The effect of restoration plantings and plant genus on soil biota

Abstract

In south-eastern Australia, shelterbelts are often established to restore ecosystem services that have been altered due to agriculture. In this thesis I aim to: 1) improve understanding of how shelterbelts affect soil biotic communities and how time since establishment may influence soil biota, 2) investigate how dominant shelterbelt tree genera (Acacia and Eucalyptus) influence soil biota, and 3) explore how changes in dominant tree genera affect key ecosystem process such as decomposition rates, microbial community structure and enzyme activities associated with carbon degradation. This thesis is structured as a compilation of connected papers. Paper I assessed earthworm composition, diversity and biomass in three land use systems: native shelterbelts, agricultural pastures and native remnant woodland fragments. Earthworm communities differed significantly among systems; with abundance, biomass and diversity greatest under pasture. Within shelterbelts I saw a shift from high earthworm biomass and density to low values with increasing time after establishment. Soil edaphic variables did not correlate strongly with earthworm biomass or density, but were correlated with earthworm community composition. Overall, the introduction of shelterbelts was associated with a decline in density and biomass of earthworms, including a decrease in the relative abundance of exotic species. Paper II investigated how the presence of shelterbelts and time since their establishment affects soil microbial communities. There was no significant effect of site type on the F:B ratio, MBC, or on MBN. Fungal community composition in shelterbelts regardless of age, was significantly different to pasture and native remnants. There was no significant difference in bacterial community composition between young shelterbelts and pastures, while middle-aged and old shelterbelts differed to pasture communities. There was a significant difference in fungal and bacterial community composition between all shelterbelts and native remnants. There was no clear evidence that microbial communities in shelterbelts show trajectories that converge towards those observed in natural remnant patches. Paper III compared soil microbial communities beneath the dominant tree genera used in shelterbelts (Acacia, Eucalyptus) and those found in adjacent pastures. The ratio of fungi to bacteria was highest under Eucalyptus trees, but did not differ between Acacia and pasture. Both fungal and bacterial communities varied at different depths in the soil profile and across sampling periods. The dominant tree genus was a significant factor in observed differences in bulk soil bacterial and fungal communities compared to the surrounding pasture. The effect of tree genus on fungal communities was more pronounced than on bacterial communities. Fungal communities not only differed between shelterbelts and pastures, but also between Acacia and Eucalyptus dominated shelterbelts. These patterns were consistent at different soil depths. Paper IV examined decomposition, enzyme activities and bacterial and fungal community profiles using a reciprocal design (litter*dominant overstory genus). Litter bags with two mesh sizes (<2mm and >2mm) were used to exclude or allow access by soil macrofauna respectively. Bags were filled with either Eucalyptus, Acacia or an equal mix of Acacia and Eucalyptus litter. After 395 days, decomposition of Acacia litter faster than Eucalyptus or mixed litter treatments, irrespective of the overstory genus. Exclusion of macrofauna had no significant effect on variables measured, other than chitin-degrading N-acetylglucosamine (NAG) activity. Distinct fungal and bacterial communities occupied each litter type and this differed between dominant overstory genera. However, these changes did not coincide with short term differences in litter decomposition rate. Show more