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a Carbon measured as mg g l.

Source: After Clinton et al. (1999) with permission of N. Z. Journal of Botany.

a Carbon measured as mg g l.

Source: After Clinton et al. (1999) with permission of N. Z. Journal of Botany.

pulses of nutrients within the forest ecosystem. In temperate zones, the spring and fall abundance of fruit body production may coincide with the high root growth and high nutrient demand by trees at these periods, a correlation that has yet to made by observation and measurement. Marumoto et al. (1982) suggested a longer turnover time for fungi than bacteria in their experimental decomposition study of killed bacteria, fungi, and combined bacteria and fungal cells. Using 14C and 15N labeling techniques for each of the cells, they showed that the rate of carbon loss as CO2 was similar between microbe sources, but that the rate of mineralization of nitrogen as both NH4 and NO3-N was slower in the decomposition of fungal cells.

Lodge (1993) discussed the role of fungi in nutrient cycling in tropical forest ecosystems (Table 2.18). These systems have large nutrient capital in plant biomass but are frequently limited by nutrient supply from soil. Much of this is caused by phosphorus binding to aluminum and iron oxides, and thereby being less plant-available. Due to high rainfall, other plant essential nutrients, nitrogen and potassium, are likely to be leached from the rooting zone. Fungal biomass (5 to 5 mg g"1 litter and 2.5 to 3 mg g"1 soil; reports of 8 to 333 g m"2) in these soils contains a large reservoir of nutrients that can be slowly released on death and decomposition. This is especially true for phosphorus, where the concentration in fungal tissues can reach 5 to 36 mg g"1 and the phosphorus content of leaf litter can increase 10-fold due to immobilization by fungi. Lodge (1993) also showed that the biomass of fungi in wet tropical forest soils is significantly and positively correlated with soil moisture and the amount of rainfall in the preceding week.

Table 2.18 Proportion of Nutrient Elements Contained in Fungal Biomass in Wet Tropical Soil Systems Demonstrating the Importance of Fungi as Nutrient Reservoirs

Element

Fungal as percentage of leaf litter

Fungal as percentage of soil extractable

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