Soil nutrients affect the attractiveness of plants to pollinators

Research led by Pennsylvania State University (Penn State) suggests that pollination is essential for many plants and that nutrients present in the soil before plants even germinate can affect their attractiveness to pollinators.

In a study conducted on cucumber plants, researchers found that, in general, greater amounts of nitrogen and phosphorus in the soil resulted in larger plants with a greater floral display, including number and size of flowers. This led to an increase in attractiveness to pollinators and greater fruit production. However, it was also found that, regardless of nitrogen and phosphorus levels, "rewards" to pollinators, such as the sugar content in nectar, the amount of nectar in female flowers, and the concentrations of proteins and lipids in pollen, remained constant.

Anthony Vaudo, a biological scientist with the US Forest Service and leader of the research, said these findings, recently published in Scientific Reports, indicate that plants can prioritize these rewards in all conditions to ensure pollinator attraction. The research also provides clues on how to restore soil after disturbances caused by human activities or natural disasters.

Christina Grozinger, professor of entomology at Penn State, emphasized the importance of understanding and predicting how changes in soil conditions influence interactions between plants and pollinators, both in crops and in natural landscapes. This is because three-quarters of our food crops depend on pollinators to bear fruit and seeds, and more than 80% of flowering plants benefit from pollinators.

To carry out the study, researchers grew cucumber plants in greenhouses at Penn State and treated them with five different fertilizer solutions, varying the concentrations and proportions of nitrogen and phosphorus. They then measured various plant characteristics and analyzed flower nectar and pollen, as well as the frequency of bee visits.

Analysis of the data showed that while more nitrogen and phosphorus were generally associated with greater growth, attractiveness to pollinators and fruit production, very high levels of nitrogen began to have negative effects on some of these traits. However, increasing phosphorus levels could mitigate these effects. The ideal nitrogen to phosphorus ratio tested was 4:1, resulting in the best overall growth, pollinator attraction and reproduction.

The complete study can be read here.