Analysis On Tending Thinning Effect Of Larix Gmelinii Forest

Thinning can effectively improve stand structure and keep ecosystem stable.So far,the effects and driving factors of thinning on aboveground and underground microbial communities are not clear.Therefore,taking Larix gmelinii as the research object,five different thinning intensities,T1(10%),T2(20%),T3(30%),T4(40%)and control(0%),were used to study the changes of stand growth factors,vegetation community and soil microbial community composition after 5 years of thinning.In addition,the response of soil microbial community to aboveground vegetation and soil physical and chemical properties was also analyzed.The main findings show that:(1)The average growth DBH of stands of Larix gmelinii forest was significantly increased compared with the contrast at 5 years after thinning of different intensities,which were increased by 0.15cm,0.34cm,0.48cm and 0.63 cm.The thinning intensity of 40% was the most significant for increasing the DBH growth of the stands.The average height of the trees also increased obviously which compared with the contrast,and the average height growth of the trees increased by 0.01m,0.02m,0.20m and 0.25m than the contrast.But the difference of the four thinning intensities was not obvious.Different thinning intensities also had some effects on the growth of the volume,of which 30%had the highest accumulation.In addition,the smaller the number of plant stand density,the lower the mortality of trees.The growth and nutrition space of trees remained after tending thinning were effectively improved.The DBH of the stands and tree height growth increased with the increase of thinning intensity.However,theie was no significant difference in tree height growth and accumulation under different thinning intensities.(2)Intensity and extreme intensity thinning significantly increased the undergrowth plant diversity and biomass of Larix gmelinii forest.Thinning could obviously increase the plant species,Menhinick richness index,Simpson index,Shannon-Wiener index,Pielou evenness index,and 40%thinning intensity in each layer,while ecological dominance index showed a decreasing trend(P<0.05).Properly increasing the intensity of thinning could promote the biomass of undergrowth vegetation layer and litter layer,and the thinning intensity of 30%was the best(P<0.05).In conclusion,the highest vegetation diversity and biomass and the best stand quality were found in the Larix gmelinii forest under the condition of 30%-40%thinning intensity.(3)The soil properties were obviously improved by extreme intensity thinning treatment.With the deepening of soil layer,SD,pH increased,WC,OM,NH4-N,AP and AK contents showed a downward trend.Compared with the control,the contents of OM,TP,NH4-N,AP and AK in the surface layer of soil increased with the increase of thinning intensity,and T 4 was the best.(4)The soil microbial diversity index was also significantly affected by thinning intensity,and the microbial diversity index increased with the increase of thinning intensity.Thinning had significant difference on Shannon and Chao index of bacteria in layer A,but had no significant difference in each layer of bacteria B and fungi.Among the dominant bacterial groups,the relative abundance of protein bacteria was higher,and the relative abundance of S.acidophilus increased with the increase of thinning intensity,and there was a significant difference(P=0.001).The relative abundance of phyllostachys was significantly higher than that of the control group.The relative abundance of layer B was significantly higher than that of layer A with the increase of thinning intensity.Among the dominant fungi,the relative abundance of basidiomycetes was the highest in all soil layers,and decreased significantly with the increase of thinning intensity,and the relative abundance of ascomycetes was opposite to that of basidiomycetes.The relative abundance of basidiomycetes was higher than that of basidiomycetes.Redundancy analysis of(RDA)further showed that TP,NH4-N,Herb.S,Herb.M and Herb.B were positively correlated with soil bacterial microorganisms,and pH,TP,NH4-N,AP were positively correlated with soil fungal microorganisms.On the whole,with the increase of thinning intensity,the stand growth factor growth was significant,vegetation diversity and biomass were increased,soil nutrient status was improved,microbial diversity and community composition were also significantly changed.Thinning intensity maintained at 30%-40%had a good effect on the maintenance of aboveground plant diversity and microbial diversity and soil nutrient conservation.