Effects Of Soil Fauna And Microbe In The Litter Decomposition Process Of Four Subtropical Forests

Litter decomposition is an important way in the process of plant and soil feedback cycle,which is closely related to the formation of soil fertility,the maintenance of forest productivity and community succession.Soil fauna and microorganisms play an important role in litter decomposition directly or indirectly.Subtropical natural secondary forest has important functions of maintaining soil nutrients,atmospheric environment and biodiversity.However,there was still little concern about the effects of soil fauna and microorganisms on litter decomposition in the subtropical natural secondary forests.In this study,three sizes of litterbags(0.01 mm,1mm and 3 mm)were used to conduct a 12-month decomposition test on leaf litter in four typical secondary forest ecosystems(coniferous forest,mixed forest,evergreen broadleaved forest,bamboo forest)in the subtropics.The mainly results were summarized as follows:(1)Litter decomposition and element release characteristics: The initial litter C/N and lignin/N ratio were coniferous forest > mixed forest > evergreen broad-leaved forest > bamboo forest.Litter mass decomposition rates were significant differences between litter type,litterbags size,decomposition time during the experiment period.Mixed and evergreen broadleaved forests decomposed faster in the early experiment period(0 d-180 d),and bamboo forests decomposed faster in the later stage(180 d-360 d).When decomposing 360 d(February),the litter decomposition rate was followed the order of bamboo forest > evergreen broad-leaved forest > mixed forest > coniferous forest.Litter decomposition rate were decomposed by 44.09%,41.53%,33.40%,30.86% in 0.01 mm litterbags,by 48.94%,45.86%,35.44%,33.24% in 1 mm litterbags,and by 47.77%,46%,10%,42.17%,33.31% in 3 mm litterbags.Moreover,according to the Olson model,the 95% litter decomposition time was followed the order of bamboo forest(4.76 years)> evergreen broad-leaved forest(4.83 years)> mixed forest(6.11 years)>coniferous forest(6.24 years).The concentrations of litter C(carbon),cellulose,and lignin decreased significantly with the decomposition time.Nitrogen(N),phosphorus(P),calcium(Ca),magnesium(Mg),zinc(Zn)concentrations increased in the early decomposition stage and then decreased,but potassium(K),iron(Fe),aluminum(Al)concentrations showed the increasing trend.Litter mass loss was significantly positively correlated with C,N,P,Fe,and Al release,and significantly negatively correlated with cellulose,lignin,C/N ratio(except mixed forests).(2)Soil animal community characteristics: the main soil animal communities in the litterbags of four forest ecosystems were the Prostigmata,Collembola,followed by the Opiliones,Oribatida,Isopoda,and Coleoptera adult.The number of soil fauna was significant differences between 1 mm and 3 mm litterbags,and soil animal diversity in coniferous forest was quite different from that in other secondary forest communities.PCA showed that there were differences in the characteristics of soil animal communities in different forests.Soil animal communities were great differences between bamboo forest and other three forests.Soil animal communities were greatly affected by litterbags in the early stage,uniformly affected by litter and litterbags in the medium-term,and mainly affected by litter in the later stage.(3)Microbial community characteristics: the dominant bacterial communities were Enterobacteriaceae,Burkholderia,Sphingomonasqia,Pseudomonas,Rhizobium in the four forest ecosystems.The relative abundance of the main bacterial communities was quite different in different litterbags.Bacterial diversity showed a gradual upward trend,and the diversity of bacteria was different,but richness and evenness showed no difference in different litterbags.Both Ascomycota and Basidiomycota were the main fungal communities in the four forest ecosystems.At the genus level,the fungal communities in the three litterbags varied greatly with sampling time and forest type.Fungal diversity rose first,decreased and then increased.Fungal communities were more sensitive to decomposition time and litter species than bacterial communities.Bacteria and fungus were mainly abundant in the semi-and humus layer under natural environment.Bacterial communities significantly varied with the litter decomposition time.Bamboo invasion increased the total bacterial and fungal community diversity in the humus layer,but decreased litter and soil microbial diversity in other decomposition periods.In addition,the diversity and composition of the bacterial community changed less than that of fungus after bamboo invasions,indicating that fungus were more vulnerable to the bamboo invasions than bacteria.(4)Effect of soil fauna on litter decomposition: litterbags(different types of animal communities)significantly affected the release of C,N,P,cellulose,lignin,K,Ca,Mg,Fe,Mn,Zn,and Al concentrations(P<0.05),except for Cu concentration.The effect of soil fauna on litter decomposition was different between bamboo forest and other three forest types.When decomposing 360 d,the contribution of micro&meso-and macro-fauna was mixed forest >evergreen broad-leaved forest > coniferous forest > bamboo forest,as well as all types was mixed forest > vergreen broad-leaved forest > bamboo forest > coniferous forest.All soil fauna promoted litter C,N,Ca,Mg,Mn,cellulose,and lignin release.(5)Synergistic effect of microorganisms and soil fauna on litter decomposition: litter species had the greater influence on microbial communities than soil fauna.Microbial communities were similar in mixed forest and evergreen broad-leaved forest.Soil fauna had a greater impact on bacterial communities than fungal communities,but are more affected by litter species and sampling time.The bacterial community was mainly affected by the C/N ratio in the early stage,C,lignin and cellulose in the middle stage,and the lignin/N ratio and Mn in the later stage.The fungal community was mainly affected by Zn,C/N ratio,lignin,N in the early stage,N,cellulose,C/N ratio,Ca,Mn in the middle stage,and Mn,C/N ratio in the later stage.In short,litter decomposition experiments show that the four ecological types of litter have different decomposition and dynamic characteristics of element release,and their decomposition characteristics are controlled by litter types,soil animals and microorganisms.Litter type is the main factor affecting soil fauna and microbial community.Litter decomposition changes the abundance and diversity of soil animal and microbial communities by affecting litter and soil nutrient residues,and then affects the decomposition rate of litters.