Study On The Influence Of Site Factors Of Arceuthobium Sichuanense Spruce Forest On The Dwarf Mistletoe(Arceuthobium Sichuanense)

Spruce dwarf mistletoe is a perennial semi parasitic seed plant. In recent years, the disease has become a main disease for natural spruce forest in the three-river source region in China and has seriously destroyed the social, economic, and ecological balance in the region. Therefore, it is of significance to find out the primary pathogenic factor of spruce dwarf mistletoe disease and effectively prevent and control it. The paper chose the infected spruce in Xianmi Forest Farm, Menyuan Hui Autonomous County, Haibei State, Qinghai Province as research objective, made a field investigation of the impact of spruce dwarf mistletoe on the growth of host spruce tree and branches through standard sample plot survey method, and analyzed why it could occur and cause disaster in a large scale within natural spruce forests. In addition, it investigated the distribution characteristics of spruce dwarf mistletoe in different slope positions and exposures within natural forests, clarified the distribution law of different slope positions of spruce dwarf mistletoe, further elaborated the damage characters of spruce dwarf mistletoe for the hosts with different tree ages, studied spruce dwarf mistletoe with different infected degrees in different periods at the physiological level, and obtained the following results:1.Main factors affecting spruce dwarf mistletoe disease. It analyzed the principal component of disease index and environmental factors of spruce dwarf mistletoe disease through SPSS software and obtained the regression equation of the disease index. It concluded that the top five factors affecting the infection index of the disease were respectively canopy density, elevation, PH value, slope, and herbaceous biomass. Among them, canopy density ranked first. According to the research results, spruce dwarf mistletoe slightly occurred or never occurred in natural forest stands with canopy density greater than 0.7. And spruce dwarf mistletoe seriously occurred in natural forest stands with canopy density from 0.4 to 0.5. Therefore, it could conclude that canopy density was negatively correlated with disease index.2. Physiological index of spruces were affected by spruce dwarf mistletoe disease. Firstly, after host spruces were infected by dwarf mistletoe, it had relatively obvious changes in phenotype. The infection level of dwarf mistletoe changed from low to high. Host spruces changed into needle color from green to yellow. When shutter weight decreased and the length of new shoot and needle was shortened, more and more lateral buds increased. When spruce dwarf mistletoe disease reached the highest(level 4), arbuscular phenomenon was extremely serious. Tree vigor dramatically weakened and was on the verge of death. Secondly, after host spruces were infected by dwarf mistletoe, it started from plan physiology and regarded the changes in MDA, proline, and chlorophyll content as an index to measure the health degree of host spruces. Among them, with the continuous increase of the infected disease degree, MDA content decreased and then increased; proline content continued to increase; chlorophyll content gradually decreased. The reason was that as spruce dwarf mistletoe disease increased its degree, host spruces continued to produce a large number of arbuscular, which competed with hosts and continued to intercept water and nutrients within spruce tree body in order to meet their own growth. It led to the situation that hosts were seriously shortage of water for a long time, then lacked nutrients, and damaged cells and cell membrane. On the other hand, hosts lost a lot of water and mineral and suffered drought for a long time, so their tree vigor continued to decline and their ability to synthesize chlorophyll was impaired. Therefore, the above changes in phenotype occurred.3.Factors affecting seed germination of spruce dwarf mistletoe. Under natural conditions, the seed preservation rate of spruce dwarf mistletoe seed on semi shady slope and semi sunny slope was below 50%. In addition, with the increase in infected disease degree, it decreased and then increased. The seed preservation rate for semi sunny slope was higher than that for semi shady slope, which showed that although spruce dwarf mistletoe spread through seed ejection, it had relatively lower seed germination rate under natural conditions; the seed germination rate of spruce dwarf mistletoe infected with different degrees of disease was smaller than 30%. In addition, the seed germination rate for semi sunny slope was higher than that for the semi shady slope, and it decreased and then increased. It was in line with the field survey result. In other words, in Xianmi Forest Farm, Menyuan Hui Autonomous County, harm degree of spruce dwarf mistletoe on semi sunny slope was obviously higher than that on semi shabby slope. Spruce dwarf mistletoe showed a lower trend from natural preservation rate to seed germination rate, which proved that Spruce dwarf mistletoe seed had a relatively long infection process.