When plants use photosynthesis to create food they must "breathe in" carbon dioxide, but in order to do so they must also lose water. This water is then evaporated into the air in a process called transpiration. The amount of water lost and carbon dioxide gained is closely related with the amount of veins a plant has within its leaves. Much of transpiration happens within a plants leaves and the higher the concentration of veins within those leaves means more water lost and carbon dioxide gained. Angiosperms (flowering plants) have leaves with many dense veins that cause them to transpire more than other types of plants, allowing them to recycle more water back into their environment.
C. Kevin Boyce and Jung-Eun Lee headed the study performing several simulated scenarios investigating the impacts of removing angiosperms from certain ecosystems. Two different ecological and atmospheric models were used to produce data that were then coupled with previously observed data concerning average rainfall and temperature. Results were particularly shocking in rainforests, which are more abundant in species and number of angiosperms than any other type of ecosystem. Angiosperms near the Amazon increased rainfall in the driest month of the year by 20 mm and decreased the length of the dry season dramatically. However, angiosperms also worsen the monsoon season, but lengthen the overall wet season by as much as 85 days. More rainfall allows plants to flourish and grow rapidly which allows for heightened plant biodiversity. More plant biodiversity means more animal biodiversity; herbivores that are attracted by the variety and abundance of plants will in turn attract predators attracted by the variety and abundance of prey. Also, due to the increased moisture produced by flowering plants, many ecosystems that contain a large amount of angiosperms have high air humidity. High levels of humidity maintain ecosystem temperatures by cooling the air temperature during the day and by allowing them to retain heat given off by the sun at night.
Boyce and Lee demonstrate in the figure below how average temperature would increase without angiosperms present in the Southern American rainforest (red-dotted line) as opposed to observed and simulated temperatures of the ecosystem with angiosperms (black and blue lines respectively).
Figure 1. (Boyce and Lee 2010)
Temperatures are observed as being consistently several degrees colder in ecosystems that contain angiosperms in comparison to the same ecosystem where angiosperms have been removed. There is a particularly large disparity between the temperatures in October the start of the rain season where increased rain provided by flowering plants is necessary to maintain temperature.
It may be that flowering plants help increase rainfall, maintain temperature and promote biodiversity, but what does this mean for us? Without angiosperms many environments we live in would probably have a much different climate. The increased humidity produced by angiosperms would cease to exist meaning increased air temperature during the day and much lower temperatures at night. The Earth, especially in tropical areas such as the rainforests of South America, would be much drier without flowering plants due to a shorter rain season. Plant growth and diversity would be compromised by the lack of rainfall and the abundance of plants would diminish. Rainforests also recycle a large portion of the Earth's oxygen, removing carbon dioxide from the atmosphere. Fewer plants in these rainforests would mean less carbon dioxide recycled which would more than likely contribute to higher temperatures all over the Earth. Therefore, flowers not only help maintain Earth's temperature, but they also prevent it from increasing. Angiosperms also play an important role in industry. For instance, in agriculture almost all produce are angiosperms such as corn, wheat and apples. Many farmers rely on rainfall for the growth of their crops and look to angiosperms to produce feed for their livestock. Flowering plants are an essential part of the world's ecosystems and our lives, providing stabilized climates, increased rainfall, heightened biodiversity and are essential elements in our diets.
References:
Boyce, C.K., Lee, J. 2010. An exceptional role for flowering plant physiology in the expansion of tropical rainforests and biodiversity. Proceedings of the Royal Society B, 277: 3437-3443.
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