Small‐scale heterogeneity of microbial N uptake in streams and its implications at the ecosystem level. Issue 5 (May 2016)

• Record Type: Journal Article
• Authors: Peipoch, Marc; Gacia, Esperança; Bastias, Elliot; Serra, Alexandra; Proia, Lorenzo; Ribot, Miquel; Merbt, Stephanie N.; Martí, Eugènia
• Is Part Of: Ecology. Volume 97:Issue 5(2016)
• Page Start: 1329
• Page End: 1344
• Publication Date: 2016-05
• Subjects: streams -- nitrogen -- heterogeneity -- emergent properties -- cross‐scale interactions; Ecology -- Periodicals; Ecology -- Periodicals; Écologie -- Périodiques; Ecologie; Écologie; Écologie animale; Écologie végétale; Ecology; Periodicals; 577.05
• DOI: 10.1890/15-1210.1
• Languages: English
• ISSNs: 0012-9658

Abstract

Abstract: 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.