Study On The Diversity Of Soil Faunal In Eucalyptus Grandis Plantation With Different Ages

Although,plantations provide timber for the human,slowing down the CO₂ concentration increase,expand land-based forest cover and depreciates the dependence of humanbeing on natural forests,a series of ecological problems has also been emerged. Among them,the study of biological diversity has been a hotpoint.Currently,the study on biodiversity of plantations was focused on the above-ground vegetations.Only a few studies were reported on the biodiversity of soil biota.However,hardly any research was carried out on the simultaneous examinations from the perspectives of above-ground and below-ground biota.Soil ecosystems are highly complex,containing a tremendous amount of species.The invertebrate component of the decomposer biota(soil fauna) affects plant growth and resource allocation via indirect processes including:(1) alteration of microbial abundance and community composition;(2) enhancement of nutrient mineralization and transfer;(3) influencing competition between plants;(4) redistribution of organic matter and nutrients and(5) enhancing leaf herbivory.There are diverse influencing the soil faunal communities,however,little information was available on the dynamics of soil faunal along with the forest ages.In this paper,at the Danling County in Sichuan Province the soil fauna composition, dominant species groups,seasonal changes and profiles distribution of 1_～10-year-old Eucalyptus grandis plantation had been studied,which were important parts of the formation of biological diversity.We also analyzed the relationship between soil faunal and the forest ages of Eucalyptus grandis plantation.Soil macrofauna was collected by handpicking method in the field,while dry mesofauna and wet soil fauna was gathered and separated by Baermann and Tullgren funnels.The results showed:1 During the four seasons,the soil fauna of Eucalyptus grandis plantation at different ages were collected totally 12,848 specimens and 30 soil fauna groups,which belongs to 33 orders,14 classes and 7 phyla(not including protozoa).Acarina,Collembola,Nematoda were dominant groups and Hymenoptera,Enchytraeidae were frequent groups,all the other 29 groups were scarce groups with low individual percentage.It indicated that the distribution of soil fauna in Eucalyptus grandis plantation was not even.2 For the Eucalyptus grandis plantation,the overall number of individuals of all the different soil fauna changed in the sixth year,while the total number of the soil fauna groups changed in the seventh year;The first exhibited the highest total individuals number and groups number.The total individuals number showed the lowest(885 specimens) in the sixth year and the total number of groups represented the lowest for the 15 categories in the seventh years,the overall declined in the first after a rising trend.3 For the different age plantations of Eucalyptus grandis,the number of groups and individuals of large or small mesofanual showed the highest value in the autumn,in addition to the lowest number of groups in the winter and the highest of wet soil fauna in the winter,the lowest in the spring.4 For the different age plantations of Eucalyptus grandis,the gathering character of the Table for profile distribution of soil fauna groups was obvious;The number of soil fauna in the withering layer was larger than the soil layer,and especially the number of wet soil fauna was very larger.The density of soil fauna was decreased with the increase of soil depth.5 For the different aged plantations of Eucalyptus grandis,the biodiversity index of soil fauna groups was different with the change of seasons.The Shannon-Wiener index showed the highest value in summer and minimum in autumn;The Pielou-dominance index represented the highest value in autumn and smallest in winter;The Simpson index reached the maximum in winter and minimum in spring;The density-group index(DG) was in the highest value in the fall and smallest spring.6 For the different aged plantations of Eucalyptus grandis,the distribution of soil fauna groups decreased firstly and increased after,similar with microbial communities and dissimilar at the changing point that the soil fauna behaved,in the sixth year and the microbial communities behaved in the seventh year,Both playing important roles in the transmission of energy and substances in the soil ecosystem for the impact of factors outside very similar.7 For the different aged plantations of Eucalyptus grandis,,the proportion of the same corrupted function groups descended with the age increased fluctuant at the beginning of the sixth year.8 For the different age plantations of Eucalyptus grandis,the number of wet soil fauna was a very large up with the propotions of 78.3%,which was a key factor causing the distribution of soil fauna in different age plantations of Eucalyptus grandis.