© 1995 Heron Publishing—Victoria, Canada
Recovery of photosynthesis in 1-year-old needles of unfertilized and fertilized Norway spruce (Picea abies (L.) Karst.) during spring
M. Strand (1) and T. Lundmark (2)
1. Department of Forest Genetics and Plant Physiology, The Swedish University of Agricultural Sciences, S-901 83 Umeå, Sweden / 2. Vindeln Experimental Forests, The Swedish University of Agricultural Sciences, S-922 91 Vindeln, Sweden / Received June 8, 1994
Summary
Photosynthetic O2 evolution and chlorophyll a fluorescence were measured in 1-year-old needles of unfertilized and fertilized trees of Norway
spruce (Picea abies (L.) Karst.) during recovery of photosynthesis from winter inhibition in northern Sweden. Measurements were made under laboratory
conditions at 20 °C. In general, the CO2-saturated rate of O2 evolution was higher in needles of fertilized trees than in needles of unfertilized trees over a wide range of incident photon
flux densities. Furthermore, the maximum photochemical efficiency of photosystem (PS) II, as indicated by the ratio of variable
to maximum fluorescence (FV/FM) was higher in needles of fertilized trees than in needles of unfertilized trees. The largest differences in FV/FM between the two treatments occurred before the main recovery of photosynthesis from winter inhibition in late May. The rate
of O2 evolution was higher in needles of north-facing branches than in needles of south-facing branches in the middle of May.
Simultaneous measurements of O2 exchange and chlorophyll fluorescence indicated that differences in the rate of O2 evolution between the two treatments were paralleled by differences in the rate of PS II electron transport determined by
chlorophyll fluorescence. We suggest that, during recovery of photosynthesis from winter inhibition, the balance between carbon
assimilation and PS II electron transport was maintained largely by adjustments in the nonphotochemical dissipation of excitation
energy within PS II.
Keywords:
chlorophyll fluorescence, fertilization, fluorescence quenching, winter inhibition.
