Abstract
When poplar trees planted at a high density are canopy-closed in plantation after 4-5 years of growth, the roots of adjacent trees will inevitably intermingle together, which possibly restricts the nutrient uptake by root system. Root pruning might stimulate the emergence of fine roots and benefit the tree growth of short-rotation poplar at the stage of canopy closing. The aim of this study is to evaluate the effects of root pruning on DBH (diameter at breast height, 1.3 m), tree height, nutrients (N, P and K) and hormones (indoleacetic acid and cytokinin) in poplar leaves, gas exchange variables (photosynthetic rate and stomatal conductance), and rhizosphere soil characteristics. Field experiment was carried out with four-yearold poplar (Populus × euramericana cv. ‘Neva’) planted in a fluvo-aquic loam soil in Shandong province, China in early April, 2008. Three root pruning treatments (severe, moderate and light degree) were conducted at the distances of 6, 8 and 10 times DBH on both inter-row sides of the trees to the depth of 30 cm, respectively. The results showed that the growth performance was obtained in the following order of treatments: moderate > light = control > severe. In the rhizophere soil, moderate and light pruning increased the microbial populations, enzymatic activities, and the concentrations of available N, P, K and organic matter. Generally, root pruning to improve tree growth and rhizosphere soil fertility can be recommended in canopy-closed poplar plantation. The appropriate selection of root pruning intensity is a pivotal factor for the effectiveness of this technique.
Highlights
In several areas of the world, the fast-growing tree species of choice belong to the genus Populus (Pontailler et al, 1999; Christersson, 1996; BilodeauGauthier, 2011)
At the end of 2008 and 2009 growing season, the diameter at breast height (DBH) increment of poplar trees treated by moderate root pruning were 7.38% and 4.59% higher than that of untreated trees (p < 0.05), respectively
Contrary to the moderate root pruning, the DBH increment was significantly decreased by the severe root pruning, which had no effect on the height growth
Summary
In several areas of the world, the fast-growing tree species of choice belong to the genus Populus (Pontailler et al, 1999; Christersson, 1996; BilodeauGauthier, 2011). All of above features enable the production of large quantities of wood in short periods of time, which can be used for different forms of processing in the timber industry, in the pulp and paper industry and as a source of energy (Fang et al, 1999). With the economic incentives and interests in fast-growing poplar hybrids for short-rotation production for pulp wood, fiber and veneer, poplar plantations have been recently established in northern plain and southwestern upland areas of China. Applied agricultural management practices are careful site preparation, selected tree species, dense design, short rotation, irrigation and fertilization throughout the whole rotation period
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