Factors controlling the formation of oxidized root channels: A review
Although root plaques and associated oxidized root channels are used for wetland identification as field indicators of wetland, hydrology, little information is available concerning their reliability as related to the environmental and biotic factors controlling their formation. Therefore, this review describes and evaluates the current state of knowledge of the factors controlling the formation of iron plaques and recommends research to address information gaps.
Both abiotic and biotic factors control the presence and degree of iron plaque formation. The most important abiotic factor is the availability of soil iron. However, the effect of site variation in soil physico-chemical characteristics (e.g., texture, organic matter, pH, Eh, and soil fertility), on iron availability and microbial activity can influence the formation and persistence of root plaques and oxidized root channels. Although the oxidizing capacity of the plant root is the most important biotic factor controlling plaque formation, only a limited number of wetland species have been evaluated for this ability, so species-specific differences are generally unknown.
Unlike some of the other hydrologic indicators used in wetland delineation (e.g., water marks on trees or sediment deposits) root plaques and oxidized root channels indicate soil saturation for a sufficient period to produce anaerobic soil conditions. Additionally, when found in conjunction with a living root, oxidized root channels indicate that the anaerobic conditions occurred within the life span of the plant root. Therefore, the presence of oxidized root channels and iron plaque surrounding living roots is a relatively good indicator of current wetland hydrologic conditions. However, research is needed to elucidate the relative abilities of different plant species to produce oxidized root channels, the temporal persistence of the root iron plaque and the role that soil physico-chemical condition plays in controlling plaque formation. Without a better understanding of the controls on iron plaque formation and disappearance, the absence of oxidized root channels, in itself, should not be used to indicate the absence of a wetland.
Key Wordswetland ecology wetland delineation iron plaques or deposits root oxygen loss wetland hydrologic indicators waterlogging
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