Abstract
The annual shoot elongation could be described by a non-linear growth model to characterize differences in its dynamics among spruce genotypes, the effect of each shoot elongation phase on the total shoot length, and the genetic differences for a particular growth phase. The terminal shoot length was measured in two open-pollinated progeny trials of Norway spruce on average once per week during the ninth growing season. For the analysis, 10% of families with the longest annual increment (shoot) and 10% with the shortest were selected for each trial. The Gompertz model was fitted to individual tree data, and the mean values of its coefficients for each group of families were obtained. Family significantly (p < 0.001) affected total shoot length and all growth rhythm parameters, with similar trends reported in both studied sites. Heritability of Gompertz model coefficients in most cases exceeded that of the tree height. The superior10% of families started shoot elongation slightly but non-significantly earlier (all p > 0.05) than the other groups of families and had more intense shoot elongation (mm per day) during the entire growing season. A strong negative relation was found between the slope coefficient of the cumulative shoot elongation lines and the total height increment. The group of families with the longest increment had flatter relative shoot elongation lines, indicating relatively more evenly distributed growth within the growing season. In contrast, families with the shortest increment tended to accumulate a higher proportion of height increment during the active growth phase and reduced relative growth intensity more rapidly. The 10% of families with the largest annual increment showed superior characteristics in all shoot elongation phases, resulting in 30–40% longer shoots compared to the 10% of families with the smallest annual increment. The significant differences in Gompertz model coefficients indicate that genotypes with favorable growth patterns might be selected.
Highlights
Norway spruce (Picea abies (L.) Karst.) is the most economically important tree species in NorthernEurope, constituting about one-third of the wood resources in the region [1]
The measurements of the terminal shoot length were successfully fitted to the Gompertz model, obtaining coefficients describing shoot elongation (Figure 1A)
Shoot elongation patterns showed differences among the divided groups of families (Table 1), and the trend was consistent in both studied sites
Summary
Norway spruce (Picea abies (L.) Karst.) is the most economically important tree species in NorthernEurope, constituting about one-third of the wood resources in the region [1]. Norway spruce (Picea abies (L.) Karst.) is the most economically important tree species in Northern. The genetic improvement of spruce began in the late 1940s [2]. The selection of superior genotypes has notably improved yield and stem quality. The reported gain for best-performing families is 21–25% for height [3] and 10–25% for stem volume [2] compared to unimproved trees. Breeding has led to a reduced rotation length by 5–10 years and an increased net present value by 30–400% in Norway [2]. In Northern Europe, climate change is associated with an extended vegetation period [5] that could enhance forest productivity but is counteracted by limitations due to early/late frosts [6,7].
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