Liliana B. Falco

Differential contribution of soil biota groups to plant litter decomposition as mediated by soil use.

Plant decomposition is dependant on the activity of the soil biota and its interactions with climate, soil properties, and plant residue inputs. This work assessed the roles of different groups of the soil biota on litter decomposition, and the way they are modulated by soil use. Litterbags of different mesh sizes for the selective exclusion of soil fauna by size (macro, meso, and microfauna) were filled with standardized dried leaves and placed on the same soil under different use intensities: naturalized grasslands, recent agriculture, and intensive agriculture fields. During five months, litterbags of each mesh size were collected once a month per system with five replicates. The remaining mass was measured and decomposition rates calculated. Differences were found for the different biota groups, and they were dependant on soil use. Within systems, the results show that in the naturalized grasslands, the macrofauna had the highest contribution to decomposition. In the recent agricultural system it was the combined activity of the macro- and mesofauna, and in the intensive agricultural use it was the mesofauna activity. These results underscore the relative importance and activity of the different groups of the edaphic biota and the effects of different soil uses on soil biota activity.

Earthworm assemblages in different intensity of agricultural uses and their relation to edaphic variables

The objective of this study was to relate earthworm assemblage structure with three different soil use intensities, and to indentify the physical, chemical, and microbiological soil variables that are associated to the observed differences. Three soil uses were evaluated: 1-Fifty year old naturalized grasslands, low use intensity; 2-Recent agricultural fields, intermediate use intensity, and 3-Fifty year old intensive agricultural fields, high use intensity. Three different sites for each soil use were evaluated from winter 2008 through summer 2011. Nine earthworm species were identified across all sampling sites. The sites shared five species: the native Microscolex dubius, and the introduced Aporrectodea caliginosa, A. rosea, Octalasion cyaneum, and O. lacteum, but they differed in relative abundance by soil use. The results show that the earthworm community structure is linked to and modulated by soil properties. Both species abundance and diversity showed significant differences depending on soil use intensity. A principal component analysis showed that species composition is closely related to the environmental variability. The ratio of native to exotic species was significantly lower in the intensive agricultural system when compared to the other two, lower disturbance systems. Microscolex dubius abundance was related to naturalized grasslands along with soil Ca, pH, mechanical resistance, and microbial respiration. Aporrectodea caliginosa abundance was related to high K levels, low enzymatic activity, slightly low pH, low Ca, and appeared related to the highly disturbed environment. Eukerria stagnalis and Aporrectodea rosea, commonly found in the recent agricultural system, were related to high soil moisture condition, low pH, low Ca and low enzymatic activity. These results show that earthworm assemblages can be good indicators of soil use intensities. In particular, Microscolex dubius, Aporrectodea caliginosa, and Aporrectodea rosea, showed different temporal patterns and species associations, due to the changes in soil properties attributable to soil use intensity, defined as the amount and type of agricultural operations.

Plant secondary succession age-related changes in landfills.

Sanitary landfills are widely used for large-scale final disposal of municipal wastes. The material covering the wastes is diverse in nature and bears propagules of different plant species, which develops spontaneously on the sites after waste disposal stops. The aim of this study was to detect the main patterns of vegetation secondary succession over the landfill cells, despite the differences in area and surface work intensity at the landfills. Over the span of two years, eight samplings were carried out on each of the 13 cells from the three active landfills in Buenos Aires. The relative cover for each plant species and the soil’s mechanic resistance were registered. The vegetation cover reached 80 % after five years and a decrease in soil´s mechanic resistance was observed 5 years after closure. Regarding the floristic composition of the assemblages, most of the herbaceous species found were native (42 %) and perennials (62 %). The dominant species in all the cells was Cynodon dactylon. The heterogeneity of the assemblages between the three places prevented the configuration of an age linked pattern. However, some regularities arise: exotics are dominant along the whole succession; meanwhile, natives gain in proportionality consistently with the age of the cells. Most of the dominant species are characteristic of perturbed environments, but in the oldest cells some species belong to the climax pampean steppe; so, an orientated human intervention would be necessary to achieve a dominance of natives.