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Concept
Phytolith
Summary
Phytoliths (from Greek, "plant stone") are rigid, microscopic structures made of silica, found in some plant tissues and persisting after the decay of the plant. These plants take up silica from the soil, whereupon it is deposited within different intracellular and extracellular structures of the plant. Phytoliths come in varying shapes and sizes. Although some use "phytolith" to refer to all mineral secretions by plants, it more commonly refers to siliceous plant remains. In contrast, mineralized calcium secretions in cacti are composed of calcium oxalates.
The silica is absorbed in the form of monosilicic acid (Si(OH)4), and is carried by the plant's vascular system to the cell walls, cell lumen, and intercellular spaces. Depending on the plant taxa and soil condition, absorbed silica can range from 0.1% to 10% of the plant's total dry weight. When deposited, the silica replicates the structure of the cells, providing structural support to the plant. Phytoliths strengthen the plant against abiotic stressors such as salt runoff, metal toxicity, and extreme temperatures. Phytoliths can also protect the plant against biotic threats such as insects and fungal diseases.
There is still debate in the scientific community as to why plants form phytoliths, and whether silica should be considered an essential nutrient for plants. Studies that have grown plants in silica-free environments have typically found that plants lacking silica in the environment do not grow well. For example, the stems of certain plants will collapse when grown in soil lacking silica. In many cases, phytoliths appear to lend structure and support to the plant, much like the spicules in sponges and leather corals. Phytoliths may also provide plants with protection. These rigid silica structures help to make plants more difficult to consume and digest, lending the plant's tissues a grainy or prickly texture. Phytoliths also appear to provide physiologic benefits. Experimental studies have shown that the silicon dioxide in phytoliths may help to alleviate the damaging effects of toxic heavy metals, such as aluminum.
Official source
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