Effect of slope position on leaf and fine root C,N and P stoichiometry and rhizosphere soil properties in Tectona grandis plantations

Little is known about C-N-P stoichiometries and content in teak(Tectona grandis)plantations in South China,which are mostly sited on hilly areas with lateritic soil,and the effect of slope position on the accumulation of these elements in trees and rhizosphere soils.Here we analyzed the C,N,P content and stoichiometry in leaves,fine roots and rhizosphere soils of trees on the upper and lower slopes of a 12-year-old teak plantation.The Kraft classification system of tree status was used to sample dominant,subdominant and mean trees at each slope position.The results showed that the C,N and P contents in leaves were higher than in fine roots and rhizosphere soils.The lowest C/N,C/P and N/P ratios were found in rhizosphere soils,and the C/N and C/P ratios in fine roots were higher than in leaves.Nutrient accumulation in leaves,fine roots and rhizosphere soils were significantly influenced by slope position and tree class with their interaction mainly showing a greater effect on rhizosphere soils.Leaf C content and C/N ratio,fine root C and P contents,and C/N and C/P ratios all increased distinctly with declining slope position.The contents of organic matter(SOM),ammonium(NH4+-N),nitrate-nitrogen(NO3--N)and available potassium(AK)in rhizosphere soils were mainly enriched on upper slopes,but exchange calcium(ECa),available phosphorus(AP),and pH were relatively lower.Variations in the C,N and P stoichiometries in trees were mainly attributed to the differences in rhizosphere soil properties.N and P contents showed significant positive linear relationships between leaf and rhizosphere soil,and C content negative linear correlation among leaves,fine roots and rhizosphere soils.Chemical properties of rhizosphere soils,particularly C/N and NH4+-N,had significant effects on the leaf nutrients in trees on the upper slope.Correspondingly,rhizosphere soil properties mainly influenced fine root nutrients on the lower slope,and soil AK was the major influencing factor.Overall,these results offer new insights for the sustainability and management of teak plantations in hilly areas.

Evolution of nutrient structure and phytoplankton composition in the Jiaozhou Bay ecosystem

The inventories of nutrients in the surface water and large phytoplankton(>69 μm) were analyzed from the data set of JERS ecological database about a typical coastal waters, the Jiaozhou Bay, China, from 1960s for N, P and from 1980s for Si. By examining long term changes of nutrient concentration, calculating stoichiometric balance, and comparing diatom composition, Si limitation of diatom production was found to be more possible. The possibility of Si limitation was from 37% in 1980s to 50% in 1990s. Jiaozhou Bay ecosystem is becoming serious eutrophication, with notable increase of NO 2 N, NO 3 N and NH 4 N from 0 1417 μmol/L, 0 5414 μmol/L, 1 7222 μmol/L in 1960s to 0 9551 μmol/L, 3 001 μmol/L, 8 0359 μmol/L in late 1990s respectively and prominent decrease of Si from 4 2614 μmol/L in 1980s to 1 5861 μmol/L in late 1990s; the nutrient structure is controlled by nitrogen; the main limiting nutrient is probably silicon; because of the Si limitation the phytoplankton community structure has changed drastically.

Spatial and Seasonal Dynamics of Dissolved and Suspended Nutrients in the Water Column of Meromictic Lake Shira

1 Introduction The vertical stratification of the water column has a significant impact on the spatial distribution of aquatic organisms,the dynamics and structure of the food web in

Ablative behavior and mechanism of SiC_(f) /SiBCZr composites prepared by PIP process

SiC_(f)/SiBCZr composites were prepared by polymer precursor impregnation and pyrolysis process with near stoichiometric ratio SiC fiber preform as reinforcement phase and SiBCZr multiphase ceramic precursor as impregnating reagent.The results highlighted that the SiC_(f)/SiBCZr composites exhibited excellent ablative properties after ablative tests at 1200℃/3600 s and 1400℃/3600 s,and the strength retention rates of the composites reached 90%and 85%,respectively.This was mainly due to the liquid sealing effect of the ablative products represented by B2O_(3) and SiO_(2)∙B_(2)O_(3),which inhibited the ablative reaction by reducing the diffusion rate of the oxidation medium,and the solid pinning effect of the substances represented by SiO_(2),ZrO_(2),and ZrSiO_(4),which could play high viscosity and high strength characteristics to improve anti-erosion ability.The above-mentioned SiC_(f)/SiBCZr composites with corrosion resistance,oxidation resistance,and ablative resistance provided a solid material foundation and technical support for the development of reusable spacecraft hot-end components.

Low-temperature growth of stoichiometric aluminum nitride films prepared by magnetic-filtered cathodic arc ion plating

A1N films were prepared on Si（100） and quartz glass substrates with high deposition rate of 30 nm-min-I at the temperature of below 85 ℃ by the magnetic-filtered cathodic arc ion plating （FCAIP） method. The as-deposited A1N films show very smooth surface and almost no macrodroplets. The films are in amorphous state, and the formation of A1N is confirmed by Nls and A12p X-ray photoelectron spectroscopy （XPS）. The XPS depth profile analysis shows that oxygen is mainly absorbed on the A1N surface. The A1N film has A1 and N concentrations close to the stoichiometric ratio with a small amount of A1203. The prepared A1N films are highly transparent over the wave- length range of 210-990 nm. The optical transmission spectrum reveals the bandgap of 6.1 eV. The present technique provides a good approach to prepare large-scale A1N films with controlled structure and good optical properties at low temperature.

Elevational patterns of carbon,nitrogen and phosphorus in understory bryophytes on the eastern slope of Gongga Mountain,China

Aims The nutrient uptake,requirement and releasing rates of bryophytes are very different from those of tracheophytes.However,it is diffi-cult to make a quantitative evaluation of bryophytes’roles in nu-trient cycling and their specific eco-physiological adaptations due to lack of knowledge of their concentrations and stoichiometric ratios of carbon(C),nitrogen(N)and phosphorus(P).To fill this gap,the present study aims to investigate:(i)what are the elevational trends of C,N and P concentrations and stoichiometric ratios of bryophytes?(ii)whether C,N and P concentrations and stoichio-metric ratios of bryophytes differ between different bryophyte types(in terms of the growth form and living substrate)?and(iii)how do the exponent scalings of N and P of bryophytes change along the elevational gradient?Methods We measured and calculated the C,N,P concentrations and stoi-chiometric ratios of bryophytes from four elevations on the eastern slope of Gongga Mountain(22 species in total).Differences in these traits among elevations,and between different bryophyte types were compared.The log-log allometric regression parameters of N and P at each elevation were also determined and compared.Important Findings The C,N and P concentrations of bryophytes showed decreasing trends with increasing elevations.More specifically,erect bryo-phytes possessed higher C and N concentrations than those of pros-trate species,and terricolous species had higher P concentration than that of corticolous and saxicolous species.Bryophytes from different elevations had an invariant allometric regression slope for P versus N.Future research at a larger scale is in need for a more generalized law of bryophytes.

Enhancing stability by tuning element ratio in 2D transition metal chalcogenides

Two-dimensional(2D)transition metal chalcogenides(TMCs)are known to be susceptible to the atmosphere,which greatly obscures the intrinsic physical and chemical properties.The quantitative origin of the instability on the atomic scale has not been well investigated due to the lack of environmentally stable TMCs sample.Here,we find the stability of the grown TMCs is strongly relevant to their initial element ratios,and thus the stoichiometric bonded TMCs have favorable stability,benefitted from the TMCs with controllable chalcogenisation.In this study,the degree of structural degradation has been quantitatively defined by the reduced element ratio of chalcogen to metal through the time-dependent characterizations,and the non-stoichiometric ratios in TMCs reveal the atomic lattices with point defects like additive bonds or vacancies inside.This study not only provides a potential view to fabricate environmentally stable TMCs based devices,but also will bring an effective feasibility of stacking stable vertical heterostructures.

Phosphorus Speciation and Nutrient Stoichiometry in the Soil-Plant System During Primary Ecological Restoration of Copper Mine Tailings

The effects of plant vegetation on phosphorus （P） speciation, pH, total carbon concentration, total nitrogen concentration, and alkaline phosphatase activities were investigated to explore the P uptake strategy of plants in low-P soil and to determine the nutrient stoichiometric ratio changes in the rhizosphere of plants （Imperata cylindrica, Miscanthus floridulus, Zoysia sinica, Artemisia lavandulaefolia, Indigofera pseudotinctoria, and Conyza canadensis） which had grown for approximately 15 years in copper mine tailings, East China. The results showed that the average pH values in the rhizosphere decreased by 0.06 1.37 compared with those in the non-rhizosphere. The alkaline phosphatase activities of the rhizosphere were significantly higher than those in the non-rhizosphere. The mean concentrations of aluminum （A1）- and iron （Fe）-bound P and Ca2-P （CaHPO4） in the rhizosphere of all plants were 5.4% to 87.7%, 49.2% to 214.2%, and 86.6% to 147.6% higher than those in the non-rhizosphere, respectively. Except for Cas-P （CasH2（PO4）6） and Cal0-P （Cal0（PO4）6（OH）2） in the rhizosphere, all kinds of inorganic P forms were negatively correlated with pH. Significant correlation was also observed among the concentrations of dominant forms of inorganic P, C, and N and alkaline phosphatase activities in the rhizosphere. Among the studied species, I. pseudotinetoria showed the most significant effect on enhancing soil available P concentration. The stoichiometric ratios of C：P and N：P were apparently higher in the rhizosphere than the non-rhizosphere, whereas these ratios were far below the ratios commonly observed in Chinese soils. These results indicated that the plant growth effectively affected P fractions possibly by changing pH, C and N concentrations, and alkaline phosphatase activity, in the rhizosphere in copper mine railings.