Sensitivity to nitrate and nitrite in pond-breeding amphibians from the Pacific northwest, USA

In static experiments, we studied the effects of nitrate and nitrite solutions on newly hatched larvae of five species of amphibians, namely Rana pretiosa, Rana aurora, Bufo boreas, Hyla regilla, and Ambystoma gracile. When nitrate or nitrite ions were added to the water, some larvae of some species reduced feeding activity, swam less vigorously, showed disequilibrium and paralysis, suffered abnormalities and edemas, and eventually died. The observed effects increased with both concentration and time, and there were significant differences in sensitivity among species. Ambrystoma gracile displayed the highest acute effect in water with nitrate and nitrite. The three ranid species had acute effects in water with nitrite. In chronic exposures, R. pretiosa was the most sensitive species to nitrates and nitrites. All species showed 15-d LC50s lower than 2 mg N-NO2 /L. For both N ions, B. boreas was the least sensitive amphibian. All species showed a high mortality at the U.S. Environmental Protection Agency- recommended limits of nitrite for warm-water fishes (5 mg N-NO2 /L) and a significant larval mortality at the recommended limits of nitrite concentration for drinking water (1 mg N-NO2 The recommended levels of nitrate for warm-water fishes (90 mg N- NO3 /L) were highly toxic for R. pretiosa and A. gracile larvaePeer reviewe

Dehydrogenase activity in Mediterranean forest soils

6 pages, 2 figures, 4 tables, 31 references. We thank Luis V. Garcia, Eduardo Gutierrez and Malole Diaz-Villa for their field assistance, and Juan Arroyo for advice on the plot design. We also thank Felipe Oliveros (director) and the staff of Los Alcornocales Natural Park for their support and cooperation in setting up the experimental plots. Personnel of TRAGSA conducted the sylvicultural practices. Rafael López and the Soil Laboratory staff at the IRNAS made chemical analyses of soil samples.The dehydrogenase activity (DHA) in the upper 10 cm of forest soils was measured in three experimental plots (1 ha) in Los Alcornocales Natural Park (southern Spain). In each plot, a silviculture treatment of thinning and shrub-clearing had been previously carried out in one half, while the other half was left as a forest control. Soil samples were taken during the dry season (July 2000) and after the first autumn rains (October 2000). The DHA of forest soil in autumn [527+/-165 nmol p-iodonitrotetrazolium formazan (INTF) g(-1) h(-1)] was almost double that in summer (289+/-95 nmol INTF g(-1) h(-1)), for one of the studied plots. During the dry season, DHA of forest control soils (324+/-85 nmol INTF g(-1) h(-1)) was higher than in the thinned and shrub-cleared forest (253+/-93 nmol INTF g(-1) h(-1)). During the autumn (wet season), however, the effects of the silvicultural practices on the soil dehydrogenase were negligible. Significant differences in DHA were found between the three sites. Multiple regression analysis identified pH as the best predictor of DHA of these soils. Other soil properties (pH, K, Ca, Mg, and soil moisture) also showed significant correlations with DHA. In addition, clay content appeared to enhance the enzyme activity. Our results suggest that thinning and shrub-clearing in Mediterranean forests seem to affect negatively the soil DHA, and their impact is more marked during the dry season. However, season and site effects are better determinants of DHA than management practices.This study was supported by the CICYTFEDER, 1FD97-0743-C03-03, project.Peer reviewe

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Abstract The dehydrogenase activity (DHA) in the upper 10 cm of forest soils was measured in three experimental plots (1 ha) in Los Alcornocales Natural Park (southern Spain). In each plot, a sylviculture treatment of thinning and shrub-clearing had been previously carried out in one half, while the other half was left as a forest control. Soil samples were taken during the dry season (July 2000) and after the first autumn rains (October 2000). The DHA of forest soil in autumn [527±165 nmol p-iodonitrotetrazolium formazan (INTF) g -1 h -1 ] was almost double that in summer (289±95 nmol INTF g -1 h -1 ), for one of the studied plots. During the dry season, DHA of forest control soils (324±85 nmol INTF g -1 h -1 ) was higher than in the thinned and shrub-cleared forest (253±93 nmol INTF g -1 h -1 ). During the autumn (wet season), however, the effects of the sylvicultural practices on the soil dehydrogenase were negligible. Significant differences in DHA were found between the three sites. Multiple regression analysis identified pH as the best predictor of DHA of these soils. Other soil properties (pH, K, Ca, Mg, and soil moisture) also showed significant correlations with DHA. In addition, clay content appeared to enhance the enzyme activity. Our results suggest that thinning and shrub-clearing in Mediterranean forests seem to affect negatively the soil DHA, and their impact is more marked during the dry season. However, season and site effects are better determinants of DHA than management practices

Capacidad de adsorción de sulfato de un suelo forestal mediterráneo.

En el presente estudio se ha evaluado la capacidad de adsorción de sulfato en un suelo forestal con vegetación mediterránea. El objetivo del trabajo es conocer la capacidad de adsorción de sulfato en cada uno de los horizontes del suelo, ya que se trata de un proceso responsable de la retención de este nutriente esencial (S) en el ecosistema, impidiendo su pérdida por lavado. La lixiviación de sulfato, además de reducir la fertilidad del suelo y generar problemas de contaminación en los ecosistemas acuáticos, conlleva asociado el lavado de bases esenciales, principalmente calcio y magnesio. La capacidad de adsorción de sulfato se analizó añadiendo al suelo cantidades crecientes de sulfato (0, 25, 100, y 300 mg SO42- L-1); una vez alcanzado el equilibrio, se midió el sulfato presente en la solución del suelo. El sulfato adsorbido se calculó como la diferencia entre el sulfato añadido y el medido en los extractos después de equilibrarse. El experimento se realizó en cada uno de los horizontes descritos en el perfil edáfico (Ah, Bw y C), así como en cuatro profundidades definidas en los 30 cm superiores del perfil (0-2.5, 2.5-10, 10-20, y 20-30 cm). Los valores de sulfato adsorbido se ajustaron al modelo de adsorción teórico descrito por la ecuación lineal de Temkin. A partir del valor de la pendiente de esa recta se estimó el coeficiente de capacidad de adsorción de sulfato. Los resultados encontrados indican que la capacidad de adsorción de sulfato aumenta conforme aumenta la profundidad, tanto en los 30 cm superficiales como en el perfil edáfico. En los horizontes Bw y C se alcanza la máxima capacidad de adsorción de sulfato, con valores muy similares en ambos horizontes. El aumento de la capacidad de adsorción de sulfato con la profundidad puede explicarse por la mayor presencia de óxidos de Fe y Al en los horizontes subsuperficiales, además de una disminución gradual de materia orgánica desde el horizonte Ah al Bw, y valores bajos de pH. En general estos suelos presentan alta capacidad de adsorción de sulfato

Patterns and ecological consequences of abiotic heterogeneity in managed cork oak forests of Southern Spain

13 pages, 3 figures, 8 tables, 64 references.Spatial heterogeneity of abiotic factors influences the structure and function of forests and must be taken into account for their conservation and sustainable management. In this study, we evaluate the heterogeneity of abiotic environmental variables in managed cork oak (Quercus suber L.) forests in southern Spain at patch, site and regional scales. The extent of spatial heterogeneity depended on the environmental variable examined and the scale considered. For example, soil Mn and P and light availability in the understorey were very heterogeneous at the regional scale, while soil N had low regional heterogeneity, but high spatial variability, at patch scale, attributed to open overstorey and grazing disturbance. There was a general trend of increasing heterogeneity with spatial scale. We also study the effects of a silvicultural practice—shrub clearing on the forest environment and its consequence for spatial heterogeneity. Shrub clearing increased understorey light and decreased its spatial heterogeneity with idiosyncratic effects on soil properties and their spatial heterogeneity at each site. Finally, we compare the heterogeneity (estimated by the coefficient of variation) obtained in these cork oak forests with a database compiled from published studies on other forest environments. The comparison revealed a remarkable extent of abiotic heterogeneity in the cork oak forests studied, suggesting that a sustainable management of these forests should combine intrinsic and human induced abiotic heterogeneity to preserve crucial ecological processes and to maintain high levels of biodiversity.This study was supported by the projects 1FD97- 0743-C03-03, Heteromed (REN2002-04041-C02-02/GLO) and Di- named (CGL2005-05830-C03-01), funded by the Spanish CICYT. Co-operative work and discussion of the manuscript was facilitated by the Spanish Network GLOBIMED and PLAS- TOFOR, AGL2004-00536/FOR to FV.Peer reviewe

Identification of a disturbance signal in larval red-legged frogs, Rana aurora

Animals that are warned about the presence of a predator are more likely to avoid and/or survive an encounter with a predator. Chemical signals released by disturbed or injured conspecifics may provide prey animals with an early warning. In this study we conducted experiments to determine whether larval red-legged frogs respond to chemical stimuli produced by disturbed conspecifics and to examine the chemical compounds that may act as the alarm signal. In laboratory tests, groups of tadpoles responded with antipredator behaviours when exposed to chemical cues of disturbed conspecifics but not when exposed to chemical cues of control (undisturbed) conspecifics. In subsequent tests, disturbed animals increased ammonium (the main metabolic waste of tadpoles) excretion relative to undisturbed individuals. When tadpoles were exposed to low-level ammonium concentrations (1 mg NH4+/litre), they responded by increasing antipredator behaviours. Our results suggest that red-legged frog tadpoles release a chemical that provides conspecifics with an early warning of predator presence, and that ammonium (NH4+) may be a component of the disturbance signal.Peer reviewe

Identification of a disturbance signal in larval red-legged frogs, Rana aurora

Animals that are warned about the presence of a predator are more likely to avoid and/or survive an encounter with a predator. Chemical signals released by disturbed or injured conspecifics may provide prey animals with an early warning. In this study we conducted experiments to determine whether larval red-legged frogs respond to chemical stimuli produced by disturbed conspecifics and to examine the chemical compounds that may act as the alarm signal. In laboratory tests, groups of tadpoles responded with antipredator behaviours when exposed to chemical cues of disturbed conspecifics but not when exposed to chemical cues of control (undisturbed) conspecifics. In subsequent tests, disturbed animals increased ammonium (the main metabolic waste of tadpoles) excretion relative to undisturbed individuals. When tadpoles were exposed to low-level ammonium concentrations (1 mg NH4+/litre), they responded by increasing antipredator behaviours. Our results suggest that red-legged frog tadpoles release a chemical that provides conspecifics with an early warning of predator presence, and that ammonium (NH4+) may be a component of the disturbance signal.Peer reviewe

Cycles biogéochimiques et bilan d´eau dans les forets caducifoliées de l´Ouest de l´Espagne (Sierra de Gata, Province de Salamanque)

6 páginas, 3 tablasBiogeochemical cycles of ten elements, water balance, and dynamics of the soil water content in four oak (Q. pyrenaica) forest, selected according to a rainfall transect in the "Sierra de Gata" mountains (Western Spain), have been studied. So, four permanent experimental plots are running on, and monitoring of bioclimatic parameters, and other data about production, growth, litter decomposition, etc, are registered. Results show that production and decomposition are independent from the annual pluviometry. Concerning the soil humidity, is observed the existence of two critical phases: autumn watering and summer dryness: during the transpiration values decrease from moderate to low, showing that in all the forest the summer dryness is a limitant factor, despite the annual total rainfall. Growth and production is higher in the forest with the lowest rainfall.Peer reviewe