Quantifying thermal adaptation of soil microbial respiration

Quantifying the rate of thermal adaptation of soil microbial respiration is essential in determining potential for carbon cycle feedbacks under a warming climate. Uncertainty surrounding this topic stems in part from persistent methodological issues and difficulties isolating the interacting effects of changes in microbial community responses from changes in soil carbon availability. Here, we constructed a series of temperature response curves of microbial respiration (given unlimited substrate) using soils sampled from around New Zealand, including from a natural geothermal gradient, as a proxy for global warming. We estimated the temperature optima (Topt) and inflection point (Tinf) of each curve and found that adaptation of microbial respiration occurred at a rate of 0.29 °C ± 0.04 1SE for Topt and 0.27 °C ± 0.05 1SE for Tinf per degree of warming. Our results bolster previous findings indicating thermal adaptation is demonstrably offset from warming, and may help quantifying the potential for both limitation and acceleration of soil C losses depending on specific soil temperatures

Zooplankton Biomass Depletion Event Reveals the Importance of Small Pelagic Fish Top-Down Control in the Western Mediterranean Coastal Waters

The influence of hydrochemistry and trophic conditions on the coastal zooplankton community’s biomass and metabolic activities was investigated along the Spanish Mediterranean coastal waters, from Algeciras Bay to Barcelona, from autumn 2011 to autumn 2012. Two hydrographic regions were differentiated: NW Alboran (ALB) and W Mediterranean (MED). Zooplankton metabolism was assessed from measurements of the electron transport system (ETS) and aminoacyl-tRNA synthetases (AARS) activities, as proxies for potential respiration and somatic growth, respectively. Zooplankton showed three to fivefold higher biomass in ALB than in MED during autumn 2011 and spring 2012. However, in autumn 2012, a drastic decrease in biomass standing stock was observed in ALB, with no significant differences between the two regions. This biomass depletion event was not associated with environmental variables, food availability or zooplankton metabolic rates, but coincided with a twofold peak of Sardina pilchardus landings in ALB. A reduced standing stock coupled with high zooplankton growth rates suggests mortality by predation as the main cause for the low zooplankton biomass typically observed in MED, and in ALB during autumn 2012.Versión del edito

Respiration and vertical carbon flux in the Gulf of Maine water column

The transport of carbon from ocean surface waters to the deep sea is a critical factor in calculations of planetary carbon cycling and climate change. This vertical carbon flux can be calculated by integrating the vertical profile of the seawater respiration rate but is rarely done because measuring seawater respiration is so difficult. However, seawater respiratory oxygen consumption is the product of the combined activity of all the respiratory electron transfer systems in a seawater community of bacterioplankton, phytoplankton, and zooplankton. This respiratory electron transfer system (ETS) is the membrane bound enzymatic system that controls oxygen consumption and ATP production in all eukaryots and in almost all bacteria and archaea. As such, it represents potential respiratory oxygen consumption. Exploiting this, we measured plankton-community ETS activity in water column profiles in the Gulf of Maine to give the potential-respiration of the water column. To interpret these potentials in terms of actual seawater respiration we made use of previous measurements of respiratory oxygen consumption and ETS activity in the Gulf of Maine to calculate a ratio of respiratory potential to actual respiration. Armed with this ratio we calculated seawater respiration depth profiles from the ETS activity measurements. These profiles were characterized by: (1) high oxygen consumption rates in the euphotic zone; (2) subsurface maxima near the subsurface chlorophyll maxima (SCM); (3) rapid declines associated with thermoclines; (4) low declining rates below 50 m; (5) and elevated values occasionally near the bottom. Sea surface values ranged from 229 to 489 pmol O2 min-1 L-1. Euphotic zone maximum values ranged from 457 to 682 pmol O2 min-1 L-1 while the minimum values below 70 m ranged from 10 to 27 pmol O2 min-1 L-1. A depth-normalized power function described the respiratory profiles between their maxima and minima. Integrating these respiratory oxygen consumption profiles from the respiratory maximum to the near bottom minimum, we calculated carbon flux profiles. The vertical carbon fluxes through the 30 m, 50 m, and 100 m levels were 3.09 ± 1.55, 1.76 ± 0.96, and 0.93 ± 0.68 μmol C min-1 m-2, respectively

Respiration of mesopelagic fish: a comparison of respiratory electron transport system (ETS) measurements and allometrically calculated rates in the Southern Ocean and Benguela Current

Mesopelagic fish are an important component of marine ecosystems, and their contribution to marine biogeochemical cycles is becoming increasingly recognized. However, major uncertainties remain in the rates at which they remineralize organic matter. We present respiration rate estimates of mesopelagic fish from two oceanographically contrasting regions: the Scotia Sea and the Benguela Current. Respiration rates were estimated by measuring the enzyme activities of the electron transport system. Regression analysis of respiration with wet mass highlights regional and inter-specific differences. The mean respiration rates of all mesopelagic fish sampled were 593.6 and 354.9 µl O2 individual−1 h−1 in the Scotia Sea and Benguela Current, respectively. Global allometric models performed poorly in colder regions compared with our observations, underestimating respiratory flux in the Scotia Sea by 67–88%. This may reflect that most data used to fit such models are derived from temperate and subtropical regions. We recommend caution when applying globally derived allometric models to regional data, particularly in cold (<5°C) temperature environments where empirical data are limited. More mesopelagic fish respiration rate measurements are required, particularly in polar regions, to increase the accuracy with which we can assess their importance in marine biogeochemical cycles

Carbon and nitrogen transformations in alpine ecosystems of the Eastern Alps, Austria

This thesis investigated net CH4 and net CO2 emissions from sites in the alpine region of the Eastern Alps, Austria. Four mature alpine sites (one dry meadow and three fen sites) were selected and the influence of abiotic (radiation, temperature, soil water conditions) and biotic (above-ground standing plant biomass) environmental controls on diurnal and seasonal emission patterns were studied. For a better understanding of the response of soil C- and N pools to global warming, the temperature sensitivity of activities involved in C- and N cycling were determined. The first part of the thesis dealt with net methane fluxes measured over a period of 24 months. During snow-free periods, average methane emissions of the fen sites ranged between 19 and 116 mg CH4 m-2 d-1. Mean emissions during snow periods were much lower, being 18 to 59% of annual fluxes. The alpine dry meadow functioned as a small methane sink during snow-free periods (-2.1 mg CH4 m-2 d-1 (2003); -1.0 mg CH4 m-2 d-1 (2004)). The diurnal and seasonal methane uptake of the dry meadow was positively related to soil temperature and negatively related to water-filled pore space (wfps). In the fen, the seasonal methane fluxes were related to soil temperature and groundwater table. The live above-ground standing plant biomass contributed to net methane fluxes only at those sites with higher water table positions. This study provided evidence that alpine fens acted as methane sources throughout the year, whereas an alpine meadow site acted as a net methane sink during snow-free periods. In the second part of the thesis the CO2 balance was estimated based on diurnal flux measurements and on the influence of photosynthetic active radiation (PAR), plant green area index (GAI), soil temperature and wfps. The daylight net ecosystem CO2 emission rate was influenced by PAR and GAI throughout snow-free seasons. The seasonal net CO2 emission rate at night was positively related to soil temperature, while low wfps reduced flux rates at the meadow and at the driest fen study site but reinforced carbon loss at the wetter fen sites. The daily average ecosystem net CO2 gain during snow-free periods at the meadow was 3.5 g CO2 m-2 d-1 and at the fen sites between 1.5 and 3.4 g CO2 m-2 d-1. The mean average daily CO2 emission during snow periods was low, being -0.9 g CO2 m-2 d-1 for the meadow and between -0.2 and -0.7 g CO2 m-2 d-1 for all fen sites. All sites function as significant annual net carbon sinks, with a net carbon gain from 50 to 121 g C m-2 a-1 (averaged over both years), irrespective of water balance. The results indicate that alpine fen sites, that have built up a large carbon stock in the past, are not expected to gain a further carbon surplus compared with meadows under the current climate. Temperature is important for regulating biological activities. The third part of the thesis focused on temperature sensitivity of soil C mineralization, N mineralization and potential enzyme activities involved in the C- and N cycle (ß-glucosidase, ß-xylosidase, N-acetyl-ß-glucosaminidase, tyrosine aminopeptidase, leucine aminopeptidase) over a temperature range of 0-30°C. The objective was to calculate Q10 values and relative temperature sensitivities (RTS) and to quantify seasonal (summer, autumn, winter) and site-specific factors. The Q10 values of C mineralization were significantly higher (average 2.0) than for N mineralization (average 1.7). The Q10 values of both activities were significantly negatively related to soil organic matter quality. In contrast, the chemical soil properties, microbial biomass and sampling date did not influence Q10 values. Analysis of RTS showed that the temperature sensitivity increased with decreasing temperature. The C- and N mineralization and potential aminopeptidase activities (tyrosine, leucine) showed an almost constant temperature dependence over 0-30°C. In contrast, ß-glucosidase, ß-xylosidase and N-acetyl-ß-glucosaminidase showed a distinctive increase in temperature sensitivity with decreasing temperature. Low temperature at the winter sampling date caused a greater increase in the RTS of all activities than in autumn and summer. Our results indicate a disproportion of the RTS for potential enzyme activities of the C- and N cycle and a disproportion of the RTS for easily degradable C compounds (ß-glucose, ß-xylose) compared with the C mineralization of soil organic matter. Thus, temperature may play an important role in regulating the decay of different soil organic matter fractions.In der vorliegenden Arbeit wurden Netto-CH4- und Netto-CO2-Emissionen alpiner Standorte der österreichischen Ostalpen untersucht. Vier Standorte (ein Trockenrasen, drei Moorstandorte) wurden ausgewählt und der Einfluss abiotischer (Strahlung, Temperatur, Bodenwassergehalt) und biotischer (oberirdische Pflanzenbiomasse) Umwelteinflüsse auf das tägliche und saisonale Emissionsmuster untersucht. Um den Einfluss der Temperatur auf die Kohlenstoff- und Stickstoff-Vorkommen im Boden zu untersuchen, wurden die Temperaturabhängigkeiten von C- und N-Umsätzen bestimmt. Der erste Teil der Arbeit befasst sich mit Netto-Methanflüssen, gemessen über einen Zeitraum von 24 Monaten. Während der schneefreien Zeit wurden 19-116 mg CH4 m-2 d-1 für die Moorstandorte ermittelt. Während der schneebedeckten Zeit waren diese Flüsse viel geringer und betrugen 18-59% der jährlichen Gesamtemissionen. Der Trockenrasen stellte während der schneefreien Zeit eine kleine Senke für Methan (-2.1 mg CH4 m-2 d-1 (2003); -1.0 mg CH4 m-2 d-1(2004)) dar. Diese Netto-Methanaufnahme des Trockenrasens korrelierte positiv mit der Bodentemperatur und negativ mit dem wassergefüllten Porenvolumen des Bodens (wfps). Im Moor ließ sich eine Beziehung des saisonalen Methanflusses mit der Bodentemperatur und dem Grundwasserstand finden. Die oberirdische grüne Pflanzenbiomasse korrelierte nur mit dem Netto-Methanfluss der Moorstandorte mit hohen Grundwasserständen. Diese Untersuchung belegt, dass alpine Moore ganzjährige Methanquellen sind, während ein alpiner Trockenrasen eine Methansenke innerhalb der schneefreien Zeit darstellt. Gegenstand des zweiten Teiles der Arbeit war die Berechnung einer CO2-Bilanz basierend auf Tagesgängen von Gasflussmessungen. Berücksichtigt wurden dabei der Einfluss von photosynthetisch aktiver Strahlung (PAR), der grüne Pflanzenflächenindex (GAI), die Bodentemperatur und das wfps. Bei Tageslicht wurden die Netto-Emissionsraten innerhalb der schneefreien Zeit von PAR und GAI gesteuert. Die Netto-Emissionsraten während der Nachtzeit korrelierten positiv mit der Bodentemperatur. Niedrige wfps-Werte führten dabei zur Verringerung der Flussraten auf dem Trockenrasen und der trockenen Moorfläche, wohingegen die Kohlenstoffverluste auf den vernässten Moorstandorten zunahmen. Während der schneefreien Zeit betrug der durchschnittliche Netto-CO2-Gewinn des Trockenrasens 3.5 g CO2 m-2 d-1 und für die Moorstandorte 1.5 bis 3.4 g CO2 m-2 d-1. Die durchschnittliche Atmung der Standorte während der schneebedeckten Periode war niedrig: -0.9 g CO2 m-2 d-1 für den Trockenrasen und -0.2 bis -0.7 g CO2 m-2 d-1 für die Moorstandorte. Unabhängig vom Wasserhaushalt waren alle Standorte, gemittelt über beide Untersuchungsjahre, signifikante Netto-C-Senken (50 bis 121 g C m-2 a-1). Die Ergebnisse zeigen, dass bei heutigen Klimaverhältnissen alpine Moore mit ihrem großen Kohlenstoffvorrat keine weitere Kohlenstofffestlegung im Vergleich zu alpinen Trockenrasen erwarten lassen. Im dritten Teil der Arbeit wurde die Temperaturabhängigkeit der bodenbürtigen C-Mineralisation, N-Mineralisation und der potentiellen Enzymreaktionen des C- und N-Kreislaufes (ß-Glucosidase, ß-Xylosidase, N-acetyl-ß-Glucosaminidase, Tyrosin-Aminopeptidase, Leucin-Aminopeptidase) für einen Temperaturbereich von 0-30°C ermittelt. Das Ziel war es, Q10-Werte und die relative Temperaturabhängigkeit (RTS) zu berechnen sowie den Einfluss verschiedener Jahreszeiten (Sommer, Herbst, Winter) und standortsspezifischer Faktoren zu ermitteln. Die Q10-Werte der C-Mineralisation (2.0) waren signifikant höher als die der N-Mineralisation (1.7). Die Q10-Werte beider Aktivitäten korrelierten negativ mit der Substratqualität. Die chemischen Bodeneigenschaften, der mikrobielle Kohlenstoffgehalt und der Zeitpunkt der Probenahme zeigten keinen Einfluss auf die Q10-Werte. Die berechneten RTS-Werte machten deutlich, dass die Temperaturabhängigkeit mit abnehmender Temperatur zunahm. Die C- und N-Mineralisation und die potentiellen Aminopeptidaseaktivitäten (Tyrosin, Leucin) wiesen eine fast konstante Temperaturabhängigkeit über den Temperaturbereich von 0-30°C auf. Im Gegensatz dazu zeigten ß-Glucosidase, ß-Xylosidase und N-acetyl-ß-Glucosaminidase einen ausgeprägten Anstieg der Temperaturabhängigkeit mit abnehmender Temperatur. Die vorherrschende tiefe Temperatur der Probenahme im Winter verursachte einen stärkeren Anstieg der RTS als dies für die Probenahme im Herbst und Sommer der Fall war. Diese Ergebnisse deuten zum einen auf eine Disproportionalität der RTS von potentiellen C-Enzymaktivitäten und N-Enzymaktivitäten hin und zum anderen auf eine Disproportionalität der Mineralisation von leicht verfügbaren C-Verbindungen (ß-Glucose, ß-Xylose) im Vergleich zur C -Mineralisation der bodenbürtigen organischen Substanz in alpinen Böden. Daher könnte die Temperatur eine wichtige Rolle bei der Regulierung des Abbaus unterschiedlicher Fraktionen der organischen, bodenbürtigen Substanz darstellen

Modeling nitrogen fixation in dead wood

A mechanistic simulation model of nitrogen fixation in dead wood was developed to help synthesize knowledge, develop hypotheses, and estimate rates of nitrogen fixation in the Pacific Northwest. In this model nitrogen fixation is directly controlled by log substrate, temperature, moisture, and oxygen content. Respiration and diffusion of oxygen indirectly affect nitrogen fixation and respiration by regulating log oxygen content. The relationships of abiotic and biotic variables on nitrogen fixation and respiration and the relationships of wood moisture and density were determined in laboratory experiments to parameterize the model. Nitrogen fixation and respiration had similar responses to temperature, with nitrogen fixation being optimum near 30°C and respiration being optimum over a broader range from 30°C to 50°C. Nitrogen fixation and respiration responded similarly to wood moisture with little activity below 50%, and optimal activity above 175% to 100% moisture content for nitrogen fixation and respiration, respectively. Nitrogen fixation was optimized at 2% 02. In contrast, respiration rates were optimal when 02 exceeded 1%. Nitrogen fixation and respiration in woody debris were significantly influenced by the degree of decay of the wood, and the woody tissue type, but not by the species of dead wood. In both the radial and longitudinal directions, the oxygen diffusion coefficient (Do2) in wood increased exponentially as the fraction of pore space in air (FPSA) increased and as density decreased. D02 in the longitudinal direction was 1.4 to 34 times greater than for the radial direction at zero and one FPSA, respectively. In comparison to independent data, the model of nitrogen fixation reasonably estimated seasonal patterns of log temperature, moisture, oxygen content, and respiration rate. The model estimates an annual nitrogen fixation rate of 0.7 kg N-ha-1 yr-1 for an oldgrowth stand at the H. J. Andrews, which is reasonably close to an independent estimate of 1.0 kg N-ha-1 yr-1 made for the same stand. Despite low annual rates of asymbiotic nitrogen fixation in wood, soil, and litter, this process can contribute 9% to 42% of a stands nitrogen inputs over succession when symbiotic fixers such as Alnus rubra and Lobaria oregana are present and absent, respectively. Managed stands with reduced levels of woody debris and litter may therefore be losing a significant nitrogen input

Mejora de la supervivencia larvaria en cultivos de moluscos mediante la mejora de las técnicas de cultivo de microalgas y la introducción de nuevas especies de microalgas

El principal objetivo del presente trabajo fue la mejora de cultivos larvarios de moluscos bivalvos a través de la mejora de la composición bioquímica de la dieta. Para ello se exploró el efecto de la aplicación de técnicas de cultivo continuo en las especies microalgales clásicas utilizadas en el cultivo larvario de moluscos para la mejora de su perfil nutricional y se evaluaron los efectos de la introducción de especies de cripófitas en la dieta. La aplicación de cultivos continuos en los que la biomasa microalgal posee un perfil nutricional estable y optimizado incrementa la robustez de estos estudios comparativos. Los resultados aquí obtenidos demuestran la importancia de la utilización de sistemas semicontinuos con elevadas tasas de renovación para la obtención de biomasa microalgal de elevada calidad, permitiendo incrementar la supervivencia y crecimiento larvario de moluscos bivalvos, tal y como ya había sido demostrado en otros animales filtradores. De entre las especies estudiadas, se enfatiza el potencial de la criptófita C. placoidea para su utilización en acuicultura, que presentó excelentes resultados no solo para la mejora de la supervivencia en el cultivo larvario de moluscos bivalvos, sino también para el cultivo del rotífero B. plicatilis