Stoichiometric Relationship Research Articles

Soil C:N:P stoichiometry in tropical forests on Hainan Island of China: Spatial and vertical variations

Soil carbon (C), nitrogen (N), and phosphorus (P) are three important elements. The study of stoichiometric relationships of soil C, N, and P in tropical forests on Hainan Island, China could improve our understanding of nutrient cycling and provide valuable information for forest management. Soil samples were collected at five different depths from 0 to 100 cm at 100 sites among four different forest types on Hainan Island, and total C, N, and P concentrations were measured. Soil C and N concentrations and soil C:P and N:P ratios declined from the surface soil layer to the deeper soil layers and soil P and C:N ratio had relatively small variations among different depths, due to that soil C and N were mostly controlled by biological processes such as photosynthesis and N2-fixation, while P was more influenced by bedrock. Large spatial variations were found for soil C, N, P concentrations and their ratios. Soil C and N concentrations were significantly influenced by longitude and vegetation cover, while soil P concentration and C:P and N:P ratios were significantly controlled by latitude. This study produced a comprehensive data set of soil C, N, and P stoichiometry, and their variation patterns and controls in the tropical forests. The information generated here could help improve ecosystem models for better understanding of forest element stoichiometry, ecosystem productivity, and plant-environment relationships.

The formation of an amorphous composite between flavonoid compounds: Enhanced solubility in both oil components and aqueous media

In this study, the formation of naringenin (NRG) amorphous composite using coformer candidates of nine selected flavonoids was investigated. The screening test showed that hesperetin (HPT) is an excellent potential coformer. The melt-quenched particles (MQPs) of NRG/HPT (molar ratio of 3/1 to 1/3) were prepared by melt-quenching method. MQPs of NRG/HPT showed the hallow-pattern in any combination ratio in powder X-ray diffraction. MQPs of NRG/HPT (1/1) showed the highest physical stability without recrystallization of NRG and HPT upon storage. Conversely, other MQPs showed recrystallization from the compound with a higher molar ratio, implying the stoichiometric relationship between NRG and HPT at a molar ratio of 1/1. The MQPs of NRG/HPT (1/1) showed significantly improved dissolution properties of both NRG and HPT in aqueous media. In addition, the MQPs of NRG/HPT (1/1) enhanced the solubility of both NRG and HPT even in oil components. Their solubility from the MQPs of NRG/HPT (1/1) increased 5-times compared to untreated compound powder in oil components. These results showed that an amorphous composite of NRG/HPT (1/1) enhances the physical stability and solubility of both NRG and HPT.

The dynamics and stoichiometry of dissolved organic carbon release by kelp.

Canopy-forming kelps are foundational species in coastal ecosystems, fixing tremendous amounts of carbon, yet we know little about the ecological and physiological determinants of dissolved organic carbon (DOC) release by kelps. We examined DOC release by the bull kelp, Nereocystis luetkeana, in relation to carbon fixation, nutrient uptake, tissue nitrogen content, and light availability. DOC release was approximately 3.5 times greater during the day than at night. During the day, N. luetkeana blades released an average of 16.2% of fixed carbon as DOC. Carbon fixation increased with light availability but DOC release did not, leading to a lower proportion of fixed carbon released as DOC at high light levels. We found no relationship between carbon fixation and DOC release rates measured concurrently. Rather, DOC release by N. luetkeana blades declined with marginal significance as blade tissue nitrogen content increased and with experimental nitrate addition, supporting the role of stoichiometric relationships in DOC release. Using a stable isotope (13 C) tracer method, we demonstrated that inorganic carbon is rapidly fixed and released by N. luetkeana blades as 13 DOC, within hours. However, recently fixed carbon (13 DOC) comprised less than 20% of the total DOC released, indicating that isotope studies that rely on tracer production alone may underestimate total DOC release, as it is decoupled from recent kelp productivity. Comparing carbon and nitrogen assimilation dynamics of the annual kelp N. luetkeana with the perennial kelp Macrocystis pyrifera revealed that N. luetkeana had significantly higher carbon fixation, DOC production and nitrogen uptake rates per unit dry mass. Both kelp species were able to perform light-independent carbon fixation at night. Carbon fixation by the annual kelp N. luetkeana is as high as 2.35kg C·m-2 ·yr-1 , but an average of 16% of this carbon (376g C·m-2 ·yr-1 ) is released as DOC. As kelp forests are increasingly viewed as vehicles for carbon sequestration, it is important to consider the fate of this substantial quantity of DOC released by canopy-forming kelps.

Hydrochemical characteristics in karst reservoirs and its implication for inorganic carbon deposition fluxes

为探究筑坝后不同水库物理、化学、生物过程对水化学和碳循环的影响，本研究对贵州三岔河流域的平寨水库、普定水库以及猫跳河流域的红枫湖水库进行研究，于2018年3月2019年1月分别在入库河流和库区采集了分层水样和沉降颗粒物，并探究水中主要离子及颗粒物通量的时空变化特征及其控制因素.结果表明，水体主要离子的主要来源受碳酸盐溶解影响，并且离子浓度受光合作用控制.红枫湖水库水体水化学类型为Ca-Mg-HCO₃-SO₄型，普定水库、平寨水库水化学类型均为Ca-HCO₃-SO₄.夏季藻类光合作用诱导碳酸盐沉淀导致水体表层Ca²⁺、HCO₃^-及溶解态Si浓度降低，其降低幅度分别为20.87%~44.25%、33.12%~51.18%、48.55%~96.34%.此外，藻类光合作用也影响C、N、Si等生源要素间的化学计量关系.Mg²⁺/Ca²⁺比值在水体垂向剖面上主要受碳酸钙沉淀的控制，而在不同水库之间则主要受流域岩性的控制.根据沉积物捕获器通量计算的平寨水库、普定水库、红枫湖水库夏季颗粒无机碳沉积通量分别为0.74、1.36、0.27 t/（km²·d），而根据水体Ca²⁺浓度降低计算的通量分别为0.31~0.64、0.35~0.99、0.09~0.29 t/（km²·d），根据水体HCO₃^-浓度降低计算的通量分别为0.30~0.65、0.29~1.26、0.12~0.33 t/（km²·d）.其红枫湖水库无机碳沉降通量的实测值与计算值接近，而平寨、普定水库实际沉降通量高于计算值，这可能是有外源输入导致.因此，利用水化学分层数据能对喀斯特水库中的无机碳沉降通量进行合理估算，并且能够得到较好的估算结果，从而指示碳循环的过程.;To explore the impact of changes in physical, chemical and biological processes on hydrochemistry and carbon cycle caused by damming, we investigated the flux of suspended particulate and the spatiotemporal variations of major cations and anions (Ca²⁺, Mg²⁺, Na⁺, K⁺, HCO₃^-, SO₄^2-, Cl^-) in three karst reservoirs in Guizhou Province, i.e. Puding Reservoir, Pingzhai Reservoir, and Lake Hongfeng, for a whole hydrological year. The results showed that carbonate weathering and algae photosynthesis controlled the spatiotemporal variations of ion concentrations. The hydro-chemical type of Lake Hongfeng is Ca-Mg-HCO₃-SO₄, while it is Ca-HCO₃-SO₄ in Puding Reservoir and Pingzhai Reservoir. During the summer period, as the result of carbonate precipitation induced by algae photosynthesis, the concentrations of Ca²⁺, HCO₃^-, and SiO₂ in the surface water decreased by 20.87%-44.25%, 33.12%-51.18%, and 48.55%-96.34%, respectively. Our results also indicated that the stoichiometric relationships among C, N, Si could be affected by photosynthesis of aquatic photosynthetic organisms. Additionally, it is found that calcite precipitation regulated the Mg²⁺/Ca²⁺ in water column. Finally, the inorganic carbon fluxes in summer period calculated by sediment traps were 0.74 t/(km²·d), 1.36 t/(km²·d), 0.27 t/(km²·d) for Pingzhai Reservoir, Puding Reservoir and respectively, which are comparable with the fluxes estimated by the concentration differences in Ca²⁺ and HCO₃^- between surface and bottom water layers. The measured fluxes of inorganic carbon in Pingzhai Reservoir and Puding Reservoir by sediment traps are higher than the calculated one, suggesting a certain amount of allochthonous inorganic carbon input due to the strong hydrological condition. Therefore, it is an alternative way to estimate the deposition flux of inorganic carbon in karst reservoirs by using vertical variations in ion concentrations in stratification period.

Body Size Plasticity of Weevil Larvae (Curculio davidi) (Coleoptera: Curculionidae) and Its Stoichiometric Relationship With Different Hosts.

Parasites obtain energy and nutrients from the host, and their body size is also usually limited by host size. However, the regulatory mechanisms that control the plasticity of parasite body sizes and the stoichiometric relationships with their hosts remain unclear. Here we investigated the concentrations of 14 elements (C, H, O, N, P, S, K, Na, Ca, Mg, Al, Fe, Mn, and Zn) in the acorns of three oak species (Quercus spp.), in their endoparasitic weevil (Curculio davidi Fairmaire) (Coleoptera: Curculionidae) larvae and in the larval feces, and the weight of weevil larvae within different hosts in a warm-temperate zone of China. Our results showed that the three acorn species exhibited significant differences in C, H, O, P, K, Mg, and Mn concentrations. However, in the weevil larvae, only P, Mn, and C:P ratio revealed significant differences. Weevil larvae preferentially absorbed and retained N, Zn, Na, and P, whereas Mn, K, Ca, and O were passively absorbed and transported. The weevil larvae weight was associated with acorn stoichiometry, and positively correlated with acorn size. Weevil larvae P decreased, but Mn and C:P increased with their weight, implying highly variable in somatic stoichiometry are coupled with the plasticity of body size. Interestingly, weevil larvae weight was negatively correlated with acorn infection rate, indicating small-size parasitic insects might have higher fitness level in parasite–host systems than larger-size ones. Our results suggest that variation in P, Mn, and C:P in parasites may play critical roles in shaping their body size and in improving their fitness.

Coupling the resource stoichiometry and microbial biomass turnover to predict nutrient mineralization and immobilization in soil

The mineralization of organic nitrogen (N) and phosphorus (P) by the soil microbial biomass, as well as microbial immobilization of their mineral forms, can be predicted from differences between the stoichiometry of organic substrate and the nutrient demand of the microbial biomass. The accuracy of such predictions, however, decreases when the nutrient demand of microbial biomass changes in response to nutrient limitation or excess. We quantified net N and P mineralization/immobilization along gradients of organic substrate stoichiometry in a short-term (2-day) incubation experiment. Gradient of organic substrate stoichiometry (water extractable organic N and P concentrations) was created by mixing soils from two spruce forest soils (from both litter and organic topsoil horizons) at five different ratios. Biological predictors (i.e., microbial carbon (C) use efficiency and microbial biomass C, N, and P) of net nutrient mineralization/immobilization were quantified, and theoretical N and P mineralization/immobilization rates were predicted using known stoichiometric relationship. Measured net N and P immobilization was lower than that predicted. Extended mathematical modelling in combination with stable isotope analysis showed that the capability of microbial community to reduce its demand for external nutrients was responsible for the difference between the predictions and observations. Active part of microbial community instantly recycled N from decaying part of microbial community and very likely utilized internal P sources (i.e. polyphosphates) when the abundance of N and P in available organic compounds was insufficient. Our results suggest that the N recycling from dead microbial biomass and the internal microbial P sources warrant further investigation. Including these mechanisms in soil biogeochemical models based on ecological stoichiometry principles could improve their predictive accuracy.

Determination of the binding of natural products to the human c-myb oncogene promoter G-quadruplex DNA by capillary electrophoresis and electrospray ionization mass spectrometry

The relationship between a drug and its target directly affects its pharmacology and efficacy. Drug-target binding ability and binding stoichiometry are essential characterization data in pharmaceutical research. The c-myb proto-oncogene encodes a crucial transcription factor that is involved in proliferation, differentiation, and maturation during hematopoiesis. Recent studies have found that the human oncogene c-myb is overexpressed in cancer tissues such as colorectal cancer. C-myb has become a potential therapeutic target for colorectal cancer, leukemia, and other cancers. A guanine (G)-rich DNA sequence located in the promoter region of c-myb can be spontaneously folded to form an intra-molecular G-quadruplex (G4) with cationic induction. The specific recognition of small molecules can stabilize this G4 folding, thus regulating the transcription and expression of c-myb. In this study, pressure assisted capillary electrophoresis frontier analysis (PACE-FA) combined with electrospray ionization mass spectrometry (ESI-MS) was used to investigate the interactions between the human c-myb promoter G4 and natural product molecules. In PACE-FA, an external pressure (no more than 13.8 kPa) in the same direction of the migration of the analyte was used in capillary electrophoresis frontier analysis (CE-FA), which greatly sped up the analysis while maintaining the accuracy of the results. Meanwhile, the combination of PACE-FA and ESI-MS could rapidly determine the affinity and stoichiometric relationship between binding molecules and targets. First, the intramolecular parallel-stranded G4 formation of the c-myb promoter sequence in the presence of cations (K+, NH4+) was investigated by circular dichroism (CD) and ESI-MS. Then, ESI-MS was used to rapidly screen the natural products for candidate molecules that bound the target G4 DNA. The binding interactions were measured by mixing the c-myb DNA with each natural product separately in a 1:4 molar ratio, and then directly infusing these mixtures into the ESI-MS system. From the ESI-MS spectra, IRa values calculated from the relative intensities of DNA and its complex ions were used to probe the binding affinities of the natural products. This parameter denotes the relative binding affinity for a small molecule with the G4 DNA. Three natural products were identified through the screen, and their binding affinities to G4 DNA were ranked as follows:pseudolaric acid B > scopolamine butylbromide > nuciferine. Considering that both specific and non-specific binding existed in the solution phase, a free solution method using PACE-FA was developed to further test the binding ability of these products to the c-myb promoter G4 DNA. In the PACE-FA experiments, the pre-equilibrated mixture of the c-myb G4 DNA and the selected ligand was injected into the capillary prior to separation. Upon applying voltage and an external pressure (6.9 kPa) to the capillary, different species of analytes in the sample migrated at their own rates due to their different sizes and charges. The results showed that scopolamine butylbromide could bind specifically to target G4 DNA with 1:1 stoichiometry and a binding constant of 1.18×105 L/mol. Nuciferine's binding to G4 DNA showed a linear increasing trend due to nonspecific binding; thus nuciferine is a nonspecific binder. Although pseudolaric acid B showed high affinity for the c-myb G4 DNA and 1:1 and 1:2 G4-bound complex ions were observed in ESI-MS measurements, the PACE-FA results indicated that pseudolaric acid B did not bind to target G4 DNA in free solution. Therefore, scopolamine butylbromide could be the best candidate to regulate the transcription of the c-myb oncogene, and is expected to be a precursor for anticancer drugs. In this work, PACE-FA has allowed for significant improvements to the conventional CE-FA technique. This combination of PACE-FA and ESI-MS not only reduced the time needed for binding analysis, but also improved the accuracy and specificity of the affinity analysis compared to conventional binding approaches. Furthermore, this combination could be used to screen other targeted drug candidates and to evaluate their interaction mechanisms.

Biogeochemistry of dissolved and particulate phosphorus speciation in the Maowei Sea, northern Beibu Gulf

Phosphorus (P) is an important biogenic element that limits algal growth, and influences primary productivity and biogeochemical cycling of other biogenic elements in freshwater and marine ecosystems. Surface water samples were collected along the salinity gradients from the western and eastern flanks of the Maowei Sea (MWS) during July 2018 for measurements of different P species, including dissolved nitrogen and silicate. Total dissolved P (TDP) dominated the total P (TP) accounting for 64.9 ± 9.7% of TP, possibly due to relatively less suspended particulate matter (<100 mg/L). Among the dissolved P species, dissolved organic P (DOP) was more abundant (DOP/TDP = 58.1 ± 20%) than dissolved inorganic P (DIP). Considering the entire dataset, the average DIP concentration (1.53 ± 0.83 μM) was lower to medium range, while DOP was relatively higher, compared to other estuaries and coastal waters bodies worldwide. Particulate P was mainly present as particulate inorganic P (PIP), which accounted for 68.5 ± 9.0% of the total particulate P (TPP). The behavior of different P species along the salinity gradients indicated that their concentrations were dominantly influenced by riverine inputs and biogeochemical processes. Intensive mariculture activities in the MWS may have also contributed to elevated DOP compared to other coastal marine systems worldwide. Apart from similar sources of input and cycling processes, the stoichiometric relationship between DIP, dissolved inorganic N (DIN) and dissolved silicate (DSi) suggested that P is potentially limiting, while Si may co-limit primary productivity. The latitudinal distribution of different P species indicated that strong transformations existed between the particulate and dissolved P phases along the salinity gradients. The negative relationship between P partitioning coefficient [log(Kd)] and salinity, and with suspended particulate matter (log[SPM]) suggested that strong particle reactivity and probable competition between dissolved P with other anions for adsorption sites influenced the partitioning of P species in surface water. Additionally, the end-member binary model showed that ~1.24–1.55 μM of DIP may have been removed through biological uptake. In summary, this study shows that the dynamic changes in the concentrations, spatial distribution, and transformation process of different P species between dissolved and particulate phases can effectively reveal the sources of P and understand the internal relationship between the biogeochemical cycling of P, stoichiometric status, and eutrophication.

Available Dissolved Organic Carbon Alters Uptake and Recycling of Phosphorus and Nitrogen from River Sediments

Concurrent with nutrient pollution, agriculture has significantly impacted the quantity, composition, and bioavailability of catchment-derived dissolved organic carbon (DOC) in stream ecosystems. Based on the stoichiometric theory, we tested the hypothesis that bioavailable DOC will stimulate the heterotrophic uptake of soluble reactive P (SRP) and inorganic nitrogen in stream sediments. In a simplified laboratory column flow-through study, we exposed stream sediments to additions of glucose, nitrate, and phosphate alone and in combination (+C, +NP, +CNP), and calculated gross and net changes in DOC and nutrients via a mass balance approach. Our results show that glucose-C increased nutrient uptake, but also that NP additions resulted in the enhanced consumption of both native and added organic C. The effects of C addition were stronger on N than P uptake, presumably because labile C stimulated both assimilation and denitrification, while part of the P uptake was due to adsorption. Internal cycling affected net nutrient uptake due to losses of dissolved organically-complexed P and N (DOP and DON). Overall, our study shows that increases in the stoichiometric availability of organic carbon can stimulate N and P sequestration in nutrient-polluted stream sediments. Future studies are required to assess the effects of complex organic carbon sources on nutrient uptake in stream sediments under different environmental conditions, and whether these stoichiometric relations are relevant for ecosystem management.

Novel spectrofluorimetric determination of brigatinib in bulk powder and human urine samples via ion-pair complex formation using eosin Y

The developed spectrofluorimetric method was successfully applied to the analysis of brigatinib (BRG) in its bulk powder form, and human urine sample.It is based on the investigation of the fluorescence spectrum behavior of the BRG-eosin Y complex. The relative fluorescence intensity (RFI) was recorded at 560 nm after excitation at 480 nm. The principle of the proposed method was thoroughly explained. All experimental parameters affecting method development were optimized. Moreover, the obtained results were fully discussed and statistically analyzed. The molar ratio method was applied to study the stoichiometric relationship between BRG and eosin Y complex. The method revealed a ratio of 1:3 for BRG-eosin Y afforded the highest RFI. The developed method was validated over the concentration range of 62.5–4000 ng mL−1. The results were compared positively with the reported method.

Stoichiometric relations of C, N, and P in urban top soils in Nanjing, China, and their biogeochemical implications

With increasing urban area and population, global cities are playing a more important role in the alteration of the global biogeochemical cycles. The aims of this study are to understand the concentrations and stoichiometric relations of biogenic elements (C, N, and P) in urban soils, further to reveal the effects of C, N, and P accumulation on the urban environment. We collected 317 surface (0–10 cm) soil samples taken from Nanjing, China, a typical city with more than 2000 years of history. These soil samples were located in different urban zones of Nanjing with different land use histories. The soil C, N, and P concentrations were determined. The stoichiometric relations of soil C, N, and P were investigated in urban soils. Meanwhile, some studies on sources of C, N, and P in diverse urban settings from literature were combined to explore the universal rule of C, N, and P cycling and their ecological and environmental effects in urban area. Compared to rural soils, more C, N, and P are accumulated in the urban soils, which also change their stoichiometric relations. The concentrations of OC, TN, and TP in urban top soils are 17.0 ± 9.69 g kg−1, 1.53 ± 0.92 g kg−1, and 1.31 ± 0.67 g kg−1, respectively. The mean atomic ratio of C:N:P is 37:3:1 in the surface of urban soils that strictly differs from natural soils in China and the whole world. The mean of C:N ratio in urban soils is similar to that of agriculture, grassland, and forest soils. However, the ratios of C:P and N:P in urban soils are much lower than that in agricultural, forest, and grassland soils. This implies that P is extremely enriched in the urban soils. The high C in urban soils are considered coming from natural and anthropogenic sources. The high N and P mainly come from anthropogenic sources. The well-constrained C:N:P ratio in rural soils does not apply for urban soils. The abnormal C:N:P ratio of urban soils is the result of unbalanced accumulation of C, N, and P from human activities. Urban soils are already an important storage of carbon. High N and P in urban soils may bring threat of surface water eutrophication and ground water contamination. These effects are expected to increase with the city development time.

Methods for assessment of body tissue composition as an indication of the energetic status in bivalve populations: A comparison of biochemical and elemental analysis

Elemental (CHN) and proximate biochemical compositions of body tissues are useful tools among the ecological indices most commonly used in evaluation of the energetic status of animal populations. Gnaiger and Bitterlich (1984) supplied procedures for the interconversion between both these measurements based on stoichiometric relationships, that were further tested using gut contents and body tissue samples of freshwater fishes. Despite a lack of validation studies, the reported conversion factors have been broadly applied in the field of body composition analysis of marine invertebrates, especially bivalve mollusks. The aim of this study was to test the applicability of those conversion equivalents in analysis of the body tissues of two congeneric clam species (Ruditapes decussatus and Ruditapes philippinarum). To this end, proximate biochemical composition, as analyzed by fractionated extraction of tissues samples and quantification using spectrophotometric methods, was converted to elemental composition, and the resulting figures were compared with those of direct CHN analysis. The results of this comparison indicate good agreement within the ranges reported, provided that ninhydrin positive substances (NPS) are incorporated in the biochemical composition analyses. The magnitude of the nonprotein N component in bivalve tissues appears to complicate the reverse computation of biochemical components from elemental composition because no accurate estimation of proteins from N contents might be possible. Additionally, a specific correction of residual water in dried samples of bivalve tissues for CHN analysis should be applied. The absence of broad differences found between species reflects the morphological, evolutionary and functional proximity between them, whereas tissue differences display the differential role that each organ plays in the organism, although other sources of variability such as diet and sex should be addressed in future research.

Quantifying effects of increased hydroperiod on wetland nutrient concentrations during early phases of freshwater restoration of the Florida Everglades

Wetland restoration requires managing long‐term changes in hydroperiod and ecosystem functions. We quantified relationships among spatiotemporal variability in wetland hydrology and total phosphorus (TP) and its stoichiometric relationships with total organic carbon (TOC:TP) and total carbon (TC:TP) and total nitrogen (TN:TP) in water, flocculent organic matter (floc), periphyton, sawgrass (Cladium jamaicense), and soil during early phases of freshwater wetland restoration—water year (WY) 2016 (1 May, 2015 to 30 April, 2016) to WY 2019—in Everglades National Park (ENP, Homestead, FL, U.S.A.). Wetland hydroperiod increased by 87 days, following restoration actions and rainfall events that increased median stage in the upstream source canal. Concentrations of TP were highest and most variable at sites closest (&lt;1 km) to canal inputs and upstream wetland sources of legacy P. Surface water TOC:TP and TN:TP ratios were highest in wetlands &gt;1 km downstream of the canal in wet season 2015 with spatial variability reflecting disturbances including droughts, fires, and freeze events. The TP concentrations of flocculent soil surface particles, periphyton, sawgrass, and consolidated soil declined, and TC:TP and TN:TP ratios increased (except soil) logarithmically with downstream distance from the canal. We measured abrupt increases in periphyton (wet season 2018) and sawgrass TP (wet season 2015 and 2018) at sites &lt;1 km from the canal, likely reflecting legacy TP loading. Our results suggest restoration efforts that increase freshwater inflow and hydroperiod will likely change patterns of nutrient concentrations among water and organic matter compartments of wetlands as a function of nutrient legacies.

Silicon application induces changes C:N:P stoichiometry and enhances stoichiometric homeostasis of sorghum and sunflower plants under salt stress

Beneficial effects of silicon (Si) on growth have been observed in some plant species, reportedly due to stoichiometric changes of C, N, and P. However, little is known about the effects on the stoichiometric relationships between C, N, and P when silicon is supplied via different modes in sorghum and sunflower plants under salt stress conditions. Therefore, the current study was performed to investigate the impact of differing modes of Si supply on shoot biomass production and C:N:P stoichiometry in sorghum and sunflower plants under salt stress. Two experiments were performed in a glass greenhouse using the strong Si-accumulator plant sorghum, as well as the intermediate type Si-accumulator sunflower, both of which were grown in pots filled with washed sand. Plant species were cultivated for 30 days in the absence or presence of salt stress (0 or 100 mM) and supplemented with one of four Si treatments: control plants (without Si), 28.6 mmol Si L−1 via foliar application, 2.0 mmol Si L−1 via nutrient solution, and combined application of foliar and nutrient solution, each group with five replications. The results revealed that supplied Si modified the C, N, and P concentrations, thereby enhancing the C:N:P stoichiometry and shoot dry matter of sorghum and sunflower plants under salt stress. Both application of Si via nutrient solution, as well as combined application via foliar and nutrient solution, increased the C:N ratio in both plant species under salt stress, but in sorghum plants decreased the C:P and N:P ratios and increased the shoot biomass production by 39%, while in sunflower plants increased the C:P and N:P ratios and increased the shoot biomass production by 24%. Our findings suggest that salt stress alleviation by Si impacts C:N:P stoichiometric relationships in a variable manner depending on the ability of the species to accumulate Si, as well as the route of Si administration.

Inclusion of alkali carboxylate salts at the two-dimensional space of layered alkali titanate via carboxylic acids intercalation

The formation of organic salts trapped at the two-dimensional (2D) space of layered solids is typically not well-defined, lacks stoichiometric relation, and depends on the chain length of the organic moieties. In contrast to this conventional salt intercalation, we report herein the inclusion of alkali carboxylates by intercalation of carboxylic acids to lepidocrocite-type alkali titanate microcrystals. The intercalated organic content of 15.9–37.0 ​wt% is high for a solid with low specific surface area (3 ​m2/g). A small interlayer expansion (~0.7 ​Å) was observed with decanoic, palmitic, and sebacic acids which form the trapped carboxylate salts. Meanwhile, acetic acid produced a typical protonic titanate as with mineral acids. The inclusion of carboxylate anion and the accompanying carboxylic acid spectator was proven by their characteristics IR vibrations. Using K0.8MyTi2-yO4 (M ​= ​Zn, Ni, Co, Fe, Mg, Li), we showed that the host-guest, acid-base interaction influenced the thermal decomposition of the intercalated species. A correlation was observed between the partial charge at the O atom (normalized by the intercalate content) vs the decomposition temperature of the trapped species. The formation of sodium carboxylates similarly occurred with sodium titanate nanotubes.

Stoichiometric flexibility and soil bacterial communities respond to nitrogen fertilization and neighbor competition at the early stage of primary succession

At the early stage of primary succession, there are deficient nutrient resources as well as competition stress among neighboring plants. Our aims were to elucidate the flexibility of tree seedlings’ stoichiometric relationships and their effects on soil microbial communities, and to determine the driving forces of species turnover during primary succession through the evaluation of carbon (C) : nitrogen (N) : phosphorus (P) stoichiometric relationships. We conducted an experiment testing N addition effect on two species from the early stage of primary succession, under intra- and interspecific competition conditions. Our results showed that higher values of δ15N-NO3− and δ13C were observed in Populus purdomii individuals than in Salix rehderiana after N application, which indicated a more efficient N uptake and water-use efficiency in P. purdomii plants. Furthermore, under N addition, the intraspecific competition of P. purdomii presented a higher urease activity, microbial biomass C (MBC), microbial N:P ratio (MBN:MBP), and phylogenetic diversity compared to the intraspecific competition of S. rehderiana. The results showed that P. purdomii seedlings influenced soil properties in a way that led to a positive feedback on their performance with an increasing N availability. In contrast, S. rehderiana seedlings influenced soil properties in a way that caused a negative feedback on their performance with increasing N. Such events can promote species turnover from Salix to Populus during succession. Additionally, DNA sequencing of soil bacterial communities showed differences in the composition of microbial communities in response to N fertilization and different competition patterns. Altogether, our results showed that plant, soil, and microbial community responses to N fertilization in a subalpine glacier forefield differed among tree species and competition patterns. This study brings new insight into mechanisms that drive species replacement and biogeochemical cycling during primary succession.

Effect of Convection on Crystal Growth of Calcium Phosphate in a Thermostat under Terrestrial and Space Conditions

Mass transfer in the process of crystal growth of octacalcium phosphate Ca8H2(PO4)6 and hydroxyapatite Ca10(OH)2(PO4)6 during mixing aqueous solutions of CaCl2 and KH2PO4 + K2HPO4 in a buffer solution KCl is simulated mathematically with regard to the stoichiometric relationship. The investigations are carried out for the weightlessness, microgravity, and normal gravity conditions. The effect of gravity (convection) on the nature of reaction component transfer in the process of crystal growth of calcium phosphate under the temperature–controlled conditions is considered. It is shown that the reaction component transfer times are less under convection mixing as compared with the purely diffusive regime, but the rate and mass of formation of calcium phosphate depend not only on the convection time and intensity but also on the convection mixing structure.

Long-term effects of restoration measures on soil C and C: nutrient ratios in a semiarid steppe

Quantifying long-term effects of restoration measures on soil carbon (C) and C: nutrient ratios is of great importance for understanding the changes in C cycle of the grassland ecosystem in degradation and restoration, and for managing the grassland for both production and soil C. We investigated soil organic C (SOC) and C: nutrient ratios within the 0–40 cm soil layer in the grasslands restored following the application of different improvement measures, i.e., shallow plowing (SP), harrowing (HA) or natural recovery (NR), and that under sustained animal grazing (GR) in Xilingol steppe (China). The results showed that SOC content and soil C/P decreased, whereas soil C/N increased, significantly with soil depth. Restoration following different measures have all improved SOC contents of grassland ecosystem, and the SOC increasing rate was greatest under NR, and had an order of NR > HA > SP > GR. No significant difference was detected in soil C accumulation rate between shallow plowed (SP: 44.9 g C m−2 yr−1) and harrowed grassland (HA: 60.3 g C m−2 yr−1), and both were significant lower than that in naturally recovered grassland (NR: 123.2 g C m−2 yr−1). Significant linear relationship existed between soil CN and CP. Restored grasslands shared the common slope of soil CN linear regression, which were significantly greater than that of grazing grassland, indicating that ecological restoration changed soil CN coupling relation, and formed a stable soil CN coupling relation. Thus, soil CN stoichiometric relation can be used as an important indicator to diagnose the stages of soil degradation or restoration succession processes of grassland ecosystem.

Total Maximum Allocated Loads on Stoichiometry of Nitrogen and Identification of Critical Form in Jiaozhou Bay, China

Total pollutant load control management for total dissolved nitrogen (TDN) is an urgent task required to gain a good water quality status in Jiaozhou Bay (JZB), China. In this paper, the stoichiometry of multiform TDN on land-ocean interactions associated with marine biogeochemical reaction (LOIMBR) was studied by modeling the load-response relationship based on a three-dimensional water quality model of nitrogen in JZB. The results showed that the stoichiometry on LOIMBR of dissolved organic nitrogen (DON), NO3-N and NH4-N was 3:1:1, with one-third of the contribution on the concentration of dissolved inorganic nitrogen (DIN) in JZB for the land-based DON loads to DIN loads. Based on the stoichiometric relationship of nitrogen forms, the total maximum allocated load (TMAL) of equivalent TDN (ETDN) was approximately 5300 t a−1 in JZB, equivalent to the TMAL of 5700, 5800 and 15600 t a−1 for NH4-N, NO3-N and DON, respectively. According to the loads of ETDN, there were four outfalls overloaded in JZB in 2015, which lie in the head of the bay. In the four overloaded outfalls, besides NO3-N, NH4-N was the critical nitrogen control form for Moshui River, while DON for Dagu River and Haibo River. The results of numerical experiments further showed that JZB will achieve good water quality after 7 years by implementation of the ‘different emission reduction’ based on TMAL of ETDN, which is significantly better than ‘equal percent removal’.

Effect of Physisorption of Collector on Activation of Flotation of Sphalerite

The studies into the mechanism of activation of sphalerite flotation by ions of heavy metals show that neither ion exchange nor electrochemistry explain the experimental facts, namely, activation of flotation of copper mineral by lead ions, activation of sphalerite flotation by zinc, or flotation in the presence of non-conducting surface layer with silver or mercury. The authors put forward the hypothesis of activation due to the effect of physisorption of a collector in elementary event of flotation. It is possible to activate froth flotation by the products of nonstoichiometric interaction between xanthate and ions of some heavy metals. The influence of the scope of deviation from the stoichiometric relation of concentrations of xanthate and activation metal salt on the collectability of the interaction products is described. The activation efficiency of the interaction products is estimated using the criterion of ‘surface flow thickness’ of the film of collector derivatives at the gas-liquid interface.