© 2003 Heron Publishing—Victoria, Canada
Chilling-dependent photoinhibition, nutrition and growth analysis of Eucalyptus nitens seedlings during establishment
Dugald C. Close (1, 2, 3, 4, 5) and Christopher L. Beadle (1, 5)
1. Cooperative Research Centre for Sustainable Production Forestry, GPO Box 252-12, Hobart, Tasmania 7001, Australia / 2. School of Plant Science, University of Tasmania, GPO Box 252-55, Hobart, Tasmania 7001, Australia / 3. School of Agricultural Science, University of Tasmania, GPO Box 252-54, Hobart, Tasmania 7001, Australia / 4. Author to whom correspondence should be addressed (Dugald.Close@ffp.csiro.au) / 5. CSIRO Forestry and Forest Products, GPO Box 252-12, Hobart, Tasmania 7001, Australia / Received April 30, 2002; accepted August 17, 2002; published online February 3, 2003
Summary
Effects of chilling-dependent photoinhibition on gas exchange, chlorophyll fluorescence, growth and nutrition of Eucalyptus nitens (Deane and Maiden) Maiden seedlings were assessed for 70 weeks after transplanting 9-month-old seedlings in early winter.
One month before transplanting, the seedlings were assigned to fertilized or nutrient-deprived treatments. Immediately after
transplanting, half the seedlings in each nutrient treatment were placed in shadecloth tree shelters. The experimental site
was at an altitude of 700 m, which is considered marginal for the establishment of E. nitens plantations in Tasmania because of low mean annual minimum temperatures.
Overnight frosts followed by sunny morning conditions in the first 20 weeks after transplanting (early June to early October)
caused severe photoinhibition. Predawn maximal photochemical efficiency (Fv/Fm) and maximum net photosynthesis (Amax) were depressed in nutrient-deprived seedlings compared with fertilized seedlings, although shading partially alleviated
this difference. Neither Fv/Fm nor Amax recovered to values observed before transplanting until > 20 weeks after transplanting. During this period, non-photochemical
quenching (NPQ) was high in seedlings in all treatments, although NPQ was lower in shaded, fertilized seedlings than in seedlings
in the other treatments.
Total foliar nitrogen (N) concentration increased up to 42 weeks after transplanting in the nutrient-deprived seedlings in
parallel with increasing relative growth rate (RGR). Fractionation of N- and phosphorus (P)-containing compounds indicated
that differences in protein N accounted for the treat- ment differences in total seedling N. Nucleic acid P increased and
inorganic P decreased during growth periods, although total seedling P remained constant. Among treated seedlings, height
growth was greatest in shaded seedlings: this was probably a result of apical dominance effects because RGR was higher in
unshaded seedlings than in shaded seedlings. Thus, the shade treatment alleviated chilling-dependent photoinhibition and maximized
growth during winter, but limited growth during warmer periods and therefore overall growth.
Keywords:
biomass, chlorophyll fluorescence, frost, gas exchange, N- and P-fractionation, nitrogen, NPQ, phosphorus, shade, shadecloth
tree shelters.
