Ecological stoichiometry of wood eating insects - changes during ontogeny

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The vast majority of produced organic matter is being stored in wood, which is though and hard to digest and decompose. Even worse: it is extremely nutritionally scarce and decomposers needs nutrients for their growth, development and maturation. Dead wood is rich in sugars (cellulose, hemicelluloses) and lignin but try to grow your body basing solely on sugars! If digested, the wood may be source of energy but it is extremely scarce in nutrients others than sugars and this scarcity is high enough to prevent growth, development and maturation of organisms developing in dead wood. It is known, however, that the wood eaters are able to survive and thrive on this low-quality food source. How they do that? During the first few years of decay, dead wood nutritional composition becomes rearranged by fungi. Ingrowing fungal tissues in dead wood are connected to nutritional patches of the environment outside of the wood. These patches may consist of organic matter that is rich in proteins or they may consist of minerals and rocks. Rocks may be diluted by fungi, and are sources of specific atoms utilized to build fungal tissues. Fungi may even “predate” on soil fauna. The acquired nutrients are translocated from the outside of dead wood to the inside through the fungal mycelium. By consuming decomposed wood that is rich in fungal tissues, the dead-wood eater is able to grow, develop and reach maturity, but even then its growth is constrained, thus slow. To cope with this limitation, wood eaters prolong their development time to the period observed in nature (several years). During this time they are able to gather all the necessary building blocks (atoms) to compose their adult bodies. The prolonged development time is feasible since the inside of dead wood provides safer environment and better climatic condition and therefore reduced mortality, compared with the outside. Growth and development of dead-wood eating beetles are co-limited by the scarcity of non-sugar nutrients, rich in essential bioelements, like N, P, K, Na, Mg, Zn and Cu. Atoms of these elements compose nutrients used for body-building and body-maintenance of growing dead-wood eater. Fungi utilize deadwood as a source of energy and while overgrowing it during first four to five years of decay they enrich and rearrange dead wood nutritionally. By doing so they create a nutritional niche for dead-wood eaters, allowing them to undergo growth and development to maturity. In turn, xylophages affect dead wood, fragmenting it, shredding it and producing frass (wood pieces mixed with excrements which may be further decomposed by microorganisms), thereby contributing to further wood decomposition and nutrient cycling on the forest floor. Thanks to complicated ecological interactions between deadwood, fungi and dead-wood eaters huge mass of most common organic matter in land ecosystems – wood - is being continuously decomposed in forest ecosystems.

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