WHAT ABOUT PLANTS UNDER WATER?
ADAPTATIONS OF SUBMERGED AQUATIC PLANTS
ABSORPTION THROUGH LEAVES
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In a tank, aquatic plants also absorb nutrients readily through their leaves & stems, especially since many aquatic plants evolved to have reduced cuticles on their leaf surfaces to enable better gaseous exchange.
All the surface cells appear to be able to absorb water, nutrients and dissolved gases directly from the surrounding water. The internal system of tubes (xylem) which normally transports water from the roots to all parts of the plant is often greatly reduced, if not absent. Thus, if these plants are removed from the water, they wilt very quickly, even if the cut stems are placed in water as the normal water transport system is poorly developed. THE 'ROOT FEEDER' MYTHFor aquatic plants that have root systems, we can feed them similarly to terrestrial plants by substrate fertilisation. Somewhere along the hobby came the myth that plants with large root systems were "root feeders" while stem plants with smaller root systems fed through their leaves.
Many plants with large root systems have large root systems because they grow in fast flowing or seasonal waters and the large root systems serves as anchors to resist being washed away, for other plants roots serve as a storage system. /
There is little correlation between the size of a plant's root system and preference to take in nutrients through the substrate or water.
The 2Hr Aquarist |
HOW DO PLANTS ABSORB NUTRIENTS?
FOLIAR FEEDING IN TERRESTRIAL PLANTS
Terrestrial plants usually absorb most of their nutrients through their roots, as this is where soil and sediment gather in nature due to gravity.
However, since the 1950s, we know that plants can absorb nutrients through their leaves/shoots as well. This technique came to be known as foliar feeding and has since been widely accepted as an effective method of fertilisation in agriculture.
However, since the 1950s, we know that plants can absorb nutrients through their leaves/shoots as well. This technique came to be known as foliar feeding and has since been widely accepted as an effective method of fertilisation in agriculture.
Foliar feeding is a widely applied agricultural method since the 1950s
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The main advantage of foliar feeding over traditional fertilisation through soil is that it can be used to provide nutrients to plants which have had their roots damaged through drought or flooding. Nutrient absorption is also quicker as the elements do not need to make the journey of traveling up the stem of the plant. The high absorption rates through the leaves mean that there is less fertiliser run-off compared to fertilising the ground.
The main disadvantage of foliar feeding is that it is more labour intensive and must be done regularly, unlike soil which provides a long term storage of nutrients. |
ROOT vs WATER FERTILISATION
CAN I FOCUS ON JUST ONE?Joe Harvey's experiment on the right shows growing out a tank with only 1 side having root fertilisation, (osmocote tabs) while having good all round water column fertilisation.
Both swords and crypts grew equally well on the side without additional root fertilisation. In fact, most easier growing plants in the hobby can be grown without a substrate, hydroponic style, as long as there are enough nutrients in the water column ( this includes many species of hardy swords & crypts). |
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WHERE ROOT FERTILISATION HELPS
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Harder/picker species such Eriocaulons can benefit from root fertilization; similarly, Alternanthera reineckii grows better in soils than inert substrates.
Root feeding often works well for many plants because we can introduce a higher concentration of nutrients at the root zone via root tabs; whereas most hobbyists aren't comfortable with dosing extremely high level of nutrients into the water column. We may not want to dose ammonia (which is very effective as a nitrogen source for plants) into the water column, but containing it in the substrate works well. WHERE SUBSTRATE HELPSSubstrates can also hold nutrients in an available form for plants through their cation exchange capacity (CEC) and bacteria activity; deeper substrate with slightly anaerobic conditions can reduce Fe3+ into the more usable Fe2+ format.
Reactive elements such as Iron and phosphates may precipitate out of the water column (depending on tank chemistry) and end up in a higher concentration in the substrate. Organic humus can bind to these elements, making them available in a format more easily assimilated by plant roots. So substrate feeding does have it's purposes and applications; it's just not the way people think. I much prefer having a leaner water column - feeding hungry plants mainly through the roots. The other benefit of using soils in an aquarium vs inert substrate is better bacteria activity, which contributes to overall biologically stability of a tank. |
for folks that want results without the complexity
"APT COMPLETE"
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For many years, I maintained more than a dozen bottles of different fertilizers and painstakingly measured the volume of separate components I required. After a while, it became clear that a pre-mixed, custom blend would be far easier (and more consistent!).
This comprehensive fertilizer contains a mix of NPK, Fe and Trace elements. It contains all essential nutrients required by plants for growth except calcium which is readily available in the water supply. It is calibrated such that weekly water changes of 25-50% gives safe accumulation rates over a long time horizon. It uses 2 different types of iron chelators for easier uptake of iron across a wide range of tank parameters. The chelated trace format with minute copper content means that livestock should not be affected: tested at 10x dose on Bloody Mary shrimps with no impact. This product is now available here! |
An early prototype of 'APT Complete' (Advanced Planted Tank Complete)
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UP NEXT...
DOSING APPROACHES
- How do I do effective root fertilisation?
- What is the best water column fertilisation approach?
- How much to dose?
THE 2HR AQUARIST GUIDE TO FERTILISERS & DOSING
dosing
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root or
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how to
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dosing
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where
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