- Effects from climate change, adaptations and
greenhouse gas reduction at 2050

Abstract:

Overview of the model setup for the Giessen FACE grassland ecosystem, including preliminary simulation results for CO2 emissions and outlook.

Abstract:

Rising atmospheric CO2 concentrations are expected to increase nitrous oxide (N2O) emissions from soils via changes in microbial nitrogen (N) transformations triggering a positive feedback reaction that could accelerate climate change. Several studies have shown N2O emission increases under elevated atmospheric CO2 (eCO2), but the underlying processes are not yet fully understood. Here we present results showing changes in soil N transformation dynamics from the Giessen Free Air CO2 Enrichment (GiFACE): a permanent grassland that has been exposed to eCO2, +20% relative to ambient concentrations (aCO2), for 15 years. We applied in the field an ammonium-nitrate fertilizer solution, in which either ammonium (NH4+) or nitrate (NO3-) was labelled with 15N. The simultaneous gross N transformation rates were analysed with a 15N tracing model and a solver method. The results confirmed that after 15 years of eCO2 the N2O emissions under eCO2 were still more than 2-fold higher than under aCO2. The tracing model results indicated that plant uptake of NH4+ did not differ between treatments, but uptake of NO3- was significantly reduced under eCO2. However, the ratio of gross production and consumption of NH4+ remained unchanged under eCO2, but decreased slightly for NO3-, which increased NO3- availability under eCO2. The N2O isotopic signature indicated that under eCO2 the sources of the additional emissions, 8407 µg N2O-N m-2 during the first 58 days after labelling, were associated with NO3- reduction (+2.0%), NH4+ oxidation (+11.1%) and organic N oxidation (+86.9%). We presume that increased root exudation under eCO2 provided an additional source of bioavailable supply of energy that triggered the stimulation of microbial soil organic matter (SOM) mineralization, as a priming effect, and an increased activity of bacterial nitrite reductase, which caused the shift in N2O:N2 emission ratio, via incomplete denitrification, explaining the positive feedback reaction of doubled N2O emissions.

Abstract:

Facing rising atmospheric CO2 concentrations, subsoils may play an important role in the global carbon (C) cycle due to the presence of unsaturated mineral surfaces. Further, macroaggregation is considered a crucial process influencing C sequestration. However, analyses on subsoil aggregation and C retention processes under long-term elevated CO2 (eCO2) are lacking. In this study we investigated the long-term effect of +20% above ambient CO2 concentration (corresponds to conditions reached 2035–2045) in a temperate grassland ecosystem at the Giessen Free Air CO2 Enrichment (Gi-FACE), Germany. A depth-dependent response of macroaggregation to eCO2 was observed: While in subsoil (15–45?cm depth) macroaggregation increased under eCO2, no CO2 induced change in macroaggregation was detected in topsoil (0–15?cm). Increased macroaggregation in subsoil coincided with higher SOC content of large macroaggregates (LM). Mean residence time (MRT) of SOC in aggregate-size classes were not different among each other under eCO2. However, macroaggregates and bulk soil differed in their MRT between soil depths. Despite increased macroaggregation and an estimated high SOC sequestration potential in subsoil we could not observe an increase in SOC content of bulk soil.

Abstract:

Soil respiration of terrestrial ecosystems, a major component in the global carbon cycle is affected by elevated atmospheric CO2 concentrations. However, seasonal differences of feedback effects of elevated CO2 have rarely been studied. At the Gießen Free-Air CO2 Enrichment (GiFACE) site, the effects of +20% above ambient CO2 concentration have been investigated since 1998 in a temperate grassland ecosystem. We defined five distinct annual seasons, with respect to management practices and phenological cycles. For a period of 3 years (2008–2010), weekly measurements of soil respiration were carried out with a survey chamber on vegetation-free subplots. The results revealed a pronounced and repeated increase of soil respiration under elevated CO2 during late autumn and winter dormancy. Increased CO2 losses during the autumn season (September–October) were 15.7% higher and during the winter season (November–March) were 17.4% higher compared to respiration from ambient CO2 plots. However, during spring time and summer, which are characterized by strong above- and below-ground plant growth, no significant change in soil respiration was observed at the GiFACE site under elevated CO2. This suggests (1) that soil respiration measurements, carried out only during the growing season under elevated CO2 may underestimate the true soil-respiratory CO2 loss (i.e. overestimate the C sequestered), and (2) that additional C assimilated by plants during the growing season and transferred below-ground will quickly be lost via enhanced heterotrophic respiration outside the main growing season.

Abstract:

Global climate change is expected to increase the frequency and intensity of extreme precipitation events, which can dramatically alter soil nitrous oxide (N2O) emissions. However, our ability to predict this effect is limited due to the lack of studies under real-world conditions. We conducted a ?eld experiment in a maize-cultivated black soil in northeast China with six treatments: control without nitrogen (N) application (CK) and N-fertilized treatments with the ratio of urea N to manure N at 100:0 (NPK), 75:25 (OM1), 50:50 (OM2), 25:75 (OM3) and 0:100 (OM4). The experimentalyear was the wettest on record with an extreme rainfall event of 178 mm occurring in summer 2013. Annual N2O emissions from CK and NPK were increased by 168% and 171%, respectively, relative to normal wet years. Extreme rainfall saturated soils, resulted in low N2O ?uxes (<20 mgNm
2 h
1) lasting for 25 d. However, N2O ?ux peaked (169e264 mgNm
2 h
1) in all treatments as the soil dried. Total N2O emissions were 0.43 e0.74 kg N ha
1 over the drying period, accounting for 47.5e51.2% of the annual budget. High N2O ?uxes occurred when the ratio of soil nitrate (NO3
) to dissolved organic carbon was 0.07e0.10 mg N mg
1 C, NO3
concentration was >3 mg N kg
1 and water-?lled pore space was 67e76%. Distinctly higher N2O ?uxes were also identi?ed during the spring thaw period, accumulating to 20.1e49.4% of the nongrowing season emissions. Emissions upon thawing were likely related to denitri?cation induced by high moisture conditions as a result of lag effect of the extreme rainfall. Annual N2O emissions progressively reduced as the ratio of urea N:manure N shifted towards manure, which was also the case during soil drying after waterlogging. Total N2O emissions were reduced by 25.6% for OM4 than NPK. Overall, our results suggest that soil N2O emissions were increased in the record wet year but a shift from urea towards manure with more N applied as starter N can minimize the N2O losses.

Abstract:

We review direct and indirect effects of climate change on both the grapevine plant as a host for phytophagous insects, as well as on grape insect pests, their natural enemies and corresponding future grape plant protection strategies. Phenology, voltinism and distribution ranges are well known traits of many arthropods influenced by temperature as the key abiotic factor and thus by current and future climate change scenarios. Case studies of grapevine pests based on data from three decades point to clear changes in phenology of grape berry moths, shifts in distribution ranges of leafhoppers as vectors of grapevine diseases and range expansion of grapevine mealybugs. These case studies also illustrate the need to include data on putatively changed tri-trophic interactions in vineyards when predicting impacts of climate change on grapevine pest insects. Hence, future pest management strategies should be based on a sound set of field data obtained for both pests and antagonists under changed abiotic conditions, which can also build the basis for refining and extending currently existing models for forecasting population levels of respective insect pests.

Abstract:

Satellite map of the Umweltbeobachtungs und Klimafolgenforschungsstation Linden

Abstract:

Future increase in atmospheric CO2 concentrations will potentially enhance grassland biomass production and shift the functional group composition with consequences for ecosystem functioning. In the “GiFACE” experiment (Giessen Free Air Carbon dioxide Enrichment), fertilized grassland plots were fumigated with elevated CO2 (eCO2) year-round during daylight hours since 1998, at a level of +20% relative to ambient concentrations (in 1998, aCO2 was 364 ppm and eCO2 399 ppm; in 2014, aCO2 was 397 ppm and eCO2 518 ppm). Harvests were conducted twice annually through 23 years including 17 years with eCO2 (1998 to 2014). Biomass consisted of C3 grasses and forbs, with a small proportion of legumes. The total aboveground biomass (TAB) was significantly increased under eCO2 (p = .045 and .025, at first and second harvest). The dominant plant functional group grasses responded positively at the start, but for forbs, the effect of eCO2 started out as a negative response. The increase in TAB in response to eCO2 was approximately 15% during the period from 2006 to 2014, suggesting that there was no attenuation of eCO2 effects over time, tentatively a consequence of the fertilization management. Biomass and soil moisture responses were closely linked. The soil moisture surplus (c. 3%) in eCO2 manifested in the latter years was associated with a positive biomass response of both functional groups. The direction of the biomass response of the functional group forbs changed over the experimental duration, intensified by extreme weather conditions, pointing to the need of long-term field studies for obtaining reliable responses of perennial ecosystems to eCO2 and as a basis for model development.

Abstract:

Biochar may become a key instrument at the nexus of managed carbon fluxes, including value added potential in soil Amelioration, climate protection, energy supply and organic waste management. This article reflects the potential use of biochar in agriculture from the perspective of the farming economy. Biochar soil amendment in crop production is regarded as a win-win Situation, both for assumed increases in cropping yields and carbon Sequestration in soil organic matter. However, an extensive review on biochar effecton crop yield has not yet been able to provide compelling arguments to foster more widespread biochar use in cropping systems. Furthermore, the half-lives of biochar are frequently shorter than commonly suggested, and other financial incentives, such as including biochar in carbon credit Systems, are not in place to compensate for the extra cost of applying biochar. As a result, we conclude with a somewhat skeptical view for a widespread use of biochar in agriculture in the near future.

Abstract:

Rising atmospheric CO2 concentrations are expected to increase nitrous oxide (N2O) emissions from soils via changes in microbial nitrogen (N) transformations. Several studies have shown that N2O emission increases under elevated atmospheric CO2 (eCO2), but the underlying processes are not yet fully understood. Here, we present results showing changes in soil N transformation dynamics from the Giessen Free Air CO2 Enrichment (GiFACE): a permanent grassland that has been exposed to eCO2, +20% relative to ambient concentrations (aCO2), for 15 years. We applied in the field an ammonium-nitrate fertilizer solution, in which either ammonium (NHþ 4 ) or nitrate (NO 3 ) was labelled with 15N. The simultaneous gross N transformation rates were analysed with a 15N tracing model and a solver method. The results confirmed that after 15 years of eCO2 the N2O emissions under eCO2 were still more than twofold higher than under aCO2. The tracing model results indicated that plant uptake of NHþ 4 did not differ between treatments, but uptake of NO 3 was significantly reduced under eCO2. However, the NHþ 4 and NO 3 availability increased slightly under eCO2. The N2O isotopic signature indicated that under eCO2 the sources of the additional emissions, 8,407 lg N2O–N/m2 during the first 58 days after labelling, were associated with NO 3 reduction (+2.0%), NHþ 4 oxidation (+11.1%) and organic N oxidation (+86.9%). We presume that increased plant growth and root exudation under eCO2 provided an additional source of bioavailable supply of energy that triggered as a priming effect the stimulation of microbial soil organic matter (SOM) mineralization and fostered the activity of the bacterial nitrite reductase. The resulting increase in incomplete denitrification and therefore an increased N2O:N2 emission ratio, explains the doubling of N2O emissions. If this occurs over a wide area of grasslands in the future, this positive feedback reaction may significantly accelerate climate change.

Abstract:

A major issue of our today's research is to help meeting the challenges of future food security. One task is to assess and develop crop management strategies adapted to predicted future climatic conditions. Yet, both the variability of environmental conditions and the uncertainty of climate projections as well as the orchestra of multiple plant responses and their interaction with the environment make it difficult to predict plant behavior in the field. Recent studies have demonstrated the usefulness of classical crop models as a tool to investigate crop productivity under predicted climate conditions. These models use data on plant architecture only to a limited extent as they usually follow a systems approach by focusing on processes for predicting dry matter production. However, plant architecture is a major determinant of the crops’ resource use efficiency. Moreover, plants show time dependent structural changes as they grow and develop, and these processes are affected by various environmental factors and stresses. Virtual plant models consider both the three-dimensional plant architecture and concepts of plant physiology. Here, we outline the way in which virtual plant modelling can further improve our understanding on the impact of climate change on food production. Greenhouse and growth chamber experiments may serve as data sources for model parameterization, in particular of response functions with respect to environmental stimuli. Data from field experiments in free air carbon enrichment (FACE) facilities, such as those obtained in the new Geisenheim FACE for special crops, may be used to evaluate virtual plant models with respect to future climatic conditions. A combination of field data and virtual plant model simulations may then allow us to assess the specific role of plant architecture in resource use efficiency and help to develop advanced strategies for future crop production.

Abstract:

The presentation of the Working package B2 at the general assembly of the FACE2FACE consortium at the 4th of July, 2017.