The Power of Silicon
To begin I will acknowledge one thing that many others have mentioned in regards to Silicon in the agriculture community. That is concept that silica, although it’s the second most abundant element on the surface of the earth (first is oxygen of course), is not considered a primary element for plants and it probably should be.
We understand as gardeners the 16 essential nutrients for plants, the macronutrients and the micronutrients. Within this range of elements Si is not included and we will review some facts on why this element is quite important in one’s garden.
In soils, silica is most commonly found in the form of SiO2 and longer chains of SiO2 become parts of different minerals, like the commonly known quartz. This form (SiO2) is not available to plants, but the slow and steady metabolic processes of microbes help convert this chemical form of silica into a plant soluble silicates (SiO4). Plants can take up silicates and there are a few forms out there that can be used as farmers and gardeners. In a natural healthy soil, silica is held in a solution form known as a silicic acid, H4SiO4 (orthosilicic acid). Maintaining a steady flow of silicic acid is a primary target of ours in the management of our ecosystems and is a primary limiting factor in soils not adequately maintained for the cyclic sustenance.
Another understanding of the Silica concentrations in plants have been observed and noted in the range of 0.2% – 10%. The concentrations of the essential elements Calcium, Magnesium, Phosphorous, and Sulfur all fall within this range for a healthy plant.
There are benefits to silica in regards to stress relief and overall vigor and resistance. When Silica is taken up into a plant it can take many modes of action, some of which are still to be elucidated. Silica enters a plant and it utilized in two ways that we currently know of and will be converted into two forms; a soluble form and polymerized form, for subsequent interactions.
The polymerized form of silica maintained in a plant will be used to enhance the plants defenses against pathogens, especially fungal pathogens (i.e. powdery milder, botrytis.) Silica in the plant has been shown to stimulate chitinases, peroxidases, polyphenol oxidases and flavonoid phytoalexins, and other phenolics which are all key to defend the plant against pathogens. To keep the explanation simple, the mechanisms by which silica is effective in pathogen defense is when enough silica has accumulated into a cell wall where the silica can toughen and increase the hardness of the cell wall enough to inhibit the enzymes the pathogens produce to break down cell walls, in turn rendering the pathogen ineffective. Proper silica supplementation has been seen to reduce fungal pathogenic stresses by up to 80%. Overall improved vigor and translocation of minerals and other elements creates a stronger more resistant plant as well which is fundamentally key in potentializing S.A.R. in a plant. When the plant polymerizes silica, it can also develop amorphous silica structures between cells and tissues and these structures are known as phytoliths. These phytoliths are accredited for rigidity, defense against pathogens and predators, and enhance plant resistance and vigor through biotic and abiotic stresses.
The soluble forms of silica within a plant help with other stresses caused by metal toxicities by enhancing the production of enzymatic and non-enzymatic antioxidants to translocate some metals (such as Mn). An increase in production of phenolics occurs and works as strong chelating agents to translocate certain metals (such as Al), both mechanisms are important and can help with microtoxicities and alleviating their imposed stress and damages.
Draught tolerance has been observed in plants using silica, this may be a result of decreased transpiration rates and the presence of phytoliths or other silicified structures providing a cooling mechanism by a suggestion of the heat load of the leaf being reduced due to their presence. This would in turn produce improved heat tolerance in plants.
Salt stress mitigation has also been observed by means of prevention of membrane oxidative damages due to the enhancement of enzymes.
There are still many features of silica to be understood and pathways to be elucidated when it comes to plant interaction. Silica is an essential element in our garden and hopefully this information helps you decide whether or not it deserves a spotlight for plant health in your operation.