| The Da'xingan Mountains is an important forestry base in China.Due to unreasonable logging and management for many years,the ecosystem functions of the Da'Xingan Mountains have been degraded,and the forest environment has deteriorated,forming a large number of secondary forests.Although the protection of forests has increased in recent years,the quality of forests is still low and ecological functions are low.This paper investigates the effects of thinning intensity on Larix gmelinii Forest in the Da'Xingan Mountains,and explores the effects of thinning on soil physicochemical properties and soil respiration in the secondary forests of the Da'Xingan Mountains.Taking the Larix gmelinii forest of the Da'Xingan Mountains as the research object,tending and thinning of different intensities were performed,including control plots(CK),13.7%,25.5%,34.4%,49.6%,and 59.9%.Collect 0?20cm soil samples and use the LI-8150 multi-channel soil carbon flux measuring instrument to determine the soil physical and chemical properties and soil respiration-related indicators in the late freezing and thawing,growing season and early freezing period,using software such as SPSS23.0 and Excel After treatment,the principal component analysis method was used to comprehensively evaluate plots with different tending thinning intensities.(1)The maximum value of soil respiration appears from 12:00 to 18:00,and the minimum value appears from 4:00 to 6:00.The average annual respiration rate from large to small is the growing season(3.82?mol·m-2·s-1)>Late freeze-thaw period(1.20 ?mol·m-2·s-1)>Early freeze period(0.83 ?mol·m-2·s-1).In the growing season,the correlation between soil respiration rate and soil temperature is significant(R2 is 0.639 to 0.865,when the thining intensity is 49.6%,R2 is 0.507),and there is a certain correlation with soil moisture(R2 is 0.430 to 0.644),The soil temperature sensitivity coefficient is higher than the non-growth season,which indicates that the forest ecological function is active during the growing season,the vegetation grows vigorously,and the microorganism and root system are frequent.The effect of tending thinning intensity on soil respiration rate in the growing season is more obvious.The trend throughout the year is:when the tending thinning intensity is low,the soil respiration rate increases with the increase of thinning intensity;when the tending thinning intensity is high,the soil respiration rate Decreases as the thinning intensity increases.(2)When the tending and thinning intensity is 25.5%?34.4%,the content of organic matter and N,P,K and other nutrient elements in the soil are higher,and the soil physical and chemical properties are the best,which is suitable for forest growth.There is no obvious seasonal difference in soil non-capillary porosity;there are significant seasonal differences in soil moisture content,soil bulk density,maximum water holding capacity,total porosity,and capillary porosity.There were no significant seasonal differences in soil pH,organic matter,total K,and available K;there were significant seasonal differences in soil total N,total P,available N,and available P.(3)Seasonal differences in soil physicochemical properties and respiration rates are significant.Soil bulk density is an indicator for determining the degree of soil compaction,and has a significant negative correlation with soil respiration in the growing season;soil porosity reflects the spatial structure of the soil,and has a significantly positive correlation with soil respiration in the growing season;soil pH is related to Soil respiration is positively correlated.When the soil is weakly acidic,it is beneficial to plant growth.The relationship between soil N,P,K and respiration varies in different seasons:in the late freeze-thaw period,soil respiration has a significantly positive correlation with total K(0.576)and available K(0.493);during the growing season Soil respiration has a significant positive correlation with total N(0.643);in the early freezing period,soil respiration has a significantly negative correlation with available P(-0.549)and total P(-0.437).(4)This study selected pH,organic matter,total N,total P,total K,available P,available N,available K,soil moisture content,soil bulk density,maximum water holding capacity,total porosity,capillary porosity,non-Capillary porosity and daily average values of soil respiration rate were used as parameters.Principal component analysis was used to establish evaluation models for different tending and thinning plots.Through comprehensive analysis,it was concluded that when the thinning intensity was 25.5%,the plot score was the highest and the transformation effect was the best.Suitable forest growth environment,moderate forest density,improved forest structure,improved soil nutrients,accelerated soil respiration rate,accelerated decomposition of humus in harvested land,increased mineral elements in the soil,and significantly improved chemical properties. |
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