Wetlands calcareous

The sensitivity of plants to zinc deficiency is variable among species. For example, oats, wheat, barley, and rye are not very sensitive, whereas potatoes, tomatoes, lucerne, and red clover have a medium sensitivity. By contrast, maize, hops, flax, and soybeans require a high level of zinc supply (Viets 1966 see also Table 3.29-3, p. 612 in Henkin 1984). Soils associated with zinc deficiency in plant are usually low in organic matter content and neutral to alkaline in reaction (Pais and Jones 1997). In Asia, zinc deficiency has been identified as the most widespread micronutritional disorder of wetland rice which occurs on sodic, calcareous, and poorly drained soils. 

In mineral wetland soils, A1 and Fe are major constituents, which regulate phosphorus solubility by forming insoluble phosphate minerals. These minerals are sensitive to changes in soil pH, whereas phosphorus minerals associated with Fe are redox sensitive. Phosphate minerals associated with A1 and Fe are stable under acidic soil conditions, and their solubility increases with an increase in pH. Solubility of calcium phosphates decreases with an increase in pH. In soils dominated by CaCOj (calcareous soils), when Ca + activity is depressed, phosphorus solubility increases. 

In calcium-dominated wetlands, high concentrations of Ca can result in formation of complex calcium phosphate compounds of varying solubilities such as calcium phosphate, dicalcium phosphate, beta-tricalcium phosphate, octacalcium phosphate, and hydroxyapatite. Under these conditions, the phosphorus concentration in the soil pore water of calcareous soils is a function of Ca + activity. Solubility of these compounds decreases with an increase in Ca content. Insoluble beta-tricalcium phosphate is more likely to be found at a high pH. Thermodynamically, apatite is the most stable compound in soils. At relatively high phosphate concentrations, dicalcium phosphate or octacalcium phosphate may form and slowly transform to the more stable phase hydroxyapatite. These precipitation reactions can occur on the surfaces of calcite. The amount of exposed surface will determine the amount of phosphorus precipitated. In a Ca-saturated clay, calcium... 

The precipitation of phosphorus as calcium phosphate has been studied extensively by soil scientists in evaluating applied fertilizer reactions. Initial adsorption of phosphorus onto calcite is followed by precipitation as calcium phosphate. Similar reactions can occur at the soil-flood-water interface of calcareous wetlands. For example, long-term phosphorus accumulation in the Everglades marsh is linearly correlated with calcium accumulation, suggesting the possibility of phosphorus and CaCOj interactions (Reddy et al., 1993). 

The Amblystegiaceae, as traditionally circumscribed, consists of between 120 and 170 species. These are most likely the most important mosses in relatively mineral-rich to calcareous wetlands in temperate to polar environments. They are also abundant in many other humid habitats of the temperate zones, as well as in wetlands at high altitudes in tropical and subtropical areas (cf., Hedenas, 1999,2003a). Because of their importance and widespread occurrence in wetland habitats... 

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