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Small‐scale heterogeneity of microbial N uptake in streams and its implications at the ecosystem level
Author(s) -
Peipoch Marc,
Gacia Esperança,
Bastias Elliot,
Serra Alexandra,
Proia Lorenzo,
Ribot Miquel,
Merbt Stephanie N.,
Martí Eugènia
Publication year - 2016
Publication title -
ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.144
H-Index - 294
eISSN - 1939-9170
pISSN - 0012-9658
DOI - 10.1890/15-1210.1
Subject(s) - spatial heterogeneity , riparian zone , cycling , streams , environmental science , ecology , spatial ecology , ecosystem , context (archaeology) , benthic zone , scale (ratio) , river ecosystem , abundance (ecology) , biology , habitat , geography , computer network , paleontology , cartography , archaeology , computer science
Large‐scale factors associated with the environmental context of streams can explain a notable amount of variability in patterns of stream N cycling at the reach scale. However, when environmental factors fail to accurately predict stream responses at the reach level, focusing on emergent properties from small‐scale heterogeneity in N cycling rates may help understand observed patterns in stream N cycling. To address how small‐scale heterogeneity may contribute to shape patterns in whole‐reach N uptake, we examined the drivers and variation in microbial N uptake at small spatial scales in two stream reaches with different environmental constraints (i.e., riparian canopy). Our experimental design was based on two 15 N additions combined with a hierarchical sampling design from reach to microhabitat scales. Regardless of the degree of canopy cover, small‐scale heterogeneity of microbial N uptake ranged by three orders of magnitude, and was characterized by a low abundance of highly active microhabitats (i.e., hot spots). The presence of those hot spots of N uptake resulted in a nonlinear spatial distribution of microbial N uptake rates within the streambed, especially in the case of epilithon assemblages. Small‐scale heterogeneity in N uptake and turnover rates at the microhabitat scale was primarily driven by power relationships between N cycling rates and stream water velocity. Overall, fine benthic organic matter (FBOM ) assemblages responded clearly to changes in the degree of canopy cover, overwhelming small‐scale heterogeneity in its N uptake rates, and suggesting that FBOM contribution to whole‐reach N uptake was principally imposed by environmental constraints from larger scales. In contrast, N uptake rates by epilithon showed no significant response to different environmental influences, but identical local drivers and spatial variation in each study reach. Therefore, contribution of epilithon assemblages to whole‐reach N uptake was mainly associated with emerging properties from small‐scale heterogeneity at lower spatial scales.