Author: Howarth, R.W.; Fisher, S.G.
Description: We investigated the effects of long-term enrichment with nitrate, phosphate, and nitrate+phosphate on the first 5 weeks of leaf detritus processing in laboratory stream microecosystems. Enrichment with nitrate+phosphate accelerated leaf weight loss and increased rates of respiration associated with the leaves. However, whole-system respiration was little changed from that observed in the control stream since respiration in the water was greatly reduced. Enrichment with phosphate alone had little effect except to lower respiration associated with leaf discs. Enrichment with nitrate alone also decreased leaf-disc respiration but resulted in a greatly increased rate of respiration in the water. Net leaching and fragmentation of carbon from the leaves was also increased by nitrate enrichment.
Nitrogen and phosphorus levels in leaf material were little affected by enrichment with nitrate or phosphorus alone. Leaves in those streams and in the control stream released nitrogen and phosphorus to the water. In contrast, percent nitrogen and phosphorus increased greatly in the leaves in the stream enriched with both nitrate and phosphate. The leaves in this system immobilized both nitrogen and phosphorus from the water.
We also studied the importance of nitrogen fixation as a vector for nitrogen incorporation associated with leaf decomposition in streams. Somewhat surprisingly, fixation by microbes associated with the leaves and by microbes suspended in the water occurred under all three experimental enrichment treatments as well as in the control, casting doubt on the effectiveness of nitrate in inhibiting nitrogenase synthesis in nature. However, N2-fixation is only a minor source of nitrogen for leaves decaying under the conditions studied.
Subject Headings: Carbon; Phosphorous; Microecosystems; Nutrients
Keywords: Carbon, nitrogen, and phosphorus dynamics during leaf decay in nutrient-enriched stream microecosystems
Publication year: 1976
Journal or book title: Freshwater Biology
Volume: 6
Issue: 3
Pages: 221-228
Find the full text : https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1365-2427.1976.tb01608.x
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Type: Journal Article
Serial number: 2694