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UNIVERSITY PARK -- Pollination is vital for many plants, and nutrients present in the soil before these plants even sprout may affect how attractive they eventually are to pollinators, according to Penn State-led research.
In a study with cucumber plants, the researchers found that in general, higher amounts of nitrogen and phosphorus in the soil resulted in larger plants and floral display, including flower number and size, leading to increased attractiveness to pollinators and increased fruit production.
However, they also found that regardless of nitrogen and phosphorus levels, pollinator "rewards" such as sugar content in nectar, the amount of nectar in female flowers, and protein and lipid concentrations in pollen stayed the same.
Anthony Vaudo, a USDA Forest Service research biological scientist who led the research while a postdoctoral scholar in entomology in Penn State's College of Agricultural Sciences, said these findings suggest that plants may prioritize these rewards in all conditions to ensure that they attract pollinators.
"We found that a plant could become more attractive with the help of certain nutrients in the soil, while also keeping the quality of its rewards consistent, which is necessary for getting bees to visit," Vaudo said. "This gives us clues for how we can best restore soil, for example, after disturbance from human activity or natural disasters."
According to the researchers, previous studies have found an association between higher nitrogen and phosphorus in the soil and faster plant growth, as well as positive effects such as number and size of flowers and pollen number and size. However, little work had been done on how these nutrients affect pollinator attraction and, ultimately, plant reproduction.
Christina Grozinger, Publius Vergilius Maro Professor of Entomology at Penn State, said that because soil nutrient conditions can change as a result of land use, climate change and land management -- such as fertilizers and grazing livestock -- it is vital to learn more about how these nutrients
affect plant growth.
"With three quarters of our food crops using pollinators to set fruit and seed, and more than 80% of flowering plants benefiting from pollinators," Grozinger said. "It is incredibly important that we begin to understand and predict how these changes in soil conditions influence plant-pollinator interactions both in crops and in natural landscapes."
For the study, the researchers raised cucumber plants in Penn State greenhouses. They treated the plants with one of five fertilizer solutions: a control that had no added nitrogen or phosphorus and four others with different nitrogen and phosphorus concentrations and ratios.
The researchers measured several characteristics of the plants, including height and above-ground biomass, the size of each plant's male and female flowers, how many flowers each plant produced, how long it took the plants to start producing flowers after seeding, and how many cucumbers each plant produced.