Typical Species Research Articles

No dramatic changes observed in subtropical radiolarian plankton assemblages during the Middle Eocene Climatic Optimum (MECO); evidence from the North Atlantic ODP Site 1051

The Middle Eocene Climatic Optimum (MECO; ca. 40 Ma) was a prominent global warming event that lasted 400 kyr and was characterized by a 4–6 °C rise in high latitude surface and deep-water temperatures. As the radiolarian plankton response to this warming event is practically unknown, whole assemblage quantitative analyses were undertaken on well-preserved radiolarian assemblages from ODP Site 1051 (western North Atlantic). Although radiolarians have apparently benefited at this site from increase in oceanic fertility induced by the MECO, this event does not appear to have had a severe impact on subtropical radiolarian fauna. No prominent faunal turnover was found in the studied interval, suggesting that subtropical radiolarians are relatively resilient to transient warming events. Likewise, variations in radiolarian assemblage composition establish that ocean warming induced only a weak ecological response. One of the most striking faunal changes associated with the MECO is the clear increase in radiolarian diversity (taxic richness), as a result of the northward migration of warm tropical radiolarian species. Similarly, several typical middle Eocene tropical species are found to be more abundant in the warmest interval. In addition to these poleward migrations, we identified three radiolarian clusters composed of warm-water or cool-water species, as well as two abundant artostrobiid species which may represent nutrient opportunists.

Plant–Soil Feedback of Companion Species during Grassland Community Succession

The responses of dominant species to plant–soil feedback (PSF) are well established; however, the changes in the PSF of companion species remain unclear. This study aims to assess the direction and intensity of PSF, determine the main factors influencing it, and interpret the ecological significance of PSF in companion species within the context of grassland community succession. Three typical companion species, namely Artemisia sacrorum, Artemisia capillaris, and Artemisia giraldii, were planted in soils at three grassland community succession stages (early, middle, and late) on the Loess Plateau. Our results indicate that during both plant growth periods, the shoot biomass of A. sacrorum, A. capillaris, and A. giraldii in early- and late-stage soils was higher than that in the middle-stage soil, suggesting consistent growth of the three companion species during the two growth periods. However, plant growth simultaneously led to a reduction in soil nutrient content and microbial biomass, resulting in an overall decrease in the biomass of the three species, indicating a negative PSF effect in companion species. In conclusion, the negative PSF observed in all three associated species explains the temporary dominance of companion species during succession. This study enhances our understanding of the mechanisms driving PSF in community succession.

Further studies on the species diversity of the marine planktonic diatom genus Skeletonema (Bacillariophyta) in the Mexican Pacific

Following recommendations on species level identification in the diatom genus Skeletonema, some papers have been published describing new species. A combination of different observation techniques (LM, SEM and TEM) and/or the use of molecular tools for an accurate identification is now required, because semicryptic species have been found. In this study, cultures were established from one water sample collected from a location in the Mexican Pacific to provide a morphological characterization of four species: Skeletonema ardens, S. grevillei, S. pseudocostatum and S. tropicum. The selected morphological features for analysis were chains, cells, chloroplasts, valves, terminal or intercalary fultoportulae and rimoportulae, and cingular bands. Two of the described species, Skeletonema ardens and S. grevillei, are new records for the Mexican Pacific. Skeletonema costatum, that has traditionally been considered as abundant, frequent, and widely spread all over the region, was not recognized in this study. Together with the four species discussed here, there are six Skeletonema species represented in the Mexican Pacific, counting with Skeletonema japonicum and S. marinoi, previously reported for the region. The coexistence of four Skeletonema species in a same water sample is remarkable, considering that only Skeletonema costatum had historically been the typical species recorded, which was additionally producing blooms in coastal waters.

Особенности микокомплекса ризосферы донника лекарственного

In the conditions of a small-scale experiment on a natural infectious background (Belgorod, Russia), a threefold excess of the CFU values of the rhizosphere of the Melilotus officinalis was revealed in comparison with the fallow soil, but the abundance of typical species in the rhizosphere and control was 63% and 77%, respectively. The Jacquard coefficient proved the high similarity of mycocomplexes of the rhizosphere of M. officinalis with the control (33%). The core of the rhizosphere microcomplex of sweet clover is the species Trichoderma lignorum. It is shown that the cultivation of sweet clover contributes to the improvement of the soil by reducing the proportion of pathogenic and allergenic species of micromycetes. The loss of the green mass of the sweet clover from septoria was recorded at the level of 20%.

Effect of extracts of petroleum ether, dichloromethane and methanol on thiophenic sulfur release during coal pyrolysis

The existing forms and thermal transformation of sulfur in high sulfur coal directly influence the efficiency of coal clean utilization by the staged pyrolysis conversion. Low molecular compounds distributed in coal are very different from the macromolecular structure of coal and play an important role during coal pyrolysis. In order to investigate the effects of low molecular compounds on the release of typical thiophenic sulfur species during coal pyrolysis by Py-GC/MS, petroleum ether, dichloromethane, and methanol were used for sequential ultrasonic extraction of Linfen coal (LFC). The compositions of extracts were detected by GC×GC/MS. Results show that three primary kinds of thiophenic sulfur species (2-methyl thiophene, benzothiophene, and dibenzothiophene) were released during coal pyrolysis and they are mainly derived from the cracking of macromolecular skeleton containing thiophenic sulfur in coal. The amounts of thiophenic sulfur released during raw coal and residues pyrolysis both increase with temperature. Besides, extracts with different compositions have different effects on the release of thiophenic sulfur during pyrolysis. In detail, the cyclization of aliphatic compounds could provide active hydrogen. On the one hand, the active hydrogen promotes the break of bridge bonds around thiophenic sulfur. On the other hand, active hydrogen may attack sulfur atoms of thiophenic sulfur, reducing the energy barriers of thiophenic sulfur decomposition. Aromatic compounds polymerize with sulfur-containing groups converting to benzothiophene and dibenzothiophene with larger molecular weight. In addition, thiophenic sulfur may be oxidized by esters to sulfones or sulfoxides, which further decompose, resulting in the inhibition effect on thiophenic sulfur formation during coal pyrolysis.

The Role of Agroforestry in Poverty Alleviation: A Case Study from Nujiang Prefecture, Southwestern China

Agroforestry has gained increasing attention as a sustainable land use mode to ensure food security, mitigate global climate change, and improve farmers’ livelihoods. Likewise, agroforestry plays a key role in alleviating poverty, mitigating climate change and achieving the Sustainable Development Goals (SDGs) in China. Lanxangia tsaoko, as a typical agroforestry species in Nujiang Prefecture, plays a vital role in improving farmers’ livelihoods. After years of development, the Lanxangia tsaoko industry (LTI) in Nujiang Prefecture has made remarkable achievements and accumulated useful experiences. Taking the development of LTI as an example, this paper analyzes the impact of agroforestry on farmers’ livelihoods and its mechanism through field survey and theoretical deduction. First, by investigating the willingness of households to choose LTI, we found that most farmers have a positive attitude toward LTI, and they actively participate in cooperative organizations. Then, by analyzing the development stage and mode of LTI in Nujiang Prefecture, we found that the industry has made significant progress under the external and internal effects. We also found that the mechanism by which agroforestry affects farmers’ livelihoods is a process in which various stakeholders, including government, enterprises, farmers, etc., participate in industrial development with their production components and advantages. Although agroforestry is an effective way to improve farmers’ livelihoods and promote sustainable agricultural development, it is also necessary to pay attention to risk prevention. This paper discusses the role of agroforestry in farmers’ livelihoods, which provides a reference for lower-income forest areas.

Evolutionary divergence of subgenomes in common carp provides insights into speciation and allopolyploid success

Hybridization and polyploidization have made great contributions to speciation, heterosis, and agricultural production within plants, but there is still limited understanding and utilization in animals. Subgenome structure and expression reorganization and cooperation post hybridization and polyploidization are essential for speciation and allopolyploid success. However, the mechanisms have not yet been comprehensively assessed in animals. Here, we produced a high-fidelity reference genome sequence for common carp, a typical allotetraploid fish species cultured worldwide. This genome enabled in-depth analysis of the evolution of subgenome architecture and expression responses. Most genes were expressed with subgenome biases, with a trend of transition from the expression of subgenome A during the early stages to that of subgenome B during the late stages of embryonic development. While subgenome A evolved more rapidly, subgenome B contributed to a greater level of expression during development and under stressful conditions. Stable dominant patterns for homoeologous gene pairs (HGs) both during development and under thermal stress suggest a potential fixed heterosis in the allotetraploid genome. Preferentially expressing either copy of a homologous gene at higher levels to confer development and response to stress indicates the dominant effect of heterosis. The plasticity of subgenomes and their shifting of dominant expression during early development, and in response to stressful conditions, provide novel insights into the molecular basis of the successful speciation, evolution, and heterosis of the allotetraploid common carp.

Combination of direct boiling and glass beads increases the purity and accuracy of bacterial DNA extraction.

Extraction of DNA is a key step in molecular biology experiments and important for counting tiny microbial individuals. Direct boiling and mechanical cell lysis like glass beads are two independent physical extraction methods, thus crossing the barriers of thresholds of magnitude in popular reagent kits or traditional spread plate method when non-equilibrium phenomenon is ongoing. The two approaches above were combined to generate a new one. In three typical microbial species, direct boiling with glass beads significantly increased the purity of DNA solution compared with some other methods (p<0.05). The qPCR results of them were closer to direct microscopy counting than some other methods. Therefore, it provides a new choice in extracting bacterial DNA for specific circumstances.

First insight into molecular diversity and DNA barcode library of epikarst-dwelling invertebrates in the Western Carpathians

DNA barcoding represents a handy tool for species identification. In addition, it serves as a complementary approach that improves the characterisation of evolutionary lineages and facilitates the detection of potentially undescribed and cryptic species. Based on the case study in the Western Carpathians, which belong to the Carpathian biodiversity hotspot, we have compiled the first DNA barcode reference library for molecular identification of invertebrates associated with epikarst, a unique, yet understudied, shallow subterranean aquatic habitat that extends at the interface between the soil and carbonate rocks. We analysed invertebrates collected in 2019-2020 from epikarst water that continuously seeps into four caves of the Demänovský Cave System in northern Slovakia. The standard barcode marker of the mitochondrial COI gene was amplified in more than 920 individuals of aquatic, semi-aquatic, and terrestrial invertebrates. The final data set consisted of 784 barcode sequences representing 36 morphospecies, the majority (98.3%) belonging to Arthropoda. Automated cluster delineation using the Barcode of Life Data System (BOLD) revealed 60 Barcode Index Numbers (BINs), of which 43 BINs were new to BOLD, representing mostly typical subterranean species. Almost 20% of the morphospecies displayed high intraspecific variation (>2.2%), suggesting the need for further investigation to assess potential taxonomic problems or cryptic diversity. Our results also indicated the existence of several yet undescribed invertebrate species and possible heteroplasmy or COI numts in the collembolan Megalothorax sp. (incertus species group). The resulting DNA barcode library represents a significant advance not only in the characterisation of epikarst biodiversity but also in the understanding of subterranean biodiversity in general, paving the way for future complex evolutionary and biogeographical studies.

Enhancement of combustion performances and reduction of combustible species emission using an additional of combustion-reaction of engine

A new concept is presented to enhance the combustion performance and to reduce the combustible species gas emission of a combustion engine. Exhaust gases are still rich in typical combustible species whose chemical energy can be harvested to increase efficiency. The idea is to provide extra time to the combustion reactions by the addition of two-post-expansion-strokes to the Otto cycle. The chemical energy of the working-gas residual combustible species is converted into an additional heat-input. The new thermodynamic cycle, called the MUB-2 cycle, is similar to an Otto cycle but has two isochoric heat-inputs instead of one. The cycle has been experimentally tested and analytically evaluated. It is found that even though the engine’s thermal-conversion efficiency is not changed, however, the average values of combustion efficiency, fuel-conversion efficiency, heat-input per cycle, and indicated work per cycle are increased by 6.42 (%), while average levels of HC, CO, and H2 are reduced by 43.86 (%), 38.58 (%), and 38.58 (%), respectively. Other advantages of the MUB-2 cycle are higher heat input per cycle and more robustly work to the changes of air-fuel mixture homogeneity over the Otto cycle, the Atkinson-Miller cycle, and other cycles that only incorporate a single combustion process.

Functional Characterization of a New Salt Stress Response Gene, PeCBL4, in Populus euphratica Oliv

Populus euphratica is a typical stress-resistant tree species that provides valuable natural genetic resources for breeding salt-tolerant plants. The calcineurin B-like (CBL)-interacting protein kinase (CIPK) network plays an important role in regulating plant responses to abiotic stresses. The aim of this study was to characterize the function of a new CBL member, PeCBL4, in response to abiotic stresses. PeCBL4 was cloned, and sequence analysis was performed. The subcellular localization of PeCBL4 was determined using the fusion expression vector of GFP. Yeast two-hybrid assays and bimolecular fluorescence complementation were performed to identify PeCIPK members that interacted with PeCBL4. PeCBL4 was then transformed into the corresponding Arabidopsis thaliana mutants. Na+ and K+ content as well as their net fluxes were determined under high salt stress and low K+ stress. Phylogenetic tree analysis showed that PeCBL4 was clustered together with PtCBL4 and belonged to the same subgroup as AtCBL4. Subcellular localization indicated that PeCBL4 was expressed on the plasma membrane. Yeast two-hybrid assays and bimolecular fluorescence complementation showed that PeCBL4 interacted with PeCIPK24 and PeCIPK26. In addition, under high salt stress, the Na+ efflux capacities of seedlings decreased in sos3 mutants, and transgenic plants of PeCBL4 enhanced efflux capacities. In addition, the overexpression of PeCBL4 negatively influenced the influx capacity of K+. PeCBL4 interacts with PeCIPK24 and PeCIPK26 and regulates Na+/K+ balance under low K+ and high salt stress.

Transfer pattern of microplastics at an individual level: A case study of two typical Sciaenidae fish in coastal waters

Microplastics (MPs) are recognized as global pollutants. The occurrence and distribution of MP transfer at the species level have been reported, but few studies have focused on the individual level. In this study, two typical migratory demersal species (Collichthys lucidus and Larimichthys polyactis, family Sciaenidae) from the coastal waters of the Lvsi fishing ground were selected to analyze the distribution characteristics of MPs in their gastrointestinal tracts and to explore the potential biomagnification of MPs in different body lengths. The results showed that the main MP color found in both species was blue (>80 %), while the main MP shape was fiber (>90 %), and the main MP polymer type was polyethylene terephthalate (PET) (>70 %). Overall, the abundance of MPs in C. lucidus (3.24 ± 1.57 pieces/fish) was higher than that in L. polyactis (2.24 ± 0.56 pieces/fish). The abundance of MPs in C. lucidus with a body length >90 mm was significantly higher than that with a body length <90 mm, and no significant difference was found in L. polyactis. We believe that the shift in feeding habits during the life history of the two species is an important factor that affects the variation in MPs between body lengths. Additionally, there was a significant positive correlation between MPs and the length (weight) of C. lucidus but no correlation in L. polyactis. There was no significant correlation between trophic level and MPs in either species. This indicated that MP bioaccumulation only occurred in C. lucidus, and MP biomagnification did not occur in either species. We suggest that further research be conducted on MPs ingested by more species at an individual level regarding the biomagnification/bioaccumulation phenomenon. This will help further elucidate the characteristics of MP transfer in the food webs of ecosystems and provide theoretical support for understanding MP pollution in coastal waters.

The effect of site preparation on vegetation restoration in young hemiboreal mixed stands

Tree logging significantly impacts environmental conditions, increases soil and air temperature, and changes the microclimate and soil hydrology. This contributes to the changes in bryophyte and vascular plant cover and species composition. Site preparation positively affects the growth of planted trees in young stands but also causes forest understorey disturbance. During site preparation in young stands by spot mounding and disc trenching methods, new microtopographies, e.g. soil tumps and hollows are made in young stands. Site preparation generally increases vascular plant diversity, but there is a lack of information about the vegetation differences between microtopography depending on different site preparation methods and soil types. The aim of this study was to investigate how the microtopography formed during site preparation by spot mounding or disc trenching affects bryophyte and vascular plant communities in hemiboreal young stands two to three years after tree logging. Spot mounding altered vegetation composition more than disc trenching. Bryophyte species cover decreased in prepared soil, but Ellenberg’s moisture value increased; therefore, site preparation before planting contributes to the conservation of typical forest bryophyte species in young stands. Hollows lead to better typical forest habitat species preservation, but soil tumps diversify environmental conditions by providing new patches for the development of grassland habitat species that are not typical in this ecosystem, but temporally provide new ecosystem services. Keywords: bryophytes, spot mounding, disc trenching, vascular plants, plant growth forms, Ellenberg’s indicator values

Predicting Carbon Storage Jointly by Foliage and Soil Parameters in Pinus pumila Stands along an Elevation Gradient in Great Khingan

Alpine dwarf pine populations are dwelling in a climate-sensitive habitat, where detection of the carbon (C) cycle is still valued for sustainability. Foliar and soil parameters are key factors that combine to jointly affect aboveground C storage in alpine ecosystems, but how they generate combined contributions to aboveground C in alp dwellers still needs more research. In this study, Pinus pumila, a typical alp dwarf pine species in a canyon of the Great Khingan Mountain, was focused on. Their natural populations were investigated for individual growth and needle and soil parameters in plots across six categorized elevations from 800 m to 1200 m. Aboveground C storage was estimated by three allometric models which were all found to increase against increases in elevation. Along the increasing elevational gradient, needle concentrations of nitrogen (N) and phosphorus (P) both showed decreasing trends, but activities of N and P assimilation enzymes and chlorophyl contents, as well as the soil contents of ammonium N and organic matter, all showed increasing trends. Multiple linear regression models indicated that elevation (parameter estimate, PE: +0.01), needle P (PE: +0.66) and chlorophyl contents (PE: +0.60) made jointly positive contributions to estimated C storage while soil pH had a negative contribution (PE: −1.80). For the purpose of sustainable C fixation by alp P. pumila populations, strategies should be considered to increase P availability and control high soil pH. Our results fill the gap about C storage and driving forces in alpine ecosystems, and their applications are not limited to being referenced by other alpine plants.

Ancient Horizontal Gene Transfers from Plastome to Mitogenome of a Nonphotosynthetic Orchid, Gastrodia pubilabiata (Epidendroideae, Orchidaceae).

Gastrodia pubilabiata is a nonphotosynthetic and mycoheterotrophic orchid belonging to subfamily Epidendroideae. Compared to other typical angiosperm species, the plastome of G. pubilabiata is dramatically reduced in size to only 30,698 base pairs (bp). This reduction has led to the loss of most photosynthesis-related genes and some housekeeping genes in the plastome, which now only contains 19 protein coding genes, three tRNAs, and three rRNAs. In contrast, the typical orchid species contains 79 protein coding genes, 30 tRNAs, and four rRNAs. This study decoded the entire mitogenome of G. pubilabiata, which consisted of 44 contigs with a total length of 867,349 bp. Its mitogenome contained 38 protein coding genes, nine tRNAs, and three rRNAs. The gene content of G. pubilabiata mitogenome is similar to the typical plant mitogenomes even though the mitogenome size is twice as large as the typical ones. To determine possible gene transfer events between the plastome and the mitogenome individual BLASTN searches were conducted, using all available orchid plastome sequences and flowering plant mitogenome sequences. Plastid rRNA fragments were found at a high frequency in the mitogenome. Seven plastid protein coding gene fragments (ndhC, ndhJ, ndhK, psaA, psbF, rpoB, and rps4) were also identified in the mitogenome of G. pubilabiata. Phylogenetic trees using these seven plastid protein coding gene fragments suggested that horizontal gene transfer (HGT) from plastome to mitogenome occurred before losses of photosynthesis related genes, leading to the lineage of G. pubilabiata. Compared to species phylogeny of the lineage of orchid, it was estimated that HGT might have occurred approximately 30 million years ago.

Water use strategy of nitraria tangutorum shrubs in ecological water delivery area of the lower inland river: Based on stable isotope data

Excessive water use in the upper and middle reaches of arid inland river basins will inevitably lead to the drying up of the lower reaches. Water allocation and ecological water delivery have been widely used as water resources management strategies in global arid regions, and the implementation of such strategies has a great impact on the downstream ecosystem. We established an ecohydrological observation system at the lower reaches of the Shiyang River, an inland river in the arid region of China. The stable hydrogen and oxygen isotope technique was used to study the influence mechanism of artificial water delivery on the water use strategy of nitraria tangutorum shrubs, the typical dominant species around Qingtu Lake. The results showed that: (1)12.33% of the water used by the dominant species in the terminal lake area came directly from ecological water delivery, 77.88% from soil water formed by water delivery, and only 9.79% from precipitation. (2)With the increase of distance, nitraria tangutorum shrubs absorbed less surface soil water and lake water, and gradually turned to using deeper soil water and precipitation. (3) Ecological water delivery cycles affected the water use strategies of nitraria tangutorum shrubs. The proportion of deep soil water used by plants increased in the non-water delivery period, and the proportion of precipitation absorbed by plants also increased. Thus, Vegetation in the terminal lake region mainly depended on ecological water use, and the amount and time of water delivery directly determined the water use of dominant species. The results help us to understand the adaptation mechanism of plants under the background of artificial water delivery in the low reaches of arid inland river basins and provide a reference for the rational use of water resources and ecological construction.

Status, characteristics, and ecological risks of microplastics in farmland surface soils cultivated with different crops across mainland China

Microplastics (MPs) in agricultural soils could affect the safety of food crops. However, most relevant studies have paid scant attention to the crop fields and focused more on MPs in farmlands with or without film mulching in different regions. To detect MPs, we investigated farmland soils with >30 typical crop species from 109 cities in 31 administrative districts across mainland China. The relative contributions of different MP sources in different farmlands were estimated in detail based on a questionnaire survey, and we also assessed the ecological risks of MPs. Our results indicated the order of MP abundances in farmlands with different crop types, namely fruit fields > vegetable fields > mixed crop fields > food crop fields > cash crop fields. For the detailed sub-types, the highest MP abundance was detected in grape fields, which was significantly higher than that in solanaceous & cucurbitaceous vegetable fields (ranked second, p < 0.05), whereas the MP abundance was lowest in cotton and maize fields. The total contributions of three potential sources, namely livestock and poultry manure, irrigation water, and atmospheric deposition to MPs, varied depending on the crop types in the farmlands. Owing to exposure to MPs, the potential ecological risks to agroecosystems across mainland China were not negligible, particularly in fruit fields. The results of the current study could provide basic data and background information for future ecotoxicological studies and relevant regulatory strategies.

Short-Term Responses of Aquatic Ecosystem and Macroinvertebrate Assemblages to Rehabilitation Actions in Martil River (North-Western Morocco)

This study aimed to evaluate the effects of the Martil River rehabilitation project and recently constructed dam infrastructures to reduce flood risks and to promote local socio-economic development on the ecological integrity of the river. The assessment focused on changes in fluvial landforms over time and the evaluation of aquatic ecosystems based on six physicochemical parameters (temperature, pH, electrical conductivity, dissolved oxygen, biochemical oxygen demand, and chemical oxygen demand), morpho-hydrological variables (stream width, water depth, and current speed), habitat indices (QBR, IHF, and MQI), and macroinvertebrate assemblages of EPT, OCH, and Chironomidae (Diptera) at five stations from autumn 2015 to spring 2018 (prior to and during the rehabilitation actions). The results showed that the river rehabilitation project led to profound changes in Martil River’s ecosystem and water quality over time. Physicochemical and habitat measurements at the rehabilitated sites revealed a major change in macroinvertebrate communities due to changes in fluvial landforms in relation to flow-sediment regimes. As a result, some typical species of lentic habitats disappeared, while alien, opportunistic, and lotic species appeared.

Afforestation vegetation uses water from very deep soil layers in the semi‐arid Loess Plateau

AbstractInvestigating the availability of water in very deep soil layers for vegetation is important for assessing the eco‐hydrological effects of the thick loess soil and optimizing soil water management and vegetation restoration initiatives. However, the proportion of soil water sourced from the soil layer deeper than 300 cm by typical afforestation species on the Loess Plateau, along with its seasonal variations, remains unclear. In this study, we examined the composition of the water sources used by two typical afforestation plant species (Caragana korshinskii and Medicago sativa) from soil depths of up to 10 m during the growing season, using isotopic analysis. The results showed that soil desiccation occurred in the soil layers of 260–1000 cm and 260–700 cm at the upper and lower slope positions, respectively, for both species plots. Relative stability of the isotopic values in &gt;260 cm soil layers explained a piston flow occurred in these layers. The contribution proportion of soil water in 260–1000 cm was at 41.7% ± 9.0% and 51.3% ± 8.8% for C. korshinskii on upper and lower slope, respectively and was at 67.6% ± 6.7% and 73.7% ± 7.0% for M. sativa on upper and lower slope, respectively. The serious soil desiccation was induced by the dependence on very deep soil water and the slow recharge with the piston flow. Meanwhile, C. korshinskii converted the main water source between 0–260 cm and 260–1000 cm in different seasons. In contrast, M. sativa used water mainly from soil layers deeper than 260 cm in June and increased the utilization proportion of deeper water sources in July and September. The persistent dependence on very deep soil water for M. sativa, induced a deeper desiccation depth as compared to C. korshinskii. Thus, thinning to the optimal leaf area index and converting to natural grassland were recommended for C. korshinskii and M. sativa plots, respectively to restore the depleted soil water and to promote water cycle.

Three-dimensional model construction and wind simulation of different tree species in farmland shelter.

Protective forests are the ecological barriers of oases in arid sand areas and can effectively prevent and control wind and sand hazards. The structural characteristics of individual trees, as the basic unit of protective forests, are the key factors affecting the protective benefits. With the typical leafless tree species of Ulan Buh Desert oasis, i.e., Populus alba var. pyramidalis, Populus nigra var. thevestina, and Populus popularis, as the research objects, and by using the ground-based LiDAR and through computational fluid dynamics (CFD), we fully explored the structural characteristics of individual trees and their surrounding aerodynamic characteristics on the basis of real 3D models. We further established the relationship between structural parameters of individual trees and wind field index. The results showed that combining AdQSM and MeshLab to build tree models had high accuracy. The wind field around the individual trees could be roughly divided into six regions, including the attenuation zone of the windward side of the plant, the acceleration zone at the top of the plant, the eddy zone, the calm zone, the transition zone, and the recovery zone of leeward side of the plant. The pressure field around individual trees showed a gradual change of high pressure on the windward side to low pressure on the leeward side. Horizontally, in the range of 20% to 50% reduction in relative wind speed, the effective protection distances were 0.21H-1.51H, 0.20H-0.91H, and 0.25H-1.64H (H was the corresponding tree height) for P. alba var. pyramidalis, P. nigra var. thevestina, and P. popularis, corresponding to effective protection areas of 18-294, 15-227, and 18-261 m2, respectively. The maximum wind speed decay rate in the vertical direction was at 0.3H height for P. alba var. pyramidalis and P. popularis, and was reflected at 0.5H height for P. nigra var. thevestina. The correlation and stepwise regression analysis of the single tree structure parameters with the wind field indicators clearly indicated that optical porosity and volume porosity dominated the protection effect. Among the wind field factors, the best regression models related to the porous coefficient were screened for three factors, including diameter at breast height, tree surface area, and optical porosity. The regression variables screened for effective protection distance and effective protection area differed among the classes.