What They Did
The researchers grew 120 zucchini plants from seed, each in
their own pot. Plants were all given the same amount of water until the first
leaves unfolded. After that, they were divided into four groups, each
simulating a different weather condition.
The control group plants received 177 mL of water each day,
adding up to the 40-year-average rainfall for the month of September. The
plants in the heavy rainfall group received 57% more water, and those in the
reduced rainfall group received 30% less. Finally, the plants in the drought
group received no water until 70% of the plants began to wilt, at which point
they were given the same amount of water as the heavy rainfall group for one
day. This was intended to simulate the pattern of severe drought followed by
heavy rainfall; in total, the plants in the drought group received 80% less
water than the control plants.
They found that plants in the heavy rainfall condition
produced more female flowers, more sugar in both male and female flowers, and
therefore more sugar per plant and a 74% increase in calories available to
pollinators. Plants in the reduced rainfall condition produced fewer female
flowers, which resulted in less sugar per plant and a 34% decrease in calories
available to pollinators. Finally, plants in the drought condition produced
fewer flowers and a lower volume and concentration of nectar per flower, resulting
in less sugar per flower and per plant and a 95% decrease in calories available
to pollinators.
Further Exploration
The rationale behind this study was to explore how climate
change might affect plant-pollinator relationships, particularly for crop
species. The researchers note that some areas are likely to get more rain, and
others are likely to experience drought. The amount of nectar offered by plants
might affect whether they get sufficient pollination: bees use a lot of energy
to harvest nectar, so they need to consistently get enough calories to make
flower visits worthwhile.
Besides the changes attributed to rainfall, higher
temperatures are also interfering with pollen production and fertilization in
some crop and garden species (see https://extension.umd.edu/resource/pollination-vegetable-crops-changing-climate/.)
Another issue is that plants and their pollinators are getting out of sync,
blooming or becoming active at different times of year in response to
temperature changes (see https://www.pollinator.org/pollinator.org/assets/generalFiles/NAPPC-climate-change-overview_english.pdf.)
Planting native species is one way to help pollinators. Penn State’s pollinator
habitat certification requires three species each of early, mid, and late
season perennials, plus four species of shrubs or trees, and three native
larval host plants (see https://pollinators.psu.edu/landscaping-for-pollinators/pollinator-habitat-certification/provide-food-sources.)
Any native plantings help, though, even if they don’t meet the full habitat
certification requirements.
Honeybees have gotten a lot of attention because of
colony-collapse disorder (see https://www.epa.gov/pollinator-protection/colony-collapse-disorder),
but the importance of native bees is becoming more widely understood as well
(see https://www.biologicaldiversity.org/campaigns/saving-the-insects/native-bees.html.)
Of course, this was only one study on one plant: we still have a lot to learn
about how other plants might respond to climate change as well as how the
pollinators themselves will be affected – but that’s a rabbit hole for another day!
https://commons.wikimedia.org/wiki/File:Cucurbita_pepo-1.JPG
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