Effects Of Airflow Temperature And Airflow Velocity On Overgrown Cucumber Seedlings

The quality of cucumber seedlings is an important factor restricting yield.Overgrowth often occurs in the process of seedling raising.How to inhibit the overgrowth of seedlings safely and without residue is a technical difficulty.In this paper,’Jinyou No.1’cucumber seedlings were used as experimental materials,and a split-plot design was used.Two airflow temperatures of25±5°C and 35±5°C were used as the main factors,and four airflow velocities of 1,3,6 and 9m/s were used as secondary factors.The seedlings were subjected to airflow disturbance test,and the seedlings without airflow disturbance were used as comparison.Digital image correlation technology was used to measure the displacement of seedling stems during airflow disturbance and the growth parameters of seedlings during growth.A linear regression model was established to explore the effects of airflow disturbance on the morphological characteristics,physiological and biochemical,anatomical structure,and mechanical properties of cucumber seedlings.The main contents and conclusions of this study are as follows:（1）Using digital image processing technology,the displacement of seedling stem in airflow disturbance was measured,and the function model of airflow velocity and seedling stem displacement was established.The growth parameters of seedlings were obtained,and then the multiple linear regression models of airflow temperature,airflow velocity and seedling growth parameters were established respectively.The results showed that higher airflow velocity increased the stability of seedlings,and higher airflow temperature was not conducive to the stability of seedlings.（2）The effects of airflow disturbance on seedling growth and photosynthetic characteristics were investigated.The results showed that the increase of airflow velocity significantly reduced the plant height,leaf length,leaf width,leaf area,leaf number,net photosynthetic rate（P_n）,stomatal conductance（g_s）,maximum photochemical efficiency（F_v/F_m）and photochemical quenching coefficient（q P）of seedlings,and increased stem diameter,underground dry and fresh weight,strong seedling index,leaf water potential value,SPAD value,intercellular CO₂ concentration（C_i）,transpiration rate（T_r）,water use efficiency（WUE）,chlorophyll fluorescence characteristic parameters Initial fluorescence（F_o）,Potential activity（F_v/F_o）and non-photochemical quenching coefficient（NPQ）.There was no significant difference in dry and fresh weight of the whole plant.The response results of seedlings after the increase of airflow temperature were opposite to the above conclusions.The treatment of25±5°C airflow temperature and 6 m/s airflow speed had the best effect on inhibiting the overgrowth of cucumber seedlings.（3）The effect of airflow disturbance on seedling microstructure was investigated.In order to maintain their own balance,cucumber seedlings offset the pressure of air flow on seedlings by inhibiting the growth of aboveground parts and increasing the growth rate of underground parts.The phenotypic structure of seedlings changed,the aboveground stems became shorter and thicker,the leaf area decreased,the underground roots became thicker,and the internal structure of seedlings changed accordingly.The results showed that with the increase of airflow velocity,there was no significant change in the lower epidermis of seedling leaves,but the thickness of leaves,upper epidermis,sponge tissue and palisade tissue increased.The thickness of stem epidermis and cortex,the diameter of vessel,vascular bundle and pith increased.The diameter and epidermal thickness of root,the diameter of vessel,vascular bundle and pith in root also increased,but the thickness of cortex decreased.Under the same airflow velocity,with the increase of airflow temperature,the thickness of leaves decreases,the internal microstructure decreases,the internodes were slender,the internal structure of stems decreases,the root system was underdeveloped,and the structure of each part of the root was small.The quality of cucumber seedlings was the best under the treatment of 25±5°C airflow temperature and 6 m/s airflow velocity.（4）The effects of airflow disturbance on biochemical components and mechanical properties of seedling stems were investigated.The results showed that the content of biochemical components in stems increased with the increase of airflow velocity.The increase of biochemical component content enhanced the hardness and toughness of stems,and the mechanical properties of stems increased accordingly.With the increase of airflow temperature,it decreased,and the airflow disturbance significantly affected the biochemical components of the stem（P（27）0.05）.The correlation degree between the biochemical components of the stem and the mechanical properties was different.The correlation degree between the elastic modulus and the biochemical components under the airflow temperature treatment was about 0.72,and the correlation degree between the biochemical components and the mechanical properties under the airflow velocity treatment was greater than 0.60,indicating that the biochemical components of the seedling stem under the airflow temperature and airflow velocity treatment had an effect on the mechanical properties of the stem.Under the treatment of 25±5°C airflow temperature and6 m/s airflow velocity,the stem hardness and toughness of cucumber seedlings were larger,and they had the ability to resist the disturbance of larger airflow velocity.