Xitle Volcano Geoheritage, Mexico City: Raising Awareness of Natural Hazards and Environmental Sustainability in Active Volcanic Areas

co-auteur étrangerInternational audienceThe conservation of geosites in a region can foster its sustainability and develop geotourism. These geosites provide geoeducation, raise people's awareness on natural hazards and increase their resilience. Low-income cities located in tectonically active areas combine high geohazards with high vulnerability and low sustainability. Geosites in these cities should be a tool to decrease people's vulnerability and foster sustainable development. Mexico City is an ideal case study for its environmental and social issues and its setting in an active 2 continental volcanic arc. The 1,700 yrs-old Xitle volcano, located in the city's SW corner, is a small scoria cone that erupted once, feeding an extensive lava field on which >600,000 people now live. The lavas are very well exposed due to thin soils and extensive quarrying. The Xitle lavas covered the first urban center in the Mexico basin, except for the main pyramid that has become a major archeological site. The cone and lavas have significant geodiversity, sustaining a unique and biodiverse ecosystem. The country's largest university preserves the lavas in an ecological reserve. We describe four exceptional geosites, assess their values, and discuss their relevance for addressing issues such as nature preservation, environmental sustainability, social inequalities, and natural hazards. The Xitle volcano provides a wide range of benefits for the city that are nonetheless unknown to its inhabitants. We describe ongoing initiatives to disseminate such information, such as the Geopedregal site, and propose ways that this heritage could be further protected and used by the city in a sustainable way

Mycorrhizas from the tropical dry forest and other fungal symbioses

Antecedentes y Objetivos: Cada vez se sabe más de la diversidad vegetal en el bosque tropical caducifolio, pero en gran medida se desconocen sus simbiosis micorrízicas. El estatus micorrízico y su morfología aportan información importante sobre su papel ecológico en estos ecosistemas. El objetivo de este trabajo fue describir la morfología y los tipos de asociaciones fúngicas que establecen algunas plantas dominantes del estrato arbóreo del bosque tropical caducifolio en época de secas y lluvias. Métodos: El muestreo de raíces se realizó en la costa del Pacífico de México en Chamela, Jalisco, de 2012 a 2014 y desde Puerto Escondido hasta Salina Cruz, Oaxaca, en 2016. Las raíces se muestrearon a través de núcleos de suelo y por rastreo desde el tronco de Achatocarpus gracilis, Achatocarpus spp., Coccoloba barbadensis, C. liebmannii, Cordia elaeagnoides, Guapira petenensis, Lonchocarpus sp., Ruprechtia fusca y R. aff. pallida. Se revisó cada raíz en el microscopio estereoscópico en busca de micorrizas; algunas se aclararon, tiñeron y se montaron en laminillas; se hicieron cortes anatómicos, se tomaron fotografías con microscopio óptico y se describieron las asociaciones rizosféricas según los referentes morfológicos para cada tipo de micorriza. Resultados clave: Todas las plantas tuvieron asociaciones micorrízicas activas en época de secas y de lluvias. Se describieron 64 morfotipos ectomicorrízicos que presentaron variantes morfológicas: zonación del manto en raicillas secundarias o formación de manto incipiente; ausencia de ramificación; ausencia de la red de Hartig o presencia con estructuras intracelulares. Achatocarpus presentó micorrizas duales de ectomicorrizas con micorrizas arbusculares. Conclusiones: Nuestros resultados coinciden en las diferencias morfológicas en las ectomicorrizas que fueron observadas previamente para Nyctaginaceae en Ecuador y Brasil, y se amplían estas observaciones a más familias dentro de Caryophyllales y la familia Fabaceae. Con estas observaciones, y lo reportado previamente, se propone un nuevo concepto morfológico de ectomicorriza “incipiente” para angiospermas tropicales.Background and Aims: The knowledge on plant diversity in the tropical dry forest is constantly increasing, but the knowledge of its mycorrhizal symbioses is scarce. The mycorrhizal status and its morphology provide important information on its ecological role in these ecosystems. The aim of this study was to describe the morphology and fungal association types that some dominant arboreal stratum plants establish in the tropical deciduous forest in both dry and rainy seasons. Methods: Root sampling was performed along the Mexico Pacific coast in Chamela, Jalisco, from 2012 to 2014, and from Puerto Escondido to Salina Cruz, Oaxaca, in 2016. Root samples were collected with soil cores and tracking them from the trunk of Achatocarpus gracilis, Achatocarpus spp., Coccoloba barbadensis, C. liebmannii, Cordia elaeagnoides, Guapira petenensis, Lonchocarpus sp., Ruprechtia fusca, and R. aff. pallida. Each root was reviewed under the stereomicroscope for mycorrhizae; some roots were clarified, stained and mounted on slides; anatomical sections were made, photographs were taken with an optical microscope and the rhizospheric associations were described according to the morphological referents for each type of mycorrhiza. Key results: All plants had active mycorrhizal associations in dry and rainy seasons. Sixty-four ectomycorrhizal morphotypes were described presenting the following morphological variants: zonation of the mantle in secondary roots or incipient mantle formation; absence of branching; absence of Hartig net or presence with intracellular structures. Achatocarpus presented dual mycorrhizae of ectomycorrhizae with arbuscular mycorrhizae. Conclusions: Our results coincide on the ectomycorrhizal morphological differences previously observed in Nyctaginaceae in Ecuador and Brazil, and we extend these observations to more families within Caryophyllales and the family Fabaceae. Our observations, together with previous reports, make us propose a new morphological concept of "incipient" ectomycorrhiza for tropical angiosperms