Assimilation of nitrate and ammonium by the Scots pine (Pinus sylvestris) seedling under conditions of high nitrogen supply

Seedlings of Scots pine ( Pinus sylvestris L.) were grown on perlite for 21 days under controlled conditions. Apart from the water control, KNO₃ (15 m M ), (NH₄)₂SO₄ (7.5 m M ), and NH₄NO₃ (15 m M ) were offered to study the effects of a high nitrogen supply on nitrogen assimilation. In some experiments 1.3 m M potassium was added to the basic ammonium solutions. In labelling studies nitrate and ammonium were 2.3 atom%¹⁵N-enriched. It was found that over the 21-day period approximately three times more ammonium-N was taken up than nitrate-N. However, nitrate and ammonium, applied simultaneously, were taken up to the same extent as if they were applied separately (additivity). The presence of K⁺ in the medium did not affect N-uptake. Among the soluble N-containing compounds nitrate, ammonium and 8 amino acids were quantified. It was found that assimilation of nitrate can cope with the uptake of NO⁻₃ under all circumstances. Neither free nitrate nor ammonium or amino acids accumulated to an extent exceeding the values of water-grown seedlings. On the other hand, in case of high ammonium supply considerably more nitrogen was taken up than could be incorporated into nonsoluble N-containing substance ('protein'). The remaining nitrogen was found to accumulate in intermediary storage pools (free NH₄⁺, glutamine, asparagine, arginine). Part of this accumulated N could be incorporated into protein when potassium was offered in the nutrient solution. It is concluded that potassium is a requirement for a high rate of protein synthesis not only in crop plants but also in conifers.     

Relationships between fungal uptake of ammonium, fungal growth and nitrogen availability in ectomycorrhizal Pinus sylvestris seedlings

 Nitrogen deposition and intentional forest fertilisation with nitrogen are known to affect the species composition of ectomycorrhizal fungal communities. To learn more about the mechanisms responsible for these effects, the relations between fungal growth, nitrogen uptake and nitrogen availability were studied in ectomycorrhizal fungi in axenic cultures and in symbiosis with pine seedlings. Effects of different levels of inorganic nitrogen (NH₄) on the mycelial growth of four isolates of Paxillus involutus and two isolates of Suillus bovinus were assessed. With pine seedlings, fungal uptake of ¹⁵N-labelled NH₄ was studied in short-term incubation experiments (72 h) in microcosms and in long-term incubation experiments (3 months) in pot cultures. For P. involutus growing in symbiosis with pine seedlings, isolates with higher NH₄ uptake were affected more negatively at high levels of nitrogen availability than isolates with lower uptake. More NH₄ was allocated to shoots of seedlings colonised by a high-uptake isolate, indicating transfer of a larger fraction of assimilated NH₄ to the host than with isolates showing lower NH₄ uptake rates. Thus low rates of N uptake and N transfer to the host may enable EM fungi avoid stress induced by elevated levels of nitrogen. Seedlings colonised by S. bovinus transferred a larger fraction of the ¹⁵N label to the shoots than seedlings colonised by P. involutus. Seedling shoot growth probably constituted a greater carbon sink in pot cultures than in microcosms, since the mycelial growth of P. involutus was more sensitive to high NH₄ in pots. There was no homology in mycelial growth rate between pure culture and growth in symbiosis, but N uptake in pure culture corresponded to that during growth in symbiosis. No relationship was found between deposition of antropogenic nitrogen at the sites of origin of the P. involutus isolates and their mycelial growth or uptake of inorganic nitrogen. Accepted: 18 September 1998     

Utilization of organic nitrogen at two different substrate pH by different ectomycorrhizal fungi growing in symbiosis with Pinus sylvestris seedlings

The aim of this study was to test the potential of four isolates of ectomycorrhizal (EM) fungi to utilize organic nitrogen (N) at two different substrate pHs. The organic N source (¹⁵N labelled lyophilised fungal mycelium) was mixed with either untreated peat/sand mixture (pH 4.9) or peat/sand mixture limed to a pH of 5.9 and put in cylindrical containers added to each pot. The content of the containers was separated from the roots of Pinus sylvestris seedlings by a nylon mesh and a 2 mm air gap to reduce diffusion of labelled N to the roots. The mycorrhizal plants (except those colonized by Suillus variegatus 2) took up significantly more ¹⁵N from the labelled mycelium than uncolonized seedlings. Liming significantly reduced the uptake of ¹⁵N by one of the EM fungi (unidentified) but not the other tested species (Paxillus involutus and two isolates of S. variegatus). The EM fungal isolates differed in their influence on the bacterial activity of the soil. This was reduced with P. involutus at both pH levels and increased with one of the two S. variegatus isolates at the high pH and with the other S. variegatus isolate at the low pH level. Liming the soil generally increased bacterial activity. The influence of liming on the proportion of organic N uptake in relation to inorganic N uptake by ectomycorrhizal trees is discussed.     

Free amino acid, ammonium and nitrate concentrations in soil solutions of a grazed coastal marsh in relation to plant growth

Soluble free amino acids, ammonium and nitrate ions as sources of nitrogen for plant growth were measured in soils of a coastal marsh grazed by snow geese in Manitoba, Canada. Amounts of nitrogen, primarily ammonium ions, increased in the latter half of the growing season and over winter, but fell to low values early in the growing season. Free amino acid concentrations relative to ammonium concentrations were highest during the period of rapid plant growth in early summer, especially in soils in the intertidal zone, where the median ratio of amino acid nitrogen to ammonium nitrogen was 0·36 and amino acid concentrations exceeded those of ammonium ions in 24% of samples. Amino acid profiles, which were dominated by alanine, proline and glutamic acid, were similar to goose faecal profiles. In a continuous flow hydroponic experiment conducted in the field, growth of the salt‐marsh grass, Puccinellia phryganodes, on glycine was similar to growth on ammonium ions at an equivalent concentration of nitrogen. When supplies of soil inorganic nitrogen are low, amino acids represent a potentially important source of nitrogen for the re‐growth of plants grazed by geese and amino acid uptake may be as high as 57% that of ammonium ions.     

褐环乳牛肝菌对樟子松和油松根际土壤真菌多样性的影响

为了解褐环乳牛肝菌Suillus luteus对樟子松Pinus sylvestris var. mongolica和油松Pinus tabulaeformis根际土壤真菌群落结构的影响,采用Illumina MiSeq高通量测序,对两种松树接种S. luteus与对照组的根际土壤真菌群落结构进行研究。结果显示,4个样品共获得原始序列347 681条,归为5个真菌门。综合各土壤样品真菌Alpha多样性指数及OTUs-Venn图,发现接种S. luteus后樟子松和油松根际土壤真菌相对丰度与对照存在一定差异。群落结构分析表明,接种S. luteus提高了樟子松和油松根际土壤担子菌和壶菌的相对丰度,抑制了子囊菌门真菌。优势属由原来的Geopora转变为Suillus。通过PCA分析与NMDS分析发现接种S. luteus后樟子松和油松根际土壤真菌群落差异性增加,且接种S. luteus后樟子松根际土壤真菌群落结构相似性显著高于油松根际土壤真菌群落结构相似性。接种S. luteus的樟子松和油松土壤真菌丰富度降低、多样性增加,接种S. luteus改变了樟子松和油松根际土壤真菌群落结构和优势真菌种群。试验结果为樟子松和油松促生真菌菌种筛选和育苗工作提供了依据。     

Organic nitrogen content and nitrate and nitrite reductase activities in tritordeum and wheat grown under nitrate or ammonium

Tritordeum is a fertile amphiploid derived from durum wheat (Triticum turgidum L. conv. durum) × a wild barley (Hordeum chilense Roem. et Schultz.). The organic nitrogen content of tritordeum grain (34 mg g^-1 DW) was significantly higher than that of its wheat parent (25 mg g^-1 DW). Leaf and root nitrogen content became higher in tritordeum than in wheat after four weeks of growth, independently of the nitrogen source (either NO₃ ^- or NH₄ ⁺). Under NO₃ ^- nutrition, tritordeum generally exhibited higher levels of nitrate reductase (NR) activity than wheat. Nitrite reductase (NiR) levels were however lower in tritordeum than in its wheat parent. In NH₄ ⁺-grown plants, both NR and NiR activities progressively decreased in the two species, becoming imperceptible after 3 to 5 weeks of growth. Results indicate that, in addition to a higher rate of NO₃ ^- reduction, other physiological factors must be responsible for the greater accumulation of organic nitrogen in tritordeum grain.     

NIR spectroscopy,mineral nitrogen analysis and soil incubations for the prediction of crop uptake of nitrogen during the growing season

To predict the amount of N taken up in above-ground plant parts during the growing season, initial mineral soil N, a soil incubation method, soil organic matter and NIR data were compared as predictors. Soil samples were taken from 15 plots cropped with winter wheat on a farm in south-western Sweden. The plots were not fertilized with N during the 1997 growing season. N contents in above-ground plant parts were measured in mid-June and in mid-August. All methods were capable of predicting the crop uptake of N reasonably well. NIR data gave at least as good predictions as the best traditional method, initial soil NO₃-N. The most important wavelengths, around 1400 and 1700 nm, and above 2000 nm, coincide with the wavelengths reported earlier to be important for the prediction of soil organic matter. However, the data suggest that other soil components influencing mineralization are also spectrally active. Since very few samples were taken, the studies need to be extended in order to be able to use the method in practice. It is recommended that further studies be instigated for the possibility of using the same NIR calibration over several years and to clarify the spatial regions that the calibrations can cover. This revised version was published online in June 2006 with corrections to the Cover Date.     

Discrimination of nitrogen isotopes during absorption of ammonium and nitrate at different nitrogen concentrations by rice (Oryza sativa L.) plants

Studies of uptake of ionic sources of N by two hydroponically grown rice (Oryza sativa L.) cultivars (paddy‐field‐adapted Koshihikari and dryland‐adapted Kanto 168) showed that the magnitude of the nitrogen isotope fractionation (?) for uptake of NH₄⁺ depended on the concentrations of NH₄⁺ and cultivar (averaging –6·1‰ for Koshihikari and –12·0‰ for Kanto 168 at concentrations from 40 to 200 mmol m^?3 and, respectively, –13·4 and –28·9‰ for the two cultivars at concentrations from 0·5 to 4 mol m^?3). In contrast, the ? for uptake of NO₃^? in similar experiments was almost insensitive to the N concentration, falling within a much narrower range (+3·2‰ to –0·9‰ for Koshihikari and –0·9‰ to –5·1‰ for Kanto 168 over NO₃^? concentrations from 0·04 to 2 mol m^?3). From longer term experiments in which Norin 8 and its nitrate‐reductase deficient mutant M819 were grown with 2 or 8 mol m^?3 NO₃^? for 30 d, it was concluded that the small concentration‐independent isotopic fractionation during absorption of this ion was not related to nitrate reductase activity.     

Interactions in the uptake of amino acids, ammonium and nitrate ions in the Arctic salt-marsh grass, Puccinellia phryganodes

The uptake of amino acids and inorganic nitrogen by roots of Puccinellia phryganodes was examined to assess the potential contribution of soluble organic nitrogen to plant nitrogen uptake in Arctic coastal marshes, where free amino acids constitute a substantial fraction of the soil‐soluble N pool. Short‐term excised root uptake experiments were performed using tillers grown hydroponically under controlled conditions in the field. The percentage reductions in ammonium uptake at moderate salinity (150 mm NaCl) compared with uptake at low salinity (50 mm NaCl) were double those of glycine, but glycine uptake was more adversely affected than ammonium uptake by low temperatures. Glycine uptake was higher at pH 5·7 than at pH 7·0 or 8·2. The glycine uptake was up‐regulated in response to glycine, whereas ammonium uptake was up‐regulated in response to ammonium starvation. Nitrate uptake was strongly down‐regulated when tillers were grown on either ammonium or glycine. In contrast to N‐starved roots, which absorbed ammonium ions more rapidly than glycine, the roots grown on glycine, ammonium and nitrate and not N‐starved prior to uptake absorbed glycine as rapidly as ammonium and nitrate ions combined. Overall, the results indicate that amino acids are probably an important source of nitrogen for P. phryganodes in Arctic coastal marshes.     

Effects of carbon and nitrate additions to soil upon leaching of nitrate,microbial predators and nitrogen uptake by plants

Amendments with glucose significantly reduced the amount of nitrate leached from a sandy soil amended with nitrate. The decrease was most likely caused by immobilisation of the nitrate into microbial cells. Populations of ciliates and flagellates and amoebae, but not nematodes, increased 7–14 days following glucose amendments. Mineralisation of the immobilised nitrate occurred during this period. Some of the mineralised nitrogen appeared to be available to ryegrass plants only if the roots exploited most of the soil during the period of maximum predator activity. After 28 days, 44% of the organic N remaining in the soil after leaching was taken up by the plants. The difference developed over the last 2 weeks when amoebal populations were large.     

The uptake of nitrate and ammonium nitrogen in Chara hispida L.: the contribution of the rhizoid

Abstract The uptake of ammonium and nitrate nitrogen by cultured plants of the green freshwater alga Chara hispida L. has been compared quantitatively with the contribution of its rhizoidal tissue. In the short-term, the rhizoid takes up 7–20% of the ammonium nitrogen, and about 15% of the nitrate that is taken up by whole plants under similar conditions. The uptake was studied over a range of both temperatures and external concentrations. The apparent activation energy for the uptake of NH₄⁺ and NO₃^? by the whole plant was found to be 50 kJ mol^?1 and 30 kJ mol^?1, respectively. For the rhizoid, the values were similar for both nitrogenous ions, 106 kJ mol^?1 and 70–100 kJ mol^?1. The rhizoidal uptake mechanism for ammonium nitrogen operates more efficiently compared to that in the whole plant. Nitrate is taken up by the rhizoid by a mechanism with a substrate affinity higher than in the plant taken as a whole. The possible ecological significance of the results is discussed.     

Influence of dolomitic lime on DOC and DON leaching in a forest soil

The influence of liming on leaching and distribution of dissolved organic carbon (DOC) and nitrogen (DON) in mineral soil was investigated in a leaching experiment with soil columns. Soil samples from separate horizons (O, A and B horizons) were collected from control and limed plots in a field liming experiment in a spruce forest in southern Sweden. The field liming (0.88 kg m^-2) had been carried out 8 years before sampling. To minimize the variation among replicates, soil profiles were reconstructed in the laboratory so that the dry weight was the same for each individual soil horizon regardless of treatment. Two soil column types were used with either the O+A horizons or the O+A+B horizons. One Norway spruce seedling (Picea abies (L.) Karst) was planted in each soil column. Average pH in the leachate water was greater in the limed treatment than in the control treatment (5.0 versus 4.0 for O+A columns and 4.3 versus 3.8 for O+A+B columns). After reaching an approximate steady state, the leaching of DOC was 3--4 times greater from the limed O+A and O+A+B columns than from the corresponding control columns but the leaching of DON increased (3.5 times) only in the limed O+A columns. There was a significant correlation between DOC and DON in the leachates from all columns except for the control O+A+B columns, which indicated a decoupling of DOC and DON retention in the B horizon in the control treatment. This might be explained by a selective adsorption of nitrogen poor hydrophobic compounds (C/N ratio: 32--77) while there was a lower retention of nitrogen rich hydrophilic compounds (C/N ratio: 14--20). Proportionally more hydrophobic compounds were leached from the limed soil compared to the unlimed soil. These hydrophobic compounds also became more enriched in nitrogen after liming so in the limed treatment nitrogen might be adsorbed at nearly the same proportion as carbon, which might explain the fact that there was no decoupling of leached DOC and DON from the B horizon after liming.     

Soil type affects nitrogen conservation in foliage of small Pinus sylvestris L. trees

Nutrient conservation in plants and soil fertility may be intricately linked. We studied nitrogen conservation in small Scots pine (Pinus sylvestrisL.) trees growing in stands on organogenic Dystric Histosols and on mineral Podzols. Nitrogen-resorption efficiency (NRE) and proficiency (NRP) of senescent needles, and mean residence time of nitrogen (MRT) were studied in relation to needle surface area, needle longevity, and leaf mass per area (LMA). Trees on Podzols had higher nitrogen concentration in green needles than the trees on Dystric Histosols, but the nitrogen concentration of yellowing needles was similar for trees on both soil types. NRE averaged 65±3.5% (mean±SD) and 56±7.2% for the trees on Podzols and Dystric Histosols, respectively. Neither NRP (0.44±0.05% and 0.35±0.07%, respectively) nor MRT (8.4±2.3 and 6.1±1.2 years) differed significantly between the stands on the two soil types. Mean needle surface area was significantly smaller in trees on Dystric Histosols (76±29 mm²) than on Podzols (131±38 mm²), whereas needle longevity varied between 2 and 4 years independently of the soil type. Trees invested, on average, the same amount of dry matter per unit of needle area on both soil types. Growth of trees, measured as increment of shoot length, was more restricted on Dystric Histosols (55±18 mm yr^–1) than on Podzols (184±44 mm yr^–1). The results of the correlation analysis applied to pooled data were inconsistent with the relations between traits of stress resistance syndrome observed in inter-specific comparisons. The study indicated that Scots pine trees relocated nitrogen from senescent foliage more efficiently on mineral Podzols than on organogenic Dystric Histosols, but the minimum nitrogen concentration of needles appeared to be similar on both soil types.     

Effects of gypsum on the uptake,assimilation and cycling of 15N-labelled ammonium and nitrate-N by perennial ryegrass

Solution culture studies have shown that plant uptake of NH₄ ⁺ and NO₃ ^- can be improved by increasing the concentration of Ca²⁺ in the root environment: the same may be true for grass grown in soil culture. An experiment was set up to see whether gypsum (CaSO₄ 2H₂O) increased the rate at which perennial ryegrass absorbed ¹⁵NH₄ ⁺ and ¹⁵NO₃ ^- from soil.The results demonstrated that gypsum increases the rates of uptake of both NH₄ ⁺ and NO₃ ^- by perennial ryegrass. However because there was little potential for mineral-N loss from the experimental system, either by gaseous emission or by N immobilization, long term improvements in fertilizer efficiency were not observed. Nitrogen cycling from shoots to roots commenced once net uptake of N into plants had ceased. Labelled N transferred thus to roots underwent isotopic exchange with unlabelled soil N. It was suggested that this exchange of N might constitute an energy drain from the plant, if plant organic N was exchanged for soil inorganic N. The fact that the exchange occurred at all cast doubt on the suitability of the ¹⁵N-isotope dilution technique for assessing fertilizer efficiency in medium to long term experiments. There was evidence that the extra NO₃ ^--N taken up by plants on the all-nitrate treatments as a result of gypsum application, was reduced in root tissue rather than in shoots, but to the detriment of subsequent root growth and N uptake.     

土壤及凋落物源氮对中亚热带森林土壤SON的影响

土壤可溶性有机氮(SON)含量虽低,却是土壤氮库中最活跃的组分之一;主要来源于凋落物分解和土壤氮素转化。但是它们各自对土壤的影响还不清楚。通过添加杉木和~(15)N标记的阔叶凋落物于土壤表面,研究针阔叶凋落物分解对土壤SON的影响,及与土壤氮的关系。结果表明:由于没有降水的淋溶影响,培养期间,凋落物SON的显著降低,并没有直接增加土壤SON。与对照比较,杉木凋落物添加显著增加了土壤无机氮的含量,而较高C/N比的阔叶凋落物在其分解初期首先需要吸收更多的土壤氨态氮。添加~(15)N标记的阔叶凋落物提高了土壤SON在培养90—210天来自凋落物的比例,在第210天高达74.8%;来自凋落物的氨态氮比例在实验30天开始增加,到第210天高达39.8%;但是对硝态氮的影响不大。结果表明,土壤SON在培养初期因受凋落物的影响,主要来自土壤有机质的分解,而来自凋落物的SON更容易矿化;且土壤源的氮更容易发生硝化作用。可见,土壤中的SON是与凋落物分解动态、以及对土壤的影响有关。     

Significance of litter- and humus-layer quality for rates and forms of N cycling in moder- to rawhumus-moder profiles under Scots pine (Pinus sylvestris L.)

Plant and Soil - In three Scots pine stands in northeastern Germany along a gradient of air pollutant deposition loads (particularly sulfate and alkaline dust), the net N release by decomposition,...