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Bryophytes attenuate anthropogenic nitrogen inputs in boreal forests
Author(s) -
GUNDALE MICHAEL J.,
DELUCA THOMAS H.,
NORDIN ANNIKA
Publication year - 2011
Publication title -
global change biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 4.146
H-Index - 255
eISSN - 1365-2486
pISSN - 1354-1013
DOI - 10.1111/j.1365-2486.2011.02407.x
Subject(s) - bryophyte , moss , taiga , nitrogen fixation , boreal , ecosystem , nitrogen , biomass (ecology) , botany , agronomy , environmental science , biology , ecology , environmental chemistry , chemistry , organic chemistry
Productivity in boreal ecosystems is primarily limited by available soil nitrogen (N), and there is substantial interest in understanding whether deposition of anthropogenically derived reactive nitrogen (N r ) results in greater N availability to woody vegetation, which could result in greater carbon (C) sequestration. One factor that may limit the acquisition of N r by woody plants is the presence of bryophytes, which are a significant C and N pool, and a location where associative cyanobacterial N‐fixation occurs. Using a replicated stand‐scale N‐addition experiment (five levels: 0, 3, 6, 12, and 50 kg N ha −1 yr −1 ; n =6) in the boreal zone of northern Sweden, we tested the hypothesis that sequestration of N r into bryophyte tissues, and downregulation of N‐fixation would attenuate N r inputs, and thereby limit anthropogenic N r acquisition by woody plants. Our data showed that N‐fixation per unit moss mass and per unit area sharply decreased with increasing N addition. Additionally, the tissue N concentrations of Pleuorzium schreberi increased and its biomass decreased with increasing N addition. This response to increasing N addition caused the P. schreberi N pool to be stable at all but the highest N addition rate, where it significantly decreased. The combined effects of changed N‐fixation and P. schreberi biomass N accounted for 56.7% of cumulative N r additions at the lowest N r addition rate, but only a minor fraction for all other treatments. This ‘bryophyte effect’ can in part explain why soil inorganic N availability and acquisition by woody plants (indicated by their δ 15 N signatures) remained unchanged up to N addition rates of 12 kg ha −1 yr −1 or greater. Finally, we demonstrate that approximately 71.8% of the boreal forest experiences N r deposition rates at or below 3 kg ha −1 yr −1 , suggesting that bryophytes likely limit woody plant acquisition of ambient anthropogenic N r inputs throughout a majority of the boreal forest.