Effects of EDTA and plant growth-promoting rhizobacteria on plant growth and heavy metal uptake of hyperaccumulator Sedum alfredii Hance

Phytoremediation is a cost-effective and environment-friendly strategy for decontaminating heavy-metal-contaminated soil.However, the practical use of phytoremediation is constrained by the low biomass of plants and low bioavailability of heavy metals in soil.A pot experiment was conducted to investigate the effects of the metal chelator ethylenediaminetetraacetic acid(EDTA) and EDTA in combination with plant growth-promoting rhizobacteria(Burkholderia sp.D54 or Burkholderia sp.D416) on the growth and metal uptake of the hyperaccumulator Sedum alfredii Hance.According to the results, EDTA application decreased shoot and root biomass by 50% and 43%, respectively.The soil respiration and Cd,Pb, Zn uptake were depressed, while the photosynthetic rate, glutathione and phytochelatin(PC) contents were increased by EDTA application.Interestingly, Burkholderia sp.D54 and Burkholderia sp.D416 inoculation significantly relieved the inhibitory effects of EDTA on plant growth and soil respiration.Compared with the control, EDTA + D416 treatment increased the Cd concentration in shoots and decreased the Pb concentration in shoots and roots, but did not change the Zn concentration in S.alfredii plants.Furthermore,EDTA, EDTA + D54 and EDTA + D416 application increased the cysteine and PC contents in S.alfredii(p < 0.05);among all tested PCs, the most abundant species was PC2, and compared with the control, the PC2 content was increased by 371.0%, 1158.6% and 815.6%,respectively.These results will provide some insights into the practical use of EDTA and PGPR in the phytoremediation of heavy-metal-contaminated soil by S.alfredii.

Design of Bionic Saw Blade for Corn Stalk Cutting

The serrated incisors of grasshopper [Chondracris rosea rosea （De Geer）] possess an advantageous capacity for cutting plant fiber. Inspired by this special geometrical structure of incisors, bionic saw blade was designed and manufactured. MATLAB software digital image processing technology was used to obtain outer margin profile from stereomicroscope pho- tograph of the serrated incisors. The outer margin profile of incisors was fitted and expressed by six-order polynomial function. To compare the cutting capacity of bionic and traditional saw blades, the internodes of dry corn stalks were cut perpendicularly. Cutting force-deformation characteristics were obtained by universal testing machine. The results of cutting experiments show that the maximum cutting force of bionic saw blade was 128.26 N, which is 15.87% lower than 152.45 N of traditional saw blade; the average cutting force of bionic saw blade was 51.56 N, which is 28.17% less than 71.78 N of traditional saw blade. Meanwhile, the cutting energy consumption of bionic saw blade was 8.95 J, which is 12.85% less than 10.27 J of traditional saw blade. Overall, the bionic saw blade can lead to noticeable reduction of the cutting force and energy. These results will be helpful for designing cutting elements of corn stalk harvesting, biomass size reduction and other processing machinery.

Hydrogen Sulfide Positively Regulates Abscisic Acid Signaling through Persulf idation of SnRK2.6 in Guard Cells

The phytohormone abscisic acid(ABA)plays pivotal roles in triggering stomatal closure and facilitating adaptation of plants to drought stress.Hydrogen sulfide(H2S),a small signaling gas molecule,is involved in ABA-dependent stomatal closure.However,how H2S regulates ABA signaling remains largely unclear.Here,we show that ABA induces the production of H2S catalyzed by L-CYSTEINE DESULFHYDRASE1(DES1)in guard cells,and H2S in turn positively regulates ABA signaling through persulfidation of Open Stomata 1(OST1)/SNF1-RELATED PROTEIN KINASE2.6(SnRK2.6).Two cysteine(Cys)sites,Cys131 and Cys137,which are exposed on the surface of SnRK2.6 and close to the activation loop,were identified to be persulfidated,which promotes the activity of SnRK2.6 and its interaction with ABA response element-binding factor 2(ABF2),a transcription factor acting downstream of ABA signaling.When Cys131,Cys137,or both residues in SnRK2.6 were substituted with serine(S),H2S_induced SnRK2_6 activity and SnRK2.6-ABF2 interaction were partially(SnRK2.6c131s and SnRK2.6c137S)or completely(SnRK2.6c131sc137S)compromised.Introduction of SnRK2.6c131s,SnRK2.6c137S,or SnRK2.6c131sc137S into the ost1-3 mutant could not rescue the mutant phenotype:less sensitivity to ABA-and H2S-induced stomatal closure and Ca2+influx as well as increased water loss and decreased drought tolerance.Taken together,our study reveals a novel post-translational regulatory mechanism of ABA signaling whereby H2S persulfidates SnRK2.6 to promote ABA signaling and ABA-induced stomatal closure.

Design and key parameter optimization of an agitated soybean seed metering device with horizontal seed filling

Since the low seed filling speed of mechanical seed metering devices reduces the low qualified rate of seed spacing during high-speed practices,it is significant to design agitated seed metering devices with horizontal seed filling that are suitable for high-speed practices.The combination of horizontal seed filling and agitated seed filling can accelerate the seed filling of mechanical seed metering devices,and improve the qualified rate of seed spacing during high-speed practices.In this study,theoretical analysis,discrete element method-based simulation and indoor bench test verification were conducted to investigate how key parameters of the agitated seed metering device with horizontal seed filling(angles,installation position and number of agitating plates,diameters of convex spoons)would affect the characteristics of soybean seed movement,seed number and seeding performance(qualified index,multiple index,missing seeding index)under different working speeds.Computer-based simulation,test design and regression analysis were combined to analyze the population moving rules and optimize the design parameters of seed metering devices.Based on the test scheme as designed,simulations were conducted on Fluent EDEM,and the optimal angle of the agitating plates was determined by analyzing the population migrating rules.Regression equations were established through the regression of test results,and used to find out the optimal design parameters(diameter of convex spoon,positions and number of agitating plates)of seed metering devices.Then the optimal parameter combination among different working conditions was determined that the angle,position and number of agitating plates were 30°,24.4 mm,and 13,respectively,and the diameter of convex spoon was 11.0 mm.With the optimal parameter combination and at the seeding speed of 12 km/h,the qualified index,multiple index and missing seeding index were 93.1%,2.1%and 4.8%,respectively.Under high-speed practices,the new seed metering device was not significantly different from the pneumatic seed metering device,but significantly outperformed the mechanical seed metering device.

Design and Tests of Biomimetic Blades for Soil-rototilling and Stubble-breaking

Biomimetic blades for soil-rototilling and stubble-breaking were designed learning from the geometrical structure of the tips of toes of mole rat （Scaptochirus moschatus）. The orientation, the number and the central angle of the biomimetic structure were taken as the testing factors. The optimal structure of the biomimetic blade was determined through the tests of soil-rototilling and stubble-breaking operation in an indoor soil bin. The optimal combination of the biomimetic structure pa- rameters is that three arc concave teeth are equally arranged on the front cutting edge with a central angle of 60°. The results of comparative tests between the optimal biomimetic blade and a conventional universal blade show the torque acting on the biomimetic blade is lower during soil-rototilling and stubble-breaking operations. The results of field tests show that the working quality of the biomimetic blades meets the requirements of the national standard of China. Tests of soil-rototilling show that, when the orientation of the biomimetic structure was at low and middle levels, the torque ofbiomimetic blades decreased from 34.17 N·m to 31.03 N·m. The torque also decreased with the increase of the number of biomimetic structure. The average torques were 34.57 N·m, 33.44 N·m and 31.37 N·m, respectively. The maximum different value between two levels of central angle was 0.41 N·m. Tests in field indicate that for soil-rototilling operation, the tillage depth is deeper than 80 mm, the soil-crushing rate （length of soil block less than 40 mm） is over 50 %, and the vegetation coverage rate is over 55 %. For stubble-breaking operation, the stubble-breaking depth is deeper than 70 ram, the stubble-breaking rate （length of stubble less than 40 mm） is over 60%, and the stubble coverage rate is over 80%, which can meet the stubble-breaking requirement of corn.

Contact parameter analysis and calibration in discrete element simulation of rice straw

Discrete element method was used to study and analyze the interaction between rice straws and between rice straw and agricultural machinery parts,thereby providing a scientific basis for post-harvest paddy field processing.Calibrations of rice straw-rice straw,rice straw-agricultural machinery part contact parameters(collision recovery coefficient,static friction coefficient and rolling friction coefficient)constitute an important prerequisite for the discrete element research process.In this study,the collision recovery coefficients of rice straw-steel and rice straw-rice straw were 0.230 and 0.357,respectively,which were calibrated by the collision method.The static friction coefficient and rolling friction coefficient of rice straw-steel were 0.363 and 0.208 respectively,which were calibrated by the inclined plate method and the slope method.The static friction coefficient and rolling friction coefficient of rice straw-rice straw were 0.44 and 0.07,respectively,which were calibrated by the split cylinder method.The paired t-test showed insignificant differences between calibration parameter simulation results and the physical test values(p>0.05).Taking the angle of repose that reflecting rice straw flow and friction characteristics as the evaluation index,the verification tests of the above calibration values indicated that the simulated angle of repose has no significant difference from the physical test value(p>0.05).The side plate lifting test on rice straw of different lengths showed no significant difference between the simulated angle of repose and the physical test value(p>0.05).This study can provide a basis for contact parameters choice in discrete element simulation analysis with rice straw-rice straw and rice straw-agricultural machinery parts as the research object.The calibration method can provide a reference for the contact parameter calibration of other crop straws.

Design and test of bionic wide-ridge soybean tilling-sowing machine

The insufficient accumulated temperature of the plow layer during spring tillage in Northeast China severely restricts soybean root growth and whole-plant development.High regional soil viscosity further complicates tilling-sowing.In order to seek a solution to these problems,field comparative tests were conducted to investigate the effects of shallow-loosening(SL)and reshaping ridge(RR)on soil temperature and soybean root growth.Compared with conventional tillage(CT),SL and RR significantly increased the soil temperatures within 0-25 cm(p<0.05)and 0-15 cm(p<0.05),respectively.In particular,higher soil temperature within 15-25 cm was established after SL than after RR(p<0.05).Additionally,SL promoted substantially more vigorous soybean development(seedling height)than RR(p<0.05),which in turn led to a significant outperformance over CT(p<0.05).Further,bionics,reverse engineering,and curve fitting were combined to design a hare claw toe bionic shallow-loosening shovel and a pangolin scale bionic ridging shovel with anti-drag functions.Field verification tests confirmed that these two bionic tillage devices outperformed the conventional tillage device in reducing tractive drag by 13%-19%.Based on the results of these tests,a 2BGD-6(110)bionic wide-ridge soybean tilling-sowing machine was designed,which was capable of shallow-loosening,reshaping ridge and sowing.The new machine significantly reduced the tractive drag,efficiently loosened the soil,increased soil temperature,and accelerated soybean root growth.This study can provide a theoretical and practical reference for soybean production in Northeast China.

Effects of seed furrow liquid spraying device on sowing quality and seedling growth of maize

The two cultivation patterns,no-tillage and ridge cultivation,are widely used in maize planting in Northeast China.However,the seed bounce in the falling process and drought seriously at the seedling stage often occur to affect the sowing quality,mean emergence time,percentage of emergence,root biomass,aboveground biomass and root shoot ratio of maize,and eventually reduces the grain yield.To solve the problems,a seed furrow liquid spraying device was designed and thereby the effects of spraying water volumes[0 L/m(V0),0.6 L/m(V1),1.2 L/m(V2)and 1.8 L/m(V3)]and nozzle types[conical nozzle(N1)and sectorial nozzle(N2)]on the sowing quality and seedling growth of maize were studied.The water volume and nozzle type had significant effects on the sowing quality(QR,CV,LD),not seedling growth(MET,PE,RB,AB,RSR)(p<0.05).Spraying water into seed furrow further humidified the soils around the maize seeds,effectively suppressing the bounce and rolling of seed and significantly promoting the growth and development of seeds.The sowing quality in the N2 treatment was significantly better than that in the N1 treatment.The qualified rate of seed spacing was increased with the increase of the water volume(V3>V2>V1>V0).However,the variability coefficient of seed spacing and lateral deviation of seed position were the opposite.The larger spraying water volume led to shorter mean emergence time(V0>V1>V2>V3)and higher percentage of emergence(V3>V2>V1>V0).The root biomass and aboveground biomass increased significantly with the enlargement of spraying water volume.Under different water volumes,the root shoot ratio differed significantly.The plants in the V1,V2 and V3 treatments had lower root shoot ratios compared with the V0 treatment.The increase of spraying water volume significantly reduced the root shoot ratio.The seed furrow liquid spraying device provides a reference for improving sowing quality and promoting seedling growth.

Design of bionic mole forelimb intelligent row cleaners

In Northeast China under no-till conditions the amount of maize stubble of the previous year's crop severely limit the quality of sowing operations by unstable operating depth of normal planter row cleaners.Thus,in this study,bionic mole forelimb intelligent row cleaners comprising of a cleaning device and a depth intelligent control system were designed.Via theoretical analysis,computer-based simulation,and test optimized design,the mechanism of bionic cleaners that possessed the forelimb motion morphology and the front claw toe structural morphology of moles was studied,the effects of structural parameters of bionic cleaners on the cleaning quality were clarified.Based on a pressure sensor,a depth intelligent control system was designed,which enhanced the depth stability of the cleaning devices.The types of bionic cleaners were identified by simulation on EDEM software.Then regression equations between different parameters and operation evaluation indices were established,and the optimal parameter combination was identified on Design-Expert software with a rotation radius of 150 mm and a motion deflection angle of 15.8°,at which the cleaning rate was 91.3%.Field tests under the optimal parameter combination showed that bionic cleaners outperformed normal planar cleaners,and the depth intelligent control system could efficiently improve the performance of the row cleaners.The straw cleaning rate of the bionic mole forelimb intelligent row cleaners under total straw mulching fields was 90.9%,which was 21.3%higher than that of normal cleaners,and the ground surfaces after operation satisfied the agricultural requirements of maize no-tillage sowing.

Persulfidation-induced Structural Change of SnRK2.6 Establishes Intramolecular Interaction between Phosphorylation and Persulfidation.

Post-translational modifications (PTMs) regulate the activity of SNF1-RELATED PROTEIN KINASE2.6 (SnRK2.6), including phosphorylation and persulfidation. Here, we report how persulfidations and phosphorylations of SnRK2.6 influence each other. The persulfidation of cysteine C131/C137 altered SnRK2.6 structure, resulted in serine S175 residue more close to aspartic acid D140, who belong to ATP-γ-phosphate proton acceptor may effectively improve the transfer efficiency of phosphate groups to S175, thus persulfidation enhanced the phosphorylation level of S175. S267 and C137 were predicted to lie in close proximity on the protein surface. The phosphorylation status of S267 positively regulated the persulfidation level at C137. Tests of responses of dephosphorylated and depersulfidated mutants to ABA and the H2S-donor NaHS during stomatal closure, water loss, gas-exchange, Ca2+ influx and drought stress revealed that S175/S267-associated phosphorylation and C131/137-associated persulfidation are essential for SnRK2.6 function in vivo. Taken together, we propose a mechanistic model in which certain phosphorylations facilitate persulfidation, which changes SnRK2.6 structure and increases its activity.

Design and experiment evaluation of furrow compaction device with opener for maize

The double-disc opener of maize precision seeder is an important component which affects sowing quality.After the double-disc opening operation,there will be many unfavorable phenomena such as a W-shaped bottom with pointed ridge,returning soil to furrow,loose and rough furrow sidewall,and large soil blocks in the furrow bottom.These phenomena often cause the problems of poor sowing depth consistency and seed spacing uniformity.In order to solve the above problems,the furrow compaction device with opener was designed to compact and reshape the original seed furrow,eventually forming a smooth and flat V-shaped seed furrow.Through theoretical calculations and kinematic analysis,the main structural parameters of the device were limited to a small range:the spring stiffness coefficient k=0.96-4.19 N/mm and the angle of the furrow compaction wheelφ=30°-60°.In the soil-bin experiment,the rotary combination design was adopted to study the effects of the parameters of the furrow compaction device with opener on the seeds location variation.The regression model of two factors with respect to each indicator was established in the Design-Expert software,revealing the effects of two factors on the indicators.Finally,the optimal structural parameters obtained were:the spring stiffness coefficient k=4.0 N/mm,and the angle of furrow compaction wheelφ=42.4°.The field test was carried out to verify the effect of the furrow compaction device with opener on the performance of precision seeder.The results showed that the average values of the sowing depth variable coefficient,the lateral deviation and the seed spacing variable coefficient respectively were 5.77%,5.1 mm and 9.54%in the treatment of the furrow compaction device with opener.All indicators were superior to the traditional double-disc opener.This research can provide references for the design of furrow opening device and maize precision seeder.

Design and experiment of a subsoiling variable rate fertilization machine

In order to improve soil fertility and fertilizer utilization,a subsoiling variable rate fertilization machine based on conservation tillage and precision agriculture was designed and tested.The relationship between suspension parameters and penetrating distance was analyzed,and a matching model between fertilizing quantity and penetrating distance was established.The variable rate fertilization control machine was developed based on an Advantech PCM-9363 industrial control mainboard.The machine operates under two patterns:DGPS-based positioning and straight-line path positioning based on a planar coordinate system.This machine can perform on-demand fertilization according to the spatial differences in soil nutrients and the prescription maps pre-set before the operation.Field experiments showed the machine has a subsoiling stability of 92.5%,a soil breaking rate of 61.1%,a maximum positioning relative error of 2.68%and a maximum variable rate fertilization error of 3.89%.The subsoiling performance and variable rate fertilization indices of this machine satisfy the requirements of GB/T24675.2-2009.The tested indices meet the national and industrial standards and satisfy the design requirements.The findings of the research can be used as the structural design of the subsoiling variable rate fertilization machine.

Optimized design and experiment of spiral-type intra-row weeding actuator for maize(Zea mays L.)planting

Mechanical weeding not only avoids crop herbicide residue but also protects the ecological environment.Compared with mechanical inter-row weeding,mechanical intra-row weeding needs to avoid crop plants,which is conducive to causing a higher rate of seedling damage.In order to realize maize(Zea mays L.)intra-row weeding,a maize intra-row weeding mechanism was designed in this study.The mechanism can detect maize seedlings by infrared beam tube,then a sliding-cutting bevel tool moves spirally amid maize seedlings,so as to eradicate intra-row weeds.A field experiment was conducted under the following experimental conditions:the bevel tool rotation speed was 800-1400 r/min,the mechanism forward speed was 4-7 km/h,and the bevel tool depth was 2-14 cm,the experimental results illustrated that the mechanism’s average weeding rate and seedling damage rate were 95.8%and 0.6%,respectively.The variance analysis showed that the primary and secondary factors that affecting the weeding rate and seedling damage rate were the same,which were bevel tool rotation speed,mechanism forward speed,bevel tool depth in soil in a descending order according to the significances.The result of the field experiment may provide a reference for intra-row weeding device design.

Growing-season soil microbial respiration response to long-term no tillage and spring ridge tillage

No tillage(NT)and spring ridge tillage(SRT)are two common applications of conservation tillage.Although conservation tillage is known to exert major control over soil microbial respiration(SMR),the growing-season SMR response to these two applications remains elusive.In order to better understand the influence of conservation tillage practices,this experiment was conducted in an experimental field using NT and SRT for 17 years.In situ measurements of SMR,soil temperature and soil water content(SWC)were performed.Soil samples were collected to analyze soil porosity,soil microbial biomass(SMB)and soil enzymatic activities.Results show that the two conservation tillage systems had a significant difference(p<0.05)in terms of SMR;the SMR of NT was 14.7 mg∙C/m^(2)∙h higher than that of SRT.In terms of soil temperature and soil enzymatic activities,the two treatments were not significantly different(p>0.05).Despite SRT increasing the proportion of micro-porosities and meso-porosities,the soil macro-porosities for NT were 7.37%higher than that of SRT,which resulted in higher bacteria and fungi in NT.Owing to SRT damaged the hypha,which had disadvantage in soil microbe protection.Inversely,less soil disturbance was a unique advantage in NT,which was in favor of improving soil macro-pores and SWC.Redundancy analyses(RDA)showed SMR was positively correlated with soil macro-pores,SMB and SWC.Furthermore,the Pearson correlation test indicated that SMB and soil enzymatic activities did not have a significant correlation(p>0.05).This study results suggest that SRT is more conducive to carbon sequestration compared with NT in cropland.

Impacts of increasing maize stalk retention amount on soil respiration and temperature sensitivity

Conservation tillage with maize stalk retention is an effective method to replenish soil nutrients.Nutrient availability plays a major role in the control of soil respiration(SR).However,it is not known how different degrees of maize stalk retention control SR and its temperature sensitivity(Q_(10)).To investigate the effect of maize stalk retention amount on SR and Q_(10),four maize(Zea mays L.)stalk retention treatments,including(i)control treatment(CT)without maize stalk retention,(ii)standing maize stalk retention(SCR),(iii)partial maize stalk retention with‘three-year cycle’(TYR)and(iv)chopped maize stalk retention(CCR)was set up.In order to investigate the differences in soil nutrient,soil organic carbon(SOC)quality and soil microbial biomass among four treatments,soil analysis with 6 replicates was conducted.The experimental results showed that SR rates were 1.07,0.88,0.59 and 0.37 g/kg of dry soil,and the average Q_(10)was 1.535,1.585,1.62 and 1.725 for CT,SCR,TYR and CCR,respectively.Increasing maize stalk retention led to the reduction of soil microbial abundance and labile carbon compositions.Pearson correlation analysis showed that soil microbial abundance had a positive correlation with SR,while labile carbon fraction had a negative correlation with Q_(10).In short,increasing the amount of maize stalk retention decreases SR while increasing Q_(10)in northeast China.This research could provide a reference value for balancing carbon sequestration and carbon decomposition in farming practice.