Permalink : http://hdl.handle.net/2115/43851

KEYWORDS : Poplar clone;Chinese white poplar (Populus tomentosa);nutrient dynamics;macronutrient elements;nutrient cycling

In order to attain a better understanding of the seasonal variations of macronutrient contents in different components and identify clones of Chinese white poplar, three representative clones in a four-year old poplar plantation were studied in each season of the year 2008. The plantation was a randomized complete block design. We collected leaves (growing seasons only), bark and xylem of twigs, branches, stem and roots with a tree trimmer knife and an increment borer in the spring (17 April), summer (14 July), autumn (23 September) and winter (9 December). Each sample was a mixture from 3-4 model trees in the block, and then digested by a H2SO4-H2O2 solution to measure N, P, K, Ca, and Mg contents. Results showed that the order of macronutrient contents in all samples was N> Ca> K> Mg> P. Seasonal changes in N, P and K contents in each component had clearly specific trends through the year, while Ca and Mg contents varied irregularly except in leaves. The P and K contents in twigs were particularly high in spring, and roots always had high K contents through the seasons. The nutrient elements contents in the bark of branches and stems were almost 1.5-4.0 times and 2.5-9.0 times higher than those in the woody tissues, respectively. According to the ANOVA of nutrient contents in each component, especially for the season factor, N, P, Ca and Mg nutrition contents in branch wood varied significantly, and in regard to the clone factor, K, Ca and Mg contents differed significantly in stem bark. Overall, macronutrient elements contents in all parts changed throughout the four seasons. To better manage these fast-growing poplars plantations, it is necessary to retain the foliage, twigs and roots in the cultivated stands, and to remove the bark of stems and branches and leave them in the stands as well.