Growth and mineral nutrition of Gmelina arborea Roxb. seedlings fertilized with four sources of nitrogen on a latosolic soil

The growth and mineral nutrition of Gmelina arborea Roxb. seedlings were investigated in response to four nitrogen-based fertilizers applied at 0, 2.5, 5.0 or 7.5 g N per plant. Nitrogen sources included NH(4)-N as ammonium sulfate, NO(3)-N as potassium nitrate, NH(4)NO(3)-N as calcium ammonium nitrate, and urea-N as urea. Seedlings fertilized with NH(4)NO(3)-N or urea-N had greater height, collar diameter, dry weight, net assimilation rate, and relative growth rate than seedlings fertilized with NH(4)-N or NO(3)-N. For all sources of nitrogen, increasing the amount of exogenously supplied N per plant promoted shoot growth more than root development, hence the root to shoot ratios of all fertilized seedlings were smaller than those of the unfertilized controls. Applications of NO(3)-N increased the nitrogen, potassium, and phosphorus concentrations of fertilized seedlings. Regardless of source, a nitrogen application of 2.5 g N per plant was apparently optimal for the growth of Gmelina seedlings on a latosolic soil.     

Effects of aluminum on growth and nutrient status of Douglas-fir seedlings grown in culture solution

Effects of Al on growth, nutrient uptake and proton efflux were studied in Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) seedlings grown for about nine months in culture solutions with a pH between 3.4 and 3.6 and with both calcium and magnesium (Ca + Mg) at a concentration of 0.1, 0.5 or 2.5 mM. In the absence of Al, plant dry matter production and root development increased with increasing concentrations of (Ca + Mg) in the culture solution. At the low and intermediate (Ca + Mg) concentrations, optimal root and shoot development were observed at an Al concentration of 4 mg l(-1). At the highest (Ca + Mg) concentration, Al up to 4 mg l(-1) did not affect growth, but at higher concentrations, it significantly reduced both shoot and root growth. As the concentration of (Ca + Mg) in the nutrient solution increased, the concentrations of Ca and Mg increased in shoots and roots also. The concentrations of Ca and Mg in the roots were unaffected by the presence of Al, whereas in the shoots they were either unaffected, or increased, by Al. Concentrations of Al in, or on, roots, or in shoots, did not change in response to changing concentrations of Ca + Mg in the nutrient medium. In general, concentrations of P and K in shoots and roots were higher in seedlings grown in nutrient solutions containing Al. Stimulation of growth by moderate concentrations of Al, which was observed at suboptimal (Ca + Mg) concentrations, was associated with a low NH(4) preference and a low root proton efflux. The Al-induced increase in internal K concentration and reduction in NH(4) preference may be explained by a lower efflux of K and NO(3), respectively.     

Family variation in nutritional and growth traits in Douglas-fir seedlings

Nitrogen (N) uptake and utilization in seedlings of six full-sib families of coastal Douglas fir (Pseudotsuga menziesii (Mirb.) Franco) known to differ in growth rate were assessed at the whole plant and root levels. Seedlings were grown in soil or aeroponically with high and low nutrient availability. Consistent family differences in growth rate and N utilization index were observed in both soil and aeroponic culture, and high-ranking families by these measures also had greater net N uptake in soil culture. Two of the three families found to be fast-growing in long-term field trials exhibited faster growth, higher N utilization indices and greater net N uptake at the seedling stage. Mean family net influx of ammonium (NH4+) and efflux of nitrate (NO3-) in the high- and low-nutrient treatments were significantly correlated with measures of mean family biomass. The high-nutrient availability treatment increased mean net fluxes of NH4+ and NO3- in roots. These results indicate that efficiency of nutrient uptake and utilization contribute to higher growth rates of trees. Nutrient-related traits should be considered in tree breeding programs, as the indications are that assessments may be made at an early stage.     

Root growth and water use efficiency of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) and lodgepole pine (Pinus contorta Dougl.) seedlings

One-year-old Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) and lodgepole pine (Pinus contorta Dougl.) seedlings were grown for 17 weeks in 100-cm deep, 7.8-liter containers. Two Douglas-fir provenances, one from a wet and one from a dry site in coastal British Columbia, and two lodgepole pine provenances, one from a wet and one from a dry site in interior British Columbia, were grown in wet (522% water content) or dry (318% water content) peat/vermiculite soil in a factorial design. Each container was sealed so that water loss occurred only through the seedling. Five harvests were made at three to five week intervals and water use, dry matter increment, root length and root weight were determined at each harvest. Stomatal conductance and shoot water potentials were measured during the last 12 weeks of the experiment. Lodgepole pine seedlings had greater dry matter production, water use, stomatal conductance and new root length than Douglas-fir seedlings. New root weight of lodgepole pine seedlings exceeded that of Douglas-fir seedlings during the last five weeks of the experiment, and specific root length (root length per unit root weight) of new roots was higher for lodgepole pine seedlings throughout the experiment. Douglas-fir seedlings showed higher water use efficiency (WUE) than lodgepole pine seedlings, and both species showed higher WUE in the dry soil treatment. Douglas-fir seedlings had lower water potentials and higher water uptake rates per unit of new root length than lodgepole pine seedlings, although water uptake rates per unit of root dry weight showed little difference between species. Soil water treatment influenced specific root length of new roots, water uptake per unit of new root length, and WUE in Douglas-fir seedlings more than in lodgepole pine seedlings.     

Effects of nitrogen source on growth and activity of nitrogen-assimilating enzymes in Douglas-fir seedlings

Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) seedlings were grown for 68 days in a growth chamber in nutrient solutions with ammonium, nitrate or ammonium nitrate as the nitrogen source. Among the nitrogen sources tested, whole-seedling biomass, relative growth rate (RGR), root and shoot elongation, and number of lateral roots, were greatest in seedlings grown with ammonium. In the absence of nitrogen, plant growth and formation of lateral roots were poor. Initially, glutamine synthetase, NAD-glutamate dehydrogenase and aspartate aminotransferase activities were high in young roots and shoots, but all three enzymatic activities decreased after one month of culture. In root apices, glutamine synthetase and aspartate aminotransferase activities were higher than NAD-glutamate dehydrogenase activity. Enzymatic activities were often higher in ammonium-fed seedlings than in seedings supplied with the other forms of nitrogen. Activities of all three enzymes were significantly reduced in seedlings grown in the absence of nitrogen. The beneficial effect of ammonium is discussed on the basis of its involvement in the assimilation pathways of Douglas-fir.     

Uptake of nitrate, ammonium and glycine by plants of Tasmanian wet eucalypt forests

A central assumption of ecosystem N cycling has been that organic N must be converted to inorganic N to be available for plant uptake, but this has been questioned by recent studies. We examined uptake of nitrate, ammonium and the amino acid glycine in three species from Eucalyptus obliqua L'Her. wet forest in Tasmania, south-eastern Australia, to test the hypothesis that all three species can take up glycine, and to compare rates of glycine uptake with rates of uptake of nitrate and ammonium uptake. The alternative hypothesis that species vary in their preference for nitrate, ammonium and glycine ("niche differentiation") was also examined. Measurements were made on the canopy dominant Eucalyptus obliqua, and two rain forest tree species found in the understory or as sub-dominants of the canopy, Nothofagus cunninghamii (Hook.) Oerst. and Phyllocladus aspleniifolius (Labill.) Hook.f. Nitrogen uptake was examined in situ with attached roots placed in uptake solutions containing equimolar concentrations (100 micromol l(-1)) of (15)N-nitrate, (15)N-ammonium and 2-(13)C(2) (15)N-glycine. Species did not differ in their preference for different forms of N (species x N form interaction, P > 0.05), and thus there was no evidence of niche differentiation. In all species, rates of uptake were highest for ammonium (11 +/- 5 micromol g(DM) (-1) h(-1); mean +/- SD, n = 108), uptake of glycine occurred at less than half this rate (4.4 +/- 2.6 micromol g(DM) (-1) h(-1)), whereas uptake of nitrate occurred at one-tenth of this rate (0.9 +/- 1.2 micromol g(DM) (-1) h(-1)). The strong positive relationship between (15)N and (13)C uptake indicated that at least 72% of glycine-N was taken up intact. These findings indicate the potential for considerable uptake of organic N in the field.     

Influence of elevated CO2 and mycorrhizae on nitrogen acquisition: contrasting responses in Pinus taeda and Liquidambar styraciflua

An understanding of root system capacity to acquire nitrogen (N) is critical in assessing the long-term growth impact of rising atmospheric CO2 concentration ([CO2]) on trees and forest ecosystems. We examined the effects of mycorrhizal inoculation and elevated [CO2] on root ammonium (NH4+) and nitrate (NO3-) uptake capacity in sweetgum (Liquidambar styraciflua L.) and loblolly pine (Pinus taeda L.). Mycorrhizal treatments included inoculation of seedlings with the arbuscular mycorrhizal (AM) fungus Glomus intraradices Schenck & Smith in sweetgum and the ectomycorrhizal (EM) fungus Laccaria bicolor (Maire) Orton in loblolly pine. These plants were then equally divided between ambient and elevated [CO2] treatments. After 6 months of treatment, root systems of both species exhibited a greater uptake capacity for NH4+ than for NO3-. In both species, mycorrhizal inoculation significantly increased uptake capacity for NO3-, but not for NH4+. In sweetgum, the mycorrhizal effect on NO3- and NH4+ uptake capacity depended on growth [C02]. Similarly, in loblolly pine, the mycorrhizal effect on NO3- uptake capacity depended on growth [CO2], but the effect on NH4+ uptake capacity did not. Mycorrhizal inoculation significantly enhanced root nitrate reductase activity (NRA) in both species, but elevated [CO2] increased root NRA only in sweetgum. Leaf NRA in sweetgum did not change significantly with mycorrhizal inoculation, but increased in response to [CO2]. Leaf NRA in loblolly pine was unaffected by either treatment. The results indicate that the mycorrhizal effect on specific root N uptake in these species depends on both the form of inorganic N and the mycorrhizal type. However, our data show that in addressing N status of plants under high [CO2], reliable prediction is possible only when information about other root system adjustments (e.g., biomass allocation to fine roots) is simultaneously considered.     

Uptake and distribution of calcium and phosphorus in beech (Fagus sylvatica) as influenced by aluminum and nitrogen

We studied the effects of excess nitrogen added as nitrate (NO(3) (-)) or ammonium (NH(4) (+)), or both, on mineral nutrition and growth of beech (Fagus sylvatica L.) plants grown at pH 4.2 in Al-free nutrient solution or in solutions containing 0.1 or 1.0 mM AlCl(3). A high external concentration of NH(4) (+) increased the concentration of nitrogen in roots, stems and leaves. The root/shoot dry weight ratio was less in plants grown in the presence of NH(4) (+) than in plants grown in the presence of NO(3) (-). The concentration of phosphorus in the roots was increased and the concentration of potassium in all parts of the plant was decreased by NH(4) (+). A high external concentration of NO(3) (-) caused a decrease in phosphorus concentrations of the root, stem and leaf. Uptake of (45)Ca(2+) by roots was reduced in the presence of high concentrations of NH(4) (+) or NO(3) (-), and a combination of high concentrations of nitrogen and aluminum further reduced the uptake of (45)Ca(2+). Uptake of phosphate ((32)P) and concentrations of phosphorus in root and shoot were increased when plants were grown in the presence of 0.1 mM Al. Exposure to 1.0 mM Al, however, reduced the concentration of phosphorus in roots and shoots and the reduction was greater when plants were grown in the presence of a high external NO(3) (-) concentration. Aluminum binds to roots, and plants grown in the presence of 1.0 mM Al had a slightly higher concentration of aluminum in roots than plants grown in the presence of 0.1 mM Al, whereas the concentration of Al in the shoot was increased 2 to 3 times in plants exposed to 1.0 mm Al. Furthermore, the effects of 1.0 mM Al on uptake of other macronutrients were quite different from the effects of 0.1 mM Al. We conclude that 0.1 mM Al facilitates uptake and transport of phosphorus in beech and that between 0.1 and 1.0 mM Al there is a dramatic change in the effects of Al on uptake and transport of divalent cations and phosphorus.     

不同N源对兴安落叶松苗木生长,养分吸收及离子平衡的影响(英文)

本文研究了不同N源对落叶松苗木干物重、养分吸收及离子平衡的影响。结果表明:施铵态N的苗木干物重小于对照处理;施硝铵态N的苗木生长与对照和施硝态N的苗木差别不大,但较施铵态N的苗木生长要好。铵态N与硝铵态N处理苗木地上部的阳离子总浓度受N水平的影响很小,而硝态N处理时则阳离子浓度增加;各处理对地上部阴离子浓度的影响均不大。在根部除硫酸根与钙离子外,阳离子与阴离子浓度均变化不大。硝态N处理的苗木具有较高的C-A值;△(C-A)/△Norg值在硝态N处理的苗木中随N供应量的增加而略有变化,但铵态N处理则明显下降;硝铵态N处理苗木的△(C-A)/△Norg值界于铵态N处理与硝态N处理之间。     

Root cold tolerance of black spruce seedlings: viability tests in relation to survival and regrowth

Root systems of 6-month-old, cold-hardened, container-grown black spruce seedlings (Picea mariana (Mill.) B.S.P.) were exposed to 0, -5, -10, -15, -20, or -22.5 degrees C. Freezing-induced damage to fine roots, coarse roots and the whole root system was assessed by various viability tests including leakage of electrolytes, leakage of phenolic compounds, water loss, root and shoot water potentials, and live root dry mass. To assess the long-term effects of freezing-induced root damage, seedling survival and regrowth were measured. Leakage of both electrolytes and phenolic compounds differed among fine roots, coarse roots, and whole root systems. In coarse roots and the whole root system, but not in fine roots, leakage of electrolytes, leakage of phenolic compounds, water loss, and root and shoot water potentials were correlated with percentage of live root dry mass which, in turn, was highly correlated with seedling survival and regrowth. Compared with live root dry mass, electrolyte and phenolic leakage, water loss, and root and shoot water potentials were less well correlated with seedling survival and regrowth. Among the viability tests, electrolyte leakage of the whole root system correlated most closely with seedling survival and regrowth. Under freezing conditions that destroyed less than 50% of each seedling's root system, about 70% of the seedlings survived and subsequent growth was little affected, whereas under freezing conditions that destroyed 70% of each seedling's root system, only about 30% of the seedlings survived and subsequent growth was reduced compared with that of undamaged plants.     

Effects of different soil treatments on growth and net nitrogen uptake of newly planted Picea abies (L.) Karst. seedlings

Five soil treatments in a 4-year-old clearcut in southern Sweden affected biomass increase and net nitrogen uptake by planted Norway spruce (Picea abies (L.) Karst.) seedlings through their on net mineralisation and root growth. The patch soil treatments studied were: (i) soil inversion in an old clearcut; (ii) mineral soil from the clearcut remaining, (iii) mineral soil from the clearcut with fertiliser application during the first season; (iv) mineral soil from a nearby uncut forest replacing the clearcut mineral soil; and (v) an untreated control. Growth increased in seedlings in treatments (i) and (iii), but growth in soil treatments with humus removal was not better than that of seedlings in untreated soil. High N uptake early in the first growing season resulted in increased growth during this season in contrast to late N uptake that resulted in a high N concentration in the seedlings after the first growing season. This in turn led to a high growth rate during the next growing season. Generally, both root growth and net N mineralisation were positively correlated to N uptake in the soil treatments. Therefore, a combination of low net N mineralisation and poor root growth as a result of high soil density appears to explain the low N uptake in seedlings in undisturbed soil. The importance of competition with field vegetation for N and water was not clear. Net mineralisation was larger in soil treatments where the humus layer was retained than where it was removed. Net N mineralisation in soil from old clearcuts was the same as in soil from fresh clearcuts.     

不同磷水平条件下彩色豆马勃对加勒比松苗木生长的作用*

将彩色豆马勃Ｃｏｋｅｒ ｅｔ ｃｏｕｃｈ子实体制成孢子悬浮液菌剂，在６个Ｐ水平处理上，接种加勒比松容器苗，育苗及造林试验的结果表明，接种苗木的生长优于未接种的，根径和干重两项指标尤为明显。Ｐ肥对容器苗的生长有明显作用，适宜的Ｐ浓度会促进菌根化苗木的生长。总体来说，在Ｐ浓度０．５％－７．０％的范围内，接种彩色豆马勃的处理最为理想。     

Nitrogen forms affect root structure and water uptake in the hybrid poplar

The study analyses the effects of two different forms of nitrogen fertilisation (nitrate and ammonium) on root structure and water uptake of two hybrid poplar (Populus maximowiczii x P. balsamifera) clones in a field experiment. Water uptake was studied using sap flow gauges on individual proximal roots and coarse root structure was examined by excavating 18 whole-root systems. Finer roots were scanned and analyzed for architecture. Nitrogen forms did not affect coarse-root system development, but had a significant effect on fine-root development. Nitrate-treated trees presented higher fine:coarse root ratios and higher specific root lengths than control or ammonium treated trees. These allocation differences affected the water uptake capacity of the plants as reflected by the higher sapflow rate in the nitrate treatment. The diameter of proximal roots at the tree base predicted well the total root biomass and length. The diameter of smaller lateral roots also predicted the lateral root mass, length, surface area and the number of tips. The effect of nitrogen fertilisation on the fine root structure translated into an effect on the functioning of the fine roots forming a link between form (architecture) and function (water uptake).     

Effect of shoot size on the gas exchange and growth of containerized Picea mariana seedlings under different watering regimes

Containerized black spruce (Picea mariana [Mill.] B.S.P.) seedlings of three different sizes (small, medium, and large) were planted in raised sand beds maintained under wet, moderately dry or dry watering regimes during the growing season. The small seedlings were of a conventional stock type. The two larger sizes were novel stock types grown in larger containers. Physiological measurements during the summer showed that the small and medium seedlings maintained nearly similar levels of gas exchanges and water status, but that the large seedlings had reduced net photosynthesis and stomatal conductance under all watering regimes. Analysis of dry masses showed comparable relative growth rates in the small and medium seedlings, but a small to null growth in the large seedlings. Examination of root relative growth rate under wet conditions revealed significant root growth in small and medium seedlings, but negligible growth in the large seedlings. It was concluded that increasing the shoot size of containerized seedlings can be achieved without increasing the susceptibility of the seedlings to water stress, as long as the vigour of the root system is maintained.     

Changes in stream chemistry associated with insect defoliation in a Pennsylvania hemlock-hardwoods forest

Disturbances to forested watersheds often lead to elevated concentrations and fluxes of solutes in stream water. We examined the solute chemistry of streams draining mostly old-growth hemlock-hardwoods forest in two adjacent watersheds on the Allegheny High Plateau in northwestern Pennsylvania before, during, and after a single season of defoliation of hardwoods by elm spanworm (Ennomos subsignarius Hübner) larvae. Concentrations of potassium, ammonium, and dissolved organic carbon increased during the defoliation or in the following month. During this same time, concentrations of sulfate, nitrate, calcium, and magnesium decreased. However, by the end of the summer, nitrate concentrations exceeded pre-defoliation concentrations (<0.4 mg NO₃-N/L) and then peaked during the following summer (1.4 mg NO₃-N/L). Nitrate concentrations declined to pre-defoliation concentrations by the end of the second summer following defoliation. Calcium and magnesium concentrations, which generally correlated most strongly with sulfate concentrations, increased in conjunction with elevated nitrate concentrations after defoliation. Increases in nitrate, calcium, and magnesium in stream water were consistent with biogeochemical changes following clearcutting and insect defoliation at other locations in eastern North America. Therefore, we hypothesize that elevated nitrification generated nitrate ions which in turn leached calcium and magnesium from soils into the streams. The short-term changes that occurred during and immediately after defoliation in our study suggest that defoliation may influence stream chemistry in other ways, as well (e.g., through the leaching of nutrients and labile carbon from insect frass and greenfall).     

Tolerance of citrus rootstock seedlings to saline stress based on their ability to regulate ion uptake and transport

Forty-five-day-old seedlings of sour orange (Citrus aurantium L.) and Citrus macrophylla Wester, the most commonly used rootstocks in lemon orchards, were grown in nutrient solutions containing 1 (control), 10, 20, 30 or 60 mM NaCl for 14 days. The effects of salinity on growth, uptake, transport and accumulation of Cl- and Na+ ions in leaves, stem and four root segments were studied. The 60 mM NaCl treatment reduced leaf dry mass more in C. macrophylla (40%) than in sour orange (20%), whereas it reduced root dry mass more in sour orange (36%) than in C. macrophylla (20%). In C. macrophylla, Cl- and Na+ uptake rates were high at the beginning of the saline treatments, but low at the end of the 14-day experiment. In contrast, sour orange showed high uptake rates at the beginning and end of the experiment. In response to increasing salinity, root and shoot concentrations of Cl- and Na+ increased in sour orange, but not in C. macrophylla. Different loading characteristics of Cl- and Na+ were observed between young and old segments of the root system. In general, old root segments reached quasi-steady-states later than young root segments. These results suggest that sour orange and C. macrophylla have different regulatory mechanisms for uptake and transport of Cl- and Na+.     

Competition for nitrogen by three sympatric species of Eucalyptus

? Nitrogen (N) exists in the soil in a variety of different forms and thus plants may avoid competition by taking up N as different chemical forms.

? This study examined the uptake of nitrate, ammonium and glycine by three co-occurring species of Eucalyptus (E. obliqua, E. radiata and E. rubida) from dry sclerophyll forest in south-eastern Australia. Species preference for N forms was determined by measuring uptake of glycine, nitrate and ammonium from ¹⁵N-labelled solutions containing equimolar 100 μmol L^? concentrations of all three N forms. KCl extracts were used to assess the relative abundance of the different forms of N in the soil’s exchangeable pool.

? KCl extracts of soil indicated that amino acids comprised 30–40% of the soluble non-protein N, while ammonium varied from 10–70% and nitrate from 5–70%. In all species, ammonium was the preferred source of nitrogen and was taken up 2.5–4.5 times faster than glycine, and 30–50 times faster than nitrate. Species did not differ in preference for N-forms (species*N-form interaction, not significant).

? This study indicates that nitrate, ammonium and amino acids are all present in soil, and thus there is the potential for niche differentiation based on chemical forms of N. However, there is no evidence that co-occurring Eucalyptus avoid competition for N by taking up different chemical forms.

     

An experimental test of a nitrogen uptake and partitioning model for young trees

Simulation models of nitrate uptake and total nitrogen partitioning during the exponential growth phase of one-year-old peach trees (Prunus persica (L.) Batsch.) were tested in an experiment with 88 plants grown in soil-filled containers. Plants were fertilized with (15)N-NO(3) (-) and nitrate uptake estimated by periodic destructive analysis of plants for excess (15)N. Partitioning of N within the trees was followed by the analysis of plant parts for total N and (15)N. The nitrate uptake model, which provides one of the main inputs to the partitioning model, is based on a simplified form of the Michaelis-Menten equation adapted to describe uptake by roots growing in soil layers. The nitrogen partitioning model considers each plant part (e.g., roots, trunk, shoots, leaves) as either a sink or a source for nitrogen. The model uses a flow equation, which is the same for all plant parts, to model the dynamics of nitrogen partitioning in the tree using increases in dry matter of various plant parts as driving force variables. The experiment demonstrated an error in the compartment organization of the partitioning model as a result of which the model failed to simulate changes in root N. A modification of the partitioning model structure to take account of the importance of trunk nitrogen reserves for root growth at the beginning of the growing season, which was indicated by the (15)N data, greatly improved prediction of root N. This modification is discussed in relation to the modeling approach.     

Differences in growth and nutrient uptake from a coarse-soil substrate by ectomycorrhizal- and fungicide-treated Picea abies seedlings

In order to quantify the importance of ectomycorrhizal fungi on nutrient uptake from the coarse-soil fraction of a haplic Cambisol (alumic), a microcosm study that allowed for nutrient budgets was designed. Ectomycorrhizal- and fungicide-treated spruce seedlings were grown on isolated and cleaned gneiss fragments (6.3 mm > Ø > 2 mm) from 90 cm soil depth. The substrate was the only source of Ca, K and Mg. Ectomycorrhizal seedlings showed no signs of nutrient deficiencies and biomass increased significantly compared to initial seedling biomass. Ectomycorrhizal seedlings seemed well adapted to survive on the coarse-soil substrate and acquired Ca, K and Mg from the coarse-soil substrate. Gneiss fragments of the ectomycorrhizal treatment were covered by fine roots and ectomycorrhizal hyphae, as observed microscopically. Fungicide-treated seedlings?? root development was retarded, and shoot biomass only increased from stored nutrient reserves of the seedlings. The suppression of EcM colonization by the fungicide Topas^® apparently caused a root growth inhibiting effect. Furthermore, the extinction of mycorrhiza initiated an increased nitrification and acidification and a consequent nutrient cation release triggered by nitrate in the drainage.     

Free amino acids and protein in Scots pine seedlings cultivated at different nutrient availabilities

Scots pine (Pinus sylvestris L.) seedlings of a provenance from northern Sweden were cultivated hydroponically for 7 weeks in a climate chamber. The nutrient solution contained either 2.5 (low-N) or 50 (high-N) mg N l(-1) with other essential elements added in a fixed optimal proportion to the nitrogen. After 5 and 7 weeks, the seedlings were analyzed for growth, total nitrogen and other essential nutrients, protein and free amino acids. Low-N seedlings grew more slowly and had higher root/shoot ratios than high-N seedlings. With respect to total nitrogen, the effect of the lower nutrient supply was mainly on the nitrogen content of the whole plant and the allocation of nitrogen among tissues, not on tissue nitrogen concentration. This was also the case for potassium, phosphorus, calcium and magnesium. The proportions by weight among these macronutrients in the whole seedlings were similar in both nutrient regimes. The proportion and concentration of sulfur were significantly lower in low-N seedlings than in high-N seedlings, because of a lower net uptake of sulfur than of other macronutrients. The shoot, needles and stem of low-N seedlings had higher concentrations of free amino acids and lower concentrations of protein than the shoot, needles and stem of high-N seedlings. Arginine dominated the pool of free amino acids in the low-N seedlings, whereas glutamine predominated in the high-N seedlings. We conclude that Scots pine seedlings accumulated soluble nitrogen as arginine when net protein synthesis was limited by factors other than nitrogen availability. Nutritional imbalance, as revealed by growth characteristics and a suboptimal proportion and concentration of sulfur in the seedlings, probably affected synthesis of S-amino acids, resulting in the diversion of assimilated nitrogen to arginine instead of protein.