Flow regime alteration effects on the organic C dynamics in semiarid stream ecosystems

There is evidence of an ongoing alteration of the flow regime owing to climate change forcing, which has resulted in substantial increases in the frequency and magnitude of extreme events such as floods and droughts. Such changes in the flow regime may have major implications in freshwater ecosystems and, in particular, in the organic carbon dynamics in semiarid stream ecosystems. Much is known about the role of extreme flow events on structuring stream ecosystems, but few studies explored the effects of extreme flow events magnitude, timing, and sequence on stream ecosystems. To assess the effect of extreme events on stream organic C dynamics, a simple and flexible modeling approach was applied to simulate the organic carbon dynamics in a simplified river reach. The river reach model was initially calibrated and tested using long-term data for stream water velocity and amount of organic carbon in sediment. After that, multiple scenarios differing in the extreme flow events (floods and droughts) sequence and magnitude were used to simulate the effects of possible flow regime changes on the stream organic carbon dynamics. Initial expectations were that: (i) an increase in the magnitude or frequency of extreme flow events would reduce the amount of organic carbon respired within the simulated river reach, and (ii) relationship between the timings of the extreme flow events and of the litterfall input would influence considerably the effects of the extreme flow events. Results pointed out that: (i) the amount of processed carbon respect the amount entering the ecosystem was affected by extreme events such floods and droughts, but the relevance of those events differed along the year, with a maximal effect during the litterfall period; (ii) extreme event timing rather than the magnitude was more relevant to the stream organic carbon dynamics; and (iii) the amount of respired carbon in the ecosystem could be amplified or reduced depending on event sequence. Increasing awareness of the role of inland waters in the global carbon cycle and the shaping role of hydrology on the stream organic carbon dynamics stress the need to better quantify carbon fluxes and the hydrological controls on these fluxes.     

Experimental fire increases soil carbon dioxide efflux in a grassland long‐term multifactor global change experiment

Numerous studies have demonstrated that soil respiration rates increase under experimental warming, although the long‐term, multiyear dynamics of this feedback are not well constrained. Less is known about the effects of single, punctuated events in combination with other longer‐duration anthropogenic influences on the dynamics of soil carbon (C) loss. In 2012 and 2013, we assessed the effects of decadal‐scale anthropogenic global change – warming, increased nitrogen (N) deposition, elevated carbon dioxide (CO₂), and increased precipitation – on soil respiration rates in an annual‐dominated Mediterranean grassland. We also investigated how controlled fire and an artificial wet‐up event, in combination with exposure to the longer‐duration anthropogenic global change factors, influenced the dynamics of C cycling in this system. Decade‐duration surface soil warming (1–2 °C) had no effect on soil respiration rates, while +N addition and elevated CO₂ concentrations increased growing‐season soil CO₂ efflux rates by increasing annual aboveground net primary production (NPP) and belowground fine root production, respectively. Low‐intensity experimental fire significantly elevated soil CO₂ efflux rates in the next growing season. Based on mixed‐effects modeling and structural equation modeling, low‐intensity fire increased growing‐season soil respiration rates through a combination of three mechanisms: large increases in soil temperature (3–5 °C), significant increases in fine root production, and elevated aboveground NPP. Our study shows that in ecosystems where soil respiration has acclimated to moderate warming, further increases in soil temperature can stimulate greater soil CO₂ efflux. We also demonstrate that punctuated short‐duration events such as fire can influence soil C dynamics with implications for both the parameterization of earth system models (ESMs) and the implementation of climate change mitigation policies that involve land‐sector C accounting.     

Wildfire–vegetation dynamics affect predictions of climate change impact on bird communities

Community‐level climate change indicators have been proposed to appraise the impact of global warming on community composition. However, non‐climate factors may also critically influence species distribution and biological community assembly. The aim of this paper was to study how fire–vegetation dynamics can modify our ability to predict the impact of climate change on bird communities, as described through a widely‐used climate change indicator: the community thermal index (CTI). Potential changes in bird species assemblage were predicted using the spatially‐explicit species assemblage modelling framework – SESAM – that applies successive filters to constrained predictions of richness and composition obtained by stacking species distribution models that hierarchically integrate climate change and wildfire–vegetation dynamics. We forecasted future values of CTI between current conditions and 2050, across a wide range of fire–vegetation and climate change scenarios. Fire–vegetation dynamics were simulated for Catalonia (Mediterranean basin) using a process‐based model that reproduces the spatial interaction between wildfire, vegetation dynamics and wildfire management under two IPCC climate scenarios. Net increases in CTI caused by the concomitant impact of climate warming and an increasingly severe wildfire regime were predicted. However, the overall increase in the CTI could be partially counterbalanced by forest expansion via land abandonment and efficient wildfire suppression policies. CTI is thus strongly dependent on complex interactions between climate change and fire–vegetation dynamics. The potential impacts on bird communities may be underestimated if an overestimation of richness is predicted but not constrained. Our findings highlight the need to explicitly incorporate these interactions when using indicators to interpret and forecast climate change impact in dynamic ecosystems. In fire‐prone systems, wildfire management and land‐use policies can potentially offset or heighten the effects of climate change on biological communities, offering an opportunity to address the impact of global climate change proactively.     

Effects of variations in simulated changes in soil carbon contents and dynamics on future climate projections

Climatic variables have major effects on all components and processes of the global carbon (C) cycle, including soil C contents and dynamics, which in turn have significant feedback effects on the global climate. We have investigated the interactive effects between soil C and projected climatic changes using the Institute of Numerical Mathematics Climate Model (INMCM) climate–C cycle model coupled to three soil organic matter dynamics models [the Lund–Potsdam–Jena (LPJ) soil biogeochemistry, ROMUL and Q models] based on three markedly differing conceptual interpretations of soil organic matter transformation (biochemical, discrete succession and continuous quality, respectively). According to simulations using all these couplings the positive effect of CO₂ fertilization on plant productivity outweighed the negative effects of increased soil temperature on soil C, consequently soils were projected to contain 10–104 Pg more C in 2100 than in the preindustrial period. However, the projected soil respiration rates tended to be higher and additional C storage lower when the LPJ soil biochemistry model was used rather than either the ROMUL or Q models. Global temperatures for 2100 predicted by the INMCM coupled to either the ROMUL or Q models were almost identical, but 0.4 °C lower than those predicted by the INMCM coupled to the LPJ soil biochemistry model. The differences in global predictions obtained with the ROMUL and Q models were smaller than expected given the fundamental difference in their formulations of the relationship between the quality and temperature sensitivity of soil organic matter decomposition.     

Conceptualising the interactive effects of climate change and biological invasions on subarctic freshwater fish

Climate change and species invasions represent key threats to global biodiversity. Subarctic freshwaters are sentinels for understanding both stressors because the effects of climate change are disproportionately strong at high latitudes and invasion of temperate species is prevalent. Here, we summarize the environmental effects of climate change and illustrate the ecological responses of freshwater fishes to these effects, spanning individual, population, community and ecosystem levels. Climate change is modifying hydrological cycles across atmospheric, terrestrial and aquatic components of subarctic ecosystems, causing increases in ambient water temperature and nutrient availability. These changes affect the individual behavior, habitat use, growth and metabolism, alter population spawning and recruitment dynamics, leading to changes in species abundance and distribution, modify food web structure, trophic interactions and energy flow within communities and change the sources, quantity and quality of energy and nutrients in ecosystems. Increases in temperature and its variability in aquatic environments underpin many ecological responses; however, altered hydrological regimes, increasing nutrient inputs and shortened ice cover are also important drivers of climate change effects and likely contribute to context‐dependent responses. Species invasions are a complex aspect of the ecology of climate change because the phenomena of invasion are both an effect and a driver of the ecological consequences of climate change. Using subarctic freshwaters as an example, we illustrate how climate change can alter three distinct aspects of species invasions: (1) the vulnerability of ecosystems to be invaded, (2) the potential for species to spread and invade new habitats, and (3) the subsequent ecological effects of invaders. We identify three fundamental knowledge gaps focused on the need to determine (1) how environmental and landscape characteristics influence the ecological impact of climate change, (2) the separate and combined effects of climate and non‐native invading species and (3) the underlying ecological processes or mechanisms responsible for changes in patterns of biodiversity.     

Changes in floral bouquets from compound‐specific responses to increasing temperatures

We addressed the potential effects of changes in ambient temperature on the profiles of volatile emissions from flowers and tested whether warming could induce significant quantitative and qualitative changes in floral emissions, which would potentially interfere with plant–pollinator chemical communication. We measured the temperature responses of floral emissions of various common species of Mediterranean plants using dynamic headspace sampling and used GC‐MS to identify and quantify the emitted terpenes. Floral emissions increased with temperature to an optimum and thereafter decreased. The responses to temperature modeled here predicted increases in the rates of floral terpene emission of 0.03–1.4‐fold, depending on the species, in response to an increase of 1 °C in the mean global ambient temperature. Under the warmest projections that predict a maximum increase of 5 °C in the mean temperature of Mediterranean climates in the Northern Hemisphere by the end of the century, our models predicted increases in the rates of floral terpene emissions of 0.34–9.1‐fold, depending on the species. The species with the lowest emission rates had the highest relative increases in floral terpene emissions with temperature increases of 1–5 °C. The response of floral emissions to temperature differed among species and among different compounds within the species. Warming not only increased the rates of total emissions, but also changed the ratios among compounds that constituted the floral scents, i.e. increased the signal for pollinators, but also importantly altered the signal fidelity and probability of identification by pollinators, especially for specialists with a strong reliance on species‐specific floral blends.     

Decadal-scale Dynamics of Water, Carbon and Nitrogen in a California Chaparral Ecosystem: DAYCENT Modeling Results

The Mediterranean climate, with its characteristic of dry summers and wet winters, influences the hydrologic and microbial processes that control carbon (C) and nitrogen (N) biogeochemical processes in chaparral ecosystems. These biogeochemical processes in turn determine N cycling under chronic N deposition. In order to examine connections between climate and N dynamics, we quantified decadal-scale water, C and N states and fluxes at annual, monthly and daily time steps for a California chaparral ecosystem in the Sierra Nevada using the DAYCENT model. The daily output simulations of net mineralization, stream flow and stream nitrate (NO₃⁻) export were developed for DAYCENT in order to simulate the N dynamics most appropriate for the abrupt rewetting events characteristic of Mediterranean chaparral ecosystems. Overall, the magnitude of annual modeled net N mineralization, soil and plant biomass C and N, nitrate export and gaseous N emission agreed with those of observations. Gaseous N emission was a major N loss pathway in chaparral ecosystems, in which nitric oxide (NO) is the dominant species. The modeled C and N fluxes of net primary production (NPP), N uptake and N mineralization, NO₃⁻ export and gaseous N emission showed both high inter-annual and intra-annual variability. Our simulations also showed dramatic fire effects on NPP, N uptake, N mineralization and gaseous N emission for three years of postfire. The decease in simulated soil organic C and N storages was not dramatic, but lasted a longer time. For the seasonal pattern, the predicted C and N fluxes were greatest during December to March, and lowest in the summer. The model predictions suggested that an increase in the N deposition rate would increase N losses through gaseous N emission and stream N export in the chaparral ecosystems of the Sierra Nevada due to changes in N saturation status. The model predictions could not capture stream NO₃⁻ export during most rewetting events suggesting that a dry-rewetting mechanism representing the increase in N mineralization following soil wetting needs to be incorporated into biogeochemical models of semi-arid ecosystems.     

Global reductions in seafloor biomass in response to climate change

Seafloor organisms are vital for healthy marine ecosystems, contributing to elemental cycling, benthic remineralization, and ultimately sequestration of carbon. Deep‐sea life is primarily reliant on the export flux of particulate organic carbon from the surface ocean for food, but most ocean biogeochemistry models predict global decreases in export flux resulting from 21st century anthropogenically induced warming. Here we show that decadal‐to‐century scale changes in carbon export associated with climate change lead to an estimated 5.2% decrease in future (2091–2100) global open ocean benthic biomass under RCP8.5 (reduction of 5.2 Mt C) compared with contemporary conditions (2006–2015). Our projections use multi‐model mean export flux estimates from eight fully coupled earth system models, which contributed to the Coupled Model Intercomparison Project Phase 5, that have been forced by high and low representative concentration pathways (RCP8.5 and 4.5, respectively). These export flux estimates are used in conjunction with published empirical relationships to predict changes in benthic biomass. The polar oceans and some upwelling areas may experience increases in benthic biomass, but most other regions show decreases, with up to 38% reductions in parts of the northeast Atlantic. Our analysis projects a future ocean with smaller sized infaunal benthos, potentially reducing energy transfer rates though benthic multicellular food webs. More than 80% of potential deep‐water biodiversity hotspots known around the world, including canyons, seamounts, and cold‐water coral reefs, are projected to experience negative changes in biomass. These major reductions in biomass may lead to widespread change in benthic ecosystems and the functions and services they provide.     

Decomposition of 13C-labelled standard plant material in a latitudinal transect of European coniferous forests: Differential impact of climate on the decomposition of soil organic matter compartments

¹³C labelled plant material was incubated in situ over 2 to 3 years in 8 conifer forest soils located on acid and limestone parent material along a north-south climatic transect from boreal to dry Mediterranean regions in western Europe. The objectives of the experiment were to evaluate the effects of climate and the soil environment on decomposition and soil organic matter dynamics. Changes in climate were simulated using a north-to-south cascade procedure involving the relocation of labelled soil columns to the next warmer site along the transect.Double exponential, decay-rate functions (for labile and recalcitrant SOM compartments) vs time showed that the thermosensitivity of microbial processes depended on the latitude from which the soil was translocated. Cumulative response functions for air temperature, and for combined temperature and moisture were used as independent variables in first order kinetic models fitted to the decomposition data. In the situations where climatic response functions explained most of the variations in decomposition rates when the soils were translocated, the climate optimised decomposition rates for the local and the translocated soil should be similar. Differences between these two rates indicated that there was either no single climatic response function for one or both compartments, and/or other edaphic factors influenced the translocation effect. The most northern boreal soil showed a high thermosensitivity for recalcitrant organic matter compartment, whereas the labile fraction was less sensitive to climate changes for soils from more southern locations. Hence there was no single climatic function which describe the decay rates for all compartments. At the end of the incubation period it was found that the heat sum to achieve the same carbon losses was lower for soils in the north of the transect than in the south. In the long term, therefore, for a given heat input, decomposition rates would show larger increases in boreal northern sites than in warm temperate regions.The changes in climate produced by soil translocation were more clearly reflected by decomposition rates in the acid soils than for calcareous soils. This indicates that the physicochemical environment can have important differential effects on microbial decomposition of the labile and recalcitrant components of SOM.     

Temperature and rainfall interact to control carbon cycling in tropical forests

Tropical forests dominate global terrestrial carbon (C) exchange, and recent droughts in the Amazon Basin have contributed to short‐term declines in terrestrial carbon dioxide uptake and storage. However, the effects of longer‐term climate variability on tropical forest carbon dynamics are still not well understood. We synthesised field data from more than 150 tropical forest sites to explore how climate regulates tropical forest aboveground net primary productivity (ANPP) and organic matter decomposition, and combined those data with two existing databases to explore climate – C relationships globally. While previous analyses have focused on the effects of either temperature or rainfall on ANPP, our results highlight the importance of interactions between temperature and rainfall on the C cycle. In cool forests (< 20 °C), high rainfall slowed rates of C cycling, but in warm tropical forests (> 20 °C) it consistently enhanced both ANPP and decomposition. At the global scale, our analysis showed an increase in ANPP with rainfall in relatively warm sites, inconsistent with declines in ANPP with rainfall reported previously. Overall, our results alter our understanding of climate – C cycle relationships, with high precipitation accelerating rates of C exchange with the atmosphere in the most productive biome on earth.     

Seasonal Variability of Particulate Organic Matter in a Mountain Stream in Central Spain

The aim of this paper was to study the influence of environmental characteristics of the Mediterranean climate on seasonal variability of particulate organic matter abundance in a mountain stream. Coarse and fine fractions of both suspended and benthic particulate organic matter were determined on 14 occasions between February 1998 and November 1999 in a second‐order Mediterranean stream in Central Spain (Arroyo Mediano). Temporal variability of suspended organic matter followed a seasonal pattern, attributed to litter‐fall inputs, instream processing, and the hydrological regime. Suspended organic matter (SOM) and its seasonal variability fall well within the range reported for streams in temperate non‐Mediterranean deciduous forest. However, we found no seasonal trend in benthic organic matter (BOM) storage, and it seems that the amount of BOM remained fairly constant throughout the year. Reach retention (evaluated as the ratio between BOM and SOM per m²) was higher in summer during reduced stream flow, mainly due to coarse particulate organic matter storage. These observations do not differ from those reported for other headwater streams in temperate forested biomes, from which we conclude that there was no evidence of a Mediterranean influence on particulate organic matter dynamics in the Mediano stream, nor probably in other headwater Mediterranean streams. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Upper thermal thresholds of shallow vs. deep populations of the precious Mediterranean red coral Corallium rubrum (L.): Assessing the potential effects of warming in the NW Mediterranean

Recent mortality outbreaks in marine ecosystems have been linked to elevated seawater temperatures associated with global climate change. Acquisition of thermotolerance data is essential, not only to determine the role of temperature in mortality outbreaks, but also to predict consequences of global warming. In the NW Mediterranean region, elevated seawater temperatures during the summer periods of 1999 and 2003 caused mass mortality of the Mediterranean red coral, Corallium rubum (L. 1758). Experiments testing the upper thermal limits of this species were carried out in aquaria using samples collected from populations from 11 to 40 m depth in the Marseilles region (NW Mediterranean, France). Samples were subjected to temperature treatments between 18 and 30 °C with an exposure time of 5 and 25 days. Three biological response variables were used to evaluate effects of the treatments: coenenchyme necrosis, polyp activity and calcification rates (⁴⁵Ca incorporation in calcareous skeleton). The results showed that exposure to 24 °C for 24 days caused a beginning of mortality only for the deep population, and to 25 °C for between 9 and 14 days caused mass mortality of both sample groups. The response variable results indicate that samples from the shallow population had greater thermotolerance of elevated seawater temperatures than the deep samples. The shallow samples showed greater polyp activity and higher calcification rate with a delayed necrosis response than the deep samples. These initial thermotolerance results combined with both hydrographic models and seawater temperature monitoring are the first step towards developing predictive tools for anticipating future effects of climate change in the red coral populations.     

Climate change predicted to cause severe increase of organic carbon in lakes

Riverine transport of organic carbon (OC) to the ocean is a significant component in the global carbon (C) cycle and the concentration of total organic carbon (TOC) in rivers and lakes is vital for ecosystem properties and water quality for human use. By use of a large dataset comprising chemical variables and detailed catchment information in ～1000 Norwegian pristine lakes covering a wide climatic range, we were able to predict TOC concentrations with high accuracy. We further predict, using a ‘space‐for‐time’ approach and a downscaled, moderate, climate change scenario, that northern, boreal regions likely will experience strong increases in OC export from catchments to surface waters. Median concentrations of OC in these lakes will increase by 65%, from the current median of 2.0–3.3 mg C L^?1. This is a long‐term effect, primarily mediated by increased terrestrial vegetation cover in response to climate change. This increase OC will have severe impacts on food‐webs, productivity and human use. Given the robustness of the estimates and the general applicability of the parameters, we suggest that these findings would be relevant to boreal areas in general.     

Temperature-driven regime shifts in the dynamics of size-structured populations

Global warming impacts virtually all biota and ecosystems. Many of these impacts are mediated through direct effects of temperature on individual vital rates. Yet how this translates from the individual to the population level is still poorly understood, hampering the assessment of global warming impacts on population structure and dynamics. Here, we study the effects of temperature on intraspecific competition and cannibalism and the population dynamical consequences in a size-structured fish population. We use a physiologically structured consumer-resource model in which we explicitly model the temperature dependencies of the consumer vital rates and the resource population growth rate. Our model predicts that increased temperature decreases resource density despite higher resource growth rates, reflecting stronger intraspecific competition among consumers. At a critical temperature, the consumer population dynamics destabilize and shift from a stable equilibrium to competition-driven generation cycles that are dominated by recruits. As a consequence, maximum age decreases and the proportion of younger and smaller-sized fish increases. These model predictions support the hypothesis of decreasing mean body sizes due to increased temperatures. We conclude that in size-structured fish populations, global warming may increase competition, favor smaller size classes, and induce regime shifts that destabilize population and community dynamics.     

Changes in Arctic marine bacterial carbon metabolism in response to increasing temperature

Arctic areas of deep-water convection have a large potential for export of organic carbon from surface waters into the deep sea and, therefore, are an important part of the global carbon cycle. As the Arctic is reportedly heating up faster than any other part of the planet, temperature-driven changes in the biogeochemical cycling in these areas can be very significant. Here, we study the regulation of bacterial carbon metabolism, which process vast amounts of organic carbon, by temperature and the availability of resources. The response of bacterial production and respiration of natural bacterial assemblages from the Fram Strait was studied by experimental manipulations of temperature and resources in combination. Both bacterial production and respiration were enhanced by temperature so that the total bacterial carbon demand increased sixfold following a temperature increase of 6°C. Respiration responded more strongly than production so that bacterial growth efficiency decreased with increasing temperature. Although neither production nor respiration was limited by resource availability under in situ conditions, the response to temperature was higher in resource-amended treatments, indicative of a substrate-temperature interaction regulating both components of bacterial metabolism. In conclusion, the results show that warming can result in a substantial increase of the carbon flow through bacteria and that most of the carbon consumed would be released as CO₂. Moreover, the results suggest that both temperature and availability of resources need to be considered to accurately be able to predict changes in bacterial carbon metabolism in response to climate change.     

Size-selective predation on pelagic microorganisms in Arctic freshwaters

Herbivorous zooplankton may have a pronounced influence on pelagicmicroorganisms in Arctic freshwaters. We quantified experimentallythe size-selective feeding of several zooplankton groups onpelagic microorganisms in high Arctic tundra systems. Our experimentsand field study focused on dominant herbivores in Arctic freshwaters,including the cladoceran Daphnia, the copepod Diaptomus andthe anostracan Branchinecta, and their effects on prey rangingin size from bacteria to large phytoplankton. Grazing experimentsshowed that Daphnia were effective predators on all types ofprey, whereas Diaptomus grazed preferentially on larger phytoplanktonwith low clearance rates for bacterial cells. Further analysisby flow cytometry indicated that Diaptomus grazed selectivelyon the largest bacteria. In contrast to the results obtainedin the controlled experiments, Arctic lakes and ponds with azooplankton community dominated by Daphnia had a higher bacterialproduction and abundance than systems not dominated by thisgrazer. This may indicate that the stimulatory effect of grazerson bacterial growth is more pronounced in natural systems, orthat factors other than zooplankton grazing are more importantin regulating bacterial abundance and production in naturalsystems. Although Arctic waters differ considerably from temperatesystems with respect to temperature and light regime, herbivore–preydynamics as well as the bacterial response to temperature appearto be similar between the climatic regions.     

Impacts of elevated terrestrial nutrient loads and temperature on pelagic food‐web efficiency and fish production

Both temperature and terrestrial organic matter have strong impacts on aquatic food‐web dynamics and production. Temperature affects vital rates of all organisms, and terrestrial organic matter can act both as an energy source for lower trophic levels, while simultaneously reducing light availability for autotrophic production. As climate change predictions for the Baltic Sea and elsewhere suggest increases in both terrestrial matter runoff and increases in temperature, we studied the effects on pelagic food‐web dynamics and food‐web efficiency in a plausible future scenario with respect to these abiotic variables in a large‐scale mesocosm experiment. Total basal (phytoplankton plus bacterial) production was slightly reduced when only increasing temperatures, but was otherwise similar across all other treatments. Separate increases in nutrient loads and temperature decreased the ratio of autotrophic:heterotrophic production, but the combined treatment of elevated temperature and terrestrial nutrient loads increased both fish production and food‐web efficiency. CDOM: Chl a ratios strongly indicated that terrestrial and not autotrophic carbon was the main energy source in these food webs and our results also showed that zooplankton biomass was positively correlated with increased bacterial production. Concomitantly, biomass of the dominant calanoid copepod Acartia sp. increased as an effect of increased temperature. As the combined effects of increased temperature and terrestrial organic nutrient loads were required to increase zooplankton abundance and fish production, conclusions about effects of climate change on food‐web dynamics and fish production must be based on realistic combinations of several abiotic factors. Moreover, our results question established notions on the net inefficiency of heterotrophic carbon transfer to the top of the food web.     

Sensitivity of a dynamic global vegetation model to climate and atmospheric CO2

The equilibrium carbon storage capacity of the terrestrial biosphere has been investigated by running the Lund–Potsdam–Jena Dynamic Global Vegetation Model to equilibrium for a range of CO₂ concentrations and idealized climate states. Local climate is defined by the combination of an observation-based climatology and perturbation patterns derived from a 4 × CO₂ warming simulations, which are linearly scaled to global mean temperature deviations, Δ T _glob. Global carbon storage remains close to its optimum for Δ T _glob in the range of ±3°C in simulations with constant atmospheric CO₂. The magnitude of the carbon loss to the atmosphere per unit change in global average surface temperature shows a pronounced nonlinear threshold behavior. About twice as much carbon is lost per degree warming for Δ T _glob above 3°C than for present climate. Tropical, temperate, and boreal trees spread poleward with global warming. Vegetation dynamics govern the distribution of soil carbon storage and turnover in the climate space. For cold climate conditions, the global average decomposition rate of litter and soil decreases with warming, despite local increases in turnover rates. This result is not compatible with the assumption, commonly made in global box models, that soil turnover increases exponentially with global average surface temperature, over a wide temperature range.     

Effect of increased atmospheric CO2 on the performance of an aquatic detritivore through changes in water temperature and litter quality

Cold water woodland streams, where terrestrially derived organic matter fuels aquatic food webs, can be affected by increases in atmospheric CO₂ concentrations, as these are predicted to lead to increases in water temperature and decreases in organic matter quality. In fact, elevated CO₂ (580 ppm) decreased the initial phosphorus concentration of birch litter by 30% compared with litter grown under ambient conditions (380 ppm). Here, we first assessed the effect of differences in litter quality on mass loss, microbial colonization and conditioned litter quality after submersion in a mountain stream for 2 weeks. Leaching did not change the relative differences between litter types, while fungal biomass was two fold higher in elevated litter. We then offered this litter (conditioned ambient and elevated) to a stream detritivore that was kept at 10 and 15 °C to assess the individual and interactive effects of increased temperature and decreased litter quality on invertebrate performance. When given a choice, the detritivore preferred elevated litter, but only at 10 °C. When fed litter types singularly, there was no effect of litter quality on consumption rates; however, the effect of temperature depended on individual size and time of collection. Growth rates were higher in individuals fed ambient litter at 10 °C when compared with individuals fed elevated litter at 15 °C. Mortality did not differ between litter types, but was higher at 15 °C than at 10 °C. Increases in temperature led to alterations in the individual body elemental composition and interacted with litter type. The performance of the detritivore was therefore more affected by increases in temperature than by small decreases in litter quality. However, it seems conceivable that in a future global warming scenario the simultaneous increases in water temperature and decreases in litter quality might affect detritivores performance more than predicted from the effects of both factors considered individually.     

The current situation and potential effects of climate change on the microbial load of marine bivalves of the Greek coastlines: an integrative review

Global warming affects the aquatic ecosystems, accelerating pathogenic microorganisms' and toxic microalgae's growth and spread in marine habitats, and in bivalve molluscs. New parasite invasions are directly linked to oceanic warming. Consumption of pathogen-infected molluscs impacts human health at different rates, depending, inter alia, on the bacteria taxa. It is therefore necessary to monitor microbiological and chemical contamination of food. Many global cases of poisoning from bivalve consumption can be traced back to Mediterranean regions. This article aims to examine the marine bivalve's infestation rate within the scope of climate change, as well as to evaluate the risk posed by climate change to bivalve welfare and public health. Biological and climatic data literature review was performed from international scientific sources, Greek authorities and State organizations. Focusing on Greek aquaculture and bivalve fisheries, high-risk index pathogenic parasites and microalgae were observed during summer months, particularly in Thermaikos Gulf. Considering the climate models that predict further temperature increases, it seems that marine organisms will be subjected in the long term to higher temperatures. Due to the positive linkage between temperature and microbial load, the marine areas most affected by this phenomenon are characterized as ‘high risk’ for consumer health.