Intraspecific Competition Of Quercus Wutaishanica And Janzen-connell Effect In Loess Plateau

Explaining the maintenance of diversity in plant communities has long been a key issue in ecology.In order to solve this problem,ecologists have proposed various theories and hypotheses to explain coexistence of different species.One of them is the Janzen-Connell hypothesis.The Janzen-Connell hypothesis states that natural enemies(herbivores and pathogens)act in a density-and/or distance-dependent manner to reduce the survival of seeds,seedlings and juvenile plants close to conspecific adult trees or in areas of high conspecific density.In recent years,there have been many researches concentrate on Janzen Connell effect,but most of them are concentrated in the tropics.It is of great significance to research it for understanding the mechanism of maintaining species diversity in the temperate forests.Quercus wutaishanica is one of the main forest species in the Loess Plateau and plays an important ecological role in the ecological environment of the region,plays an important ecological role.Therefore,it is of great significance to effectively protect and utilize it.Researching population structure characteristics and intraspecific competition intensity is beneficial to explore and guide artificial tending and provide useful reference for effective protection and utilization of Quercus wutaishanica.This study investigated a sample plot of Quercus wutaishanica forest in the Loess Plateau,studied the individual distribution,population structure and intraspecific competition of this population,and analyzed the genetic diversity level,heterozygosity level and genetic relationship of this population by SSR molecular markers.The main results are as follows:(1)In this population,there was almost no sapling distribution around the larger adult individuals,but a large number of seedlings distribution;saplings are generally distributed far away from the adult plants,and there is no obvious seedling aggregation around.(2)The population structure is mainly small diameter class,and the number of individuals in each diameter class generally decreases with the increase of diameter class.The population structure is obvious pyramid type,showing the growth type population.(3)In this population,the relationship between DBH and competition intensity of Quercus wutaishanica showed as follows: competition intensity decreased with the increase of diameter class,competition index decreased faster when DBH is smaller,and gradually flattens with the increase of DBH.(4)The genetic diversity of Quercus wutaishanica population is at a high level,which indicates that Quercus wutaishanica in a small scale can still maintain a rich genetic diversity,and the number of heterozygotes in the population is relatively uniform.(5)In the analysis of the spatial distance of the individuals with close relationship,it is found that a large number of individuals are distributed in the range of 6 ~ 22 m from the individuals with the largest DBH of the same branch,and reach the peak in the range of 10 ~ 13 m.the curve formed is similar to the population recruitment curve in the Janzen-Connell hypothesis.