Effect Of Thinning On Wood Stakes Decomposition And Fungal Community Under Pinus Tabuliformis Carriére Plantations

Chinese pine(Pinus tabuliformis Carriere)is an endemic tree species and one of the important afforestation species in Northern China.It is important to detect how thinning influence on organic matter decomposition process and improve the mechanism of thinning treatments from the aspect of fungal community.This study was conducted in a Chinese pine plantation located in Pingquan county,Hebei province.The study plots(20 m × 20 m)were thinned to three stand densities:low(3290 trees/hm2),moderate(2770 trees/hm2),and heavy(2200 trees/hm2),and an unthinned control(4700 trees/hm2).Wood stakes of trembling aspen(Populus tremuloides Michx.),Chinese pine and loblolly pine(Pinus taeda L.)were used as indices of wood decomposition.All stakes were placed on top of the litter layer(hereafter referred to as surface stakes)and in the mineral soil(hereafter referred to as mineral stakes).The stand growth was investigated before thinning(201 1)and after thinning(2014).Mass loss of wood stakes and wood-inhabiting fungal communities were detected from 2013 to 2015.Thinning treatments,species of stakes and sampling time all had significant effect on wood stake decomposition and fungal communities in both surface and mineral soil.The results showed that:(1)Thinning had significant influence on stand growth.The number of small trees in the forest was gradually reduced with thinning intensities,while the number of large diameter trees was increased resulting better stand structure.Compared to the unthinned control,the DBH growth was increased by 30%in moderate thinning and 26%in heavy thinning.In terms of cumulative growth,low thinning,moderate thinning,and heavy thinning were improved by 14%,19%and 27%,respectively.However,there was no height growth differences among unthinned and thinned plots.(2)Mass loss of surface stakes was improved by 125%in low thinning than in the unthinned control.While mass loss of mineral stakes was increased 13.9%in moderate thinning as compared to the control.For species of stakes,Chinese pine and aspen decomposed fastest on surface soil and in mineral soil,mass losses were 9.7%and 57.1%,respectively.Mass loss of Chinese pine and lobollly pine was increased 6.3%and 15.2%in bottom soil compared to the top soil.The decomposition rate of all the surface stakes is still growing after 3.5 years deployed with 13.4%mass loss,whereas mineral stakes decomposition rate tends to slow down and then level off with time.In addition,mass loss of surface stakes had positively correlation with wood moisture content(r>0.35).(3)Initial wood carbohydrate,lignin,C,and N concentrations were significantly different between aspen and loblolly pine stakes,but were consistent within each species before placement in the control and thinned treatments.Loblolly pine had higher initial lignin content(3 1.3%)and C/N ratio(661.4)than aspen,but aspen had 0.1 10%N content higher than loblolly pine which was only 0.078%.However,there was no correlation between mass loss and initial quality.Both aspen and loblolly pine had relative higher lignin content and relative lower carbohydrate content after one year decomposition.Compared to loblolly pine,Chinese pine had 23.9%more earlywood proportion and the mass loss increased with increasing earlywood proportion(R2=0.203).Mass loss had positively correlation with strength loss for the three species of wood stakes and aspen had the strongest correlation with R2=0.53.(4)Thinning treatment,species of stakes and sampling time all had significant influence on wood-inhabiting fugnal communities especially in mineral soil.The number of correlated fungi was decreased after thinning but Chinese pine as the native species had much more correlated and indicator fungal species.Most correlated fungal species occurred in 2015.Operational taxonomic units(OTUs)richness was decreased after thinning on surface soil.However,OTUs richness was increased after thinning in mineral soil except in low thinning in 2014 and moderate thinning in 2015.Three trophic modes were increased at first and then decreased with thinning intensities,the peak values of saprotroph and symbiotroph were 101 and 72 OTUs occurred in low thinning treatments.Fungal community composition was different among aspen,Chinese pine and loblolly pine,while the dominant species were all Ascomycete.Fungal community composition was changed with time on surface and mineral soil.The dynamic of fungal richness and trophic modes was more complex in mineral soil where there was interactions among thinning,species of stakes and sampling time.(5)We analyzed the individual fungal samples which were decomposed one year in mineral soil.The main results indicated that:OTUs richness in bottom of stakes was decreased by 36.9%than in top of stakes.Ascomycete and Basidiomycete in upper soil were 1.64 times and 1.47 times than in lower soil.The relationship between mass loss of wood stakes and OTUs richness was different in each group(eg,thinning treatments,species of stakes and soil depths).In moderately,heavily thinned plots and the unthinned plots,OTUs richness was descreasd quickly with wood stake decomposition when mass loss was less than 20%,while when mass loss was more than 40%,the OTUs richness decreased slowly and then began to stabilize.In conclusion,on the one hand,thinning improved the distribution of Pinus tabuliformis size-class and increased stand growth;on the other hand,it decreased the fungal richness and then weakened the internal competition of fungal community,meantime,increased Saprotroph and Symbiotroph and finally resulting accelerated decomposition of organic matter.