Spacing of silver birch seedlings grown in containers of equal size affects their morphology and its variability.

Silver birch (Betula pendula Roth) seedlings were grown individually in containers arranged in rows radiating from a central point (Nelder plot) at densities spanning the range from 207 to 891 plants m(-2). Height of one set of seedlings was measured at weekly intervals and additional seedlings were harvested each week for dry mass and leaf area measurements. Height and shoot:root dry mass ratio increased with plant density. Seedling-to-seedling variability in dry mass, but not height, increased with increasing plant density. The red to far-red (R:FR) photon ratio in horizontally propagated radiation decreased with increasing density, even when plant densities and leaf area index values were low. In a separate experiment, elongating internodes of seedlings were irradiated locally by red and far-red light emitting diodes and stem elongation measured. Far-red light markedly increased stem elongation, suggesting that changes in light quality sensed by growing internodes are involved in the observed responses to growth density.

Drought stress alters the concentration of wood terpenoids in Scots pine and Norway spruce seedlings.

Drought is known to have an impact on the resistance of conifers to various pests, for example, by affecting resin flow in trees. Little is known, however, about the quantitative and qualitative changes in resin when trees are growing in low moisture conditions. We exposed Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) seedlings to medium and severe drought stress for two growing seasons and analyzed the monoterpenes and resin acids in the main stem wood after two years of treatment. In addition to secondary chemistry, we measured the level of nutrients in the needles and the growth response of seedlings. After the first year of treatment, drought stress did not affect the growth of seedlings, but in the second year, shoot growth was retarded, especially in Scots pine. In both conifer species, severe drought increased the concentrations of several individual monoterpenes and resin acids. Total monoterpenes and resin acids were 39 and 32% higher in severe drought-treated Scots pine seedlings than in the controls, and 35 and 45% higher in Norway spruce seedlings. In Scots pine needles, the concentrations of nitrogen and phosphorus increased, while magnesium and calcium decreased compared to controls. In Norway spruce needles, nutrient concentrations were not affected. The results suggest that drought stress substantially affects both the growth of conifers and the chemical quality of the wood. We discuss the potential trade-off in growth and defense of small conifer seedlings.

Leaching of nitrogen and phosphorus during production of forest seedlings in containers.

Little information is available concerning the contamination risk caused by forest seedling nurseries to local surface and ground waters compared with agricultural and horticultural production. Leaching of nitrogen (N) and phosphorus (P) through peat growing medium in containers and nutrient uptake of seedlings were monitored in production of silver birch (Betula pendula Roth), Norway spruce [Picea abies (L.) Karst], and Scots pine (Pinus sylvestris L.) seedlings. About half of the applied nutrients (total amount applied = 149 to 260 kg N ha(-1) and 60 to 108 kg P ha(-1)) was premixed into the peat medium, as is usual in Finnish nursery practice, and the other half was applied to seedlings in liquid form with mobile booms. Depending on tree species, 11 to 19% of the applied N was recovered in leachates and 15 to 63% in seedlings. The undiscovered proportion varied from 19 to 71%. The amounts of leached N were 19 to 41 kg ha(-1). Only 5 to 31% of the applied P was recovered in seedlings; 16 to 64% (11 to 56 kg ha(-1)) was found in leachates. Total N and P load to the environment may increase substantially if nutrients applied in liquid fertilization outside container trays are included. Consequently, it is important to determine the sources of nutrient load in container seedling production to mitigate the risk of environment contamination.

Resource partitioning to growth, storage and defence in nitrogen-fertilized Scots pine and susceptibility of the seedlings to the tarnished plant bug Lygus rugulipennis.

We tested how variable nitrogen availability affects the above-and below-ground growth of first-year Scots pine (Pinus sylvestris L.) seedlings and carbon allocation to defensive allelochemicals and storage. Concentrations of free ammo acids were considered as indicators of nutritive quality. Suitability of seedlings for polyphagous Lygus rugulipennis Popp. (Heteroptera: Miridae) was tested with oviposition preference and nymphal growth experiments. At the end of the growing season, needle length increased while root hiomass decreased with elevated N fertilization, but shoot length was not affected. Concentration of starch in needles and roots, representing carbon storage, was not significantly affected by N fertilization, although there was a decrease in the starch concentration of needles when nitrogen input increased. Nitrogen fertilization significantly increased the pool of total and non-essential ammo acids in the shoots. Arginine, proline and glutamine were the individual ammo acids most affected by elevated N. Of the carbon-based defence compounds, total resin acid concentrations in shoots were significantly reduced with elevated nitrogen in 9-wk-old seedlings. Palustric acid and neoabietic acid were the most affected individual) resin acids, where as foliar monoterpenes were not influenced by N availability. Total phenolics in shoot and root showed variable response. The increasing effect of nitrogen on the oviposition rate of Lygus females was almost linear. Mean relative growth rate of the nymphs was significantly affected by the level of N fertilization. but the mortality of nymphs was high in all treatments. The results suggest that in nitrogen-rich environments the needle growth of small Scots pine seedlings is improved, but their Susceptibility to insect attack is increased and they remain less defended as predicted by the carbon/nutrient balance hypothesis. Total phenolics and resin acids, representing phenylalanine and mevalonic acid pathways, respectively, were both reduced by increased nitrogen availability. Together with the simultaneous increase of foliar free nitrogen in the form amino acids, the nutritive value of seedlings is ameliorated and this might explain susceptibility of nursery-grown. N fertilized seedlings to polyphagous Lygus bugs.