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.     

Uptake of 15N-labelled alanine,ammonium and nitrate in Pinus sylvestris L. ectomycorrhiza growing in forest soil treated with nitrogen,sulphur or lime

The uptake of ¹⁵N-labelled alanine, ammonium and nitrate was studied in ectomycorrhizal morphotypes of intact Pinus sylvestris seedlings. PCR-RFLP analysis of the ITS-region of fungal rDNA was used to identify the morphotypes. Seedlings were grown in forest soil collected at an experimental site in southern Sweden. The treatments compared were a control, N fertilisation (600 kg N ha^-1 as urea), sulfur application (1200 kg S ha^-1) and lime application (6000 kg CaCO₃ ha^-1). The forest, which had been dominated by Picea abies, was clear-cut two years before the forest soil was sampled. Soil was also collected from an adjacent standing forest. The aim of the present study was to detect changes in the ectomycorrhizal communities in forest soils and relate these changes to the functional parameter of uptake of nitrogen from organic (alanine and protein) and inorganic (ammonium and nitrate) sources.Liming resulted in the detection of a morphotype not found in other samples, and one morphotype was only found in samples from the standing forest (the fungi in these two morphotypes could not be identified). All mycorrhizal root tips showed a higher ¹⁵N concentration after exposure to different nitrogen forms than non-mycorrhizal long roots. Uptake of¹⁵ N from a labelled solution of alanine or ammonium was higher (about tenfold) than uptake from a ¹⁵N-labelled solution of nitrate. Uptake of ammonium and alanine varied between 0.2 and 0.5 mg N g^-1 h^-1 and between 0.1 and 0.33 mg N g^-1 h^-1, respectively, among the different morphotypes.In seedlings grown in the control soil and in soil from standing forest, alanine and ammonium were taken up to a similar degree from a supply solution by all morphotypes, whereas ammonium uptake was higher than alanine uptake in seedlings grown in lime-treated soil (about twofold) and, to a lesser extent, in the nitrogen- and sulfur-treated soils. The higher ammonium uptake by morphotypes from the limed soil was confirmed in pure culture studies. In cases where ammonium was used as the N source, an isolate of the S. variegatus morphotype collected in the limed soil produced more biomass compared with isolates of S. variegatus collected in nitrogen- or sulphur-treated soil. One isolate of a silvery white morphotype produced about equal amounts of biomass on alanine and ammonium, whereas all S. variegatus isolated performed better with ammonium as their N source. Based on the results it is hypothesised that liming can induce a shift in the ectomycorrhizal community, favouring individuals that mainly utilise inorganic nitrogen over those that primarily utilise organic nitrogen.     

Implications of pre- and post-fertilizing changes in growth and nitrogen pools following multiple applications of nitrogen fertilizer to a Pinus radiata stand over 12 years

Around the world large tracts of forest, previously available for production, have been reserved for nature conservation. This means that wood supply must be met from a reduced land base, including land of low productivity. In addition there are likely to be increasing demands on the use of managed forests for sequestering C as one means of reducing the build up of atmospheric CO2. One way for the forest industry to meet the demands of increased production would be through the use of fertilizers. Substantially increased growth from fertilizer N application has been measured in many cases while, in the northern hemisphere, atmospheric N deposition has been associated with increased growth in some forests.The possibility of using fertilizer N to increase growth, and the effect on the forest and soil, was studied in a research trial area in north-east Tasmania, Australia. Nitrogen was applied for 12 years to a 16 year old P. radiata stand in a low rainfall zone. Growth and foliar nutrient concentrations were measured to age 34 years, to determine change after attainment of steady state growth at age 25 years, and following cessation of fertilizing at age 29 years. Biomass sampling was carried out at ages 25 years, 29 years, and 34 years.Growth at the steady peak rate achieved in the fertilizer plots, of 31 m3 ha-1 periodic annual increment, was accompanied by changes in the N nutrient pools. Surface applied N built up in the surface litter layer while this layer was increasing, from 15 t ha-1 to nearly 50 t ha-1, and fertilizer was being applied between ages 25 and 29 years. Decline of total N in the soil, between ages 25 and 29 years, indicated continued uptake from that source even though fertilizer was being applied. Subsequent increases in soil N, through leaching from the litter layer, followed cessation of fertilizing.Following cessation of annual applications of N fertilizer, growth rates declined by less than 15% and remained substantially (>150%) above the control growth rates for 4 years. Over a 3 year period foliar N concentrations declined steadily, to the same as control plots, although mass of needles was not reduced 5 years after cessation of fertilizer applications and remained significantly above that of the control plots.Without fertilizers, N for new foliage must be supplied from internal recycling and from mineralization of litter and soil organic matter. There were net losses of N from the foliage and the wood, estimated at around 12 kg N ha-1 yr-1, for the fertilized trees for the 5 years following cessation of fertilizing. This indicated retention and recycling within the tree of a considerable proportion of the 104 kg N ha-1 in the foliage, at age 29 years. As rates of mineralization of soil N were likely to be low, this retention of N within the tree was important in maintaining growth rates.In the forest ecosystems investigated, with low initial content of soil organic matter and N, fertilizer N produced improved tree health and substantially increased growth, thus providing the opportunity to manage this forest for increased wood production or C sequestration. Although there was a substantial build up of N and C in the litter on the fertilized treatment, incorporation of N and C into the mineral soil was slow. Over 12 years 1.34 t N ha-1 had been applied, comparable to 40 years of atmospheric deposition at 30 kg N ha-1. There were no signs of detrimental effects from this application.     

Growth and biomass partitioning of Anthriscus sylvestris (L.) Hoffm. and Festuca ovina (L.) at different relative addition rates of nitrogen

Anthriscus sylvestris (L.) Hoffm., is characteristic of productive habitats, and Festuca ovina of unproductive ones. The two species were grown at steady-state growth with either free access to all nutrients or severe nitrogen limitation. The maximum relative growth rate of the two species was similar-about 0.20 day^-1. Root:shoot partitioning at nitrogen limitation differed between the species. A. sylvestris allocated less biomass to fine-roots than at free access and F. ovina allocated more.     

沙地樟子松带状混交林土壤碳氮磷化学计量特征

探究不同沙地樟子松混交林土壤碳氮磷化学计量变化规律,为其混交经营提供科学依据.以沙地樟子松纯林为对照,在沙地樟子松×榆树及沙地樟子松×怀槐带状混交林中,沿沙地樟子松和伴生树种两个方向在距离混交中心0、1、2、3和4 m处的不同土层采集土样,分析土壤有机C、全N、全P、速效N、速效P含量及其计量比的特征.结果表明: 沙地樟子松混交林土壤有机C、全N和速效N含量高于纯林, 沙地樟子松与榆树混交主要增加了深层土壤有机C和全N含量,以及C/N和C/P, 沙地樟子松与怀槐混交提高了土壤N含量, 降低了P含量.随着远离混交林中心,沙地樟子松×榆树混交林中沙地樟子松林带的土壤C/N先升高后降低,全P和速效P含量下降,N/P增加;榆树林带土壤C/N下降,速效P含量先升高后降低.沙地樟子松×怀槐混交林土壤全N含量在沙地樟子松林带先降低后升高,在怀槐林带先升高后降低.沙地樟子松混交林提高了土壤C、N储量,沙地樟子松应与榆树行间混交,与怀槐间隔2行混交.     

Characterizing nitrogen dynamics, retention and transport in a tropical rainforest stream using an in situ15N addition

1. This study was part of the Lotic Intersite Nitrogen eXperiment (LINX); a series of identical ¹⁵NH₄ tracer additions to streams throughout North America. ¹⁵NH₄Cl was added at tracer levels to a Puerto Rican stream for 42 days. Throughout the addition, and for several weeks afterwards, samples were collected to determine the uptake, retention and transformation pathways of nitrogen in the stream. 2. Ammonium uptake was very rapid. Nitrification was immediate, and was a very significant transformation pathway, accounting for over 50% of total NH₄ uptake. The large fraction of NH₄ uptake accounted for by nitrification (a process that provides energy to the microbes involved) suggests that energy limitation of net primary production, rather than N limitation, drives N dynamics in this stream. 3. There was a slightly increased ¹⁵N label in dissolved organic nitrogen (DON) the day after the ¹⁵NH₄ addition was stopped. This DO¹⁵N was < 0.02% of DON concentration in the stream water at the time, suggesting that nearly all of the DON found in‐stream is allochthonous, or that in‐stream DON production is very slow. 4. Leptophlebiidae and Atya appear to be selectively feeding or selectively assimilating a very highly labelled fraction of the epilithon, as the label found in the consumers became much higher than the label found in the food source. 5. A large spate (>20‐fold increase in discharge) surprisingly removed only 37% of in‐stream fine benthic organic matter (FBOM), leaves and epilithon. The fraction that was washed out travelled downstream a long distance (>220 m) or was washed onto the stream banks. 6. While uptake of ¹⁵NH₄ was very rapid, retention was low. Quebrada Bisley retained only 17.9% of the added ¹⁵N after 42 days of ¹⁵N addition. Most of this was in FBOM and epilithon. Turnover rates for these pools were about 3 weeks. The short turnover times of the primary retention pools suggest that long‐term retention (>1 month) is minimal, and is probably the result of N incorporation into shrimp biomass, which accounted for < 1% of the added ¹⁵N.     

Soil nitrogen transformations and nitrate utilization by Deschampsia flexuosa (L.) Trin. at two contrasting heathland sites

Two Dutch heathland sites Hoorneboeg (HB) and Ede, dominated by Deschampsia flexuosa and differing in nitrate production, were sampled for an entire growing season. A large number of soil and plant parameters were monitored in an attempt to assess the contribution of nitrate in the N supply and its assimilation by Deschampsia.Average NO₃ ^– and NH₄ ⁺ concentrations (mg kg^–1) in the top 10-cm depth were 0.03 and 2.2, respectively, for HB, and 2.1 and 6.7, respectively, for Ede. Laboratory incubations of intact cores and experiments with FH-layer suspensions showed significantly higher mineralization and nitrification rates for the Ede site during most of the season. Nitrification was largely controlled by the rate of net N-mineralization, which in turn was highly affected by soil moisture. Nitrate production was virtually zero at HB and accounted for 25% of the net N-mineralization at Ede.Shoot chemical composition showed no essential differences for the two sites, but mean in vivo (current) foliar NRA was almost 2-fold higher at Ede than at HB, indicating some utilization of nitrate at the former location. At the HB site with essentially no nitrate production, however, enzyme activities were clearly higher than basal constitutive levels in NH₄ ⁺-fed plants. Apparently, shoot NRA at the HB site became positively affected by factors other than nitrate availability and/or showed disproportional increases in response to atmospheric nitrate inputs. Root NRA displayed the same low basal level at the two sites. Nitrate fertilization (100 kg N ha^–1) yielded maximally induced foliar NRAs similar to levels found in hydroponic nitrate plants. Although no accumulation of free NO₃ ^– was observed in shoots from fertilized plots, increases in foliar concentrations of both organic N and carboxylates clearly indicated nitrate assimilation. Root NRA showed no response to nitrate addition.It is concluded that current NRA measurements in Deschampsia at heathland sites are of limited value only, especially when interpreted in isolation. A combined approach, using concurrently conducted soil and plant analyses, will allow the extent of nitrate utilization in the field to be best characterized.Publication 2013 of the Netherlands Institute of Ecology.FAX no corresponding author: +31 8306 23227     

Seasonal flooding,nitrogen mineralization and nitrogen utilization in a prairie marsh

Flooding can be an important control of nitrogen (N) biogeochemistry in wetland ecosystems. In North American prairie marshes, spring flooding is a dominant feature of the physical environment that increases emergent plant production and could influence N cycling. I investigated how spring flooding affects N availability and plant N utilization in whitetop (Scolochloa festucacea) marshes in Manitoba, Canada by comparing experimentally spring-flooded marsh inside an impoundment with adjacent nonflooded marsh. The spring-flooded marsh had net N mineralization rates up to 4 times greater than nonflooded marsh. Total growing season net N mineralization was 124 kg N ha^–1 in the spring-flooded marsh compared with 62 kg N ha^–1 in the nonflooded marsh. Summer water level drawdown in the spring-flooded marsh decreased net N mineralization rates. Net nitrification rates increased in the nonflooded marsh following a lowering of the water table during mid summer. Growing season net nitrification was 33 kg N ha^–1 in the nonflooded marsh but < 1 kg N ha^–1 in the spring-flooded marsh. Added NO₃ ^–1 induced nitrate reductase (NRA) activity in whitetop grown in pot culture. Field-collected plants showed higher NRA in the nonflooded marsh. Nitrate comprised 40% of total plant N uptake in the nonflooded marsh but <1% of total N uptake in the spring-flooded marsh. Higher plant N demand caused by higher whitetop production in the spring-flooded marsh approximately balanced greater net N mineralization. A close association between the presence of spring flooding and net N mineralization and net nitrification rates indicated that modifications to prairie marshes that change the pattern of spring inundation will lead to rapid and significant changes in marsh N cycling patterns.     

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.     

Canopy structure and leaf nitrogen distribution in a stand of Lysimachia vulgaris L. as influenced by stand density

Summary A hypothesis that a dense stand should develop a less uniform distribution of leaf nitrogen through the canopy than an open stand to increase total canopy photosynthesis was tested with experimentally established stands of Lysimachia vulgaris L. The effect of stand density on spatial variation of photon flux density, leaf nitrogen and specific leaf weight within the canopy was examined. Stand density had little effect on the value of the light extinction coefficient, but strongly affected the distribution of leaf nitrogen per unit area within a canopy. The open stand had more uniform distribution of leaf nitrogen than the dense stand. However, different light climates between stands explained only part of the variation of leaf nitrogen in the canopy. The specific leaf weight in the canopy increased with increasing relative photon flux density and with decreasing nitrogen concentration.     

Effects of thinning in a Pinus sylvestris L. stand on foliar water relations of Fagus sylvatica L. seedlings planted within the pinewood

Planting of beech in old Scots pine plantations could facilitate the extension of adjoining small natural populations of beech in the centre of the Iberian Peninsula. To be successful the survival and growth of seedlings after outplanting must be compatible with microclimatic conditions within thinned pine woods. The present paper deals with water relations in beech seedlings following the variation of available radiation and water as a result of thinning. The seedlings were established under an old Scots pine plantation. After pine felling, four situations were generated in terms of radiation. Hemispherical photographs were taken, and global relative irradiance was calculated for every treatment. During two growing seasons predawn water potential (O_pd) was measured and leaf water parameters were derived from P-V curves. The O_pd diminished through the season in all four situations, and the highest values were found when pine density was lowest. Osmotic potential at turgor lost (O?_o) was higher in early summer. A negative relationship was found between osmotic potential at full turgor (O_?full) and symplast solute content on a dry weight basis (N_s). Under the lowest irradiance (unthinned pine trees), O_?full and O_?o were the highest and the bulk modulus of elasticity ()_max) the lowest; )_max decreased in response to the lowest O_pd measured at the end of summer 1998. It was followed by a reduction in the symplastic relative water content and N_s, irrespective of the irradiance. Osmotic adjustment, as a drought tolerance mechanism, was limited under shade conditions (unthinned pine trees), restricting the acclimation of beech seedlings to drought. Therefore, the presence of overstory, necessary for a successful implantation, should not be extended for too many years because of the risk of negative effects on growth and survival, particularly after frequent dry summers.     

Interactive effects of soil warming and fertilization on root production, mortality, and longevity in a Norway spruce stand in Northern Sweden

The effects of soil warming and nitrogen availability on root production, longevity and mortality were studied using minirhizotrons in irrigation (C), fertilized (F), heated (H), and heated‐fertilized (HF) plots in a Norway spruce stand in northern Sweden from October 1996 to October 1997. Irrigation was included in all treatment plots. Heating cables were used to maintain the soil temperature in heated plots at 5°C above that in unheated plots during the growing season. A Kaplan–Meier approach was used to estimate the longevity of fine roots and Cox proportional hazards regression to analyze the effects of the H, F, and HF treatments on the risk of root mortality. The proportion of annual root length production contributed by winter–spring production amounted to 52% and 49% in heated plots and heated‐fertilized plots, respectively. The annual root length production in C plots was significantly higher than in other treatments, while the HF treatment gave significantly greater production compared with the F treatment. The risk of mortality (hazard ratio) relative to C plots was higher in H plots (358%) and F plots (191%). The interaction between heating and fertilizing was strongly significant. The increase in the risk of root mortality in combined fertilization and heating (103%) was lower than that in the H or F plots. The results show that nitrogen addition combined with warmer temperatures decreases the risk of root mortality, and fine root production is a function of the length of the growing season. In the future, fertilization combined with the warmer temperatures expected to follow predicted climatic change may increase root production in boreal forests at low fertility sites.     

Global patterns and substrate‐based mechanisms of the terrestrial nitrogen cycle

Nitrogen (N) deposition is impacting the services that ecosystems provide to humanity. However, the mechanisms determining impacts on the N cycle are not fully understood. To explore the mechanistic underpinnings of N impacts on N cycle processes, we reviewed and synthesised recent progress in ecosystem N research through empirical studies, conceptual analysis and model simulations. Experimental and observational studies have revealed that the stimulation of plant N uptake and soil retention generally diminishes as N loading increases, while dissolved and gaseous losses of N occur at low N availability but increase exponentially and become the dominant fate of N at high loading rates. The original N saturation hypothesis emphasises sequential N saturation from plant uptake to soil retention before N losses occur. However, biogeochemical models that simulate simultaneous competition for soil N substrates by multiple processes match the observed patterns of N losses better than models based on sequential competition. To enable better prediction of terrestrial N cycle responses to N loading, we recommend that future research identifies the response functions of different N processes to substrate availability using manipulative experiments, and incorporates the measured N saturation response functions into conceptual, theoretical and quantitative analyses.     

Nitrogen mineralization and H+ transfers in a Scots pine (Pinus sylvestris L.) forest soil as affected by liming

H⁺ production due to N uptake in a mature Scots pine stand subjected to high NH₄ ⁺ deposition was previously estimated to amount to approx. 2.2 kmol ha^-1 y^-1. The question whether H⁺ transfers related to N mineralization (ammonification and nitrification) offset or corroborate this proton production is investigated in the present research. To determine N mineralization, soil cores were used of which both ends were closed with layers of ion exchange resin (IER) to prevent influx and efflux of ions. The effect of liming on N mineralization and the resulting H⁺ production was investigated in 7 incubation periods of each ca. 8 wk. Because of its high mobility NO₃ accumulated in both IER layers at the expense of that in the incubated forest floor and mineral soil. Net N mineralization in the soil cores as a whole amounted to 40 and 77 kg N ha^-1 in 384 d in the control and limed plots, respectively. In both treatments ca. 65% of mineralized N was nitrified. H⁺ production due to N mineralization amounted to approx. 1.2 kmol ha^-1 y^-1 in the control and limed plots. Liming reduced the amount of C in the forest floor, but not forest floor mass, because of an increased mixing with mineral particles.