| At present,the plantation in Northeast China has the problem of slow decomposition due to poor litter quality,especially the serious decline of coniferous plantation.By studying the biological mechanism of litter decomposition in plantation,understanding the role of soil organisms in litter decomposition and its contribution to litter decomposition,it can provide solutions for the current phenomenon of serious soil fertility decline in artificial forests.Taking Larch gmelinii and Fraxinus mandshurica plantations in Northeast China as the research objects,the litter decomposition bag method with different pore sizes(0.01 mm small pore size,2.00 mm medium pore size and 4.00 mm large pore size)was used to carry out a one-year litter decomposition test from October 2020 to October 2021.During this period,samples were collected before soil freezing,melting,growing season and defoliation period.Combined with the characteristics of soil invertebrates and fungal communities,the role of soil organisms in litter decomposition in needle and broad-leaved plantations was discussed.The results show that:(1)There were significant differences in litter decomposition rate among different litter types and pore sizes.The decomposition rates of Fraxinus mandshurica forest litter bags with large aperture,medium aperture and small aperture were 70.1%、71.8% and 73.1%,and the decomposition rates of Larch gmelinii forest litter were 40.5%、39.7% and 41.1%,which showed that the decomposition rate of litter in Fraxinus mandshurica forest > Larch gmelinii forest,the decomposition rate of large pore size > medium pore size > small pore size.The total nitrogen content showed a trend of first increasing and then decreasing with the decomposition time,and there were significant differences between different pore sizes in the growing season and deciduous stage(p<0.05).The dynamic change of organic carbon content did not have a consistent law,which was different due to the different types of litter and pore size.There were differences,the carbon-nitrogen ratio showed a downward trend on the whole,and the carbon-nitrogen ratio of the Larch gmelinii forest was higher than that of the Fraxinus mandshurica forest.(2)The characteristics of soil invertebrate communities showed significant differences with litter types and decomposition processes.During the whole litter decomposition period,a total of 8,652 soil invertebrates were collected in the litter bags of Fraxinus mandshurica forest,and 6,899 were collected in litter bags of Larch gmelinii forest.For medium pore size > large pore size.The results showed that the dominant groups of Fraxinus mandshurica forest were Oribatida,Enchytraeidae,onychiuriclae and prostigmata,and the dominant groups of Larch gmelinii forest were Oribatida,hypogastruridae and prostigmata.The richness index and diversity index of soil invertebrates in the litter of Fraxinus mandshurica forest were significantly higher than those in litter of Larch gmelinii forest,and the functional groups of soil invertebrates changed with the type of litter and the process of decomposition.(3)The number of individuals and groups of soil invertebrates were significantly correlated with the decomposition rate and the content of nutrient elements in the process of litter decomposition of different pore sizes in Fraxinus mandshurica and Larch gmelinii forests.Soil invertebrate functional groups were significantly correlated with litter decomposition rate.In the early stage of decomposition in November,before soil freezing,omnivorous and predatory properties were significantly correlated with litter decomposition(P<0.05).From decomposition to July growing season,mycophagous and saprophagous soil invertebrates were significantly negatively correlated with litter decomposition(P<0.01).The total contribution rate of soil invertebrates to Fraxinus mandshurica forest litter was 18.0%,and the contribution rate to Larch gmelinii forest was 34.5%.Contribution of small and medium soil invertebrates >large soil invertebrates.(4)During the litter decomposition process,the fungal community characteristics were different with the litter type and decomposition time.Fungal community composition at the phylum level involves Ascomycota,Basidiomycota,Rozellomycota,Mortierellomycota,Mucoromycete and some undetermined fungi,the main dominant community is Ascomycota,At the genus level,the fungal communities in the two pore sizes were significantly different in different decomposition stages and different litter types.During the process of litter decomposition,the fungal abundance varied greatly with the litter type and sampling time,and the relative abundance was the highest at the later of the decomposition test,and the relative abundance of Fraxinus mandshurica forest was greater than that of Larch gmelinii forest.The fungal community diversity and richness in the later stage of litter decomposition were significantly higher than those in the early stage,and the fungal diversity and richness in the Fraxinus mandshurica forest were higher than those in the Larch gmelinii forest.(5)The two kinds of litter decomposition rates were significantly positively correlated with the fungal richness index(Chao1 index and Ace index)(p<0.05).The litter decomposition rate of Larch gmelinii forest was significantly positively correlated with fungal community diversity index(Shannon index)(p<0.01),and the organic C content and C/N ratio of Fraxinus mandshurica forest were extremely significantly positively correlated with fungal Chao1 index(p<0.01),which was significantly positively correlated with the Ace index(p<0.05);There were significant differences in soil invertebrate community characteristics and fungal community characteristics with litter types and decomposition time.Contribution of soil invertebrates to litter decomposition in coniferous plantation > broad-leaved forest,contribution of small and medium soil invertebrates to litter decomposition > large soil invertebrates.The microbial community abundance and diversity in the litter of broad-leaved plantation were higher,and the fungus richness and diversity increased significantly at the end of the decomposition test,which in turn promoted the faster decomposition of litter. |
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