Decompostion : The Dark Side Of Aquatic Gardening

There are moments in the hobby where beautiful healthy plants like Elatine triandra, Staurogyne repens, Eriocaulon, Downoi Helferi and cryptocoryne suddenly take a turn for the worse and melt with no warning. Melting inherently isn’t terrible when isolated to an individual plant but wild fire melt spreading across a tank can be unsettling.

Before describing preventive measures, it is helpful to first understand what is happening.

When part of a plant dies, decomposition occurs and what we relate as melt. Decomposition is the natural process of dead animal or plant tissue being rotted or broken down. This process is carried out by invertebrates, fungi and bacteria. The result of decomposition is that the building blocks required for life can be recycled.

During the process of decomposition, the decomposers provide food for themselves by extracting chemicals from the dead bodies or organic wastes; using these to produce energy. The decomposers will then produce waste of their own.  In turn, this will also decompose, eventually returning nutrients to the soil. These nutrients can then be taken up by the roots of living plants enabling them to grow and develop, so that organic material is naturally recycled.  Virtually nothing goes to waste in nature.  When an animal dies and decomposes, usually only the bones remain, but even these will decompose over a much longer period of time.

Decomposition of plant matter occurs in several stages. It begins with leaching by water; the most easily lost and soluble carbon compounds are liberated in this process. Another early process is physical breakup or fragmentation of the plant material into smaller bits which have greater surface area for microbial colonization and attack. In smaller dead plants, this process is largely carried out by the soil invertebrate fauna, whereas in the larger plants, primarily parasitic life-forms such as insects and fungi play a major breakdown role and are not assisted by numerous detritivore species. Following this, the plant detritus (consisting of cellulose, hemicellulose, microbial products, and lignin) undergoes chemical alteration by microbes. Different types of compounds decompose at different rates. This is dependent on their chemical structure.

For instance, lignin is a component of wood, which is relatively resistant to decomposition and can in fact only be decomposed by certain fungi, such as the black-rot fungi. Said fungi are thought to be seeking the nitrogen content of lignin rather than its carbon content. Lignin is one such remaining product of decomposing plants with a very complex chemical structure causing the rate of microbial breakdown to slow. Warmth determines the speed of plant decay, with the rate of decay increasing as heat increases, i.e. a plant in a warm environment will decay over a shorter period of time. In most grassland ecosystems, natural damage from fire, insects that feed on decaying matter, termites, grazing mammals, and the physical movement of animals through the grass are the primary agents of breakdown and nutrient cycling, while bacteria and fungi play the main roles in further decomposition.

Situations like post shipment damage, transition from to submersed, hard to soft waters are all possibilities but hardly ever definitive.

Trouble areas and resolution

1. Stagnant areas
Zones in the aquarium where current is low or non-existent prohibit the chemical exchange of plants through the water column. Often under dense carpets, melt occurs as detritus begins to form and starts to spread indiscriminately to adjacent flora. Where there is a detris build up, simply swirl around the substrate to lift the debris into the water column for siphoning. Adjust filter return flow or add additional powerheads to encourage flow.

2. Post shipment plants

Plants that are improperly packed may experience extreme temperatures, compression which are the two deadliest causes of loss. stem plants may often arrive with melted or dropped leaves with bare stems remaining.
Where plant melt is visible, amputate the damaged areas.

3. Dense/compact growth
Plants that have been neglected and grow compact or densely need to be pruned and portioned out. All plants need space to stretch and rubbing often encourages damage which leads to rotting and melt. Do not leave maintenance duties for too long.

4. Water parameters
Plants have tolerances for a variety of water paramenters. Many varieties from west africa can tolerate higher temperatures and alkaline environments where those of South America and asia associate better with acidic cooler waters. When dealing with more demanding species, acclimation considerations may be required.

5. Inadequate light
High light plants grown under lower or lesser quality light may not survive and begin melting. Know your species and abide by their environmental needs. This should be high on the priority list when selecting plants.

6. Fertilizer/toxicity burn
This is commonly seen when root tabs are placed too near to root feeder plants or when planting in a newly established aquarium with aquasoil. Please use root tabs sparingly as they generally are positioned far enough so roots creep towards them and learn about aqua soil cycling before using.

7. Nutrient starvation

The opposite of #6 is transitioning a plant grown in soil to inert gravel. A good example is planting a high tech grown plant into a low tech environment. Insufficent CO2. It will not be pretty. and likely will not last.
In summary, Melting is an event that requires prompt attention as it may spread on to healthy plants without warning. Leaving this event unattended for several hours could make the difference between losing 2-3 plants and losing 2/3rd of an established carpet. Do not be afraid to sacrifice a few plants to save the majority. Watch for signs and take action!

Thanks for reading!

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The Aquatic Plant Society
The Aquatic Plant Society is dedicated to promoting the science and aesthetic of the Planted Aquarium. We are committed to a responsible and environmentally conscious pursuit of the hobby, and invite all to share in and add to our knowledge.