[Nitrogen and phosphorus stoichiometry of aquatic macrophytes in Kaidu River of Xinjiang and the potential influencing factors].

Nitrogen (N) and phosphorus (P) are two common mineral elements constraining plant growth. Nutrients in aquatic macrophytes are mainly absorbed from water and sediments, and thus elemental composition in plant tissues can reflect the nutritional status in freshwater ecosystems. Kaidu River is an important river flowing through the alpine meadows, deserts, and desert oases in Xinjiang. Herein, samples of aquatic macrophytes, water, and sediments across the Kaidu River were collected. Foliar stoichiometric characteristics of N and P in plants were examined among life forms and phylogeny. The differences and correlations among the stoichiometric characteristics of plants, water bodies, and sediments in the upstream and downstream and across different land use types were elaborated. Results showed that the means of leaf N and P concentrations and N/P mass ratio were 24.9 mg·g-1, 2.49 mg·g-1, and 12.6, respectively. There were significant differences in the leaf N and P stoichiometry among various life forms. Specifically, leaf N and P concentrations in submerged species were significantly higher than that in floating-leaved species and emergent species. The N/P of floating-leaved species was 19.2 and significantly higher than that in other two life-forms, indicating that their growth might be limited by P. Leaf N and P concentrations were higher in the upstream than in the downstream. Nitrogen contents in water and sediment were the higher in the upstream of the river. Compared with the river reaches in farming areas, the higher N and P concentrations of aquatic macrophytes in the grassland regions might be related to the higher contents of organic matter in grassland soils and of animal slurries from flocks and herds, suggesting that grazing exerted larger impact on the stoichiometric characteristics of the Kaidu River ecosystem. Our findings highlighted that overgrazing might accelerate the deterioration of water quality in the upstream of the Kaidu River, disturb the balance of N and P in the aquatic ecosystem, and potentially influence the biogeochemical cycling.

[Leaf C:N:P stoichiometry of 67 plant species and its relations with climate factors across the deserts in Xinjiang, China.] / 新疆67ç§è’æ¼ æ¤ç‰©å¶ç¢³æ°®ç£·è®¡é‡ç‰¹å¾åŠå ¶ä¸Žæ°”å€™çš„å ³ç³».

Desert ecosystem has unique drought-enduring plants and stoichiometric characteristics. We collected leaf samples of 67 plant species from 63 desert sites in Xinjiang, and explored foliar carbon (C), nitrogen (N) and phosphorus (P) stoichiometry and the relationship between leaf nutrient stoichiometry and climatic factors. The results showed that the average content of leaf C, N and P in these plants were 394, 18.4 and 1.14 mg·g-1, respectively. The mean values of C:N, C:P and N:P were 28, 419 and 18, respectively. In general, shrubs had higher leaf N content than trees and herbs, while leaf P content was lower (higher) in shrubs than in herbaceous plants (trees). Plants with C3 photosynthesis pathway had higher leaf C, N, C:P and N:P than those with C4 pathway. With increasing mean annual precipitation, leaf C first decreased and then increased, while both leaf N and P showed the opposite trend. Leaf C:N and C:P first decreased and then increased, while leaf N:P changed insignificantly. With increasing mean annual temperature, leaf C first decreased and then increased, and leaf N and P decreased, while leaf C:P and N:P increased. Leaf C:N did not change significantly with mean annual temperature. Mean annual precipitation generally showed stronger control on the variation of leaf nutrient stoichiometry than MAT and plant functional types. These results could help predict responses of the biogeochemical cycling of C, N and P to the global climate changes and provide reference and basic data for biogeochemical modeling in the arid regions.

[Optimal operating condition of ICP-aES for determination of soil nutrients extracted by Mehlich 3 through solution simulation].

As a key process of fertilization with soil test, the determination of soil effective nutrients has received great attention in recent years. Based on a series of standard solution mixtures, which simulate the soil nutrients extracted by Mehlich 3 (M3) reagent, the optimal operating condition of ICP-AES was explored in a systematic way. The results show that the 20 key nutrient elements (P, K, Ca, Mg, Na, Fe, Mn, Cu, Zn, Cd, Cr, Pb, Ni, Al, B, Mo, S, Si, Se, and As) in the solutions can be determined correctly and proficiently when ICP-AES is set at 0.80 L x min(-1) of carrier gas flux, with observation height 15 mm and power 1200 W. This study supplies a primary experimental foundation for establishing the determination technique of essential nutrient elements, extracted from soils in China with the general soil-nutrient extractant M3 reagent.

[Stoichiometry of multi-elements in the zinc-cadmium hyperaccumulator Thlaspi caerulescens grown hydroponically under different zinc concentrations determined by ICP-AES].

Thlaspi caerulescens is commonly known as a zinc (Zn) and cadmium (Cd) hyperaccumulator, which can be used to clean up the Zn- and/or Cd-contaminated soil. However, it is unclear whether high soil Zn concentrations will stimulate undue accumulations of other elements to such an extent as to cause the nutrient unbalance in the soil. To address this question, the inductively coupled plasma-atomic emission spectrometry (ICP-AES) was employed to investigate the effect of Zn on the stoichiometry of Zn, Cd, K, P, Mg, Ca, Fe, Mn and Cu in T. caerulescens (Ganges ecotype) exposed to low, middle and high Zn concentrations (5, 50 and 500 micromol x L(-1), respectively) in a hydroponic experiment. The results showed that there were no significant variations in contents of Cd, K, P, Mg, Ca, Fe, Mn and Cu in the shoot of T. caerulescens, however, the Zn content in the shoot and root with 500 mciromol x L(-1) Zn treatment increased as much as 13 times higher than that with low Zn exposure, indicating that the plant is capable of Zn hyperaccumulating. The authors' study suggests that it is improbable to induce soil nutrient unbalance when T. caerulescensis (Ganges) is used for phytoremediation of Zn-contaminated soil, in that over-uptake of nutrient elements from the soil other than Zn was not observed, at least for the elements K, P, Mg, Ca, Fe, Mn and Cu.

[Study on the response of middle and trace elements in Humulus scandens leaves to atmospheric reactive nitrogen with ICP-AES].

Based on field measurements, the effects of atmospheric reactive nitrogen (ARN) on the middle/trace element concentrations in the leaves of wild plant humulus scandens were analyzed. Leaves of H. scandens were collected from six sites around Beijing in the North China Plain, and the concentrations of Ca, Mg, S, Fe, Mn, Cu, Zn, B, and Na in the leaves were determined with inductively coupled plasma atomic emission spectrometry (ICP-AES). The results showed that element concentrations in leaves ranked as Ca (41 106) > S (8 370) > Mg (6 628) > Fe(476) > Na (92) > B (78) > Mn (49) > Zn (38) > Cu (15) mg x kg(-1) dry matter; There were no significant difference in any of the individual element in the H. scandens leaves along the gradient of ARN, suggesting that the increasing demand of H. scandens for middle/trace elements, induced by the enhanced nitrogen availability from ARN, was not yet beyond the nutrient-supply limits of the local soils. This study offers reference to scientific assessments of the middle/trace element status in terrestrial herbaceous plants under the global background of increasing nitrogen deposition.

[Application of ICP-MS to species determination of Pb, As and Cd in hoggery waste].

Distribution of heavy metal species in animal wastes needs to be monitored to control the heavy metal pollution during the utilization of wastes. Here, ICP-MS was applied to determine the speciation of Pb, As and Cd in the wastes from two hoggeries in the suburb of Beijing. The air-dried and finely ground samples were digested by HNO3-HClO4, or, sequentially extracted with BCR procedure before content determination of heavy metals. The total concentrations of Pb, As and Cd were 29.0, 28.2 and 0.288 mg x kg(-1) dry weight (DW) in the fresh hoggery wastes respectively, and 19.7, 28.2 and 0.134 mg x kg(-1) DW in the dry-cleaning waste, respectively. The concentrations of the three metals in both fresh and dry-cleaning wastes were all lower than the control standards for urban wastes for agricultural use promulgated by the national government, although As was close to the control value. Over 50% of Pb, As and Cd in the fresh waste were exchangeable/carbonate species, and less than 20% were organic/sulphide. However, species distributions of the heavy metals changed markedly after the process of dry-cleaning. The fraction of highly ecotoxic species (exchangeable/carbonate bound and Fe/Mn oxide bound) in the dry-cleaning waste decreases by 5%-25% for the three metals, indicating reduced risks of heavy metal pollutions when dry-cleaning wastes are applied to farmlands. This study contributes basic data for the resource utilization and ecological security assessment of hoggery wastes from Beijing.