canopies and intercanopies. Soil characteristics differed significantly more between sites than among positions. The site effects observed in this current study provide evidences that this species may occupy a relatively broad soil niche.

Respuestas de los atributos fotosintéticos y estequiométricos a la aridez en las especies y tipos funcionales de dos comunidades del desierto sonorense

Antecedentes: Las plantas de zonas secas han desarrollado adaptaciones para el uso eficiente del agua (UEA), aunque la limitación de nutrientes y exceso de irradiancia también afectan su desempeño. Altas tasas de fotosíntesis y contenido de nitrógeno foliar reportado previamente parecen contradecir la alta UEA en sus especies y comunidades. Preguntas: ¿Cómo son los atributos foliares ecofisiológicos y estequiométricos en especies desérticas? ¿Favorecen las especies desérticas la mayor eficiencia en el uso del agua y/o nutrientes? Especies de estudio: Calliandra eriophylla, Cercidium microphyllum, Encelia farinosa, Eysenhardtia orthocarpa, Fouquieria diguetii, Fouquieria macdougalii, Ipomoea arborescens, Jatropha cardiophylla, Jatropha cordata, Larrea tridentata, Mimosa laxiflora, Olneya tesota y Prosopis velutina. Sitio y años de estudio: Desierto Sonorense, Región central de Sonora, México. Agosto- septiembre de 2019. Métodos: Se midieron y analizaron atributos ecofisiológicos y estequiométricos foliares en especies y tipos funcionales de dos comunidades. Resultados: Se encontró mayor variabilidad en atributos fotosintéticos y de la fluorescencia que en la composición elemental y cocientes estequiométricos. Las especies en el sitio árido mostraron tendencias de mayores tasas fotosintéticas e integridad fotoquímica y baja UEA. En la comunidad semiárida los atributos foliares se asociaron con mayor composición elemental (Nmass, Pmass), menores cocientes estequiométricos y eficiencia de uso de nitrógeno (EUN). Conclusiones: Los atributos foliares de las especies y tipos funcionales del Desierto Sonorense se correlacionaron con los mecanismos de fotoprotección y no las eficiencias de uso de recursos instantáneas, privilegiando la ganancia de C a largo plazo.

Soil nitrogen response to shrub encroachment in a degrading semi-arid grassland

Transitions from grass- to shrub-dominated states in drylands by woody plant encroachment represent significant forms of land cover change with the potential to alter the spatial distribution and cycling of soil resources. Yet an understanding of how this phenomenon impacts the soil nitrogen pool, which is essential to primary production in arid and semi-arid systems, is poorly resolved. In this study, we quantified how the distribution and speciation of soil nitrogen, as well as rates of free-living biological nitrogen fixation, changed along a gradient of increasing mesquite (Prosopis velutina Woot.) cover in a semi-arid grassland of the southwestern US. Our results show that site-level concentrations of total nitrogen remain unchanged with increasing shrub cover as losses from inter-shrub areas (sum of grass and bare-soil cover) are proportional to increases in soils under shrub canopies. However, despite the similar carbon-to-nitrogen ratio and microbial biomass of soil from inter-shrub and shrub areas at each site, site-level concentrations of inorganic nitrogen increase with shrub cover due to the accumulation of ammonium and nitrate in soils beneath shrub canopies. Using the acetylene reduction assay technique, we found increasing ratios of inorganic nitrogen to bioavailable phosphorus inhibit rates of biological nitrogen fixation by free-living soil bacteria. Overall, these results provide a greater insight into how grassland-to-shrubland transitions influence the soil N pool through associated impacts on the soil microbial biomass.

ACTIVIDAD ANTIOXIDANTE DE EXTRACTOS DE HOJA DE MEZQUITE (Prosopis velutina)

El mezquite (Prosopis velutina) es una planta tradicionalmente utilizada por el hombre y animales como alimento en ciertas regiones de México. Además, también es considerada medicinal debido a que posee ciertas propiedades biológicas, las cuales son atribuidas a la presencia de fitoquímicos como los compuestos fenólicos. El objetivo fue evaluar la composición y actividad antioxidante de extractos de hoja de mezquite obtenidos con diferentes solventes. Los extractos se obtuvieron utilizando como solventes de extracción, agua (EAM), etanol y agua (1:1) (EAEM) y etanol (EEM); una vez obtenidos se evaluaron determinando presencia de posibles compuestos tóxicos (alcaloides, cianógenos y saponinas); el contenido de fenoles y flavonoides totales (CFT y CFvT); así como la actividad antioxidante de los extractos mediante la inhibición del radical DPPH• y el poder reductor (FRAP). Los resultados mostraron que en los extractos no se encontró la presencia de compuestos tóxicos; que los valores más altos de rendimiento de extracción fueron para el EAEM (21.4%); y que el mayor CFT y CFvT (> 50 mg/g), así como la actividad antioxidante la presentó el EEM (34%). Por lo que, el EEM pudiera ser utilizado como aditivo en la industria farmacéutica o como ingrediente en la formulación de alimentos.

Soil nitrogen response to shrub encroachment in a degrading semiarid grassland

Transitions from grass- to shrub-dominated states in drylands by woody plant encroachment represent significant forms of land cover change with the potential to alter the spatial distribution and cycling of soil resources. Yet an understanding of how this phenomenon impacts the soil nitrogen pool, which is essential to primary production in arid and semiarid systems, is poorly resolved. In this study, we quantified how the distribution and speciation of soil nitrogen, as well as rates of free-living biological nitrogen fixation, changed along a gradient of increasing mesquite (Prosopis velutina Woot.) cover in a semiarid grassland of the Southwestern US. Our results show that site-level concentrations of total nitrogen remain unchanged with increasing shrub cover as losses from intershrub areas (sum of grass and bare-soil cover) are proportional to increases in soils under shrub canopies. However, despite the similar carbon-to-nitrogen ratio and microbial biomass of soil from intershrub and shrub areas at each site, site-level concentrations of inorganic nitrogen increase with shrub cover due to the accumulation of ammonium and nitrate in soils beneath shrub canopies. Using the acetylene reduction assay technique, we found increasing ratios of inorganic nitrogen-to-bioavailable phosphorus inhibit rates of biological nitrogen fixation by free-living soil bacteria. Consequently, we conclude that shrub encroachment has the potential to significantly alter the dynamics of soil nitrogen cycling in dryland systems.

Características anatómicas, físico-mecánicas y de maquinado de la madera de mezquite (Prosopis velutina Wooton)

Las características anatómicas, físico-mecánicas y de maquinado de la madera de mezquite (Prosopis velutina) fueron determinadas. Se recolectaron en el estado de Sonora cinco trozas de dos metros a partir del tocón. El estudio anatómico se efectuó conforme a lo estipulado por la IAWA. Las propiedades físico-mecánicas se evaluaron de acuerdo a las normas DIN. El maquinado se efectuó de forma manual y para la evaluación de la superficie se tomó como base la norma ASTM D 1666-87. La madera presentó porosidad difusa a semianular. Duramen con abundantes depósitos de color ámbar en vasos, parénquima axial y radial. Longitud y espesor promedio de fibras de 863 μm y 4.3 μm. Parénquima paratraqueal aliforme, confluente de alas anchas. Radios medulares homocelulares. Cristales prismáticos abundantes en cámaras de parénquima axial. Densidad básica de la madera muy alta (0.79 g cm-3) y con buena estabilidad dimensional. La resistencia a la flexión se clasificó como media (17 N mm-2), y bajo módulo de elasticidad (1 232 N mm-2). En resistencia a la compresión longitudinal se clasificó como muy alta (87 N mm-2), y el módulo de elasticidad bajo (1 915 N mm-2). La resistencia al impacto es regular (51 kJ m-2). Al cizallamiento se considera como dura (19 N mm-2). La dureza Brinell se califica como muy alta (tangencial 72 y radial 73 N mm-2, longitudinal 96 N mm-2). Buena respuesta al encolado (Nivel 5; 7 N mm-2). Su maquinado se califica como bueno, por lo que se deben utilizar herramientas de corte provistas con pastillas de carburo de tungsteno.

Plants from the abandoned Nacozari mine tailings: evaluation of their phytostabilization potential

Phytostabilization is a remediation technology that uses plants for in-situ stabilization of contamination in soils and mine tailings. The objective of this study was to identify native plant species with potential for phytostabilization of the abandoned mine tailings in Nacozari, Sonora in northern Mexico. A flora of 42 species in 16 families of angiosperms was recorded on the tailings site and the abundance of the most common perennial species was estimated. Four of the five abundant perennial species showed evidence of regeneration: the ability to reproduce and establish new seedlings. A comparison of selected physicochemical properties of the tailings in vegetated patches with adjacent barren areas suggests that pH, electrical conductivity, texture, and concentration of potentially toxic elements do not limit plant distribution. For the most abundant species, the accumulation factor for most metals was <1, with the exception of Zn in two species. A short-term experiment on adaptation revealed limited evidence for the formation of local ecotypes inProsopis velutinaandAmaranthus watsonii. Overall, the results of this study indicate that five native plant species might have potential for phytostabilization of the Nacozari tailings and that seed could be collected locally to revegetate the site. More broadly, this study provides a methodology that can be used to identify native plants and evaluate their phytostabilization potential for similar mine tailings.