Mesofaunal assemblages in soils of selected crops under diverse cultivation practices in central South Africa, with notes on collembola occurrence and interactions

[摘要] English: Soil is a complex medium, comprised of both biotic and abiotic components.Interactions between these components are responsible for the beneficial servicesprovided within different ecosystems. The biotic component, which is also referred toas the active role players in the soil, is responsible for these services. The incidenceof these organisms is influenced by the abiotic factors, which act as filteringmechanisms that select for certain species to occur within certain areas. Consideringan ever-increasing human population, these services could prove beneficial, since itcould improve crop yields at minimal cost without exploiting the soil resource. Manyfarmers are now changing their farming methods to more sustainable andconservation focused practices to try and reduce the disruption of soil communitystructures and to optimize the complexity and resilience of these communities.Disturbances lower the complexity of soil communities and therefore limit the servicesthat could be provided. This study focused on the fluctuations in diversity of selectedrole players within the soil medium due to the presence of certain agricultural practicesand environmental changes.Sampling for this project was conducted at six localities in the Free State Provincebetween 2011 and 2014. Three of the localities are located in the Nama Karoo Biomeand the other three in the Grassland Biome. The farms Vaaldam, Koppieskraal,Thornberry and Klein Brittanje were selected due to the diversity of agriculturalpractices and management strategies applied. The rest of the localities were theParadys Experimental Farm, which is the experimental farm of the University of theFree State, where a pesticide trial was conducted and the farm Eureka, which wasexposed to pollutants from a goldmine tailings dam. The variation in events and thegeneral environment posed the perfect opportunity to observe and evaluatefluctuations in the diversity of the selected faunal groups within the relevant soils.Sampling was conducted in the porosphere of each plant. All the plants selected forsampling were in optimal condition and away from the edges of the field. Sampleswere marked and transported to the lab where the organisms were extracted by meansof the Berlese-Tullgren funnel extraction method. Sorting and identification were subsequently completed from which a reference collection was compiled and storedin ethanol.Fluctuations in the diversity of the selected fauna was observed throughout this study.Agricultural practices had a definite influence on the severity of these fluctuations.Mechanical and chemical disturbances usually had a reduction effect on the diversityat first, which was followed by an increase in the abundance of certain opportunisticspecies. In some cases, these increases were quite severe, since certain specieswould flourish in the absence of competition and predator pressure, especially in thecase of introduced species. Incorporation of stubble into the soil should be carefullymanaged, as this could create problems such as compaction. In spite of a certaindegree of compaction, it was still found that soils with a higher organic componentwere more resilient in the presence of disturbances. Stubble-burning influenced thevertical distribution of soil mesofauna due to the condensation effect of such an event.The influence of chemicals depend on the persistence of the chemical used, as wellas the complexity of the community before exposure. In already compromised areas,the effect of chemicals were far more detrimental to the community structure than at anatural site where a single application was done. The effect of pollutants from atailings dam reduced the diversity considerably and only a few species were presentat these sites. For species to occur within this heavy metal polluted area, they mustbe able to either tolerate or avoid the pollutants.It was clear that each locality with its specific influencing factors selected for certainspecies to be present. Fields that were minimally disturbed and where organicmaterials were incorporated into, the soils had a higher tolerance to disturbances. Thiswas due to a more complex community structure within the soil, thus indicating thateven in the presence of a disturbance, these soils could still provide services.

[发布机构] University of the Free State