Gross nitrification rates in four Japanese forest soils: heterotrophic versus autotrophic and the regulation factors for the nitrification

Measurements of gross NH ₄ ⁺ and NO ₃ ^? production in forest soils were conducted using the ¹⁵N pool dilution method. Mineral topsoils (0?C10?cm depth) were collected from four forests from northern to southern Japan with a natural climate gradient to elucidate the mechanisms regulating gross nitrification rates in forest soils. Additionally, we attempted to evaluate the relative importance of heterotrophic nitrification in gross total nitrification using acetylene as a specific inhibitor of autotrophic nitrification. Distinct differences were found among sites in the gross rates of NH ₄ ⁺ production (3.1?C11.4?mg?N?kg^?1?day^?1) and gross total nitrification (0.0?C6.1?mg?N?kg^?1?day^?1). The rates of gross heterotrophic nitrification were low in this study, indicating that heterotrophic nitrification is of minor importance in most forest mineral topsoils in Japan. Significant relations were found between gross autotrophic nitrification and gross NH ₄ ⁺ production, soil N, and soil C concentrations, but none was found between gross autotrophic nitrification and soil pH. We determined the critical value of the gross NH ₄ ⁺ production rates for gross autotrophic nitrification under which no gross autotrophic nitrification occurred, as well as the critical soil C/N ratio above which gross autotrophic nitrification ceased. Results show that tight coupling of production and consumption of NH ₄ ⁺ prevents autotrophic nitrifiers from utilizing NH ₄ ⁺ as long as NH ₄ ⁺ availability is low.     

Effects of organic residue management and legume cover on growth of pine seedlings, nutrient leaching and soil properties

? The short-term effect of organic residue management on the growth and nutrition of Pinus pinaster Ait. seedlings, and on nutrient leaching and chemical properties of an acid soil was assessed through a lysimeter experiment. Treatments included absence, placement on the soil surface, and incorporation into the soil (with and without legume cover cropping) of organic residues (forest floor litter or forest floor litter plus harvest residues).

? Residues placed on the soil surface enhanced seedling growth. Organic residues reduced nutrient losses (NO ₃ ^? , Ca and Mg) and resulted in nutrient accumulation in the soil. Harvest residues positively affected K seedling nutrition status and enhanced K soil accumulation.

? Legume cover cropping reduced soil nutrient losses (N, Ca, Mg and K) during the early stage of seedling growth; it also improved seedling nutrition status (N and P), but without any effect on growth.

? Harvest residues plus forest floor litter placed on the soil surface was the most appropriate management to both reduce nutrient losses through leaching and increase height of seedlings at the end of the experimental period (two years).

     

Nitrogen mineralization after clearcutting and residue management in a second rotation Eucalyptus globulus Labill. stand in Galicia (NW Spain)

? The effects of clearcutting and of different slash management procedures on N mineralization were assessed in a Eucalyptus globulus Labill. stand in Galicia (N W Spain). Treatments were no clearcutting (control), clearcutting combined with scattering, scattering + fertilization, windrowing, and two types of slash burning with two levels of severity: broadcast burning and windrow burning. Changes in mineral N were monitored in the soil during the 18 months following the treatments. Eleven years later, the treatment effects were again evaluated during a twelve month period to assess long-term effects.

? During the first study period, slash burning led to a marked increase in the contents of N-NH ₄ ⁺ , N-NO ₃ ^? and N-mineralization in topsoil layers (0–10 cm). In contrast, clearcutting followed by either scattering or windrowing of residues had no effect on mineral N in the top soil or in situ mineralization, relative to the control. Ammonium was the predominant form of mineral N. No residual effects of the treatments were detected eleven years later.

? Fire severity, in relation to slash burn type, had significant negative effects on post-burn N mineralization and nitrification in the first period studied, but no long-term residual effects were observed. Some practical consequences for sustainable management of such stands are suggested.

     

Fall fertilization of Pinus resinosa seedlings: nutrient uptake, cold hardiness, and morphological development

? Fall fertilization may increase plant nutrient reserves, yet associated impacts on seedling cold hardiness are relatively unexplored.

? Bareroot red pine (Pinus resinosa Ait.) seedlings in north-central Minnesota, USA were fall fertilized at the end of the first growing season with ammonium nitrate (NH₄NO₃) at 0, 11, 22, 44, or 89 kg N ha^?1. Seedling morphology and cold hardiness [assessed by freeze induced electrolyte leakage (FIEL)] were evaluated six weeks after fertilization and following the second growing season.

? Seedling height and number of needle primordia increased with fertilizer rate for both sampling years. Seedlings fertilized with 44 and 89 kg N ha^?1 attained target height (15 cm) after the second growing season. Shoot and root N concentration increased after the first growing season in fall fertilized seedlings compared to controls. Fall fertilized seedlings had lower FIEL (i.e., increased cold hardiness) compared to controls when tested at ?40 °C after the first growing season, but no significant differences in FIEL of control and fertilized seedlings were observed after the second growing season.

? Results suggest that fall fertilization of red pine seedlings can help render desired target height in the nursery, while maintaining or increasing cold hardiness levels.

     

Nitrogen leaching from a forest soil exposed to fire retardant with and without fire: A laboratory study

The application of Long Term fire Retardants (LTRs) for forest fire prevention and/or suppression purposes can result in chemicals leaching, from soil to the drainage water, during the annual rain fall period. In leachates, large concentrations of nitrogen (N), one of the major components of LTRs, could affect the groundwater quality. N leaching due to the application of a nitrogen phosphate based LTR was studied in laboratory microcosms. The concentrations of nitrate (NO ₃ ^? -N) and ammonium nitrogen (NH ₄ ⁺ -N) were measured in the resulting leachates from pots with forest soil and pine seedlings (Pinus halepensis) alone and in combination with fire. Up to 30% of the total N in the retardant was lost to leaching, primarily as NO ₃ ^? -N. The vegetation seems to decrease to some extent the N leaching. The N leaching from treated pots with a burnt tree is lower compared with that from treated pots with a living tree, due to the partial N volatilization during the fire. Although this is a laboratory study, these results may be considered as rough indications of LTR environmental implications, due to the leaching of a significant part of the retardant’s N into groundwater.     

Effects of a spruce budworm outbreak on element export below the rooting zone: a case study for a balsam fir forest

? Spruce budworm outbreaks are among the major natural disturbances affecting the dynamics and functioning of Canadian boreal forests. However, the element losses potentially associated with spruce budworm outbreaks have not been quantified.

? We evaluated the influence of spruce budworm outbreaks on nutrient export from boreal forest soils by comparing nutrient leaching losses during a spruce budworm outbreaks episode (1981–1984) to an unperturbed period (1999–2003) in a calibrated catchment located in a balsam fir forest.

? Nutrient soil leaching losses were significantly higher during the spruce budworm outbreaks (1981–1984) for N-NO₃ (30.1 fold), K (8.3 fold), N-NH₄ (6.2 fold), Mg (2.7 fold) and SO₄ (2.2 fold), as compared to an unperturbed period (1999–2003). When the recurrence of spruce budworm outbreaks (33 years) and a plausible average length of such events (5 years) are taken into consideration, it is estimated that in the long term, 5.6 more NO₃, 1.5 more K and 1.2 more NH₄ are leached from the soil profile during outbreaks.

? The important leaching losses during spruce budworm outbreaks, when added to the losses due to tree harvesting and fire (and acid deposition for K), may have considerable effects on soil fertility and ecosystem sustainability.

     

Mycorrhization, growth and nutrition of Pinus halepensis seedlings fertilized with different doses and sources of nitrogen

? Although fertilization is commonly used in nurseries, the effects of high level of nitrogen on Pinus halepensis mycorrhization are still unknown.

? The effect of fertilization at different N levels (low-LN: 35 mg/plant; medium-MN: 60 mg/plant; high-HN: 120 mg/plant), differing N sources (ammonium-(NH₄)₂SO₄; nitrate-HNO₃; ammonium+nitrate-NH₄NO₃) and inoculation with Pisolithus tinctorius and Lactarius deliciosus on the mycorrhization, growth and nutrient status of P. halepensis has been studied.

? P. tinctorius 3SR showed higher mycorrhizal ability (100% of mycorrhizal seedlings) than L. deliciosus (nearer to 50%). The application of increasing doses of N resulted in a significant reduction of mycorrhizal seedlings but no differences were observed between NH₄ and NO₃as N source at the 60 mg N/plant dose applied. The effects of fertilization on growth were mainly observed in uninoculated plants. The use of NH₄ increased growth in non-mycorrhized plants. Nutrient status was similar in all cases except for K concentration, which was higher in plants mycorrhized with P. tinctorius. Interactions between inoculation and fertilization were found, mycorrhizal effects appearing only at LN fertilization.

? It is advisable to avoid high doses of N fertilization in order to produce mycorrhizal P. halepensis seedlings.

     

Variations in water use by a mature mangrove of Avicennia germinans, French Guiana

? In the tropical intertidal zones, little is known on water uptake by mangroves. Transpiration rates are generally measured at leaf level, but few studies exist on water use at tree or stand levels.

? The objective of this study was to measure sap flow in trees of different sizes to appreciate the range of variation in water use that may exist in a site dominated by 80% mature Avicennia germinans.

? The results showed that from the dry to the wet season the mean water use increased from 3.2 to 5.3 dm³ d^?1 in small trees (DBH ～ 13 cm), from 11.5 to 30.8 dm³ d^?1 in medium trees (～24 cm) and from 40.8 to 64.1 dm³ d^?1 in large ones (～45 cm).

? Sapwood remained active up to a depth of 8 cm with radial variations within the stem. Weak correlations were obtained with VPD and net radiation.

? This study confirmed that transpiration was larger under low levels of salinity. Water use at stand level (～1900 living stems ha^?1) was estimated to be in the range of 5.8 to 11.8 m³ ha?1 d^?1 according to the season.

     

Genetic structure of Tunisian natural carob tree (Ceratonia siliqua L.) populations inferred from RAPD markers

? Seven RAPD markers were used to assess the genetic diversity and structure of ten Tunisian natural Ceratonia siliqua L. populations from different geographic and bioclimatic zones.

? The species maintain a high diversity within population as estimated by the percentage of polymorphic loci and Shannon’s index (P% = 76.31, $\bar H'_{pop} = 0.569$ ). The range of variation between populations was large. Populations from the upper semi-arid bioclimates, with more continuous distribution area showed the highest level of variation.

? A high genetic differentiation among populations (Φ_ST = 0.250 and $\bar G_{ST} = 0.347$ ), as a result of population isolation was revealed. Nevertheless, the genetic structure is in accordance with bioclimate indicating that ecological factors also should influence differentiation. Populations from the sub-humid, upper semi-arid and mean semi-arid zones clustered together and were distinct from those of the lower semi-arid ones.

? Conservation strategy should be made according to the level of polymorphism within population and bioclimate.

     

Genetic parameters for grain angle in 28-year-old Norway spruce progeny trials and their parent seed orchard

? Sawn wood which acquires twist during drying is a substantial problem for the sawmill industry and is to a large extent caused by spiralled grain in the tree.

? In this study, the feasibility of using spiral grain angles as a selection trait in Norway spruce (Picea abies (L.) Karst) tree breeding and the extent of grain angle and its breeding values were investigated. Grain angles under bark and diameter were measured at breast height in three 28-year-old Norway spruce progeny trials and in their parent seed orchard.

? The mean grain angle value was 1.76° in the progeny trials and 1.84° in the seed orchard. Estimated genetic standard deviations for grain angle were almost 1°. Progeny trial heritabilities (H ² > 0.3) were larger than the seed orchard heritability (H ² = 0.24). Genotype by environment interaction among the progeny trials was negligible for grain angle. Progeny trial grain angles exhibited genetic correlation with seed orchard grain angles in the range 0.66 to 0.84.

? Thus, mature wood grain angles are also under considerable genetic control, raising the opportunity to reduce the occurence of left-grained trees, which are prone to producing twisted wood.

     

Use of wood shrinkage characteristics in breeding of fast-grown Acacia auriculiformis A. Cunn. ex Benth in Vietnam

u| li]? Genotypic variation in wood total and partial shrinkage, basic density and growth traits was estimated in 51÷2 year old Acacia auriculiformis trees in a clonal test. li]? In the tangential, radial and longitudinal directions, the mean values were 2.64%, 1.64% and 0.77% for partial shrinkage, and 5.92%, 3.23%, and 0.96% for total shrinkage, respectively. Total and partial transverse shrinkage were significantly greater in sapwood than in heartwood. li]? Clonal repeatability (H _C ² ) estimates for partial shrinkage were lower than those for total shrinkage, and heartwood shrinkages had lower H _C ² than those for sapwood. Estimates of H _C ² were from 0.32 to 0.38 for total transverse shrinkage, comparable to H _C ² for both total and partial volumetric shrinkages (0.40 and 0.32, respectively). However, H _C ² for longitudinal shrinkages, total and partial coefficients of anisotropy were only from 0.09 to 0.18. li]? The genotypic coefficients of variation of all shrinkage traits varied from 5.45% to 8.02%. Total shrinkage was strongly positively correlated with partial shrinkage in each dimension. Genotypic correlations were not significant between shrinkage and growth traits or density. Strong and significant correlations between transverse shrinkage in heartwood and sapwood (0.87) indicated that juvenile shrinkage is a good genetic indicator of this trait in older trees. Utilisation du retrait du bois dans l’amélioration de l’Acacia auriculiformis A. Cunn. ex Benth à croissance rapide au Vietnam.     

Comparison of model forms for estimating stem taper and volume in the primary conifer species of the North American Acadian Region

? The performance of ten commonly used taper equations for predicting both stem form and volume in balsam fir [Abies balsamea (L.) Mill], red spruce[Picea rubens (Sarg.)], and white pine[Pinus strobus (L.)] in the Acadian Region of North America was investigated.

? Results show that the Kozak (2004) and Bi (2000) equations were superior to the other equations in predicting diameter inside bark for red spruce and white pine, while the Valentine and Gregoire (2001) equation performed slightly better for balsam fir.

? For stem volume, the Clark et al. (1991) equation provided the best predictions across all species when upper stem diameter measurements were available, while the Kozak (2004) and compatible taper equation of Fang et al. (2000) performed well when those measurements were unavailable.

? The incorporation of crown variables substantially improved stem volume predictions (mean absolute bias reduction of 7–15%; root mean square error reduction of 10–15%) for all three species, but had little impact on stem form predictions.

? The best taper equation reduced the predicted root mean square error by 16, 39, and 45% compared to estimates from the widely used Honer (1965) regional stem volume equations for balsam fir, red spruce, and white pine, respectively.

? When multiple taper equations exist for a certain species, the use of the geometric mean of all predictions is an attractive alternative to selecting the “best” equation.

     

Effect of severe thermal treatment on spruce and beech wood lignins

? The structure, proportion and mode of assembly of lignin, celluloses and hemicelluloses have marked effects on the reaction mechanisms during thermal treatment and therefore have a strong influence on the quality of the final product. The effect of treatment conditions, including severe conditions (up to 553 K) and treatment duration (up to 8 h) on the structure of native spruce and beech lignins was studied.

? Lignin content was determined by the Klason method and lignin structure was evaluated by thioacidolysis.

? The results highlighted the strong reactivity of the native spruce and beech lignins towards severe heat treatments. The distinct susceptibility of syringyl (S) and guaiacyl (G) units towards thermal treatment is confirmed by comparing the data for beech and spruce samples. The most severe treatment of spruce wood (280 °C) induced a dramatic enrichment in lignin content together with the almost complete disappearance of G lignin units, whereas a more moderate treatment substantially changed lignin structure by degradation reactions that affect the p-hydroxyphenyl (H) and G lignin units similarly.

? Thioacidolysis revealed that the thermal treatment induces the appearance of vinyl ether structures in spruce lignins. The decreased yield of the G and S thioacidolysis monomers reflects the progressive disappearance of G and S lignin units only involved in β-O-4 bonds and the formation of condensed linkages in proportions related to treatment severity. In severe conditions, β-O-4 linked S units are more degraded than their G homologues.

     

Competition for nitrogen by three sympatric species of Eucalyptus

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

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

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

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

     

Site preparation and competing vegetation control affect loblolly pine long-term productivity in the southern Piedmont/Upper Coastal Plain of the United States

? A site preparation study was established in 1986 to evaluate the effect of different site preparation treatments on growth and yield of loblolly pine (Pinus taeda L.) plantations on the Piedmont and Upper Coastal Plain regions of the southern United States. Site preparation treatments included: (1) burn only, (2) chop-burn, (3) shear-pile-disk, (4) chop-herbicide-burn, (5) herbicide-burn, and (6) herbicide-burn-herbicide.

? The data from the available 19 installations at age 21 were analyzed with separate analysis of variance and a multilevel nonlinear mixed-effects modeling approach.

? The herbicide-burn-herbicide treatment significantly increased average Dbh, height, basal area and volume per hectare compared to all other treatments. The burn only treatment consistently ranked worst and was followed by the chop-burn treatment. The shear-pile-disk and chop-herbicide-burn treatments had similar overall growth pattern, and will approach the same level of pine volume as the herbicide-burn treatment.

? Loblolly pine mean annual increment in volume (m³ ha^?1 y^?1) at age 21 by treatment were: herbicide-burn-herbicide (17.9), shear-pile-disk (16.1), herbicide-burn (15.9), chop-herbicide-burn (15.4), chop-burn (14.3), and burn (11.2).

? An additional chop or herbicide treatment to the burn treatment significantly increased loblolly pine yield. Complete control of both herbaceous and woody completion enhanced long-term pine productivity.

     

Litterfall production in forests located at the Pre-delta area of the Paraná River (Argentina)

? The objectives of this study were to measure litterfall production of the four floodplain forest types and to analyze the relationship between litterfall (forest type, dominant species, and organic fractions) and flood pulses.

? Litterfall production was measured in two mono-specific stands of Salix humboldtiana or Tessaria integrifolia, respectively, and two mixed forests dominated by A. inundata or Nectandra angustifolia, during 1998 and the 2000–2002 periods.

? Mono-specific stands presented similar productivities (6.8 and 6.5 Mg dry matter ha^?1 y^?1, respectively), but differed significantly from the two other. The highest litterfall production was obtained during the large flood that occurred during 1998, decreasing later throughout the study period. Leaves were the dominant fraction of litterfall, followed by branches, flowers, and fruits.

? Only S. humboldtiana, T. integrifolia and A. inundata forests showed distinct patterns of litterfall production, depending on the flooding pulse. N. angustifolia did not show a distinctive litterfall pattern.

? The forests studied here presented patterns of litter production associated with the flood pulse according to its location along a topographic gradient, that controls the litter productivity of these forests.

     

Within-tree variations in the surface free energy of wood assessed by contact angle analysis

Although the heterogeneity of wood could preclude assessment of the performances of adhesion, the within-tree variations in its thermodynamic properties still remain unexplored. This study analyzed the surface free energy of wood (γ _W ) calculated by the geometric mean approach along the radius and at different sampling heights in black spruce and balsam fir with a statistical model, employing apparent contact angles of three testing liquids. Sampling height and species affected the apparent contact angles, and consequently the polar ( $ \gamma_{W}^{P} $ ) and dispersed ( $ \gamma_{W}^{D} $ ) components of γ _W , but no significant difference was observed along the radius. On average, γ _W was 43.77?mJ?m^?2 at the stem base and gradually decreased, attaining 27.19?mJ?m^?2 at 14?m of height. $ \gamma_{W}^{P} $ was markedly higher than $ \gamma_{W}^{D} $ with an opposite pattern along the tree height. These findings demonstrated the huge variability in γ _W along the stem, which could be related to the structural or chemical features of wood.     

Evidence of altitudinal increase in photosynthetic capacity: gas exchange measurements at ambient and constant CO2 partial pressures

? Because all microclimatic variables change with elevation, it is difficult to compare plant performance and especially photosynthetic capacity at different elevations. Indeed, most previous studies investigated photosynthetic capacity of low- and high-elevation plants using constant temperature, humidity and light but varying CO₂ partial pressures (P _{CO 2}).

? Using gas exchange measurements, we compared here maximum assimilation rates (A _max) at ambient and constant-low-elevation P _{CO 2}for two temperate tree species along an altitudinal gradient (100 to 1600 m) in the Pyrénées mountains.

? Significant differences in A _max were observed between the CO₂ partial pressure treatments for elevations above 600 m, the between-treatment differences increasing with elevation up to 4 μmol m^?2 s^?1. We found an increase in A _max with increasing elevation at constant-low-elevation P _{CO 2} but not at ambient P _{CO 2} for both species. Given a 10% change in P _{CO 2}, a proportionally higher shift in maximum assimilation rate was found for both species.

? Our results showed that high elevation populations had higher photosynthetic capacity and therefore demonstrated that trees coped with extreme environmental conditions by a combination of adaptation (genetic evolution) and of acclimation. Our study also highlighted the importance of using constant CO₂ partial pressure to assess plant adaptation at different elevations.

     

Spring frost and decay fungi are implicated in suppressing aspen re-growth following partial cleaning in juvenile stands

? Aspen (Populus tremuloides Michx.) regenerates at high densities following manual cleaning.

? Ten-year-old stands located near Lac La Biche and Peace River, Alberta were manually cleaned to three densities (0, 500 or 1 500 stems ha^?1) at three times (bud set, dormancy or bud flush) to test the hypothesis that maintaining residual aspen reduces regeneration.

? At Lac La Biche up to 98% of the aspen regeneration died in the partially-cleaned plots compared to 67% at Peace River five years post-treatment. A spring frost in the second growing season at Lac La Biche is hypothesized to be the inciting factor predisposing the stump sprouts to infection by decay fungi such as Armillaria root rot, resulting in reduced density and height of the aspen regeneration at Lac La Biche relative to Peace River. Drought and ungulate herbivory provided additional stresses. The high mortality of aspen regeneration at Lac La Biche shifted the understory regeneration from aspen to balsam poplar (Populus balsamifera L.).

? These results indicate that maintaining 1 500 stems ha^?1 of residual aspen will not effectively control the re-sprouting of aspen; however, the vulnerability of aspen regeneration to spring frost and other stressors can nearly eradicate the re-growth of aspen.