Human activities have drastically accelerated Earth’s major biogeochemical cycles, altering the the nitrogen (N) and phosphorus (P) cycles.
Combined effects of cumulative nutrient inputs and biogeochemical processes that occur in freshwater under anthropogenic eutrophication could lead to myriad shifts in N:P stoichiometry in global freshwater ecosystems, but this was not yet well-assessed.
In a new study in the journal Ecology Letters researchers from Peking University and CREAF-CSIC evaluated the characteristics of N and P stoichiometries in bodies of freshwater and their herbaceous macrophytes across human-impact levels, regions and periods.
Freshwater and its macrophytes had higher N and P concentrations and lower N:P ratios in heavily than lightly human-impacted environments, further evidenced by spatiotemporal comparisons across eutrophication gradients. N and P concentrations in freshwater ecosystems were positively correlated and N:P ratio was negatively correlated with population density in China.
“Our findings indicate that anthropogenic eutrophication might thus shift aquatic ecosystems from a state of predominant P limitation to being potentially limited or co-limited by N, or by other factors such as light, especially in rapidly developing regions such as China” said Zhengbing Yan, researcher from Peking University.
“These results indicate a faster accumulation of P than N in human-impacted freshwater ecosystems, which could have large effects on the trophic webs and biogeochemical cycles of estuaries and coastal areas by freshwater loadings, and reinforces the importance of rehabilitating these ecosystems”, said Prof. Josep Penuelas from CREAF-CSIC Barcelona.
The ERC Synergy Imbalance-P project has been running for two years already. A lot of work has been done and some other still needs to be carried out. It is, therefore, time for us to meet again in a confortable city such as Paris.
The format will be similar to last time, researchers will present some of their work/results/projects within the Imbalance-P in short talks of about 15 minutes allowing participants to ask some questions. It is also planned to have time to allow researchers to discuss within the different working groups (experimental, synthesis, modelling…) and among them.
The main aims of the Paris meeting are to:
Present and discuss past, present and future work within the Imbalance-P project.
Share and discuss the results obtained by the different groups.
Develop synergies amongst groups and researchers by increasing collaboration through sharing thoughts, ideas, objectives, experiments, observations and data.
Create a venue where co-authors of different manuscripts can get together to forward their writing and possibilities for such activities to be initiated.
Rice is the staple food for more than 50% of the world’s population. Reliable prediction of changes in rice yield is thus central for maintaining global food security. This is an extraordinary challenge.
In a new study in the journal Nature Plants researchers compare the sensitivity of rice yield to temperature increase derived from field warming experiments and three modelling approaches: statistical models, local crop models and global gridded crop models.
Field warming experiments produce a substantial rice yield loss under warming, with an average temperature sensitivity of −5.2 % per degree of warming. Local crop models give a similar sensitivity (−6.3 %), but statistical and global gridded crop models both suggest less negative impacts of warming on yields (−0.8 % and −2.4 7%, respectively).
Using data from field warming experiments, researchers further propose a conditional probability approach to constrain the large range of global gridded crop model results for the future yield changes in response to warming by the end of the century (from −1.3% to −9.3% per degree of warming). The constraint implies a more negative response to warming (−8.3 %) and reduces the spread of the model ensemble by 33%. This yield reduction exceeds that estimated by the International Food Policy Research Institute assessment (−4.2 to −6.4% ).
“Our study suggests that without CO2 fertilization, effective adaptation and genetic improvement, severe rice yield losses are plausible under intensive climate warming scenarios” said Dr. Chuang Zhao, researcher from Peking University.
“The long-term perspective of climate change allows us to prepare agricultural production systems for this challenge, but suitable policies must be put in place in the near future, given that targeted research on adaptation options and their large-scale implementation will require considerable time”, said Prof. Josep Penuelas from CREAF-CSIC Barcelona.
A new global analysis finds that warming temperatures will trigger the release of trillions of kilograms of carbon from the planet’s soils, driven largely by the losses of carbon in the world’s colder places.
New Haven, Conn. – For the past two decades, scientists have speculated that rising global temperatures may alter the ability of soils to store huge amounts of carbon. If warming accelerates the release of carbon stored in the soil, it could trigger a dangerous feedback effect that could have runaway effects on climate change. Yet, despite thousands of studies around the world, we have remained unclear about whether soil carbon storage will increase or decrease in response to warming.
Finally, a global perspective has allowed us to see past the mixed results of single-site studies to see the global patterns in this effect.
In a new study in the journal Nature researchers find that warming will drive the loss of trillions of kg of carbon from the soil. A conservative estimate by the researchers suggest that this value will exceed 55 trillion kg by 2050.
This value would represent up to 17% on top of current anthropogenic emissions that we expect over that time.
The results are based on an analysis of soil carbon data from dozens of warming experiments conducted all over the world in the past 20 years.
Using this worldwide dataset, the researchers generated a global map of the sensitivity of soil carbon to warming, showing that carbon loss is greatest in the world’s colder places, at high latitudes, where massive stocks of carbon have built up over thousands of years and slow microbial activity has kept them relatively secure.
“Soil carbon stores are greatest in places like the Arctic and the sub-Arctic, where the soil is cold and often frozen. In those conditions microbes are less active and so carbon has been allowed to build up over many centuries,” said lead author Thomas Crowther, at the Yale School of Forestry & Environmental Studies (F&ES).
“But as you start to warm those areas, the microbes become more active, that’s when the carbon losses are likely to happen,” Crowther said. “The scary thing is, these cold regions are the places that are expected to warm the most under climate change.”
The study predicts that for one degree of warming, about 30 petagrams of soil carbon will be released into the atmosphere, or about 2-3 times as much as is emitted annually due to human-related activities. This is a sobering prospect, given that the planet is likely to warm by 2 degrees Celsius by mid-century.
Other scientists on the team include Marc Estiarte and Josep Peñuelas from CREAF, as well as collaborating researchers from more than 30 other institutions.
Marc Estiarte commented on the value of the results: “We suspected that cold regions were key because warming could potentially reverse the carbon-accumulating pressure that cold temperatures have been exerting since such a long time”
The results represent a warn because “the vulnerability of the northern soil carbon pool is a threat to the stabilization of the CO2 concentrations in the atmosphere due to the positive feedback that can unfold between climate warming and soil carbon losses to the atmosphere”, in the words of Josep Peñuelas.
Understanding these processes at a global scale is critical for our understanding of climate change. “Getting a handle on these kinds of feedbacks is essential if we’re going to make meaningful projections about future climate conditions. Only then can we generate realistic greenhouse gas emission targets that are effective at limiting climate change,” said Crowther.
More information: T. W. Crowther et al, Quantifying global soil carbon losses in response to warming, Nature (2016). DOI: 10.1038/nature20150
In evergreen conifers, where the foliage amount changes little with season, accurate detection of the underlying “photosynthetic phenology” from satellite remote sensing has been difficult, causing errors in terrestrial photosynthetic carbon uptake models. This represents a challenge for global models of ecosystem carbon uptake.
In a new study in the journal Proceedings of the National Academy of Sciences researchers find a close correspondence between seasonally changing foliar pigment levels, expressed as chlorophyll/carotenoid ratios, and evergreen photosynthetic activity, leading to a “chlorophyll/carotenoid index” (CCI) that tracks evergreen photosynthesis at multiple spatial scales.
When calculated from NASA’s Moderate Resolution Imaging Spectroradiometer satellite sensor, the CCI closely follows the seasonal patterns of daily gross primary productivity of evergreen conifer stands measured by eddy covariance.
This discovery provides a way of monitoring evergreen photosynthetic activity from optical remote sensing, and indicates an important regulatory role for carotenoid pigments in evergreen photosynthesis. “This methodology could improve the assessment of the evergreen component of the terrestrial carbon budget, which has been elusive” said Prof. Josep Peñuelas.
“Improved methods of monitoring photosynthesis from space can improve our understanding of the global carbon budget in a warming world of changing vegetation phenology”, said Prof. John Gamon.
Citation: Gamon, J., Huemmrich, J.K.F., Wong, C.Y.F., Ensminger, I., Garrity, S., Hollinger, D.Y., Noormets, A., Peñuelas, J. 2016. A remotely sensed pigment index reveals photosynthetic Q:1 phenology in evergreen conifers. Proceedings of the National Academy of Sciences, 2016. In press
This photo shows measurements of carbon flux from soil at Toolik Field Station in Arctic Alaska. Credit: Jianwu Tang
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, which is 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 world’s largest dataset to date of soil respiration response to experimental warming.
One prediction from the 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.
Soil scientists are struggling to find evidences of soil acclimation to warming, as indicated by some individual field experiments, but the current study found limited evidence of it.
“The occurrence of acclimation would provide some relieve on the positive feedback between warming and CO2 release by respiration from soil” says Marc Estiarte, a member of the research teams at CREAF.
The information provided by the study will be critical to improve the soil-atmosphere interactions in the Earth-system models. The results of the study “will greatly improve our mechanistic understanding of how carbon dynamics change with climate warming”, in the words of Josep Peñuelas, a member of the research teams at CREAF
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.
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