Trumbore S.,Max Planck Institute for Biogeochemistry |
Trumbore S.,University of California at Irvine |
Brando P.,Institute Pesquisa Ambiental da Amazonia |
Brando P.,Woods Hole Oceanographic Institution |
Hartmann H.,Max Planck Institute for Biogeochemistry
Science | Year: 2015
Humans rely on healthy forests to supply energy, building materials, and food and to provide services such as storing carbon, hosting biodiversity, and regulating climate. Defining forest health integrates utilitarian and ecosystem measures of forest condition and function, implemented across a range of spatial scales. Although native forests are adapted to some level of disturbance, all forests now face novel stresses in the form of climate change, air pollution, and invasive pests. Detecting how intensification of these stresses will affect the trajectory of forests is a major scientific challenge that requires developing systems to assess the health of global forests. It is particularly critical to identify thresholds for rapid forest decline, because it can take many decades for forests to restore the services that they provide. © 2015, American Association for the Advancement of Science. All rights reserved.
News Article | October 26, 2016
A new study shows that hypoxia, i.e. low oxygen conditions, in European lakes started in 1850, becoming more widespread after 1900, long before the use of chemical fertilizers and climate change. A Canadian and European research team has identified urban expansion as the reason for the low amounts of bioavailable oxygen in numerous European lakes in past centuries. Published in Proceedings of the National Academy of Sciences, the findings of this study directed by postdoctoral fellow Jean-Philippe Jenny and Professor Pierre Francus of INRS suggest that increased waste water pollution at the turn of the 20th century boosted the lakes' biological productivity, which in turn led to a rise in oxygen consumption. The researchers analyzed information such as climate, land use, and lake sediment data from more than 1,500 European watersheds. For the first time, they compared reconstructions of land occupancy and land use dynamics on a continental scale to their own data of oxygen depletion over the past 300 years. This allowed them to identify urban waste, primarily phosphorus, as the factor responsible for triggering hypoxia at the bottom of lakes starting at the beginning of the 20th century. "Accurately identifying the source of the nutrient responsible for oxygen depletion was a real challenge because of the variations in environmental stress factors throughout the region and their interactions, as well as the reliability of long term data," explains Professor Francus of the INRS Centre Eau Terre Environnement. "Point and diffuse sources have always contributed to nutrient supplies in lakes, but at intensities that vary in time and space," adds Jean-Philippe Jenny, now affiliated with the Max Planck Institute for Biogeochemistry in Germany. "Our results show that urban point sources of phosphorus are the dominant cause of eutrophication of European lakes during the Anthropocene." The researchers recognize, however, that during recent decades, diffuse sources have gradually become the major cause of fresh water eutrophication in developed countries with the increase in the use of chemical fertilizers and the elimination of point sources due to the installation of waste treatment plants. "Despite the many cleanup initiatives in the 1980s, the deepest layers in the lakes we studied still are not being reoxygenated and the hypoxia persists. This illustrates the importance of studying historical land use and the need to put long-term strategies in place to maintain and restore water quality in lakes," say the study's authors. Published in Proceedings of the National Academy of Sciences, the article "Urban point sources of nutrients were the leading cause for the historical spread of hypoxia across European lakes" is the result of an international research partnership involving researchers from Quebec, other Canadian provinces, Germany, Finland, and France. The principal author is Jean-Philippe Jenny of the INRS Centre Eau Terre Environnement. This study was produced by the Varve Working Group under the International Geosphere-Biosphere Programme, IGBP-PAGES (Past Global Changes). It received funding from the National Sciences and Engineering Research Council of Canada, the Canada Research Chair in Fresh Water Ecology and Global Change, Fonds de recherche du Québec - Nature et technologies, and the Academy of Finland. DOI: pnas.1605480113
Schulze E.D.,Max Planck Institute for Biogeochemistry
Forest Ecology and Management | Year: 2014
The following overview summarizes observational and experimental approaches to study plant and ecosystem processes, starting from physiological mechanisms up to continental carbon balances mainly based on Eurosiberian data. It is shown that different observational scales are needed to interpret and predict phenomena at various resolutions and that observational studies cannot replace controlled experiments. Both sources are essential. © 2013 Elsevier B.V.
Hartmann H.,Max Planck Institute for Biogeochemistry
Global Change Biology | Year: 2011
Trees are exceptional organisms that have evolved over some 385 million years and have overtaken other plants in order to harvest light first. However, this advantage comes with a cost: trees must transport water all the way up to their crowns and inherent physical limitations make them vulnerable to water deficits. Because climate change scenarios predict more frequent extreme drought events, trees will increasingly need to cope with water stress. Recent occurrences of climate change-type droughts have had severe impacts on several forest ecosystems. Initial experimental studies have been undertaken and show that stomatal control of water loss hinders carbon assimilation and could lead to starvation during droughts. Other mechanisms of drought-induced mortality are catastrophic xylem dysfunction, impeded long-distance transport of carbohydrates (translocation) and also symplastic failure (cellular breakdown). However, direct empirical support is absent for either hypothesis. More experimental studies are necessary to increase our understanding of these processes and to resolve the mystery of drought-related tree mortality. Instead of testing the validity of particular hypothesis as mechanisms of drought-induced tree mortality, future research should aim at revealing the temporal dynamics of these mechanisms in different species and over a gradient of environmental conditions. Only such studies will reveal whether the struggle for light will become a struggle for water and/or for carbon in drought-affected areas. © 2010 Blackwell Publishing Ltd.
Thoms C.,Max Planck Institute for Biogeochemistry |
Gleixner G.,Max Planck Institute for Biogeochemistry
Soil Biology and Biochemistry | Year: 2013
The linkage between tree diversity and the soil food web in temperate deciduous forest ecosystems remains uncertain. Using microbial phospholipid fatty acids (PLFAs), we analyzed the effect of tree species composition on microbial communities from topsoil collected in Hainich National Park, Germany. Previous results had shown minimal direct effects of tree species on the microbial community in autumn, most likely due to low plant activity and high nutrient and energy input from litterfall. However, microbial composition was affected indirectly through an influence of tree species on soil pH. In this study, we analyzed PLFA profiles in early summer and compared them with the results from autumn sampling. We hypothesized that plant-based traits would have stronger direct effects on the abundance and structure of the microbial community during the photosynthetically active period. The results showed that the soil microbial community differed more markedly between the tree diversity levels in early summer than in autumn. The acidifying character of the decaying beech litter strongly influenced the soil pH values and structured the soil microbial community indirectly in early summer as it had in autumn. However, the measured differences in the microbial composition in early summer could be attributed primarily to litter quality. This direct influence of plant traits appeared to be eclipsed in autumn because of the high nutrient supply from fresh litter input. Following litter decomposition in the topsoil, however, litter-based plant traits emerged as a factor structuring the soil microbial community in early summer. Our results suggest that the PLFAs i14:0 and i15:0, indicative of Gram-positive bacteria, are strongly involved in decomposition processes and may be promoted by readily available nutrients. Furthermore, our results indicate that a dense root network in association with arbuscular mycorrhizal fungi strongly supported microbial growth in the more diverse forest stands. High proportions of arbuscular mycorrhizal fungi (PLFA 16:1ω5), root-associated microorganisms (PLFAs 16:1ω9, 16:1ω7, 17:1ω8 and 18:1ω7) and bacterial grazers (PLFA 20:5) characterized the microbial community in early summer on these study plots. We conclude that microbial communities are strongly influenced by abiotic controls. However, seasonal differences in litter decomposition rates and root activity should be considered in the analysis of the effects of tree diversity or species on soil microbial communities © 2013 Elsevier Ltd.
Gleixner G.,Max Planck Institute for Biogeochemistry
Ecological Research | Year: 2013
Current attempts to explain the persistence of carbon in soils focuses on explanations such as the recalcitrant plant residues and the physical isolation of substrates from decomposers. A pool of organic matter that can persist for centuries to millennia is hypothesized because of the evidence provided by the persistence of pre-disturbance C in fallow or vegetation change experiments, and the radiocarbon age of soil carbon. However, new information, which became available through advances in the ability to measure the isotope signatures of specific compounds, favors a new picture of organic matter dynamics. Instead of persistence of plant-derived residues like lignin in the soil, the majority of mineral soil is in molecules derived from microbial synthesis. Carbon recycled multiple times through the microbial community can be old, decoupling the radiocarbon age of C atoms from the chemical or biological lability of the molecules they comprise. In consequence is soil microbiology, a major control on soil carbon dynamics, which highlights the potential vulnerability of soil organic matter to changing environmental conditions. Moreover, it emphasizes the need to devise new management options to restore, increase, and secure this valuable resource. © 2013 The Author(s).
Asner G.P.,Stanford University |
Levick S.R.,Stanford University |
Levick S.R.,Max Planck Institute for Biogeochemistry
Ecology Letters | Year: 2012
Herbivores cause treefalls in African savannas, but rates are unknown at large scales required to forecast changes in biodiversity and ecosystem processes. We combined landscape-scale herbivore exclosures with repeat airborne Light Detection and Ranging of 58 429 trees in Kruger National Park, South Africa, to assess sources of savanna treefall across nested gradients of climate, topography, and soil fertility. Elephants were revealed as the primary agent of treefall across widely varying savanna conditions, and a large-scale 'elephant trap' predominantly removes maturing savanna trees in the 5-9 m height range. Treefall rates averaged 6 times higher in areas accessible to elephants, but proportionally more treefall occurred on high-nutrient basalts and in lowland catena areas. These patterns were superimposed on a climate-mediated regime of increasing treefall with precipitation in the absence of herbivores. These landscape-scale patterns reveal environmental controls underpinning herbivore-mediated tree turnover, highlighting the need for context-dependent science and management. © 2012 Blackwell Publishing Ltd/CNRS.
Sierra C.A.,Max Planck Institute for Biogeochemistry
Biogeochemistry | Year: 2012
Previous theoretical analyses based on Arrhenius kinetics and thermodynamics have shown that the temperature sensitivity of low-quality substrate is higher than that of high-quality substrate. Because soils store large amounts of low-quality carbon, understanding its response to increasing temperatures will help to predict the response of atmospheric CO 2 to climate change. However, empirical studies do not provide conclusive evidence to corroborate this theoretical argument. Although there are various possible reasons for this disagreement, the theory behind this argument has not been scrutinized carefully. Based on a simple mathematical analysis of the Arrhenius equation it is shown here that low-quality substrates are less temperature sensitive when analyzed in absolute rather than in relative terms, a result that may seem counterintuitive to previous theory. However, this is a paradox intrinsic to the Arrhenius equation and it is often ignored within the 'quality-temperature' debate. In fact, different measures commonly used to analyze the temperature sensitivity of different substrates can provide apparently different and contradictory results even though they are based on the same basic principles. Distinguishing between absolute and relative measures of sensitivity is essential for understanding the sensitivity of respiration to environmental change. An analysis of the available empirical evidence on this topic shows that most studies actually agree with the Arrhenius and thermodynamics theory, with less disagreement than previously thought. To address some of the issues identified here, a formal theoretical framework is proposed to study the sensitivity of respiration rates with respect to changes in multiple drivers of decomposition. © 2011 Springer Science+Business Media B.V.
Zaehle S.,Max Planck Institute for Biogeochemistry
Philosophical transactions of the Royal Society of London. Series B, Biological sciences | Year: 2013
Interactions between the terrestrial nitrogen (N) and carbon (C) cycles shape the response of ecosystems to global change. However, the global distribution of nitrogen availability and its importance in global biogeochemistry and biogeochemical interactions with the climate system remain uncertain. Based on projections of a terrestrial biosphere model scaling ecological understanding of nitrogen-carbon cycle interactions to global scales, anthropogenic nitrogen additions since 1860 are estimated to have enriched the terrestrial biosphere by 1.3 Pg N, supporting the sequestration of 11.2 Pg C. Over the same time period, CO2 fertilization has increased terrestrial carbon storage by 134.0 Pg C, increasing the terrestrial nitrogen stock by 1.2 Pg N. In 2001-2010, terrestrial ecosystems sequestered an estimated total of 27 Tg N yr(-1) (1.9 Pg C yr(-1)), of which 10 Tg N yr(-1) (0.2 Pg C yr(-1)) are due to anthropogenic nitrogen deposition. Nitrogen availability already limits terrestrial carbon sequestration in the boreal and temperate zone, and will constrain future carbon sequestration in response to CO2 fertilization (regionally by up to 70% compared with an estimate without considering nitrogen-carbon interactions). This reduced terrestrial carbon uptake will probably dominate the role of the terrestrial nitrogen cycle in the climate system, as it accelerates the accumulation of anthropogenic CO2 in the atmosphere. However, increases of N2O emissions owing to anthropogenic nitrogen and climate change (at a rate of approx. 0.5 Tg N yr(-1) per 1°C degree climate warming) will add an important long-term climate forcing.
Zaehle S.,Max Planck Institute for Biogeochemistry
Philosophical Transactions of the Royal Society B: Biological Sciences | Year: 2013
Interactions between the terrestrial nitrogen (N) and carbon (C) cycles shape the response of ecosystems to global change. However, the global distribution of nitrogen availability and its importance in global biogeochemistry and biogeochemical interactions with the climate system remain uncertain. Based on projections of a terrestrial biosphere model scaling ecological understanding of nitrogen-carbon cycle interactions to global scales, anthropogenic nitrogen additions since 1860 are estimated to have enriched the terrestrial biosphere by 1.3 Pg N, supporting the sequestration of 11.2 Pg C. Over the same time period, CO2 fertilization has increased terrestrial carbon storage by 134.0 Pg C, increasing the terrestrial nitrogen stock by 1.2 Pg N. In 2001-2010, terrestrial ecosystems sequestered an estimated total of 27 Tg N yr-1 (1.9 Pg C yr-1), of which 10 Tg N yr-1 (0.2 Pg C yr-1) are due to anthropogenic nitrogen deposition. Nitrogen availability already limits terrestrial carbon sequestration in the boreal and temperate zone, and will constrain future carbon sequestration in response to CO2 fertilization (regionally by up to 70% compared with an estimate without considering nitrogen-carbon interactions). This reduced terrestrial carbon uptake will probably dominate the role of the terrestrial nitrogen cycle in the climate system, as it accelerates the accumulation of anthropogenic CO2 in the atmosphere. However, increases of N2O emissions owing to anthropogenic nitrogen and climate change (at a rate of approx. 0.5 Tg N yr-1 per 1°C degree climate warming) will add an important long-term climate forcing. © 2013 The Author(s) Published by the Royal Society. All rights reserved.