Pollination is vital to many plants, and nutrients in the soil before these plants germinate may affect how attractive they ultimately become to pollinators, according to Penn State-led research.
In a study of cucumber plants, researchers found that, in general, higher amounts of nitrogen and phosphorous in the soil resulted in larger plants and flower widths, including flower number and flower size, resulting in increased pollinator attractiveness and higher fruit production.
However, they also found that regardless of nitrogen and phosphorus levels, pollinators “bonuses” such as sugar content in nectar, amount of nectar in female flowers, and protein and lipid concentrations in pollen remained the same.
Anthony Fudeau, a research biologist with the US Department of Agriculture’s Forest Service who led the research while a postdoctoral researcher in entomology at Penn State’s College of Agricultural Sciences, said the findings — which were recently published in Scientific reportsIt is suggested that plants may prioritize these rewards under all circumstances to ensure that they attract pollinators.
“We found that a plant can become more attractive with the help of certain nutrients in the soil, while also maintaining the quality of its bounty, which is essential for visiting bees,” said Fudu. “This gives us clues as to how best to restore soils, for example, after disturbances from human activity or natural disasters.”
According to the researchers, previous studies have found an association between higher soil nitrogen and phosphorus and faster plant growth, as well as positive effects such as the number and size of flowers and the number and size of pollen grains. However, little work has been done on how these nutrients affect attracting pollinators and, ultimately, plant reproduction.
Because soil nutrient conditions can change as a result of land use, climate change, and land management — such as fertilizer and livestock grazing — it is necessary to learn more about how these nutrients affect plant growth, said Christina Grozinger, a professor of entomology at Publius Vergilius Maro at Penn State.
“With three-quarters of our food crops using pollinators to set fruit and seeds, and more than 80% of flowering plants benefit from pollinators,” Grosinger said, “it is extremely important that we begin to understand and predict how these changes in soil conditions will influence plant-pollinator interactions in Both crops and landscaping.”
For the study, the researchers raised cucumber plants in Pennsylvania greenhouses. They treated the plants with one of five fertilizer solutions: a control with no added nitrogen or phosphorus and four others with different concentrations and ratios of nitrogen and phosphorus.
The researchers measured several characteristics of the plants, including height and biomass above ground, the size of each plant’s male and female flowers, the number of flowers each plant produced, how long it took for the plants to start producing flowers after sowing, and how many cucumbers each plant produced. They also analyzed flower nectar and pollen, as well as how often bumblebees visited.
After analyzing the data, the researchers found that while more nitrogen and phosphorus was generally associated with increased growth, pollinator attractiveness and fruit production, very high levels of nitrogen began to have negative effects on some of these traits. However, increasing phosphorus levels can mitigate this.
Overall, they found that the ideal ratio of nitrogen to phosphorus they tested was 4:1, resulting in the best overall growth, pollinator attraction, and reproduction.
Junpeng Mu, a researcher at Mianyang Normal University who visited Penn State while working on this project, said he thinks it’s particularly interesting that some traits of male flowers — such as the number and size of flowers per plant, nectar concentration and pollen count per plant — are particularly interesting. Flower- Varies with soil nutrients, but female flower traits were not.
“These results give us a better understanding of the mechanisms that underlie the interactions between plants and pollinators, as well as the processes of the agroecosystem,” Mo said.
In addition, Voodoo said he expects the findings will also be useful in his current position, where it will be part of an effort to rehabilitate areas of forest that have been felled. He said that the soil is often very compacted from heavy machinery that passed through these areas, as well as lacking in nutrients.
“After loosening the soil, we will apply a material called biochar to increase the soil’s ability to hold water and bind nutrients,” Fudu said. “Then, we can begin to reintroduce plants and pollinators to the area. I’m grateful for my experience from this study, which has given me a good start to doing some real-world applications.”
Anthony de Voodoo et al., Effects of Soil Nutrition on Floral Traits, Pollinator Attraction, and Fitness in Cucumber (Cucumis sativus L.), Scientific reports (2022). DOI: 10.1038/s41598-022-26164-4
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