Response of Douglas fir seedlings to phosphorus fertilization and influence of temperature on this response

Summary Effects of P fertilizers on growth of Douglas fir (Pseudotsuga menziesii var.menziesii (Mirb.) Franco.) seedlings were examined in pots and nursery beds. In pot experiments levels of P equivalent to 300 kg/ha were adequate for maximum growth over 14–18 weeks and resulted in available soil P levels of 80 ppm after 15 weeks' growth. Maximum growth in pots was obtained with shoot P concentrations of 0.18%–0.20%, with higher values at lower temperatures, but the optimum concentration for one-year old (1-0) nursery seedlings was 0.16% P. Growth of seedlings was greatly restricted at a soil temperature of 5°C and an air temperature of 12°C. At a soil temperature of 10°C and an air temperature of 14°C seedling P requirement was greater than at soil and air temperatures of 20°C.Comparison showed that monammonium phosphate was more effective than calcium superphosphate in stimulating growth in pots and nursery. Triple superphosphate was also effective in the nursery. Diammonium phosphate, potassium dihydrogen phosphate and phosphoric acid had no advantages as P sources in the nursery. Available P levels of 100–130 ppm, in the loamy sand and sandy loam nurseries studied, and needle P concentrations of 0.18%, when sampled in October, were associated with maximum growth of two-year old (2-0) seedlings.P fertilization decreased root/shoot ratio, but did not alter the allometric relationship of shoot to root. Improving P status from a low level increased root growth capacity in 2-0 seedlings and P fertilization of potted seedlings increased dry weight/height ratio. Uptakes per seed bed ha of 236 kg N, 31 kg P, 81 kg K and 73 kg Ca by 2-0 seedlings were comparable with, or greater than, uptake rates of agricultural crops. Recoveries of 6–11% of P from fertilizer were recorded in the nursery.     

Differential male reproductive success in Douglas fir

Summary Differential male reproductive success was studied in clones at two seed orchards of Douglas fir, Pseudotsuga menziesii (Mirb.) Franco. The performance of tester pollen parents was compared in controlled pollinations with two-parent pollen mixes. Marker pollen homozygous for a rare IDH allele was the genetic marker in each pollen mix. The resulting seeds were analyzed electrophoretically. At both seed orchards, the proportion of seeds sired by tester pollen significantly varied among the tester pollen parents. Tester pollen parents did not perform the same across all seed parents. The significant interaction effect was evidence of male-female complementarity. These results suggest a genetic basis to differential male reproductive success in Douglas fir.     

Effect of phosphorus fertilization on water stress in Douglas fir seedlings during soil drying

A growth chamber experiment was conducted to determine if P fertilization to enhance the P nutrition of otherwise N and P deficient Douglas fir [Pseudotsuga menziesii (Mirb.) Franco] seedlings reduces water stress in the seedlings during drought periods. Seedlings were grown in pasteurized mineral soil under well-watered conditions and fertilized periodically with a small amount of nutrient solution containing P at either of three levels: 0, 20, or 50 mg P L^-1. By age 6 mo, leaf nutrient analysis indicated that N and P were deficient in control (0 mg P L^-1) seedlings. The highest level of P fertilization, which doubled leaf P concentration, did not affect plant biomass, suggesting that N deficiency was limiting growth. When these seedlings were subjected to drought, there was no effect of P fertilization on leaf water potential or osmotic potential. Furthermore, P fertilized seedlings had lower stomatal conductance and net photosynthesis rate. These results indicate that enhanced P nutrition, in the presence of N deficiency, does not reduce water stress in Douglas fir seedlings during drought periods.     

Coinoculation of aseptically grown Douglas fir with pairs of ectomycorrhizal fungi

Douglas fir seedlings grown under aseptic conditions in a peat-vermiculite substrate were inoculated with four pairs of ectomycorrhizal fungi to assess the relative inoculum dosages needed to establish two mycorrhizal fungi simultaneously in the same root system. The dual fungal combinations tested were: Pisolithus arhizus + Rhizopogon subareolatus, P. arhizus + R. roseolus, Laccaria bicolor + P. arhizus and L. bicolor + R. subareolatus. A total of 12 ml of inocula per plant was applied at the rates: 0+12, 3+9, 6+6, 9+3, 12+0, and 0+0 (v+v) for each combination. After 3 months growth, the number of mycorrhizas and uninfected short roots as well as the total plant biomass produced were recorded. Inoculations were successful with the fungal combinations P. arhizus + R. subareolatus and L. bicolor + P. arhizus. Plants developed P. arhizus and R. subareolatus mycorrhizas only at the rate 9Pa + 3Rs; at other rates tested, only monospecific mycorrhizas were formed. Plants developed L. bicolor and P. arhizus mycorrhizas at the three rates containing both fungi. L. bicolor behaved as an aggressive root colonizer and its level of root colonization remained constant at increasing rates of P. arhizus inoculum. L. bicolor displaced R. subareolatus at all inocula rates. P. arhizus displaced R. roseolus except at the rate 3Pa + 9Rr, with only a low number of mycorrhizas formed by either fungus. Total plant biomass was significantly increased by the presence of any fungal combination up to four times the values for uninoculated controls. P. arhizus and R. subareolatus were more effective in promoting plant growth and stimulating short root formation than either L. bicolor or R. roseolus.     

Effects of a two-year application of ammonium sulphate on growth,nutrient uptake,and rhizosphere microflora of juvenile Douglas-fir

Deposition of ammonium sulphate is often cited as a major factor causing forest dieback in The Netherlands. In this study, three-year-old Douglas-firs (Pseudotsuga menziesii [Mirb.] Franco) were potted and subsequently treated for two years with ammonium sulphate solutions, corresponding to total annual N applications of 5, 50 and 200 kg ha^-1 yr^-1. After 6, 18 and 23 months, five trees per treatment were harvested, and growth, nutrient concentrations, mycorrhizal frequency and bacterial population on the roots were determined, together with soil chemical factors. At the highest treatment level, ammonium accumulated in the soil causing increases in H⁺ and Al-ion concentrations. Dry plant weights and root/shoot ratio were not significantly affected but the specific root length, i.e. length per gram dry weight, decreased significantly with increasing ammonium application. Mycorrhizal frequency and total bacterial population on the roots were also reduced. Reduced uptake of nutrients, especially phosphorus, was associated with these changes in the soil chemical and biological status. Extrapolation of the results to natural ecosystems should be done with great care, but undoubtedly, a potential danger exists for natural, often poorly buffered-systems, since accumulation of ammonium occurs continuously over many years.     

Effects of water and nutrient applications in a Scots pine stand to tree growth and nutrient cycling

In a Scots pine forest stand, demineralized water and a complete set of nutrients with water were applied to the soil by means of frequent irrigation for four years in order to eliminate water and nutrient shortage of the trees. Apart from this optimization, dissolved (NH₄)₂SO₄ was irrigated at a rate of 120 kg N ha^-1 y^-1 to create a situation of N excess. Effect of treatments on tree growth and chemical composition of soil water and vegetation were monitored. From the first treatment year onwards basal area growth increased by ca. 35% as a result of the increased water supply. Nutrient applications increased K and P concentrations in pine needles immediately, but growth was enhanced only in the fourth treatment year and coincided with an improved K supply. Most of the applied P and K was retained in the soil, and only 6% was recovered in the vegetation. Tree nutrient status did not respond on Ca and Mg applications, whereas Ca and Mg seepage losses were increased with ca. 5 kg ha^-1 y^-1. The applied NH₄ was mostly retained in the 0–20 cm surface soil and caused a drastic increase of Al in soil solution. Tree growth was stimulated initially by extra NH₄, but was hampered after three years obviously because of a decreased P nutrition. The applied base cations were absorped to the soil and the accompanying anions were leached, thus temporarily increasing the acidification of the soil solution.     

Hydraulic control of stomatal conductance in Douglas fir [Pseudotsuga menziesii (Mirb.) Franco] and alder [Alnus rubra (Bong)] seedlings

Experiments were conducted on 1-year-old Douglas fir [Pseudotsuga menziesii (Mirb.) Franco] and 2- to 3-month-old alder [Alnus rubra (Bong)] seedlings growing in drying soils to determine the relative influence of root and leaf water status on stomatal conductance (g_c). The water status of shoots was manipulated independently of that of the roots using a pressure chamber that enclosed the root system. Pressurizing the chamber increases the turgor of cells in the shoot but not in the roots. Seedling shoots were enclosed in a whole-plant cuvette and transpiration and net photosynthesis rates measured continuously. In both species, stomatal closure in response to soil drying was progressively reversed with increasing pressurization. Responses occurred within minutes of pressurization and measurements almost immediately returned to pre-pressurization levels when the pressure was released. Even in wet soils there was a significant increase in g_c with pressurization. In Douglas fir, the stomatal response to pressurization was the same for seedlings grown in dry soils for up to 120 d as for those subjected to drought stress over 40 to 60 d. The stomatal conductance of both Douglas fir and alder seedlings was less sensitive to root chamber pressure at higher vapour pressure deficits (D), and stomatal closure in response to increasing D from 1.04 to 2.06 kPa was only partially reversed by pressurization. Our results are in contrast to those of other studies on herbaceous species, even though we followed the same experimental approach. They suggest that it is not always appropriate to invoke a ‘feedforward’ model of short-term stomatal response to soil drying, whereby chemical messengers from the roots bring about stomatal closure.     

Nitrogen metabolism of Douglas fir and Scots pine as affected by optimal nutrition and water supply under conditions of relatively high atmospheric nitrogen deposition

Nitrogen metabolism of the needles of 40-year-old Douglas fir and Scots pine trees, growing in two forest stands on cation-poor and acidic sandy soil with a relatively high atmospheric nitrogen deposition was studied. The composition of the free amino acid (FAA) pool, the concentrations of total nitrogen and soluble protein and the activities of glutamine synthetase (GS) and glutamate dehydrogenase (GDH) were determined in the needles. An excessive nitrogen supply by a high atmospheric nitrogen deposition in both forest stands was indicated by the high concentrations of total nitrogen and the amino acids arginine, glutamic acid, glutamine and aspartic acid in control trees. In addition the effect of optimal nutrition and water supply (fertigation) on the needle nitrogen metabolism was evaluated. The total concentration of the FAA pool in needles of both tree species was lower in the fertigated than in the non-fertigated (control) trees, except for 1-year-old needles of Scots pine, in which the concentration after fertigation did not differ from the control. The lower total FAA concentration in the fertigated trees could be attributed to arginine, the concentration of which was on average 60% lower than in the control. Neither the concentration of soluble protein nor the activity of GS were influenced by fertigation. The activity of GDH in fertigated trees only differed significantly from the control in October. Scots pine needles had higher concentrations of protein (50%) and higher activities of GS (44%) and GDH (25%) than Douglas fir needles. Possible explanations for the lower vitality of Douglas fir compared to Scots pine are given.     

Impact of Douglas-fir and Scots pine seedlings on plagioclase weathering under acidic conditions

The weathering of soil minerals in forest ecosystems increases nutrient availability for the trees. The rate of such weathering and its relative contribution to forest tree nutrition, is a major issue when evaluating present and potential forest stand productivity and sustainability. The current paper examines the weathering rate of plagioclase with and without Douglas-fir or Scots pine seedlings, in a laboratory experiment at pH 3–4 and 25 °C. All nutrients, with the exception of Ca, were supplied in sufficient amounts in a nutrient solution. The objective of the experiment was to evaluate the potential of trees to mobilise Ca from the mineral plagioclase that contained 12% of Ca. Amounts of nutrients supplied in the nutrient solution, amounts accumulated in the living tissue of the seedlings and amounts leached from the experimental vessels, were measured. A weathering balance, accounting for leached + accumulated − supplied amounts, was established. Bio-induced weathering, defined as the weathering increase in the presence of trees, relative to the weathering rate without trees (geochemical weathering; control vessels), under the present experimental conditions, explained on average, 40% of total weathering (biological + geochemical). These conditions appeared more beneficial to Scots pine (higher relative growth rate, higher Ca incorporation) than to Douglas-fir.     

Douglas-fir root biomass and rooting profile in relation to soils in a mid-elevation area (Beaujolais Mounts,France)

Douglas-fir is the main reforestation species in the French Massif Central area (14 000 ha), but little is known about its rooting strategy in different soil conditions. This information has important implications for the choice of better soils for settling Douglas-fir, and consequently limiting risks of failure, pests or diseases. As a result, the influence of edaphic conditions on rooting patterns of dominant Douglas-fir was studied over a large range of ecological conditions in a mid-elevation area of the French Massif Central (Beaujolais Mounts). Root systems were studied extensively using the trench profile wall technique and the sector method in 74 pure and evenly aged Douglas-fir stands. The stands were chosen as being representative of soil conditions among 165 stands in an auto-ecological study. The rooting patterns were related to seven typical soil profiles, and to root profile groups. Results stressed that edaphic constraints due to substratum and soil structures have a strong influence on root system morphology. Important variations in root biomass and vertical distribution were highlighted among soils. Small fine root biomass is maximal for soils with no major edaphic constraints. The vertical distribution of fine root biomass is positively correlated for some soil types with organic C, total N, and most cations. For some types it was negatively correlated with the amount of exchangeable aluminum and coarse fragments, and with constraining rock facies. Harsher soils however, showed no correlation between soil chemical variables and fine-root biomass. A practical implication is that Douglas-fir seems to be a pliable and adaptive species: variation in habit and root system biomass are considerable within a study area which was presumed uniform.     

Effect of dual inoculation of Douglas fir with the ectomycorrhizal fungus Laccaria laccata and mycorrhization helper bacteria (MHB) in two bare-root forest nurseries

Douglas fir (Pseudotsuga menziesii) seedlings in two bare-root forest nurseries were inoculated with the ectomycorrhizal fungus Laccaria laccata, together or not with one of five mycorrhization helper bacteria isolated from L. laccata sporocarps or mycorrhizas and previously selected by in vitro and glasshouse screenings. With the most efficient MHB isolates, when compared to the control with no bacteria, the percent of mycorrhizal short roots was increased from 60 to 90 or from 80 to 100, depending on the nursery, with inoculation doses as low as 10⁶ living cells per m². A dual inoculum made of calcium alginate beads containing the two microorganisms appears to be a valuable technique for increasing the efficiency of ectomycorrhizal inoculation of planting stocks in forest nurseries.     

Nitrogen uptake in a Norway spruce stand following ammonium sulphate application,fertigation, irrigation,drought and nitrogen-free-fertilisation

The above-ground accumulation of N,N uptake and litter quality resulting from improved or deteriorated availability of water and nutrients in a 25 year old Norway spruce stand in SW Sweden (as part of the Skogaby project) is presented. Treatment include irrigation; artificial drought; ammonium sulphate addition; N-free-fertilisation and irrigation with liquid fertilisers including a complete set of nutrients according to the Ingested principle (fertigation). At start of the experiment the stand contained 86.5 t dry mass and 352 kg N ha⁻¹. The following three years the annual N uptake in untreated trees was 32 kg N ha⁻¹ to be compared with the annual N throughfall of 17 kg ha⁻¹. Simultaneously, the treatment with ammonium sulphate and liquid fertilisation resulted in 48 and 56 kg ha⁻¹ y⁻¹, respectively, in treatment specific N-uptake following an application of 100 kg N ha⁻¹ y⁻¹. Addition of a N-free fertiliser resulted in improved N-uptake by 19 kg N ha⁻¹ y⁻¹ and irrigation by 10 kg N ha⁻¹ y⁻¹, compared to control. A linear relation between total above-ground dry mass production and N-uptake was found for trees growing with similar water availability. Dry mass production increased with increased water availability given the same N-uptake. It is concluded that the studied stand this far is not N saturated', as N fertilisation resulted in both increased N uptake and increased growth. Addition of a N-free-fertiliser resulted in increased uptake of N compared to the control, indicating an increased mineralisation rate or uptake capacity of the root system. The linear relation between N uptake and biomass production shows that at this study site N is a highly limiting factor for growth.     

Chloroplast DNA restriction fragment length polymorphism in Sequoia sempervirens D. Don Endl., Pseudotsuga menziesii (Mirb.) Franco,Calocedrus decurrens (Torr.), and Pinus taeda L.

Summary The extent and type of chloroplast DNA restriction fragment length polymorphism was determined among individual tree samples of coast redwood, Douglas fir, incense-cedar, and loblolly pine. A total of 107 trees was surveyed for three restriction enzymes (BamHI, EcoRI, HindIII) and six chloroplast DNA probes from petunia (P3, P4, P6, P8, P10, S8). The probes comprise 64% of the petunia chloroplast genome. Polymorphisms were detected in all species but loblolly pine. Coast redwood and incense-cedar had a small number of rare variants, whereas Douglas fir had one highly polymorphic region of insertions/deletions in sequences revealed by the P6 probe from petunia. The mutation hotspot is currently being studied by DNA sequence analysis.     

Effects of past logging and grazing on understory plant communities in a montane Colorado forest

Throughout Pinus ponderosa–Pseudotsuga menziesii forests of the southern Colorado Front Range, USA, intense logging and domestic grazing began at the time of Euro-American settlement in the late 1800s and continued until the early 1900s. We investigated the long-term impacts of these settlement-era activities on understory plant communities by comparing understory composition at a historically logged and grazed site to that of an environmentally similar site which was protected from past use. We found that species richness and cover within functional groups rarely differed between sites in either upland or riparian areas. Multivariate analyses revealed little difference in species composition between sites on uplands, though compositional differences were apparent in riparian zones. Our findings suggest that settlement-era logging and grazing have had only minor long-term impacts on understories of upland Front Range P. ponderosa–P. menziesii forests, though they have had a greater long-term influence on riparian understories, where these activities were likely the most intense. This article was written and prepared by US Government employees on official time, and therefore it is in the public domain and not subject to copyright.     

Response of Douglas-fir and amabilis fir to split-root nutrition with inorganic and organic nitrogen

There is limited understanding of the spatial plasticity of conifer root growth in response to inorganic and organic nitrogen (N). In this study, slow-growing amabilis fir and fast-growing Douglas-fir, and slow- and fast-growing seedlots of the latter species were examined for their ability to proliferate roots preferentially in compartments of sand/peat medium enriched in organic and inorganic forms of N. In one experiment, N was supplied as 7.1 or 0.71 mM ammonium, nitrate and ammonium nitrate, and in a second experiment, N was supplied as ammonium or glycine. The seedlings’ ability to compensate for the starvation of a portion of the root system was assessed by measuring biomass of leaves, stems and roots, and foliar N concentration. Both fast- and slow-growing seedlots of Douglas-fir and slow-growing amabilis fir were able to proliferate roots in compartments of soil enriched with inorganic and organic N. In the first experiment, whole plant and root biomass was greatest when N was provided as ammonium followed by nitrate, and in the second experiment, seedling whole and root biomasses did not differ between ammonium and glycine treatments. All seedlings were able to compensate for the starvation of a portion of the root system, thus total plant biomass did not differ between split-root treatments; however, foliar N contents were lower in the 7.1/0.71 mM inorganic N split-root treatments. Foliar N concentrations were also lower in seedlings supplied with glycine.     

Effects of nitrogen fertilization of grapefruit trees on soil acidification and nutrient availability in a Riviera fine sand

Nitrogen (N) fertilizer applied in the NH4+ form results in some degree of soil acidification, which could influence nutrient availability to plants and nutrient losses through leaching. Effects of various N rates (0 – 168 kg N ha-1 yr-1) on soil acidification and nutrient availability were investigated in a Riviera fine sand with 26-year-old white Marsh grapefruit (Citrus paradisi MacFadyen) trees. Soil pH significantly decreased with increasing NH4–N rates. Application of 112 kg N ha-1 yr-1 for four years decreased the pH by 0.7 to 1.7 unit. Soil acidification was greater when the NH4+ form of N fertilizer was applied as dry soluble granular material compared to fertigation or controlled release forms. The marked effect of NH4–N fertilization on the pH of the Riviera fine sand was due to its low buffering capacity. Soil acidification increased the concentration of extractable Fe and P but decreased that of K, Zn and Mn. Soil pH was positively correlated with concentration of Ca, but negatively with concentrations of Fe, Mn and Zn in six-month-old spring flush leaves of the grapefruit trees. Leaf P concentrations, however, were poorly correlated with soil pH. This study also demonstrated an increase in leaching of P and K below the grapefruit trees rootzone with a decrease in soil pH.     

Two-dimensional gel electrophoresis of proteins for genetic studies in douglas fir (Pseudotsuga menziesii)

A method of two-dimensional gel electrophoresis of proteins from Douglas fir needles is described. Extraction in the presence of sodium dodecyl sulfate (SDS) and 2-mercaptoethanol followed by heating at 100°C produces reliable two-dimensional gels which are convenient for genetic studies. Three genotypes from different geographical origins have been compared: among 225 loci expressed, 22 display regulatory variations and 7 show allelic variations. Thus it is now possible to undertake the genetic study of Douglas fir using this powerful technique.This work was supported in part by Grant ATP PIRDES 508 444 from the INRA-CNRS.     

Rhizosphere pH along different root zones of Douglas-fir (Pseudotsuga menziesii), as affected by source of nitrogen

Douglas-fir, grown on strongly acid soil (pH-H₂O 3.87), was fertilized with ammonium, nitrate or ammonium nitrate as N-source. Rhizosphere pH along the root axis was measured with microelectrodes. Pure ammonium supply resulted in acidification of the rhizosphere, almost along the entire root axis; only the extreme root tip was slightly alkaline compared with the bulk soil. With nitrate supply, the alkalization of the rhizosphere at the root tip was considerably stronger than with ammonium supply and the length of the alkalization zone greater, extending over the entire growth zone of the root. Acidification of the rhizosphere along the older parts of the root was less pronounced in the case of nitrate. It is concluded that nitrate nutrition enables the plant to protect its most essential root zone from the adverse effects of strong acidity by locally raising the rhizosphere pH.     

Factors controlling throughfall chemistry in a balsam fir canopy: A modeling approach

This paper presents a model of water flux and throughfall concentrations of K⁺ and NH ₄ ⁺ in a subalpine balsam fir forest. The model is based on a multi-layer submodel of hydrologic flow. Cloud water deposition and evaporation are incorporated as separate submodels. Chemical exchange is parameterized with diffusion resistances and internal foliar concentrations determined from leaching experiments on isolated canopy components. The model is tested against within-storm throughfall measurements and found to agree reasonably well in most instances. Some specific departures from observed data are noted, of which some can be explained. Differences between observed and modeled concentrations of K⁺ early in the storm events suggest that pre-storm conditions, which were not modeled, are important in controlling the chemical exchange.Responses of throughfall chemistry to changes in rain rate, rain concentration, and stand surface area index (SAI) were investigated by simulation with the model. Increasing rain rates increased leaching of K⁺ and uptake of NH ₄ ⁺ . Increasing concentrations of K⁺ in rain decreased slightly the amount of K⁺ leached, but increasing concentration of NH ₄ ⁺ in rain increased NH ₄ ⁺ uptake proportionately. Increasing canopy SAI increased the leaching of K⁺ and the uptake of NH ₄ ⁺ , with the pattern of the increase dependent on rain rate.