Ducklow H.W.,Ecosystems Center |
Doney S.C.,Woods Hole Oceanographic Institution
Annual Review of Marine Science | Year: 2013
For more than a decade there has been controversy in oceanography regarding the metabolic state of the oligotrophic subtropical gyres of the open ocean. Here we review the background of this controversy, commenting on several issues to set the context for a moderated debate between two groups of scientists. In one of the two companion articles, Williams et al. (2013) take the view that these gyres exhibit a state of net autotrophy-that is, their gross primary production (GPP) exceeds community respiration (R) when averaged over some suitably extensive region and over a long duration. In the other companion article, Duarte et al. (2013) take the opposite view, that these gyres are net heterotrophic, with R exceeding the GPP. This idea-that large, remote areas of the upper ocean could be net heterotrophic-raises a host of fundamental scientific questions about the metabolic processes of photosynthesis and respiration that underlie ocean ecology and global biogeochemistry. The question remains unresolved in part because the net state is finely balanced between large opposing fluxes and most current measurements have large uncertainties. This challenging question must be studied against the background of large, anthropogenically driven changes in ocean ecology and biogeochemistry. Current trends of anthropogenic change make it an urgent problem to solve and also greatly complicate finding that solution. © 2013 by Annual Reviews. All rights reserved.
News Article | November 14, 2016
WOODS HOLE, Mass. -- While scientists and policy experts debate the impacts of global warming, the Earth's soil is releasing roughly nine times more carbon dioxide to the atmosphere than all human activities combined. This huge carbon flux from soil -- due to the natural respiration of soil microbes and plant roots -- begs one of the central questions in climate change science. As the global climate warms, will soil respiration rates increase, adding even more carbon dioxide to the atmosphere and accelerating climate change? Previous experimental studies of this question have not produced a consensus, prompting Marine Biological Laboratory scientists Joanna Carey, Jianwu Tang and colleagues to synthesize the data from 27 studies across nine biomes, from the desert to the Arctic. Their analysis is published this week in Proceedings of the National Academy of Sciences. This represents the largest dataset to date of soil respiration response to experimental warming. One prediction from this synthesis is that rising global temperatures result in regionally variable responses in soil respiration, with colder climates being considerably more responsive. "Consistently across all biomes, we found that soil respiration increased with soil temperature up to about 25° C (77° F)," says Carey, a postdoctoral scientist in the MBL Ecosystems Center. Above the 25° C threshold, respiration rates decreased with further increases in soil temperature. "That means the Arctic latitudes, where soil temperatures rarely, if ever, reach 25° C , will continue to be most responsive to climate warming. Because there is so much carbon stored in frozen soils of the Arctic, this has really serious repercussions for future climate change," Carey says. The team also found that soil microbes in experimental warming studies showed no sign of adaptation -- meaning a muted respiration response to rising temperatures -- in all of the biomes studied, except desert and boreal forest. This indicates that "soils will typically respond strongly to increasing temperature by releasing more carbon dioxide," says Tang, lead investigator of the study. To understand how global carbon in soils will respond to climate change, the authors stress, more data are needed from under- and non-represented regions, especially the Arctic and the tropics. Other MBL scientists who contributed to this study include Mary Heskel, Jerry Melillo, Edward B. Rastetter, and Gaius R. Shaver. Carey, Joanna A. et al (2016) Temperature response of soil respiration largely unaltered with experimental warming. Proc. Natl. Acad. Sci. DOI: 10.1073/pnas.1605365113 The Marine Biological Laboratory (MBL) is dedicated to scientific discovery - exploring fundamental biology, understanding marine biodiversity and the environment, and informing the human condition through research and education. Founded in Woods Hole, Massachusetts in 1888, the MBL is a private, nonprofit institution and an affiliate of the University of Chicago.
News Article | November 16, 2016
While scientists and policy experts debate the impacts of global warming, Earth's soil is releasing roughly nine times more carbon dioxide to the atmosphere than all human activities combined. This huge carbon flux from soil -- due to the natural respiration of soil microbes and plant roots -- raises one of the central questions in climate change science. As the global climate warms, will soil respiration rates increase, adding even more carbon dioxide to the atmosphere and accelerating climate change? Previous experimental studies of this question have not produced a consensus, prompting Marine Biological Laboratory scientists Joanna Carey, Jianwu Tang and colleagues to synthesize the data from 27 studies across nine biomes, from the desert to the Arctic. Their analysis is published this week in Proceedings of the National Academy of Sciences. This represents the largest dataset to date of soil respiration response to experimental warming. One prediction from this synthesis is that rising global temperatures result in regionally variable responses in soil respiration, with colder climates being considerably more responsive. "Consistently across all biomes, we found that soil respiration increased with soil temperature up to about 25° C (77° F)," says Carey, a postdoctoral scientist in the MBL Ecosystems Center. Above the 25° C threshold, respiration rates decreased with further increases in soil temperature. "That means the Arctic latitudes, where soil temperatures rarely, if ever, reach 25° C , will continue to be most responsive to climate warming. Because there is so much carbon stored in frozen soils of the Arctic, this has really serious repercussions for future climate change," Carey says. The team also found that soil microbes in experimental warming studies showed no sign of adaptation -- meaning a muted respiration response to rising temperatures -- in all of the biomes studied, except desert and boreal forest. This indicates that "soils will typically respond strongly to increasing temperature by releasing more carbon dioxide," says Tang, lead investigator of the study. To understand how global carbon in soils will respond to climate change, the authors stress, more data are needed from under- and non-represented regions, especially the Arctic and the tropics.
News Article | January 6, 2016
Protected areas such as rainforests occupy more than one-tenth of the Earth’s landscape, and provide invaluable ecosystem services, from erosion control to pollination to biodiversity preservation. They also draw heat-trapping carbon dioxide (CO ) from the atmosphere and store it in plants and soil through photosynthesis, yielding a net cooling effect on the planet. Determining the role protected areas play as carbon sinks — now and in decades to come — is a topic of intense interest to the climate-policy community as it seeks science-based strategies to mitigate climate change. Toward that end, a study in the journal Ambio estimates for the first time the amount of CO sequestered by protected areas, both at present and throughout the 21st century as projected under various climate and land-use scenarios. Based on their models and assuming a business-as-usual climate scenario, the researchers projected that the annual carbon sequestration rate in protected areas will decline by about 40 percent between now and 2100. Moreover, if about one-third of protected land is converted to other uses by that time, due to population and economic pressures, carbon sequestration in the remaining protected areas will become negligible. “Our study highlights the importance of protected areas in slowing the rate of climate change by pulling carbon dioxide out of the atmosphere and sequestering it in plants and soils, especially in forested areas,” said Jerry Melillo, the study’s lead author. Melillo is a distinguished scientist at the Marine Biological Laboratory (MBL) in Woods Hole, Massachusetts, and former director of the MBL’s Ecosystems Center. “Maintaining existing protected areas, enlarging them and adding new ones over this century are important ways we can manage the global landscape to help mitigate climate change.” Based on a global database of protected areas, a reconstruction of global land-use history, and a global biogeochemistry model, the researchers estimated that protected areas currently sequester 0.5 petagrams (500 billion kilograms) of carbon each year, or about 20 percent of the carbon sequestered by all land ecosystems annually. Using an integrated modeling framework developed by the MIT Joint Program on the Science and Policy of Global Change, they projected that under a rapid climate-change scenario that extends existing climate policies; keeps protected areas off-limits to development; and assumes continued economic growth and a 1 percent annual increase in agricultural productivity, the annual carbon sequestration rate in protected areas would fall to about 0.3 petagrams of carbon by 2100. When they ran the same scenario but allowed for possible development of protected areas, they projected that more than one-third of today’s protected areas would be converted to other uses. This would reduce carbon sequestration in the remaining protected areas to near zero by the end of the century. (The protected areas that are not converted would be the more marginal systems that have low productivity, and thus low capacity to sequester carbon.) Based on this analysis, the researchers concluded that unless current protected areas are preserved and expanded, their capacity to sequester carbon will decline. The need for expansion is driven by climate change: As the average global temperature rises, so, too, will plant and soil respiration in protected and unprotected areas alike, thereby reducing their ability to store carbon and cool the planet. “This work shows the need for sufficient resources dedicated to actually prevent encroachment of human activity into protected areas,” said John Reilly, one of the study’s coauthors and the co-director of the MIT Joint Program on the Science and Policy of Global Change. The study was supported by the David and Lucille Packard foundation, the National Science Foundation, the U.S. Environmental Protection Agency, and the U.S. Department of Energy.
Sistla S.A.,University of California at Santa Barbara |
Moore J.C.,Colorado State University |
Simpson R.T.,Colorado State University |
Gough L.,University of Texas at Arlington |
And 2 more authors.
Nature | Year: 2013
High latitudes contain nearly half of global soil carbon, prompting interest in understanding how the Arctic terrestrial carbon balance will respond to rising temperatures. Low temperatures suppress the activity of soil biota, retarding decomposition and nitrogen release, which limits plant and microbial growth. Warming initially accelerates decomposition, increasing nitrogen availability, productivity and woody-plant dominance. However, these responses may be transitory, because coupled abiotic-biotic feedback loops that alter soil-temperature dynamics and change the structure and activity of soil communities, can develop. Here we report the results of a two-decade summer warming experiment in an Alaskan tundra ecosystem. Warming increased plant biomass and woody dominance, indirectly increased winter soil temperature, homogenized the soil trophic structure across horizons and suppressed surface-soil-decomposer activity, but did not change total soil carbon or nitrogen stocks, thereby increasing net ecosystem carbon storage. Notably, the strongest effects were in the mineral horizon, where warming increased decomposer activity and carbon stock: a 'biotic awakening' at depth. © 2013 Macmillan Publishers Limited. All rights reserved.
Hobbie J.E.,Ecosystems Center |
Hobbie E.A.,University of New Hampshire
Biogeochemistry | Year: 2012
In radioisotope studies in plankton, bacteria turn over the nanomolar ambient concentrations of dissolved amino acids within a few hours. Uptake follows Michaelis-Menten kinetics. In contrast, within minutes the very abundant bacteria and fungi in soil take up all labeled amino acids added at nanomolar to millimolar final concentrations; uptake kinetics accordingly cannot be measured. This rapid uptake agrees with earlier findings that soil microbes exist in a starving or low-activity state but are able to keep their metabolism poised to take up amino acids as they become available. How can this rapid uptake of added amino acids be reconciled with persistent soil concentrations of 10-500 μM of total dissolved amino acids? Although respiration of added amino acid carbon has been used to deduce uptake kinetics, the data indicate that in both soil and in eutrophic natural waters constant percentages of individual amino acids are respired; this percentage varies from less than 10% of the amount taken up for basic amino acids to more than 50% for acidic amino acids. We conclude that relatively fixed internal metabolic processes control the percent of amino acid respired and that the μM concentrations of amino acid measured in water extracts from soil are unavailable to microbes. Instead, these relatively high concentrations reflect amino acids in soils that are chemically protected, hidden in pores, or released from fine roots and microbes during sample preparation. © 2010 Springer Science+Business Media B.V.
Johnson D.S.,Ecosystems Center
Marine Ecology Progress Series | Year: 2011
In salt marshes, high-marsh habitats are infrequently flooded (typically only during spring tides). Organisms in these habitats, however, may still be susceptible to the effects of increased nutrients delivered by tidal water (i.e. eutrophication). In a Massachusetts salt marsh, I examined the responses of the epibenthic invertebrates in the Spartina patens-dominated high marsh to long-term (7 yr) and landscape-level (4?5 ha) nutrient enrichment. In this ecosystemlevel experiment, nutrients (N and P; ∼15× reference conditions) were added to the flooding waters of tidal creeks-which flooded the high marsh during spring tides-to mimic cultural eutrophication. Three detritivores: Melampus bidentatus (gastropod), Philoscia vittata (isopod), and Orchestia grillus (amphipod) numerically dominated the benthic invertebrate community (97% by abundance). These species had higher densities (47 to 199% increase) in enriched versus reference creeks. Melampus size structure shifted to larger individuals with enrichment. End-of-season aboveground biomass and detritus stocks of S. patens did not differ between treatments; thus, increased litter quality and/or alternative food-source increases (e.g. microbes) led to increased detritivore density/biomass. Predator densities (spiders and Tabanus larvae) increased 125 to 160% with enrichment, likely due to increased prey densities (including Orchestia and Philoscia). Analysis of similarities (ANOSIM) revealed that communities were dissimilar between treatments; differences were driven primarily by changes in detritivore abundance. These results suggest that despite being infrequently flooded and thus infrequently exposed to elevated nutrients, high-marsh invertebrates are susceptible to eutrophication. Hence, the high marsh should be integrated into our understanding of how eutrophication impacts saltmarsh functioning. © Inter-Research 2011.
Shaver G.R.,Ecosystems Center
Philosophical transactions of the Royal Society of London. Series B, Biological sciences | Year: 2013
Net ecosystem exchange (NEE) of C varies greatly among Arctic ecosystems. Here, we show that approximately 75 per cent of this variation can be accounted for in a single regression model that predicts NEE as a function of leaf area index (LAI), air temperature and photosynthetically active radiation (PAR). The model was developed in concert with a survey of the light response of NEE in Arctic and subarctic tundras in Alaska, Greenland, Svalbard and Sweden. Model parametrizations based on data collected in one part of the Arctic can be used to predict NEE in other parts of the Arctic with accuracy similar to that of predictions based on data collected in the same site where NEE is predicted. The principal requirement for the dataset is that it should contain a sufficiently wide range of measurements of NEE at both high and low values of LAI, air temperature and PAR, to properly constrain the estimates of model parameters. Canopy N content can also be substituted for leaf area in predicting NEE, with equal or greater accuracy, but substitution of soil temperature for air temperature does not improve predictions. Overall, the results suggest a remarkable convergence in regulation of NEE in diverse ecosystem types throughout the Arctic.
Rastetter E.B.,Ecosystems Center
Frontiers in Ecology and the Environment | Year: 2011
Organisms require about 30 essential elements to sustain life. The cycles of these elements are coupled to one another through the specific physiological requirements of the organisms. Here, I contrast several approaches to modeling coupled biogeochemical cycles using an example of carbon, nitrogen, and phosphorus accumulation in a Douglas-fir (Pseudotsuga menziesii) forest ecosystem and the response of that forest to elevated atmospheric carbon dioxide concentrations and global warming. Which of these approaches is most appropriate is subject to debate and probably depends on context; nevertheless, this question must be answered if scientists are to understand ecosystems and how they might respond to a changing global environment. © The Ecological Society of America.
Vallino J.J.,Ecosystems Center
Philosophical Transactions of the Royal Society B: Biological Sciences | Year: 2010
We examine the application of the maximum entropy production principle for describing ecosystem biogeochemistry. Since ecosystems can be functionally stable despite changes in species composition, we use a distributed metabolic network for describing biogeochemistry, which synthesizes generic biological structures that catalyse reaction pathways, but is otherwise organism independent. Allocation of biological structure and regulation of biogeochemical reactions is determined via solution of an optimal control problem in which entropy production is maximized. However, because synthesis of biological structures cannot occur if entropy production is maximized instantaneously, we propose that information stored within the metagenome allows biological systems to maximize entropy production when averaged over time. This differs from abiotic systems that maximize entropy production at a point in space - time, which we refer to as the steepest descent pathway. It is the spatio-temporal averaging that allows biological systems to outperform abiotic processes in entropy production, at least in many situations. A simulation of a methanotrophic system is used to demonstrate the approach. We conclude with a brief discussion on the implications of viewing ecosystems as self-organizing molecular machines that function to maximize entropy production at the ecosystem level of organization. © 2010 The Royal Society.