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We present a comprehensive, high-quality dataset characterizing soil–vegetation and land surface processes from continuous measurements conducted in two climatically contrasting study regions in southwestern Germany: the warmer and drier Kraichgau region with a mean temperature of 9.7 ∘C and annual precipitation of 890 mm and the cooler and wetter Swabian Alb with mean temperature 7.5 ∘C and annual precipitation of 1042 mm. In each region, measurements were conducted over a time period of nine cropping seasons from 2009 to 2018. The backbone of the investigation was formed by six eddy-covariance (EC) stations which measured fluxes of water, energy and carbon dioxide between the land surface and the atmosphere at half-hourly resolution. This resulted in a dataset containing measurements from a total of 54 site years containing observations with a multitude of crops, as well as considerable variation in local growing-season climates. The presented multi-site, multi-year dataset is composed of crop-related data on phenological development stages, canopy height, leaf area index, vegetative and generative biomass, and their respective carbon and nitrogen content. Time series of soil temperature and soil water content were monitored with 30 min resolution at various points in the soil profile, including ground heat fluxes. Moreover, more than 1200 soil samples were taken to study changes of carbon and nitrogen contents. The dataset is available at https://doi.org/10.20387/bonares-a0qc-46jc (Weber et al., 2021). One field in each region is still fully set up as continuous observatories for state variables and fluxes in intensively managed agricultural fields.

Despite the large body of research surrounding crop growth parameters, there is still a lack of systematic assessments on how harvestable yields of different crop types respond to varying levels of shading. However, with the advent of agrivoltaic systems, a technology that combines energy and food production, shade tolerance of cropping systems is becoming increasingly important. To address this research gap, a meta-analysis with data from two experimental approaches (intercropping and artificial shading with cloths, nets or solar panels) was performed. The aim was to quantitatively assess the susceptibility of different temperate crop types to increasing levels of shading. Crop type specific yield response curves were developed as a function of reduction in solar radiation, estimating relative crop yields compared to the unshaded controls. Only studies that reported reduction in solar radiation and crop yield per area in temperate and subtropical areas were included. The results suggested a nonlinear relationship between achieved crop yields and reduction in solar radiation for all crop types. Most crops tolerate reduced solar radiation up to 15%, showing a less than proportional yield decline. However, significant differences between the response curves of the following crop types existed: Berries, fruits and fruity vegetables benefited from reduction in solar radiation up to 30%. Forages, leafy vegetables, tubers/root crops, and C3 cereals initially showed less than proportional crop yield loss. In contrast, maize and grain legumes experienced strong crop yield losses even at low shade levels. The results provide a set of initial indicators that may be used in assessing the suitability of crop types for shade systems, and thus for agrivoltaic or other dual land-use systems. Detailed yield response curves, as provided by this study, are valuable tools in optimizing the output of annual crop components in these systems.

The present study evaluated the interactive effects of global change and heavy metals on the growth and development of three soybean [Glycine max (L.) Merrill] cultivars and the consequences on yield and food safety. Soybean cultivars (Alim 3.14 from Argentina, and ES Mentor and Sigalia, from Germany) were grown until maturity in heavy metals polluted soils from the Rhine Valley, Germany, at two CO

Agrivoltaic (AV) systems integrate the production of agricultural crops and electric power on the same land area through the installation of solar panels several meters above the soil surface. It has been demonstrated that AV can increase land productivity and contribute to the expansion of renewable energy production. Its utilization is expected to affect crop production by altering microclimatic conditions but has so far hardly been investigated. The present study aimed to determine for the first time how changes in microclimatic conditions through AV affect selected agricultural crops within an organic crop rotation. For this purpose, an AV research plant was installed near Lake Constance in south-west Germany in 2016. A field experiment was established with four crops (celeriac, winter wheat, potato and grass-clover) cultivated both underneath the AV system and on an adjacent reference site without solar panels. Microclimatic parameters, crop development and harvestable yields were monitored in 2017 and 2018. Overall, an alteration in microclimatic conditions and crop production under AV was confirmed. Photosynthetic active radiation was on average reduced by about 30% under AV. During summertime, soil temperature was decreased under AV in both years. Furthermore, reduced soil moisture and air temperatures as well as an altered rain distribution have been found under AV. In both years, plant height of all crops was increased under AV. In 2017 and 2018, yield ranges of the crops cultivated under AV compared to the reference site were −19 to +3% for winter wheat, −20 to +11% for potato and −8 to −5% for grass-clover. In the hot, dry summer 2018, crop yields of winter wheat and potato were increased by AV by 2.7% and 11%, respectively. These findings show that yield reductions under AV are likely, but under hot and dry weather conditions, growing conditions can become favorable.

Atmospheric CO₂ enrichment affects C3 crops both directly via increased carbon gain and improved water use efficiency and indirectly via higher temperatures and more frequent climatic extremes. Here we investigated the response of spring wheat (Triticum aestivum L. cv. Triso) to CO₂ enrichment (550 vs. 380 µmol/mol) and heat, applied as a constant +4°C increase or a typical heat wave either before or after anthesis, or as two typical heat waves before and after anthesis. We applied a climate chamber approach closely mimicking ambient conditions. CO₂ enrichment increased above-ground biomass and yield by c. 7 and 10%, but was not able to compensate for adverse heat stress effects, neither before nor after anthesis, with few exceptions only. Yield depression due to heat stress was most severe when two heat waves were applied (−19%). This adverse effect was, however, compensated by CO₂ enrichment. Applying heat stress before or after anthesis did not exert different effects on yield for both +4°C warming and heat wave application. However, +4°C depressed yield more than a heat wave at ambient CO₂, but not so at elevated CO₂. Thus, the interactive effects were complex and prediction of future wheat yield under CO₂ enrichment and climate extremes deserves more attention.

The carbon (C) sequestration potential of croplands has recently become a subject of debate because it may contribute significantly to global climate change mitigation. By contrast, carbon dioxide (CO2) emissions from German croplands have continuously increased over the past decades as a result of soil organic carbon (SOC) losses. Contrasting results, however, have been obtained on the C sink or source function of European croplands based on long-term experiments and rather recent eddy covariance (EC) measurements. Over a period of eight years (2010–2017), we measured the net ecosystem exchange (NEE) of CO2 on six intensively managed cropland sites in two climatically different regions of southwest Germany (Kraichgau (KR) and Swabian Jura (SJ)) using the EC technique. Additionally, we measured aboveground crop biomass at three development stages and estimated management-related C inputs and exports. The inter-annual on-site variability of cumulated annual NEE was large, and neither the region nor the different sites significantly affected NEE budgets. Winter rapeseed showed the lowest CO2 uptake capacity among the observed crops, and the mean annual NEE in the years with winter rapeseed harvest was significantly lower compared to winter wheat, silage maize and winter barley. On average over 46 site-years, annual NEE showed a distinct CO2 uptake of −2580 kg CO2-C ha−1 yr−1. Considering management-related C fluxes, the resulting net biome productivity (NBP) indicated a C source function of the study sites with mean annual losses of 1190 kg C ha−1 yr−1. Due to high C removals after whole plant harvests, silage maize cropping resulted in significantly higher C losses of 4280 kg C ha−1 yr−1 compared to winter rapeseed, winter wheat and winter barley, with mean annual NBPs of 1430, −188 and −1340 kg C ha−1 yr−1, respectively. Consequently, a higher share of exported C in annual NBP resulted in higher C losses. We conclude that the recently increased importance of silage maize in crop rotations destabilizes SOC stocks, threatening the efforts in enhancing soil C sequestration. This calls for further investigations on the C sequestration potentials of more diverse crop rotations including perennial phases.

Spring wheat plants were grown under two CO2 concentrations (380 and 550 μmol mol−1) and two temperature treatments (ambient and post-anthesis heat stress) to investigate the effects of elevated CO2 and heat stress on grain protein quality. Contents of protein components, glutenin macropolymers (GMP) and amino acids in grains decreased due to elevated CO2, while increased by high temperature. The combination of elevated CO2 and heat stress increased the contents of total protein and albumin, but decreased the contents of gliadin and glutenin, while the content and particle size distribution of GMP as well as the contents of amino acids were not significantly affected. Furthermore, we found that the content and particle size distribution of GMP were not only determined by the contents of proteins and high-molecular-weight glutenin subunits, but also related to the contents of amino acids containing disulfide bonds, which favor the formation of large insoluble polymers.

Elevated CO2 (eCO2 ) generally promotes increased grain yield (GY) and decreased grain protein concentration (GPC), but the extent to which these effects depend on the magnitude of fertilization remains unclear. We collected data on the eCO2 responses of GY, GPC and grain protein yield and their relationships with nitrogen (N) application rates across experimental data covering 11 field grown wheat (Triticum aestivum) cultivars studied in eight countries on four continents. The eCO2 -induced stimulation of GY increased with N application rates up to ~200 kg/ha. At higher N application, stimulation of GY by eCO2 stagnated or even declined. This was valid both when the yield stimulation was expressed as the total effect and using per ppm CO2 scaling. GPC was decreased by on average 7% under eCO2 and the magnitude of this effect did not depend on N application rate. The net effect of responses on GY and protein concentration was that eCO2 typically increased and decreased grain protein yield at N application rates below and above ~100 kg/ha respectively. We conclude that a negative effect on wheat GPC seems inevitable under eCO2 and that substantial N application rates may be required to sustain wheat protein yields in a world with rising CO2 .

Aims The general aim of this meta-analysis is to synthesize and summarize the mean response of barley yield variables to elevated CO2 (eCO2) and how temperature and nitrogen (N) affect the CO2-induced yield responses of barley. Methods A meta-analysis procedure was used to analyze five yield variables of barley extracted from 22 studies to determine the effect size and the magnitude concerning eCO2 and its interaction with temperature and N. Results CO2 enrichment increased aboveground biomass (23.8%), grain number (24.8%), and grain yield (27.4%). The magnitude of the responses to eCO2 was affected by genotype, temperature, nitrogen, and CO2 exposure methods. Genotype “Anakin” shows the highest CO2 response of aboveground biomass (47.1%), while “Bambina” had the highest grain number (58.4%). Grain yield response was observed to be higher for genotypes “Alexis” (38.1%) and “Atem” (33.7%) under eCO2. The increase of aboveground biomass and grain yield was higher when plants were grown under eCO2 in combination with higher N (151–200 kg ha−1). The interaction between eCO2 and three different temperature levels was analyzed to identify the impacts on barley yield components. The results revealed that the CO2-induced increase in grain number and grain yield was higher in combination with a temperature level of 21–25 °C as compared to lower levels (2 was higher in growth chambers than in other CO2 exposure methods. Moreover, a higher response of aboveground biomass and grain yield to eCO2 was observed for pot-grown plants compared to field-grown. Conclusions Overall, results suggest that the maximal barley production under eCO2 will be obtained in combination with high N fertilizer and temperature levels (21–25 °C).

We present a comprehensive, high-quality dataset characterising soil-vegetation and land-surface processes from continuous measurements conducted in two climatically contrasting study regions in South West Germany: the warmer and drier Kraichgau region with a mean temperature of 9.7 °C and annual precipitation of 890 mm, and the cooler and wetter Swabian Alp with mean temperature 7.5 °C and annual precipitation 1042 mm. In each region, measurements were conducted over a time period of nine cropping seasons from 2009 to 2018. The backbone of the investigation was formed by six eddy-covariance stations (EC) which measured fluxes of water, energy and carbon dioxide between the land surface and the atmosphere at half-hourly resolution. This resulted in a dataset containing measurements from a total of 54 site*years containing observations with a multitude of crops, as well as considerable variation in local growing season climates. The presented multi-site, multi-year data set is composed of crop-related data on phenological development stages, canopy height, leaf area index, vegetative and generative biomass and their respective carbon and nitrogen content. Time series of soil temperature and soil water content were monitored with 30-min resolution at various points in the soil profile, including ground heat fluxes. Moreover, more than 1,200 soil samples were taken to study changes of carbon and nitrogen contents. The data set was uploaded to the Pangaea database and can be accessed at https://doi.org/10.20387/bonares-a0qc-46jc (for the review process, please refer to the data availability section). One station in each region has now been set up as continuous observatories of state variables and fluxes in intensively managed agricultural fields.

Increasing air and soil temperatures and changes in precipitation patterns as consequences of climate change will affect crop production in agricultural ecosystems. The combined effects of soil warming and altered precipitation on the productivity and product quality of oil crops are not yet well studied. Winter oilseed rape (OSR) (Brassica napus L., cv. Mercedes) was field-grown under elevated soil temperature (+2.5 &deg, C), reduced precipitation amount (&minus, 25%), reduced precipitation frequency (&minus, 50%) both separately and in combination in order to investigate effects on crop development, seed yield, and seed quality. Soil warming accelerated crop development during early plant growth and during spring. At maturity, however, plants in all treatments were similar in quantitative (aboveground biomass, seed yield) and qualitative (protein and oil content, amino acids, fatty acids) parameters. We observed the long-term effects of the precipitation manipulation on leaf size, leaf senescence and biomass allocation. Seed yield was not affected by the altered climatic factors, perhaps due to adaptation of soil microorganisms to permanent soil warming and to relatively wet conditions during the seed-filling period. Overall, OSR performed well under moderate changes in soil temperature and precipitation patterns, thus, we observed stable seed yield without negative impacts on nutritive seed quality.

Soil organic carbon (SOC) losses under a changing climate are driven by the temperature sensitivity of SOC mineralization (usually expressed as Q10, the multiplier of activity with 10 °C temperature increase). The activation energy theory (AET) suggests that, due to higher activation energies, the more complex the carbon, the higher is mineralization Q10. However, studies on Q10 have been inconsistent with regard to AET. Measurements of potential soil enzymes activity Q10 even contradicted AET: Phenoloxidase (representing complex carbon) had consistently lower Q10 than the more labile xylanase and glucosidase. This study used two approaches of examining Q10 in SOC modeling: 1) Bayesian calibration (BC) and 2) using different measured enzyme Q10 as proxies for mineralization Q10 of different SOC pools. The SOC model was DAISY (S. Hansen et al., 2012). BC informed Q10 by field measured data, while the second approach tested if directly using enzyme Q10 (of phenoloxidase, glucosidase and xylanase) for DAISY pools improved simulation results. Both approaches used the temperature sensitive measurements of CO2 evolution and soil microbial biomass. The measured enzyme Q10 were from field manipulation experiments with bare fallow and vegetated plots in the two regions of Kraichgau and Swabian Jura in Southwest Germany. The enzyme-derived Q10 were used for modelling those fields and furthermore for in‑situ litterbag decomposition experiments at 20 sites in the same region. Two further laboratory experiments with temperature manipulation were included: an incubation of the field residues into soil and an incubation of bare soil from the start and year 50 of a long duration bare fallow (from Ultuna). The BC made use of CO2 and microbial data to inform about the range of Q10 of different carbon pools for the individual experiments and combined data.The BC of the residue incubation experiment constrained Q10 for metabolic (~3) and structural litter (~2). Estimated 95% credibility intervals did not overlap. The BC for Ultuna could constrain the slow and fast SOC pool with Q10 ~2.8 and ~3, respectively, but credibility intervals of both pools overlapped. The Q10 of field experiments, which had most abundant data, could not be constrained by BC, probably because their annual temparature variability was too low. However, the model errors of the field experiment could be reduced by the second approach, when the Q10 of phenoloxidase was used for to the structural litter pool as well as for the fast and slow SOC pools. Thus regional enzyme Q10 improved the model fit but only for regional simulations. Therefore, they could be useful proxies when natural temperature range is too small to inform temperature sensitivity by BC. Any trends found in this study contradicted AET, both from measured enzymes and BC of the incubation experiments. This calls for alternative Q10 hypotheses and the need for individual Q10 values for different SOC pool rather than a general one. BC approaches would benefit from a wider temperature range of field experiments and understanding what causes variable enzyme Q10 could help to improve future SOC models.

Rising demand for solar power generation will lead to increased land use competition, and thus to potential economic and social conflict. A solution to this challenge is to produce food and energy within an agrophotovoltaics (APV) system. Since 2017, governments in Japan, France, Massachusetts (USA), South Korea, and China have introduced policies supporting APV implementation. Governments considering APV implementation – e.g. in India and Germany – for evidence-based policy making are demanding information on how levelized cost of electricity (LCOE) of APV differs from that of conventional ground-mounted photovoltaics (PV), as well as on how additional costs associated with APV installation relate to the benefit of maintaining agricultural activity under APV. Data for a techno-economic price-performance ratio calculation has been retrieved from an inter- and transdisciplinary APV case study in Germany. We observed that the LCOE of APV with €0.0828 kWh−1 is 38% higher than that of ground-mounted PV, resulting in an annual cropland preservation price of €9,052 ha−1 a−1. The annual revenue of potato and winter wheat production under APV resulted in a performance of €10,707 ha−1 a−1 and €1,959 ha−1 a−1 respectively, leading to a beneficial price-performance ratio of 0.85 for potato production and, with a ratio of 4.62, a disadvantageous result for winter wheat. Overall, APV is not necessarily recommended in crop rotating systems. However, in combination with permanent cultures – e.g. berries, fruits, or wine grapes – as the price for these types of applications is lower, while at the same time providing higher performance by optimizing techno-ecological synergies.

Interactions between vegetation and atmosphere have a large impact on weather and climate. During the last decade, enormous efforts have been made to improve the representation of vegetation dynamics in land surface models (LSM). The present study extends the LSM Noah-MP by the dynamic crop growth model Gecros that enables simulating the development of crop stands in a weather-driven manner. This extension is a pre-requisite to simulate two-way climate-crop interactions in climate projections. Based on a comprehensive five-year dataset on energy- and water fluxes, and soil water and crop data from two different climate regions of southwest Germany, we adapted the crop growth model Gecros, integrated it with Noah-MP, calibrated the coupled model for winter wheat and maize and tested its robustness in multiple-year validation runs against independent measurements. This sound data set yielded a robust parameterization that performed well both in calibration and in validation runs over in total 16 seasons. Due to pronounced differences in phenology among maize cultivars, wheat simulations were better than maize simulations. The simulated dynamics in leaf area index of wheat and maize differed largely from the one used in standard Noah-MP simulations. The new model yielded pronounced differences in the partitioning of evapotranspiration into transpiration and soil evaporation. The added value of the improved description of vegetation dynamics needs to be evaluated in high-resolution coupled crop-climate simulations in future.

The spatial variability of topsoil water content (SWC) is often expressed through the relationship between its spatial mean 〈θ〉 and standard deviation σθ. The present study tests the concept that a reasonably performing land surface model (LSM) should be able to produce σθ–〈θ〉 data pairs that fall into a polygon, spanned by the cloud of observed data and two anchor points: σθ at the permanent wilting point σθ–〈θwp〉 and σθ at saturation σθ–〈θs〉. A state-of-the-art LSM, Noah-MP, was driven by atmospheric forcing data obtained from eddy covariance field measurements in two regions of southwestern Germany, Kraichgau (KR) and Swabian Alb (SA). KR is characterized with deep loess soils, whereas the soils in SA are shallow, clayey, and stony. The simulations series were compared with SWC data from soil moisture networks operating in the two study regions. The results demonstrate that Noah-MP matches temporal 〈θ〉 dynamics fairly well in KR, but performs poorly in SA. The best match is achieved with the van Genuchten–Mualem representation of soil hydraulic functions and site-specific rainfall, soil texture, green vegetation fraction (GVF) and leaf area index (LAI) input data. Nevertheless, most of the simulated σθ–〈θ〉 pairs are located outside the envelope of measurements and below the lower bound, which shows that the model smooths spatial SWC variability. This can be mainly attributed to missing topography and terrain information and inadequate representation of spatial variability of soil texture and hydraulic parameters, as well as the model assumption of a uniform root distribution.

CONTEXT Dual land-use systems allow for a high land-use efficiency and are becoming increasingly relevant amid the rising scarcity of land. Agrivoltaics is a prominent example, yet there are farming system-specific trade-offs when simultaneously producing agricultural output and photovoltaic power. OBJECTIVE Our objective is to report a novel analytical F ramework to assess the E conomic benefits and the AD option P otential of dual L and- U se S ystems (FEADPLUS). The framework is developed with the goal of enabling a straightforward application in large farm-level datasets. METHODS FEADPLUS is grounded in neoclassical economic theory and applied to the case of agrivoltaics. An annualized profitability condition is derived and decomposed to identify the main components determining the agrivoltaic systems' economic viability, allowing for a comprehensive analysis of farm-specific synergies and trade-offs. Modifications enable calculation of the break-even electricity tariff and the relative change in agricultural contribution margin below the agrivoltaic system. The framework's functionality is demonstrated using data for cereal and vegetable farming systems on the Filder Plain, Southern Germany. RESULTS AND CONCLUSIONS We show that farm-specific characteristics explain differences in the adoption potential under equal solar radiations. Cereal and vegetable farms could adopt agrivoltaics at a tariff of 8.63 and 9.00 EUR-cents kWh−1, respectively. Yet, the agricultural contribution margins from land cultivated below the agrivoltaics system decline by 40.3% and 73.9%, respectively. The decline is due to shading effects on crop yields, higher machinery and labor costs, and the foregone agricultural contribution margins from area lost due to the agrivoltaics mounting structure. In the presence of such trade-offs, the adoption of agrivoltaics is more profitable for farms growing low-value crops, such as cereals, than high-value crops like vegetables. Our sensitivity analyses show that this may change if there are synergies, e.g., positive shading effects on yield. Moreover, they indicate that agricultural contribution margins in some scenarios, which could incentivize farmers to abandon farming below the agrivoltaics system. This highlights the need for policymakers to put adequate safeguards in place. SIGNIFICANCE Dual land-use systems are still understudied, but their high land-use efficiency becomes increasingly relevant in light of the mounting pressures on land. FEADPLUS is the first framework that allows estimation of economic benefits and adoption potential across farming systems and specific technology setups under different policy designs. To this end, it meets researchers' demands for a simple tool and allows for many extensions, e.g., incorporation of stochastics or aspects of (dynamic) optimization and economies of scale.

HOSUT wheat, enhanced in grain sucrose transport, has a superior performance for yield-related traits, partially phenocopies effects from CO2 enrichment, and benefits more from high N fertilization., Crop yield stability must be ensured under future climate conditions such as elevated CO2 and high temperatures. We tested ‘HOSUT’, a winter wheat line expressing a grain-targeted sucrose transporter of barley in response to combinations of CO2 enrichment, a heat wave, and high nitrogen fertilization. Compared with wild-type Certo, HOSUT had a superior performance for grain yield, aboveground biomass, and ears per plant, obviously due to transgene activity in developing grains and young vegetative sinks. HOSUT grains were larger and contained more endosperm cells. HOSUT and high CO2 effects similarly improved phenological and yield-related traits. Significant HOSUT–CO2 interactions for biomass of stems, ears, grain yield, nitrogen yield, and grain number revealed that Certo was promoted by CO2 enrichment, whereas HOSUT responded weakly. CO2 enrichment strongly reduced and HOSUT effects weakly reduced grain nitrogen, storage proteins, and free amino acids. In contrast to CO2 enrichment, HOSUT effects did not impair grain micronutrient concentrations. Significant HOSUT–nitrogen fertilization interactions for ear biomass, grain yield, grain number per plant, and harvest index indicated that HOSUT benefited more from additional nitrogen. The heat wave decreased aboveground and ear biomass, grain yield, harvest index, grain size, and starch and water use, but increased grain sucrose concentration.

Elevated carbon dioxide (eCO2) is well known to stimulate plant photosynthesis and growth. Elevated carbon dioxide&rsquo, s effects on crop yields are of particular interest due to concerns for future food security. We compiled experimental data where field-grown wheat (Triticum aestivum Linnaeus) was exposed to different CO2 concentrations. Yield and yield components were analyzed by meta-analysis to estimate average effects, and response functions derived to assess effect size in relation to CO2 concentration. Grain yield increased by 26% under eCO2 (average ambient concentration of 372 ppm and elevated 605 ppm), mainly due to the increase in grain number. The response function for grain yield with CO2 concentration strongly suggests a non-linear response, where yield stimulation levels off at ~600 ppm. This was supported by the meta-analysis, which did not indicate any significant difference in yield stimulation in wheat grown at 456&ndash, 600 ppm compared to 601&ndash, 750 ppm. Yield response to eCO2 was independent of fumigation technique and rooting environment, but clearly related to site productivity, where relative CO2 yield stimulation was stronger in low productive systems. The non-linear yield response, saturating at a relatively modest elevation of CO2, was of large importance for crop modelling and assessments of future food production under rising CO2.

International audience; AbstractThe expansion of renewable energies aims at meeting the global energy demand while replacing fossil fuels. However, it requires large areas of land. At the same time, food security is threatened by the impacts of climate change and a growing world population. This has led to increasing competition for limited land resources. In this context, the combination of photovoltaics and plant production — often referred to as agrophotovoltaic (APV) or agrivoltaic systems — has been suggested as an opportunity for the synergistic combination of renewable energy and food production. Although this technology has already been applied in various commercial projects, its practicability and impact on crop production have hardly been investigated. In this review, we give a short summary of the current state of the art and prospective opportunities for the application of APV systems. In addition, we discuss microclimatic alterations and the resulting impacts of APV on crop production. Our main findings are that (1) crop cultivation underneath APV can lead to declining crop yields as solar radiation is expected to be reduced by about one third underneath the panels. However, microclimatic heterogeneities and their impact on crop yields are missing reference and thus, remain uncertain. (2) Through combined energy and crop production, APV can increase land productivity by up to 70%. (3) Given the impacts of climate change and conditions in arid climates, potential benefits are likely for crop production through additional shading and observed improvements of water productivity. (4) In addition, APV enhances the economic value of farming and can contribute to decentralized, off-grid electrification in developing and rural areas, thus further improving agricultural productivity. As such, APV can be a valuable technical approach for more sustainable agriculture, helping to meet current and prospective needs of energy and food production and simultaneously sparing land resources.

Agrivoltaic (AV) systems increase land productivity through the combined production of renewable energy and food. Although several studies have addressed their impact on crop production, many aspects remain unexplored. The objective of this study was to determine the effects of AV on the cultivation of celeriac, a common root vegetable in Central Europe. Celeriac was cultivated in 2017 and 2018 as part of an organically managed on-farm experiment, both underneath an AV system and in full-sun conditions. Under AV, photosynthetic active radiation was reduced by about 30%. Monitoring of crop development showed that in both years, plant height increased significantly under AV. Fresh bulb yield decreased by about 19% in 2017 and increased by about 12% in 2018 in AV, but the changes were not significant. Aboveground biomass increased in both years under AV, but only increased significantly in 2018. As aboveground biomass is a determinant of root biomass at harvest in root vegetables, bulb yields may be further increased by a prolonged vegetation period under AV. Compound analysis of celeriac bulbs did not show any clear effects from treatment. As harvestable yields were not significantly reduced, we concluded that celeriac can be considered a suitable crop for cultivation under AV.

Combining agriculture and photovoltaics on the same land area gains in attention and political support in a growing number of countries accompanied by notable research activities in France, USA and Korea, amongst others. This study assesses the technical feasibility of agrivoltaic (APV), while it gives insights on how to design an APV system. Furthermore, it analyses the electrical yield and the behavior and productivity of four crops grown in Germany's largest agrivoltaic research facility installed in 2016 near Lake Constance within the research project APV-RESOLA by Fraunhofer Institute for Solar Energy Systems ISE. The German design differs from most other agrivoltaic approaches by allowing for a wide range of machine employment, facilitated by a vertical clearance of 5 m and a width clearance of up to 19 m. Crops cultivated under the APV system and on the reference field under a crop rotation scheme include potato, celeriac, clover grass and winter wheat. The land use efficiency measured by the Land Equivalent Ratio (LER) indicated a rise between 56% and 70% in 2017 while the dry and hot summer in 2018 demonstrated that the agrivoltaic system could increase land productivity by nearly 90%. Radiation simulations showed that deviating from full south by around 30° resulted in equal distribution of radiation on ground level, representing the basis for the agrivoltaic design. Considering climate change and increasing land scarcity, our overall results suggest a high potential of agrivoltaics as a viable and efficient technology to address major challenges of the 21rst century.

The direction and magnitude of change of soil organic carbon (SOC) stocks due to global warming depend strongly on the temperature sensitivity (e.g., Q10) of carbon mineralization. To date, most multi-pool SOC models assume a general Q10 of 2 despite experimental evidence suggesting different Q10 for different carbon fractions. The aim of this study was to test if the use of experimentally derived pool specific Q10 values improves the performance of SOC models. Five contrasting data sets from three field experiments and two laboratory incubations were used to study the link between carbon pool recalcitrance and Q10 using two different approaches: a) Bayesian calibration of the Daisy SOC model parameters to infer Q10 of SOC and crop-litter pools, and b) using measured Q10 values of carbon degrading enzymes as proxies for Q10 of different Daisy pools. Namely β-glucosidase (median Q10 of 1.82) was assigned to metabolic litter and phenol/peroxidase (1.35) to structural litter and both SOC pools. To partition litter-carbon and SOC into model pools, the lignin-to-nitrogen ratio and the ratio of aliphatic/aromatic-carboxylate carbon were used, respectively. Measurements included soil microbial biomass, soil carbon dioxide (CO2) evolution and remaining carbon in soils and crop-litter. In the Bayesian calibration, strong differences in inferred Q10 values of the same pools between experiments suggested that intrinsic substrate recalcitrance was not the main driver of temperature sensitivity. For field experiment simulations, both the Q10 values derived by Bayesian calibration and measured enzyme Q10 were centered around values below 2, contrasting with high Q10 values for mineralization under laboratory incubations (close to 3). Furthermore, assigning measured phenol/peroxidase Q10 values to the slow crop-litter as well as both SOC pools and β-glucosidase to the fast crop-litter pool (approach b), could significantly improve model performance compared to using the default Q10 value of 2 for all pools. Root-mean-squared-deviation reductions were between 3 and 10% for field experiments, with no change in the laboratory experiments. Thus, site specific Q10 values of soil enzymes show potential as proxies for pool specific Q10. We present a new conceptual framework to explain the observed differences in temperature sensitivities between experiments as a result of two fundamental driving factors classified in a) state variables, that fluctuate in time, and b) soil properties, that are constant over decades. Measured enzyme Q10 values were interpreted as a proxy incorporating both factors. More than intrinsic substrate recalcitrance, the state variables such as physical protection, substrate abundance and unfavorable conditions for microorganisms control temperature sensitivity of mineralization. To reduce the uncertainty in global SOC simulations under a changing climate, their relative contributions should be disentangled and then implemented into SOC models.

The amendment of biochar to agricultural soils is presumed to mitigate global warming through long-term carbon (C) sequestration. In addition, biochar may support microbial biomass and diversity as well as plant growth by the improvement of soil properties. So far, no information is available on the stability of biochar and the effects of biochar on soil microbial and plant properties under predicted soil warming at the field scale. We investigated the impacts of biochar addition (Miscanthus pyrochar, 30 t ha−1, August 2013) and long-term soil warming (+2.5 °C, since July 2008) and their interactive effects on microbial biochar-C utilization and physical, chemical and microbial soil properties of a silty-loamy stagnic Luvisol in a temperate agroecosystem (Stuttgart, Germany) over one year under winter rapeseed (Brassica napus). Three months after biochar application (November 2013), microbial abundances remained unaffected, indicating that readily available C from fresh biochar had been consumed before sampling. However, we found evidence for initial decomposition of more recalcitrant biochar-C by fungi under soil warming after three months. We suggest that the added biochar was very stable, since increased biochar degradation by fungi could not be detected after seven and twelve months. Nevertheless, during spring 2014, biochar reduced water loss in warmed soil by 16 % and decreased negative effects of soil dryness on microbial abundances by up to 80 %. In addition, the positive effect of biochar on soil moisture affected canopy height of winter rapeseed in the non-warmed plots in the early growth stages, although it did not change the final aboveground biomass in the first year after biochar application. Overall, biochar could be an appropriate tool for C sequestration by improving or maintaining soil fertility and productivity in temperate agroecosystems under future elevated temperatures.

The energy balance of eddy covariance (EC) measurements is typically not closed. This so-called energy balance closure (EBC) problem has been a long-standing issue in micrometeorology. It is a main challenge in evaluating and interpreting EC flux data. EBC is crucial for validating and improving regional and global climate models. To investigate the reasons behind EBC more closely for agro-ecosystems, we analysed EC measurements from two climatically contrasting regions (Kraichgau (KR) and Swabian Jura (SJ)) in southwest Germany. Data were taken at six fully equipped EC sites from 2010 to 2017. The gap in EBC was quantified by ordinary linear regression, by the energy balance ratio (EBR) between turbulent fluxes and available energy, and by the residual energy term. In order to examine potential reasons for differences in EBC, we compared the EBC under varying environmental conditions and investigated a wide range of possible controls. Statistical analyses were conducted for the whole data set to test the effects of different regions, years, sites and crops on EBC. We also investigated whether EBC was a function of buoyancy, friction velocity, or atmospheric stability. The time-variable footprints of all EC stations were estimated based on data measured in 2015, complemented by micro-topographic analyses along the prevailing wind direction. The lowest mean annual energy balance gap was 17 % in KR and 13 % in SJ. Highest EBRs were commonly measured for winds originating from the prevailing wind direction. The variation of EBC was higher in winter than in summer. The measurement site exerted a statistically significant effect on EBC, but not crop or region. The spread of EBR distinctly narrowed under unstable atmospheric conditions, strong buoyancy, and high friction velocities. Smaller footprint areas led to better EBC due to increasing homogeneity. Flow distortions of winds that first travelled past the back head of the anemometer affected EBC negatively.

Elevated CO

Spring wheat plants were grown under two CO

The energy balance of eddy covariance (EC) flux data is normally not closed. Therefore, at least if used for modeling, EC flux data are usually post-closed, i.e. the measured turbulent fluxes are adjusted so as to close the energy balance. At the current state of knowledge, however, it is not clear how to partition the missing energy in the right way. Eddy flux data therefore contain some uncertainty due to the unknown nature of the energy balance gap, which should be considered in model evaluation and the interpretation of simulation results. We propose to construct the post-closure method uncertainty band (PUB), which essentially designates the differences between non-adjusted flux data and flux data adjusted with the three post-closure methods (Bowen ratio, latent heat flux (LE) and sensible heat flux (H) method). To demonstrate this approach, simulations with the NOAH-MP land surface model were evaluated based on EC measurements conducted at a winter wheat stand in Southwest Germany in 2011, and the performance of the Jarvis and Ball–Berry stomatal resistance scheme was compared. The width of the PUB of the LE was up to 110 W m–2 (21% of net radiation). Our study shows that it is crucial to account for the uncertainty of EC flux data originating from lacking energy balance closure. Working with only a single post-closing method might result in severe misinterpretations in model-data comparisons.

Susceptibility of crops to drought may change under atmospheric CO2 enrichment. We tested the effects of CO2 enrichment and drought on the older malting barley cultivar Golden Promise (GP) and the recent variety Bambina (BA). Hypothesizing that CO2 enrichment mitigates the adverse effects of drought and that GP shows a stronger response to CO2 enrichment than BA, plants of both cultivars were grown in climate chambers. Optimal and reduced watering levels and two CO2 concentrations (380 and 550 ppm) were used to investigate photosynthetic parameters, growth and yield. In contrast to expectations, CO2 increased total plant biomass by 34 % in the modern cultivar while the growth stimulation was not significant in GP. As a reaction to drought, BA showed reduced biomass under elevated CO2, which was not seen in GP. Grain yield and harvest index (HI) were negatively influenced by drought and increased by CO2 enrichment. BA formed higher grain yield and had higher water-use efficiency of grain yield and HI compared to GP. CO2 fertilization compensated for the negative effect of drought on grain yield and HI, especially in GP. Stomatal conductance proved to be the gas exchange parameter most sensitive to drought. Photosynthetic rate of BA showed more pronounced reaction to drought compared to GP. Overall, BA turned out to respond more intense to changes in water supply and CO2 enrichment than the older GP.

Data from three Swedish open-top chamber and four German FACE experiments were combined to derive response functions for elevated CO2 (eCO2) effects on Cd, Zn, Mn, protein, grain yield, grain mass and grain number of wheat. Grain yield and grain number were increased by ∼6% and ∼7%, respectively, per 100 ppm CO2; the former effect was linked to plant nitrogen status. Grain mass was not influenced by eCO2, whereas Cd concentration was reduced. Unlike Zn, Mn and protein, effects on Cd yield were not related to effects on grain yield. Yields of Mn, Zn and (weakly) protein were positively affected by eCO2. For protein, grain yield, grain mass and grain number, the results were consistent among the FACE and OTC experiments. A key conclusion was that yields of essential nutrients were enhanced (Mn > Zn > protein), although less than grain yield, which would not be expected from a simple dilution model.

Increasing concentrations of carbon dioxide and heavy metals in soils through pollution are serious problems worldwide. In the present study, we investigated the impacts of elevated atmospheric CO2 and fly ash (FA)-amended soil on the physiological response (chlorophyll content, non-structural carbohydrates, oil and total proteins) of soybean [Glycine max (L.) Merrill] at three growth stages (vegetative, reproductive and maturity). An increase in plant growth and biomass was observed at elevated CO2 and for moderate concentrations of FA in amended soils in all development plant stages. In contrast to these results, a different response pattern was found for the chlorophyll content and non-structural carbohydrates in relation to the developmental stage, showing that even though in the vegetative growth stage the highest concentration of chlorophylls corresponded to elevated CO2 conditions. An opposite result was observed during the grainfilling stage (reduction of chlorophylls of 15 % at ambient CO2 conditions for the treatments 10, 15, and 25 % of FA), which probably is related with the distribution of nutrients at this stage. Regarding to oil and total protein content an increase was observed at elevated CO2 and high concentrations of FA in amended soils. Our findings demonstrate that elevated CO2 and FA-amended soils alter the physiological response of soybean affecting the crop quality. Fil: Rodriguez, Judith Hebelen. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto Multidisciplinario de Biología Vegetal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto Multidisciplinario de Biología Vegetal; Argentina Fil: Klumpp, Andreas. Universidad de Hohenheim. Instituto de Paisaje y Ecologia Vegetal. Especialidad En Ecologia Vegetal y Ecotoxicologia; Alemania Fil: Högy, Petra. Universidad de Hohenheim. Instituto de Paisaje y Ecologia Vegetal. Especialidad En Ecologia Vegetal y Ecotoxicologia; Alemania Fil: Fangmeier, Andreas. Universidad de Hohenheim. Instituto de Paisaje y Ecologia Vegetal. Especialidad En Ecologia Vegetal y Ecotoxicologia; Alemania Fil: Maestri, Damian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Córdoba. Instituto Multidisciplinario de Biología Vegetal (p); Argentina Fil: Lamarque, Alicia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto Multidisciplinario de Biología Vegetal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto Multidisciplinario de Biología Vegetal; Argentina Fil: Labuckas, Diana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto Multidisciplinario de Biología Vegetal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto Multidisciplinario de Biología Vegetal; Argentina Fil: Pignata, María Luisa. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto Multidisciplinario de Biología Vegetal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto Multidisciplinario de Biología Vegetal; Argentina

Reliable regional climate projections need improved land-surface-atmosphere models in which land-surface exchange, in particular the role of the vegetation, is well represented. To get a better understanding of the land-surface exchange and as a data basis for model development, parameterization and validation, long-term eddy-covariance measurements were performed over agricultural landscapes in two regions of Southwest Germany with different regional climate: near the northern Upper Rhine Valley with a mild climate and on the Swabian Jura, a low mountain range plateau where the climate is colder and wetter. At each study site we installed three eddy-covariance weather stations and monitored the soil water regime as well as the crop development. We describe the characteristics of the study sites, the experimental field work and data processing. The dynamics of water vapor and energy fluxes over winter wheat, winter oilseed rape and silage maize were evaluated for the time period from 2009 to 2011. The accuracy of the measured energy and matter fluxes limited by statistics and instrumental noise error was better than 10 %. Energy fluxes and albedo were closely linked to crop development. The albedo increased and decreased with LAI. Albedo values up to 0.28 were measured over flowering oilseed rape. The winter crops developed faster in the milder climate. The daily average of latent heat flux was about 10–20 Wm−2 higher and that of sensible heat flux about 5–15 Wm−2 lower there in comparison with the colder climate. Differences between both regions with regard to the turbulent fluxes are assigned to be mainly due to differences in vapor pressure deficit. Actual and prevailing weather conditions had a large impact on energy fluxes so that notable differences of flux dynamics were observed not only between the regions but also at one site for the same crop in different years. The observed long-term flux dynamics are discussed with respect to phenology, regional climate and the impact of prevailing weather conditions.

In agricultural production, land-use decisions are components of economic planning that result in the strategic allocation of fields. Climate variability represents an uncertainty factor in crop production. Considering yield impact, climatic influence is perceived during and evaluated at the end of crop production cycles. In practice, this information is then incorporated into planning for the upcoming season. This process contributes to attitudes toward climate-induced risk in crop production. In the literature, however, the subjective valuation of risk is modeled as a risk attitude toward variations in (monetary) outcomes. Consequently, climatic influence may be obscured by political and market influences so that risk perceptions during the production process are neglected. We present a utility concept that allows the inclusion of annual risk scores based on mid-season risk perceptions that are incorporated into field-planning decisions. This approach is exemplified and implemented for winter wheat production in the Kraichgau, a region in Southwest Germany, using the integrated bio-economic simulation model FarmActor and empirical data from the region. Survey results indicate that a profitability threshold for this crop, the level of "still-good yield" (sgy), is 69 dt ha-1 (regional mean Kraichgau sample) for a given season. This threshold governs the monitoring process and risk estimators. We tested the modeled estimators against simulation results using ten projected future weather time series for winter wheat production. The mid-season estimators generally proved to be effective. This approach can be used to improve the modeling of planning decisions by providing a more comprehensive evaluation of field-crop response to climatic changes from an economic risk point of view. The methodology further provides economic insight in an agrometeorological context where prices for crops or inputs are lacking, but farmer attitudes toward risk should still be included in the analysis.

Elevated carbon dioxide (eCO2) stimulates wheat grain yield, but simultaneously reduces protein/nitrogen (N) concentration. Also, other essential nutrients are subject to change. This study is a synthesis of wheat experiments with eCO2, estimating the effects on N, minerals (B, Ca, Cd, Fe, K, Mg, Mn, Na, P, S, Zn), and starch. The analysis was performed by (i) deriving response functions to assess the gradual change in element concentration with increasing CO2 concentration, (ii) meta-analysis to test the average magnitude and significance of observed effects, and (iii) relating CO2 effects on minerals to effects on N and grain yield. Responses ranged from zero to strong negative effects of eCO2 on mineral concentration, with the largest reductions for the nutritionally important elements of N, Fe, S, Zn, and Mg. Together with the positive but small and non-significant effect on starch concentration, the large variation in effects suggests that CO2-induced responses cannot be explained only by a simple dilution model. To explain the observed pattern, uptake and transport mechanisms may have to be considered, along with the link of different elements to N uptake. Our study shows that eCO2 has a significant effect on wheat grain stoichiometry, with implications for human nutrition in a world of rising CO2.

Elevated carbon dioxide (eCO2) stimulates wheat grain yield, but simultaneously reduces protein/nitrogen (N) concentration. Also, other essential nutrients are subject to change. This study is a synthesis of wheat experiments with eCO2, estimating the effects on N, minerals (B, Ca, Cd, Fe, K, Mg, Mn, Na, P, S, Zn), and starch. The analysis was performed by (i) deriving response functions to assess the gradual change in element concentration with increasing CO2 concentration, (ii) meta-analysis to test the average magnitude and significance of observed effects, and (iii) relating CO2 effects on minerals to effects on N and grain yield. Responses ranged from zero to strong negative effects of eCO2 on mineral concentration, with the largest reductions for the nutritionally important elements of N, Fe, S, Zn, and Mg. Together with the positive but small and non-significant effect on starch concentration, the large variation in effects suggests that CO2-induced responses cannot be explained only by a simple dilution model. To explain the observed pattern, uptake and transport mechanisms may have to be considered, along with the link of different elements to N uptake. Our study shows that eCO2 has a significant effect on wheat grain stoichiometry, with implications for human nutrition in a world of rising CO2.

The carbon (C) isotope signature of solid materials such as plants and soil, or gaseous samples (atmospheric or soil air), can be used as a useful tool for investigations of the C cycle. In gaseous samples, stability of δ13C of carbon dioxide (CO2) in air during storage represents a problem. We tested the long-term storage effect of δ13C originated from CO2 in vials both capped with butyl or butyl coated with polytetrafluoroethylene (PTFE) on the internal surface. Therefore, pure CO2, depleted in 13C, was stored for up to 736 days. In addition, the relevance of long-term storage for ecological soil air data collected from a free-air CO2 enrichment (FACE) experiment located in Stuttgart (Germany) during one growing period with a maximum storage period of 210 days was judged. With increasing storage time, a change in isotopic composition towards less depleted δ13C was observed. The changes in δ13C were highest at the beginning of the storage period and decreased over time, which could be described with an asymptotic model. The maximum change in δ13C was less than 2 ‰ and lower for vials capped with butyl/PTFE septa. In the FACE experiment, the comparison between corrected and uncorrected data showed that δ13C originated from soil air changed within this data set by up to 1 ‰. The calculation of the fraction of plant derived C resulted in an underestimation of up to 10 %. The storage effect should be taken into consideration when interpreting δ13C values in order to avoid miscalculations.

Interactions between the soil, the vegetation, and the atmospheric boundary layer require close attention when predicting water fluxes in the hydrogeosystem, agricultural systems, weather, and climate. However, land-surface schemes used in large-scale models continue to show deficiencies in consistently simulating fluxes of water and energy from the subsurface through vegetation layers to the atmosphere. In this study, the multiphysics version of the Noah land-surface model (Noah-MP) was used to identify the processes, which are most crucial for a simultaneous simulation of water and heat fluxes between land surface and the lower atmosphere. Comprehensive field data sets of latent and sensible heat fluxes, ground heat flux, soil moisture, and leaf area index from two contrasting field sites in South-West Germany are used to assess the accuracy of simulations. It is shown that an adequate representation of vegetation-related processes is the most important control for a consistent simulation of energy and water fluxes in the soil-plant-atmosphere system. In particular, using a newly implemented submodule to simulate root growth dynamics has enhanced the performance of Noah-MP. We conclude that further advances in the representation of leaf area dynamics and root/soil moisture interactions are the most promising starting points for improving the simulation of feedbacks between the subsoil, land surface and atmosphere in fully coupled hydrological and atmospheric models.

[1] Six models with differing representation of the physical process in the coupled soil-plant system are tested to simultaneously reproduce the dynamics of soil water contents, evapotranspiration, and leaf area index during a growing season of winter wheat at two contrasting field plots in the Kraichgau and the Swabian Alb regions in South-West Germany. The main aim of the study is the assessment of the performance and the identification of structural deficits of the models LEACHN, SUCROS, CERES, GECROS, and SPASS as well as the land-surface model CLM3.5. The calibration of each model is posed in a multiobjective framework with three different objective functions that summarize the fit between model simulations and the three observation types. The AMALGAM evolutionary search algorithm is utilized to simultaneously estimate the most important soil hydraulic and plant parameters. The six models exhibit a wide variability in the trade-offs between the fitting to the data types. Mechanistic process description, particularly of the root system, reduces the trade-off considerably for the SPASS and GECROS models. These models adequately simulate the reduction of root water uptake and transpiration during senescence under nonlimited soil water supply. The SPASS model in particular shows an overall better performance as compared to the more simpler models which is related to an adequate level of structural complexity in the interplay of all model compartments combined with a relatively low parameter sensitivity to the weighting scheme in the multiobjective optimization. The dynamic consideration of the root system formation is particularly important, which is simulated quite detailed in the SPASS model as a function of nitrogen (N) and water availability in the different soil horizons. The proposed multiobjective calibration procedure proved to be very useful to identify processes that are important to adequately simulate the coupled soil-plant system. The consideration of these processes and our insights about the value of different data types for model calibration is expected to lead to more accurate, predictive land-surface models.

In this study, we developed and analyzed a new model for the simulation of photosynthetic active nitrogen ( N P ) turnover dynamics in crops and assessed its impact on the acclimation of canopy photosynthesis to atmospheric CO 2 enrichment. Typical canopy models assume a vertical exponential decline of light interception following the Beer–Lambert law and vertical distributions of leaf N P contents directly proportional to the light distribution. This assumption is often inconsistent with experimental observations. We therefore modified and extended the photosynthesis model of the GECROS crop model to consider the trade-off that occurs between the use of degraded N P for plant growth and the synthesis of new N P . This model extension thus enabled the examination of the CO 2 -induced down-regulation of photosynthesis hypothesis using a crop model. The simulation results of the original and modified GECROS model were compared and evaluated based upon measurements of field-grown spring wheat. The modified GECROS model better simulated the dynamics of crop growth under varying atmospheric CO 2 concentrations. Furthermore, the application of different temperature functions to N P degradation strongly influenced the simulation results, revealing the necessity for improving the understanding of the temperature dependence of N P turnover for different crop species and varieties. In conclusion, the redistribution of nitrogen within the plant and its alternative use either for growth or the optimization of the photosynthetic apparatus is an important mechanism for crop growth acclimation to regionally changing climatic conditions and in particular, atmospheric CO 2 enrichment.

Spring wheat (Triticum aestivum L. cv. Triso) was grown in a free-air carbon dioxide (CO2) enrichment (FACE) system at Stuttgart–Hohenheim (Germany) in 2008 to examine effects on crop yield and grain quality. Elevated CO2 had no significant impacts on aboveground biomass and grain yield components except for an increase in thousand grain weight by 5.4% with size distribution shifted towards larger grains. Total grain protein concentration decreased by 7.9% under CO2 enrichment, and protein composition was altered. Total gliadins and their single types (ω5-gliadins, ω1,2-gliadins, α-gliadins, and γ-gliadins) were reduced, while albumins/globulins, total glutenins and their subunits were not influenced. The gluten proteins (gliadins plus glutenins) were lowered by 11.3% in the high-CO2 treatment, whereas proportions of gluten protein types were slightly affected as only ω1,2-gliadins decreased. Accordingly, all proteinogenic amino acids were decreased by 4.2 to 7.9% in concentrations per unit flour mass, although partly below the level of statistical significance. In contrast, the composition of amino acids on a per protein basis remained unaffected except for a decline in serine. Among the minerals, the concentrations of calcium, magnesium, iron and cobalt decreased, while an increase was observed for boron. The concentrations of total non-structural carbohydrates and starch decreased, whereas fructose, raffinose and fructan increased. Total lipid concentration remained unaffected by the CO2 enrichment, whereas the grain carbon/nitrogen relation was increased by 8.5%. Implications may occur for consumer nutrition and health, and for industrial processing, thus breeding of new wheat cultivars that exploit CO2 fertilisation and maintain grain quality properties is regarded as one potential option to assure the supply chain for the future.