Study of the microbial interactions of the planktonic communities in environmental gradients

Las comunidades microbianas juegan un papel crucial en los ciclos biogeoquímicos en la naturaleza. El fitoplancton y el bacterioplancton están en la base de la red alimentaria microbiana en los sistemas acuáticos, siendo el principal productor y descomponedor de carbono orgánico, respectivamente. En los sistemas acuáticos, estas comunidades están controladas por el dinamismo característico y la heterogeneidad de las variables ambientales en los ecosistemas pelágicos. Una de las mejores maneras de entender cómo las comunidades se ven afectadas por las variables ambientales es estudiando los gradientes ecológicos, que son cambios espaciotemporales progresivos de características bióticas y / o abióticas dentro de un ecosistema. Muchos ecosistemas presentan notables gradientes ambientales, en los que las interacciones entre las comunidades microbianas y el efecto que estos fuertes gradientes abióticos tienen sobre ellos, son poco conocidos. Sin esta información, es difícil predecir cómo la estructura de la comunidad microbiana, su funcionalidad y, en mayor medida, el ecosistema mismo, podrían responder a los cambios ambientales futuros. Aquí mostramos cómo las comunidades microbianas y sus interacciones en los gradientes ambientales estudiados aquí, un transecto longitudinal en un estuario tropical y un gradiente vertical en un embalse ácido, se ven fuertemente afectados por cambios en las condiciones ambientales en el espacio y el tiempo. En el estuario tropical, se observó una marcada zonación en términos de productividad desde la cabeza hasta la boca del estuario, siendo la producción neta diaria positiva sólo en el medio del gradiente del estuario. Las fuertes entradas de carbono orgánico disuelto al estuario tropical durante la temporada de lluvias podrían potencialmente cambiar el ecosistema a un sistema impulsado en mayor grado por el carbono alóctono, lo que lleva a una mayor importancia de la actividad del bacterioplancton. En contraste, durante la estación seca, los patrones de similaridad revelaron un notable acoplamiento directo (por carbono orgánico disuelto) entre grupos de fitoplancton y bacterioplancton. En el embalse ácido, durante la estratificación, se demostró un fuerte acoplamiento entre el fitoplancton que forma un máximo profundo de clorofila en el metalimnion y la producción de dióxido de carbono por parte del bacterioplancton en el hipolimnion, mediante un modelo de transporte reactivo 1-D, lo que indica que el carbono inorgánico puede ser el nutriente limitante de la comunidad de fitoplancton en lagos ácidos. La composición filogenética y los rasgos celulares del bacterioplancton cambiaron en paralelo entre las fases de estratificación y de mezcla, lo que sugiere que ambos niveles estructurales de esta comunidad están vinculados entre sí y se ven afectados por las variables ambientales. En general, nuestros resultados demuestran cómo los gradientes ambientales afectan a las comunidades microbianas a diferentes niveles, incluidas las características celulares, fisiología, estructura filogenética, distribuciones espacio-temporales de diferentes poblaciones y propiedades a nivel del ecosistema, como la producción neta del ecosistema y el metabolismo. Este enfoque de múltiples niveles es esencial para comprender la función ecológica de la comunidad microbiana en ecosistemas complejos y predecir cambios futuros en respuesta al forzamiento climático y antropogénico.Microbial communities play a primordial role in the biogeochemical cycles in nature. Phytoplankton and bacterioplankton are at the base of the microbial food web in aquatic systems, being the main producer and decomposer of organic carbon, respectively. In aquatic systems, these communities are controlled by the characteristic dynamism and heterogeneity of the environmental variables in pelagic ecosystems. One of the best ways to understand how communities are affected by environmental variables is by studying ecological gradients, which are progressive spatiotemporal changes of biotic and/or abiotic characteristics within an ecosystem. Many ecosystems present remarkable environmental gradients in which the interactions between the microbial communities and the effect these strong abiotic gradients have on them are poorly known. Without this information it is difficult to predict how the structure of microbial community, its functionality and in a greater extent the ecosystem itself, might respond to future environmental changes. Here we show how the microbial communities and their interactions in the environmental gradients studied here, a longitudinal transect in a tropical estuary and a vertical gradient in an acid reservoir, are strongly affected by the changes in the environmental conditions in space and time. In the tropical estuary, a marked zonation in terms of productivity was observed from the head to the mouth of the estuary, being daily net production only positive in the middle of the estuarine gradient. The strong dissolved organic carbon inflows to the tropical estuary during the rainy season could potentially change the ecosystem to a system driven in a higher degree by allochthonous carbon leading to a higher importance of bacterioplankton activity. In contrast, during the dry season, remarkable direct (by dissolved organic carbon) coupling between phyto- and bacterioplankton groups were revealed from the similarity of the patterns. In the acid reservoir, during stratification, a strong coupling between the phytoplankton that forms a deep chlorophyll maximum in the metalimnion and the bacterial carbon dioxide production in the hypolimnion was demonstrated by a 1-D reactive transport model, indicating that inorganic carbon can be the limiting nutrient for phytoplankton community in acid lakes. The phylogenetic composition and cell traits of bacterioplankton changed in parallel between stratification and mixing seasons suggesting that both structural levels of this community are linked each other and are affected by the environmental variables. Overall, our results demonstrate how the environmental gradients affect the microbial communities at different levels, including single cell characteristics, physiology, phylogenetic structure, spatiotemporal distributions of different populations and ecosystem level properties like net ecosystem production and metabolism. This multilevel approach is essential to understand the ecological function of the microbial community in complex ecosystems and predict future changes in response to climate and anthropogenic forcing.186 página

Coupling between microbial assemblages and environmental drivers along a tropical estuarine gradient

The change in the community structure of phytoplankton and bacterioplankton, and in the degree of coupling between them as well as the environmental conditions, have substantial impacts on the transfer of energy to higher trophic levels and finally on the fate of organic matter. The microbial community structure, usually described only by the abundance of the different taxonomic or functional groups, can be extended to include other levels of descriptors, like physiological state and single-cell properties. These features play a role in the ecological regulation of microbial communities but are not generally studied as additional descriptors of the community structure. Here, we show the changes in abundance and single-cell characteristics based on flow cytometry measurements of picocyanobacteria, photoautotrophic pico- and nanoeukaryotes, and heterotrophic bacteria during the rainy and dry seasons along the estuarine gradient of the inner Gulf of Nicoya. The spatiotemporal distribution of these microbial assemblages showed different patterns in surface and bottom waters along the estuarine gradient and seasonally, both in their abundances and single-cell traits, which suggest differences in their ecological regulation. The changes in the structure of the microbial community along the estuary correlated most significantly with the changes in environmental variables during the dry season. This seems to occur due to changes in salinity, concentration and lability of DOC, concentration of DIN and PO43− and net community production, largely affected by the differences in the river flow. In addition, during the dry season, small-size phytoplankton and bacterioplankton assemblages, characterised by abundance and single-cell traits, presented a higher level of coupling, leading to a more complex ecological network with respect to the rainy season

Size fractionated phytoplankton biomass and net metabolism along a tropical estuarine gradient

Size structure of phytoplankton determines to a large degree the trophic interactions in oceanic and coastal waters and eventually the destiny of its biomass. Although, tropical estuarine systems are some of the most productive systems worldwide compared to temperate systems, little is known about phytoplankton biomass size fractions, their contribution to net metabolism, or the ecological factors driving phytoplankton size distribution in tropical estuaries. Hence, we measured the size-fractionated biomass and net metabolism of the plankton community along a salinity and nutrient gradient in the Gulf of Nicoya estuary (Costa Rica), during the dry season. Respiration (23.6 mmol O2 m−3 h−1) was highest at the estuary head, whereas maximum net primary production (23.1 mmol O2 m−3 h−1) was observed in the middle of the estuary, coinciding with the chlorophyll a maximum (15.9 mg m−3). Thus, only the middle section of the estuary was net autotrophic (2.9 g C m−2 d−1), with the rest of the estuary being net heterotrophic. Regression analysis identified light availability, and not nutrients, as the principal factor limiting primary production in the estuary due to increased turbidity. The changes in net metabolism along the estuary were also reflected in the phytoplankton's size structure. Although micro- and picophytoplankton were the most productive fractions overall, in the middle section of the estuary nanophytoplankton dominated primary production, chlorophyll, and autotrophic biomass

What makes a cyanobacterial bloom disappear? A review of the abiotic and biotic cyanobacterial bloom loss factors

Cyanobacterial blooms present substantial challenges to managers and threaten ecological and public health. Although the majority of cyanobacterial bloom research and management focuses on factors that control bloom initiation, duration, toxicity, and geographical extent, relatively little research focuses on the role of loss processes in blooms and how these processes are regulated. Here, we define a loss process in terms of population dynamics as any process that removes cells from a population, thereby decelerating or reducing the development and extent of blooms. We review abiotic (e.g., hydraulic flushing and oxidative stress/UV light) and biotic factors (e.g., allelopathic compounds, infections, grazing, and resting cells/programmed cell death) known to govern bloom loss. We found that the dominant loss processes depend on several system specific factors including cyanobacterial genera-specific traits, in situ physicochemical conditions, and the microbial, phytoplankton, and consumer community composition. We also address loss processes in the context of bloom management and discuss perspectives and challenges in predicting how a changing climate may directly and indirectly affect loss processes on blooms. A deeper understanding of bloom loss processes and their underlying mechanisms may help to mitigate the negative consequences of cyanobacterial blooms and improve current management strategies