| Fokienia hodginsii Henry et Thomas is the only rare species of Fokienia sp.in the Cupressaceae family,it has beautiful shape,straight trunk,flexible adaptability and better abilitiy of water conservation.Its cultivation prospect is broad with good ornamental value,ecological value and economic value.In recent years,the scale and area of F.hodginsii planted have been expanded continuously,but the level of forest management has not kept pace with it’s development.And global warming and frequent extreme climates have caused biological disasters in F.hodginsii planted stands to become more serious,resulting in a series of problems,for example a decrease in the rate of merchantable volume and survival.It has become one of the major obstacles to restricting the development of F.hodginsii planted stands,and it continues to threaten the achievements of ecological civilization construction.In this study,the several survey sites were set up in the main distribution areas of F.hodginsii,containing Anxi county,Nanjing county,Lianjiang county and other counties in Fujian province.The major pests and diseases that occurred throughout the year were identified,diagnosed,or analyzed using the combination methods of field observations,insect rearing indoor and disease isolation and identification to determine the key pests and diseases of F.hodginsii.Specifically,conduct detailed investigations on the species of key pests and diseases to understand their time and space patterns.Feeding preference of key pests to F.hodginsii at different ages was studied baed on the infestation rate.I also observed the structure difference of skin infested by termites at different level,to explore the relationship between infestation degree and ages of tree,and determine nutrition substances and secondary substances from different trees with different ages to analyze the the relationship between infestation degree and ages of tree,and attempt to find the reasons what makes different resistance between differen ages.These findings will be very helpful to give some contribution to resistance programme in the future.The results showed that there were 3 species of pests and diseases occurring throughout the year,including 2 species of pests and 1 species of disease.The insect pests was identified as Odontotermes formosanus Shiraki and Dasychira sp,and the disease was Rosellinia sp..Further investigation results showed that O.formosanus were widely distributed and occurred in the above three counties,with a damage rate of up to 56.7%in the partially F.hodginsii planted stand.The worker generally prefer to feed on the stem bark of F.hodginsii to form a nick or circumcision wound and block the nutrient delivery,and finally cause the cypress tree to weaken and even die.Dasychira sp.mainly damages the leaves of F.hodginsii and is sporadic distribution in Anxi County,with a low population density.Rosellinia sp.was mainly distributed in Anxi,and it was particularly harmful to the grafted wood of F.hodginsii.The rate of susceptible plants in the area was 28.36%,and the average disease index was 22.5.The investigation found that the damage dynamics of the key pest O.formosanus on the establishment of F.hodginsii were as follows:In F.hodginsii’s planted stand at different slope positions,the rate of damage on the uphill and mid-slope positions is generally higher than that on the downslope,and there was a very significant difference between uphill and downhill positions(p<0.05).It is suggested that the termites preferred to take food on the uphill position planted plants,the reason may be because the slope of water conditions,soil fertility and other ecological factors were better than the uphill position,making the establishment of the F.hodginsii stronger.In the multiple forest stands in Anxi and Nanjing County,the victimization rate in one-year-old F.hodginsii planted stand planted was significantly higher than that in two-year-old or four-year-old(p<0.05),the table shows that termites preferred to damage the seedlings with weaker vigor.By observing the injury degree of different family seedlings planted in the termite eruption,it was found that termites had no obvious preference to the feeding choice of different families(p>0.05).When observing the annual dynamics of Termites on one-year-old F.hodginsii planted stand,it was found that the peak period of damage was May to September,second is during March to April and October to November,other months were less harmful.In summary,O.formosanus usually erupted in summer at high temperatures with high-risk seedlings in the uphill position of F.hodginsii planted stand and the preference for feeding one year old.Forest ages and slope position were two important factors that cause the difference in insect resistance between F.hodginsii and O.formosanus.The results showed that the damage rate of one-year old stands was as high as 50%,the damage rate of forest stands after 2 years is concentrated at about 10%,but the difference between the damage rates of different slope positions within the same forest stand will not exceed 20%.It can be seen that the resistance of stand to insects caused by the difference of age is much larger than the influence of slope position factor.Therefore,for the bark tissue at the stem of 1-4 years old,the bark thickness and other indicators were measured or observed,meanwhile integrated anthrone method to measure the contents of soluble sugar assay technique and other nutrients and secondary substances measurement techniques.Disscussion on the Causes of Insect-resistance Formation,Bark Structure and Content of Ingredients in F.hodginsii planted stand.The results were as follows:(1)The damage rate of termite was negatively correlated with bark thickness,thickness of waxy layer and flatness,and was positively correlated with the number of cracks on the bark surface at different ages.(2)polysaccharides the content of soluble protein,flavone and total phenol showed no significant difference among samples from different barks at different ages,but the content of soluble sugar and tannin in 2 kinds of contents showed significant(p<0.05),and the soluble sugar and tannin in bark were positively correlated with the performance of resistance to insect in stand.The above results showed that there were many factors for the formation of insect resistance in F.hodginsii.The bark thickness,morphology of the waxy layer,and soluble sugar and tannin content of the inclusions may be closely related to their existence,among them,as an indicative secondary biomass of plant insect resistance,tannin might be a monitoring substance to identify it’s resistance of F.hodginsii to infestation of O.formosanus. |
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