Application of Stable Isotope Techniques in Studies of Carbon and Nitrogen Biogeochemical Cycles of Ecosystem

Stable isotope techniques have been proved useful as tools for studying the carbon (C) and nitrogen (N) biogeochemical cycles of ecosystem. This paper firstly introduced the basic principles and the distribution characteristics of stable isotope, then reviewed the recent advances and applications of stable isotope in the C and N biogeochemical cycles of ecosystem. By applying the 13 C natural abundance technique, ecologists are able to understand the photosynthetic path and CO 2 fixation of plants, the CO 2 exchange and C balance status of ecosystem, the composition, distribution and turnover of soil organic C and the sources of organic matter in food webs, while by using the 13 C labeled technique, the effects of elevated CO 2 on the C processes of ecosystem and the sources and fate of organic matter in ecosystem can be revealed in detail. Differently, by applying the 15 N natural abundance technique, ecologists are able to analyze the biological N 2 -fixation, the N sources of ecosystem, the N transformation processes of ecosystem and the N trophic status in food webs, while by using the 15 N labeled technique, the sources, transformation and fate of N in ecosystem and the effects of N input on the ecosystem can be investigated in depth. The applications of both C and N isotope natural abundance and labeled techniques, combined with the elemental, other isotope ( 34 S) and molecular biomarker information, will be more propitious to the investigation of C and N cycle mechanisms. Finally, this paper concluded the problems existed in current researches, and put forward the perspective of stable isotope techniques in the studies on C and N biogeochemical cycles of ecosystem in the future.

Diperoxo Complexes of Vanadium（V） Containing Mannich Base Ligands

The vanadium（V） peroxo complexes containing Mannich base ligands having composition Na[VO（O2）2（L-L）]·H2O [where L-L=morpholinobenzyl acetamide （MBA）, piperidinobenzyl acetamide （PBA）, morpholinobenzyl benzamide （MBB）, piperidinobenzyl benzamide （PBB）, morpholinomethyl benzamide （MMB）, piperidinomethyl benzamide （PMB）, morpholinobenzyl formamide （MBF）, piperdinobenzyl formamide （PBF）] have been reported. The complexes have been prepared by stirring vanadium pentoxide with excess of 30% aque- ous-H202 followed by treatment with ethanolic solution of the ligand and finally maintained the pH of the reaction mixture by adding dilute solution of sodium hydroxide. The synthesized complexes have been characterized by various physico-chemical techniques, via elemental analysis, molar conductivity, magnetic susceptibility measure- ments, infra red, electronic, mass, ~H NMR spectral and TGA/DTA studies. These studies revealed that the synthesized complexes are uni-univalent electrolytes and diamagnetic in nature. The ligands are bound to metal in a bi- dentate mode through carbonyl oxygen and the ring nitrogen. Thermal analysis result provides conclusive evidence for the presence of one molecule of lattice water in the complexes. Mass spectra confirm the molecular mass of the complexes.

Examination of n-T_(9) conditions required by N=50,82,126 waiting points in r-process

We examined the conditions of neutron density(n) and temperature(T9) required for the N = 50, 82,and 126 isotopes to be waiting points(WP) in the r-process. The nuclear mass based on experimental data presented in the AME2020 database(AME and AME ± Δ) and that predicted using FRDM,WS4, DZ10, and KTUY models were employed in our estimations. We found that the conditions required by the N = 50 WP significantly overlap with those required by the N = 82 ones, except for the WS4 model. In addition, the upper(or lower) bounds of the n-T9 conditions based on the models are different from each other due to the deviations in the two-neutron separation energies.The standard deviations in the nuclear mass of 108 isotopes in the three N = 50, 82, and 126 groups are about rms = 0.192 and 0.434 Me V for the pairs of KTUY-AME and WS4-KTUY models,respectively. We found that these mass uncertainties result in a large discrepancy in the nn-T_(9) conditions, leading to significant differences in the conditions for simultaneously appearing all the three peaks in the r-process abundance. The newly updated FRDM and WS4 calculations can give the overall conditions for the appearance of all the peaks but vice versa for their old versions in a previous study. The change in the final r-process isotopic abundance due to the mass uncertainty is from a few factors to three orders of magnitude. Therefore, accurate nuclear masses of the r-process key nuclei, especially for 76 Fe,81Cu,127Rh,132Cd,192Dy, and 197Tm, are highly recommended to be measured in radioactive-ion beam facilities for a better understanding of the r-process evolution.

comCompetition for resources is ameliorated by niche differentiation between Solidago virgaurea life-history stages in the Arctic

Aims competition has been shown to modify the niche breadth of coex-isting species,but within-species interactions have received little attention.Establishing small juvenile individuals and established,larger,sexually reproducing adult individuals represent two life-his-tory stages within species.We investigated the nitrogen and carbon resource use of adult and juvenile individuals and similarity of sym-biotic fungal community composition in these two plant life stages.We used the plant Solidago virgaurea growing in a simplified system in the low Arctic as model species.Methods Isotopic signatures(foliarδ15N and foliarδ13c)were analysed to characterize nitrogen acquisition and water-use efficiency of the plants.Symbiotic root fungal community composition was esti-mated by cloning and sequencing small subunit ribosomal RNA gene.Important Findings The isotopic signatures differed significantly between the life stages,indicating that the establishing juvenile cohort used relatively more amino acids or gained N through mycorrhizal symbiosis in com-parison to the established adult plants.Symbiotic fungal commu-nities did not differ between the two plant cohorts suggesting a possibility that the plants shared the same mycorrhizal network.We conclude that competition-mediated differences in plant resource use may create niche differentiation between the two life-history stages and enable them to coexist.