Understanding the impact of the heterogeneity of the ecological environment on biodiversity is a key issue in ecology. Topographical heterogeneity was potentially important in grassland systems to ...create or change habitats for grasshopper settlement and foraging. Yet, there was little knowledge of how grasshopper communities respond to plant communities along the altitude gradient. We investigated the role of plant communities on grasshopper diversity with geostatistical methods to test the effects of heterogeneity in the natural grassland on the upper reaches of the Heihe River, Qilian Mountains. To aim the goal of the study, nonreturn experiments were used to collect the grasshoppers’ diversity and populations, and the plant’s community was sampled at the same location. The results showed that the semivariograms of grasshopper abundance and plant communities were both nonlinear models, while the grasshopper abundance typically produces heterogeneity with a larger range and nuggets than plant communities (except the plant coverage range in the model, range <1.5 m). The two communities presented the spatial distribution pattern of aggregated distribution, and the spatial trend is more intense in the northeast-southwest direction than in the northwest-southeast. The grasshopper species developed a good selection on microenvironment to habitat and the distribution consistent with plants, forming the horizontal distribution with a flaky and plaque distribution pattern. The relationship between grasshoppers and plants was highly dependent on the altitude, and grasshopper abundance has a positive correlation with plant richness (
F
= 0.68) and plant coverage (
F
= 0.32) and has a negative correlation with plant height (
F
= 0.13). In summary, the spatial distribution and correlation characteristics of plant communities and grasshoppers formed a plaque heterogeneity structure under the altitude gradients.
Soil aggregation is closely related to the soil organic carbon sequestration, both of which plays an important role in the stability of the soil carbon pool. However, the results of the impact of yak ...grazing intensity on the soil carbon process in alpine meadows have been unclear. With the marsh meadow as the research object in the Gahai wetland of the east Qinghai-Tibet Plateau, we analyzed the influence of different grazing intensities on the allocation of mass, stability and aggregate-associated organic carbon content of aggregates in the surface soil (0-20cm) of pasture by the Le Bissonnais method. The results showed that the mass of aggregates in the particle size class of > 0.2-mm was the highest among the pastures with different grazing intensities. Compared with the no grazing grassland, light grazing promoted the formation of macro aggregates in the particle size class of > 1-mm and improved the stability of soil aggregates. The degree of soil agglomerations and stability of aggregates decreased, and the macro aggregates gradually transformed into micro aggregates ( 2-mm and 0.05). This result shows that light grazing, which is a reasonable yak grazing intensity in the study area, is conducive to the formation of a good soil structure in the area and improves the soil carbon sequestration capacity.
•The accuracy of NPP and phenology was improved using a spatiotemporal fusion algorithm.•Over the past 20 years, NPP showed an increasing trend, SGS and EGS advanced, and LGS showed a prolonged ...trend.•The relationship between NPP and phenological indicators was significantly different among the different vegetation types.
Phenology is a key measure of how well an ecosystem functions and is pivotal in revealing vegetation productivity. Net Primary Productivity (NPP) and phenology have profound implications for the exploration of regional ecosystem processes. Several studies have investigated the effects of phenological indicators on NPP. However, these studies were carried out at a coarse resolution, making it difficult to obtain sufficient information on vegetation structure and dynamics; they also, potentially underestimate how productivity is influenced by phenology. This work uses fused NDVI images employing the ESTARFM model to determine how vegetation NPP reacts to phenology in the northern Qinghai-Tibet Plateau. The results showed that NPP was only 59.93 gC·m−2·year -1. The start of the growing season (SGS) was concentrated from March to May, whereas the end of the growing season (EGS) spanned from late September to early November. The length of the growing season (LGS) spanned 4–8 months during 2000–2020, NPP showed an increasing trend, SGS and EGS advanced, and LGS showed a prolonged trend. SGS and EGS were negatively correlated with NPP and seasonal temperature, however NPP was positively correlated with seasonal precipitation. LGS was positively correlated with NPP and interannual temperature, whereas it was negatively correlated with interannual precipitation. This study will aid in providing an accurate understanding of how NPP responds to phenological dynamics. Concurrently, collective understanding of terrestrial ecosystem responses to changes on a global scale will be advanced.
Background
The study of soil organic carbon characteristics and its relationship with soil environment and vegetation types is of great significance to the evaluation of soil carbon sink provided by ...inland salt marshes. This paper reports the characteristics of soil organic carbon fractions in 0–50 cm soil layers at four vegetation communities of the Qinwangchuan salt marsh.
Results
(1) The soil organic carbon content of Phragmites australis community (9.60 ± 0.32
g
/kg) was found to be higher than that of Salicornia europae (7.75 ± 0.18
g
/kg) and Tamarix ramosissima (4.96 ± 0.18
g
/kg) and Suaeda corniculata community (4.55 ± 0.11
g
/kg). (2) The soil dissolved organic carbon, particulate organic carbon and soil microbial biomass carbon in 0–50 cm soil layer of Phragmites australis community were higher, which were 0.46 ± 0.01
g
/kg, 2.81 ± 0.06
g
/kg and 0.31 ± 0.01
g
/kg, respectively. (3) Soil organic carbon was positively correlated with dissolved organic carbon, particulate organic carbon, and microbial biomass carbon, and negatively correlated with easily oxidized organic carbon. (4) Above-ground biomass has a strong direct positive effect on soil organic carbon, total nitrogen and pH have a strong direct positive effect on microbial biomass carbon content, pH and average density have a strong direct negative effect on easily oxidized organic carbon, and particulate organic carbon.
Conclusions
The interaction between plant community characteristics and soil factors is an important driving factor for soil organic carbon accumulation in inland salt marshes.
The spatiotemporal evolution of population urbanization and its relationship with economic variables are important aspects of socioeconomic research and essential for revealing the mechanism of urban ...construction and evolution. To study the spatial heterogeneity and influencing mechanisms of population urbanization in the upper reaches of the Yellow River, this study investigated the spatial distribution and dynamic evolution of population urbanization using nuclear density analysis, exploratory spatial data analysis and the geographical detector model. The results showed that the rate of population urbanization in the upper reaches of the Yellow River increased annually since 2000 and that the nuclear density curve changed from a single–peaked mode in 2000 to a double–peaked mode in 2018. The spatial distribution of the population urbanization level was uneven, that is, high in the north and low in the south, with substantial spatial agglomeration and spatial autocorrelation. The main distribution of hot spots was in the Yinchuan area in the north, while cold spots were distributed mainly in the south. Analysis revealed that changes in population urbanization level were mainly attributable to the influence of economic and employment opportunities, such as regional GDP, GDP per capita, proportion of tertiary industry in GDP, and total retail sales of consumer goods.
The high cycle fatigue behaviour of the Al–Si alloy extracted from a cylinder head is investigated through experiments and finite element simulations. Due to the complexity of the structure and the ...differences in cooling rates and local melt flow, the microstructure characteristics of the cylinder head studied exhibit high spatial heterogeneity. The scatter of the fatigue life of the alloy is high, which is significantly affected by the microstructure, especially by crack nucleation pores. The characteristics of the nucleation pores have a great effect on the dissipated inelastic energy (Wp) around the pores, which is used as the indicator for crack nucleation. Wp has the highest sensitivity to pore shape, followed by pore location and pore size. The nonlinear empirical relationship between Wp and pore characteristics is established with high reliability and accuracy, and the crack nucleation model is modified by considering pore characteristics. Based on the multistage fatigue model and the modified crack nucleation model, the fatigue life of cast Al–Si alloy extracted from cylinder heads can be predicted accurately within a feasible scatter band.
The response analysis of plant leaf traits and photosynthetic physiological characteristics to flooding is helpful to understand the leaf construction model and photosynthesis mechanism of marsh ...wetland plants in the flooded habitats. The sample area was divided into three levels based on the length of the still water retention time in the lake flooding area of Xiaosugan Lake wetland: I(mild flooded field, still water retention 60-90 d), II(moderately flooded area, still water retention 90-150 d), III(heavy flooded area, still water retention 150-210 d). The results showed that with the increasing still water retention time, the soil moisture was gradually increased, the soil salinity and photosynthetically active radiation were gradually reduced, the coverage and density of wetland communities were increased, the aboveground biomass exhibited increase first and decrease afterwards, the leaf area of Glaux maritima L increased and the leaf thickness, net photosynthetic rate, stomatal conductance decreased, the
In view of the non-uniform distribution of mechanical properties of cast aluminum alloy cylinder head, the mechanical properties evaluation and microstructure heterogeneity of cylinder head were ...studied. The results showed that the head plate position of the cylinder head has the best mechanical properties and microstructure characterization, followed by the floor plate and the thick partition plate. The mechanical properties of the floor plate position attenuate with increasing temperature. From 23°C to 300°C, the tensile strength and yield strength decrease in the same range, but the break elongation changes most obviously. The mechanical properties and microstructure characterization of cylinder head in-situ sampling satisfy the Hall-Petch relationship. If the required ultimate tensile strength is not less than 255MPa, the upper threshold of the grain size, by considering the error limit of the Hall-Petch relationship, is 603.4μm, and the upper threshold of secondary dendrite arm spacing is 69.1μm. Meanwhile, established the relationship between hardness and yield strength, the average error of the nonlinear model is 4.35%. The prediction accuracy of the nonlinear model is sufficient to meet the actual needs of the engineering.
The relationship between plant functional groups and habitats is an important topic of the research of ecology. It can reveal the mechanism of plant environmental adaption, community construction, ...and can predict the changes of vegetation. In order to study adaption of the functional groups to different habitats in the arid area such as wetland, desert and gobi on a local scale, the composition and functional traits of functional groups in different habitats of desert areas were studied in Jiayuguan Caohu National Wetland Park based on the data of plant functional traits. The results showed that, with the change of habitat conditions, the soil water moisture, salt content, bulk density, pH value and other soil properties changed significantly. The composition of plant functional groups and functional traits changed adaptively. The functional traits of vegetation in the marsh wetland were mainly clonal plant, C4 photosynthetic pathway, and rhizomatous plant. The salt marsh wetland were mainly wax-coating, leaf or stem succulence, and CS strategy type. Dune habitats were with hairiness, thickened or long roots, annual, and CR strategy type, while Gobi with reduced leaves, thickened or long roots, entomophilous, and chamaephyte. On the local scale, habitat heterogeneity, especially soil heterogeneity, is an important environmental factor affecting the composition of plant communities and the changes of plant functional traits.
The root architecture determines the root distribution and the search efficiency of water and nutrients, which is the result of the adaptability of plant roots and stress habitats. The object of this ...study was to examine the relationship between root forks and link number, branch angle of Pedicularis kansuensis in response to density conditions. The study site was located in Gahai Wetland, Gansu Province, China(102.08°-102.47° E, 33.97°-34.32° N). The altitude of the study site is 3430-3435 m, whereas the average annual temperature is 2.3℃. Sixty samples(1 m×1 m) were set up along the river bank to investigate the density of P. kansuensis in August 2016. Population density was categorized as low(I, 10-31 plant/m~2), medium(II, 32-53 plant/m~2), and high(III, 54-75 plant/m~2). The density, height, coverage, and above-ground biomass of the plant communities were recorded from 1 m × 1 m plots in the three densities with six replications. Thirty plants of P. kansensis were selected; the above-ground parts of those plants were cut while roots were collected by excavating the whole root system, and both were taken back to lab. Afterwards, the soil cores(30 cm × 30 cm × 50 cm) were dug from six grids(30 cm × 30 cm) in three densities. The sieve(mesh size = 0.25 mm) was used to clean the soil core in the nearby river, and the roots were taken to the lab. Afterwards, we adopted a method to stratify sampling(0-50 cm). In the laboratory, the roots were scanned with Win-RHIZO to measure the root forks and link number. The biomasses of different plots were put in an oven(at 105℃ for 30 min) for green removal, and drying(at 80℃ for 12 h), and then measured. Similarly, the soil moisture content was also measured by oven-drying(at 105℃ for 24 h). The results showed that as the population density changed from high-medium to low-medium, the coverage, height and above-ground biomass, root forks and external link number of the P. kansuensis decreased, whereas the below-ground biomass, root internal link number, and branch angle of P. kansuensis increased. The was an allometric relation between the root forks and link number, and branch angle of P. kansuensis. Additionally, the growth speed of the root internal link number and branch angle was greater than the decrease speed of root forks and external link number. The allometric slope of the root forks and external link number decreased, but that of the root forks and internal link number and branch angle increased. With a change in density, the root forks and external link number of P. kansuensis decreased, and the root internal link number and branch angle increased. These results revise the ecological adaptation mechanism of plant populations to multiple resource competitions in alpine wetlands under the restriction of density.
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