Leaves Adjust to Changing Environment

many stems of bright green leaves shaped like long thin arrowheads

Biological Strategy

Duck potato

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Image: USFWS Mountain Prairie / Wikimedia Commons / CC BY - Creative Commons Attribution alone

Adapt Phenotype

Living systems evolve over time in response to selective pressures. Selective pressures are environmental factors that reduce the reproductive success of some individuals in a population. Genetic makeup (genotype) is one way in which living systems mitigate selective pressures, but another is adaptable phenotypes. A phenotype is an observable characteristic that can be thought of as the expression of the genotype, combined with modifications caused by the environment or developmental conditions. Individuals, populations, or ecosystems that have phenotypes capable of reducing the effects of selective pressures can survive. Some plants, for example, modify their leaf shape in response to changing environmental conditions. A single olive tree has variable leaf shapes on sunny compared to shady areas of the tree, yet the next year, those same buds may develop differently shaped leaves.

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Store Gases

Living systems sometimes store gases, such as oxygen, to help maximize respiration or for a variety of other purposes. Gases are often difficult to store because they dissipate and can easily escape. Therefore, most gas storage in living systems can only be temporary. Some examples are fish swim bladders used to control buoyancy, and respiratory sacs in birds that help them maximize access to oxygenated air.

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Capture, Absorb, or Filter Gases

Oxygen, carbon dioxide, and nitrogen are all gases of particular importance to living systems. Living systems obtain these gases from water and air by trapping them, absorbing them across surfaces, or filtering them. Gases are low in density and viscosity, and when dissolved in liquids, are very low in concentration–so extracting them requires specialized strategies. As a result, living systems use the properties of gases, liquids, and solids to assist in capture, absorption, and filtering. For example, fish gills have many filaments to create a large surface area to maximize how many blood vessels come in close contact with oxygen dissolved in the water.

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Flowering Plants

Clade Angiosperms (“receptacle seed”): Dandelions, oaks, grasses, cacti, apples

With 416 families containing some 300,000 known species, angiosperms are the most diverse group of plants, and they can be found around the globe in a wide variety of habitats. They are characterized by seeds that grow enclosed in ovaries, which are enclosed in flowers. The floral organs then develop into fruits of myriad kinds and dimensions, from simple seed casings on maples to elaborate fleshy growths like papayas. The oldest flower known from fossils, Montsechia vidalii, appeared during the Jurassic Period 130 million years ago. They are the primary food source for herbivorous animals, which in turn makes them the indirect food source for carnivores as well.

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Leaves of Sagittaria latifolia allow survival in fluctuating water levels by changing leaf type.

“Fluctuations in water levels are a common feature of wetlands (Chapter 2). Consequently, wetland plants can encounter a variety of water depths seasonally and interannually. Even submersed plants may have to endure periods without standing water and most have a terrestrial form. Not surprisingly, wetland plants show a great deal of phenotypic plasticity (Fig. 4.9), and this allows them to adjust their growth as water levels change. One type of phenotypic plasticity that is widespread among macrophytes is heterophylly (Wells and Pigliucci 2000; Minorsky 2003; Dorken and Barrett 2004). Heterophylly is the ability to produce different leaf types (Figs 4.6 and 4.9). Two kinds of leaves are commonly produced by herbaceous wetland species, submerged and aerial. Submerged leaves are thin, lack or have a greatly reduced cuticle, and lack functional stomata. Aerial leaves are thicker, have a cuticle, and have stomata (Fig. 4.6). Changes in leaf shape, size, and thickness and petiole or leaf/shoot length are common in facultatively heterophyllous species. The porosity of their roots can also change significantly as soils become anoxic after flooding in flood-responders (Fig. 4.7). These morphological responses primarily serve as a way to improve oxygen uptake by leaves, the volume of internal gas storage, and the efficiency of internal gas redistribution by diffusion.” (van der Valk 2006:67)

Last Updated October 21, 2016

References

Book

The Biology of Freshwater Wetlands (Biology of Habitats)

February 8, 2021 | Arnold G. van der Valk

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