Canadian Forest Service Publications
Short-term growth and morphological responses to nitrogen availability and plant density in hybrid poplars and willows. 2015. Mamashita, T.; Larocque, G.R.; DesRochers, A.; Beaulieu, J.; Thomas, B.R.; Mosseler, A.; Major, J.; Sidders, D. Biomass & Bioenergy 81:88-97.
Issued by: Laurentian Forestry Centre
Catalog ID: 36164
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Morphological characteristics of poplar and willow clones were determined in order to identify main characteristics leading to superior growth under increased plant competition with low or high nitrogen (N) availability. Seven hybrid poplar (Populus spp. including one hybrid aspen) and five willow (Salix spp.) clones were grown under greenhouse conditions for 13 weeks at three spacings (20 x 20, 35 x 35, and 60 x 60 cm) and two N levels (20 and 200 mg kg-1). The decrease in spacing from 60 to 20 cm reduced leaf area by 50% but clones had similar aboveground biomass per tree under all spacings, with increasing their height per unit leaf area. More productive clones had greater leaf area (+102%), leaf area per unit plant biomass (+12%) and lower root-to-shoot ratios (-27%) compared to less productive clones. There were positive relationships between leaf area and above-ground biomass per tree for both more and less productive clones. Compared to low N level and 60 cm spacing, trees growing in high N level and 20 cm spacing reached similar root collar diameter, crown width, and leaf area values and even greater height, suggesting that an addition of N could help mitigate negative effects of tree competition.
Plain Language Summary
This study involving young fast-growing poplar and willow clones has shown that reducing the space between the trees (from 60 to 20 cm) reduces leaf area by 50%. However, aboveground biomass remains relatively unchanged, which can be explained by an increase in tree height per unit of leaf area when spacing is decreased.
Comparing the growth of trees separated by 60 cm with low nitrogen levels with that of trees separated by 20 cm with high nitrogen levels revealed that collar diameter, crown width and leaf area were similar in both groups of trees. In terms of height, trees separated by 20 cm may even outgrow those separated by 60 cm. Nitrogen fertilization may therefore minimize the negative effects of tree competition. The goal of the study was to develop a method that would significantly shorten the selection process of the most productive clones per area unit for the purpose of bioenergy production, based on physiological and morphological parameters. The morphological characteristics of seven poplar clones and five willow clones with three different spacing levels and two nitrogen fertilization levels were studied.