Grain Yield,Biomass Accumulation,and Leaf Photosynthetic Characteristics of Rice under Combined Salinity-Drought Stress

Simultaneous stresses of salinity and drought often coincide during rice-growing seasons in saline lands,primarily due to insufficient water resources and inadequate irrigation facilities.Consequently,combined salinity-drought stress poses a major threat to rice production.In this study,two salinity levels(NS,non-salinity;HS,high salinity)along with three drought treatments(CC,control condition;DJ,drought stress imposed at jointing;DH,drought stress imposed at heading)were performed to investigate their combined influences on leaf photosynthetic characteristics,biomass accumulation,and rice yield formation.Salinity,drought,and their combination led to a shortened growth period from heading to maturity,resulting in a reduced overall growth duration.Grain yield was reduced under both salinity and drought stress,with a more substantial reduction under the combined salinity-drought stress.The combined stress imposed at heading caused greater yield losses in rice compared with the stress imposed at jointing.Additionally,the combined salinity-drought stress induced greater decreases in shoot biomass accumulation from heading to maturity,as well as in shoot biomass and nonstructural carbohydrate(NSC)content in the stem at heading and maturity.However,it increased the harvest index and NSC remobilization reserve.Salinity and drought reduced the leaf area index and SPAD value of flag leaves and weakened the leaf photosynthetic characteristics as indicated by lower photosynthetic rates,transpiration rates,and stomatal conductance.These reductions were more pronounced under the combined stress.Salinity,drought,and especially their combination,decreased the activities of ascorbate peroxidase,catalase,and superoxide dismutase,while increasing the contents of malondialdehyde,hydrogen peroxide,and superoxide radical.Our results indicated a more significant yield loss in rice when subjected to combined salinity-drought stress.The individual and combined stresses of salinity and drought diminished antioxidant enzyme activities,inhibited leaf photosynthetic functions,accelerated leaf senescence,and subsequently lowered assimilate accumulation and grain yield.

Implications for identification of principal stress directions from acoustic emission characteristics of granite under biaxial compression experiments

The rock fracture characteristics and principal stress directions are crucial for prevention of geological disasters.In this study,we carried out biaxial compression tests on cubic granite samples of 100 mm in side length with different intermediate principal stress gradients in combination with acoustic emission(AE)technique.Results show that the fracture characteristics of granite samples change from‘sudden and aggregated’to‘continuous and dispersed’with the increase of the intermediate principal stress.The effect of increasing intermediate principal stress on AE amplitude is not significant,but it increases the proportions of high-frequency AE signals and shear cracks,which in turn increases the possibility of unstable rock failure.The difference of stress in different directions causes the anisotropy of rock fracture and thus leads to the obvious anisotropic characteristics of wave velocity variations.The anisotropy of wave velocity variations with stress difference is probable to identify the principal stress directions.The AE characteristics and the anisotropy of wave velocity variations of granite under two-dimensional stress are not only beneficial complements for rock fracture characteristic and principal stress direction identification,but also can provide a new analysis method for stability monitoring in practical rock engineering.

A continuous and long-term in-situ stress measuring method based on fiber optic. Part I: Theory of inverse differential strain analysis

A method for in-situ stress measurement via fiber optics was proposed. The method utilizes the relationship between rock mass elastic parameters and in-situ stress. The approach offers the advantage of long-term stress measurements with high spatial resolution and frequency, significantly enhancing the ability to measure in-situ stress. The sensing casing, spirally wrapped with fiber optic, is cemented into the formation to establish a formation sensing nerve. Injecting fluid into the casing generates strain disturbance, establishing the relationship between rock mass properties and treatment pressure.Moreover, an optimization algorithm is established to invert the elastic parameters of formation via fiber optic strains. In the first part of this paper series, we established the theoretical basis for the inverse differential strain analysis method for in-situ stress measurement, which was subsequently verified using an analytical model. This paper is the fundamental basis for the inverse differential strain analysis method.

Support design method for deep soft-rock tunnels in non-hydrostatic high in-situ stress field

Due to the long-term plate tectonic movements in southwestern China,the in-situ stress field in deep formations is complex.When passing through deep soft-rock mass under non-hydrostatic high in-situ stress field,tunnels will suffer serious asymmetric deformation.There is no available support design method for tunnels under such a situation in existing studies to clarify the support time and support stiffness.This study first analyzed the mechanical behavior of tunnels in non-hydrostatic in-situ stress field and derived the theoretical equations of the ground squeezing curve(GSC)and ground loosening curve(GLC).Then,based on the convergence confinement theory,the support design method of deep soft-rock tunnels under non-hydrostatic high in-situ stress field was established considering both squeezing and loosening pressures.In addition,this method can provide the clear support time and support stiffness of the second layer of initial support.The proposed design method was applied to the Wanhe tunnel of the China-Laos railway in China.Monitoring data indicated that the optimal support scheme had a good effect on controlling the tunnel deformation in non-hydrostatic high in-situ stress field.Field applications showed that the secondary lining could be constructed properly.

Performance of water-coupled charge blasting under different in-situ stresses

Water-coupled charge blasting is a promising technique to efficiently break rock masses.In this study,numerical models of double boreholes with water-coupled charge are established using LS-DYNA and are calibrated by the tests of rock masses subjected to explosion loads to examine its performance.The crack levels of rock mass induced by water-coupled charge blasting and air-coupled charge blasting are first compared.It is found that water-coupled charge blasting is more appropriate to fracture deep rock mass than air-coupled charge blasting.In addition,the effects of rock properties,water-coupled charge coefficients,and borehole connection angles on the performance of water-coupled charge blasting are investigated.The results show that rock properties and water-coupled charge coefficients can greatly influence the crack and fragmentation levels of rock mass induced by water-coupled charge blasting under uniform and non-uniform in-situ stresses.However,changing borehole-connection angles can only affect crack and fragmentation levels of rock mass under non-uniform in-situ stresses but barely affect those under uniform in-situ stresses.A formula is finally proposed by considering the above-mentioned factors to provide the design suggestion of water-coupled charge blasting to fracture rock mass with different in-situ stresses.

Influences of clean fracturing fluid viscosity and horizontal in-situ stress difference on hydraulic fracture propagation and morphology in coal seam

The viscosity of fracturing fluid and in-situ stress difference are the two important factors that affect the hydraulic fracturing pressure and propagation morphology. In this study, raw coal was used to prepare coal samples for experiments, and clean fracturing fluid samples were prepared using CTAB surfactant. A series of hydraulic fracturing tests were conducted with an in-house developed triaxial hydraulic fracturing simulator and the fracturing process was monitored with an acoustic emission instrument to analyze the influences of fracturing fluid viscosity and horizontal in-situ stress difference on coal fracture propagation. The results show that the number of branched fractures decreased, the fracture pattern became simpler, the fractures width increased obviously, and the distribution of AE event points was concentrated with the increase of the fracturing fluid viscosity or the horizontal in-situ stress difference. The acoustic emission energy decreases with the increase of fracturing fluid viscosity and increases with the increase of horizontal in situ stress difference. The low viscosity clean fracturing fluid has strong elasticity and is easy to be compressed into the tip of fractures, resulting in complex fractures. The high viscosity clean fracturing fluids are the opposite. Our experimental results provide a reference and scientific basis for the design and optimization of field hydraulic fracturing parameters.

Characteristic stress variation and microcrack evolution of granite subjected to uniaxial compression using acoustic emission methods

The size of mineral grain has a significant impact on the initiation and propagation of microcracks within rocks.In this study,fine-,medium-,and coarse-grained granites were used to investigate microcrack evolution and characteristic stress under uniaxial compression using the acoustic emission(AE),digital image correlation(DIC),and nuclear magnetic resonance(NMR)measurements.The experimental results show that the characteristic stress of each granite decreased considerably with increasing grain sizes.The inflection points of the b-value occurred earlier with an increase in grain sizes,indicating that the larger grains promote the generation and propagation of microcracks.The distribution characteristics of the average frequency(AF)and the ratio of rise time to amplitude(RA)indicate that the proportion of shear microcracks increases with increasing grain size.The NMR results indicate that the porosity and the proportion of large pores increased with increasing grain size,which may intensify the microcrack evolution.Moreover,analysis of the DIC and AE event rates suggests that the high-displacement regions could serve as a criterion for the degree of microcrack propagation.The study found that granites with larger grains had a higher proportion of high-displacement regions,which can lead to larger-scale cracking or even spalling.These findings are not only beneficial to understand the pattern of microcrack evolution with different grain sizes,but also provide guidance for rock monitoring and instability assessment.

Load-bearing characteristics and energy evolution of fractured rock masses after granite and sandstone grouting

Experiments on grouting-reinforced rock mass specimens with different particle sizes and features were carried out in this study to examine the effects of grouting reinforcement on the load-bearing characteristics of fractured rock mass.The strength and deformation features of grouting-reinforced rock mass were analyzed under different loading manners;the energy evolution mechanism of grouting-reinforced rock mass specimens with different particle sizes and features was investigated;the energy dissipation ratio and post-peak stress decreasing rate were employed to evaluate the bearing stability of grouting-reinforced rock mass.The results show that the strength and ductility of granite-reinforced rock mass(GRM)under biaxial loading are higher than that of sandstone-reinforced rock mass(SRM)under uniaxial loading.Besides,the energy evolution characteristics of grouting-reinforced rock mass under uniaxial and biaxial loading mainly could be divided into early,middle,and late stages.In the early stage,total,elastic,and dissipation energies were quite small with flatter curves;in the middle stage,elastic energy increased rapidly,whereas dissipation energy increased slowly;in the late stage,dissipation energy increased sharply.The energy dissipation ratio was used to represent the pre-peak plastic deformation.Under uniaxial loading,this ratio increased as the particle size increased and the pre-peak plastic deformation of grouting-reinforced rock mass became larger;under biaxial loading,it dropped as the particle size increased,and the pre-peak plastic deformation of grouting-reinforced rock mass became smaller.The post-peak stress decline rate A_(v) was used to assess the post-peak bearing performance of grouting-reinforced rock mass.Under uniaxial loading,parameter A_(v) exhibited reduction as the particle size kept increasing,and the ability of post-peak of grouting-reinforced rock mass to allow deformation development was greater,and the bearing capacity was greater;under biaxial loading,A_(v) increased with the particle size,and the ability of post-peak of grouting-reinforced rock mass to allow deformation development was low and the bearing capacity was reduced.The findings are considered instrumental in improving the stability of the roadway-surrounding rock by granite and sandstone grouting.

Study on Sealing Characteristics of Sliding Seal Assembly of Aircraft Hydraulic Actuator

The hydraulic actuator,known as the"muscle"of military aircraft,is responsible for flight attitude adjustment,trajectory control,braking turn,landing gear retracting and other actions,which directly affect its flight efficiency and safety.However,the sealing assembly often has the situation of over-aberrant aperture fit clearance or critical over-aberrant clearance,which increases the failure probability and degree of movable seal failure,and directly affects the flight efficiency and safety of military aircraft.In this paper,the simulation model of hydraulic actuator seal combination is established by ANSYS software,and the sealing principle is described.The change curve of contact width and contact pressure of combination seal under the action of high-pressure fluid is drawn.The effects of different oil pressure,fit clearance and other parameters on the sealing performance are analyzed.Finally,the accelerated life test of sliding seal components is carried out on the hydraulic actuator accelerated life test rig,and the surface morphology is compared and analyzed.The research shows that the O-ring is the main sealing element and the role of the check ring is to protect and support the O-ring to prevent damage caused by squeezing into the fit clearance,so the check ring bears a large load and is prone to shear failure.Excessive fit clearance is the main factor affecting the damage of the check ring,and the damage parts are mainly concentrated at the edge of the sealing surface.This paper provides a theoretical basis for the design of hydraulic actuator and the improvement of sealing performance.

Stress response characteristics of BFRP anchors on loess mudstone slope under rainfall conditions

To investigate the stress response characteristics and shear stress transfer mechanism of BFRP(basalt fiber reinforced plastics)anchors under rainfall conditions and to explore the reinforcement effect of BFRP anchors,a comparative indoor physical model test was conducted in this study using loess mudstone slope as a typical case,and multi-attribute response data,such as slope displacement,BFRP anchor strain and axial force,were obtained.Based on the variation law of slope displacement,it can be concluded that the deformation displacement of the slope on the side reinforced by BFRP anchors is smaller than that of slopes reinforced with steel anchors;the bearing capacity of BFRP anchor is given priority in time,and the anchoring effect of BFRP anchor at the top of the slope is given priority,and the axial force value of anchor is characterized by a surface amplification effect in space;the axial force is higher around the anchor head and tends to decay as a negative exponential function as the anchor extends in the direction of the interior of the slope;the shear stress of BFRP anchor and anchorage body are unevenly distributed along the axial direction,with the maximum value occurring in the free section near the slope surface and decreases as the BFRP anchor extends towards the interior of the slope.These results can provide a theoretical basis for the optimal design of BFRP anchors.

Water infiltration and soil-water characteristics of compacted loess under applied vertical stress

Additional stress formed by postconstruction buildings in loess-filling areas affects water infiltration in soil and causes soil deformation.To investigate this effect,under constant water head,vertical infiltration tests on compacted loess with two initial dry densities for different applied vertical stresses were developed using vertical stresscontrollable one-dimensional soil columns.The timehistory curves of vertical deformation,wetting front depth,cumulative infiltration depth,volumetric water content(VWC)and suction were measured,and the soil-water characteristic curves(SWCCs)were determined.The results showed that:(1)the infiltration ability of the soil column weakens with increasing applied vertical stress and initial dry density;(2)vertical deformation increases rapidly at first and then tends to be stable slowly at the consolidation and wetting-induced deformation stage,and is positively correlated with applied vertical stress and is negatively correlated with initial dry density.The stability time of wetting-induced deformation and the corresponding wetting front depth increase with the increase of applied vertical stress,while they decrease obviously when initial dry density increases;(3)the influence of applied vertical stress on soilwater characteristics in soil columns with various initial dry densities is related to the deformation depth of soil column.The VG(Van Genuchten)model is suitable for fitting the SWCCs at different monitoring positions.A normalized SWCC model introducing the applied vertical stress was proposed for each initial dry density using the mathematical relationship between the fitting parameters and the applied vertical stress.

Osmotic Regulation,Antioxidant Enzyme Activities and Photosynthetic Characteristics of Tree Peony(Paeonia suffruticosa Andr.)in Response to High-Temperature Stress

Tree peony(Paeonia suffruticosa Andr.)is a traditional Chinese flower,which prefers cool weather.However,high temperature in summer in the middle and lower reaches of the Yangtze River restricts its growth and development.In this study,osmotic regulation,antioxidant enzyme activities,and photosynthetic characteristics of tree peony in response to high-temperature stress were investigated.The results showed that high-temperature stress had destroyed the cell membrane,manifested as the increased relative electrical conductivity and malondialdehyde content.Moreover,high-temperature stress led to excessive accumulation of reactive oxygen species,thereby,activating antioxidant enzyme activities.Also,photosynthetic parameters and chlorophyll fluorescence parameters directly reflected the damage to the photosystem II reflection center under high-temperature stress.In addition,high-temperature stress led to stomatal closure and chloroplast damage.This study revealed the physiological responses of tree peony to high-temperature stress,laying a foundation for the promotion of tree peony in high-temperature areas and the improvement of high-temperature resistance.

Expression Characteristics of AaHsp90 Gene in Antheraea assamensis under Different Temperature and Starvation Stress

[Objectives]To investigate the effects of different temperature and starvation stress on the expression of AaHsp90 and reveal the molecular mechanism of adaptation to environment in Antheraea assama.[Methods]Taking the normal feeding group at 26℃as the control,the expression change of AaHsp90 was detected by real-time PCR in midgut,fat body and hemlymph after high temperature stress at 38℃,low temperature stress at 4℃and starvation stress separately for different time on the third day of the fifth larvae.[Results]The expression of AaHsp90 in midgut,fat body and hemlymph of Antheraea assama were increased obviously at first and then decreased sharply with the prolongation of treatment time at 38℃.There has a certain inhibitory effect on the expression of AaHsp90 in midgut,fat body and hemolymph after treatment with 4℃for different time.After treatment with starvation,the AaHsp90 expression were increased at 12 and 18 h and decreased sharply at 24 h in midgut,fat body and hemolymph of A.assama.[Conclusions]Comprehensive analysis showed that high temperature and starvation stress can induce the expression of AaHsp90,while low temperature stress mainly suppressed its expression.It was suggested that the AaHsp90 protein may play an important role in the process of adaptation to high temperature and starvation stress in A.assama.

Effects of Heat Stress during Seed Filling Stage on Brassica napus Seed Oil Accumulation and Chlorophyll Fluorescence Characteristics

As global temperature rise,the threat of heat stress to rapeseed production is becoming more obvious.Exploring the response characteristics of two important biological pathways,oil accumulation and photosynthesis,to heat stress during B.napus seed filling is helpful in the genetic improvement of heat-tolerant rapeseed.The effects of heat stress on seed oil accumulation and chlorophyll fluorescence characteristics of 29 B.napus germplasms with different oil content and environmental sensitivity,including 6 rapeseed varieties which exhibited environmentsensitive/insensitive and with high,medium or low oil content,were tested by whole plant heat stress or the in vitro silique culture system.Both assay exhibited similar trend on oil content of the rapeseed germplasms.The heat effect on the chlorophyll fluorescence kinetic parameters F_(v)/F_(m),ETR and Y(Ⅱ)were also consistent.Heat stress significantly decreased oil content,although there was abundant genetic variation on heat tolerance among the genotypes.Correlation analysis showed that the decrease rate of F_(v)/F_(m) of silique heat-stressed B.napus developing seed was positive correlative to the decrease rate of mature seed oil content of the whole plant heat-stressed rapeseed(R=0.9214,P-value<0.01).Overall,the results indicated that heat stress inhibited oil accumulation and photosynthesis in B.napus developing seed.The decrease rate of chlorophyll fluorescence parameter F_(v)/F_(m) of heat-stressed developing seed could be used as the index of heat tolerant rapeseed identification.Further,two heat insensitive rapeseed varieties with high oil content were identified.

Effects of Water Stress on Photosynthesis and Fluorescence Characteristics in Peony

[ Objective] Study on the photosynthesis and fluorescence characteristics in peony under water stress. [ Method ] The two peony varieties Huhong and Luoyanghong were treated by different water stress for determining the photosynthesis and fluorescence characteristics. [ Result ] With the aggravation of water stress, the net photosynthetic rate （Pn） and stomatal conductance （Gs） decreased, while the intercellular CO2 concentration （Ci） increased. Drought could decrease Pn, constrain gas exchange and change the daily photosynthesis. Fo of peony leaf increased and Fv/Fm decreased under water stress especially water logging, causing the inactivation of the PS II reaction center, and the chlorophyll fluorescence characters gradually recovered until afternoon. [ Conclusion] The 75% soil relative water content （SRWC） is the best condition for growth of peony. Compared with drought, water logging is more unfit for the growth of peony. For the two varieties, Huhong assumed more tolerance to drought, accordingly more adaptability.

Effects of Antimony Stress on Photosynthetic Characteristics of Vegetable Leaves

[Objective] This study aimed to investigate the effects of different concen- trations of antimony and modifier calcium magnesium phosphate on photosynthetic characteristics of edible amaranth, flowering Chinese cabbage, spinach and flowering Chinese cabbage. [Method] By outdoor potting simulation experiment, soil matrixes containing 10.00, 20.00, 50.00, 70.00 and 100.00 mg/kg antimony （Sb3＋） were pre- pared; soil without antimony was used as control （CK）. Each pot was loaded with 0.10 kg/kg vegetable special fertilizer, mixed evenly, and divided into two shares： one share was supplemented with 1.75 g/kg modifier calcium magnesium phosphate and mixed evenly; the other share contained no calcium magnesium phosphate. Af- ter the generation of three true leaves, seedlings with uniform growth were trans- planted into the prepared soil matrixes, eights seedlings per pot. Vegetable seedlings were watered regularly to maintain 70% of field capacity. After 45 d, veg- etable plants were harvested and washed clean with distilled water for measurement of indicators of photosynthetic characteristics. [Result] With the increase of antimony concentration, relative chlorophyll content （SPAD value） and net photosynthetic rate of four vegetable species increased first and then declined, while stomatal conduc- tance of vegetable leaves was linearly reduced. [Conclusion] Appropriately adding modifier calcium magnesium phosphate can effectively improve the photosynthetic characteristics of four vegetable species and reduce the toxic effects of heavy metal antimony on vegetables.

Preliminary Study on the Accumulation Characteristics of Mineral Elements in Potted Poa crymophila under Drought and Water Stress

[Objective] This study was conducted to explain the mechanism of the accumulation characteristics of mineral elements in alpine grassland plants. [Method] Cultivated alpine grassland plant, Poa crymophila, was treated with drought and wa- ter stress, and then the samples were collected and analyzed. [Result] Compared with the control group, under drought and water stress, multiple mineral elements tended to accumulate and increase, and there were significant differences in the contents of Cu, Mn, Ni and P （P〈0.05）. [Conclusion] Under drought and water stress, mineral elements in potted Poa crymophila tended to accumulate and in- crease, which is the adaption and response of Poa crymophila to drought and water stress, as well as the re-verification of the starvation effect hypothesis of mineral effects. The starvation effect of mineral elements is one of the endogenic forces for the accumulation and differentiation of mineral elements in grassland plants.

Effect of Lead Stress on Growth Characteristics and Physiological Indexes of Alternanthera philoxeroides

[Objective] The paper aimed to discuss effects of different concentrations of lead stress on Alternanthera philoxeroides growth and physiological indices,to explore phytoremediation methods for removal of lead pollution. [Method] A. philoxeroides in water culture was treated with different concentration of lead,and then,its external injury was observed,its growth and physiological indexes were measured. [Result] A. philoxeroides biomass and chlorophyll content decreased; conductivity and malonaldehyde （MDA ） content were increased; the SOD,POD and CAT activities showed a trend of first increase and then decrease with increase in concentration of lead stress. [Conclusion] With increase in lead concentration,the cell membrane permeability increased and MDA had a higher accumulation,antioxidant enzymes activity decreased,the normal oxidative metabolism of A. philoxeroides was severely affected,leading it to wilt.

Salt Stress Effect on the Growth and Physiological Characteristics of Three New Varieties of Lagerstroemia indica

The effects of different concentrations of NaCI （0, 0.10%, 0.25%, 0.40%, 0.55%, 0.70%） on the growth and physiological characteristics of three new varieties of Lagerstroemia indica were studied by pot experiment in the plastic greenhouses. The results showed that under different NaCI concentrations, the relative height in- crement and the relative diameter increment of L. indica were restrained obviously; the contents of chlorophyll a, chlorophyll b, carotenoid and GSH decreased with in- crease of NaCI concentration; and the content of MDA increased with increase of NaCI concentration. Through the determination and comparison of physiological in- dexes, and analysis of correlativity, NaCI tolerance of the three new L. indica vari- eties ranked as L. indica ＇Pink Velour＇〉L. indica ＇Dynamite＇〉L. indica ＇Red Rock- et＇. This is consistent with the results of the morphological characteristics after Na- CI stress.

Numerical analysis on mechanical difference of sandstone under in-situ stress,pore pressure preserved environment at depth

Deep in-situ rock mechanics considers the influence of the in-situ environment on mechanical properties,differentiating it from traditional rock mechanics.To investigate the effect of in-situ stress,pore pressure preserved environment on the mechanical difference of sandstone,four tests are numerically modeled by COMSOL:conventional triaxial test,conventional pore pressure test,in-situ stress restoration and reconstruction test,and in-situ pore pressure-preserved test(not yet realized in the laboratory).The in-situ stress restoration parameter is introduced to characterize the recovery effect of in-situ stress on elastic modulus and heterogeneous distribution of sandstone at different depths.A random function and nonuniform pore pressure coefficient are employed to describe the non-uniform distribution of pore pressure in the in-situ environment.Numerical results are compared with existing experimental data to validate the models and calibrate the numerical parameters.By extracting mechanical parameters from numerical cores,the stress-strain curves of the four tests under different depths,in-situ stress and pore pressure are compared.The influence of non-uniform pore pressure coefficient and depth on the peak strength of sandstone is analyzed.The results show a strong linear relationship between the in-situ stress restoration parameter and depth,effectively characterizing the enhanced effect of stress restoration and reconstruction methods on the elastic modulus of conventional cores at different depths.The in-situ pore pressurepreserved test exhibits lower peak stress and peak strain compared to the other three tests,and sandstone subjected to non-uniform pore pressure is more prone to plastic damage and failure.Moreover,the influence of non-uniform pore pressure on peak strength gradually diminished with increasing depth.