Relationship Between Response Strategy To Phosphorus Deficiency And Ethylene Emission From Roots Of Cunninghamia Lanceolata

Phosphorus is a nutrient necessary for plants to maintain their own growth and development.Once the plants are in the state of phosphorus deficiency,many kinds of metabolism in the body will be hindered.However,the high fixed rate of phosphorus in soil and the slow diffusion rate make most of the soil Phosphorus is difficult to be directly absorbed and utilized by plants.Cunninghamia lanceolata(Lamb.)Hook.is a unique fast-growing tree species in southern China,with high yield,good material,and easy breeding.It has been widely planted in 17 provinces and regions in China.However,for a long time the way of multi-generation cultivating of Chinese fir has exacerbated the predicament of limited growth of soil available phosphorus.Based on the improvement of phosphorus utilization efficiency of Chinese fir,the research team of the advisor group has screened out the efficient utilization of phosphorus in Chinese fir,and preliminary studies found that these genotypes responded to low-phosphorus stress through a series of strategies such as reducing the photosynthetic rate of leaves,changing the morphology of roots,increasing organic acid secretion in the roots,and dissolving root tissue in the cortex.Changes in these response indicators are all conducive to enhance the ability of root to find phosphorus,or to accelerate the body's phosphorus cycle to resist the adversity.However,early discovery of low phosphorus stress conditions also releases ethylene from Chinese fir roots.Although ethylene is involved in the regulation of plant life,it is closely related to plant resistance.However,the continuous release of ethylene will cause plants to consume large amounts of energy.This is inconsistent with the strategy of common plants in nature to cope with adversity.In view of this,we hypothesize that under low-phosphorus stress,Chinese fir will reduce its release to the outside world in order to save energy,and increase the accumulation within the root tissue to increase its sensitivity,so as to induce the Chinese fir response to low-phosphorus stress.On the other hand,if external sources can provide sufficient inhibitors of ethylene or ethylene synthesis in Chinese fir,will the response strategies of Chinese fir to low-phosphorus stress be changed?In view of this,the experiment has completed the following test to verify the conjectures.The effect of low phosphorus stress on the release of ethylene from roots of Chinese fir seedlings was studied by selecting 6 months 1.5 generations of two half sib families No.32 and No.25 in Wuyi National Forest Farm,Zhangping,Fujian.Designing of 2 different phosphorus treatment(P0:0 mmol·L-1 KH2PO4;P1:1 mmol·L-1 KH2PO4)of indoor sand culture experiment,another set of two containers of different phosphorus levels and seedlings as the blank,collected the rhizosphere of ethylene in the low phosphorus stress respectively after 7d,14 d and 21 d at 10:00 in the morning in situ,measured height and ground diameter,seedling root morphology index change,phosphorus distribution and utilization under different test conditions of each seedling,by analyzing the change of above indexes and the correlation with ethylene content of root,illustrated the regulation of ethylene productionin root of Chinese fir seedlings under low phosphorus stress.And 6 months old and homogeneous No.25 seedlings were selected as the tested materials again,set as two phosphorus level(P0,P1),three reagents treatment in different phosphorus levels(E+:200 mg/L ehtephon;0:aditive free;E-:5 umol/L Ethylene synthesis inhibitor CoCl2),one month later,using the headspace collecting ethylene of root,and determining height,ground diameter,root morphology index changes,element distribution and utilization of Chinese fir seedlings P,photosynthetic parameters,root activity,root cortex dissolution rate of each seedling under different test conditions.Based on the analysis of the above indexes and the correlation analysis between the ethylene content and the above indexes,the law of ethylene generation in Chinese fir under the condition of low phosphorus stress and the ecophysiology response strategy were clarified.Main results are as follows:(1)Under the low-phosphorus stress,the ethylene emission of the roots of two Chinese fir seedlings was significantly lower than that of the normal phosphorus supply,and the No.25 was higher than the No.32.With the prolongation of stress time,ethylene production in roots of No.25 first decreased sharply and then slowly increased,while the ethylene release from roots of No.32 continued to decline.(2)The No.25 with high ethylene emission is more resistant to low phosphorus than the No.32 with low ethylene release.Under low phosphorus stress,the seedling height and ground diameter of the two families were lower than normal phosphorus supply,but the root system of the No.25,the content of underground phosphorus and physiological plasticity(Pr/Ps)were higher than the No.32.The seedling height,increment of ground diameter,and phosphorus content in both families increased with the increase of ethylene release from roots,but the physiological plasticity decreased with the increase.The ratios of root to shoot,root length and root volume of the No.25 were reduced with the increase of ethylene release from the root system,and No.32 showed the opposite rule.(3)Both low-phosphorus stress and exogenous ethylene induced more endogenous ethylene production in the roots of Chinese fir seedlings,and the increase of more endogenous ethylene induced by exogenous ethylene can enhance the ability of seedling roots to pick up phosphorus,Phosphorus utilization in the body also increased.Ethylene content in the roots of Chinese fir seedlings treated with low-phosphorus stress was higher than that of normal phosphorus treatment,while the total phosphorus accumulation,above-ground phosphorus content,and underground phosphorus content of Chinese fir seedlings treated with exogenous ethylene were all higher than those of normal phosphorus supply.Addition of exogenous ethylene treatment promoted the growth of seedling root length,root average diameter,and root volume increment.Ethylene content in roots of Chinese fir seedlings treated with exogenous ethylene at different phosphorus supply levels was higher than that without additives and higher than that of ethylene inhibitors,and exogenous ethylene treatment inhibited seedling height growth and promoted the growth of ground diameter.(4)Exogenous ethylene has a certain inhibitory effect on photosynthetic capacity of Chinese fir.Under low phosphorus stress,the addition of reagents inhibited the stomatal conductance and intercellular CO2 concentration to varying degrees.The intercellular CO2 concentration increased with the increase of exogenous ethylene and ethylene content,but the net photosynthetic rate,stomatal conductance,and transpiration rate decreased.Under the condition of low phosphorus stress,the addition of exogenous ethylene inhibited the enzyme activity of Chinese fir roots.Exogenous ethylene and ethylene content were positively correlated with peroxidase activity and superoxide dismutase activity,and negatively correlated with catalase activity and polyphenol oxidase activity.(5)Both exogenous ethylene and low-phosphorus stress can dissolve the cortical tissue of the root system.Under low phosphorus stress,the solubility of root cortex treated with no added reagent was higher than that of normal phosphorus,but after adding exogenous ethylene treatment,the root cortical solubility under different phosphorus supply levels was higher than that without adding reagent.Under low phosphorus stress,the solubility of root cortex in Chinese fir seedlings treated with ethylene inhibitors slowed the dissolution of root cortex caused by low phosphorus,but aggravated the root cortical solubility under normal phosphorus supply.(6)In summary,under low phosphorus stress,Chinese fir can reduce energy expenditure by reducing ethylene emission from roots,increase endogenous ethylene content in roots to increase its sensitivity,and thus increase the phosphorus content of Chinese fir seedlings to enhance the low phosphorus tolerance ability of Chinese fir families.Addition of exogenous ethylene will induce more endogenous ethylene production in Chinese fir seedlings,thereby inhibiting stomatal conductance,intercellular CO2 concentration,and reducing photosynthetic consumption.Finally,it promoted the obvious proliferation of various morphological indexes of the root system,effectively enhanced the phoshophos ability of Chinese fir roots,and increased the degree of dissolution of root cortical cells and the activity of root enzymes,which increased the utilization rate of phosphorus in Chinese fir.