Details

Autor(en) / Beteiligte

• Houle, D
• Marty, C
• Duchesne, L

Titel

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

Ist Teil von

• Oecologia, 2015-01, Vol.177 (1), p.29-37

Ort / Verlag

Berlin/Heidelberg: Springer-Verlag

Erscheinungsjahr

2015

Quelle

MEDLINE

Beschreibungen/Notizen

• 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 Quebec, 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.