Abstract
The coupling between nitrification and N
2
gas production to recycle ammonia back to the atmosphere is a key step in the nitrogen cycle that has been researched widely. An assumption for ...such research is that the products of nitrification (nitrite or nitrate) mix freely in the environment before reduction to N
2
gas. Here we show, in oxic riverbeds, that the pattern of N
2
gas production from ammonia deviates by ~3- to 16-fold from that predicted for denitrification or anammox involving nitrite or nitrate as free porewater intermediates. Rather, the patterns match that for a coupling through a cryptic pool, isolated from the porewater. A cryptic pool challenges our understanding of a key step in the nitrogen cycle and masks our ability to distinguish between sources of N
2
gas that 20 years’ research has sought to identify. Our reasoning suggests a new pathway or a new type of coupling between known pathways in the nitrogen cycle.
We measured the production of N₂ gas from anammox and denitrification simultaneously in intact sediment cores at six sites along a transect of the continental shelf (50 m) and deeper slope (2000 m) ...in the North Atlantic. Maximum rates of total N₂ production were measured on the shelf and were largely due to denitrification, with anammox contributing, on average, 33% of this production. On the continental slope, the production of N₂ gas decreased but the proportion due to anammox reached a maximum of 65%. This change in both amount and dominant pathway of N₂ production could be explained largely by the concentration of organic carbon at each site. With increasing carbon the total production of N₂ increased rapidly while the response of anammox was not significant. On the continental slope, total N₂ production fell below 2 µmol N m⁻ h⁻¹ and anammox was strongly related (r = 0.95) to denitrification but the relative magnitude of anammox to denitrification (1.65:1) suggested that anammox could not be fuelled by $NO_2^ - $ from denitrification alone. On the shelf, however, where total N₂ production was predominantly greater than 2 µmol N m⁻² h⁻¹, no relationship between anammox and denitrification was found and anammox remained constant at 1.4 µmol N m⁻² h⁻¹. Despite the constancy and greater availability of $NO_3^ - $ and lower temperatures on the continental slope, the significance of anammox to the total production of N₂ appears primarily controlled by the overall rate of N₂ production.
Organism size is one of the key determinants of community structure, and its relationship with abundance can describe how biomass is partitioned among the biota within an ecosystem. An outdoor ...freshwater mesocosm experiment was used to determine how warming of∼4 °C would affect the size, biomass and taxonomic structure of planktonic communities. Warming increased the steepness of the community size spectrum by increasing the prevalence of small organisms, primarily within the phytoplankton assemblage and it also reduced the mean and maximum size of phytoplankton by approximately one order of magnitude. The observed shifts in phytoplankton size structure were reflected in changes in phytoplankton community composition, though zooplankton taxonomic composition was unaffected by warming. Furthermore, warming reduced community biomass and total phytoplankton biomass, although zooplankton biomass was unaffected. This resulted in an increase in the zooplankton to phytoplankton biomass ratio in the warmed mesocosms, which could be explained by faster turnover within the phytoplankton assemblages. Overall, warming shifted the distribution of phytoplankton size towards smaller individuals with rapid turnover and low standing biomass, resulting in a reorganization of the biomass structure of the food webs. These results indicate future environmental warming may have profound effects on the structure and functioning of aquatic communities and ecosystems.
Warming alters the metabolic balance of ecosystems Yvon-Durocher, Gabriel; Jones, J. Iwan; Trimmer, Mark ...
Philosophical transactions - Royal Society. Biological sciences,
07/2010, Letnik:
365, Številka:
1549
Journal Article
Recenzirano
Odprti dostop
The carbon cycle modulates climate change, via the regulation of atmospheric CO2, and it represents one of the most important services provided by ecosystems. However, considerable uncertainties ...remain concerning potential feedback between the biota and the climate. In particular, it is unclear how global warming will affect the metabolic balance between the photosynthetic fixation and respiratory release of CO2 at the ecosystem scale. Here, we present a combination of experimental field data from freshwater mesocosms, and theoretical predictions derived from the metabolic theory of ecology to investigate whether warming will alter the capacity of ecosystems to absorb CO2. Our manipulative experiment simulated the temperature increases predicted for the end of the century and revealed that ecosystem respiration increased at a faster rate than primary production, reducing carbon sequestration by 13 per cent. These results confirmed our theoretical predictions based on the differential activation energies of these two processes. Using only the activation energies for whole ecosystem photosynthesis and respiration we provide a theoretical prediction that accurately quantified the precise magnitude of the reduction in carbon sequestration observed experimentally. We suggest the combination of whole-ecosystem manipulative experiments and ecological theory is one of the most promising and fruitful research areas to predict the impacts of climate change on key ecosystem services.
The elemental composition of phytoplankton (C:N:P stoichiometry) is a critical factor regulating nutrient cycling, primary production and energy transfer through planktonic food webs. Our ...understanding of the multiple direct and indirect mechanisms through which temperature controls phytoplankton stoichiometry is however incomplete, increasing uncertainty in the impacts of global warming on the biogeochemical functioning of aquatic ecosystems. Here, we use a decade-long warming experiment in outdoor freshwater ponds to investigate how temperature-driven turnover in species composition and shifts in stoichiometric traits within species through local thermal adaptation contribute to the effects of warming on seston stoichiometry. We found that experimental warming increased seston C:P and N:P ratios, while the C:N ratio was unaffected by warming. Temperature was also the dominant driver of seasonal variation in seston stoichiometry, correlating positively with both C:P and N:P ratios. The taxonomic composition of the phytoplankton community differed substantially between the warmed and ambient treatments indicating that warming resulted in differential sorting of species from the regional pool. Furthermore, taxonomic composition also changed markedly over the year within each of the warmed and ambient treatments, highlighting substantial temporal turnover in species. To investigate whether local adaptation also played an important role in shaping the effects of warming on seston stoichiometry, we isolated multiple strains of the cosmopolitan alga,
from across the warmed and ambient mesocosms. We found that warmed isolates had higher C:P and N:P ratios, shifts that were comparable in direction and magnitude to the effects of warming on seston stoichiometry. Our results suggest that both species sorting and local adaptation are likely to play important roles in shaping the effects of warming on bulk phytoplankton stoichiometry and indicate that major shifts in aquatic biogeochemistry should be expected in a warmer world.
Aim: The average carbon-to-nitrogen-to-phosphorus ratio (C:N:P) of marine algae is known to be tightly coupled to that of the inorganic pools of C, N and P in the ocean interior (i.e. the Redfield ...ratio), and therefore plays a key role in regulating the C and N cycles in the ocean. The C:N:P ratio of algae also varies substantially, both within and among taxa, in response to variation in the abiotic environment, raising the possibility that biogeochemical controls on the marine C and N cycles may shift as a result of climate change. Howerer, the role of temperature in driving phenotypic variation in stoichiometry within algal taxa, as well as biogeographic variation in particulate C, N and P among oceanic regions, remains largely unresolved. Location: Global. Methods: To assess the extent to which temperature controls algal stoichiometry we performed two complementary meta-analyses. First, we characterized the global temperature dependence of algal stoichiometry by analysing field data that encompassed 767 estimates of C:N:P from 22 oceanic sites spanning over 130° of latitude. Second, we characterized the within-species acclimation responses of C:N:P stoichiometry to temperature by analysing data that encompassed 17 experiments, 9 species and 4 taxonomic classes. Results: The geographic analyses demonstrated that the N:P and C:P ratios of marine algae were best predicted by latitudinal variation in average sea-surface temperature, and that both ratios increased 2.6-fold from 0 to 30 °C. These global-scale temperature responses, which largely reflect geographic variation in the species compositions of algal assemblages, were of similar magnitude to the average within-species response of the N:P and C:P ratios to experimental temperature manipulations. Main conclusions: The congruence between field and experimental observations suggests that temperature-dependent physiological mechanisms operating at the subcellular level play an important role in determining the stoichiometry of algae in the world's oceans.
Abstract
Nitrous oxide (N
2
O) is a potent climate gas, with its strong warming potential and ozone-depleting properties both focusing research on N
2
O sources. Although a sink for N
2
O through ...biological fixation has been observed in the Pacific, the regulation of N
2
O-fixation compared to canonical N
2
-fixation is unknown. Here we show that both N
2
O and N
2
can be fixed by freshwater communities but with distinct seasonalities and temperature dependencies. N
2
O fixation appears less sensitive to temperature than N
2
fixation, driving a strong sink for N
2
O in colder months. Moreover, by quantifying both N
2
O and N
2
fixation we show that, rather than N
2
O being first reduced to N
2
through denitrification, N
2
O fixation is direct and could explain the widely reported N
2
O sinks in natural waters. Analysis of the nitrogenase (
nifH
) community suggests that while only a subset is potentially capable of fixing N
2
O they maintain a strong, freshwater sink for N
2
O that could be eroded by warming.
Biodiversity loss is occurring rapidly worldwide, yet it is uncertain whether few or many species are required to sustain ecosystem functioning in the face of environmental change. The importance of ...biodiversity might be enhanced when multiple ecosystem processes (termed multifunctionality) and environmental contexts are considered, yet no studies have quantified this explicitly to date. We measured five key processes and their combined multifunctionality at three temperatures (5, 10 and 15 °C) in freshwater aquaria containing different animal assemblages (1–4 benthic macroinvertebrate species). For single processes, biodiversity effects were weak and were best predicted by additive‐based models, i.e. polyculture performances represented the sum of their monoculture parts. There were, however, significant effects of biodiversity on multifunctionality at the low and the high (but not the intermediate) temperature. Variation in the contribution of species to processes across temperatures meant that greater biodiversity was required to sustain multifunctionality across different temperatures than was the case for single processes. This suggests that previous studies might have underestimated the importance of biodiversity in sustaining ecosystem functioning in a changing environment.
Phytoplankton are key components of aquatic ecosystems, fixing CO2 from the atmosphere through photosynthesis and supporting secondary production, yet relatively little is known about how future ...global warming might alter their biodiversity and associated ecosystem functioning. Here, we explore how the structure, function, and biodiversity of a planktonic metacommunity was altered after five years of experimental warming. Our outdoor mesocosm experiment was open to natural dispersal from the regional species pool, allowing us to explore the effects of experimental warming in the context of metacommunity dynamics. Warming of 4°C led to a 67% increase in the species richness of the phytoplankton, more evenly-distributed abundance, and higher rates of gross primary productivity. Warming elevated productivity indirectly, by increasing the biodiversity and biomass of the local phytoplankton communities. Warming also systematically shifted the taxonomic and functional trait composition of the phytoplankton, favoring large, colonial, inedible phytoplankton taxa, suggesting stronger top-down control, mediated by zooplankton grazing played an important role. Overall, our findings suggest that temperature can modulate species coexistence, and through such mechanisms, global warming could, in some cases, increase the species richness and productivity of phytoplankton communities.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Angiosperm genome sizes (GS) range c. 2400-fold, and as nucleic acids are amongst the most phosphorus- (P) and nitrogen (N)-demanding cellular biomolecules, we test the hypothesis that a key ...influence on plant biomass and species composition is the interaction between N and P availability and plant GS.
We analysed the impact of different nutrient regimes on above-ground biomass of angiosperm species with different GS, ploidy level and Grime's C-S-R (competitive, stresstolerant, ruderal) plant strategies growing at the Park Grass Experiment (Rothamsted, UK), established in 1856.
The biomass-weighted mean GS of species growing on plots with the addition of both N and P fertilizer were significantly higher than that of plants growing on control plots and plots with either N or P. The plants on these N + P plots are dominated by polyploids with large GS and a competitive plant strategy.
The results are consistent with our hypothesis that large genomes are costly to build and maintain under N and P limitation. Hence GS and ploidy are significant traits affecting biomass growth under different nutrient regimes, influencing plant community composition and ecosystem dynamics. We propose that GS is a critical factor needed in models that bridge the knowledge gap between biodiversity and ecosystem functioning.
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