Temporal patterns of inorganic nitrogen uptake by mature sugar maple (Acer saccharum Marsh.) and red spruce (Picea rubens Sarg.) trees using two common approaches

Background: Plant uptake of nitrogen influences many ecosystem processes, yet uptake by trees in northern forests of the United States has not been quantified throughout the growing season.

Aims: To measure NH₄ ⁺ and NO₃ ^? uptake by mature sugar maple (Acer saccharum) and red spruce (Picea rubens) trees during the early, mid and late growing season.

Methods: At Hubbard Brook Experimental Forest, New Hampshire, we used two approaches to measure nitrogen uptake capacity by mature trees: an in situ depletion method using intact roots and an ex situ ¹⁵N tracer method using excised roots.

Results: NH₄ ⁺ uptake was greater than NO₃ ^? for both methods and tree species (P < 0.05). NH₄ ⁺ uptake was lowest during the early growing season, while NO₃ ^? uptake was lowest during the late growing season. Measured rates of NH₄ ⁺ uptake were 2–3 orders of magnitude greater using the in situ depletion method compared with the ex situ ¹⁵N tracer method.

Conclusions: These results demonstrate seasonal differences in nitrogen uptake by two dominant tree species in a northern forest and show that the method employed can significantly impact measured rates of uptake, which could have implications for understanding the magnitude of plant nitrogen uptake and for cross-study comparisons of this process.     

Uptake of water and solutes through twigs of Picea abies (L.) Karst

Summary Uptake of water and magnesium chloride solution was investigated through the outer surface of twigs of Picea abies (L.) Karst. Water uptake was determined by using pressure/volume (P/V) curves of the twigs as a basis for calculation to avoid problems of superficial extraneous water. When water was sprayed on bark and needles of 3- to 7-year-old twigs at a xylem water potential of -1.00 MPa, they absorbed as much as 80 mm³ water in 200 min/g twig dry weight as the twig water potential recovered to -0.15 MPa. With fluorescent dyes, pathways for absorption of water and solutes through the twig bark were found, particularly through the radially orientated ray tissue. In addition to uptake by mass flow, magnesium could also diffuse along a concentration gradient from the twig surface into the xylem. In the field, the magnitude of these uptake processes would depend on the concentration of elements deposited by atmospheric precipitation, the concentration gradient between the plant surface and the xylem sap, the xylem water potential and the intensity and duration of each precipitation event.     

Role of Arbuscular Mycorrhizal Fungi in Uptake of Phosphorus and Nitrogen From Soil

Abstract

Colonization of plant roots by arbuscular mycorrhizal fungi can greatly increase the plant uptake of phosphorus and nitrogen. The most prominent contribution of arbuscular mycorrhizal fungi to plant growth is due to uptake of nutrients by extraradical mycorrhizal hyphae. Quantification of hyphal nutrient uptake has become possible by the use of soil boxes with separated growing zones for roots and hyphae. Many (but not all) tested fungal isolates increased phosphorus and nitrogen uptake of the plant by absorbing phosphate, ammonium, and nitrate from soil. However, compared with the nutrient demand of the plant for growth, the contribution of arbuscular mycorrhizal fungi to plant phosphorus uptake is usually much larger than the contribution to plant nitrogen uptake. The utilization of soil nutrients may depend more on efficient uptake of phosphate, nitrate, and ammonium from the soil solution even at low supply concentrations than on mobilization processes in the hyphosphere. In contrast to ectomycorrhizal fungi, nonsoluble nutrient sources in soil are used only to a limited extent by hyphae of arbuscular mycorrhizal fungi. Side effects of mycorrhizal colonization on, for example, plant health or root activity may also influence plant nutrient uptake.     

Interaction between atmospheric and pedospheric nitrogen nutrition in spruce (Picea abies L. Karst) seedlings

The effect of NO₂ fumigation on root N uptake and metabolism was investigated in 3-month-old spruce (Picea abics L. Karst) seedlings. In a first experiment, the contribution of NO₂ to the plant N budget was measured during a 48 h fumigation with 100mm³m^?3 NO₂. Plants were pre-treated with various nutrient solutions containing NO₂ and NH₄⁺, NO₃^? only or no nitrogen source for 1 week prior to the beginning of fumigation. Absence of NH₄⁺ in the solution for 6d led to an increased capacity for NO₃^? uptake, whereas the absence of both ions caused a decrease in the plant N concentration, with no change in NO₃^? uptake. In fumigated plants, NO₂ uptake accounted for 20–40% of NO₃^? uptake. Root NO₃^? uptake in plants supplied with NH₄⁺plus NO₃^? solutions was decreased by NO₂ fumigation, whereas it was not significantly altered in the other treatments. In a second experiment, spruce seedlings were grown on a solution containing both NO₂ and NH₄⁺ and were fumigated or not with 100mm³m^?3 NO₂ for 7 weeks. Fumigated plants accumulated less dry matter, especially in the roots. Fluxes of the two N species were estimated from their accumulations in shoots and roots, xylem exudate analysis and ¹⁵N labelling. Root NH₄⁺ uptake was approximately three times higher than NO₃^? uptake. Nitrogen dioxide uptake represented 10–15% of the total N budget of the plants. In control plants, N assimilation occurred mainly in the roots and organic nitrogen was the main form of N transported to the shoot. Phloem transport of organic nitrogen accounted for 17% of its xylem transport. In fumigated plants, neither NO₃^? nor NH₄⁺ accumulated in the shoot, showing that all the absorbed NO₂ was assimilated. Root NO₃^? reduction was reduced whereas organic nitrogen transport in the phloem increased by a factor of 3 in NO₂-fimugated as compared with control plants. The significance of the results for the regulation of whole-plant N utilization is discussed.     

Nitrate Uptake and Reduction of Aseptically Cultivated Spruce Seedlings, Picea abies (L.) Karst

Spruce (Picea abies (L.) Karst.) seedlings were asepticallycultivated and the effects of different N-nutrition on net uptakeand reduction of nitrate were investigated. The characteristicsof nitrate uptake were calculated, K_s as 0?2 mol m^–3 andV_max as 18 µmol g^–1 d^–1. Low pH, and Al³⁺ in the medium caused adecrease in nitrate uptake rate. An in vivo assay was set upwhich allowed the measurement of NRA in both roots and needlesof spruce seedlings. The in vivo nitrate reductase activitywas repressed by ammonium and stimulated by nitrate. Nitratereduction was similar to nitrate uptake, negatively affectedby low pH and ammonium. Therefore, a limited N-supply to spruceseemed to occur when pH was low in the rhizosphere combinedwith the presence of Al³⁺ and . Key words: Spruce, nitrate uptake, nitrate reduction     

Inheritance of bud-set and bud-flushing in Picea abies (L.) Karst

Summary Diallel crosses were made between clones of a French and a Swedish provenance of Picea abies. The former is characterized by a long critical night length for bud-set and a late flushing of the buds; the latter by a short critical night length for bud-set and an early flushing of the buds. The F₁ hybrid seedlings and their French and Swedish intraprovenance half-sibs were tested over three growth periods in the phytotron at the College of Forestry, Stockholm. In comparison with intraprovenance half-sibs, the hybrid progenies gave, on average, an intermediate response for the photoperiodic control over budset and for the temperature requirements for bud-flushing. This indicates the prevalence of additive action of multiple factors in the determination of the photoperiodic and temperature response. However, individual interprovenance hybrid progenies revealed a range of responses, and in certain combinations the response of these hybrids and their intraprovenance half-sibs coincided. By selection of suitable parents, interprovenance crosses can be used to produce hybrids with desired photoperiodic characteristics and temperature requirements.With gratitude and appreciation we dedicate this paper to Åke Gustafsson at the occasion of his 70th birthday, April 8, 1978     

Triacylglycerols in the seeds of northern Scots pine,Pinus sylvestris L., and Norway spruce,Picea abies (L.) Karst.

The geographical variation in the composition of triacylglycerols in seeds of Scots pine (Pinus sylvestris L.) and Norway spruce [Picea abies (L.) Karst.], grown in Finland, was analyzed. The total lipid content of pine seeds was slightly higher in the northernmost provenance (68 °50N), whereas the lipid content of spruce seeds was not affected systematically by the geographical origin of the seeds. The species studied differed in the proportions of fatty acids in their triacylglycerols, though the three most abundant components were the same, i.e. oleic acid (181 n9), linoleic acid (182n-6) and 5,9,12-octadecatrienoic acid (183 5c9c12c). These fatty acids corresponded to more than 80 mol% of the total fatty acids. According to mass spectrometric analyses, the triacylglycerols of both spruce and pine seeds consisted of the same molecular species with 52–56 acyl carbons, but in different proportions. Molecules with 54 acyl carbons represented approximately 75% of the pine and 85% of the spruce triacylglycerols, with the most abundant molecular species being 545, 546 and 547. Some minor differences in the fatty acid composition of triacylglycerols of pine seeds from different seed collecting areas were found: the proportion of linoleic acid slightly increased whereas that of 5,11,14-eicosatrienoic acid decreased towards the northern origins. Similar differences were not found in the proportions of fatty acids in spruce seed lots. Furthermore, the proportions of triacylglycerols in both pine and spruce seeds from northern and southern collecting areas were not significantly different. The higher content of total lipids in spruce seeds compared with pine seeds may be due to the structure of the seed coat, and the lipophilic layers inside it, acting as a barrier to imbibition.     

Effects of acid irrigation and liming on nitrate reduction and nitrate content of Picea abies (L.) Karst. and Oxalis acetosella L.

Nitrate reductase activities (NRA) and nitrate concentration per unit biomass in Picea abies (L.) Karst. roots from four different soil horizons and in leaves and roots of the frequent field-layer species Oxalis acetosella L. were measured on six different irrigation and liming treatments within the Höglwald project, S-Bavaria, Germany. Liming increased and acid irrigation reduced soil nitrate availability when compared to control plots. Nitrate assimilation capacities of the respective plant compartments per unit of soil volume or ground area were calculated from the NRA per unit of biomass and from the biomass distribution on the various treatments.Mean NRA per unit of biomass in Picea abies roots ranged between 0.23 and 0.09 mol NO ₂ ^- g_-1 d.w. h_-1 without significant effects of soil horizon or treatment. Limed and non-limed treatments showed for Picea different root distributions within the soil profile, but root biomass per unit of ground area (295 to 220 g d.w. m^-2) was not affected by the various treatments. Thus, nitrate assimilation capacity of Picea roots per unit of ground area ranged between 19.5 and 11.4 mol NO ₂ ^- m^-2 h_-1 without major treatment effects.In laminae of Oxalis acetosella mean NRA per unit of biomass ranged between 2.91 and 0.27 mol NO ₂ ^- g_-1 d.w. h_-1 and, in contrast to Picea abies, treatment effects were found with NRA on limed plots increased and on acid irrigated plots reduced when compared to control plots. Mean leaf biomass of Oxalis per unit of ground area ranged between 9.57 and 0.66 g d.w. m^-2 and responded in a similar manner to the various treatments. Thus, for the Oxalis leaf NRA per unit of ground area (27.85 to 0.18 mol NO₂ m^-2 h_-1) a cumulative response to the variations in nitrate availability was found.The different responses of Picea abies and Oxalis acetosella to changes in soil nitrate availability are discussed with respect to their suitability to prevent soil nitrate leaching.     

Effect of artificial soil acidification and liming on growth and nutrient status of mycorrhizal roots of Norway spruce (Picea abies [L.] Karst.)

Effects of soil acidification and liming on biomass responses and free Al, Ca, K, Mg, Mn and P contents of mycorrhizal roots of mature Norway spruce (Picea abies [L.] Karst.) were studied at Höglwald Forest in Southern Germany.At the untreated site, mycorrhizal root biomass was lower in the acid humus (pH = 3.3) than in the less acid upper (0–5 cm) mineral soil (pH 4.1). Mycorrhizal roots from the humus contained 10% of the level free Al in mycorrhizal roots from the upper mineral soil. During seven years of soil acidification the quantity of mycorrhizal roots remained unaffected in the humus and the upper mineral soil, perhaps due to the high buffering capacity of the humus which prevented a significant alteration of the nutrient status of the roots. However, two years after soil acidification had been terminated, the percentage of mycorrhizal roots in the humus decreased, possibly because the free root concentrations of K had decreased.On the other hand, six years after liming, there was a two-fold increase of the annual mean quantity of mycorrhizal roots in the humus. Compensatory liming (acid irrigation after liming) had a similar effect on mycorrhizal root production in the humus. However, two years after acid irrigation had been terminated a decrease of mycorrhizal roots in the upper mineral soil (0–5 cm) was observed. Since the total amount of mycorrhizal roots in the humus and upper mineral soil remained constant, compensatory liming produced a shift in fine roots to the humus layer.The higher mass of living mycorrhizal roots in the upper mineral soil (0–5 cm) as compared to the humus of the untreated plot as well as the increased mass of mycorrhizal roots in the humus after liming or compensatory liming are both attributed to an increase in pH to 4.5 rather than alleviation of Al toxicity.     

The ion concentration of dew condensed on Norway spruce (Picea abies (L.) Karst.) and Scots pine (Pinus sylvestris L.) needles

Summary Dew droplets collected with pipettes from coniferous needles were analysed for their ionic composition. Almost all samples of dew taken from Scots pine trees (Pinus sylvestris) showed significantly higher ion concentrations than those taken from Norway spruce trees (Picea abies). This can be explained by the micromorphology of the needle surface. The higher microscale roughness of the wax layer of a pine needle causes a more efficient flux of atmospheric aerosol particles compared to the spruce needle surface. Dew on coniferous needles is shown to be capable of maintaining pH values below 3 for several hours.     

Respiration and photosynthesis in cones of Norway spruce (Picea abies (L.) Karst.)

Summary Dark respiration and photosynthetic carbon dioxide refixation in purple and green Picea abies cones were investigated from budbreak to cone maturity. The rate of dark respiration per unit dry weight and CO₂ refixation capacity decreased during cone maturation. At the beginning of the growing season, photosynthetic CO₂ refixation could reduce the amount of CO₂ released by respiration in green and purple cones by 50% and 40%, respectively. The seasonal performance of the components of the cone carbon balance was calculated using information on the seasonal course of respiration, refixation capacity and the light response curves of cone photosynthesis, as well as the actual light and temperature regime in the field. The daily gain of CO₂ refixation reached 28%–34% of respiration in green and 22%–26% in purple cones during the first month of their growth, but decreased later in the season. Over the entire growth period refixation reduced carbon costs of cone production in both cone colour polymorphs by 16%–17%.     

Root distribution in a Norway spruce (Picea abies (L.) Karst.) stand subjected to drought and ammonium-sulphate application

Results of the spatial distribution of fine roots are reported from a Norway spruce (Picea abies (L.) Karst.) in SW Sweden stand subjected to drought (D) and ammonium-sulphate application (NS). The sampling was carried out by excavating monoliths in segments of 0.5 × 0.5 × 0.1 m to a depth of one meter. Root data also included in the study were obtained by excavating whole trees and soil coring.The data suggest a fairly deep distribution pattern of fine roots (< 1 mm in diameter) in the study area compared with other forest sites in SW Sweden. The weight fraction of living fine roots in the LFH-horizon amounted to 53, 36 and 55% of the total fine-root biomass and 12, 30 and 32% of the total fine-root necromass (dead fine roots) in the control, D and NS-treatment areas respectively. Drought seemed to result in a redistribution of fine roots to deeper mineral soil horizons. Ammonium sulphate application led to the reverse, viz, a concentration of fine roots to the LFH-horizon. A significantly smaller fine-root necromass was indicated in the LFH-horizon of the control areas compared with both the D and NS-treatment areas, suggesting a high mortality of fine roots in these areas. A heavy dry matter fraction accumulates in roots > 1 mm in diameter and in stumps. These root fraction, were frequently found between the trees, although the stump constitutes an important fraction in terms of dry weight.     

Effects of varied soil nitrogen supply on Norway spruce (Picea abies [L.] Karst.)

During a seven-month period the effect of different nitrogen (N) availability in soil on growth and nutrient uptake was studied in three-year-old Norway spruce (Picea abies [L.] Karst.) trees. The plants were grown in pots on N-poor forest soil supplied with various amounts and forms (inorganic and organic) of N. Increasing supply of inorganic N (as NH₄NO₃) increased the formation of new shoots and shoot dry weight. The root/shoot dry weight ratio of new growth was drastically decreased from 1.6 in plants without N supply to 0.5 in plants supplied with high levels of NH₄NO₃. This decrease in root/shoot dry weight ratio was associated with distinct changes in root morphology in favour of shorter and thicker roots. The addition of keratin as organic N source did neither affect growth nor root morphology of the trees. The amount of N taken up by plants was closely related to the supply of inorganic N, and trees supplied with highest levels of NH₄NO₃ also had the highest N contents in the dry matter of needles and roots. In contrast, N contents in needles of trees grown without additional N, or with keratin supply, were in the deficiency range. Supply of NH₄NO₃ decreased the contents of phosphate (P) and potassium (K) and therefore markedly increased N/P and N/K ratios in the needles. On the other hand, the contents of calcium (Ca), magnesium (Mg), and manganese (Mn) in the needles were increased in the plants supplied with inorganic N, suggesting high soil availability and promotion of uptake of these divalent cations by high nitrate uptake. The observed effects on root/shoot dry weight ratio, root morphology, and mineral nutrient composition of the needles indicated that high inorganic N supply may increase above-ground productivity but at the same time decrease the tolerance of trees against soil-borne (e.g. deficiency of other mineral nutrients) stress factors. Deceased 21 September 1996 Deceased 21 September 1996     

Seasonal ionic fluctuations and annual growth rates in stands of Pinus silvestris L. and Picea abies Karst. (L.)

Seasonal variations in potassium, calcium, nitrogen, phosphorus, and magnesium contents of needles from two different stands of Pinus silvestris L. and Picea abies (L.) Karst. were determined monthly during a period of two years, and the growth rates once a year during five years. The stands were growing on sand or on clay. The supposed transport of potassium to the shoot during autumn could not be demonstrated. The nutrient status of pine and spruce growing on sand and clay was very similar, except for calcium and magnesium. There were only small differences in ion contents between pine and spruce, except for calcium. On soils with low water-holding capacity, the available water in dry years is the limiting factor affecting the growth rate of spruce but not of pine. It is concluded that the nutrient status of the leaves, the growth rates and the available water in the soil are factors that should have an important part in any discussion of fertilization of coniferous forests.     

Mineral nutrient imbalances and arginine concentrations in needles of Picea abies (L.) Karst. from two areas with different levels of airborne deposition

Summary This study evaluated the utility of free arginine concentrations as a possible alternative to mineral nutrient concentrations as an indicator of mineral nutrient imbalances in Norway spruce [Picea abies (L.) Karst.]. The concentrations of mineral nutrients and arginine were measured in the needles of spruce trees from two areas in Sweden, one with high (15–30 kg ha^–1 year^–1) airborne N deposition, and one with lower (1–4 kg ha^–1 year^–1) deposition. The spruce needles from the area with high deposition in southern Sweden had elevated concentrations of free arginine, especially on peat sites. No increase in concentrations was found in the low deposition area in northern Sweden. The arginine concentrations on different sampling occasions were consistent for each site and for individual trees. Trees on peat sites in the south seemed to suffer from P deficiency in relation to N availability. A tendency for K deficiency in needles from peat sites was also found. Needles from trees on mor plots showed acceptable levels of these nutrient elements. Sites in the northern area showed low N concentrations, but the ratios between the different mineral elements analyzed in this study and N were within ranges normally found. A low P/N ratio correlated to high free arginine concentration. The threshold for elevated arginine concentrations is crossed when P/N ratios drop below 0.07–0.08. A tendency for increased arginine levels when ratios between N and the other mineral elements are low was also found, although it was not as strong as that for the P/N ratio. The results are discussed in relation to mineral nutrient imbalances in spruce stands caused by airborne deposition.