Growth,biomass allocation and water use efficiency of two wheat cultivars in a mediterranean environment; a pot experiment under field conditions

Plants of two bread wheat cultivars,Triticum aestivum L. Katya Al and Mexipak 65, were grown in pots during the crop season in the field in NW Syria, a region with a Mediterranean climate. The experiment involved two treatments. Control plants were well-watered throughout the experiment (watering to 0.22 g water g^–1 dry soil). In the second treatment, water was withheld from the plants until soil water content had decreased to 0.10 g water g^–1 dry soil, the level that was maintained thereafter. Water use was measured by weighing the pots, and growth by destructive sampling. Growth of Katya and Mexipak was similar. Mexipak had a lower (though not significant atp<0.05) plant water use efficiency (WUE_p) in both treatments due to higher rates of water loss. On a leaf area basis differences in water use were especially high since Mexipak had a smaller total leaf area. In spite of a smaller investment in photosynthesizing area, Mexipak achieved similar growth as Katya. Carbon isotope discrimination and organic nitrogen concentration (both higher for Mexipak) suggest that Mexipak accomplished higher mean net photosynthetic rates with a higher mean leaf diffusive conductance, higher intercellular carbon dioxide partial pressure, and possibly a greater investment in the photosynthetic apparatus compared to Katya. Differences in carbon isotope discrimination suggest a larger difference in average photosynthetic WUE (net photosynthesis/transpiration) than in plant WUE. This could indicate that loss of carbon in respiration was greater in Katya. Gas exchange measurements on the youngest fully expanded leaves showed only minor differences between the cultivars. It is hypothesized that Mexipak, with a smaller total leaf area, is able to maintain high leaf conductance and photosynthesis for a longer period of time during the day or during the life span of leaves.     

A critical review of labelling techniques used to quantify rhizosphere carbon-flow

The rhizosphere is a major sink for photo-assimilated carbon and quantifying inputs into this sink is one of the main goals of rhizosphere biology as organic carbon lost from plant roots supports a higher microbial population in the rhizosphere compared to bulk soil. Two fundamentally different¹⁴CO₂ labelling strategies have been developed to estimate carbon fluxes through the rhizosphere — continuous feeding of shoots with labelled carbon dioxide and pulse-chase experiments. The biological interpretation that can be placed on the results of labelling experiments is greatly biased by the technique used. It is the purpose of this paper to assess the advantages, disadvantages and the biological interpretation of both continuous and pulse labelling and to consider how to partition carbon fluxes within the rhizosphere.     

Use of decreasing foliar carbon isotope discrimination during water limitation as a carbon tracer to study whole plant carbon allocation

Foliar carbon isotope discrimination (Δ) of C₃ plants decreases in water‐deficit situations as discrimination by the photosynthetic primary carboxylation reaction decreases. This diminished Δ in leaves under water deficit can be used as a tracer to study whole plant carbon allocation patterns. Carbon isotope composition (δ¹³C value) of leaf hot water extracts or leaf tissue sap represents a short‐term integral of leaf carbon isotope discrimination and thus represents the δ¹³C value of source carbon that may be distributed within a plant in water‐deficit situations. By plotting the δ¹³C values of source carbon against the δ¹³C values of sink tissues, such as roots or stems, it is possible to assess carbon allocation to and incorporation into sink organs in relation to already present biomass. This natural abundance labelling method has been tested in three independent experiments, a one‐year field study with the fruit tree species Ziziphus mauritiana and peach (Prunus persica), a medium‐term drought stress experiment with Ziziphus rotundifolia trees in the glasshouse, and a short‐term drought stress experiment with soybean (Glycine max). The data show that the natural abundance labelling method can be applied to qualitatively assess carbon allocation in drought‐stressed plants. Although it is not possible to estimate exact fluxes of assimilated carbon during water deficit the method represents an easy to use tool to study integrated plant adaptations to drought stress. In addition, it is a less laborious method that can be applied in field studies as well as in controlled experiments, with plants from any developmental stage.     

Partitioning pattern of carbon flux in a Kobresia grassland on the Qinghai‐Tibetan Plateau revealed by field 13C pulse‐labeling

Characterizing the carbon turnover in terrestrial ecosystems is critical for understanding and predicting carbon dynamics in ecosystems. We used in situ¹³C pulse labeling to track photosynthetic carbon fluxes from shoot to roots and to soil in a Kobresia humilis meadow on the Qinghai‐Tibet Plateau. We found that about 36.7% of labeled carbon was translocated out from the shoots within the first 24 h after photosynthetic uptake. This is equivalent to 66.1% of total ¹³C moving out from the shoot during the 32‐day chase period, indicating a rapid and large translocation of newly fixed carbon to belowground parts in these alpine plants. 58.7% of the assimilated ¹³C was transferred belowground. At the end of the chase phase, 30.9% was retained in living roots, 3.4% in dead roots, 17.2% lost as belowground respiration and 7.3% remained in the soil. In the four carbon pools (i.e., shoots, living roots, dead roots, and soil pools), living roots consistently had the highest proportion of ¹³C in the plant–soil system during the 32 days. Based on the ¹³C partitioning pattern and biomass production, we estimate a total of 4930 kg C ha^?1 was allocated belowground during the vegetation growth season in this alpine meadow. Of this, roots accumulated 2868 kg C ha^?1 and soils accumulated 613 kg C ha^?1. This study suggests that carbon storage in belowground carbon pools plays the most important role in carbon cycles in the alpine meadow.     

定量稳定性同位素探针技术及其在微生物生态学研究中的应用

定量稳定性同位素探针技术(qSIP)是将生态系统中微生物分类性状与代谢功能联系起来的有效工具,能够定量测定特定环境中单个微生物类群暴露于同位素示踪剂后微生物代谢活动或生长速率.qSIP技术采用定量PCR与高通量测序技术并结合稳定同位素探针技术(SIP),通过向环境样品添加标记底物进行培养,提取微生物生物标记物,利用超高...     

Proteotypic profiling of LHCI from Chlamydomonas reinhardtii provides new insights into structure and function of the complex

We used isotope dilution MS to measure the stoichiometry of light‐harvesting complex I (LHCI) proteins with the photosystem I (PSI) core complex in the green alga Chlamydomonas reinhardtii. Proteotypic peptides served as quantitative markers for each of the nine gene products (Lhca1–9) and for PSI subunits. The quantitative data revealed that the LHCI antenna of C. reinhardtii contains about 7.5 ± 1.4 subunits. It further demonstrated that the thylakoid LHCI population is heterogeneously composed and that several lhca gene products are not present in 1:1 stoichiometries with PSI. When compared with vascular plants, LHCI of C. reinhardtii possesses a lower proportion of proteins potentially contributing to far‐red fluorescence emission. In general, the strategy presented is universally applicable for exploring subunit stoichiometries within the C. reinhardtii proteome.     

A model of the long-term response of carbon allocation and productivity of forests to increased CO2concentration and nitrogen deposition

We present a simple theoretical analysis of the long term response of forest growth and carbon allocation to increased atmospheric [CO₂] and N deposition. Our analysis is based on a recent model which predicts that plant light-use efficiency increases with [CO₂] but is independent of plant N supply. We combine that model with simple assumptions for nitrogen fluxes in the soil. A quasi-equilibrium analysis of the short term tree and soil pools is then used to develop a simple graphical depiction of the long term carbon and nitrogen supply constraints on total growth, stem growth and foliar allocation. Our results suggest that long-term growth responses to [CO₂] and N deposition depend strongly on the extent to which stem allocation and foliage allocation are coupled. At one extreme (‘no coupling’), when stem allocation is fixed and independent of foliage allocation, there is no response of total growth or stem growth to increased [CO₂] unless N deposition increases. At the other extreme (‘linear coupling’), when stem allocation is proportional to foliage allocation, there is a significant long-term increase in total growth following a doubling of [CO₂], even when N deposition is unchanged, but stem growth decreases because of a long-term decrease in foliage allocation. For both types of coupling, total growth and stem growth increase with increasing N deposition. In the case of linear coupling, however, the N deposition response of stem growth is significantly larger than that of total growth, because of a long-term increase in foliage allocation. We compare our results with those obtained previously from an alternative model of canopy light-use efficiency involving a dependence on the foliar N:C ratio in addition to [CO₂]. Our results highlight the need for more experimental information on (i) the extent to which canopy light-use efficiency is independent of N supply, and (ii) the relationship between foliage allocation and stem allocation.     

Synthesis of a 13C-Labeled Tracer for Stream DOC: Labeling Tulip Poplar Carbon with 13CO2

Ecosystem tracer-level additions would benefit from a stable isotope-labeled source of complex organic molecules. We tested a method to label tree C with ¹³C and create a stable isotope tracer for stream dissolved organic carbon (DOC) using tulip poplar (Liriodendron tulipifera L.) seedlings. In 2000, seedlings were grown with 0.82 moles of ¹³CO₂ to assess the distribution and level of ¹³C enrichment in the tree tissues. In 2001, seedlings were grown with 25 times more ¹³CO₂ to generate tissues with a ¹³C signal strong enough for a ¹³C-DOC stream tracer addition. ¹³C enrichment in the trees varied in each year and by tissue age and type. Tissues formed during labeling (new) were more enriched in ¹³C than tissues established prior to the ¹³CO₂ injection (old). Stems were most enriched in ¹³C in both new and old tissues. A higher percentage of ¹³CO₂ was incorporated into seedlings in 2000 (59% ±1) than 2001 (43% ±0). Percent ¹³C incorporation among tree tissue types paralleled biomass distributions. Although tree C and ¹³C were equally soluble in both years, a greater percentage of tree C went into solution in 2001 (30%) than 2000 (20%). The water-soluble tree C accounted for approximately 12% of the injected ¹³CO₂ and had both humic and polysaccharide components. Results from a whole-stream ¹³C-DOC tracer addition demonstrated that tree C could be sufficiently labeled with ¹³CO₂ to create a stream DOC isotope tracer with some polymeric constituents.     

A systematic analysis of backbone amide assignments achieved via combinatorial selective labelling of amino acids

With the advent of high-yield cell-free expressions systems, many researchers are exploiting selective isotope labelling of amino acids to increase the efficiency and accuracy of the NMR assignment process. We developed recently a combinatorial selective labelling (CSL) method capable of yielding large numbers of residue-type and sequence-specific backbone amide assignments, which involves comparing cross-peak intensities in ¹H–¹⁵N HSQC and 2D ¹H–¹⁵N HNCO spectra collected for five samples containing different combinations of ¹³C- and ¹⁵N-labelled amino acids [Parker MJ, Aulton-Jones M, Hounslow A, Craven C J (2004) J Am Chem Soc 126:5020–5021]. In this paper we develop a robust method for establishing the reliability of these assignments. We have performed a detailed statistical analysis of the CSL data collected for a model system (the B1 domain of protein G from Streptococcus), developing a scoring method which allows the confidence in assignments to be assessed, and which enables the effects of overlap on assignment fidelity to be predicted. To further test the scoring method and also to assess the performance of CSL in relation to sample quality, we have applied the method to the CSL data collected for GFP in our previous study.     

Effects of six years atmospheric CO2 enrichment on plant,soil, and soil microbial C of a calcareous grassland

Stimulated plant production and often even larger stimulation of photosynthesis at elevated CO₂ raise the possibility of increased C storage in plants and soils. We analysed ecosystem C partitioning and soil C fluxes in calcareous grassland exposed to elevated CO₂ for 6 years. At elevated CO₂, C pools increased in plants (+23%) and surface litter (+24%), but were not altered in microbes and soil organic matter. Soils were fractionated into particle size and density separates. The amount of low-density macroorganic C, an indicator of particulate soil C inputs from root litter, was not affected by elevated CO₂. Incorporation of C fixed during the experiment (C_new) was tracked by C isotopic analysis of soil fractions which were labelled due to ¹³C depletion of the commercial CO₂ used for atmospheric enrichment. This data constrains estimates of C sequestration (absolute upper bound) and indicates where in soils potentially sequestered C is stored. C_new entered soils at an initial rate of 210±42 g C m^–2 year^–1, but only 554±39 g C_new m^–2 were recovered after 6 years due to the low mean residence time of 1.8 years. Previous process-oriented measurements did not indicate increased plant–soil C fluxes at elevated CO₂ in the same system (¹³C kinetics in soil microbes and fine roots after pulse labelling, and minirhizotron observations). Overall experimental evidence suggests that C storage under elevated CO₂ occurred only in rapidly turned-over fractions such as plants and detritus, and that potential extra soil C inputs were rapidly re-mineralised. We argue that this inference does not conflict with the observed increases in photosynthetic fixation at elevated CO₂, because these are not good predictors of plant growth and soil C fluxes for allometric reasons. C sequestration in this natural system may also be lower than suggested by plant biomass responses to elevated CO₂ because C storage may be limited by stabilisation of C_new in slowly turned-over soil fractions (a prerequisite for long-term storage) rather than by the magnitude of C inputs per se.