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

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.

Selection of Superior Clones by Stability Analysis of Growth Performance in Populus davidiana Dode at Age 12

Stability parameters and clone x site interactions for 12-year volume were investigated in seven Populus davidiana (Korean aspen) clonal trials in South Korea. Either 24 or 38 clones were tested in each of the seven sites. All sources of variables such as clone, site, and clone x site interaction were statistically significant (p < 0.01) in the analysis of variance. The average volume of 3,199 trees was 0.043 m3. The different types of stability were shown from selected clones against the test means for volume. Clone Palkong 2 represents a relatively unstable clone that is sensitive to site changes and had greater adaptability to favorable sites. Five clones, Odae 19, Taehyun 9, Sunyeo 4, Sokwang 31, and Taehyun 3, were selected as superior clones based on stability parameters and mean volume. The selected clones have average stability and performed in a predictable manner over different planting sites. A positive relationship between stability parameters and the clone mean performance for volume was noted in this study.