Effects Of Biotic And Abiotic Factors On Productivity In A Mixed Broadleaved-Korean Pine Forest

Stability of productivity plays a very important role in promoting ecosystem functions,services,and resilience.Understanding the drivers of productivity is the basis for our understanding of the functions of natural ecosystems.At present,the explanation for the impact of biotic factors on productivity is mainly based on the niche complementarity hypothesis,biomass ratio hypothesis and vegetation quantity hypothesis,and the explanation of the impact of abiotic factors on productivity is mainly based on the soil fertility hypothesis and the indirect effect of topography.However,the specific effects of various factors on different ecosystems are different,and there are many variables for measuring each factor.In addition,the respective roles of big trees and small trees in the study of the drivers of productivity are still unclear,which require further research.Based on the niche complementarity hypothesis,the biomass ratio hypothesis,the vegetation quantity hypothesis of abiotic factors,and the soil fertility hypothesis of abiotic factors,this study constructed the optimal model of the structural equation model of a 30-ha plot of the mixed broadleaved-Korean.The direct,indirect and total impacts of all paths in the model were quantified.It was found that the vegetation quantity hypothesis was the most important factor affecting productivity,and among them,the big tree played a major role,but the impact of small trees on productivity could not be ignored.In addition,soil was the second major factor affecting productivity.The effect of soil moisture was higher than that of soil nutrients,and this result was more pronounced in big trees.But soil had a negative effect on productivity,proving that higher availability of soil nutrients increased competition,resulting in higher mortality and turnover rates.The phylogenetic diversity based on the niche complementarity hypothesis and the community-weighted mean values of leaf dry matter content based on the biomass ratio hypothesis jointly affected productivity through opposing action mechanisms,and mainly affected productivity by affecting the initial biomass of small trees.This study conducted a one-way ANOVA analysis,compared whether productivity was different between different topographies,and compared the strength and weakness of the relationship between each variable and productivity in the optimal model of the structural equation model between different topographies.It was found that productivity was higher at steeper slopes and at higher altitudes.At the same time,the negative correlation between soil moisture and productivity was more pronounced at steep slopes.The positive correlation between the biomass ratio hypothesis represented by leaf dry matter content and productivity was more pronounced at steeper slopes.The traits with higher dry matter content could better adapt to the stand conditions restricted by water.Productivity was higher at the semi-sunny slope and sunny slope,which proved that sufficient light was conducive to the improvement of productivity.This study revealed the effects of biotic and abiotic factors on productivity of the mixed broadleave-Korean pine forests,and studied the different effects of big trees and small trees,respectively.This will help to better understand the functions of the mixed broadleaved-Korean pine forest ecosystem,and will provide a basis for formulating protection and management measures for the original mixed broadleaved-Korean pine forest.