Symbiosis – the ways that plant interacts

Plants of the same and different species interact with each other in the ecosystem actively or inactively in many different ways. The ecological relationships are known as symbiosis, which means “living together”. It is a relationship between any type of close and long-term biological interaction between two different biological organisms, mainly commensalism, mutualism, parasitism, and other types of interaction. The organisms, known as symbiont, can be of the same or different species of plants and animals. Generally, the organism with larger biomass is considered as the host while the smaller is a symbiont.

Commensalism is the interaction between host and symbiont that benefits one of the species, but neither harms nor helps the other. It is often denoted as +/0, where + indicated the species that gained benefits, while 0 means the species gained no advantages nor disadvantages. Commensalism is more common in nature as compared to mutualism and parasitism. For example, epiphytes are the plants that cling on trees but not parasitic. Epiphytes such as mosses, liverworts, lichens, orchids, air plants, ferns, and bromeliads grow on tree trunks for better light conditions and avoid herbivores. Epiphytes are mostly shade-tolerant species that strongly depends on the trees to provide their dim habitat. Some wildflower species grow optimally under the trees in shaded and forest floor environments. Epiphytes usually obtain the water through the moisture in the air or from the rain as well as the debris accumulating around it and some specialized structures that helped to retain the water source. Yet the survival and reproduction of the host trees are not affected by the epiphytes.

Mutualism is an interaction that brings a win-win situation to both species, which is indicated as (+/+). Many relationships involved mutualism is between plants and animals. For example, plants provide honey to pollinators, while pollinators help the plants to pollinate. Fruiting plants give the source of food as fruits to animals while animals disperse the seeds from an area to another area. Intercropping in agriculture practice, which is the cultivation of two or more crops simultaneously in the same field, normally brings benefits to all parties through improved soil conditions, better light, water, and pest management. However, these mutualisms among plants do not occur naturally in the wild. After all, as autotrophic, plants survive by photosynthesis with sunlight and taking nutrients from the soil, not from other plants. The closest example would be the relationship between fungus and plants, in which mycorrhizae around the roots of the plants get carbohydrates from plants and provide limiting nutrients such as phosphorus to the plant as a return. Lichen is another typical example of mutualism, in which fungus stores the water and provides mechanical structure to alga, as a return, algae supply carbohydrate to fungi by photosynthesis. Lichen is plant-like, but not plants.

Commensalism and mutualism are considered as positive interactions. While parasitism is an interaction that symbiont gets the benefits while the host is harmed by the relationship. Parasitism is an exploitative interaction that is indicated by +/- and is very common in nature, that about one-third of the species on earth are parasites. Parasitic plants made up of one percent of angiosperms. Some parasites change the behavior of their host in the ways that there is an increase in the likelihood parasites affect the survival of the host significantly in terms of reproduction as well as the density of the host population directly or indirectly. Few parasitic plants derive some or all of the nutrients from living on the hosts. Parasitic plants have haustoria, a structure of modified roots, that can penetrate the host plants then connect to the conductive system such as xylem and phloem for food and nutrients. Parasitic plants such as mistletoe and Rafflesia sp.. can “detect” or locate their host plants by the chemicals by the shoots and root of the host in the air or soil. Rafflesia sp. is host-specific, which only target on the vine of Tetrastigma sp..

Other ecological interactions are competition and predation. Competition (-/-) in plants sometimes benefits the plants in the big picture. Plants of the same species are more likely to compete for the same nutrient composition in an area. They also compete for water, space, and sunlight among each other. Therefore, plants have various seed dispersal strategies utilizing the wind, river, or moving animals, finding new land to reduce the competition between the mother plants and the progeny. The design for the competition is to produce large quantities of seeds or offsprings, normally in thousands or millions, most will be wiped out during the adventure, but even if only one plant succeeds, its the success of the group. The survived plant species usually have better characteristics such as many attractive flowers, more robust stem, and root systems. Predation (+/-)  is referring to the interaction that involved a small organism (prey) as a victim or as food and a giant organism (predator) as a hunter. The typical examples of predation in plants can be observed from carnivorous plants such as Venus flytrap, pitchers, and flypapers that obtain nutrients from preying insects and small animals using various trapping mechanisms.

Another symbiosis, saprophytism is the interaction and the ability of the individual organism to live in dead or decaying organic matters. The plants are known as saprophytes. Most fungi are saprophytes that are usually found on rotten wood. However, a few flowering plants saprophytes including the Indian pipe plants and plants of the families of Pyrolaceae, Orchidaceae, and Burmanniaceae. Most saprophytes do not possess chlorophyll, therefore are unable to produce food for themselves. They strongly depend on the decaying organic matter by breaking down the organic matter into their food with the aid of some enzymes. However, it’s more accurate to describe them as mycotrophic parasitic plants because they receive nutrients through mycorrhizal fungus as they do carry out photosynthesis.

The symbiotic interaction allows plants to communicate with each other, it’s the language of plants in which they talk to each other for their own interests. The communications are often done through chemotaxis in which plants are attracted by the light, water, space, and nutrients. The networks through these interactions allow maximizing energy circulation and space usage and eventually contribute to a more diversified ecosystem.

Further readings:

Urry, L. A., Cain, M. L., Wasserman, S. A., Minorsky, P. V., & Reece, J. B. (2017). Campbell biology. Pearson Education, Incorporated.