Desert evergreen shrubs, which are adapted to low-fertility ecosystems, generally exhibit limited responses to increased nutrient availability and tend to absorb and store nutrients rather than synthesize new tissues. The objective of this work was to analyze the effect of nitrogen fertilization combined with soil water availability on growth, nitrogen content, and nitrogen use efficiency on four shrubs (Atriplex lampa, Capparis atamisquea, Larrea cuneifolia, and Senecio subulatus) from the Monte Desert. In a 120-day glasshouse experiment in Mendoza, Argentina, we compared the effects of three levels of nitrogen fertilization combined with two levels of water availability on seedling biomass, nitrogen content, water potential, and nitrogen use efficiency. Fertilization induced a higher biomass on A. lampa under high water availability and on C. atamisquea regardless of water level. Shoot:root ratios of these two species were lower under water stress without fertilization. On the other hand, L. cuneifolia presented lower root biomass and lower water potential with N fertilization. All species when fertilized exhibited higher nitrogen content and lower nitrogen use efficiency. Also, A. lampa and L. cuneifolia presented higher nitrogen content under water stress conditions. In conclusion, some desert shrubs (A. lampa and C. atamisquea) were able to take advantage of increased nitrogen availability producing more biomass. Understanding seedlings response to nitrogen and water availability on arid lands is critically important to develop adequate revegetation techniques of degraded areas.Communicated by Katinka Ruthrof.
RESUMEN.Conocer las diferentes estrategias de las especies arbustivas de zonas áridas permite seleccionarlas para restaurar un sitio determinado. De acuerdo con el esquema de estrategias de Grime, las plantas de zonas áridas divergen principalmente en dos tipos: por un lado, estrés-tolerantes; por el otro, ruderales. Los objetivos fueron evaluar el efecto de tres niveles de estrés hídrico sobre el crecimiento y sobre algunos caracteres ecofisiológicos de Atriplex lampa, Larrea cuneifolia y Senecio subulatus, y determinar las estrategias de estas especies frente al estrés hídrico para poder seleccionarlas luego en programas de restauración. Para ello se aplicaron tres niveles de estrés hídrico (se regó cuando el contenido hídrico del suelo disminuyó hasta 50, 70 y 85%, control, estrés hídrico moderado y severo, respectivamente) a 60 plantines por especie en invernáculo, se construyeron curvas presión-volumen y se determinó el peso seco, parámetros hídricos, índices ecofisiológicos asociados a la tolerancia a la sequía, y se obtuvieron las estrategias según Grime mediante la herramienta StrateFy. En condiciones de estrés hídrico severo, las tres especies acumularon menos materia seca y disminuyeron su área foliar, y el crecimiento de S. subulatus fue el que más se vio afectado. Atriplex lampa y L. cuneifolia mostraron un bajo contenido de materia seca foliar, y A. lampa presentó menor área foliar específica. A través de estos caracteres foliares se clasificaron las tres especies como estrés-tolerantes según Grime. También, se observó que A. lampa y L. cuneifolia realizan ajuste osmótico en condiciones de estrés hídrico, mientras que S. subulatus mantiene potenciales hídricos altos y no modifica sus parámetros hídricos. Ante lo expuesto, S. subulatus presenta pocos mecanismos para enfrentar el estrés hídrico y podría utilizarse para restaurar micrositios donde se acumule agua, mientras que por sus características estrés-tolerantes, A. lampa y L. cuneifolia se recomiendan para usarlas ampliamente en la restauración de áreas degradadas del Monte.[Palabras clave: estrés-tolerante, ruderal, triángulo de Grime, curvas presión-volumen, Atriplex lampa, Larrea cuneifolia, Senecio subulatus] ABSTRACT. Water stress coping strategies for three shrub species of the Monte desert and their relevance for restoration. Knowing the different strategies of shrub species in arid zones allows selecting them to restore a specific site. According to Grime's strategy scheme, plants of arid zones diverge into two main types: stresstolerant, on the one hand, and ruderal, on the other. The objective of this study was to evaluate the adaptations to water stress of three shrub species (Atriplex lampa, Larrea cuneifolia and Senecio subulatus) widely distributed along the Monte region, as to be able to select them properly in future restoration projects. Three levels of water stress (watered when soil water content decreased by 50, 70 and 85%, control, moderate and severe water stress, respectively) were applied to 60 seedlings per species in a g...
Mimosa ephedroides is an endemic shrub from western Argentina. The knowledge of the germination response of this species to different environmental factors contribute to its efficient use in ecological restoration projects. This study aimed to examine aspects of seed quality, seed dormancy, and the effect of temperature, water and saline stress on the germination of this species. Also, the effect of seed storage time on the viability and the percentage of germinated seeds were evaluated. Experiments were carried out in controlled growth chambers. Germination percentage and mean germination time were calculated. It was found that this species has non-dormant seeds. Concerning abiotic factors, the optimum temperature for germination ranged from 20 to 30 ºC, it presented high germination percentages even at moderate and severe water stress (-1.12 MPa), and the germination percentages decreased with increasing salinity levels from 300 mM NaCl. In short periods (up to 36 months), seed storage at room temperature (18ºC) was adequate, not affecting the viability and the germination power of the seeds. These results constitute a contribution to the knowledge of the autecological aspects of this endemic species, support its incorporation for restoration projects, and aid to an efficient use of native seeds for direct seeding or seedling production. Highlights Mimosa ephedroides seeds are non- dormant, show high viability and rapid germination (>24 h). This shrub is able to germinate in a wide range of temperatures and under moderate and severe water stress. High salinity levels (<300 Mm NaCl) negatively affected seed germination. Seed storage for short periods (<5 years) at room temperature (18ºC) did not affect seed viability and germination.
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