One-year-old Norway spruce (Picea abies (L.) Karst.) seedlings were grown hydroponically in a growth chamber to investigate the effects of low and high nutrient availability (LN; 0.25 mM N and HN; 2.50 mM N) on growth, biomass allocation and chemical composition of needles, stem and roots during the second growing season. Climatic conditions in the growth chamber simulated the mean growing season from May to early October in Flakaliden, northern Sweden. In the latter half of the growing season, biomass allocation changed in response to nutrient availability: increased root growth and decreased shoot growth led to higher root/shoot ratios in LN seedlings than in HN seedlings. At high nutrient availability, total biomass, especially stem biomass, increased, as did total nonstructural carbohydrate and nitrogen contents per seedling. Responses of stem chemistry to nutrient addition differed from those of adult trees of the same provenance. In HN seedlings, concentrations of alpha-cellulose, hemicellulose and lignin decreased in the secondary xylem. Our results illustrate the significance of retranslocation of stored nutrients to support new growth early in the season when root growth and nutrient uptake are still low. We conclude that nutrient availability alters allocation patterns, thereby influencing the success of 2-year-old Norway spruce seedlings at forest planting sites.
We examined the effects of a long-term nutrient-optimization treatment on the acquisition and allocation of biomass, carbon (C), and nitrogen (N) in young Norway spruce (Picea abies (L.) Karst.) growing in northern Sweden. After 12 years of fertilization the absolute biomass of stem, needles, living branches, and stump and coarse roots was more than doubled by nutrient optimization (irrigation liquid fertilization treatment, IL), but the standing biomass of fine and small roots was unaffected compared with that of control trees. Biomass allocation among aboveground organs was not plastic to nutrient optimization and only the relative proportion of dead branches was reduced by nutrient optimization. Within the crown, biomass allocation to living branches was shifted towards the apex in IL trees. The N content in IL trees was substantially higher than in control trees. Most of the total N was allocated to needles and most of the needle N was found in the middle stratum of the living crown in both treatments, although the N concentration of current-year and older needles increased towards the apex in IL trees but not in control trees. The C concentration in the biomass components was not affected by the optimized fertilization. The results clearly show that there is a large potential to increase biomass production of Norway spruce (C sequestration) in the Nordic countries. This would secure the supply of raw material for the forest industry at the same time as the demand for biofuel from forest biomass is increasing.
We examined effects of nutrient availability and changing root zone temperature (RZT) on growth, gas exchange and plasma membrane H(+)-ATPase (PM-ATPase) activity of roots of 1-year-old Scots pine (Pinus sylvestris L.) seedlings during spring flushing. The 6-week growth-chamber experiment was carried out in hydroponic cultures that supplied the seedlings with low (0.5 mM N) or high (3 mM N) nutrient concentration and two rates of increase in RZT were simulated: slow warming (SW-treatment) and fast warming (FW-treatment). Air temperature, humidity, and light conditions were similar in all treatments. Growth of roots and shoots was retarded at low RZT, and fresh mass increment of roots was closely correlated with RZT sum. High nutrient availability increased nitrogen concentrations of needles and stems, but only at RZTs >13 degrees C. Low RZT and low availability of nutrients suppressed gas exchange of the seedlings. Real PM-ATPase activity was highly dependent on RZT. At high RZTs, real PM-ATPase activity was affected by nutrient availability but this effect was related to root growth. We conclude that, under conditions of high nutrient availability, Scots pine seedlings can compensate for the suppressive effects of long-term exposure to low RZT by rapidly accelerating growth, gas exchange and root metabolism, but only when RZT has increased above a threshold value, which was 13 degrees C in this study.
To ascertain whether the growth rhythm of roots differs from that of the shoot, the seasonal pattern of dry mass allocation was determined in 1-year-old Scots pine (Pinus sylvestris L.) seedlings. Gas exchange, chlorophyll fluorescence, and the dynamics of starch and soluble sugars were examined to understand the role of stored carbon and that of current photosynthates in meeting the sink demand of plant organs. In this growth-chamber experiment, hydroponic cultures supplied the seedlings with low (0.25 mM N) or high (2.5 mM N) nutrient level. The climatic conditions in the chamber simulated the weather conditions from May to mid-October in southern Finland. Root growth was most intense at the end of the growing season, at which time shoot growth slowed down. Nutrient level did not affect the growth rhythm of the roots, but the total production of root biomass was favoured by high level of nutrients. The response of root growth to root zone temperature (RZT) was not the same over the growing season, indicating that the sensitivity of root growth to RZT depends on the growth phase of the seedling. The growth rhythm of the roots is probably regulated by several internal and external factors and their interactions, including RZT and availability of photosynthates.Résumé : Les auteurs ont déterminé le patron saisonnier d'allocation de masse sèche chez des semis de pin sylvestre (Pinus sylvestris L.) âgés d'un an dans le but de vérifier si le rythme de croissance des racines diffère de celui des pousses. Les échanges gazeux, la fluorescence de la chlorophylle et la dynamique de l'amidon et des sucres solubles ont été examinés afin de comprendre le rôle des réserves de carbone et des produits courants de la photosynthèse face au puits que représente la demande par les organes de la plante. Dans cette expérience en chambre de croissance, les semis en culture hydroponique ont été exposés à des niveaux faible (0,25 mM N) ou élevé (2,5 mM N) de nutriments. Les conditions climatiques dans les chambres de croissance correspondaient aux conditions climatiques du mois de mai à la mi-octobre dans le sud de la Finlande. La croissance des racines était plus intense à la fin de la saison de croissance au moment où la croissance des pousses ralentissait. Le niveau de nutriments n'a pas affecté le rythme de croissance des racines mais la production totale de biomasse racinaire était favorisée par un niveau élevé de nutriments. La réponse de la croissance racinaire à la température dans la rhizosphère n'était pas la même pendant toute la saison de croissance. Cela indique que la sensibilité de la croissance racinaire à la température dans la rhizosphère dépend de la phase de croissance dans laquelle se trouve le semis. Le rythme de croissance des racines est probablement régulé par plusieurs facteurs internes et externes et leurs interactions, incluant la température dans la rhizosphère et la disponibilité des produits de la photosynthèse.[Traduit par la Rédaction] 1578Iivonen et al.
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