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  • 1
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    Widespread reduction in sun-induced fluorescence from the Amazon during the 2015/2016 El Niño
    The Royal Society ; 2018
    In:  Philosophical Transactions of the Royal Society B: Biological Sciences Vol. 373, No. 1760 ( 2018-11-19), p. 20170408-
    Details
    In: Philosophical Transactions of the Royal Society B: Biological Sciences, The Royal Society, Vol. 373, No. 1760 ( 2018-11-19), p. 20170408-
    Abstract: The tropical carbon balance dominates year-to-year variations in the CO 2 exchange with the atmosphere through photosynthesis, respiration and fires. Because of its high correlation with gross primary productivity (GPP), observations of sun-induced fluorescence (SIF) are of great interest. We developed a new remotely sensed SIF product with improved signal-to-noise in the tropics, and use it here to quantify the impact of the 2015/2016 El Niño Amazon drought. We find that SIF was strongly suppressed over areas with anomalously high temperatures and decreased levels of water in the soil. SIF went below its climatological range starting from the end of the 2015 dry season (October) and returned to normal levels by February 2016 when atmospheric conditions returned to normal, but well before the end of anomalously low precipitation that persisted through June 2016. Impacts were not uniform across the Amazon basin, with the eastern part experiencing much larger (10–15%) SIF reductions than the western part of the basin (2–5%). We estimate the integrated loss of GPP relative to eight previous years to be 0.34–0.48 PgC in the three-month period October–November–December 2015. This article is part of a discussion meeting issue ‘The impact of the 2015/2016 El Niño on the terrestrial tropical carbon cycle: patterns, mechanisms and implications’.
    Type of Medium: Online Resource
    ISSN: 0962-8436 , 1471-2970
    URL: Article
    DOI: 10.1098/rstb.2017.0408
    RVK:
    WA 15000
    Language: English
    Publisher: The Royal Society
    Publication Date: 2018
    detail.hit.zdb_id: 1462620-2
    SSG: 12
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  • 2
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    Spring enhancement and summer reduction in carbon uptake during the 2018 drought in northwestern Europe
    The Royal Society ; 2020
    In:  Philosophical Transactions of the Royal Society B: Biological Sciences Vol. 375, No. 1810 ( 2020-10-26), p. 20190509-
    Details
    In: Philosophical Transactions of the Royal Society B: Biological Sciences, The Royal Society, Vol. 375, No. 1810 ( 2020-10-26), p. 20190509-
    Abstract: We analysed gross primary productivity (GPP), total ecosystem respiration (TER) and the resulting net ecosystem exchange (NEE) of carbon dioxide (CO 2 ) by the terrestrial biosphere during the summer of 2018 through observed changes across the Integrated Carbon Observation System (ICOS) network, through biosphere and inverse modelling, and through remote sensing. Highly correlated yet independently-derived reductions in productivity from sun-induced fluorescence, vegetative near-infrared reflectance, and GPP simulated by the Simple Biosphere model version 4 (SiB4) suggest a 130–340 TgC GPP reduction in July–August–September (JAS) of 2018. This occurs over an area of 1.6 × 10 6 km 2 with anomalously low precipitation in northwestern and central Europe. In this drought-affected area, reduced GPP, TER, NEE and soil moisture at ICOS ecosystem sites are reproduced satisfactorily by the SiB4 model. We found that, in contrast to the preceding 5 years, low soil moisture is the main stress factor across the affected area. SiB4’s NEE reduction by 57 TgC for JAS coincides with anomalously high atmospheric CO 2 observations in 2018, and this is closely matched by the NEE anomaly derived by CarbonTracker Europe (52 to 83 TgC). Increased NEE during the spring (May–June) of 2018 (SiB4 −52 TgC; CTE −46 to −55 TgC) largely offset this loss, as ecosystems took advantage of favourable growth conditions. This article is part of the theme issue ‘Impacts of the 2018 severe drought and heatwave in Europe: from site to continental scale’.
    Type of Medium: Online Resource
    ISSN: 0962-8436 , 1471-2970
    URL: Article
    DOI: 10.1098/rstb.2019.0509
    RVK:
    WA 15000
    Language: English
    Publisher: The Royal Society
    Publication Date: 2020
    detail.hit.zdb_id: 1462620-2
    SSG: 12
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  • 3
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    The CO 2 record at the Amazon Tall Tower Observatory: A new opportunity to study processes on seasonal and inter‐annual scales
    Wiley ; 2022
    In:  Global Change Biology Vol. 28, No. 2 ( 2022-01), p. 588-611
    Details
    In: Global Change Biology, Wiley, Vol. 28, No. 2 ( 2022-01), p. 588-611
    Abstract: High‐quality atmospheric CO 2  measurements are sparse in Amazonia, but can provide critical insights into the spatial and temporal variability of sources and sinks of CO 2 . In this study, we present the first 6 years (2014–2019) of continuous, high‐precision measurements of atmospheric CO 2 at the Amazon Tall Tower Observatory (ATTO, 2.1°S, 58.9°W). After subtracting the simulated background concentrations from our observational record, we define a CO 2 regional signal ( ) that has a marked seasonal cycle with an amplitude of about 4 ppm. At both seasonal and inter‐annual scales, we find differences in phase between and the local eddy covariance net ecosystem exchange (EC‐NEE), which is interpreted as an indicator of a decoupling between local and non‐local drivers of . In addition, we present how the 2015–2016 El Niño‐induced drought was captured by our atmospheric record as a positive 2σ anomaly in both the wet and dry season of 2016. Furthermore, we analyzed the observed seasonal cycle and inter‐annual variability of together with net ecosystem exchange (NEE) using a suite of modeled flux products representing biospheric and aquatic CO 2 exchange. We use both non‐optimized and optimized (i.e., resulting from atmospheric inverse modeling) NEE fluxes as input in an atmospheric transport model (STILT). The observed shape and amplitude of the seasonal cycle was captured neither by the simulations using the optimized fluxes nor by those using the diagnostic Vegetation and Photosynthesis Respiration Model (VPRM). We show that including the contribution of CO 2 from river evasion improves the simulated shape (not the magnitude) of the seasonal cycle when using a data‐driven non‐optimized NEE product (FLUXCOM). The simulated contribution from river evasion was found to be 25% of the seasonal cycle amplitude. Our study demonstrates the importance of the ATTO record to better understand the Amazon carbon cycle at various spatial and temporal scales.
    Type of Medium: Online Resource
    ISSN: 1354-1013 , 1365-2486
    URL: Issue
    URL: Article
    DOI: 10.1111/gcb.v28.2
    DOI: 10.1111/gcb.15905
    Language: English
    Publisher: Wiley
    Publication Date: 2022
    detail.hit.zdb_id: 2020313-5
    SSG: 12
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  • 4
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    Sun-induced fluorescence and near-infrared reflectance of vegetation track the seasonal dynamics of gross primary production over Africa
    Copernicus GmbH ; 2021
    In:  Biogeosciences Vol. 18, No. 9 ( 2021-05-10), p. 2843-2857
    Details
    In: Biogeosciences, Copernicus GmbH, Vol. 18, No. 9 ( 2021-05-10), p. 2843-2857
    Abstract: Abstract. The carbon cycle of tropical terrestrial vegetation plays a vital role in the storage and exchange of atmospheric CO2. But large uncertainties surround the impacts of land-use change emissions, climate warming, the frequency of droughts, and CO2 fertilization. This culminates in poorly quantified carbon stocks and carbon fluxes even for the major ecosystems of Africa (savannas and tropical evergreen forests). Contributors to this uncertainty are the sparsity of (micro-)meteorological observations across Africa's vast land area, a lack of sufficient ground-based observation networks and validation data for CO2, and incomplete representation of important processes in numerical models. In this study, we therefore turn to two remotely sensed vegetation products that have been shown to correlate highly with gross primary production (GPP): sun-induced fluorescence (SIF) and near-infrared reflectance of vegetation (NIRv). The former is available from an updated product that we recently published (Sun-Induced Fluorescence of Terrestrial Ecosystems Retrieval – SIFTER v2), which specifically improves retrievals in tropical environments. A comparison against flux tower observations of daytime-partitioned net ecosystem exchange from six major biomes in Africa shows that SIF and NIRv reproduce the seasonal patterns of GPP well, resulting in correlation coefficients of 〉0.9 (N=12 months, four sites) over savannas in the Northern and Southern hemispheres. These coefficients are slightly higher than for the widely used Max Planck Institute for Biogeochemistry (MPI-BGC) GPP products and enhanced vegetation index (EVI). Similarly to SIF signals in the neighboring Amazon, peak productivity occurs in the wet season coinciding with peak soil moisture and is followed by an initial decline during the early dry season, which reverses when light availability peaks. This suggests similar leaf dynamics are at play. Spatially, SIF and NIRv show a strong linear relation (R〉0.9; N≥250 pixels) with multi-year MPI-BGC GPP even within single biomes. Both MPI-BGC GPP and the EVI show saturation relative to peak NIRv and SIF signals during high-productivity months, which suggests that GPP in the most productive regions of Africa might be larger than suggested.
    Type of Medium: Online Resource
    ISSN: 1726-4189
    URL: Article
    URL: Article
    DOI: 10.5194/bg-18-2843-2021
    DOI: 10.5194/bg-18-2843-2021-supplement
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2021
    detail.hit.zdb_id: 2158181-2
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  • 5
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    Leaf-scale quantification of the effect of photosynthetic gas exchange on Δ〈sup〉17〈/sup〉O of atmospheric CO〈sub〉2〈/sub〉
    Copernicus GmbH ; 2020
    In:  Biogeosciences Vol. 17, No. 14 ( 2020-07-31), p. 3903-3922
    Details
    In: Biogeosciences, Copernicus GmbH, Vol. 17, No. 14 ( 2020-07-31), p. 3903-3922
    Abstract: Abstract. Understanding the processes that affect the triple oxygen isotope composition of atmospheric CO2 during gas exchange can help constrain the interaction and fluxes between the atmosphere and the biosphere. We conducted leaf cuvette experiments under controlled conditions using three plant species. The experiments were conducted at two different light intensities and using CO2 with different Δ17O. We directly quantify the effect of photosynthesis on Δ17O of atmospheric CO2 for the first time. Our results demonstrate the established theory for δ18O is applicable to Δ17O(CO2) at leaf level, and we confirm that the following two key factors determine the effect of photosynthetic gas exchange on the Δ17O of atmospheric CO2. The relative difference between Δ17O of the CO2 entering the leaf and the CO2 in equilibrium with leaf water and the back-diffusion flux of CO2 from the leaf to the atmosphere, which can be quantified by the cm∕ca ratio, where ca is the CO2 mole fraction in the surrounding air and cm is the one at the site of oxygen isotope exchange between CO2 and H2O. At low cm∕ca ratios the discrimination is governed mainly by diffusion into the leaf, and at high cm∕ca ratios it is governed by back-diffusion of CO2 that has equilibrated with the leaf water. Plants with a higher cm∕ca ratio modify the Δ17O of atmospheric CO2 more strongly than plants with a lower cm∕ca ratio. Based on the leaf cuvette experiments, the global value for discrimination against Δ17O of atmospheric CO2 during photosynthetic gas exchange is estimated to be -0.57±0.14 ‰ using cm∕ca values of 0.3 and 0.7 for C4 and C3 plants, respectively. The main uncertainties in this global estimate arise from variation in cm∕ca ratios among plants and growth conditions.
    Type of Medium: Online Resource
    ISSN: 1726-4189
    URL: Article
    URL: Article
    DOI: 10.5194/bg-17-3903-2020
    DOI: 10.5194/bg-17-3903-2020-supplement
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2020
    detail.hit.zdb_id: 2158181-2
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  • 6
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    The power of forecasts to advance ecological theory
    Wiley ; 2023
    In:  Methods in Ecology and Evolution Vol. 14, No. 3 ( 2023-03), p. 746-756
    Details
    In: Methods in Ecology and Evolution, Wiley, Vol. 14, No. 3 ( 2023-03), p. 746-756
    Abstract: Ecological forecasting provides a powerful set of methods for predicting short‐ and long‐term change in living systems. Forecasts are now widely produced, enabling proactive management for many applied ecological problems. However, despite numerous calls for an increased emphasis on prediction in ecology, the potential for forecasting to accelerate ecological theory development remains underrealized. Here, we provide a conceptual framework describing how ecological forecasts can energize and advance ecological theory. We emphasize the many opportunities for future progress in this area through increased forecast development, comparison and synthesis. Our framework describes how a forecasting approach can shed new light on existing ecological theories while also allowing researchers to address novel questions. Through rigorous and repeated testing of hypotheses, forecasting can help to refine theories and understand their generality across systems. Meanwhile, synthesizing across forecasts allows for the development of novel theory about the relative predictability of ecological variables across forecast horizons and scales. We envision a future where forecasting is integrated as part of the toolset used in fundamental ecology. By outlining the relevance of forecasting methods to ecological theory, we aim to decrease barriers to entry and broaden the community of researchers using forecasting for fundamental ecological insight.
    Type of Medium: Online Resource
    ISSN: 2041-210X , 2041-210X
    URL: Issue
    URL: Article
    DOI: 10.1111/mee3.v14.3
    DOI: 10.1111/2041-210X.13955
    Language: English
    Publisher: Wiley
    Publication Date: 2023
    detail.hit.zdb_id: 2528492-7
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  • 7
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    Exploring the potential of Δ17O in CO2 for determining mesophyll conductance
    Oxford University Press (OUP) ; 2023
    In:  Plant Physiology Vol. 192, No. 2 ( 2023-05-31), p. 1234-1253
    Details
    In: Plant Physiology, Oxford University Press (OUP), Vol. 192, No. 2 ( 2023-05-31), p. 1234-1253
    Abstract: Mesophyll conductance to CO2 from the intercellular air space to the CO2–H2O exchange site has been estimated using δ18O measurements (gm18). However, the gm18 estimates are affected by the uncertainties in the δ18O of leaf water where the CO2–H2O exchange takes place and the degree of equilibration between CO2 and H2O. We show that measurements of Δ17O (i.e.Δ17O=δ17O−0.528×δ18O) can provide independent constraints on gm (gmΔ17) and that these gm estimates are less affected by fractionation processes during gas exchange. The gm calculations are applied to combined measurements of δ18O and Δ17O, and gas exchange in two C3 species, sunflower (Helianthus annuus L. cv. ‘sunny’) and ivy (Hedera hibernica L.), and the C4 species maize (Zea mays). The gm18 and gmΔ17 estimates agree within the combined errors (P-value, 0.876). Both approaches are associated with large errors when the isotopic composition in the intercellular air space becomes close to the CO2–H2O exchange site. Although variations in Δ17O are low, it can be measured with much higher precision compared with δ18O. Measuring gmΔ17 has a few advantages compared with gm18: (i) it is less sensitive to uncertainty in the isotopic composition of leaf water at the isotope exchange site and (ii) the relative change in the gm due to an assumed error in the equilibration fraction θeq is lower for gmΔ17 compared with gm18. Thus, using Δ17O can complement and improve the gm estimates in settings where the δ18O of leaf water varies strongly, affecting the δ18O (CO2) difference between the intercellular air space and the CO2–H2O exchange site.
    Type of Medium: Online Resource
    ISSN: 0032-0889 , 1532-2548
    URL: Article
    DOI: 10.1093/plphys/kiad173
    RVK:
    WA 15000
    Language: English
    Publisher: Oxford University Press (OUP)
    Publication Date: 2023
    detail.hit.zdb_id: 2004346-6
    detail.hit.zdb_id: 208914-2
    SSG: 12
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  • 8
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    Changes in surface hydrology, soil moisture and gross primary production in the Amazon during the 2015/2016 El Niño
    The Royal Society ; 2018
    In:  Philosophical Transactions of the Royal Society B: Biological Sciences Vol. 373, No. 1760 ( 2018-11-19), p. 20180084-
    Details
    In: Philosophical Transactions of the Royal Society B: Biological Sciences, The Royal Society, Vol. 373, No. 1760 ( 2018-11-19), p. 20180084-
    Abstract: The 2015/2016 El Niño event caused severe changes in precipitation across the tropics. This impacted surface hydrology, such as river run-off and soil moisture availability, thereby triggering reductions in gross primary production (GPP). Many biosphere models lack the detailed hydrological component required to accurately quantify anomalies in surface hydrology and GPP during droughts in tropical regions. Here, we take the novel approach of coupling the biosphere model SiBCASA with the advanced hydrological model PCR-GLOBWB to attempt such a quantification across the Amazon basin during the drought in 2015/2016. We calculate 30–40% reduced river discharge in the Amazon starting in October 2015, lagging behind the precipitation anomaly by approximately one month and in good agreement with river gauge observations. Soil moisture shows distinctly asymmetrical spatial anomalies with large reductions across the north-eastern part of the basin, which persisted into the following dry season. This added to drought stress in vegetation, already present owing to vapour pressure deficits at the leaf, resulting in a loss of GPP of 0.95 (0.69 to 1.20) PgC between October 2015 and March 2016 compared with the 2007–2014 average. Only 11% (10–12%) of the reduction in GPP was found in the (wetter) north-western part of the basin, whereas the north-eastern and southern regions were affected more strongly, with 56% (54–56%) and 33% (31–33%) of the total, respectively. Uncertainty on this anomaly mostly reflects the unknown rooting depths of vegetation. This article is part of a discussion meeting issue ‘The impact of the 2015/2016 El Niño on the terrestrial tropical carbon cycle: patterns, mechanisms and implications’.
    Type of Medium: Online Resource
    ISSN: 0962-8436 , 1471-2970
    URL: Article
    DOI: 10.1098/rstb.2018.0084
    RVK:
    WA 15000
    Language: English
    Publisher: The Royal Society
    Publication Date: 2018
    detail.hit.zdb_id: 1462620-2
    SSG: 12
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