It's hard to imagine
air being in short supply—after all, we’re surrounded by it. And, in most cases,
availability of air isn’t a limiting factor in plant growth. Let’s look at some
cases where it is.Most plants take in air through
their leaf stomata. Roots, however, also need oxygen for respiration, which is why most
plants won’t survive in saturated soil. Plants growing in swampy regions have evolved
some interesting ways to cope with soils deficient in oxygen.
- The black mangrove grows in shallow water or mud, and sends
out "air roots", or pneumoatophores, that poke up above the water surface to
take in air.
- Water lilies have stomata on their upper leaf surfaces,
instead of on the undersides of the leaves like most plants.
- Many aquatic and wetland plants have interior chambers in
the leaf petioles and stems through which oxygen diffuses to the plant roots.
Here are some other examples of interesting adaptations
plants have for getting the air they need.
- Some plants growing in damp environments carry their
stomata on raised stalks. This helps increase air circulation around them and prevents
them from being blocked by water drops.
- Plants growing fully submersed must meet their oxygen
requirements from oxygen dissolved in the water. These plants often have highly dissected,
or feathery, leaves. This characteristic dramatically increases the surface area of the
leaf and maximizes the plant’s ability to take in dissolved oxygen. (Think of
a fish’s gills—the feathery form maximizes surface area, and therefore oxygen
absorption.)
- You may have noticed small spots or lines on the bark of
many woody plants’ twigs. These are small pores called lenticels, consisting of
loosely-packed cork cells, and provide a pathway for air to reach the twigs’ growing
tissues.
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