Biomechanical Response of the Root System in Tomato Seedlings under Wind Disturbance

Wind disturbance as a green method can effectively prevent the overgrowth of tomato seedlings,and its mechanism may be related to root system mechanics.This study characterized the biophysical mechanical properties of taproot and lateral roots of tomato seedlings at five seedling ages and seedling substrates with three different moisture content.The corresponding root system-substrate finite element(FE)model was then developed and validated.The study showed that seedling age significantly affected the biomechanical properties of the taproot and lateral roots of the seedlings and that moisture content significantly affected the biomechanical properties of the seedling substrate(p<0.05).The established FE model was sensitive to wind speed,substrate moisture content,strong seedling index,and seedling age and was robust.The multiple linear regression equations obtained could predict the maximum stress and strain of the root system of tomato seedlings in the wind field.The strong seedling index had the greatest impact on the biomechanical response of the seedling root system during wind disturbance,followed by wind speed.In contrast,seedling age had no significant effect on the biomechanical response of the root system during wind disturbance.In the simulation,no mechanical damage was observed on the tissue of the seedling root system,but there were some strain behaviors.Based on the plant stress resistance,wind disturbance may affect the growth and development of the root system in the later growth stage.In this study,finite element and statistical analysis methods were combined to provide an effective approach for indepth analysis of the biomechanical mechanisms of wind disturbances that inhibit tomato seedlings’growth from the root system’s perspective.

Effect of CO_2 Enrichment on the Growth and Nutrient Uptake of Tomato Seedlings

Exposing tomato seedlings to elevated CO2 concentrations may have potentially profound impacts on the tomato yield and quality. A growth chamber experiment was designed to estimate how different nutrient concentrations influenced the effect of elevated CO2 on the growth and nutrient uptake of tomato seedlings. Tomato (Hezuo 906) was grown in pots placed in controlled growth chambers and was subjected to ambient or elevated CO2 (360 or 720μL L-1) and four nutrient solutions of different strengths (1/2-, 1/4-, 1/8-, and 1/16-strength Japan Yamazaki nutrient solutions) in a completely randomized design. The results indicated that some agricultural characteristics of the tomato seedlings such as the plant height, stem thickness, total dry and fresh weights of the leaves, stems and roots, the G value (G value = total plant dry weight/seedling age), and the seedling vigor index (seedling vigor index = stem thickness/(plant height×total plant dry weight) increased with the elevated CO2, and the increases were strongly dependent on the nutrient solution concentrations, being greater with higher nutrient solution concentrations. The elevated CO2 did not alter the ratio of root to shoot. The total N, P, K, and C absorbed from all the solutions except P in the 1/8- and 1/16-strength nutrient solutions increased in the elevated CO2 treatment. These results demonstrate that the nutrient demands of the tomato seedlings increased at elevated CO2 concentrations.

Exogenous Nitric Oxide Involved in Subcellular Distribution and Chemical Forms of Cu^(2+) Under Copper Stress in Tomato Seedlings

Nitric oxide（NO）,a bioactive signaling molecule,serves as an antioxidant and anti-stress agent under abiotic stress.A hydroponics experiment was conducted to investigate the effects of sodium nitroprusside（SNP）,a NO donor,on tomato seedlings exposed to 50 μmol L-1CuCl 2.The results show that copper is primarily stored in the soluble cell sap fraction in the roots,especially after treatment with Cu＋SNP treatment,which accounted for 66.2% of the total copper content.The copper concentration gradually decreased from the roots to the leaves.In the leaves,exogenous NO induces the storage of excess copper in the cell walls.Copper stress decreases the proportion of copper integrated with pectates and proteins,but exogenous NO remarkably reverses this trend.The alleviating effect of NO is blocked by hemoglobin.Thus,exogenous NO is likely involved in the regulation of the subcellular copper concentrations and its chemical forms under copper stress.Although exogenous NO inhibited the absorption and transport of excess copper to some extent,the copper accumulation in tomato seedlings significantly increased under copper stress.The use of exogenous NO to enhance copper tolerance in some plants is a promising method for copper remediation.

Effects of elevated CO_2 concentration on growth and water usage of tomato seedlings under different ammonium/nitrate ratios

Increasing atmospheric CO2 concentration is generally expected to enhance photosynthesis and growth of agricultural C3 vegetable crops, and therefore results in an increase in crop yield. However, little is known about the combined effect of elevated CO2 and N species on plant growth and development. Two growth-chamber experiments were conducted to determine the effects of NH4^＋/NO3^- ratio and elevated CO2 concentration on the physiological development and water use of tomato seedlings. Tomato was grown for 45 d in containers with nutrient solutions varying in NH4^＋/NO3^- ratios and CO2 concentrations in growth chambers. Results showed that plant height, stem thickness, total dry weight, dry weight of the leaves, stems and roots, G value （total plant dry weight/seedling days）, chlorophyll content, photosynthetic rate, leaf-level and whole plant-level water use efficiency and cumulative water consumption of tomato seedlings were increased with increasing proportion of NO3- in nutrient solutions in the elevated CO2 treatment. Plant biomass, plant height, stem thickness and photosynthetic rate were 67%, 22%, 24% and 55% higher at elevated CO2 concentration than at ambient CO2 concentration, depending on the values of NH4^＋/NO3^- ratio. These results indicated that elevating CO2 concentration did not mitigate the adverse effects of 100% NH4^＋-N （in nutrient solution） on the tomato seedlings. At both CO2 levels, NH4^＋/NO3^- ratios of nutrient solutions strongly influenced almost every measure of plant performance, and nitrate-fed plants attained a greater biomass production, as compared to ammonium-fed plants. These phenomena seem to be related to the coordinated regulation of photosynthetic rate and cumulative water consumption of tomato seedlings.

Promotive Effects of Alginate-Derived Oligosaccharides on the Inducing Drought Resistance of Tomato

In order to determine the role of alginate-derived oligosaccharides (ADO) in drought stress resistance of tomato (Ly-copersicon esculentum Miller) seedlings, the leaves were exposed to different concentrations of ADO (0.05%, 0.10%, 0.20%, 0.30% and 0.50%) after drought stress was simulated by exposing the roots to 0.6 molL-1 PEG-6000 solution for 6 h. Changes in biomass, electrolyte leakage and malondialdehyde (MDA), free proline, total soluble sugars (TSS) and abscisic acid (ABA), the enzyme activities of catalase (CAT), superoxide dismutase (SOD), peroxidase (POD) and phenylalanine ammonia-lyase (PAL) were measured to investigate the effects of ADO treatment. The results showed that the treatment with an ADO concentration of 0.20% exhibited the highest performance of drought stress resistance in the tomato seedlings by decreasing the electrolyte leakage and the concentration of MDA, increasing the contents of free proline, TSS and ABA, and increasing the activities of CAT, SOD, POD and PAL after treatment with ADO. It is suggested that changes in electrolyte leakage, MDA, osmotic solutes, ABA, anti-oxidative enzyme and PAL activities were responsible for the increased drought stress resistance in tomato seedlings. To our best knowledge, this is the first report of the effect of ADO treatment on enhancing the drought stress resistance of tomato seedlings.

Effects of Cu2+ and Cd2+ Stress on Growth and POD Activity of Tomato Seedling

The growth situation and peroxidase （POD） of seedlings of two tomato cultivars were investigated under the stress of different concentrations of Cu^2＋ and Cd^2＋ . The toxicity differences of Cu^2＋ and Cd^2＋ to tomato seedlings and the corresponding differences between two tomato cultivars were observed through the stress trial with the ahove two heavy metal ions, The resubs showed that low concentration of Cu^2＋ and Cd^2＋ could promote the growth and could enhance the POD activity of tomato seedlings, while high concentratiun Cu^2＋ and Cd^2＋ could inhibit seedling growth and POD activity of tomato seedlings. Cd^2＋ functioned more obviously than that of Cu^2＋ , two tomato cultivars also presented difference in response to heavy metal stress.

Studies on Tomato Seedling Quality Indices Under Simulated Shipping and Storage Conditions

Indices of the tomato seedling quality maintenance level after production before field planting were studied through simulated experiments, small—scale operation, indoor analyses and measurements, and field observation. The results showed that under simulated shipping and storage conditions, seedling quality change following different durations (days) of shipping and storage was correlated significantly or even very significantly with certain physiological and morphological indices. With various measured indices following different periods of shipping and storage treatment subjected to multinomial successive regressive correlation analysis, the principal factors influencing seedling quality maintenance level are identified to be chlorophyll content →dry short weight → leaf freshness index in order of their importance. Significance analysis with multinomial fitted equation indicated that correlations between any one of above three factors and the growth index after field planting reached very significant difference level.

Development of single row automatic transplanting device for potted vegetable seedlings

In China,low degree of automation seriously affects the working efficiency and quality in vegetable transplanting.As one of the most important vegetables in China even in the world,tomato was taken as the research object in this study.An automatic single-row transplanting device was designed,based on the statistical analysis of the physical and mechanical properties of tomato seedlings of a typical variety.Based on the technology of mechatronics,the device integrated the functions of transporting seedling tray,automatic seedling extraction and mechanical planting.The kinematics orthogonality solution combined with the dynamic sequence solution method was used to optimize and analyze the kinematic parameters of the automatic seeding mechanism,and the“sickle”trajectory was obtained.According to the position and movement requirement for taking and dropping seedling,the mechanical conditions and the working parameters of key execution parts were obtained by using analytic drawing method to analyze the mechanical condition of seedling collecting mechanism.The transplanting experiment was conducted at room temperature of 25°C,and the age and moisture content of the seedlings were 40 d and 55%,respectively.The results showed that the highest success rate was 92.59%,and the lowest rate of leakage was 23.13%,when the transplanting frequency was 60 plants/min.The lowest success rate was 77.78%,and the highest rate of leakage was 38.75%,when transplanting frequency was 120 plants/min.When the transplanting frequency is between 60-90 plants/min,the device can meet the requirement of high speed transplanting for potted vegetable seedling.

Development of a metering mechanism with serial robotic arm for handling paper pot seedlings in a vegetable transplanter

This paper describes the development of an automated metering mechanism for vegetable transplanter.It consisted of a 3-DOF serial robotic arm and an automatic feeding conveyor.The robotic arm was developed to pick and drop tomato seedlings raised in biodegradable paper pots.The volume of each pot was 50 cm^(3)(3.5 cmdiameter and 5.2 cmheight)with a maximumtotalweight of 47 g including potmix and seedling.Amatrix type feeding conveyorwas developed to convey the pot seedlings to a predefined positionwhere the robotic armcould pick up these seedlings one by one.LDR(Light Dependent Resistor)-LED(Light Emitting Diode)sensing unit was used to perform the intermittent movement of the conveyor.The developed system was evaluated under both laboratory and field conditions.The robotic arm was able to pick and drop 20 seedlings per minute and its effective cycle time per handling one seedling was varying from 2.5 to 3.1 s.Power consumption of the conveyor of the developed system and the robotic arm was 18 W and 16 W,respectively.The conveying,metering and overall efficiency of the developed metering mechanism under laboratory condition were 96.83%,95.91%and 92.86%,respectively as compared to 94.7%,93.28%and 88.33%,under field condition.The developed robotic armbasedmeteringmechanismwas simple,light inweight and effectively handled the pot seedlings without damage and would thus help in mechanizing transplanting of vegetable seedlings.