Microbial incorporation of nitrogen in stream detritus

• Published in: Hydrobiologia Vol. 464; no. 1-3; pp. 27 - 35
• Main Authors: SANZONE, Diane M, TANK, Jennifer L, MEYER, Judy L, MULHOLLAND, Patrick J, FINDLAY, Stuart E. G
• Format: Journal Article
• Language: English
• Published: Dordrecht Springer 01.11.2001; Springer Nature B.V
• Subjects: Animal and plant ecology; Animal, plant and microbial ecology; Biofilms; Biological and medical sciences; Chloroform; Creeks; Creeks & streams; Detritus; Environmental research; Fresh water ecosystems; Fumigation; Fundamental and applied biological sciences. Psychology; Fungi; General aspects. Techniques; Leaves; Methods and techniques (sampling, tagging, trapping, modelling...); Microbial ecology; Microbiology; Nitrogen; Organic matter; Research parks; Streams; Synecology; USA, New Hampshire, Bear Brook; USA, North Carolina, Upper Ball Creek; USA, Tennessee, Walker Branch; Various environments (extraatmospheric space, air, water); Wood; North Carolina; United States; North America; America; USA, Tennessee; USA, North Carolina; USA, New Hampshire; Organic matter; Fumigation; Chloroform; Forest zone; Detritus; Plant leaf; Method; Radioisotope; Nitrogen; Wood waste; Freshwater environment; Fungi; Nitrogen cycle; Nitrogen fixation; Bacteria; Stream; Microbial community; Thallophyta
• ISSN: 0018-8158; 1573-5117
• DOI: 10.1023/A:1013930102876

We adapted the chloroform fumigation method to determine microbial nitrogen (N) and microbial incorporation of ^sup 15^N on three common substrates [leaves, wood and fine benthic organic matter (FBOM)] in three forest streams. We compared microbial N and ^sup 15^N content of samples collected during a 6-week ^sup 15^N-NH^sub 4^ tracer addition in each stream. The ^sup 15^N was added during late autumn to Upper Ball Creek, a second-order stream at the Coweeta Hydrologic Lab, North Carolina, U.S.A.; during spring to Walker Branch, a first-order stream on DOE's Oak Ridge National Environmental Research Park, Tennessee; and during summer to Bear Brook, a first-order stream in the Hubbard Brook Experimental Forest, New Hampshire. FBOM was the largest component of organic matter and N standing stock in all streams. Microbial N represented the highest proportion of total N in leaves and least in FBOM in Walker Branch and Bear Brook. In Upper Ball Creek, the proportion of microbial N was higher in FBOM than in used biofilm or on leaves. Standing stock of microbial N on leaves and in FBOM ranged from 37 mg N m^sup -2^ in Bear Brook to 301 mg N m^sup -2^ in Walker Branch. Percent of detrital N in living microbial cells was directly related to total microbial biomass (fungal and bacterial biomass) determined from microscopic counts. [partial differential]^sup 15^N values for microbes were generally higher than for bulk detritus, which would result in higher [partial differential]^sup 15^N values for animals preferentially consuming or assimilating microbial cells. The proportion of ^sup 15^N taken up by detritus during the ^sup 15^N experiments that remained in microbial cells by the end of the experiments was highest for wood biofilm in Upper Ball Creek (69%), leaves in Walker Branch (65%) and FBOM in Upper Ball Creek (31%). Lower retention proportions (<1-25%) were observed for other substrates. Our results suggest that microbial cells associated with leaves and wood biofilm were most active in ^sup 15^N-NH^sub 4^ immobilization, whereas microbial cells associated with FBOM immobilized little ^sup 15^N from stream water.[PUBLICATION ABSTRACT]