Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    Robust cropping systems to tackle pests under climate change. A review
    Lamichhane, J.R. ; Barzman, M. ; Booij, C.J.H. ; Boonekamp, P.M. ; Desneux, N. ; Huber, L. ; Kudsk, P. ; Langrell, S.R.H. ; Ratnadass, A. ; Ricci, P. ; Sarah, J.L. ; Messéan, A. - \ 2015
    Agronomy for Sustainable Development 35 (2015)2. - ISSN 1774-0746 - p. 443 - 459.
    phoma stem canker - plant-disease - change impacts - oilseed rape - pseudomonas-aeruginosa - puccinia-striiformis - range expansion - food security - tuta-absoluta - elevated co2
    Agriculture in the twenty-first century faces the challenge of meeting food demands while satisfying sustainability goals. The challenge is further complicated by climate change which affects the distribution of crop pests (intended as insects, plants, and pathogenic agents injurious to crops) and the severity of their outbreaks. Increasing concerns over health and the environment as well as new legislation on pesticide use, particularly in the European Union, urge us to find sustainable alternatives to pesticide-based pest management. Here, we review the effect of climate change on crop protection and propose strategies to reduce the impact of future invasive as well as rapidly evolving resident populations. The major points are the following: (1) the main consequence of climate change and globalization is a heightened level of unpredictability of spatial and temporal interactions between weather, cropping systems, and pests; (2) the unpredictable adaptation of pests to a changing environment primarily creates uncertainty and projected changes do not automatically translate into doom and gloom scenarios; (3) faced with uncertainty, policy, research, and extension should prepare for worst-case scenarios following a “no regrets” approach that promotes resilience vis-à-vis pests which, at the biophysical level, entails uncovering what currently makes cropping systems resilient, while at the organizational level, the capacity to adapt needs to be recognized and strengthened; (4) more collective approaches involving extension and other stakeholders will help meet the challenge of developing more robust cropping systems; (5) farmers can take advantage of Web 2.0 and other new technologies to make the exchange of updated information quicker and easier; (6) cooperation between historically compartmentalized experts in plant health and crop protection could help develop anticipation strategies; and (7) the current decline in skilled crop protection specialists in Europe should be reversed, and shortcomings in local human and financial resources can be overcome by pooling resources across borders
    Spatial heterogeneity in stomatal features during leaf elongation: an analysis using Rosa hybrida
    Fanourakis, D. ; Heuvelink, E. ; Carvalho, S.M.P. - \ 2015
    Functional Plant Biology 42 (2015)8. - ISSN 1445-4408 - p. 737 - 745.
    relative air humidity - gas-exchange - elevated co2 - conductance - leaves - size - density - adaptation - ontogeny - growth
    Within-leaf heterogeneity in stomatal traits poses a key uncertainty in determining a representative value for the whole leaf. Accounting for this heterogeneity, we studied stomatal initiation on expanding leaves and estimated stomatal conductance (gs) of mature leaves. The entire lamina was evaluated at four percentages of full leaflet elongation (FLE; leaflet length relative to its final length) in Rosa hybrida L. plants grown at 60% relative air humidity (RH), and at 100% FLE following cultivation at elevated (95%) RH. Over 80% of the stomata were initiated between 33 and 67% FLE, whereas stomatal growth mostly occurred afterwards. At 100% FLE, the heterogeneity in stomatal density was the result of uneven stomatal differentiation, while an uneven differentiation of epidermal cells contributed to this variation only at elevated RH. Noticeable within-leaf differences (up to 40%) in gs were calculated at 100% FLE. Avoiding leaflet periphery decreased this heterogeneity. Despite the large promotive effect of elevated RH on stomatal and pore dimensions, the within-leaf variation remained unaffected in all characters, besides pore aperture (and, thus, gs). The noted level of within-leaf variation in stomatal features demands a sampling scheme tailored to the leaf developmental stage, the feature per se and the evaporative demand during growth.
    Tree growth variation in the tropical forest: understanding effects of temperature, rainfall and CO2
    Schippers, P. ; Sterck, F.J. ; Vlam, M. ; Zuidema, P.A. - \ 2015
    Global Change Biology 21 (2015)7. - ISSN 1354-1013 - p. 2749 - 2761.
    water-use efficiency - global vegetation models - woody-tissue respiration - leaf-area index - elevated co2 - thermal-acclimation - carbon sink - scaling relationships - stomatal conductance - primary productivity
    Tropical forest responses to climatic variability have important consequences for global carbon cycling, but are poorly understood. As empirical, correlative studies cannot disentangle the interactive effects of climatic variables on tree growth, we used a tree growth model (IBTREE) to unravel the climate effects on different physiological pathways and in turn on stem growth variation. We parameterized the model for canopy trees of Toona ciliata (Meliaceae) from a Thai monsoon forest and compared predicted and measured variation from a tree-ring study over a 30-year period. We used historical climatic variation of minimum and maximum day temperature, precipitation and carbon dioxide (CO2) in different combinations to estimate the contribution of each climate factor in explaining the inter-annual variation in stem growth. Running the model with only variation in maximum temperature and rainfall yielded stem growth patterns that explained almost 70% of the observed inter-annual variation in stem growth. Our results show that maximum temperature had a strong negative effect on the stem growth by increasing respiration, reducing stomatal conductance and thus mitigating a higher transpiration demand, and – to a lesser extent – by directly reducing photosynthesis. Although stem growth was rather weakly sensitive to rain, stem growth variation responded strongly and positively to rainfall variation owing to the strong inter-annual fluctuations in rainfall. Minimum temperature and atmospheric CO2 concentration did not significantly contribute to explaining the inter-annual variation in stem growth. Our innovative approach – combining a simulation model with historical data on tree-ring growth and climate – allowed disentangling the effects of strongly correlated climate variables on growth through different physiological pathways. Similar studies on different species and in different forest types are needed to further improve our understanding of the sensitivity of tropical tree growth to climatic variability and change.
    Intercropping affects the rate of decomposition of soil organic matter and root litter
    Cong, W. ; Hoffland, E. ; Li, L. ; Janssen, B.H. ; Werf, W. van der - \ 2015
    Plant and Soil 391 (2015)1-2. - ISSN 0032-079X - p. 399 - 411.
    plant-species richness - experimental grassland ecosystems - nitrogen deposition - northwest china - elevated co2 - diversity - biodiversity - mineralization - rhizosphere - carbon
    Aims - Intercropping increases aboveground and belowground crop productivity, suggesting potential for carbon sequestration. Here we determined whether intercropping affects decomposition of soil organic matter (SOM) and root litter. Methods - We measured in the laboratory and the field the breakdown of SOM, root litter of maize, wheat, or faba bean, litter mixtures, and a standard substrate (compost) in soils from a long term intercropping experiment. Results - Soil organic matter from intercrop plots decomposed faster than SOM from monocrop plots, but compost decomposed at similar rates in different soils. Faster SOM decomposition was associated with lower soil C:N ratio. Root litter mixtures of maize and wheat decomposed as expected from single litters, but litter mixture of maize and faba bean decomposed faster than expected, both in the laboratory and in the field. Root litter decomposed slowly in maize/wheat intercrop soil compared to the two monocropped soils in the laboratory, but the effect was absent in the field. Conclusions - Intercropping increases SOM decomposition, presumably through reduced SOM recalcitrance resulting from lower C:N ratio, higher litter input and better N retention. Depending on the crop combination, also non-additive effects of root litter mixing can enhance organic matter decomposition in intercropping soils.
    Forest resilience and tipping points at different spatio-temporal scales: approaches and challenges
    Reyer, C.P.O. ; Brouwers, N. ; Rammig, A. ; Brook, B.W. ; Holmgren, M. ; Villela, D.M. - \ 2015
    Journal of Ecology 103 (2015)1. - ISSN 0022-0477 - p. 5 - 15.
    global vegetation model - climate-change impacts - amazon rain-forest - carbon-dioxide - elevated co2 - tree mortality - boreal forest - regime shifts - primary productivity - critical transitions
    1. Anthropogenic global change compromises forest resilience, with profound impacts to ecosystem functions and services. This synthesis paper reflects on the current understanding of forest resilience and potential tipping points under environmental change and explores challenges to assessing responses using experiments, observations and models. 2. Forests are changing over a wide range of spatio-temporal scales, but it is often unclear whether these changes reduce resilience or represent a tipping point. Tipping points may arise from interactions across scales, as processes such as climate change, land-use change, invasive species or deforestation gradually erode resilience and increase vulnerability to extreme events. Studies covering interactions across different spatio-temporal scales are needed to further our understanding. 3. Combinations of experiments, observations and process-based models could improve our ability to project forest resilience and tipping points under global change. We discuss uncertainties in changing CO2 concentration and quantifying tree mortality as examples. 4. Synthesis. As forests change at various scales, it is increasingly important to understand whether and how such changes lead to reduced resilience and potential tipping points. Understanding the mechanisms underlying forest resilience and tipping points would help in assessing risks to ecosystems and presents opportunities for ecosystem restoration and sustainable forest management.
    Uncertainties in predicting rice yield by current crop models under a wide range of climatic conditions
    Li, T. ; Hasegawa, T. ; Yin, X. ; Zhu, Y. ; Boote, K. ; Adam, M. ; Bregaglio, S. ; Buis, S. ; Confalonieri, R. ; Fumoto, T. ; Gaydon, D. ; Marcaida III, M. ; Nakagawa, H. ; Oriol, P. ; Ruane, A.C. ; Ruget, F. ; Singh, B. ; Singh, U. ; Tang, L. ; Yoshida, H. ; Zhang, Z. ; Bouman, B. - \ 2015
    Global Change Biology 21 (2015)3. - ISSN 1354-1013 - p. 1328 - 1341.
    air co2 enrichment - high-temperature stress - elevated co2 - spikelet fertility - night temperature - carbon-dioxide - growth - sterility - face - productivity
    Predicting rice (Oryza sativa) productivity under future climates is important for global food security. Ecophysiological crop models in combination with climate model outputs are commonly used in yield prediction, but uncertainties associated with crop models remain largely unquantified. We evaluated 13 rice models against multi-year experimental yield data at four sites with diverse climatic conditions in Asia and examined whether different modeling approaches on major physiological processes attribute to the uncertainties of prediction to field measured yields and to the uncertainties of sensitivity to changes in temperature and CO2 concentration [CO2]. We also examined whether a use of an ensemble of crop models can reduce the uncertainties. Individual models did not consistently reproduce both experimental and regional yields well, and uncertainty was larger at the warmest and coolest sites. The variation in yield projections was larger among crop models than variation resulting from 16 global climate model-based scenarios. However, the mean of predictions of all crop models reproduced experimental data, with an uncertainty of less than 10% of measured yields. Using an ensemble of eight models calibrated only for phenology or five models calibrated in detail resulted in the uncertainty equivalent to that of the measured yield in well-controlled agronomic field experiments. Sensitivity analysis indicates the necessity to improve the accuracy in predicting both biomass and harvest index in response to increasing [CO2] and temperature.
    No growth stimulation of tropical trees by 150 years of CO2 fertilization but water-use efficiency increased
    Sleen, J.P. van der; Groenendijk, P. ; Vlam, M. ; Anten, N.P.R. ; Boom, A. ; Bongers, F. ; Pons, T.L. ; Terburg, G. ; Zuidema, P.A. - \ 2015
    Nature Geoscience 8 (2015). - ISSN 1752-0894 - p. 24 - 28.
    rising atmospheric co2 - carbon-dioxide - climate-change - elevated co2 - forest trees - responses - ecosystems - vegetation - feedbacks - lessons
    The biomass of undisturbed tropical forests has likely increased in the past few decades (1, 2), probably as a result of accelerated tree growth. Higher CO2 levels are expected to raise plant photosynthetic rates (3) and enhance water-use efficiency (4), that is, the ratio of carbon assimilation through photosynthesis to water loss through transpiration. However, there is no evidence that these physiological responses do indeed stimulate tree growth in tropical forests. Here we present measurements of stable carbon isotopes and growth rings in the wood of 1,100 trees from Bolivia, Cameroon and Thailand. Measurements of carbon isotope fractions in the wood indicate that intrinsic water-use efficiency in both understorey and canopy trees increased by 30–35% over the past 150 years as atmospheric CO2 concentrations increased. However, we found no evidence for the suggested concurrent acceleration of individual tree growth when analysing the width of growth rings. We conclude that the widespread assumption of a CO2-induced stimulation of tropical tree growth may not be valid.
    Climate change and European forests: What do we know, what are the uncertainties, and what are the implications for forest management?
    Lindner, M. ; Fitzgerald, J.B. ; Zimmermann, N.E. ; Reyer, C. ; Delzon, S. ; Maaten, E. van der; Schelhaas, M. ; Lasch, P. ; Eggers, J. ; Maaten-Theunissen, M. van der; Suckow, F. ; Psomas, A. ; Pouler, B. ; Hanewinkel, M. - \ 2014
    Journal of Environmental Management 146 (2014). - ISSN 0301-4797 - p. 69 - 83.
    water-use efficiency - change impacts - elevated co2 - change risks - face sites - scots pine - drought - carbon - shift - trees
    The knowledge about potential climate change impacts on forests is continuously expanding and some changes in growth, drought induced mortality and species distribution have been observed. However despite a significant body of research, a knowledge and communication gap exists between scientists and non-scientists as to how climate change impact scenarios can be interpreted and what they imply for European forests. It is still challenging to advise forest decision makers on how best to plan for climate change as many uncertainties and unknowns remain and it is difficult to communicate these to practitioners and other decision makers while retaining emphasis on the importance of planning for adaptation. In this paper, recent developments in climate change observations and projections, observed and projected impacts on European forests and the associated uncertainties are reviewed and synthesised with a view to understanding the implications for forest management. Current impact assessments with simulation models contain several simplifications, which explain the discrepancy between results of many simulation studies and the rapidly increasing body of evidence about already observed changes in forest productivity and species distribution. In simulation models uncertainties tend to cascade onto one another; from estimating what future societies will be like and general circulation models (GCMs) at the global level, down to forest models and forest management at the local level. Individual climate change impact studies should not be uncritically used for decision-making without reflection on possible shortcomings in system understanding, model accuracy and other assumptions made. It is important for decision makers in forest management to realise that they have to take long-lasting management decisions while uncertainty about climate change impacts are still large. We discuss how to communicate about uncertainty - which is imperative for decision making - without diluting the overall message. Considering the range of possible trends and uncertainties in adaptive forest management requires expert knowledge and enhanced efforts for providing science-based decision support.
    Going underground: root traits as drivers of ecosystem processes
    Bardgett, R.D. ; Mommer, L. ; Vries, F.T. de - \ 2014
    Trends in Ecology and Evolution 29 (2014)12. - ISSN 0169-5347 - p. 692 - 699.
    soil microbial communities - plant functional traits - climate-change - biogeochemical significance - nutrient-acquisition - carbon sequestration - economics spectrum - species richness - water transport - elevated co2
    Ecologists are increasingly adopting trait-based approaches to understand how community change influences ecosystem processes. However, most of this research has focussed on aboveground plant traits, whereas it is becoming clear that root traits are important drivers of many ecosystem processes, such as carbon (C) and nutrient cycling, and the formation and structural stability of soil. Here, we synthesise emerging evidence that illustrates how root traits impact ecosystem processes, and propose a pathway to unravel the complex roles of root traits in driving ecosystem processes and their response to global change. Finally, we identify research challenges and novel technologies to address them.
    How do various maize crop models vary in their responses to climate change factors?
    Bassu, S. ; Brisson, N. ; Durand, J. ; Boote, K.J. ; Lizaso, J. ; Jones, J.W. ; Rosenzweig, C. ; Ruane, A.C. ; Adam, M. ; Baron, C. ; Basso, B. ; Biernath, C. ; Boogaard, H.L. ; Conijn, S. ; Corbeels, M. ; Deryng, D. ; Sanctis, G. De; Gayler, S. ; Grassini, P. ; Hatfield, J.L. ; Hoek, S.B. ; Izaurralde, C. - \ 2014
    Global Change Biology 20 (2014)7. - ISSN 1354-1013 - p. 2301 - 2320.
    water-use efficiency - air co2 enrichment - simulation-model - elevated co2 - systems simulation - nitrogen dynamics - carbon-dioxide - yield - wheat - agriculture
    Potential consequences of climate change on crop production can be studied using mechanistic crop simulation models. While a broad variety of maize simulation models exist, it is not known whether different models diverge on grain yield responses to changes in climatic factors, or whether they agree in their general trends related to phenology, growth, and yield. With the goal of analyzing the sensitivity of simulated yields to changes in temperature and atmospheric carbon dioxide concentrations [CO2], we present the largest maize crop model intercomparison to date, including 23 different models. These models were evaluated for four locations representing a wide range of maize production conditions in the world: Lusignan (France), Ames (USA), Rio Verde (Brazil) and Morogoro (Tanzania). While individual models differed considerably in absolute yield simulation at the four sites, an ensemble of a minimum number of models was able to simulate absolute yields accurately at the four sites even with low data for calibration, thus suggesting that using an ensemble of models has merit. Temperature increase had strong negative influence on modeled yield response of roughly -0.5 Mg ha-1 per °C. Doubling [CO2] from 360 to 720 µmol mol-1 increased grain yield by 7.5% on average across models and the sites. That would therefore make temperature the main factor altering maize yields at the end of this century. Furthermore, there was a large uncertainty in the yield response to [CO2] among models. Model responses to temperature and [CO2] did not differ whether models were simulated with low calibration information or, simulated with high level of calibration information.
    Plant species richness promotes soil carbon and nitrogen stocks in grasslands without legumes
    Cong, W. ; Ruijven, J. van; Mommer, L. ; Deyn, G.B. de; Berendse, F. ; Hoffland, E. - \ 2014
    Journal of Ecology 102 (2014)5. - ISSN 0022-0477 - p. 1163 - 1170.
    diversity-productivity relationship - functional composition - biodiversity experiment - ecosystem function - elevated co2 - communities - impacts - time - complementarity - sequestration
    1.The storage of carbon (C) and nitrogen (N) in soil is important ecosystem functions. Grassland biodiversity experiments have shown a positive effect of plant diversity on soil C and N storage. However, these experiments all included legumes, which constitute an important N input through N2-fixation. Indeed, the results of these experiments suggest that N2 fixation by legumes is a major driver of soil C and N storage. 2.We studied whether plant diversity affects soil C and N storage in the absence of legumes. In an 11-year grassland biodiversity experiment without legumes, we measured soil C and N stocks. We further determined above-ground biomass productivity, standing root biomass, soil organic matter decomposition and N mineralization rates to understand the mechanisms underlying the change in soil C and N stocks in relation to plant diversity and their feedbacks to plant productivity. 3.We found that soil C and N stocks increased by 18% and 16% in eight-species mixtures compared to the average of monocultures of the same species, respectively. Increased soil C and N stocks were mainly driven by increased C input and N retention, resulting from enhanced plant productivity, which surpassed enhanced C loss from decomposition. Importantly, higher soil C and N stocks were associated with enhanced soil N mineralization rates, which can explain the strengthening of the positive diversity–productivity relationship observed in the last years of the experiment. 4.Synthesis. We demonstrated that also in the absence of legumes, plant species richness promotes soil carbon (C) and nitrogen (N) stocks via increased plant productivity. In turn, enhanced soil C and N stocks showed a positive feedback to plant productivity via enhanced N mineralization, which could further accelerate soil C and N storage in the long term.
    How light competition between plants affects their response to climate change
    Loon, M.P. van; Schieving, F. ; Rietkerk, M. ; Dekker, S.C. ; Sterck, F.J. ; Anten, N.P.R. - \ 2014
    New Phytologist 203 (2014)4. - ISSN 0028-646X - p. 1253 - 1265.
    leaf-area index - co2 enrichment face - canopy carbon gain - elevated co2 - atmospheric co2 - stomatal conductance - terrestrial ecosystems - nitrogen availability - global change - gas-exchange
    How plants respond to climate change is of major concern, as plants will strongly impact future ecosystem functioning, food production and climate. Here, we investigated how vegetation structure and functioning may be influenced by predicted increases in annual temperatures and atmospheric CO2 concentration, and modeled the extent to which local plant–plant interactions may modify these effects. A canopy model was developed, which calculates photosynthesis as a function of light, nitrogen, temperature, CO2 and water availability, and considers different degrees of light competition between neighboring plants through canopy mixing; soybean (Glycine max) was used as a reference system. The model predicts increased net photosynthesis and reduced stomatal conductance and transpiration under atmospheric CO2 increase. When CO2 elevation is combined with warming, photosynthesis is increased more, but transpiration is reduced less. Intriguingly, when competition is considered, the optimal response shifts to producing larger leaf areas, but with lower stomatal conductance and associated vegetation transpiration than when competition is not considered. Furthermore, only when competition is considered are the predicted effects of elevated CO2 on leaf area index (LAI) well within the range of observed effects obtained by Free air CO2 enrichment (FACE) experiments. Together, our results illustrate how competition between plants may modify vegetation responses to climate change.
    Global dependence of field-observed leaf area index in woody species on climate: a systematic review
    Iio, A. ; Hikosaka, K. ; Anten, N.P.R. ; Nakagawa, Y. ; Ito, A. - \ 2014
    Global Ecology and Biogeography 23 (2014)3. - ISSN 1466-822X - p. 274 - 285.
    net primary production - nitrogen availability - forest ecosystems - plant canopy - elevated co2 - productivity - model - water - dynamics - balance
    Aim Leaf area index (LAI) is one of the key variables related to carbon, water and nutrient cycles in terrestrial ecosystems, but its global distribution patterns remain poorly understood.We evaluated the dependence of LAI on mean annual temperature (MAT) and wetness index (WI; a ratio of annual precipitation to potential evapotranspiration) for three plant functional types (PFTs: deciduous broadleaf, DB; evergreen conifer, EC; evergreen broadleaf, EB) at the global scale. Location Global. Methods We developed a new global database of unprecedented size (2606 published values) of field-observed LAI (site-specific maximum) values for vegetation of woody species. To maximize the generic applicability of our analysis, we standardized the definition of LAI, and corrected or excluded potentially erroneous data obtained from indirect optical methods. Results The global dependence of LAI on MAT showed a reverse S-shaped pattern, in which LAI peaked at around 8.9 and 25.0°C and was lowest at around -10.0 and 18.8°C. The dependence on WI followed a saturation curve levelling off at around logWI = 0.30. LAI for evergreen forests increased linearly with increasing WI, but that for DB showed a curvilinear pattern saturating at log WI = 0.03. EC forests had higher LAI values than those of DB forests under cool conditions (MAT = 8.9°C), but similar values under temperate conditions (MAT = 8.9–18.8°C). Main conclusions This analysis of global LAI-climate relationships supports the general belief that temperature limits LAI under cool conditions whereas water availability plays a predominant role under other conditions. We also found that these patterns differed significantly between PFTs, suggesting that the LAI of different PFTs may respond differently to climate change. Our study provides a broad empirical basis for predicting the global distribution of LAI and for analysing the effects of global climate change on vegetation structure and function.
    Hydrological droughts in the 21st century, hotspots and uncertainties from a global multimodel ensemble experiment
    Prudhomme, C. ; Giuntoli, L. ; Robinson, E.L. ; Clark, D.B. ; Arnell, N.W. ; Dankers, R. ; Fekete, B.M. ; Franssen, W.H.P. - \ 2014
    Proceedings of the National Academy of Sciences of the United States of America 111 (2014)9. - ISSN 0027-8424 - p. 3262 - 3267.
    climate-change - carbon-dioxide - elevated co2 - models - extremes - cycle - face
    Increasing concentrations of greenhouse gases in the atmosphere are expected to modify the global water cycle with significant consequences for terrestrial hydrology. We assess the impact of climate change on hydrological droughts in a multimodel experiment including seven global impact models (GIMs) driven by bias-corrected climate from five global climate models under four representative concentration pathways (RCPs). Drought severity is defined as the fraction of land under drought conditions. Results show a likely increase in the global severity of hydrological drought at the end of the 21st century, with systematically greater increases for RCPs describing stronger radiative forcings. Under RCP8.5, droughts exceeding 40% of analyzed land area are projected by nearly half of the simulations. This increase in drought severity has a strong signal-to-noise ratio at the global scale, and Southern Europe, the Middle East, the Southeast United States, Chile, and South West Australia are identified as possible hotspots for future water security issues. The uncertainty due to GIMs is greater than that from global climate models, particularly if including a GIM that accounts for the dynamic response of plants to CO2 and climate, as this model simulates little or no increase in drought frequency. Our study demonstrates that different representations of terrestrial water-cycle processes in GIMs are responsible for a much larger uncertainty in the response of hydrological drought to climate change than previously thought. When assessing the impact of climate change on hydrology, it is therefore critical to consider a diverse range of GIMs to better capture the uncertainty.
    The Agricultural Model Intercomparison and Improvement Project (AgMIP): Protocols and pilot studies
    Rosenzweig, C. ; Jones, W. ; Hatfield, J.L. ; Ruane, A.C. ; Boote, K.J. ; Thorburn, P. ; Antle, J.M. ; Nelson, G.C. ; Porter, C. ; Janssen, S.J.C. ; Asseng, S. ; Basso, B. ; Ewert, F. ; Wallach, D. ; Baigorria, G. ; Winter, J.M. - \ 2013
    Agricultural and Forest Meteorology 170 (2013). - ISSN 0168-1923 - p. 166 - 182.
    stochastic weather generators - climate-change research - cropgro-soybean model - integrated assessment - us agriculture - system model - elevated co2 - yield - impacts - variability
    The Agricultural Model Intercomparison and Improvement Project (AgMIP) is a major international effort linking the climate, crop, and economic modeling communities with cutting-edge information technology to produce improved crop and economic models and the next generation of climate impact projections for the agricultural sector. The goals of AgMIP are to improve substantially the characterization of world food security due to climate change and to enhance adaptation capacity in both developing and developed countries. Analyses of the agricultural impacts of climate variability and change require a transdisciplinary effort to consistently link state-of-the-art climate scenarios to crop and economic models. Crop model outputs are aggregated as inputs to regional and global economic models to determine regional vulnerabilities, changes in comparative advantage, price effects, and potential adaptation strategies in the agricultural sector. Climate, Crop Modeling, Economics, and Information Technology Team Protocols are presented to guide coordinated climate, crop modeling, economics, and information technology research activities around the world, along with AgMIP Cross-Cutting Themes that address uncertainty, aggregation and scaling, and the development of Representative Agricultural Pathways (RAPs) to enable testing of climate change adaptations in the context of other regional and global trends. The organization of research activities by geographic region and specific crops is described, along with project milestones. Pilot results demonstrate AgMIP's role in assessing climate impacts with explicit representation of uncertainties in climate scenarios and simulations using crop and economic models. An intercomparison of wheat model simulations near Obregón, Mexico reveals inter-model differences in yield sensitivity to [CO2] with model uncertainty holding approximately steady as concentrations rise, while uncertainty related to choice of crop model increases with rising temperatures. Wheat model simulations with mid-century climate scenarios project a slight decline in absolute yields that is more sensitive to selection of crop model than to global climate model, emissions scenario, or climate scenario downscaling method. A comparison of regional and national-scale economic simulations finds a large sensitivity of projected yield changes to the simulations’ resolved scales. Finally, a global economic model intercomparison example demonstrates that improvements in the understanding of agriculture futures arise from integration of the range of uncertainty in crop, climate, and economic modeling results in multi-model assessments.
    Nitrogen Addition and Warming Independently Influence the Belowground Micro-Food Web in a Temperate Steppe
    Li, Q. ; Bai, H. ; Liang, W. ; Xia, J. ; Wan, S. ; Putten, W.H. van der - \ 2013
    PLoS ONE 8 (2013)3. - ISSN 1932-6203
    climate-change manipulations - species composition - community structure - plant-communities - organic-matter - northern china - soil nematodes - global change - elevated co2 - deposition
    Climate warming and atmospheric nitrogen (N) deposition are known to influence ecosystem structure and functioning. However, our understanding of the interactive effect of these global changes on ecosystem functioning is relatively limited, especially when it concerns the responses of soils and soil organisms. We conducted a field experiment to study the interactive effects of warming and N addition on soil food web. The experiment was established in 2006 in a temperate steppe in northern China. After three to four years (2009–2010), we found that N addition positively affected microbial biomass and negatively influenced trophic group and ecological indices of soil nematodes. However, the warming effects were less obvious, only fungal PLFA showed a decreasing trend under warming. Interestingly, the influence of N addition did not depend on warming. Structural equation modeling analysis suggested that the direct pathway between N addition and soil food web components were more important than the indirect connections through alterations in soil abiotic characters or plant growth. Nitrogen enrichment also affected the soil nematode community indirectly through changes in soil pH and PLFA. We conclude that experimental warming influenced soil food web components of the temperate steppe less than N addition, and there was little influence of warming on N addition effects under these experimental conditions.
    Tropical forests and global change: filling knowledge gaps
    Zuidema, P.A. ; Baker, P.J. ; Groenendijk, P. ; Schippers, P. ; Sleen, J.P. van der; Vlam, M. ; Sterck, F.J. - \ 2013
    Trends in Plant Science 18 (2013)8. - ISSN 1360-1385 - p. 413 - 419.
    water-use efficiency - climate-change - rain-forest - tree-rings - elevated co2 - pervasive alteration - western thailand - traits determine - growth-patterns - atmospheric co2
    Tropical forests will experience major changes in environmental conditions this century. Understanding their responses to such changes is crucial to predicting global carbon cycling. Important knowledge gaps exist: the causes of recent changes in tropical forest dynamics remain unclear and the responses of entire tropical trees to environmental changes are poorly understood. In this Opinion article, we argue that filling these knowledge gaps requires a new research strategy, one that focuses on trees instead of leaves or communities, on long-term instead of short-term changes, and on understanding mechanisms instead of documenting changes. We propose the use of tree-ring analyses, stable-isotope analyses, manipulative field experiments, and well-validated simulation models to improve predictions of forest responses to global change.
    Physiological mechanisms in plant growth models: do we need a supra-cellular systems biology approach?
    Poorter, H. ; Anten, N.P.R. ; Marcelis, L.F.M. - \ 2013
    Plant, Cell & Environment 36 (2013)9. - ISSN 0140-7791 - p. 1673 - 1690.
    nitrogen-use efficiency - net assimilation rate - leaf-area - elevated co2 - carbon gain - tomato plants - gas-exchange - chemical-composition - biomass production - critical-appraisal
    In the first part of this paper, we review the extent to which various types of plant growth models incorporate ecophysiological mechanisms. Many growth models have a central role for the process of photosynthesis; and often implicitly assume C-gain to be the rate-limiting step for biomass accumulation. We subsequently explore the extent to which this assumption actually holds and under what condition constraints on growth due to a limited sink strength are likely to occur. By using generalized dose–response curves for growth with respect to light and CO2, models can be tested against a benchmark for their overall performance. In the final part, a call for a systems approach at the supra-cellular level is made. This will enable a better understanding of feedbacks and trade-offs acting on plant growth and its component processes. Mechanistic growth models form an indispensable element of such an approach and will, in the end, provide the link with the (sub-)cellular approaches that are yet developing. Improved insight will be gained if model output for the various physiological processes and morphological variables (‘virtual profiling’) is compared with measured correlation networks among these processes and variables. Two examples of these correlation networks are presented
    Climate Change and Potato Production in Contrasting South African Agro-Ecosystems 3. Effects on Relative Development Rates of Selected Pathogens and Pests
    Waals, J.E. van der; Krüger, K. ; Franke, A.C. ; Haverkort, A.J. ; Steyn, J.M. - \ 2013
    Potato Research 56 (2013)1. - ISSN 0014-3065 - p. 67 - 84.
    late-blight epidemics - phytophthora-infestans - meloidogyne-incognita - myzus-persicae - virus-y - transmission efficiency - alternaria-solani - plant-diseases - soil texture - elevated co2
    A set of daily weather data simulations for 1961 to 2050 were used to calculate past and future trends in pest and disease pressure in potato cropping systems at three agro-ecologically distinct sites in South Africa: the Sandveld, the Eastern Free State and Limpopo. The diseases and pests modelled were late blight, early blight and brown spot, blackleg and soft rot, root-knot nematodes and the peach-potato aphid Myzus persicae (as indicator of Potato virus Y and Potato leaf roll virus). The effects of climate on trends in relative development rates of these pathogens and pests were modelled for each pathogen and pest using a set of quantitative parameters, which included specific temperature and moisture requirements for population growth, compiled from literature. Results showed that the cumulative relative development rate (cRDR) of soft rot and blackleg, root-knot nematodes and M. persicae will increase over the 90-year period in the areas under consideration. The cRDR of early blight and brown spot is likely to increase in the wet winter and wet summer crops of the Sandveld and Eastern Free State, respectively, but remains unchanged in the dry summer and dry winter crops of the Sandveld and Limpopo, respectively. Climate change will decrease the cRDR of late blight in all of the cropping systems modelled, except in the wet winter crop of the Sandveld. These results help to set priorities in research and breeding, specifically in relation to management strategies for diseases and pests.
    Whole-canopy carbon gain as a result of selection on individual performance of ten genotypes of a clonal plant
    Vermeulen, P.J. ; Anten, N.P.R. ; Stuefer, J.F. ; During, H.J. - \ 2013
    Oecologia 172 (2013)2. - ISSN 0029-8549 - p. 327 - 337.
    herb potentilla-reptans - phenotypic plasticity - leaf-area - evolutionary stability - adaptive dynamics - root competition - modular concept - elevated co2 - nitrogen-use - grain yield
    Game theoretical models predict that plant competition for light leads to reduced productivity of vegetation stands through selection for traits that maximize carbon gains of individuals. Using empirical results from a 5-year competition experiment with 10 genotypes of the clonal plant Potentilla reptans, we tested this prediction by analyzing the effects of the existing leaf area values on the carbon gain of the different genotypes and the consequent whole canopy carbon gain. We focused on specific leaf area (SLA) due to its role in the trade-off between light capture area and photosynthetic capacity per unit area. By combining a canopy model based on measured leaf area and light profiles with a game theoretical approach, we analyzed how changes in the SLA affected genotypic and whole-stand carbon gain. This showed that all genotypes contributed to reduced stand productivity. The dominant genotype maximized its share of total carbon gain, resulting in lower than maximal absolute gain. Other genotypes did not maximize their share. Hypothetical mutants of the dominant genotype were not able to achieve a higher carbon gain. Conversely, in other genotypes, some mutations did result in increased carbon gain. Hence, genotypic differences in the ability to maximize performance may determine genotype frequency. It shows how genotypic selection may result in lower carbon gains of the whole vegetation, and of the individual genotypes it consists of, through similar mechanisms as those that lead to the tragedy of the commons.
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