Bacteriana en el suelo en ecosistemas oligotróficos: una revisión crítica

El fósforo (P) es un elemento esencial para la vida, por lo cual entender los mecanismos que permiten su disponibilidad en el suelo es prioritario. Debido a la complejidad de la dinámica de este nutriente, aún existen varios procesos que no están claramente entendidos, principalmente en los ecosistemas oligotróficos. En la presente revisión se analiza literatura relacionada con procesos involucrados en la disponibilidad del P, dándole énfasis al papel de las bacterias. La forma química disponible del P es el ortofosfato, pero por su alta reactividad y demanda de la biota, esta forma es rápidamente disminuida de la solución del suelo. Por lo que es necesario que la biota adquiera este elemento de otras formas químicas. Entre ellas, las formas orgánicas representan la principal fuente de este nutriente mediante la mineralización bioquímica producto principalmente de la comunidad bacteriana del suelo. Entre los compuestos organofosforados, los ésteres de fosfatos son los más fáciles de mineralizar, por la poca demanda energética en la producción de las enzimas involucradas en dicho proceso. Por otro lado, la mineralización de los fosfonatos puede representar una fuente alternativa de P disponible, a pesar de que se había considerado que esta forma química no era accesible por la complejidad de sus moléculas. En general, una estrategia exitosa para la adquisición de P en ecosistemas donde dicho elemento es limitado, depende de la presencia de una maquinaria genética capaz de sintetizar las diferentes enzimas que mineralizan compuestos orgánicos con demandas energéticas diferentes (fosfohidrolasas, fosfonatasas y C-P liasas), además de la presencia de transportadores específicos de membrana y la disponibilidad de C como fuente de energía. Aún faltan estudios integrados que permitan elucidar el movimiento del P en los ecosistemas y cómo esto puede ser controlado y llevado a cabo por las bacterias que habitan en el suelo

Phosphorus Recycling, Biocontrol, and Growth Promotion Capabilities of Soil Bacterial Isolates from Mexican Oak Forests: An Alternative to Reduce the Use of Agrochemicals in Maize Cultivation

Six bacteria (Bacillus velezensis 13, Bacillus subtillis 42, Pseudomonas fluorescens E221, Pseudomonas Poae EE12, Rahnella sp. EM1, and Serratia sp. EM2) isolated from the soil and litter of Mexican oak forests were characterized by identifying their ability to acquire phosphorus from different sources, analyzed for their biocontrol capabilities against two different phytopathogenic fungi, and finally tested for their ability to stimulate the germination of maize seeds and promotion of maize seedling growth. The greatest capacity to biocontrol the mycelial growth of phytopathogenic fungi Botrytis cinerea and Fusarium oxysporum was found in B. velezensis 13 and B. subtillis 42. P. poae EE12 and P. fluorescens E221 significantly promoted germination and the length of the primary root in Zea mays. Rahnella sp. EM1 and Serratia sp. EM2 could produce indole compounds related to auxin synthesis and increased the fresh weight of the maize seedlings. Together, these isolates represent an alternative to reduce the use of agrochemicals in maize cultivation. In general, soil microorganisms from Mexican oak forests represent a source of genetic resources for the sustainable management and conservation of soils for agricultural use

The response of soil microbial communities to variation in annual precipitation depends on soil nutritional status in an oligotrophic desert

Background Soil microbial communities (SMC) play a central role in the structure and function of desert ecosystems. However, the high variability of annual precipitation could results in the alteration of SMC and related biological processes depending on soil water potential. The nature of the physiological adjustments made by SMC in order to obtain energy and nutrients remains unclear under different soil resource availabilities in desert ecosystems. In order to examine this dynamic, the present study examined the effects of variation in annual precipitation on physiological adjustments by the SMC across two vegetation-soil systems of different soil organic matter input in an oligotrophic desert ecosystem. Methods We collected soil samples in the Cuatro Ciénegas Basin (Mexico) under two vegetation covers: rosetophylous scrub (RS) and grassland (G), that differ in terms of quantity and quality of organic matter. Collections were conducted during the years 2011, 2012, 2013 and 2014, over which a noticeable variation in the annual precipitation occurred. The ecoenzymatic activity involved in the decomposition of organic matter, and the concentration of dissolved, available and microbial biomass nutrients, were determined and compared between sites and years. Results In 2011, we observed differences in bacterial taxonomic composition between the two vegetation covers. The lowest values of dissolved, available and microbial nutrients in both cover types were found in 2012. The G soil showed higher values of dissolved and available nutrients in the wet years. Significant positive correlations were detected between precipitation and the ratios Cmic:Nmic and Cmic:Pmic in the RS soil and Cmic:Pmic and Nmic:Pmic in the G soil. The slopes of the regression with Cmic and Nmic were higher in the G soil and lower in the RS soil. Moreover, the SMC under each vegetation cover were co-limited by different nutrients and responded to the sum of water stress and nutrient limitation. Discussion Soil community within both sites (RS and G) may be vulnerable to drought. However, the community of the site with lower resources (RS) is well adapted to acquire P resources by ecoenzyme upregulation during years with adequate precipitation, suggesting that this community is resilient after drought occurs. Under the Global Climate Change scenarios for desert ecosystems that predict reduced annual precipitation and an increased intensity and frequency of torrential rains and drought events, the soil microbial communities of both sites could be vulnerable to drought through C and P co-limitation and reallocation of resources to physiological acclimatization strategies in order to survive

Agricultural land-use change in a Mexican oligotrophic desert depletes ecosystem stability

Background Global demand for food has led to increased land-use change, particularly in dry land ecosystems, which has caused several environmental problems due to the soil degradation. In the Cuatro Cienegas Basin (CCB), alfalfa production irrigated by flooding impacts strongly on the soil. Methods In order to analyze the effect of such agricultural land-use change on soil nutrient dynamics and soil bacterial community composition, this work examined an agricultural gradient within the CCB which was comprised of a native desert grassland, a plot currently cultivated with alfalfa and a former agricultural field that had been abandoned for over 30 years. For each site, we analyzed C, N and P dynamic fractions, the activity of the enzyme phosphatase and the bacterial composition obtained using 16S rRNA clone libraries. Results The results showed that the cultivated site presented a greater availability of water and dissolved organic carbon, these conditions promoted mineralization processes mediated by heterotrophic microorganisms, while the abandoned land was limited by water and dissolved organic nitrogen. The low amount of dissolved organic matter promoted nitrification, which is mediated by autotrophic microorganisms. The microbial N immobilization process and specific phosphatase activity were both favored in the native grassland. As expected, differences in bacterial taxonomical composition were observed among sites. The abandoned site exhibited similar compositions than native grassland, while the cultivated site differed. Discussion The results suggest that the transformation of native grassland into agricultural land induces drastic changes in soil nutrient dynamics as well as in the bacterial community. However, with the absence of agricultural practices, some of the soil characteristics analyzed slowly recovers their natural state

Almacenes y flujos de carbono en ecosistemas áridos y semiáridos de México: síntesis y perspectivas

Los ecosistemas áridos y semiáridos constituyen un tercio de la superficie terrestre global y un 60% del territorio mexicano, pero poco se sabe sobre su importancia en el ciclo del carbono (C). Este trabajo sintetiza y analiza la información disponible sobre almacenes, flujos y controles de la dinámica del C en las regiones áridas y semiáridas de México. En estos ecosistemas, la productividad neta del ecosistema, la respiración del suelo, la producción y la descomposición de la hojarasca están determinadas por la variabilidad de la precipitación, aunque la descomposición depende también de la radiación solar y temperatura. El suelo es el principal almacén de C, representa 45 y 90% del C en la biomasa del matorral y pastizal, respectivamente. Las regiones semiáridas podrían almacenar más C orgánico e inorgánico que las regiones áridas. El cambio de uso de suelo disminuye hasta en 50% el C orgánico del suelo (COS), pero las especies vegetales formadoras de islas de fertilidad y de recursos amortiguan el impacto de la perturbación en el almacenamiento del C, al actuar como “hotspots” de conservación y trasformación del COS. Las biocostras también controlan la acumulación del COS, debido a su rápida respuesta a la humedad que potencia los flujos del C y la transformación de los nutrimentos en el suelo. El COS controla la estequiometría microbiana que regula la disponibilidad de otros nutrimentos en el suelo. La información sobre la dinámica del C para las regiones áridas y semiáridas de México es aún escasa y fragmentada, ya que la mayoría se limita al COS, en los primeros 30 cm del perfil, sin considerar el C inorgánico del suelo. En consecuencia, es necesario y urgente estandarizar metodologías para cuantificar los almacenes y flujos a diferentes escalas espacio-temporales en los ecosistemas áridos y semiáridos del país

Threats to soil biodiversity - global and regional trends

Using the information provided on the main threats in the ten ecoregions present in the six world regions (Table of threats for Sub-Saharan Africa, South West Pacific, Latin America and Caribbean, North Africa and Near East, North America and Europe; FAOand ITPS, 2015), a summary table of the main threats common to these ecoregions was produced. This exercise showed that the most widespread threat to soil biodiversity in the world was the loss of SOM and SOC, and that this could be associated with other threats such as deforestation and agricultural intensification (both linked withland use change) and with climate change (particularly in tundra). This clearly shows the importance of sustainable management and conservation practices, to maintain this resource in soils, which represents one of the bases for the soils food webs. Deforestation and agricultural intensification were also major threats worldwide, being important intropical and temperate broad leaf and mixed forests and temperate and montane grassland sand boreal forests/taiga, although the level of available information on the topic was highly variable, depending on the particular world regions where these ecoregions occur. The ecoregions with the highest number of threats were the deserts and dry shrublands, the tropical and subtropical grasslands, and the temperate broad leaf and mixed forests. Invasive species also represented an important threat, particularly in Mediterranean and temperate forests and tundra.Fil: Brown, George. Ministerio da Agricultura Pecuaria e Abastecimento de Brasil; BrasilFil: Cooper, Miguel. Universidade do Sao Paulo. Escola Superior de Agricultura Luiz de Queiroz; BrasilFil: Kobayashi, Mónica. Food And Agriculture Organization Of The United Nations; ItaliaFil: Orgiazzi, Alberto. No especifíca;Fil: Domínguez, Anahí. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Instituto de Ciencias de la Tierra, Biodiversidad y Ambiente - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Ciencias de la Tierra, Biodiversidad y Ambiente; ArgentinaFil: Dias Turetta, Ana Paula. No especifíca;Fil: Franco, André. No especifíca;Fil: Zaitsev, Andrey. No especifíca;Fil: Winding, Anne. No especifíca;Fil: Foereid, Bente. No especifíca;Fil: Singh, Brajesh. No especifíca;Fil: Guerra, Carlos. No especifíca;Fil: Rojas, Claudia. No especifíca;Fil: Spurgeon, David. No especifíca;Fil: Aksoy, Ece. No especifíca;Fil: Moreira, Fátima Maria. No especifíca;Fil: Bautista, Francisco. No especifíca;Fil: Xu, Jianming. No especifíca;Fil: Rousk, Johannes. No especifíca;Fil: Bedano, José Camilo. Universidad Nacional de Rio Cuarto. Facultad de Cs.exactas Fisicoquimicas y Naturales. Instituto de Ciencias de la Tierra, Biodiversidad y Ambiente. - Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Cordoba. Instituto de Ciencias de la Tierra, Biodiversidad y Ambiente.; ArgentinaFil: Bagyaraj, Joseph D.. No especifíca;Fil: Saxena, Krishna. No especifíca;Fil: da Silva, Laura Fernanda Simões. No especifíca;Fil: Tedersoo, Leho. No especifíca;Fil: Byrne, Loren. No especifíca;Fil: Callaham, Mac A.. No especifíca;Fil: Choudhary, Madhu. No especifíca;Fil: Aller, M. Fernanda. No especifíca;Fil: Delgado Baquerizo, Manuel. No especifíca;Fil: García Orenes, Maria Fuensanta. No especifíca;Fil: Tsiafouli, Maria. No especifíca;Fil: de Graaf, Marie. No especifíca;Fil: Hart, Miranda. No especifíca;Fil: Thuita, Moses. No especifíca;Fil: Karanja, Nancy. No especifíca;Fil: Fromin, Nathalie. No especifíca;Fil: Eisenhauer, Nico. No especifíca;Fil: Kaneko, Nobuhiro. No especifíca;Fil: Mele, Pauline. No especifíca;Fil: Pastor, Pilar Andres. No especifíca;Fil: Ochoa-Hueso, Raul. No especifíca;Fil: Kuperman, Roman. No especifíca;Fil: Ichami, Stephen. No especifíca;Fil: Fonte, Steven J.. No especifíca;Fil: Santillan, Vinisa Saynes. No especifíca;Fil: Tapia Torres, Yunuen. No especifíca