Geoscience Reference
In-Depth Information
by the host tree as well. Mychorrizal fungi are also present in the root mass and
assist the epiphyte in nutrient absorption. An amazing variety of lichens, mosses,
liverworts, ferns, cacti, orchids, and bromeliads, to name a few, are epiphytic. Spe-
cies diversity studies have found that a typical tropical canopy tree has at least 50
kinds of epiphytes living on it. Some epiphytes even grow on other epiphytes.
Nonphotosynthetic plants.
Nonphotosynthetic plants are heterotrophs—organisms
that need food from other organisms—that live on the forest floor. Some are para-
sites that derive their nutrients by tapping into the roots or stems of photosynthetic
species.
Rafflesia arnoldi
, a root parasite of a liana, has the world's largest flower,
more than 3 ft (91 cm) in diameter. It produces an odor similar to rotting flesh to
attract pollinating insects. Saprophytes, more correctly called saprotrophs, can be
nonphotosynthetic plants, fungi, and bacteria that derive their nutrients from
decaying organic matter. Other nonphotosynthetic plants are parasitic, such as
some orchids that use mychorrhizal fungus to facilitate food absorption.
Plant adaptations have already been mentioned in terms of life strategies and
placement in the canopy layers. Tropical trees and shrubs have developed adapta-
tions to expedite germination or seed dispersal as well. Some have large, fleshy
fruits that attract birds, mammals, and even fish as dispersal agents. The animals
will digest the flesh, leaving the seed to germinate in a new location. Plants grow-
ing in flooded forests have fruits that float. Additional plant adaptations include
strategies that enhance reproduction, or in some cases, predation. Many tropical
plants have evolved a mutualistic relationship with their pollinator either in terms
of attracting them to the flower through color, scent, or nectar, or by mimicry—
looking like the pollinator's mate, for example. Carnivorous plants create sweet or
bad smelling nectar that is attractive to their prey.
Root Systems
The forest may be the most obvious part of the biome, but what underlies the
immense and lush trees is a system of roots that support the trees, the backbone of
the forest. Little work has been done on the root systems within the tropical rainfor-
est; however, some basic types of roots and their roles within the rainforest are
understood. Aerial roots are common among tropical plants. They can provide a
measure of stability in unstable substrates and are a means of aboveground aeration
in water-soaked soils. For stranglers, aerial roots provide initial anchorage and sub-
sequent feeding and support.
Symbiotic or mutualistic associations of the root systems of trees with soil
microorganisms have been receiving more attention by researchers. The process of
recycling nutrients from the decaying material into the plant is largely dependent
on the activity of soil microbes, which aid in decomposition and in root absorption
of the nutrients. Complex shallow roots form a wide network with microbes pro-
viding a larger surface area to absorb the resources necessary to maintain the tallest
of trees.
