Plant Physiology - Musienko, M. M. 2001

Heterotrophic Plant Nutrition
Saprophytes

Saprophytic Nutrition involves the utilization of organic matter from decomposing PLANT AND ANIMAL remains. While widely known among Algae, this mode of nutrition also occurs in angiosperms.

According to V.Yu. Semenenko, The ability to grow on organic media in the dark or in the light in the absence of СО₂ is characteristic of most species of blue-green, green, yellow-green, and other algal groups. Under certain conditions, their representatives switch from phototrophic nutrition to the assimilation of various Organic compounds, thereby exhibiting heterotrophic or photoheterotrophic Types of nutrition, often combining both. For instance, diatoms are predominantly photoautotrophic organisms containing chlorophylls a, c, b, e-carotenes, and xanthophylls, with fats as the End products of their photosynthetic activity. For optimal development, however, they also require an additional source of organic matter, specifically vitamin В₁₂. Deep-sea diatoms can transition entirely from autotrophic to heterotrophic nutrition, with some chlorophyll-free forms classified as obligate heterotrophs.

It should be noted that the transition to photoheterotrophic or heterotrophic nutrition is accompanied by the induction of additional enzyme systems. Such organisms directly utilize organic carbon sources, such as acetate via The Glyoxylate cycle and glucose via the hexokinase reaction. Algae are also capable of shifting from the assimilation of inorganic nitrate nitrogen to organic nitrogen sources, including amides, urea, and Amino Acids. Heterotrophic nitrogen assimilation has been thoroughly demonstrated experimentally in many algae as a facultative form of nitrogen nutrition.

The metabolic plasticity of algal nutrition has enabled them to achieve wide geographic distributions and occupy diverse ecological niches.

Research into algal nutrition pathways has facilitated the Introduction of numerous species into industrial-scale cultivation.

In angiosperms, saprophytic nutrition is relatively rare. These plants perform little to no Photosynthesis, instead relying on pre-formed organic matter derived from decaying plant and animal remains. This is characteristic of epiphytes—plants that grow on trees and shrubs (Fig. 139). For example, species of Myrmecodia are found in the tropical forests of Southeast Asia. The stems of these subshrubs form large tubers, often covered with spines, within the passages of which ants establish their colonies. As demonstrated through radioactive tracer studies, Myrmecodia utilizes the waste left by these ants as a source of nutrients.

Among orchids, mycotrophic forms are also found

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Fig. 139. Epiphytic plant

which rely on Symbiosis with Fungi. Frequently, this involves a symbiotic relationship where fungi act as the actual saprophytes, associating with higher plants in the form of mycorrhizae.