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Response of canopy nitrogen uptake to a rapid decrease in bulk nitrate deposition in two eastern Canadian boreal forests

Summary

Pubished in Oecologia 177(1): 29-37. https://doi.org/10.1007/s00442-014-3118-0

A few studies have reported a recent and rapid decline in NO3− deposition in eastern North America. Whether this trend can be observed at remote boreal sites with low rates of N deposition and how it could impact canopy uptake (CU) of N remain unknown. Here we report trends between 1997/1999 and 2012 for precipitation, throughfall N deposition as well as inorganic N CU for two boreal forest sites of Québec, Canada, with contrasted N deposition rates and tree species composition. NO3− bulk deposition declined by approximately 50 % at both sites over the studied period while no change was observed for NH4+. As a result, the contribution of NH4+ to inorganic N deposition changed from ~33 % to more than 50 % during the study period. On average, 52–59 % of N deposition was intercepted by the canopy, the retention being higher for NH4+ (60–67 %) than for NO3– (45–54 %). The decrease in NO3– bulk deposition and the increase in the NH4+:NO3− ratio had important impacts on N–canopy interactions. The contribution of NH4+ CU to that of total inorganic N CU increased at both sites but the trend was significant only at Tirasse (lowest N deposition). At this site, absolute NO3− CU significantly decreased (as did total N CU) during the study period, a consequence of the strong relationship (r2 = 0.88) between NO3− bulk deposition and NO3− CU. Our data suggest that N interactions with forest canopies may change rapidly with changes in N deposition as well as with tree species composition.

Sector(s): 

Forests

Categorie(s): 

Scientific Article

Theme(s): 

Ecosystems and Environment, Forestry Research, Forests

Departmental author(s): 

Duchesne, Louis, Houle, Daniel

Author(s)

HOULE, Daniel, Charles MARTY and Louis DUCHESNE

Year of publication :

2014

Format :

Paper

Keywords :

dépositions d'ézote, interception, forêt boréale, exutoire, pluvio-lessivats, écosystèmes et environnement, article scientifique de recherche forestière, ecosystems and environment, nitrogen deposition, canopy uptake, boreal forest, stream water, throughfall

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