Stoichiometric Indices Research Articles

Comparison of C, N and P Stoichiometry in Different Organs of Fraxinus velutina

Velvet ash (Fraxinus velutina Torr.) is a dioecious tree species, which is widely used as a part of urban greeneries in saline land of North China. Female and male trees have different nutrient allocation trade-offs in dioecious species. As the fruit production consumes a lot of nutrients, female F. velutina plants grow slowly and are vulnerable to insects and diseases. Ecological stoichiometry can be used to study the physiological mechanism of the growth difference between female and male plants. The purpose of this study was to compare the seasonal patterns of C, N and P stoichiometry and their trade-offs in different organs of female and male F. velutina plants planted in urban green spaces. The fruit C, N and P contents of female F. velutina plants were all lower than those of leaves in the early growing season, but higher than those of leaves in the middle and late growing season. During most months, the leaf C and P contents of females were higher than those of males, while the leaf N content was lower than that of males, which was consistent with the sex-specific resource requirements for reproduction (i.e., high carbon requirements for ovules and high nitrogen demands for pollen). Compared to the females, there were more significant correlations between the stoichiometric indices (element contents and their ratios) of branches and leaves in male plants, and this difference may be related to the fact that the male plants were not involved in nutritional allocation for fruits. The leaf N/P of F. velutina was lower than 14 in the whole growing season, which indicated N limitation. The female and male plants of F. velutina had different sex-specific resource requirements for sex organ formation.

Shifts in chemical and microbiological properties belowground of invader Ageratina adenophora along an altitudinal gradient

Abstract Tropical mountain ecosystems are usually colonized by numerous invasive plant species and represent an ideal ‘natural laboratory’ to study the effects of altitude on plant invasion. The aim of this study was to investigate the soil chemical and microbiological properties along an altitudinal gradient on a mountain colonized by the invader Ageratina adenophora. Rhizosphere soil of A. adenophora was collected over an altitudinal gradient (1400–2400 m) in Ailao Shan, China. We determined soil organic carbon (C), nutrient contents, enzyme activities, bacterial community composition as well as C and nitrogen (N) contents of the plant roots. Ecoenzymatic stoichiometric indices were calculated to estimate the relative C, N or P limitations of the microbial community. There was a significant effect of altitude on soil organic C in the rhizosphere, and a turning point in these measured variables was detected at an altitude of 2000 m. At low elevations, the rapid growth of invasive plants depleted the deficient phosphorus (P) in tropical soils, leading to microbial P limitation; at high elevations, microbes invested more energy to obtain C from resistant litter, leading to microbial C limitation. Bacterial beta diversity and soil pH contributed most to the altitudinal differences in ecoenzymatic stoichiometry, and Proteobacteria and Acidobacteria were the dominant bacterial phyla that determined the nutrient uptake status of microorganisms. These results demonstrate how microbial nutrient acquisition belowground of A. adenophora along an altitudinal gradient, which could contribute to further knowledge about the effects of altitude on biological invasion.

Ecological stoichiometry of plant-soil-enzyme interactions drives secondary plant succession in the abandoned grasslands of Loess Plateau, China

Ecological stoichiometry is the study of the interaction and balance of multiple chemical elements in ecological processes. However, how ecological stoichiometric interactions among plants, soils, and enzymes in the rhizosphere affect secondary plant succession is largely unknown. In this study, we collected the dominant and main companion species Artemisia capillaris, A. sacrorum, and Stipa bungeana, along a secondary succession chronosequence (7, 12, 17, 22, and 32-year) following a cropland abandonment in the Loess Plateau, China. We measured the carbon (C), nitrogen (N) and phosphorus (P) concentrations of plant shoots and roots, as well as the concentrations of C, N, P, available N (aN), available P (aP), and the activity of one C-acquiring enzyme (β-glucosidase (BG)), two N-acquiring enzymes (N-acetylglucosaminidase (NAG), leucineaminopeptidase (LAP)), and one P-acquiring enzyme (alkaline phosphatase (AP)) found in the rhizospheric soil to explore the C:N:P stoichiometry that drives secondary plant succession. The C:P and N:P ratios in the shoots of dominant plant species significantly decreased to a minimum value at the 22-year site and then increased with plant secondary succession. Compared with the 7-year site, the rhizosphere soil C:P and N:P ratios, and enzyme N:P ratios (ln(NAG + LAP):ln(AP)) increased 103.6%, 72.0%, and 221.3%, respectively, but enzyme C:N ratios (ln(BG):ln(NAG + LAP)) decreased 48.2% in the dominant plant species at the 32-year site. Principal component analysis indicated that the stoichiometry characteristics of the plant-soil-enzyme continuum differed for each plant species and succession stage. Stoichiometric homeostasis indices for the plant species indicated a relatively strong homeostasis, while redundancy analysis revealed that the variations in soil BG, NAG, and AP activity and enzyme C:N ratio had significant effects on the stoichiometries and nutrient concentrations of the plant tissues. The results indicated that rhizosphere stoichiometry is a powerful tool for evaluating plant-soil interactions in terrestrial ecosystems and that the variation in rhizospheric soil enzyme activity driving the secondary succession of plants.

Effects of tree species and topography on soil and microbial biomass stoichiometry in Funiu Mountain, China

BackgroundSoil and microbial biomass stoichiometry plays an important role in understanding nutrient cycling in terrestrial ecosystems. However, studies on soil and microbial biomass stoichiometry in forests are rare. This study investigated the effect of tree species and topographic factors on the ecological stoichiometry of soil and soil microbial biomass.MethodsThree types of forest stands (Quercus variabilis, Larix principis-ruprechtii, and Cotinus coggygria Scop.) in the Beiru River basin of Funiu Mountain were analyzed in September 2018. Six slope positions (sunny bottom slope, sunny middle slope, sunny top slope, shady bottom slope, shady middle slope, and shady top slope) were selected, and the total number of sampling plots was 108. The stoichiometric indices of soil and microbial biomass were determined.ResultsAt a depth of 0–10 cm, the soil organic C contents in different stands followed the order of C. coggygria (27.7 ± 5.2 g/kg) > Q. variabilis (24.5 ± 4.9 g/kg) > L. principis-ruprechtii (20.8 ± 4.3 g/kg) (P < 0.05). The soil organic C contents at depths of 0–10 cm with different slope aspects and at different slope positions also showed significant differences (P < 0.05). The highest MBC content was observed at the slope bottom (1002 ± 157 mg/kg), whereas the lowest was observed at the slope top (641 ± 98.3 mg/kg). Redundancy analysis showed that the contribution of tree species to these differences was 57.1%, whereas that of topographical factors was 36.2%.ConclusionsTree species more significantly affected soil nutrients and microbial biomass C, N and P than did topographic factors.

Analysis of the conformational polymorph crystal structures by means of molecular Voronoi-Dirichlet polyhedra

The nonvalent interactions in the crystal structures of 16 conformational polymorphs of the CaHbNcOdSe composition (a, b, c, d, and e are stoichiometric indices), including 5-methyl-2-[(2-nitrophenyl)amino]-3-thiophenecarbonitrile (“ROY”) (which has seven different modifications), have been analyzed using the characteristics of molecular Voronoi-Dirichlet polyhedra. It is established that a unique combination of implementable types of intra- and intermolecular nonvalent contacts corresponds to each conformational polymorph.

Tutorial on a chemical model building by least-squares non-linear regression of multiwavelength spectrophotometric pH-titration data

Although the modern instrumentation enables for the increased amount of data to be delivered in shorter time, computer-assisted spectra analysis is limited by the intelligence and by the programmed logic tool applications. Proposed tutorial covers all the main steps of the data processing which involve the chemical model building, from calculating the concentration profiles and, using spectra regression, fitting the protonation constants of the chemical model to multiwavelength and multivariate data measured. Suggested diagnostics are examined to see whether the chemical model hypothesis can be accepted, as an incorrect model with false stoichiometric indices may lead to slow convergence, cyclization or divergence of the regression process minimization. Diagnostics concern the physical meaning of unknown parameters β qr and ɛ qr , physical sense of associated species concentrations, parametric correlation coefficients, goodness-of-fit tests, error analyses and spectra deconvolution, and the correct number of light-absorbing species determination. All of the benefits of spectrophotometric data analysis are demonstrated on the protonation constants of the ionizable anticancer drug 7-ethyl-10-hydroxycamptothecine, using data double checked with the SQUAD(84) and SPECFIT/32 regression programs and with factor analysis of the INDICES program. The experimental determination of protonation constants with their computational prediction based on a knowledge of chemical structures of the drug was through the combined MARVIN and PALLAS programs. If the proposed model adequately represents the data, the residuals should form a random pattern with a normal distribution N(0, s 2), with the residual mean equal to zero, and the standard deviation of residuals being near to experimental noise. Examination of residual plots may be assisted by a graphical analysis of residuals, and systematic departures from randomness indicate that the model and parameter estimates are not satisfactory.

Spectrophotometric and 27‐Al NMR Characterization of Aluminum(III) Complexes with l‐Histidine

The complex formation between l‐histidine (HHis) and aluminum(III) ion in water solutions was studied by UV spectrophotometric and 27‐Al NMR measurements at 298 K. UV spectra were measured on solutions in which the total concentration of histidine was from 15.0 to 50.0 mmol/dm3 and the concentration ratio of histidine to aluminum was varied from 3∶1 to 10∶1 in the pH range between 4.2 and 6.0. The spectra were taken in the wavelength interval 240–340 nm. Nonlinear least‐squares treatment of the spectrophotometric data indicates the formation of the complexes Al(HHis)3+, Al(His)2+, Al(HHis)His2+, and Al2(OH)His4+ with the overall formation constants βp,q,r: log β1,1,1=11.90±0.04, log β1,1,0=7.25±0.08, log β1,2,1=20.1±0.1, and log β2,1,1=5.92±0.12 (p, q, r are stoichiometric indices for metal, ligand, and proton, respectively). 27Al‐NMR spectra were taken on solutions with the concentration of aluminum 50 mmol/dm3 and that of histidine 250 mmol/dm3. In the pH interval 5.0–6.1, two resonances at 9.5 ppm and 12.0 ppm were assigned to Al(HHis)2+ and Al(HHis)(His)2+ (or Al(OH)(HHis)2 2+), respectively.

CPLET computer program for evaluation of colligative property equilibrium data

Abstract Colligative property equilibrium data, in particular vapour-pressure osmometry, can be evaluated with the CPLET program using the general least squares method whilst applying pit-mapping, simplex, Davidon-Fletcher-Powell and Monte Carlo minimizing routines. From the measurement of colligative property as a function of the reactant concentrations, the “best” set of complexes and corresponding equilibrium constants are found. The stoichiometry of the species can be directly searched for via simultaneous regression estimation of equilibrium constants and stoichiometric indices. A correction of the analytical concentration of the compound under study and/or calculation of the impurity concentration are also possible. The program, written in Fortran 77 for PCs includes a complete statistical analysis of residuals.

Computer evaluation of water sorption on ion exchangers

Water sorption on an ion exchanger can be described by formation of several hydrates. The general least squares program WSLET based on the “pit-mapping” approach has been written for evaluating such equilibria. It is written in FORTRAN 77 for use on personal computers. Besides finding the best values for the equilibrium constants of the various hydrates the program also searches for best values of the stoichiometric indices by using the so-called ESI-method. The program is provided with least-squares procedures and blocks for statistical analysis of the residuals as well as for data simulation. It has been tested with data on the strong base resin Dowex 1 as well as on simulated data. In the present paper an illustrative example is given together with data simulation. It is found that in most cases WSLET helps to find a better fit than earlier models quite efficiently, showing the advantage of the ESI method in combination with least-squares methods.

Computer-aided determination of the composition and stability of complex compounds in solutions with complicated equilibria

Determination of the number of complexes and the stoichiometric indices in their chemical formulae is the most difficult problem in simulating chemical equilibria from data on composition/property relationships. In the interactive approach presented here, test models are modified by adding new species which should quickly increase the agreement of the model with experiment, and complexes are eliminated from redundant models. Modification of models is based on investigation of simple mathematical relationships between the variation of equilibrium composition and the changes in the concentrations of the predominant components caused by the formation of new species. The elimination of complexes is based on finding species with small equilibrium concentrations, which do not affect the measured property at all experimental points. Various programs are applied for the calculation of equilibrium constants; the algorithm used is described. The problems of verifying the adequacy of models and refining experiment design are discussed. Examples of simulation are presented.

Computation in kinetics, III. A new method for kinetic model search based on simultaneous regression estimation of rate constants, stoichiometry and/or reaction order

A method for kinetic model search based on a simultaneous regression estimation of rate constants, stoichiometric indices and/or reaction orders is proposed. The advantage is that (i) the search is faster and more economical than the classical trial and error approach, and (ii) standard deviations of stoichiometric indices and/or of reaction orders are obtained. A modified version of the KILET program is submitted.

Multiparametric curve fitting—XI: Polet computer program for estimation of formation constants and stoichiometric indices from normalized potentiometric data

The FORTRAN computer program POLET(84) analyses a set of normalized potentiometric titration curves to find a chemical model, i.e., the number of species present and their stoichiometry, and to determine the corresponding stability constants log β pqrs and unknown stoichiometric indices p, q, r, and s of up to quaternary M p L q Y r H s complexes. The program belongs to the ABLET family, based on the LETAG subroutine, and can use an algorithmic and/or heuristic minimization strategy, or a beneficial combination of both. The data, a set of potentiometric titration curves plotted as volume and potential, are converted into normalized variables (formation function, pH) and then a computer-assisted search for a chemical model by POLET(84) is applied. The procedure for efficient application of POLET(84) in an equilibrium analysis is described and the program is validated by use of literature and simulated data. The reliability of the chemical model and its parameters is established by the degree-of-fit achieved, and the closeness of the stoichiometric indices to integral values.

Multiparametric curve fitting—X: A structural classification of programs for analysing multicomponent spectra and their use in equilibrium-model determination

A functional structure-classification of programs for analysis of spectra elucidates their efficiency for determination of the stoichiometric indices, stability constants and molar absorptivities of complex species. SQUAD (84) introduces new functional units for ( i) determination of the number of light-absorbing species, ( ii) a rigorous fitness test, ( iii) plotting three-dimensional graphs of a paraboloid minimum response-surface as a function of two selected parameters, and a graph of the fitted absorbance response-plane, ( iv) simultaneous estimation of stoichiometric indices and stability constants, ( v) simulation of an absorbance matrix data by loading with random errors related to the instrumental variance of the absorbance. A guide to experimental procedure and computational strategy for chemical model determination is given and nine diagnostic tools useful in finding the number of species present and their stoichiometry and stability constants by regression analysis of spectra are tested, by use of literature data.

Multiparametric curve fitting—IX : Simultaneous regression estimation of stoichiometry and stability constants of complexes

A chemical model ( i.e., the number of complexes, their stoichiometry and stability constants with molar absorptivities) in solution equilibria may be established by ( i) the trial-and-error method in which stability constants are estimated for an assumed set of complexes in the mixture and a fitness test is used to resolve a choice of plausible models to find the true one; ( ii) the simultaneous estimation of the stoichiometry and stability constants for species divided into “certain” species for which the parameters β pqr , ( p, q, r) are known and held constant, and “uncertain” species with unknown parameters which are determined by regression analysis. The interdependence of stability constants and particular sets of stoichiometric indices requires that the computational strategy should be chosen carefully for each particular case. The benefits and limitations of both approaches are compared by means of examples of potentiometric titration data analysis by the POLET(84) program and of spectrophotometric data analysis by the SQUAD(84) program. A strategy for efficient computation is suggested.