Diversity of non-crop plants and arthropods in soybean agro-ecosystems in South Africa

Abstract

Soybean is widely cultivated in the Grassland Biome of South Africa (>700 000 ha per annum). Yet the possible effects large-scale cultivation of soybean has on biodiversity in adjacent habitat is not fully understood. It is important to expand current data in order to assess and adapt methods of agriculture – where possible – to ensure the future functionality of soybean agro-ecosystems. This study aimed to describe plant and arthropod species assemblages, diversity patterns and relationships between plant and arthropod diversity within soybean agro-ecosystems in South Africa. Surveys were conducted in three treatment zones, i.e., the soybean crop, field boundary (transition zone between soybean fields and adjacent habitat) and adjacent untransformed grassland. A total of 4910 individuals and 320 plant species and 9216 individuals and 373 arthropod morpho-species were recorded from 60 plots (5 localities x 2 sites x 2 transects x 3 treatments). The soybean crop had significantly lower plant and arthropod diversity than adjacent habitats. Plant diversity remained the same between the field boundary and grassland. A higher diversity of arthropods was collected in the boundary than the grassland. These results suggest soybean fields had no adverse effects on biodiversity patterns in the adjacent habitat. However, the boundary, dominated by alien plant species, did contain a significantly different plant species composition from the untransformed grassland that was mirrored by unique assemblages of arthropods. This suggests that disturbance, resulting from the soybean crop, led to species losses and gains that changed the plant and arthropod species composition of the field boundary but had no effect on grassland beyond the boundary (>50 m). Correlations between plant and arthropod species richness and diversity index values were generally weak and non-significant suggesting other factors, for instance, plant functional and structural diversity, may be important to explain arthropod diversity. Unique species assemblages and high diversity of plants and arthropods in the boundary and untransformed grassland suggest that these zones may have important conservation value in soybean agro-ecosystems by supporting unique species and ecosystem services.