Above-and Below-ground Biodiversity Across A Range Of Eucalyptus Grandis Plantation Ages

It is increasingly recognized that the large area development of commercial plantations affects the native biodiversity. Understanding of the biodiversity pattern can provide an important scientific basis for plantation management. Issues around the loss of diversity caused by fast-growing tree plantations have aroused controversy for many years. A crucial problem in the most studies was being conducted in the short-term rotation eucalyt plantations with a certain plantation age, which might limit our understanding of the actual plantation ecosystem process. Furthermore, above- and below-ground components of forest ecosystems interact implicitly. Complex interactions between above-belowground biodiversity may provide important feedbacks regulating ecosystem. Therefore, above- and below-ground biodiversity (soil microbe and soil fauna) in the Eucalyptus grandis plantations with a range of plantation ages (1-10 years) converted from cropland, therefore, were simultaneously measured in order to obtain an understanding of eucalypt effects on biodiversity.1 Germination rates of the three target species decreased with the increase of the concentrations of eucalyptu roots extracts. At the lowest concentration, little variation was observed on germination rate among the treatments from plantations with different ages. The highest dose roots extracts from 4 years old E. grandis showed the strongest inhibitory effects on the germinations of all target specie, the inhibitory rates were about 48%,51.2%,56.56%, respectively. Seedling's growth of the three target plants were reduced as the concentration of root extract increase and toxic effect of extract was much more pronounced for younger E. grandis. Soils of 4 years old E. grandis plantation exhibited the most remarkable inhibitory effect on the targe plant, followed by 2 years old. However, after 4 years old, the inhibitory effect was weakened and a stimulatory effect was presented with the increased forest ages on germination and growth of target. Twenty eight allelopathic potential compounds were confirmed present in roots extracts of E. grandis. The contene of that were in great abundance before E. grandis rotation age. Thirty eight chemical components were found in E. grandis rhizosphere soils and were in great abundance in younger stands. Twenty common components including alkane, aromatic ester, arene and phenol have been observed both in root and rhizosphere soils.2 A total of 77 species from 44 families with shrub and herbaceous species dominated were recorded across 1-10 year old E. grandis plantations. The species richness and abundance of understory plants increased in the first 3 years and then decreased in the following 2 years, however, those indices thereafter increased by 4.60 and 4.83 times in the 10-year plantation compared to 1-year stands, respectively. The species number of life forms and growth forms over roatation age (10-year old) increased by 4.09 and 5.22 times compared to 1-year old stands. Regardless of the stand age, phanerophytes have a large amount (27.27-66.67%) followed by chamaephytes (16.67-31%), hemicryptophytes (4.16-27.27%). After 10 years, the number of phanerophytes species increased by 10.67 times. It is worth noting that broad leaved herb occurred all along the 10 year old stands.β-diversity reflecting the successional rates of understory community were higher before rotation age but lower over rotation age. The species richness and diversity indices of herb species were significantly higher than shrub layer in younger stands (1 to 4 years), thereafter lower than shrub species in 5 years old plantations and paralleled with shrub layer in older E. grandis.3 The samples in the ten year-old sites in autumn yielded 3068,4355,8326,3690 individuals of soil animals from thirty taxonomic genera belonging to seven phylum, fourteen class, and thirty three orders. More abundant soil fauna communities occurred in organic horizons (about 1.2-2.3 times that in top soil) and decreased with soil depths except for the conversely vertical distribution in soil in the 6 th and 8 th year plantations). The density of micro-fauna was quantitatively more abundant than meso- and macro-fauna regardless of plantation age. A large amount of micro-mesofauna occurred in the litter layer. Fewer amounts of meso-fauna but considerably abundant micro-fauna were found in the studied soil. The densities of macrofauna (Hymenoptera dominated), mesofauna (Acarina and Collembolan dominated), microfauna (nematode and enchytraeidae dominated) in the 10-year plantation. In spring, soil faunal density decreased (4.560×104 ind. m-2-2.627×104 ind. m-2) before rotation age, and then increased with forest age, it was 2.02 times over rotation age (10-year stands) than that in 1 year-old stands. In summer, soil faunal density increased in the first 2 years and then decreased and was lowest in 4 years, thereafter increased with forest age, the density in 10 year stands was 2.47 times higher than 1a. In autumn, soil faunal density decreased from 7.40 in the 1-year plantation to 5.77×104 ind. m-2 in the 4-year plantation, and then increased to 22.31×104 ind. m-2 in the 10-year stand. In winter, the soil faunal density increased with fluctuation, was lower in 2 year-old plantations (1.51×10 4 ind. m-2) and peaked in 8 year-old plantations (9.44×104 ind. m-2), it in 10 year old plantations was 2.41 times higher than the lth year. DG indix were ranked as autumn, spring, summer, winter and the other diversity indices didn't showed similar seasonally trend. Soil protozoa density increased in the first 2 years and decreasd from 3 to 6 years and then increased with forest age, it in 10 year old plantations was 2.30 times higher than 1 year old plantations.4 The abundance and the proportions of omnivores, saprozoic, predators and phytophage groups were varied with forest age. In the four seasons, the proportions of predators or phytophage were lower and with the phytophage groups lowest and decreased insignificantly with the increasing forest ages. The abundance and proportion of predators in summer and winter increased and decreased in spring and autumn insignificantly. The abundance of the omnivores groups decreased in the first 5years and increased with plantation age, the proportion of it fluctuated and increased significantly with plantation age. In the four seasons, the abundance of the omnivores groups in 10a were 10.6,14.5,4.71,9.20 times, the proportion of that in 10a were 4.63,4.34,1.57,2.26 times higher than in 1 year old plantations. The abundance of saprozoic groups decreased before and in rotation age (1-5 or 6a), and then increased significantly with forest age in spring, summer, autumn. In winter, the abundance of saprozoic groups increased significantly from 1-3year, and decreased from 3 to 5 year, thereafter increased with plantation age. The proportion of the group fluctuated and decreased with plantation age; The abundance of the group in 10 year old Kgrandis plantations were 1.17,1.15,2.50,2.26 times than 1 year old plantations; the proportion of that were 0.51,0.34,0.83,0.56 times than in 1 year old plantations. No similarly seasonal trend was found on the functional groups of soil fauna; the common characteristics were that the abundance and proportions of the varied groups were higher in autumn.5 In four seasons, bacteria quantitatively dominated the soil microbe in E. grandis regardless of plantation age, follwed by actinomycete and fungi. The counts of the microbes were higher in organic horizons and decreased with soil depths except for the converse distribution in certain year old stands. Although the seasonal difference of different types of soil microbe. The microbial counts decreased before rotation and then increased with the plantation age, the connts in four seasons increased by 1.97,0.85,2.21,1.50 from 1 to 10 year-old plantations. Although the variation of the three microbe type, they all showed similarly seasonal trend viz. autumn> spring>summer> spring. The soil microbe counts in 4a in winter reached the minium (21.79×106 CFU·g-1), and peaked in 10a in autumn (132.61×106 CFU·g-1). The diversity indices generally represent the following trend viz. Shannon-wiener and Pielou index increased in the first 3 or 4 years and then decrease with forest age. Simpson index showed a converse trend.6 MBC and MBN concentration were higher in surface soil (0-10cm) and decreased with soil depths, MBC content decreased in fluctuation with plantation age in younger stands, and then increased with forest age. From 1 to 10 years, MBC content increased from 455.59 mg Kg-1to 2138 mg Kg-1 in spring; It increased by 3.94times,1.82 and 3.94times in summer, autumn and winter respectively. Soil MBN decreased before rotation age (1-4 years), and thereafter increased. The MBN concentration increased by 3.59,3.26,1.83,6.59 times. A similar seasonally trend was found in MBC, ranked as autumn, winter, spring, summer. No seasonally similar trend was found in MBN.7 There were significantly positive correlations between plant richness, soil faunal abundance (macro-, meso- and micro-fauna), and the the abundance of culturable soil microbeand microbial biomass except for the soil fauna trophic groups (Omnivores and Saprozoic fauna). There were significant correlations between above and below-ground diversity indices. Abundance and diversity indices of plants and soil biota were significantly correlated with soil properties. The understory vegetation in E.grandis plantations reestablished after 10 years afforestation. After 10 years, the abundance of soil microbe and its diversity indices were higher than crop lands but lower than Pinus massoniana (> 30a). There were no signicant varations of soil faunal density and diversity indices between (< 4a) E.grandis plantations before rotation age and crop lands, but significant varations were found between plantations over rotation age and crop lands. Soil faunal density and diversity indices in E.grandis plantaions before rotation age and in rotation age varied significantly, but varied not signicantly in plantaions over the rotation age, when compared with Pinus massoniana (> 30a) stands.