© 2007 Heron Publishing—Victoria, Canada
Shoot biomass growth is related to the vertical leaf nitrogen gradient in Salix canopies
Martin Weih (1, 2) and Ann-Christin Rönnberg-Wästjung (3)
1. Department of Crop Production Ecology, Swedish University of Agricultural Sciences, P.O. Box 7043, SE-750 07 Uppsala, Sweden / 2. Corresponding author (martin.weih@vpe.slu.se) / 3. Swedish University of Agricultural Sciences, Department of Plant Biology and Forest Genetics, P.O. Box 7080, SE-750 07 Uppsala,
Sweden / Received January 4, 2007; accepted February 26, 2007; published online August 1, 2007
Summary
Plant canopy optimization models predict that leaf nitrogen (N) distribution in the canopy will parallel the vertical light
gradient, and numerous studies with many species have confirmed this prediction. Further, it is predicted that for a given
canopy leaf area, a low vertical light extinction coefficient will promote rapid growth. Therefore, the ideal canopy of fast-growing
plants should combine high leaf area index with a low light extinction coefficient; the latter being reflected in a flat vertical
leaf N gradient throughout the canopy. Based on data from an experimental Salix stand (six varieties) grown on agricultural land in central Sweden, we tested the hypothesis that shoot growth is correlated
with vertical leaf N gradient in canopies of hybrid willows bred for biomass production, which could have implications for
Salix breeding.
Tree improvement research requires screening of growth-related traits in large numbers of plants, but assessment of canopy
leaf N gradients by chemical analysis is expensive, time-consuming and destructive. An alternative to analytical methods is
to estimate leaf N gradients nondestructively with an optical chlorophyll meter (SPAD method). Here we provide a specific
calibration for interpreting SPAD data measured in hybrid willows grown in biomass plantations on fertile agricultural land.
Based on SPAD measurements, a significant and inverse relationship (r2 = 0.88) was found between shoot biomass growth and vertical leaf N gradient across canopies of six Salix varieties.
Keywords:
bio-fuels, breeding, chlorophyll fluorescence, nitrogen economy, SPAD, Sweden.
