Kisel som växtstärkande medel
en litteraturstudie
Sammanfattning
Kisel (Si) är det näst vanligaste ämnet (drygt 25 %) i berggrunden. Bara en del av detta är tillgängligt som monokiselsyra, den form i vilken kisel är upptagbart för växter. Jordens kiselinnehåll är beroende av bergets vittring. Mycket höga halter av kisel återfinns i naturen i vulkaniska substrat (pimpsten innehåller drygt 66 % Si och scoria närmare 47 % Si), i diatomit (ett mineral bestående av resterna från encelliga kiselhaltiga alger, s.k. diatoméer) innehållande 66 % Si, scoria approximatly 47% Si), in diatomite (a mineral consisting of the remainings of single celled algae, diatoms containing < 40 % Si) and in some clays (30-60% Si). Plant species differ in silica uptake. Higher plants can be devided into three categories (1) plants with active uptake, (2) plants with passive uptake, and (3) plants that avoid silica. Also the deposition site for silica varies between plant species. However older plantparts usually contain more silica than younger ones. Once the compound has been deposited it becomes completely immobile in the plant.
Silica is usually not viewed as an essential nutrient for plants. In order to be considered essential to plants, it is required that the plant is not able to complete it´s life cycle without this element. Today there is no evidence that silica would have this effect. On the other hand there are many studies that show beneficial effects of silica on plants. Among these silica has shown to have a protecting effect against attack of plant pathogens, primary fungi. It has been proposed that silica acts as a mechanical barrier, by depositing under the plant epidermis and thereby restraining the fungal hyphae from penetrating the plant. There are also distinct indication that silica might decrease the plant´s transpiration, increase photosynthetic activity, and promote uptake of other elements.