Effect Of Low Root Zone Temperature On Growth And Rhizosphere Soil Environment Of Cucumber Grafted Seedlings

One of the bottlenecks of overwintering production of facility cucumber in northern alpine region is low ground temperature.The lowe root zone temperature directly affects the physiological function of the root system,as well as the normal physiological activity of shoots.However,the importance of increasing the temperature in the interior of the facility has not been given sufficient attention.Systematic studies on soil environment,carbon and nitrogen metabolism in the root zone are not yet complete.In addition,the two rootstocks used in production of grafted seedlings also lack of research on the root zone of low temperature stress.Therefore,in this paper,the black root pumpkin grafted seedlings,white seed pumpkin grafted seedlings and self-rooted seedlings of Jinyou 35 were used as materials to set different root zone temperatures?suitable temperature?18-20???suboptimal temperature?13-15???low temperature?8-10???.The effects of root zone low temperature on the soil environment,growth and development,Oxidative system and osmotic adjustment substances,carbon metabolism and nitrogen metabolism.The effects of root zone low temperature on soil environment and cucumber physiological mechanisms and the response mechanism of different rootstocks grafted seedlings to root zone low temperature stress were clarified.In order to improve the selection of geothermal stocks to provide technical guidance and support.The results were as follows:?1?Under suboptimal temperature and low temperature Stress,Decrease of organic matter content and EC value in soil,while the content of total nitrogen,available nitrogen,available phosphorus,available potassium and pH increased.Meanwhile,the activities of urease,phosphatase,invertase and catalase in soil were also inhibited,the number of bacteria,fungi and actinomycetes in soil decreased with the decrease of root zone temperature.Under the same temperature treatment,the content of organic matter and EC value of"black seed"were higher than that of"white seed"and"self root"in the soil,and the content of total nitrogen,available nitrogen,available phosphorus and available potassium were lower than"white root"and"self root",while the enzyme activities and soil microorganisms of the"black seed"are also higher than the"white seed"and"self root".The above studies showed that the soil environment of cucumber seedlings was changed by the low temperature of root region,in which the soil environment of"black seed"was small,the activity of soil enzyme was high,and the number of soil microbes was more.?2?Under suboptimal temperature and low temperature Stress,the growth and absorption of root system of cucumber seedlings were severely inhibited,which was manifested by the inhibition of root length,root surface area,root volume,root tip number and root fork number.In addition,the study of isotope missing technology showed that the lower root zone temperature also inhibited the uptake and utilization of nitrogen in cucumber seedlings,the absorption of ¹⁵N in Cucumber stems and leaves was reduced,the absorption of ¹⁵N in cucumber root system was promoted.Especially when the low temperature of root zone was 8-10?,the utilization rate of ¹⁵N was in turn"black seed">"white seed">"self root".the root morphology index of the"Black seed"was higher than"white seed"and"self root","self root"was the lowest.?3?Under suboptimal temperature and low temperature Stress,the activity of SOD and POD decreased in the root of cucumber,the accumulation of active oxygen,the aggravation of membrane oxidation,the increase of malondialdehyde content,the destruction of the whole structure of the plasma membrane,the increase of the permeability of electrolyte.At the same time,it also significantly increased the content of osmoregulation substances such as soluble protein and proline and so on,which is beneficial to improve the chilling resistance of plants.the activity of SOD and POD and the content of soluble protein and proline in the root of"black seed"were higher than that of"white seed"and"self root".The content of MDA and the permeability of electrolyte was lower than"white seed"and"self root",so the anti low temperature stress of"black seed"was stronger than"white seed"and"self root".?4?Under suboptimal temperature and low temperature Stress,the growth and biomass accumulation of cucumbers and the photosynthetic capacity of cucumber leaves were inhibited in varying degrees.The root zone low temperature inhibited plant height,stem diameter and leaf area,dry weight and dry weight of the whole plant,and increased dry weight and root crown ratio in the ground.At the same time,the SPAD value of cucumber leaves decreased,and the net photosynthesis rate and transpiration rate,intercellular CO2 concentration and stomatal conductance decreased with the decrease of root zone temperature,the SPAD value and the photosynthetic parameters of"black seed"were higher than that of"white seed"and"self root".At the same time,the biomass accumulation and the above ground morphological indexes of the"black seed"were higher than that of"white seed"and"self root",and the SPAD value of"self root",photosynthetic parameters,above ground morphology and dry matter content were the minimum,the root and crown ratio is the highest.?5?Under suboptimal temperature and low temperature Stress,the activity of key enzymes and content of product in carbon metabolism of cucumber seedling leaves were determined.The results showed that the activity of Rubisco,sucrose phosphate synthetase?SPS?and sucrose synthase?SS?in cucumber leaves decreased with the decrease of root temperature,and the content of starch,sucrose and fructose decreased,and the activity of Rubisco enzyme,sucrose phosphate synthase?SPS?and sucrose synthase?SS?in the leaves of"black seed"was higher than that of"white seed"and"self root",The content of starch,sucrose and fructose was also higher than that of"white seed"and"self root".Thus,it can be seen that the low temperature of root zone inhibited the activity of enzymes needed for carbon metabolism of cucumber seedlings,resulting the decrease in the synthesis of organic matter.Among them,"black seed"has strong stress resistance and high enzyme activity required for carbon metabolism,so the content of carbon metabolites in leaves is higher.?6?Under suboptimal temperature and low temperature Stress,the activities of key enzymes and main nitrogen contents in the leaves and roots of cucumber seedlings were determined.The results showed that the root zone low temperature inhibited the content of ammonium nitrogen and nitrate nitrogen in the leaves and roots of cucumber seedlings,as well as the activity of nitrate reductase?NR?,glutamine synthetase?GS?and glutamate synthase?GOGAT?,which the key enzymes in the nitrogen assimilation process.the activity of key enzymes and the content of ammonium nitrogen and nitrate nitrogen in the nitrogen assimilation process in the leaves and roots of"black seed"were higher than that of"white seed"and"self root".It was proved that the root zone low temperature inhibited the assimilation of nitrogen and the absorption of nitrogen in the cucumber seedlings,which provided the reduction of enzyme and protein in the carbon metabolism,and then influenced the growth of cucumber,the nitrogen metabolism level of"black seed"was the highest,which was beneficial to the morphogenesis of the plant body and other metabolic activities.