Regulation of the Growth and Activity of Leaf-decomposing Fungi by Dissolved Nutrients (N and P) in Streams

真菌已被证明在溪流中以碎屑为基础的食物链中发挥关键作用，调节能量流动。然而，直到最近，还没有可用的方法来确定真菌在任何环境中的瞬时生长速度。因此，关于真菌产量或通过真菌群落的能量流动的定量数据是不可用的。最近报道了一种通过测定~(14)C-乙酸酯掺入麦角甾醇的速率来估算天然真菌群落瞬时生长速率的方法。拟议的研究旨在调整和评估这种方法，以用于溪流中分解叶片的真菌群落。实验室研究将确定将醋酸盐并入麦角甾醇的最佳条件，并确定将并入率转换为个别真菌种类的生长率的因素。将利用对生长在叶片材料上的单个物种的实验室研究，将14C-乙酸法确定的生长速度和产量估计值与独立于真菌生物量、呼吸和分生孢子产量变化确定的产量估计值进行比较。然后，该方法将被用来估计在水化学不同的两条溪流中叶子分解期间真菌群落的生长速度和产量。这些结果将与其他活性指标进行比较，包括总微生物呼吸量、总微生物生物量和溪流真菌的产孢率。这些研究将有助于评估一种新的方法，该方法有可能对我们对环境中真菌活动的理解产生重大影响，并应有助于提供有关溪流中真菌生产力的必要信息。

Fungi have been demonstrated to play key roles in mediating energy flow in the detritus-based food chains in streams. Until recently, however, there have been no methods available that would allow determination of instantaneous growth rates of fungi in any environment. Consequently, quantitative data concerning fungal production or flow of energy through the fungal community are not available. A method for estimating instantaneous growth rates of natural fungal communities by determining rates of incorporation of 14C-acetate into ergosterol was recently described. The proposed studies are designed to adapt and evaluate this method for use on the leaf-decomposing fungal communities in streams. Laboratory studies will establish optimum conditions for the incorporation of acetate into ergosterol and determine factors for converting incorporation rates into growth rates of individual fungal species. Laboratory studies of individual species growing on leaf material will be used to compare estimates of growth rates and production determined by the 14C-acetate method with production estimates determined independently from changes in fungal biomass, respiration and conidium production. The method will then be used to estimate growth rates and production of fungal communities during the decomposition of leaves in two streams that differ in water chemistry. These results will be compared with other measures of activity including total microbial respiration, total microbial biomass and sporulation rates of stream fungi. These studies will contribute to the assessment of a new method that has the potential to make a significant impact on our understanding of fungal activities in the environment and should contribute needed information concerning the productivity of fungi in streams.