Changes in needle nitrogen partitioning and photosynthesis during 80 years of tree ontogeny in Picea abies

摘要

Needle nitrogen partitioning and photosynthesis of Norway spruce were studied in a forest chronosequence in JcTrvselja Experimental Forest, Estonia. Current- and previous-year shoots were sampled from upper and lower canopy positions in four stands, ranging in age from 13 to 82 years. A/c i curves were determined to obtain maximum carboxylation rate (V cmax) and maximum rate of electron transport (J max), whereas needle nitrogen partitioning into carboxylation (P R), bioenergetics associated with electron transport (P B) and thylakoid light harvesting components (P L) was calculated from the values of V cmax, J max and leaf chlorophyll concentration. The greatest changes in studied needle characteristics took place between tree ages of 13 and 26 years, and this pattern was independent of needle age and canopy position. Needle mass per projected area (LMA) was lowest in the 13-year-old stand and mass-based nitrogen concentration (NM) was generally highest in that stand. The values of LMA were significantly higher and those of NM lower in the 26-year-old stand. Mass-based V cmax and J max were highest in the 13-year-old stand. Area-based photosynthetic capacity was independent of tree age. The proportion of photosynthetic nitrogen (P R, P B and P L) was highest and that of non-photosynthetic nitrogen lowest in the 13-year-old stand. Current-year needles had lower LMA and P L, but higher photosynthetic capacity compared to 1-year-old foliage. Needles from lower canopy positions exhibited lower LMA, area-based nitrogen concentration and photosynthetic capacity than needles from upper canopy. The period of substantial reductions in needle photosynthetic capacity and changes in nitrogen partitioning coincides with the onset of reproductive phase during tree ontogeny.