© 2002 Heron Publishing—Victoria, Canada
Fertilization has little effect on light-interception efficiency of Picea abies shoots
Sari Palmroth (1, 2, 3), Pauline Stenberg (4), Sampo Smolander (5), Pekka Voipio (6) and Heikki Smolander (6)
1. Department of Limnology and Environmental Protection, P.O. Box 62, FIN-00014, University of Helsinki, Finland / 2. Author to whom correspondence should be addressed (sari.palmroth@duke.edu) / 3. Nicolas School of the Environment and Earth Sciences, Box 90328, Duke University, Durham, NC 27708, USA / 4. Department of Forest Ecology, P.O. Box 27, FIN-00014, University of Helsinki, Finland / 5. Rolf Nevanlinna Institute, P.O. Box 4, FIN-00014, University of Helsinki, Finland / 6. Finnish Forest Research Institute, Suonenjoki Research Station, FIN-77600 Suonenjoki, Finland / Received December 3, 2001; accepted April 13, 2002; published online October 1, 2002
Summary
We investigated effects of nutrient availability on shoot structure and light-interception efficiency based on data from control
(C) and irrigated + fertilized (IL) trees of Norway spruce (Picea abies (L.) Karst.). The sampling of 1-year-old shoots was designed to cover the variation in canopy exposure within the live crown
zone, where current-year shoots were still found. Canopy openness was used as a measure of light availability at the shoot's
position. Openness values for the sample shoots ranged from 0.02 to 0.77 on the IL plot, and from 0.10 to 0.96 on the C plot.
Among needle dimensions, needle width increased most with canopy openness. At fixed canopy openness, needle width was larger,
and the ratio of needle thickness to width was smaller in IL trees than in C trees. Specific needle area (SNA) and the ratio
of shoot silhouette area to total needle area (STAR) decreased with canopy openness, so that the combined effect was a threefold
decrease in the ratio of shoot silhouette area to unit dry mass (SMR = STAR × SNA) along the studied range of openness values.
This means that the light-interception efficiency of shoots per unit needle dry mass was three times higher for the most shaded
shoots than for sun shoots. A test of the effect of fertilization on the relationships of SNA, STAR and SMR indicated statistically
significant differences in both slope and intercept for SNA and STAR, and in the intercept for SMR. However, the differences
partly cancelled each other so that, at medium values of canopy openness, differences between treatments in predicted SNA,
STAR and SMR were small. At 0.5 canopy openness, predicted STAR of IL shoots was 6.1% larger than STAR of C shoots, but SMR
of IL shoots was 10% smaller than that of C shoots. The results suggest that light-interception efficiency per unit needle
area or mass of the shoots is not greatly affected by fertilization.
Keywords:
LAI, nitrogen, Norway spruce, structural acclimation.
