Effects of nitrogen additions on nitrogen resorption and use efficiencies and foliar litterfall of six tree species in a mixed birch and poplar forest, northeastern China

Abstract

We studied nitrogen (N) resorption efficiencies (NRE), N use efficiencies (NUE), carbon-to-nitrogen ratios of green (C:Ngreen) and senesced (C:Nsenesced) foliage, and foliar litterfall for six tree species under three N treatments (control, no N addition; low N addition, 2.5 g N·m–2·year–1; and high N addition, 5.0 g N·m–2·year–1) in a mixed birch and poplar forest in northeastern China in 2007 and 2008. N additions were initiated in 2006. NRE, NUE, C:Ngreen, and C:Nsenesced were significantly decreased by N additions and tended to decrease with increasing N addition treatments. N additions significantly increased foliar litterfall of Acer mono Maxim., Betula platyphylla Sukatschev, Pinus koraiensis Siebold & Zucc., and Populus davidiana Dode and slightly altered litterfall of Fraxinus mandschurica Rupr. and Populus koreana Rehder. High N addition changed foliar litterfall of A. mono, F. mandschurica, P. davidiana, and P. koreana more than low N addition, whereas an opposite pattern was found for B. platyphylla and P. koraiensis. Our study showed that foliar litterfall responses to N additions varied among tree species, but this could not be predicted by the interspecific differences in NRE, NUE, C:Ngreen, and C:Nsenesced under each of the three N treatments.