Browsing by Subject "TERRESTRIAL ECOSYSTEMS"

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  • Ruiz-Benito, Paloma; Vacchiano, Giorgio; Lines, Emily R.; Reyer, Christopher P.O.; Ratcliffe, Sophia; Morin, Xavier; Hartig, Florian; Mäkelä, Annikki; Yousefpour, Rasoul; Chaves, Jimena E.; Palacios-Orueta, Alicia; Benito-Garzón, Marta; Morales-Molino, Cesar; Camarero, J. Julio; Jump, Alistair S.; Kattge, Jens; Lehtonen, Aleksi; Ibrom, Andreas; Owen, Harry J.F.; Zavala, Miguel A. (2020)
    Climate change is expected to cause major changes in forest ecosystems during the 21st century and beyond. To assess forest impacts from climate change, the existing empirical information must be structured, harmonised and assimilated into a form suitable to develop and test state-of-the-art forest and ecosystem models. The combination of empirical data collected at large spatial and long temporal scales with suitable modelling approaches is key to understand forest dynamics under climate change. To facilitate data and model integration, we identified major climate change impacts observed on European forest functioning and summarised the data available for monitoring and predicting such impacts. Our analysis of c. 120 forest-related databases (including information from remote sensing, vegetation inventories, dendroecology, palaeoecology, eddy-flux sites, common garden experiments and genetic techniques) and 50 databases of environmental drivers highlights a substantial degree of data availability and accessibility. However, some critical variables relevant to predicting European forest responses to climate change are only available at relatively short time frames (up to 10-20 years), including intra-specific trait variability, defoliation patterns, tree mortality and recruitment. Moreover, we identified data gaps or lack of data integration particularly in variables related to local adaptation and phenotypic plasticity, dispersal capabilities and physiological responses. Overall, we conclude that forest data availability across Europe is improving, but further efforts are needed to integrate, harmonise and interpret this data (i.e. making data useable for non-experts). Continuation of existing monitoring and networks schemes together with the establishments of new networks to address data gaps is crucial to rigorously predict climate change impacts on European forests.
  • Flechard, Chris R.; van Oijen, Marcel; Cameron, David R.; de Vries, Wim; Ibrom, Andreas; Buchmann, Nina; Dise, Nancy B.; Janssens, Ivan A.; Neirynck, Johan; Montagnani, Leonardo; Varlagin, Andrej; Loustau, Denis; Legout, Arnaud; Ziemblinska, Klaudia; Aubinet, Marc; Aurela, Mika; Chojnicki, Bogdan H.; Drewer, Julia; Eugster, Werner; Francez, Andre-Jean; Juszczak, Radoslaw; Kitzler, Barbara; Kutsch, Werner L.; Lohila, Annalea; Longdoz, Bernard; Matteucci, Giorgio; Moreaux, Virginie; Nefte, Albrecht; Olejnik, Janusz; Sanz, Maria J.; Siemens, Jan; Vesala, Timo; Vincke, Caroline; Nemitz, Eiko; Zechmeister-Boltenstern, Sophie; Butterbach-Bahl, Klaus; Skiba, Ute M.; Sutton, Mark A. (2020)
    The effects of atmospheric nitrogen deposition (N-dep) on carbon (C) sequestration in forests have often been assessed by relating differences in productivity to spatial variations of N-dep across a large geographic domain. These correlations generally suffer from covariation of other confounding variables related to climate and other growth-limiting factors, as well as large uncertainties in total (dry + wet) reactive nitrogen (N-r) deposition. We propose a methodology for untangling the effects of N-dep from those of meteorological variables, soil water retention capacity and stand age, using a mechanistic forest growth model in combination with eddy covariance CO2 exchange fluxes from a Europe-wide network of 22 forest flux towers. Total N-r deposition rates were estimated from local measurements as far as possible. The forest data were compared with data from natural or semi-natural, non-woody vegetation sites. The response of forest net ecosystem productivity to nitrogen deposition (dNEP/dN(dep)) was estimated after accounting for the effects on gross primary productivity (GPP) of the co-correlates by means of a meta-modelling standardization procedure, which resulted in a reduction by a factor of about 2 of the uncorrected, apparent dGPP/dN(dep) value. This model-enhanced analysis of the C and N-dep flux observations at the scale of the European network suggests a mean overall dNEP/dN(dep) response of forest lifetime C sequestration to N-dep of the order of 40-50 g C per g N, which is slightly larger but not significantly different from the range of estimates published in the most recent reviews. Importantly, patterns of gross primary and net ecosystem productivity versus N-dep were non-linear, with no further growth responses at high N-dep levels (N-dep > 2.5-3 gNm(-2) yr(-1)) but accompanied by increasingly large ecosystem N losses by leaching and gaseous emissions. The reduced increase in productivity per unit N deposited at high N-dep levels implies that the forecast increased N-r emissions and increased N-dep levels in large areas of Asia may not positively impact the continent's forest CO2 sink. The large level of unexplained variability in observed carbon sequestration efficiency (CSE) across sites further adds to the uncertainty in the dC/dN response.
  • Forrest, M.; Eronen, J. T.; Utescher, T.; Knorr, G.; Stepanek, C.; Lohmann, G.; Hickler, T. (2015)
    There is an increasing need to understand the pre-Quaternary warm climates, how climate-vegetation interactions functioned in the past, and how we can use this information to understand the present. Here we report vegetation modelling results for the Late Miocene (11-7 Ma) to study the mechanisms of vegetation dynamics and the role of different forcing factors that influence the spatial patterns of vegetation coverage. One of the key uncertainties is the atmospheric concentration of CO2 during past climates. Estimates for the last 20 million years range from 280 to 500 ppm. We simulated Late Miocene vegetation using two plausible CO2 concentrations, 280 ppm CO2 and 450 ppm CO2, with a dynamic global vegetation model (LPJ-GUESS) driven by climate input from a coupled AOGCM (Atmosphere-Ocean General Circulation Model). The simulated vegetation was compared to existing plant fossil data for the whole Northern Hemisphere. For the comparison we developed a novel approach that uses information of the relative dominance of different plant functional types (PFTs) in the palaeobotanical data to provide a quantitative estimate of the agreement between the simulated and reconstructed vegetation. Based on this quantitative assessment we find that pre-industrial CO2 levels are largely consistent with the presence of seasonal temperate forests in Europe (suggested by fossil data) and open vegetation in North America (suggested by multiple lines of evidence). This suggests that during the Late Miocene the CO2 levels have been relatively low, or that other factors that are not included in the models maintained the seasonal temperate forests and open vegetation.
  • Sun, Tao; Hobbie, Sarah E.; Berg, Björn; Zhang, Hongguang; Wang, Qingkui; Wang, Zhengwen; Hättenschwiler, Stephan (2018)
    Decomposition is a key component of the global carbon (C) cycle, yet current ecosystem C models do not adequately represent the contributions of plant roots and their mycorrhizae to this process. The understanding of decomposition dynamics and their control by traits is particularly limited for the most distal first-order roots. Here we followed decomposition of first-order roots and leaf litter from 35 woody plant species differing in mycorrhizal type over 6 years in a Chinese temperate forest. First-order roots decomposed more slowly (k = 0.11 +/- 0.01 years(-1)) than did leaf litter (0.35 +/- 0.02 years(-1)), losing only 35% of initial mass on average after 6 years of exposure in the field. In contrast to leaf litter, nonlignin root C chemistry (nonstructural carbohydrates, polyphenols) accounted for 82% of the large interspecific variation in first-order root decomposition. Leaf litter from ectomycorrhizal (EM) species decomposed more slowly than that from arbuscular mycorrhizal (AM) species, whereas first-order roots of EM species switched, after 2 years, from having slower to faster decomposition compared with those from AM species. The fundamentally different dynamics and control mechanisms of first-order root decomposition compared with those of leaf litter challenge current ecosystem C models, the recently suggested dichotomy between EM and AM plants, and the idea that common traits can predict decomposition across roots and leaves. Aspects of C chemistry unrelated to lignin or nitrogen, and not presently considered in decomposition models, controlled first-order root decomposition; thus, current paradigms of ecosystem C dynamics and model parameterization require revision.
  • Liu, Licheng; Zhuang, Qianlai; Zhu, Qing; Liu, Shaoqing; van Asperen, Hella; Pihlatie, Mari (2018)
    Carbon monoxide (CO) plays an important role in controlling the oxidizing capacity of the atmosphere by reacting with OH radicals that affect atmospheric methane (CH4) dynamics. We develop a process-based biogeochemistry model to quantify the CO exchange between soils and the atmosphere with a 5 min internal time step at the global scale. The model is parameterized using the CO flux data from the field and laboratory experiments for 11 representative ecosystem types. The model is then extrapolated to global terrestrial ecosystems using monthly climate forcing data. Global soil gross consumption, gross production, and net flux of the atmospheric CO are estimated to be from -197 to -180, 34 to 36, and -163 to -145 TgCOyr(-1) (1 Tg = 10(12) g), respectively, when the model is driven with satellite-based atmospheric CO concentration data during 2000-2013. Tropical evergreen forest, savanna and deciduous forest areas are the largest sinks at 123 TgCOyr(-1). The soil CO gross consumption is sensitive to air temperature and atmospheric CO concentration, while the gross production is sensitive to soil organic carbon (SOC) stock and air temperature. By assuming that the spatially distributed atmospheric CO concentrations (similar to 128 ppbv) are not changing over time, the global mean CO net deposition velocity is estimated to be 0.16-0.19mms 1 during the 20th century. Under the future climate scenarios, the CO deposition velocity will increase at a rate of 0.0002-0.0013 mms 1 r(-1) during 2014-2100, reaching 0.20-0.30 mm s(-1) by the end of the 21st century, primarily due to the increasing temperature. Areas near the Equator, the eastern US, Europe and eastern Asia will be the largest sinks due to optimum soil moisture and high temperature. The annual global soil net flux of atmospheric CO is primarily controlled by air temperature, soil temperature, SOC and atmospheric CO concentrations, while its monthly variation is mainly determined by air temperature, precipitation, soil temperature and soil moisture.
  • Raivonen, Maarit; Smolander, Sampo; Backman, Leif; Susiluoto, Jouni; Aalto, Tuula; Markkanen, Tiina; Mäkelä, Jarmo; Rinne, Janne; Peltola, Olli; Aurela, Mika; Lohila, Annalea; Tomasic, Marin; Li, Xuefei; Larmola, Tuula; Juutinen, Sari; Tuittila, Eeva-Stiina; Heimann, Martin; Sevanto, Sanna; Kleinen, Thomas; Brovkin, Victor; Vesala, Timo (2017)
    Wetlands are one of the most significant natural sources of methane (CH4) to the atmosphere. They emit CH4 because decomposition of soil organic matter in waterlogged anoxic conditions produces CH4, in addition to carbon dioxide (CO2). Production of CH4 and how much of it escapes to the atmosphere depend on a multitude of environmental drivers. Models simulating the processes leading to CH4 emissions are thus needed for upscaling observations to estimate present CH4 emissions and for producing scenarios of future atmospheric CH4 concentrations. Aiming at a CH4 model that can be added to models describing peatland carbon cycling, we composed a model called HIMMELI that describes CH4 build-up in and emissions from peatland soils. It is not a full peatland carbon cycle model but it requires the rate of anoxic soil respiration as input. Driven by soil temperature, leaf area index (LAI) of aerenchymatous peat-land vegetation, and water table depth (WTD), it simulates the concentrations and transport of CH4, CO2, and oxygen (O-2) in a layered one-dimensional peat column. Here, we present the HIMMELI model structure and results of tests on the model sensitivity to the input data and to the description of the peat column (peat depth and layer thickness), and demonstrate that HIMMELI outputs realistic fluxes by comparing modeled and measured fluxes at two peatland sites. As HIMMELI describes only the CH4-related processes, not the full carbon cycle, our analysis revealed mechanisms and dependencies that may remain hidden when testing CH4 models connected to complete peatland carbon models, which is usually the case. Our results indicated that (1) the model is flexible and robust and thus suitable for different environments; (2) the simulated CH4 emissions largely depend on the prescribed rate of anoxic respiration; (3) the sensitivity of the total CH4 emission to other input variables is mainly mediated via the concentrations of dissolved gases, in particular, the O-2 concentrations that affect the CH4 production and oxidation rates; (4) with given input respiration, the peat column description does not significantly affect the simulated CH4 emissions in this model version.
  • Gaillard, M. -J.; Sugita, S.; Mazier, F.; Trondman, A. -K.; Brostrom, A.; Hickler, T.; Kaplan, J. O.; Kjellstrom, E.; Kokfelt, U.; Kunes, P.; Lemmen, C.; Miller, P.; Olofsson, J.; Poska, A.; Rundgren, M.; Smith, B.; Strandberg, G.; Fyfe, R.; Nielsen, A. B.; Alenius, T.; Balakauskas, L.; Barnekow, L.; Birks, H. J. B.; Bjune, A.; Bjorkman, L.; Giesecke, T.; Hjelle, K.; Kalnina, L.; Kangur, M.; van der Knaap, W. O.; Koff, T.; Lageras, P.; Latalowa, M.; Leydet, M.; Lechterbeck, J.; Lindbladh, M.; Odgaard, B.; Peglar, S.; Segerstrom, U.; von Stedingk, H.; Seppä, H. (2010)
  • Zanella, Augusto; Berg, Björn; Ponge, Jean-Francois; Kemmers, Rolf H. (2017)
    Humusica 1 and 2 Applied Soil Ecology Special issues are field guides for humipedon classification. Contrary to other similar manuals dedicated to soil, the objects that one can describe with these guides are living, dynamic, functional, and relatively independent soil units. This is the reason to why the authors dedicated the whole article number 2 to functional considerations even before readers could go in the field and face the matter to be classified. Experienced lectors can overstep many of the sections reported in this article. If the titles of sections "1 A functional classification", "2 What is a humus system?" and "3 Energetic considerations in terrestrial systems" stimulate the reader's curiosity, then we suggest to pass through them. Otherwise, only section "4 Climatic, plant litter, or nutritional constraints?" is crucial. Readers will understand how the soil works in terms of litter and Carbon accumulation, which one(s) among climatic, vegetational, or geological factors that intervene and strongly affect the formation processes of terrestrial (oxygenated) soils. The article concludes with a debate about a tergiversated question: can temperature influence humus decomposition? Preceding statements were used for explaining how the biological soil net can store in the soil a maximum of energy in the form of SOM, by raising a plateau partially independent of climatic conditions.
  • Li, T.; Zhang, W.; Zhang, Q.; Lu, Y.; Wang, G.; Niu, Z.; Raivonen, M.; Vesala, T. (2015)
    Natural wetlands are among the most important sources of atmospheric methane and thus important for better understanding the long-term temporal variations in the atmospheric methane concentration. During the last 60 years, wetlands have experienced extensive conversion and impacts from climate warming which might result in complicated temporal and spatial variations in the changes of the wetland methane emissions. In this paper, we present a modeling framework, integrating CH4MODwetland, TOPMODEL, and TEM models, to analyze the temporal and spatial variations in CH4 emissions from natural wetlands (including inland marshes/swamps, coastal wetlands, lakes, and rivers) in China. Our analysis revealed a total increase of 25.5 %, averaging 0.52 gm(-2) per decade, in the national CH4 fluxes from 1950 to 2010, which was mainly induced by climate warming. Larger CH4 flux increases occurred in northeastern, northern, and northwestern China, where there have been higher temperature rises. However, decreases in precipitation due to climate warming offset the increment of CH4 fluxes in these regions. The CH4 fluxes from the wetland on the Qinghai-Tibet Plateau exhibited the lowest CH4 increase (0.17 gm(-2) per decade). Although climate warming has accelerated CH4 fluxes, the total amount of national CH4 emissions decreased by approximately 2.35 Tg (1.91-2.81 Tg), i.e., from 4.50 Tg in the early 1950s to 2.15 Tg in the late 2000s, due to the wetland loss totalling 17.0 million ha. Of this reduction, 0.26 Tg (0.24-0.28 Tg) was derived from lakes and rivers, 0.16 Tg (0.13-0.20 Tg) from coastal wetlands, and 1.92 Tg (1.54-2.33 Tg) from inland wetlands. Spatially, northeastern China contributed the most to the total reduction, with a loss of 1.68 Tg. The wetland CH4 emissions reduced by more than half in most regions in China except for the Qinghai-Tibet Plateau, where the CH4 decrease was only 23.3 %.
  • Ge, Jielin; Berg, Bjorn; Xie, Zongqiang (2017)
    Leaf habit of tree species (evergreen versus deciduous) is proposed to be an important determinant of leaf litter decomposition, but it remains largely understudied as to how climatic regulation of litter decomposition differs between leaf habits. We isolated the relative role of climate and leaf habit in leaf litter decomposition by investigating the latitudinal pattern of leaf litter decomposition for Chinese broad-leaved tree species. Litter decomposition rate decreased with latitude, which was largely driven by mean annual temperature (MAT). Evergreen and deciduous broad-leaved tree species shared similar decomposition rate where they coexisted. Leaf litter decomposition of evergreen broad-leaved tree species was more sensitive to MAT than that of the deciduous species, whereas leaf litter decomposition of the deciduous trees was more sensitive than that of the evergreen to mean annual precipitation. Climatic variables explained more variation in leaf litter decomposition than did leaf habit alone. Our findings support the conventional paradigm that climate is a dominant regulator of leaf litter decomposition over broad geographical scales, notwithstanding recent studies calling into question this paradigm. While leaf habit alone does not predict leaf litter decomposition very well where both evergreen and deciduous species coexisted, the direction and strength of shift in leaf litter decomposition diverged between leaf habits across the climatic gradient. These findings underscore the urgent need to consider the impacts of changes in leaf habits when predicting leaf litter decomposition in response to climate change.
  • Gautam, Mukesh Kumar; Lee, Kwang-Sik; Berg, Bjorn; Song, Byeong-Yeol (2020)
    Evaluating the decomposition-based change dynamics of various elements in plant litter is important for improving our understanding about their biogeochemical cycling in ecosystems. We have studied the concentrations of major, trace, and rare earth elements (REEs) (34 elements) in green tissue litter, and soil and their dynamics in the decomposing litters of successional annual fleabane (Erigeron annuus) and silvergrass (Miscanthus sinensis). Concentrations of major and trace elements in the litter of annual fleabane were 1.02-2.71 times higher compared to silvergrass. For REEs the difference between the two litter types for elements studied was in the range of 1.02-1.29 times. Both the litters showed a general decrease in the concentrations of elements in the initial stages of decomposition (60-90 days). All the major and trace elements (except for Na) in silvergrass showed a net increase in concentration at the end of the decomposition study (48.9-52.5% accumulated mass loss). Contrastingly, a few trace elements (Mn, Mo, Sr, Zn, Sb, and Cd) in annual fleabane showed a net decrease in their concentrations. For REEs, there was an increase in concentrations as well as in net amounts in both litter types. Similarities observed in the dynamics together with high and significant correlations among them likely suggest their common source. The higher concentrations of REEs in soil likely suggest its role in the net increase in REEs' concentrations and amount in litter during decomposition. (C) 2020 Elsevier B.V. All rights reserved.
  • Tsuruta, Aki; Aalto, Tuula; Backman, Leif; Krol, Maarten C.; Peters, Wouter; Lienert, Sebastian; Joos, Fortunat; Miller, Paul A.; Zhang, Wenxin; Laurila, Tuomas; Hatakka, Juha; Leskinen, Ari; Lehtinen, Kari E. J.; Peltola, Olli; Vesala, Timo; Levula, Janne; Dlugokencky, Ed; Heimann, Martin; Kozlova, Elena; Aurela, Mika; Lohila, Annalea; Kauhaniemi, Mari; Gomez-Pelaez, Angel J. (2019)
    We estimated the CH4 budget in Finland for 2004?2014 using the CTE-CH4 data assimilation system with an extended atmospheric CH4 observation network of seven sites from Finland to surrounding regions (Hyytiälä, Kj?lnes, Kumpula, Pallas, Puijo, Sodankylä, and Utö). The estimated average annual total emission for Finland is 0.6?±?0.5 Tg CH4 yr?1. Sensitivity experiments show that the posterior biospheric emission estimates for Finland are between 0.3 and 0.9 Tg CH4 yr?1, which lies between the LPX-Bern-DYPTOP (0.2 Tg CH4 yr?1) and LPJG-WHyMe (2.2 Tg CH4 yr?1) process-based model estimates. For anthropogenic emissions, we found that the EDGAR v4.2 FT2010 inventory (0.4 Tg CH4 yr?1) is likely to overestimate emissions in southernmost Finland, but the extent of overestimation and possible relocation of emissions are difficult to derive from the current observation network. The posterior emission estimates were especially reliant on prior information in central Finland. However, based on analysis of posterior atmospheric CH4, we found that the anthropogenic emission distribution based on a national inventory is more reliable than the one based on EDGAR v4.2 FT2010. The contribution of total emissions in Finland to global total emissions is only about 0.13%, and the derived total emissions in Finland showed no trend during 2004?2014. The model using optimized emissions was able to reproduce observed atmospheric CH4 at the sites in Finland and surrounding regions fairly well (correlation > 0.75, bias
  • Trondman, A. -K.; Gaillard, M. -J.; Mazier, F.; Sugita, S.; Fyfe, R.; Nielsen, A. B.; Twiddle, C.; Barratt, P.; Birks, H. J. B.; Bjune, A. E.; Bjorkman, L.; Brostrom, A.; Caseldine, C.; David, R.; Dodson, J.; Doerfler, W.; Fischer, E.; van Geel, B.; Giesecke, T.; Hultberg, T.; Kalnina, L.; Kangur, M.; van der Knaap, P.; Koff, T.; Kunes, P.; Lageras, P.; Latalowa, M.; Lechterbeck, J.; Leroyer, C.; Leydet, M.; Lindbladh, M.; Marquer, L.; Mitchell, F. J. G.; Odgaard, B. V.; Peglar, S. M.; Persson, T.; Poska, A.; Roesch, M.; Seppä, H.; Veski, S.; Wick, L. (2015)
    We present quantitative reconstructions of regional vegetation cover in north-western Europe, western Europe north of the Alps, and eastern Europe for five time windows in the Holocene [around 6k, 3k, 0.5k, 0.2k, and 0.05k calendar years before present (bp)] at a 1 degrees x1 degrees spatial scale with the objective of producing vegetation descriptions suitable for climate modelling. The REVEALS model was applied on 636 pollen records from lakes and bogs to reconstruct the past cover of 25 plant taxa grouped into 10 plant-functional types and three land-cover types [evergreen trees, summer-green (deciduous) trees, and open land]. The model corrects for some of the biases in pollen percentages by using pollen productivity estimates and fall speeds of pollen, and by applying simple but robust models of pollen dispersal and deposition. The emerging patterns of tree migration and deforestation between 6k bp and modern time in the REVEALS estimates agree with our general understanding of the vegetation history of Europe based on pollen percentages. However, the degree of anthropogenic deforestation (i.e. cover of cultivated and grazing land) at 3k, 0.5k, and 0.2k bp is significantly higher than deduced from pollen percentages. This is also the case at 6k in some parts of Europe, in particular Britain and Ireland. Furthermore, the relationship between summer-green and evergreen trees, and between individual tree taxa, differs significantly when expressed as pollen percentages or as REVEALS estimates of tree cover. For instance, when Pinus is dominant over Picea as pollen percentages, Picea is dominant over Pinus as REVEALS estimates. These differences play a major role in the reconstruction of European landscapes and for the study of land cover-climate interactions, biodiversity and human resources.
  • Rinne, Janne; Tuittila, Eeva-Stiina; Peltola, Olli; Li, Xuefei; Raivonen, Maarit; Alekseychik, Pavel; Haapanala, Sami; Pihlatie, Mari; Aurela, Mika; Mammarella, Ivan; Vesala, Timo (2018)
    We have analyzed decade-long methane flux data set from a boreal fen, Siikaneva, together with data on environmental parameters and carbon dioxide exchange. The methane flux showed seasonal cycle but no systematic diel cycle. The highest fluxes were observed in July-August with average value of 73 nmol m(-2) s(-1). Wintertime fluxes were small but positive, with January-March average of 6.7 nmol m(-2) s(-1). Daily average methane emission correlated best with peat temperatures at 20-35 cm depths. The second highest correlation was with gross primary production (GPP). The best correspondence between emission algorithm and measured fluxes was found for a variable-slope generalized linear model (r(2) = 0.89) with peat temperature at 35 cm depth and GPP as explanatory variables, slopes varying between years. The homogeneity of slope approach indicated that seasonal variation explained 79% of the sum of squares variation of daily average methane emission, the interannual variation in explanatory factors 7.0%, functional change 5.3%, and random variation 9.1%. Significant correlation between interannual variability of growing season methane emission and that of GPP indicates that on interannual time scales GPP controls methane emission variability, crucially for development of process-based methane emission models. Annual methane emission ranged from 6.0 to 14 gC m(-2) and was 2.7 +/- 0.4% of annual GPP. Over 10-year period methane emission was 18% of net ecosystem exchange as carbon. The weak relation of methane emission to water table position indicates that space-to-time analogy, used to extrapolate spatial chamber data in time, may not be applicable in seasonal time scales.
  • Zhu, Yuhao; Merbold, Lutz; Leitner, Sonja; Pelster, David E.; Okoma, Sheila Abwanda; Ngetich, Felix; Onyango, Alice Anyango; Pellikka, Petri; Butterbach-Bahl, Klaus (2020)
    Aims Decomposition of manure deposited onto pasture from grazing animals represents an important process for carbon (C) and nitrogen (N) cycles in grassland systems. However, studies investigating manure decomposition are scarce; especially in sub-Saharan Africa (SSA). Methods In this study, we measured decomposition of three types of animal manure (cattle, sheep, goat) over >1 year using litter bags at four climatically different sites across Kenya. Results Manure dry matter, total C, total N and ammonium concentrations decreased exponentially, with the most rapid decrease occurring during the first few weeks following application, followed by slower changes during the following 2-3 months. Rates of N mineralization were lower than those for C mineralization, resulting in decreasing C/N ratios over time. Generally, cattle manure decomposed faster than sheep or goat manure despite having a higher initial C/N ratio and lower N concentration, with decomposition rates for dry matter ranging from 0.200 to 0.989 k year(-1). Cellulose decomposed first, while lignin concentrations increased among all manure types and at all sites. Conclusions We found that total manure decomposition rates were positively correlated with cumulative precipitation and aridity index, but negatively correlated with mean temperature. Our results show much slower decomposition rates of manures in semi-arid tropical environments of East Africa as compared to the few previous studies in temperate climates.
  • Kotze, David Johan; Ghosh, Subhadip; Hui, Nan; Jumpponen, Ari; Lee, Benjamin P. Y-H; Lu, Changyi; Lum, Shawn; Pouyat, Richard; Szlavecz, Katalin; Wardle, David A.; Yesilonis, Ian; Zheng, Bangxiao; Setala, Heikki (2021)
    An increasingly urbanized world is one of the most prominent examples of global environmental change. Across the globe, urban parks are designed and managed in a similar way, resulting in visually pleasing expansions of lawn interspersed with individually planted trees of varying appearances and functional traits. These large urban greenspaces have the capacity to provide various ecosystem services, including those associated with soil physicochemical properties. Our aim was to explore whether soil properties in urban parks diverge underneath vegetation producing labile or recalcitrant litter, and whether the impact is affected by climatic zone (from a boreal to temperate to tropical city). We also compared these properties to those in (semi)natural forests outside the cities to assess the influence of urbanization on plant-trait effects. We showed that vegetation type affected percentage soil organic matter (OM), total carbon (C) and total nitrogen (N), but inconsistently across climatic zones. Plant-trait effects were particularly weak in old parks in the boreal and temperate zones, whereas in young parks in these zones, soils underneath the two tree types accumulated significantly more OM, C and N compared to lawns. Within climatic zones, anthropogenic drivers dominated natural ones, with consistently lower values of organic-matter-related soil properties under trees producing labile or recalcitrant litter in parks compared to forests. The dominating effect of urbanization is also reflected in its ability to homogenize soil properties in parks across the three cities, especially in lawn soils and soils under trees irrespective of functional trait. Our study demonstrates that soil functions that relate to carbon and nitrogen dynamics-even in old urban greenspaces where plant-soil interactions have a long history-clearly diverged from those in natural ecosystems, implying a long-lasting influence of anthropogenic drivers on soil ecosystem services.