Soybean crops may benefit from forest pollinators

Abstract

Increasing evidence indicates that pollinator diversity and pollination services are highly threatened by the destruction and fragmentation of natural habitats and the intensification of agricultural landscapes. Here we analyze the bee visiting ensemble on soybean flowers and the effects of pollinator visits on soybean reproductive success, within a fragmented Chaco forest landscape embedded in a soybean matrix in central Argentina. We assessed visitation rates in relation to distance from the forest (5, 50 and 100m) compared soybean bee assemblages with those on wild flowers in the nearby forest fragments, and carried out an exclosure experiment in order to assess the contribution of insect visits to soybean reproductive success. We also analyzed the relationship between visitor body size and the distance from the forest to the visited flower. Five species belonging to two families of bees were observed visiting soybean flowers. The bee species observed on soybean were well represented in the forest, and Apis mellifera was the most abundant species, visiting soybean flowers at all studied distances from the forest. Instead, wild visitors displayed a turnover of species throughout those distances, with smaller species being restricted to the forest proximity and replaced by larger ones toward the interior of the crop. Total visitation rates were significantly and negatively affected by distance to the forest. All plant productivity variables measured in the exclosure experiments were significantly improved in exposed flowers, duplicating the values observed without pollinators. The present study offers preliminary evidence linking forest proximity to higher visitation rates and presence of wild pollinators on soybean flowers thus providing for the first time, evidence of the forest role as pollinator donor for the soybean crop. It also shows that pollinator activity matters for this crop, leading to increased soybean yield. Further research on this topic is necessary in order to provide informed guidelines to enhance soybean production while simultaneously promoting natural habitat conservation.