Physical and mechanical properties and microstructures of submarine soils in the Yellow Sea

In recent years,the exploration of seabed has been intensified,but the submarine soils of silt and sand in the Yellow Sea area have not been well investigated so far.In this study,the physical and mechanical properties of silt and sand from the Yellow Sea were measured using a direct shear apparatus and their microstructures were observed using a scanning electron microscope.The test results suggest that the shear strength of silt and sand increases linearly with the increase of normal stress.Based on the direct shear test,the scanning electron microscope was used to observe the section surface of sand.It is observed that the section surface becomes rough,with many“V”‐shaped cracks.Many particles appear on the surface of the silt structure and tend to be disintegrated.The X‐ray diffraction experiment reveals that the sand and silt have different compositions.The shear strength of sand is slightly greater than that of silt under high stress,which is related to the shape of soil particles and the mineral composition.These results can be a reference for further study of other soils in the Yellow Sea;meanwhile,they can serve as soil parameters for the stability and durability analyses of offshore infrastructure construction.

Impact of wetting-drying cycles and acidic conditions on the soil aggregate stability of yellow‒brown soil

Soil aggregate is the basic structural unit of soil,which is the foundation for supporting ecosystem functions,while its composition and stability is significantly affected by the external environment.This study was conducted to explore the effect of external environment(wetting-drying cycles and acidic conditions)on the soil aggregate distribution and stability and identify the key soil physicochemical factors that affect the soil aggregate stability.The yellow‒brown soil from the Three Gorges Reservoir area(TGRA)was used,and 8 wetting-drying conditions(0,1,2,3,4,5,10 and 15 cycles)were simulated under 4 acidic conditions(pH=3,4,5 and 7).The particle size distribution and soil aggregate stability were determined by wet sieving method,the contribution of environmental factors(acid condition,wetting-drying cycle and their combined action)to the soil aggregate stability was clarified and the key soil physicochemical factors that affect the soil aggregate stability under wetting-drying cycles and acidic conditions were determined by using the Pearson’s correlation analysis,Partial least squares path modeling(PLS‒PM)and multiple linear regression analysis.The results indicate that wetting-drying cycles and acidic conditions have significant effects on the stability of soil aggregates,the soil aggregate stability gradually decreases with increasing number of wetting-drying cycles and it obviously decreases with the increase of acidity.Moreover,the combination of wetting-drying cycles and acidic conditions aggravate the reduction in the soil aggregate stability.The wetting-drying cycles,acidic conditions and their combined effect imposes significant impact on the soil aggregate stability,and the wetting-drying cycles exert the greatest influence.The soil aggregate stability is significantly correlated with the pH,Ca^(2+),Mg^(2+),maximum disintegration index(MDI)and soil bulk density(SBD).The PLS‒PM and multiple linear regression analysis further reveal that the soil aggregate stability is primarily influenced by SBD,Ca^(2+),and MDI.These results offer a scientific basis for understanding the soil aggregate breakdown mechanism and are helpful for clarifying the coupled effect of wetting-drying cycles and acid rain on terrestrial ecosystems in the TGRA.

Effects of Vegetation Restoration Age on Soil C:N:P Stoichiometry in Yellow River Delta Coastal Wetland of China

Vegetation restoration can alter carbon(C),nitrogen(N),and phosphorus(P)cycles in coastal wetlands affecting C:N:P stoichiometry.However,the effects of restoration age on soil C:N:P stoichiometry are unclear.In this study,we examined the re-sponses of soil C,N,and P contents and their stoichiometric ratios to vegetation restoration age,focusing on below-ground processes and their relationships to aboveground vegetation community characteristics.We conducted an analysis of temporal gradients based on the'space for time'method to synthesize the effects of restoration age on soil C:N:P stoichiometry in the Yellow River Delta wetland of China.The findings suggest that the combined effects of restoration age and soil depth create complex patterns of shifting soil C:N:P stoichiometry.Specifically,restoration age significantly increased all topsoil C:N:P stoichiometries,except for soil total phosphorus(TP)and the C:N ratio,and slightly affected subsoil C:N:P stoichiometry.The effects of restoration age on the soil C:N ratio was well constrained owing to the coupled relationship between soil organic carbon(SOC)and total nitrogen(TN)contents,while soil TP con-tent was closely related to changes in plant species diversity.Importantly,we found that the topsoil C:N:P stoichiometry was signific-antly affected by plant species diversity,whereas the subsoil C:N:P stoichiometry was more easily regulated by pH and electric con-ductivity(EC).Overall,this study shows that vegetation restoration age elevated SOC and N contents and alleviated N limitation,which is useful for further assessing soil C:N:P stoichiometry in coastal restoration wetlands.

Persistence of fertilization effects on soil organic carbon in degraded alpine wetlands in the Yellow River source region

In the restoration of degraded wetlands,fertilization can improve the vegetation-soil-microorganisms complex,thereby affecting the organic carbon content.However,it is currently unclear whether these effects are sustainable.This study employed Biolog-Eco surveys to investigate the changes in vegetation characteristics,soil physicochemical properties,and soil microbial functional diversity in degraded alpine wetlands of the source region of the Yellow River at 3 and 15 months after the application of nitrogen,phosphorus,and organic mixed fertilizer.The following results were obtained:The addition of nitrogen fertilizer and organic compost significantly affects the soil organic carbon content in degraded wetlands.Three months after fertilization,nitrogen addition increases soil organic carbon in both lightly and severely degraded wetlands,whereas after 15 months,organic compost enhanced the soil organic carbon level in severely degraded wetlands.Structural equation modeling indicates that fertilization decreases the soil pH and directly or indirectly influences the soil organic carbon levels through variations in the soil water content and the aboveground biomass of vegetation.Three months after fertilization,nitrogen fertilizer showed a direct positive effect on soil organic carbon.However,organic mixed fertilizer indirectly reduced soil organic carbon by increasing biomass and decreasing soil moisture.After 15 months,none of the fertilizers significantly affected the soil organic carbon level.In summary,it can be inferred that the addition of nitrogen fertilizer lacks sustainability in positively influencing the organic carbon content.

Effect of Different Land Use Patterns on Physical Properties of Soil Water in Yellow River Wetland in Shaanxi Province

[Objective] This study was to reveal the effect of different land use patterns on physical characteristics of soil water in the Yellow River wetland in Shaanxi Province.[Method]Taking Yellow River wetland in Shaanxi Province as experimental plot,we compared the physical properties of the soil water under different land use patterns and studied the physical properties and the change law of soil water during the wetland degeneration process.[Result]Under different land use patterns,soil bulk density rose with the increase of soil depth.During the degeneration process of from river wetland to reclaimed wetland（paddy field）,finally to abandoned land owing to salinization,the mean soil bulk density reduced correspondingly from 1.474 to 1.522 g/cm3,finally to 1.593 g/cm3 when abandoned.Accompanying wetland degeneration,soil became compact increasingly,and the indicators of soil porosity（total porosity,capillary porosity,non-capillary porosity）were also reduced with the change of land use patterns,in which,capillary porosity and total porosity reached the extremely significant level with the change of land use patterns,and non-capillary porosity reached significant level.The changes of soil porosity condition accelerated the deterioration of wetland.Under different land use patterns,the maximum soil moisture capacity,capillary moisture capacity and minimum moisture capacity all showed a similar change law.Compared with wetland,the maximum soil moisture capacity of reclaimed land（paddy field）and salinized land respectively decreased by 5.7% and 22.3%,capillary moisture capacity by 0.2% and 19.4%,minimum moisture capacity by 2.7% and 15.9%.Of the three land use patterns,wetland displayed both higher water holding capacity and water drainage capacity over reclaimed land（paddy field）and salinized land.By comparison with wetland,the reclaimed land（paddy field）and salinized land respectively decreased by 12.4% and 15.2% in total water holding capacity,and by 2.7% and 15.9% in total water drainage capacity.[Conclusion]To conserve the water resource in Yellow River wetland,regulate the hydrological cycle and enhance drought and water logging resistances,it should be noted that reasonable countermeasures be taken to exploit the state-owned forest land and paddy field around the wetland and the related resources.

Comparisons of Simulations of Soil Moisture Variations in the Yellow River Basin Driven by Various Atmospheric Forcing Data Sets

Based on station observations, The European Centre for Medium-Range Weather Forecasts reanalysis （ERA40）, the National Centers for Environmental Prediction/National Center for Atmospheric Research （NCEP/NCAR） reanalysis and Princeton University＇s global meteorological forcing data set （Princeton）, four atmospheric forcing fields were constructed for use in driving the Community Land Model version 3.5 （CLM3.5）. Simulated soil moisture content throughout the period 1951-2000 in the Yellow River basin was validated via comparison with corresponding observations in the upper, middle, and lower reaches. The results show that CLM3.5 is capable of reproducing not only the characteristics of intra-annual and annual variations of soil moisture, but also long-term variation trends, with different statistical significance in the correlations between the observations and simulations from different forcing fields in various reaches. The simulations modeled with station-based atmospheric forcing fields are the most consistent with observed soil moisture, and the simulations based on the Princeton data set are the second best, on average. The simulations from ERA40 and NCEP/NCAR are close to each other in quality, but comparatively worse to the other sources of forcing information that were evaluated. Regionally, simulations are most consistent with observations in the lower reaches and less so in the upper reaches, with the middle reaches in between. In addition, the soil moisture simulated by CLM3.5 is systematically greater than the observations in the Yellow River basin. Comparisons between the simulations by CLM3.5 and CLM3.0 indicate that simulation errors are primarily caused by deficiencies within CLM3.5 and are also associated with the quality of atmospheric forcing field applied.

Petroleum Hydrocarbon Degradation Potential of Soil Bacteria Native to the Yellow River Delta

The bioremediation potential of bacteria indigenous to soils of the Yellow River Delta in China was evaluated as a treatment option for soil remediation. Petroleum hydrocarbon degraders were isolated from contaminated soil samples from the Yellow River Delta. Four microbial communities and eight isolates were obtained. The optimal temperature, salinity, pH, and the ratios of C, N, and P (C:N:P) for the maximum biodegradation of diesel oil, crude oil, n-alkanes, and polyaromatic hydrocarbons by indigenous bacteria were determined, and the kinetics changes in microbial communities were monitored. In general, the mixed microbial consortia demonstrated wider catabolic versatility and faster overall rate of hydrocarbon degradation than individual isolates. Our experimental results demonstrated the feasibility of biodegradation of petroleum hydrocarbon by indigenous bacteria for soil remediation in the Yellow River Delta.

Changes in sediment discharge in a sediment-rich region of the Yellow River from 1955 to 2010: implications for further soil erosion control

The well-documented decrease in the discharge of sediment into the Yellow River has attracted considerable attention in recent years. The present study analyzed the spatial and temporal variation of sediment yield based on data from 46 hydrological stations in the sediment-rich region of the Yellow River from 1955 to 2010. The results showed that since 1970 sediment yield in the region has clearly decreased at different rates in the 45 sub-areas controlled by hydrological stations. The decrease in sediment yield was closely related to the intensity and extent of soil erosion control measures and rainstorms that occurred in different periods and sub-areas. The average sediment delivery modulus（SDM） in the study area decreased from 7,767.4 t/（km^2·a） in 1951–1969 to 980.5 t/（km^2·a） in 2000–2010. Our study suggested that 65.5% of the study area with the SDM below 1,000 t/（km^2·a） is still necessary to control soil deterioration caused by erosion, and soil erosion control measures should be further strengthened in the areas with the SDM above 1,000 t/（km^2·a）.

Effect of Hydrological Connectivity on Soil Carbon Storage in the Yellow River Delta Wetlands of China

Hydrological connectivity has significant effects on the functions of estuarine wetland ecosystem.This study aimed to examine the dynamics of hydrological connectivity and its impact on soil carbon pool in the Yellow River Delta,China.We calculated the hydrological connectivity based on the hydraulic resistance and graph theory,and measured soil total carbon and organic carbon under four different hydrological connectivity gradients(Ⅰ0‒0.03,Ⅱ0.03‒0.06,Ⅲ0.06‒0.12,Ⅳ0.12‒0.39).The results showed that hydrological connectivity increased in the north shore of the Yellow River and the south tidal flat from 2007 to 2018,which concentrated in the mainstream of the Yellow River and the tidal creek.High hydrological connectivity was maintained in the wetland restoration area.The soil total carbon storage and organic carbon storage significantly increased with increasing hydrological connectivity fromⅠtoⅢgradient and decreased inⅣgradient.The highest soil total carbon storage of 0‒30 cm depth was 5172.34 g/m^(2),and organic carbon storage 2764.31 g/m^(2)inⅢgradient.The hydrological connectivity changed with temporal and spatial change during 2007‒2018 and had a noticeable impact on soil carbon storage in the Yellow River Delta.The results indicated that appropriate hydrological connectivity,i.e.0.08,could effectively promote soil carbon storage.

Diversity analysis of soil dematiaceous hyphomycetes from the Yellow River source area:Ⅰ

Twenty-four soil samples of eight ecosystem-types around the Yellow River source area were investigated for the number and specific composition of soil dematiaceous hyphomycetes by dilution plate technique. And then the co-relationship between genus species of soil dematiaceous hyphomycetes and ecosystem-types was analyzed. The results show that the amount and species distribution of soil dematiaceous hyphomycetes had an obvious variability in different ecosystem-types, and that the dominant genus species varied in the eight ecosystem-types studied, with Cladosporium being the dominant genus in seven of the eight ecosystem-types except wetland. The index of species diversity varied in different ecosystem-types. The niche breadth analysis showed that Cladosporium had the highest niche breadth and distributed in all ecosystem-types, while the genera with a narrow niche breadth distributed only in a few ecosystem-types. The results of niche overlap index analysis indicated that Stachybotrys and Torula, Doratomyces and Scolecobasidium, Cladosporium and Chrysosporium had a higher niche overlap, whereas Arthrinium and Gliomastix, Phialophora and Doratomyces, Oidiodendron and Ulocladium had no niche overlap.

An evaluation of soil moisture from AMSR-E over source area of the Yellow River, China

In this study,in-situ soil moisture measurements are used to evaluate the accuracy of three AMSR-E soil moisture prod ucts from NASA(National Aeronautics and Space Administration),JAXA(Japanese Aerospace Exploration Agency)and VUA(Vrije University Amsterdam and NASA)over Maqu County,Source Area of the Yellow River(SAYR),China.Re sults show that the VUA soil moisture product performs the best among the three AMSR-E soil moisture products in the study area,with a minimum RMSE(root mean square error)of 0.08(0.10)m3/m3 and smallest absolute error of 0.07(0.08)m3/m3 at the grassland area with ascending(descending)data.Therefore,the VUA soil moisture product is used to describe the spatial variation of soil moisture during the 2010 growing season over SAYR.The VUA soil moisture product shows that soil moisture presents a declining trend from east south(0.42 m3/m3)to west north(0.23 m3/m3),with good agreement with a general precipitation distribution.The center of SAYR presents extreme wetness(0.60 m3/m3)dur ing the whole study period,especially in July,while the head of SAYR presents a high level soil moisture(0.23 m3/m3)in July,August and September.

Spatial-temporal variations in near-surface soil freeze-thaw cycles in the source region of the Yellow River during the period 2002–2011 based on the Advanced Microwave Scanning Radiometer for the Earth Observing System(AMSR-E) data

Detecting near-surface soil freeze-thaw cycles in high-altitude cold regions is important for understanding the Earth＇s surface system, but such studies are rare. In this study, we detected the spatial-temporal variations in near-surface soil freeze-thaw cycles in the source region of the Yellow River（SRYR） during the period 2002–2011 based on data from the Advanced Microwave Scanning Radiometer for the Earth Observing System（AMSR-E）. Moreover, the trends of onset dates and durations of the soil freeze-thaw cycles under different stages were also analyzed. Results showed that the thresholds of daytime and nighttime brightness temperatures of the freeze-thaw algorithm for the SRYR were 257.59 and 261.28 K, respectively. At the spatial scale, the daily frozen surface（DFS） area and the daily surface freeze-thaw cycle surface（DFTS） area decreased by 0.08% and 0.25%, respectively, and the daily thawed surface（DTS） area increased by 0.36%. At the temporal scale, the dates of the onset of thawing and complete thawing advanced by 3.10（±1.4） and 2.46（±1.4） days, respectively; and the dates of the onset of freezing and complete freezing were delayed by 0.9（±1.4） and 1.6（±1.1） days, respectively. The duration of thawing increased by 0.72（±0.21） day/a and the duration of freezing decreased by 0.52（±0.26） day/a. In conclusion, increases in the annual minimum temperature and winter air temperature are the main factors for the advanced thawing and delayed freezing and for the increase in the duration of thawing and the decrease in the duration of freezing in the SRYR.

Information Extraction Method of Soil Salinity in Typical Areas of the Yellow River Delta Based on Landsat Imagery

In order to get RS method to extract soil salinity of the Yellow River Delta, we set Kenli County as typical Yellow River Delta to be research area and get data of soil salinity through field investigation. By using RS image of Landsat-8 of March 14, 2014 and analyzing information features of each band and surface spectral features of research areas, we select out sensitive bands and build Soil Salinity Information Extraction (SSIE) model and vegetation index NDVI model for comparison. And then, we accordingly classify grades of soil salinity and get soil salinity information by decision tree approach based on expert knowledge. The results show that overall accuracy of SSIE model is 93.04% and coefficient of Kappa is 0.7869, while overall accuracy of NDVI model is 83.67% and coefficient of Kappa is 0.7017 respectively. By comparing with measured proportions of each class, we see that results from SSIE model is more accurate, which indicates significant advantage for soil salinity information extraction. This research provides scientific basis to get and monitoring soil salinity of the Yellow River Delta region quickly and accurately.

Soil Organic Carbon Contents and Stocks in Coastal Salt Marshes with Spartina alterniflora Following an Invasion Chronosequence in the Yellow River Delta,China

Plant invasion alters the fundamental structure and function of native ecosystems by affecting the biogeochemical pools and fluxes of materials and energy. Native(Suaeda salsa) and invasive(Spartina alterniflora) salt marshes were selected to study the effects of Spartina alterniflora invasion on soil organic carbon(SOC) contents and stocks in the Yellow River Delta. Results showed that the SOC contents(g/kg) and stocks(kg/m^2) were significantly increased(P < 0.05) after Spartina alterniflora invasion of seven years, especially for the surface soil layer(0–20 cm). The SOC contents exhibited an even distribution along the soil profiles in native salt marshes, while the SOC contents were gradually decreased with depth after Spartina alterniflora invasion of seven years. The natural ln response ratios(Ln RR) were applied to identify the effects of short-term Spartina alterniflora invasion on the SOC stocks. We also found that Spartina alterniflora invasion might cause soil organic carbon losses in a short-term phase(2–4 years in this study) due to the negative Ln RR values, especially for 20–60 cm depth. And the SOCD in surface layer(0–20 cm) do not increase linearly with the invasive age. Spearman correlation analysis revealed that silt + clay content was exponentially related with SOC in surface layer(Adjusted R^2 = 0.43, P < 0.001), suggesting that soil texture could play a key role in SOC sequestration of coastal salt marshes.

Effects of red-yellow soil acidification on seed germination of Chinese pine

Acid treatments significantly change the physical and chemical properties of red yellow soil by lowering its pH value and leaching out aluminum(Al) ions that are harmful to the growth of plants. The structure of soil will be damaged, resulting in higher viscosity, higher water retention rate and lower air permeability of the soil. The germination rate of Chinese pine( Pinus tabulacformic Carr. ) seeds sowed in soil treated with sulphuric acid(H 2SO 4) decreased compared to that for untreated soil. The direct cause was the large amount of Al ions leached out because of low pH values(≥3.5). The added acid decreased the soil aggregation and increased the number of micro aggregates(under 250 μm in diameter). Such changes increased the soil's viscosity, which tied the pine needles to the soil after the seeds had germinated and prevented the seedlings from fully developing.

Soil hydraulic conductivity and its influence on soil moisture simulations in the source region of the Yellow River——take Maqu as an example

Saturated hydraulic conductivity and unsaturated hydraulic conductivity which are influenced by soil are two important factors that affect soil water transport.In this paper,data supplied by the Chinese Academy of Sciences are used to determine true unsaturated hydrology values.Furthermore,in combination with observed,model simulation and experimental data,an improved saturated hydraulic conductivity parameterization scheme is carried out in CLM4.5 at a single point in the summer.The main results show that:(1)After improving saturated hydraulic conductivity in CLM4.5 through a parameterization modification,it is found that shallow layer soil moisture increases compared to the initial value;and(2)The numerical values of unsaturated hydraulic conductivities in the model are obviously larger than experimental values.By substituting the BrooksCorey soil water characteristic curve into the Mualem model,the value of unsaturated hydraulic conductivity is modified;(3)By using the modified value,it is found that the attenuating magnitude of simulated soil moisture caused by each rainfall event is reduced.The soil moisture variation in shallow layers(5,10 and 20 cm)could be better displayed.

Soil Phosphorus Release to the Water Bodies in the Upland Fields of Yellow Soil Areas and Impacting Factor

Soil phosphorus release to the water bodies in the upland fields of yellow soil areas and impacting factor was studied in Guizhou province. The results showed that the content of dissolved active P of surface runoff from various upland fields of yellow-soil were significantly different, which the concentrations of dissolved active P of runoff correlated with the contents of available-P, amorphous oxides of A1, and organic matter in the soils. The amount of soil phosphorus release to the water bodies affected by the level of applying P fertilizer and the process of corn growth, which with fertilizing from 150 to 900 kg P205 ha^-1 in the soil with high P level, the average contents of dissolved active P in the permeability-water of the soil increased from 0.020 mg L^-1 to 0.137 mg L^-1. The amount of soil phosphorus release to the water bodies also affected by environmental factor, which the amount of soil phosphorus release significantly increased under the conditions that temperature is 30℃-35℃, water/soil ratios is 15：1-25：1, submergence-time by water is 12-18 h and pH value of acid rains is 3.82-3.73.

Soil and plant responses to degradation of alpine grassland in source region of the Yellow River

Land degradation has been rapidly taking place in source region of the Yellow River in China. This study was conducted during 2008 in Maduo County to investigate soil and plant changes in relation to land degradation. Several results were derived from this work. First, the soil organic carbon (SOC) and total nitrogen (TN) decreased significantly on the extremely degraded land comparing with the natural grassland. Second, soil bulk density increased as land degradation worsened. Soil bulk density of the extremely degraded land was significantly greater than that of the grassland. Third, pH showed no obvious variation pattern. Finally, aboveground biomass decreased from grassland to the moderately degraded land. But aboveground biomass increased on the extremely degraded land and very extremely degraded land with most aboveground biomass inedible for livestock.

Effects of muddy water irrigation with different sediment gradations on nitrogen transformation in agricultural soil of Yellow River Basin

Muddy water irrigation has been widely practiced in the Yellow River Basin for agricultural production and is an important method of economical and intensive utilization of water resources.In this study,the effects of sediment gradation,sand content,and soil moisture content on nitrogen(N)transformation were studied through a series of experimental tests.The results indicated that muddy water irrigation significantly affected agricultural soil physical and biological properties as well as N transformation.Soil bulk density,total porosity,pH,and microbial enzyme activities significantly correlated with N transformation as affected by the interaction between sediment and soil moisture.Sediment addition generally increased the soil bulk density and reduced the soil porosity and pH significantly,and the optimum moisture for promotion of the N transformation rate was 80%of the water-filled pore space.Therefore,muddy water irrigation has a potentially long-term influence on agricultural N cycles in semi-arid regions of northwestern China.This could provide a theoretical basis for scientific and rational use of muddy water for irrigation.

Critical effects on the photosynthetic efficiency and stem sap flow of poplar in the Yellow River Delta in response to soil water

To explore the critical relationships of photosynthetic efficiency and stem sap flow to soil moisture,two-year-old poplar saplings were selected and a packaged stem sap flow gauge,based on the stem-heat balance method,and a CIRAS-2 portable photosynthesis system were used.The results show that photosynthetic rates(P_(n)),transpiration rates(T_(r)),instantaneous water use efficiency(WUE)and the stem sap flow increased initially and then decreased with decreasing soil water,but their critical values were different.The turning point of relative soil water content(W_(r))from stomatal limitation to nonstomatal limitation of P_(n)was 42%,and the water compensation point of P_(n)was 13%.Water saturation points of P_(n)and T_(r)were 64%and 56%,respectively,and the WUE was 71%.With increasing soil water,the apparent quantum yield(AQY),light saturation point(LSP)and maximum net photosynthetic rate(P_(n)max)increased first and then decreased,while the light compensation point(LCP)decreased first and then increased.When W_(r)was 64%,LCP reached a lower value of 30.7µmol m^(-2)s^(-1),and AQY a higher value of 0.044,indicating that poplar had a strong ability to utilize weak light.When W_(r)was 74%,LSP reached its highest point at 1138.3µmol·m^(-2)s^(-1),indicating that poplar had the widest light ecological amplitude and the highest light utilization efficiency.Stem sap flow and daily sap flow reached the highest value(1679.7 g d^(-1))at W_(r)values of 56%and 64%,respectively,and then declined with increasing or decreasing W_(r),indicating that soil moisture significantly affected the transpiration water-consumption of poplar.Soil water was divided into six threshold grades by critical values to maintain photosynthetic efficiency at different levels,and a W_(r)of 64-71%was classified to be at the level of high productivity and high efficiency.In this range,poplar had high photosynthetic capacity and efficient physiological characteristics for water consumption.The saplings had characteristics of water tolerance and were not drought resistant.Full attention should be given to the soil water environment in the Yellow River Delta when planting Populus.