Root exudation of carbohydrates and cations from barley in response to drought and elevated CO2

Plant and Soil - Citrate secretion is a kind of typical strategy for plant against aluminum (Al) toxicity. However, the signaling process in Al-activated citrate secretion needs to be clarified....     

Increase of photosynthesis and starch in potato under elevated CO2 is dependent on leaf age

Potato plants (Solanum tuberosum cv. Bintje) were grown in open top chambers under ambient (400 microL L(-1)) and elevated CO2 (720 microL L(-1)). After 50 days one half of each group was transferred to the other CO2 concentration and the effects were studied in relation to leaf age (old, middle-aged and young leaves) in each of the four groups. Under long-term exposure to elevated CO2, photosynthesis increased between 10% and 40% compared to ambient CO2. A subsequent shift of the same plants to ambient CO2 caused a 20-40% decline in photosynthetic rate, which was most pronounced in young leaves. After shifting from long-term ambient to elevated CO2, photosynthesis also increased most strongly in young leaves (90%); these experiments show that photosynthesis was downregulated in the upper young fully expanded leaves of potato growing long-term under elevated CO2. Soluble sugar content in all leaf classes under long-term exposure was stable irrespective of the CO2 treatment, however under elevated CO2 young leaves showed a strongly increased starch accumulation (up to 400%). In all leaf classes starch levels dropped in response to the shift from 720 to 400 microL L(-1) approaching ambient CO2 levels. After the shift to 720 microL L(-1), sucrose and starch levels increased, principally in young Leaves. There is clear evidence that leaves of different age vary in their responses to changes in atmospheric CO2 concentration.     

Phytotoxicity of tin mine waste and accumulation of involved heavy metals in common buckwheat (Fagopyrum esculentum Moench)

Extraction and processing of cassiterite (SnO₂) left large tailings with high concentrations of tin, tungsten, molybdenum and lithium. Information on the phytotoxicity of mine waste is important with regard to ecological hazards. Exposure studies help to identify plants useful for the stabilization of waste tips and the phytomining of metals. A greenhouse study was performed using a dilution series of mine waste and four crops, a halophytic and a metallophytic species to derive dose response curves. Based on effective doses for growth reductions, sensitivity increased in the following order: maize > common buckwheat > quinoa > garden bean. Element analyses in different species and compartments of common buckwheat grown in a mixture of standard soil and 25% of the mine waste showed that only low levels of the metals were taken up and that transfer to seed tissues was negligible. As indicated by soil metal levels prior to and after the experiment, only lithium and arsenic proved to be plant available and reached high levels in green tissues while seed levels were low. The experiment confirmed differences in the uptake of metals with regard to elements and species. Common buckwheat is a suited candidate for cultivation on metal polluted soils.     

Growth, senescence and water use efficiency of spring oilseed rape (Brassica napus L. cv. Mozart) grown in a factorial combination of nitrogen supply and elevated CO2

Atmospheric CO₂ enrichment is expected to affect the resource use efficiency of C3 plants with respect to water, nutrients and light in an interactive manner. The responses of oilseed rape (OSR) to elevated CO₂ have not much been addressed. Since the crop has low nitrogen use efficiency, the interactive effects of CO₂ enrichment and nitrogen supply deserve particular attention.Spring OSR was grown in climate chambers simulating the seasonal increments of day length and temperature in South-Western Germany. Three levels of N fertilisation representing 75, 150 and 225 kg ha⁻¹ and two CO₂ concentrations (380 and 550 μmol mol⁻¹) were used to investigate changes in source-sink relationships, plant development and senescence, water use efficiency of the dry matter production (WUE_prod.), allocation patterns to different fractions, growth, yield and seed oil contents. Seven harvests were performed between 72 and 142 days after sowing (DAS).Overall, plant performance in the chambers was comparable to the development under field conditions. While CO₂ responses were small in the plants receiving lowest N-levels, several significant N × CO₂ interactions were observed in the other treatments. Increasing the N availability resulted in longer flowering windows, which were furthermore extended at elevated CO₂ concentrations. Nevertheless, significantly less biomass was allocated to reproductive structures under elevated CO₂, while the vegetative C-storing organs continued to grow. At the final harvest shoot mass of the CO₂ exposed plants had increased by 9, 8 and 15% in the low, medium and high N treatments. Root growth was increased even more by 17, 43 and 33%, respectively and WUE_prod. increased by 23, 42 and 35%. At the same time, seed oil contents were significantly reduced by CO₂ enrichment in the treatments with ample N supply.Obviously, under high N-supply, the CO₂ fertilisation induced exaggerated growth of vegetative tissues at the expense of reproductive structures. The interruption of source-sink relationships stimulated the formation of side shoots and flowers (branching out). While direct effects of elevated CO₂ on flowering can be excluded, we assume that the increased growth under high N and CO₂ supply created nutrient imbalances which hence affected flowering and seed set.Nevertheless, the final seed macronutrient concentrations were slightly increased by elevated CO₂, indicating that remobilisation of nutrients from the sources (leaves) to the sinks (seeds) remained effective. These findings were supported by the lower nitrogen concentrations in senescing leaves and probably increased N remobilisation to other plant parts under elevated concentrations of CO₂. All the same, CO₂ enrichment caused a decline in seed oil contents, which may translate into a reduced crop quality.     

Free-air CO2 enrichment in a wheat-weed assembly – effects on water relations

In a three-year free-air CO₂ enrichment study (Mini-FACE), spring wheat associated with typical arable weeds were grown under present and elevated atmospheric carbon dioxide concentrations [CO₂] (ambient air+150 μmol mol^?1). Analyses of plant stable carbon isotope ratios and in vivo measurements of leaf gas exchange were used to describe the CO₂ effects on water relations. For most species examined elevated [CO₂] significantly increased the intrinsic water-use efficiency (A/g_s) as derived from carbon isotope analyses. In some of the species, seasonal averages of the ratio between leaf internal to atmospheric CO₂ (c_i/c_a) were found to be significantly reduced by elevated [CO₂]. Periodic leaf gas exchange measurements confirmed the increased water-use efficiency, but significant CO₂ effects became evident only over the entire season by carbon isotope analysis. In both types of analysis conducted, spring wheat was found to react significantly different from all other species examined. The relation between A/g_s and biomass production was significantly influenced by elevated [CO₂] in all three years of the study. At the end of the drier growing seasons 2003 and 2004, the soil water content tended to be increased in the CO₂ enriched plots indicating a water saving effect. These observations demonstrate the impact of elevated [CO₂] on plant water relations with a likely positive feedback leading to higher soil water availability. Due to the differences in the CO₂ responses of spring wheat compared to the weeds we suggest that rising [CO₂] may cause shifts in the species composition of crop-weed communities.     

Influence of long-term CO2 storage on δ13C in vials capped with butyl and butyl/PTFE caps and the relevance for ecological samples

Background

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.

Methods

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.

Results

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 %.

Conclusion

The storage effect should be taken into consideration when interpreting δ¹³C values in order to avoid miscalculations.     

Quantifying greenhouse gases from the production,transportation and utilization of charcoal in developing countries: a case study of Kampala,Uganda

Purpose

This study aims to quantify greenhouse gases (GHGs) from the production, transportation and utilization of charcoal and to assess the possibilities of decreasing greenhouse gases (GHGs) from the charcoal industry in general in Uganda. It also aims to assess the emission intensity of the Ugandan “charcoal production” sector compared to that of some other major charcoal producing nations.

Methods

This work was done in accordance with ISO 14040 methodology for life-cycle assessment (LCA), using GABi 4.0—a software for life-cycle assessment. A cradle-to-grave study was conducted, excluding emissions arising from machinery use during biomass cultivation and harvesting. The distance from charcoal production locations to Kampala was estimated using ArcGIS 10.0 software and a GPS tool. Emission data from a modern charcoal production process (PYREG methane-free charcoal production equipment), which complies with the German air quality standards (TA-Luft), was compared with emissions from a traditional charcoal production process. Four coupled scenarios were modelled to account for differences in the quantity of greenhouse gases emitted from the “traditional charcoal production phase”, “improved charcoal production phase (biomass feedstock sourced sustainably and unsustainably)”, “transportation phase” and “utilization phase”. Data for this study was obtained via literature review and onsite measurements.

Results and discussion

The results showed that greenhouse gases emitted due to charcoal supply and use of traditional production technique in Kampala was 1,554,699 tCO₂eq, with the transportation phase accounting for approximately 0.15 % of total greenhouse gases emitted. The utilization phase (charcoal cookstoves) emitted 723,985 tCO₂eq (46.6 %), while the charcoal production phase emitted 828,316 tCO₂eq (53.3 %). Changing the charcoal production technology from a traditional method to an improved production method (PYREG charcoal process) resulted in greenhouse gases reductions for the city of 230,747 tCO₂eq; however, by using sustainably sourced biomass, this resulted in reductions of 801,817 tCO₂eq.

Conclusions

This study showcased and quantified possible GHG emission reduction scenarios for the charcoal industry in Uganda. The result of 3 tCO₂eq emitted per tonne of charcoal produced, using earth mound method, can be applied to other countries in Eastern Africa where similar charcoal production methods are used; this will allow for somewhat better regional estimates of the inventory of greenhouse gas emissions from the production of charcoal. The results of this study also suggests that the primary use of charcoal for cooking will lead to increases in GHG emissions and increases in deforestation on the long term, if legal frameworks are not made to ensure that biomass used for charcoal production is obtained via sustainable sources or if alternative cheap energy-generating technologies for cooking are not developed and deployed to the masses.     

Atmospheric CO2 enrichment and drought stress modify root exudation of barley

Rising CO₂ concentrations associated with drought stress is likely to influence not only aboveground growth, but also belowground plant processes. Little is known about root exudation being influenced by elements of climate change. Therefore, this study wanted to clarify whether barley root exudation responds to drought and CO₂ enrichment and whether this reaction differs between an old and a recently released malting barley cultivar. Barley plants were grown in pots filled with sand in controlled climate chambers at ambient (380 ppm) or elevated (550 ppm) atmospheric [CO₂] and a normal or reduced water supply. Root exudation patterns were examined at the stem elongation growth stage and when the inflorescences emerged. At both dates, root exudates were analyzed for different compounds such as total free amino acids, proline, potassium, and some phytohormones. Elevated [CO₂] decreased the concentrations in root exudates of some compounds such as total free amino acids, proline, and abscisic acid. Moreover, reduced water supply increased proline, potassium, electric conductivity, and hormone concentrations. In general, the modern cultivar showed higher concentrations of proline and abscisic acid than the old one, but the cultivars responded differentially under elevated CO₂. Plant developmental stage had also an impact on the root exudation patterns of barley. Generally, we observed significant effects of CO₂ enrichment, watering levels, and, to a lesser extent, cultivar on root exudation. However, we did not find any mitigation of the adverse effects of drought by elevated CO₂. Understanding the multitude of relationships within the rhizosphere is an important aspect that has to be taken into consideration in the context of crop performance and carbon balance under conditions of climate change.     

Total nitrogen deposition at key growing stages of maize and wheat as affected by pot surface area and crop variety

Atmospheric nitrogen (N) deposition is a serious problem on the North China Plain (NCP) because it imposes a considerable nutrient burden on the local environment. However, it also makes a substantial contribution to agricultural crop N requirements. The integrated total N input (ITNI) system is a method to quantify total atmospheric N deposition by using ¹⁵N-labeled monitor plants grown in pots. The effect of pot surface area and variety of indicator plant on the amount of airborne N input quantified by the ITNI system was investigated in this study. Total N deposition to the soil-maize/soil-wheat plant system at key growth stages was also quantified to improve N-fertilizer recommendations. When indicator plants having a high space requirement were used a correction factor was needed and this could be obtained only by simulating commercial field conditions, especially plant density, because the factor depends largely on pot area or the difference in plant density between pot conditions and field conditions. The total airborne N input measured by the ITNI system was not influenced by the variety of monitoring plant. N deposition was 20?C25 kg N ha^?1 during growth from three expanded leaf to ten expanded leaf and also from ten expanded leaf to maturity of maize. N deposition was 29.1 kg N ha^?1 between planting and the jointing stage and 10.1 kg N ha^?1 from jointing to maturity of wheat. This high measured N deposition indicates that N deposition should be taken into account when calculating the N fertilizer requirements of maize and wheat in this region.     

Abundance and activity of nitrate reducers in an arable soil are more affected by temporal variation and soil depth than by elevated atmospheric [CO2

Elevated atmospheric carbon dioxide concentrations ([CO(2) ]) might change the abundance and the function of soil microorganisms in the depth profile of agricultural soils by plant-mediated reactions. The seasonal pattern of abundance and activity of nitrate-reducing bacteria was studied in a Mini-FACE experiment planted with oilseed rape (Brassica napus). Three depths (0-10, 10-20 and 20-30 cm) were sampled. Analyses of the abundances of total (16S rRNA gene) and nitrate-reducing bacteria (narG, napA) revealed strong influences of sampling date and depth, but no [CO(2)] effects. Abundance and activity of nitrate reducers were higher in the top soil layer and decreased with depth but were not related to extractable amounts of nitrogen and carbon in soil. Dry periods reduced abundances of total and nitrate-reducing bacteria, whereas the potential activity of the nitrate reductase enzyme was not affected. Enzyme activity was only weakly correlated to the abundance of nitrate-reducing bacteria but was related to NH(4) (+) and NO(3) (-) concentrations. Our results suggest that in contrast to the observed pronounced seasonal changes, the elevation of atmospheric [CO(2) ] has only a marginal impact on nitrate reducers in the investigated arable ecosystem.