Ingestad, T. and Kahr, M. 1985. Nutrition and growth of coniferous seedlings at varied reiative nitrogen addition rate. -Physiol. Plant. 65: 109-116.The growth of two provenances of Pinits sylvestris L. were compared with two provenances of Picea abies (L.) Karst. and with Pinus contorta Dougl. when grown in solution cultures with low nutrient Goncentratiotis. Nitrogen was added at different exponentially increasing rates, and the other nutrients were added at a rate high enough to ensure free access of them to the seedlings. During an initial period of the culture (a lag phase), when the internal nutrient status was changing from optimum to the level of the treatment, deficiency symptoms appeared. The needles yellowed and the root/shoot ratio increased. The initial phase was followed by a period of exponential growth and steady-state nutrition. The needles turned green again, and the root/shoot ratio stabilized af a level characteristic of the treatment. These patterns were the same as previously reported for other free species. The relative growth rate during exponential growth was numerically closely equaS fo the relative nitrogen addition rate. The maximum relative growth rafes were about 6 to 7.5% dry weight increase day^V This is a much lower maximum than for broadleaved species (about 20 to 30% day^') under similar growth conditions. The internal nitrogen concentrations of the seedlings and the relative growth rates were stable during fhe exponential period. Close linear relationships were found between fhese parameters and the relative addition rate up to maximum growth. During steady state the relative growth rates of the different plant parts were equal. However, there were large differences between genotypes in absolute root growth rate at the same seediing size because of differences in root/shoot ratio. Lodgepole pine had fhe highest root growth rafe, whereas that of Norway spruce, especially the southern provenance, was remarkably low. Yet, Norway spruce had a high ability fo utilize available nutrients. In treatments wifh free nufrienf access,, growfh allocation to the shoot had a high priority in all genotypes, buf there was still a marked tendency for luxury uptake of nutrients. Nitrogen productivity (growfh rate per unit of nitrogen) was lower than in broadleaved species and highest in lodgepoie pine. The relevance of the dynamic factors,, i.e. maximum relative growth rate, nutrient upfake rate, nitrogen productivity, growth allocation and roof growfh rate, are discussed wifh regard to conifer characteristics and selection value.Additional key words -Genotypes, growth allocation, net uptake rafe of nutrients, nifrogen producfivify, nufrietit proportions, provenance differences, relative addition rate, relative growth rafe, root growth rafe.T. Ingestad (reprint requests), Swedish Univ.

Growth and nutrition of hydroponically cultivated birch seedlings (Betula pendula Roth.) were investigated at various magnesium (Mg) availabilities. Suboptimum Mg conditions were created by adding Mg once per hour in exponentially increasing amounts at one of four relative addition rates (R(Mg)): 0.05, 0.10, 0.15 or 0.20 day(-1). Seedlings given free access to Mg were used as controls. After an acclimation period, the relative growth rate of the seedlings attained the same value as the corresponding relative rate of Mg addition. In all suboptimum Mg treatments, deficiency symptoms in the form of chloroses and necroses developed in the older leaves, both during and after the phase of growth acclimation. The severity of these symptoms was correlated with the availability of Mg. The relative growth rate of seedlings was linearly correlated with plant Mg status. The root fraction of the total biomass decreased from 22% in control plants to 8% in plants receiving the lowest rate of Mg addition. A shift in Mg availability from free access to R(Mg) = 0.05 day(-1) decreased the photosynthetically active leaf area per plant weight, despite a concomitant increase in the leaf weight ratio (leaf dry weight/plant dry weight) from 0.61 to 0.75. The loss in assimilating leaf area was mainly a consequence of enhanced leaf mortality and formation of necroses, and to a minor extent attributable to increased carbon costs for leaf area production. A decrease in starch concentration was observed in leaves showing Mg-deficiency symptoms, whereas the starch concentration in healthy leaves was unaffected by Mg availability. It was concluded that shortage of carbohydrates constituted the major growth constraint, particularly for roots, under Mg-limiting conditions.

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Microsomal fractions from wheat (Triticum vulgare) and oat (Avena sativa) roots were used to study Mg2+ and Ca2+ activated adenosine triphosphatases, their dependence of pH, and how Mg2+ and Ca2+ compete or add in stimulation and inhibition. Wheat gives a high proportion of Ca2+ stimulated ATPase. Less effect is obtained with Mg2+. The characteristics of oar ATPase are the reverse. The ATPase from the wheat roots depends on the mineral nutrition. A kinetïc analysis shows one site, where Mg2+ and Ca2+ at low concentrations (or complexes between the di‐valents and ATP) cooperate in the activation of the ATPase. The action of this site is more dearly expressed at pH 6.0 than at 6.8, and more clearly in the preparations from low salt roots than in those from high salt conditions. In another site, which is particularly evident in preparations from high salt roots tested at pH 6.8, high concentrations of Mg2+ inhibit the ATPase; this inhibition is competitively relieved by Ca2+. The specific activity of the ATPase from high salt roots of wheat is higher than that from low salt roots, although the amount of protein of the fraction studied remains the same, when calculated per g fresh weight of the roots.

Scots pine (Pinus sylvestris L.), and Norway spruce (Picea abies (L.) Karst.) seedlings, inoculated with Suillus bovinits (L. ex Fr.) O. Kuntze and Paxillus involutus (Batsch) Fr., were grown on sloping plastic plates in growth units. A circulating nutrient solution flowed continuously over the plates. Nutrients in balanced proportions previously found to be appropriate for conifers, were added at a specified relative addition rate, in exponentially increasing amounts. The conductivity of the solution was kept low and stable (<50 μS cm−1). No carbohydrates were added. Seedling nitrogen concentration and relative growth rate attained steady states in both inoculated and uninoculated treatments. The fungi infected the short roots within a few days and formed typical mantles and Hartig nets. This occurred in all treatments, including conditions of free access to nutrients, in which the nutrient concentration of the seedlings was optimal. The growth rate of the extramatrical mycelium was very high.