Response Of Functional Traits Of Regeneration Seedlingof Quercus Variabilis Plantation To Thinning And Its Environmental Interpretation

Thinning is one of the common measures in the forest management process.With the entire growth and development process of the forest from canopy to maturity,the tending thinning measures guided by the near-natural management theory can optimize the stand structure,reduce the competition between individual trees,and improve the forest,microclimate,adjust the ecological succession of understory vegetation,and enhance the comprehensive benefits of the forest.As the most sensitive link in the process of stand succession,the survival status of understory renewal seedlings directly affects the species composition and forest growth dynamics of forest communities.The growth and development dynamics of renewal seedlings can reveal the community’s continuity and judge the forest regeneration potential.Plant functional traits are relatively stable states formed by genetic variation and natura] selection in long-term environmenta] changes,such as morphological structure and physiological characteristics of plants.Studying the effect of thinning on renewed seedlings and their functional traits,and using the understory light environment and soil environmental factors to explain this effect is an important basis for scientific determination of forest tending measures and intensity,it is of great significance to the sustainable management of the entire forest ecosystem and the sustainable use of forestry.This paper takes the 40-year-old Gwe/twsplantation in Dengfeng state-owned Forest Farm as the research object,selects representative forest stands for thinning in the forest farm,and compares the non-thinning stands with the same growth environment and similar geographical locations as controls,set a fixed sample plot of 100 m x 100 m in the forest stand,carry out renewal diversity survey,and sample the soil and seedlings to obtain the light index in the forest.Studying the effects of thinning on the functional traits of understory regeneration seedlings of Quercus variabilis plantation,and to analyze the relationship between soil physical and chemical properties,under-street light environment indicators and the functional traits of the regeneration seedlings,which is helpful to study management measures on understory natural regeneration and stand growth The dynamic impact provides a theoretical basis for the sustainable management of forest resources and the enhancement of ecosystem functions.Main findings:1、The regeneration density of thinning plots was 3442 plants hm"2,and the proportion of seedling regeneration was Quercus variabilis: Quercus aliena Bl.: Cotinus coggygria Scop.:Broussonetia papyrifera =767: 62: 31: 1,the renewal ratio of each species are larger than non-thinning plot;Compared with uncut plots,the number of young seedlings under the forest,Shannon-Wiener diversity index（0.42）,Simpson diversity index（0.2）,richness index（4）and evenness index（0.3）were all found increase.2、The average height of regenerated seedlings（47.75cm）and chlorophyll content（50.52SPAD）in thinning plots were higher than that in non-thinning plots,but the difference was not significant,The number of leaves（55）,leaf area（1732.46 cm²）,base diameter（0.93cm）,root volume（29.34 cm3）,and seedling biomass were significantly higher than the corresponding index values in the unthinned plot（P <0.05）;However,after thinning,the ratio of regenerated seedling root to shoot（1.38）decreased,the nitrogen content of each organ increased,and the phosphorus content decreased.Therefore,thinning enhanced leaf photosynthesis and resource acquisition capacity.3、Compared with the non-thinned Quercus variabilis plantation,the canopy opening（24.89%）,leaf area index（1.32）and leaf inclination angle（46.18 °）of the main forest layer after thinning were increased;direct PPFD(5.48mol·m^-2·d^-1),diffuse PPFD(5.25mol·m^-2·d^-1),total PPFD under-forest(10.72mol·m^-2·d^-1),and PAR(86.92μmol·m^-2·s^-1)are all significantly increased（P <0.05）,thinning obviously improved the light conditions under the forest.Correlation analysis between under-forest photoenvironmental factors and functional trait indexes of rcgenoated seedlings showed that direct PPFD under the forest had a significant positive correlation with SLA,leaf area ratio,and base diameter of regenerated seedling leaves（P <0.05）;and diffuse PPFD under the forest had a significant positive correlation with LA,SLA,leaf biomass,leaf area ratio,and renewed seedling base diameter（P<0.05）.4、After thinning,the soil density of soil thickness 0 ¹0cm and 10 ²0cm decreased,soil porosity,non-capillary water storage and organic carbon content increased;soil pH and available potassium decreased significantly（P <0.05）.The correlation analysis results of soil physical and chemical characteristics indexes and functional trait indexes of renewed seedlings show that soil porosity is significantly positively correlated with main root length,root surface area,and total nitrogen content of stems（P <0.05）;Soil organic carbon was significantly positively correlated with the renewed seedling LA,SLA,STN,total root length and root surface area（P <0.05）;Soil alkaline nitrogen was significantly positively correlated with SLA and STP（P <0.05）;The soil available phosphorus had a very significant positive correlation with STK content（P <0.01）,while the available potassium had a significant positive correlation with LTP,STP,RDMC,RTP（P <0.05）.5、Based on the correlation analysis,according to the results of PCA analysis,14 environmental factors related to the fimctional properties of the renewed seedlings,such as soil porosity,can be resolved into 5 independent principal components with a cumulative contribution rate of 81.615%.The results of multiple regression analysis showed that leaf area,leaf dry matter content and root dry matter content were most affected by soil organic carbon and soil total nitrogen content,respectively.