Fungal growth, production, and sporulation during leaf decomposition in two streams

Abstract

I examined the activity of fungi associated with yellow poplar (Liriodendron tulipifera) and white oak (Quercus alba) leaves in two streams that differed in pH and alkalinity (a hard water stream [pH 8.0] and a soft water stream [pH 6.7]) and contained low concentrations of dissolved nitrogen (<35 microg liter(-1)) and phosphorus (<3 microg liter(-1)). The leaves of each species decomposed faster in the hard water stream (decomposition rates, 0.010 and 0.007 day(-1) for yellow poplar and oak, respectively) than in the soft water stream (decomposition rates, 0.005 and 0.004 day(-1) for yellow poplar and oak, respectively). However, within each stream, the rates of decomposition of the leaves of the two species were not significantly different. During the decomposition of leaves, the fungal biomasses determined from ergosterol concentrations, the production rates determined from rates of incorporation of [(14)C]acetate into ergosterol, and the sporulation rates associated with leaves were dynamic, typically increasing to maxima and then declining. The maximum rates of fungal production and sporulation associated with yellow poplar leaves were greater than the corresponding rates associated with white oak leaves in the hard water stream but not in the soft water stream. The maximum rates of fungal production associated with the leaves of the two species were higher in the hard water stream (5.8 mg g(-1) day(-1) on yellow poplar leaves and 3.1 mg g(-1) day(-1) on oak leaves) than in the soft water stream (1.6 mg g(-1) day(-1) on yellow poplar leaves and 0.9 mg g(-1) day(-1) on oak leaves), suggesting that effects of water chemistry other than the N and P concentrations, such as pH or alkalinity, may be important in regulating fungal activity in streams. In contrast, the amount of fungal biomass (as determined from ergosterol concentrations) on yellow poplar leaves was greater in the soft water stream (12.8% of detrital mass) than in the hard water stream (9.6% of detrital mass). This appeared to be due to the decreased amount of fungal biomass that was converted to conidia and released from the leaf detritus in the soft water stream.

FIG. 1

AFDM of leaf detritus remaining in the two streams. Symbols: ●, means for white oak; ○, means for yellow poplar. The error bars indicate standard errors of the means.

FIG. 2

Mean daily temperatures in the two streams.

FIG. 3

Ergosterol concentrations (expressed in micrograms per gram of leaf detritus AFDM) associated with leaves during decomposition in the two streams. Symbols: ●, means for white oak; ○, means for yellow poplar. The error bars indicate standard errors of the means.

FIG. 4

Nitrogen concentrations (expressed as a percentage of leaf AFDM) associated with leaves during decomposition in the two streams. Symbols: ●, means for white oak; ○, means for yellow poplar. The error bars indicate standard errors of the means.

FIG. 5

Rates of fungal production (expressed in milligrams of fungus per gram of leaf detritus AFDM per day) associated with leaves during decomposition in the two streams. Symbols: ●, means for white oak; ○, means for yellow poplar. The error bars indicate standard errors of the means.

FIG. 6

Sporulation rates (expressed in number of spores produced per milligram of leaf detritus AFDM per day) associated with leaves during decomposition in the two streams. Symbols: ●, means for white oak; ○, means for yellow poplar. The error bars indicate standard errors of the means.