Herself’s Houston Garden

The world is a cooler, wetter place because of flowering plants, according to new climate simulation results published in the journal Proceedings of the Royal Society B. The effect is especially pronounced in the Amazon basin, where replacing flowering plants with non–flowering varieties would result in an 80 percent decrease in the area covered by ever–wet rainforest.

The simulations demonstrate the importance of flowering–plant physiology to climate regulation in ever–wet rainforest, regions where the dry season is short or non–existent, and where biodiversity is greatest.

“The vein density of leaves within the flowering plants is much, much higher than all other plants,” said the study’s lead author, C. Kevin Boyce, Associate Professor in Geophysical Sciences at the University of Chicago. “That actually matters physiologically for both taking in carbon dioxide from the atmosphere for photosynthesis and also the loss of water, which is transpiration. The two necessarily go together. You can’t take in CO2 without losing water.”

This higher vein density in the leaves means that flowering plants are highly efficient at transpiring water from the soil back into the sky, where it can return to Earth as rain.

“That whole recycling process is dependent upon transpiration, and transpiration would have been much, much lower in the absence of flowering plants,” Boyce said. “We can know that because no leaves throughout the fossil record approach the vein densities seen in flowering plant leaves.”

For most of biological history there were no flowering plants—known scientifically as angiosperms. They evolved about 120 million years ago, during the Cretaceous Period, and took another 20 million years to become prevalent. Flowering species were latecomers to the world of vascular plants, a group that includes ferns, club mosses and confers. But angiosperms now enjoy a position of world domination among plants.

“They’re basically everywhere and everything, unless you’re talking about high altitudes and very high latitudes,” Boyce said.

Dinosaurs walked the Earth when flowering plants evolved, and various studies have attempted to link the dinosaurs’ extinction or at least their evolutionary paths to flowering plant evolution. “Those efforts are always very fuzzy, and none have gained much traction,” Boyce said.

Boyce and Lee are, nevertheless, working toward simulating the climatic impact of flowering plant evolution in the prehistoric world. But simulating the Cretaceous Earth would be a complex undertaking because the planet was warmer, the continents sat in different alignments and carbon– dioxide concentrations were different.

“The world now is really very different from the world 120 million years ago,” Boyce said. Read more

Read the paper
An exceptional role for flowering plant physiology in the expansion of tropical rainforests and biodiversity

I recently attended a Lunch Bunch at Mercer on ‘Insect and Plant Interactions’, if you have a chance to hear that talk I strongly recommend it.

In your garden is an evolutionary arms race that has gone on since plants and insects first appeared on earth. Sometimes there are truces, sometimes one or both will adapt, and sometimes it’s all out war.

Plants have developed many defense mechanisms to protect themselves from herbivore insects ( about half of all insects  ) including chemical toxins, physical barriers, trickery, but sometimes resort to a symbiotic relationship with the insect.

Some plants can send warnings to other plants when they are under attack by insects. These warnings are volatile organic compounds the leaves release into the air. Nearby plants sense the compounds and begin to ramp up their toxin production. This saves the plant from spending energy making toxins when they are not needed. Trees attacked by pine bark beetles will do this, legumes are also know to release warning chemicals when under attack.

Sometimes plants release chemicals that attract beneficial insects for pollination or to attack herbivores. Some plants create chemicals that make them undigestable to insects. Other plants release compounds to repel insects ( deet ). Some common beans create toxins that when eaten by caterpillars will prevent proper butterfly development. Nicotine is a toxin to ward off tobacco pests.

Physical barriers take the form of thorns ( roses ), hairs ( lamb’s ear ), thick walled leaves ( cactus), and grit on the leaves (bamboo).  Plants that are wounded may release antibacterial chemicals and cell strengtheners to wounded areas.

Trickery by plants is more common than you’d expect. The passionflora vine has little nodules at the base of the leaves. These nodules look like butterfly eggs. When butterflies mistake these for other butterfly eggs, they move on and look for a less crowded place to lay their eggs.

Some plants have gone proactive and eat the insects. ( Venus flytraps, pitcher plants ). These plants either trap by trickery or close when a trigger hair is touched and capture, dissolve and eat the insect.

Waterlilies sacrifice a bee for each pollination. In the first stage the lily holds water in the cup. The bee arrives to drink but drowns because the plant has put surfactant into the water. The pollen that the bee has carried from previous flowers is released to fertilize the murderer. The next day the flower opens, dries and produces its own pollen for the next bee to collect and carry off.

Other plants are slightly less proactive predators. Pipevines attract flies who climb into the flower and are trapped in the bulb at the bottom by hairs that face in along the tube. After the fly created a ruckus getting covered in pollen the flower relaxes in the morning to let the fly escape and pollinate the next pipevine flower.

There are many symbiotic relationships, flowers have colors in visible and infrared light as well as scents and shapes to attract bees. Some like bluebonnets change color to announce whether there is nectar remaining.

Others give off heat and or less pleasant scents to attract beetles and flies. ( Sago, stapeliads, aroids )

Some plants provide shelter for ants who in turn protect the plant from other predators and feed the plant. Some ant species will even strip bare competing foliage plants.

Many species of plants and insects have developed a one to one relationship, wipe out the insect and you wipe out the plant species. ( yucca, Senita cactus/moth )

Insects continue to evolve ways around plant defenses including neutralizing or becoming resistant to plant toxins. For instance monarch butterfly caterpillars feed on toxic milkweed, black swallow tail butterflies on pipevines. Sometimes these insects use the ingested toxin to become toxic to their own predators.

Clever carnivorous insects will hang out on a plant, wait for the plants predator insect and have it for dinner. Some like ranching ants will milk and ranch the aphids that feed on a plant.

Sometimes only one or a few insects can eat a given plant, providing no food for competing insect species. (monarchs and milkweed ). Others like locusts, adapt to eat anything and everything in their path. Yet other insects can evolve to learn to eat the parts of the plants that do not contain a toxin.

All of which makes the garden a fascinating place.

More information for the curious:
Ecological Genomics of Plant-Insect Interactions
Plant insect interactions: An evolutionary arms race

One of the most fascinating things about plant and insect evolution is the defenses they mount to protect themselves from prey. Often plants or insects become toxic to the critters that eat them. Sometimes they grow to look like closely related toxic plants.

Milkweed has taken a different approach. It grows faster to better feed the caterpillars. This is great news for us monarch lovers. Monarchs have evolved to resist the toxins in milkweed. Tracing milkweed back it appears milkweed has given up on growing better hairs and more toxic latex and decided to concentrate on faster growth and repair.

The adage that your enemies know your weaknesses best is especially true in the case of plants and predators that have co-evolved: As the predators evolve new strategies for attack, plants counter with their own unique defenses.

Milkweed is the latest example of this response, according to Cornell research suggesting that plant may be shifting away from elaborate defenses against specialized caterpillars toward a more energy-efficient approach. Genetic analysis reveals an evolutionary trend for milkweed plants away from resisting predators to putting more effort into repairing themselves faster than caterpillars — particularly the monarch butterfly caterpillar — can eat them. . . . [ read more Milkweed's evolutionary approach to caterpillars: Counter appetite with fast repair]