The response ofPinus caribaea mor. var. Hondurensis seedlings to nitrogen,phosphorous and potassium fertilizers

Summary A soil pot culture experiment was conducted to study the response ofPinus caribaea var. hondurensis seedlings to the N, P, K fertilizers in a 3³ factorial combination of nutrients in four replicates. For this purpose, seedlings were grown in plastic pots in soils collected from Bahau pine experimental area. These soils belong to Durian series and are generally poor in nutrients.The seedlings were supplied with 112 kg/ha, 336 kg/ha and 560 kg/ha (100 lb/ac, 300 lb/ac and 500 lb/ac) of N, P, K in solution form in all possible combinations. Periodic growth measurements were taken and dry matter production was estimated at the conclusion of the experiment.The results indicate that phosphorous is the most important nutrient for the height growth of seedlings. The absolute height increment under the best treatment combination (N₁P₃K₁) was about threefolds (25.7cm) compared to 8.8 cm in the control. It was also found that higher levels of N and K, though not beneficial to height growth, resulted in better radial growth and more dry matter production compared to control plants. However, highest levels of N and K in the present experiment produced inhibitory influence as regards height growth even in the presence of low level of phosphorous.The study indicates that application of phosphorous at least at the rate of 560 kg/ha per plant is necessary on this type of soil to boost the initial height growth ofPinus caribaea var. hondurensis. Nitrogen at the rate of 336 kg/ha and potassium at the rate of 112 kg/ha will induce better radial growth.     

Biomass Enhancement in Maize and Soybean in Response to Glutamate Dehydrogenase Isomerization

The relationship between nutrient composition, crop biomass, and glutamate dehydrogenase (GDH) isoenzyme pattern was investigated in soybean (Glycine max) and maize (Zea mays) by monitoring the nutrient induced isomerization of the enzyme from the seedling stage to the mature crop. GDH was extracted from the leaves of the plants, and the isoenzymes were fractionated by isoelectric focusing followed by native polyacrylamide gel electrophoresis. The isomerization V_max values for soybean GDH, similar to maize GDH increased curvilinearly from 200 – 400 μmol mg⁻¹ min⁻¹ as the inorganic phosphate nutrient applied to the soil decreased from 50 − 0 mM. In soybean, combinations of N and K, P, or S nutrients induced the acidic and neutral isoenzymes, and gave biomass increases 25 – 50 % higher than the control plant. GDH isoenzymes were suppressed in soybean that received nutrients without N, K, or P and accordingly the biomass was about 30 % lower than the control. Treatment of maize with NPK nutrients increased the GDH V_max values from 138.9 at the vegetative to 256.4 μmol mg⁻¹ min⁻¹ at the reproductive phase, and suppressed the basic isoenzymes, but induced both the acidic and neutral isoenzymes thereby inducing seed production (27.0 ± 1.4 g per plant); whereas both the acidic and basic isoenzymes were suppressed in the control maize, and seeds did not develop. Simultaneous induction of the acidic, neutral, and basic isoenzymes of GDH indicated the occurrence of senescence. Therefore in maize and soybean, the induction of the acidic and basic isoenzymes of GDH led to the enhancement of biomass. This revised version was published online in July 2006 with corrections to the Cover Date.     

Biomass responses to elevated CO<Subscript>2</Subscript>, soil heterogeneity and diversity: an experimental assessment with grassland assemblages

While it is well-established that the spatial distribution of soil nutrients (soil heterogeneity) influences the competitive ability and survival of individual plants, as well as the productivity of plant communities, there is a paucity of data on how soil heterogeneity and global change drivers interact to affect plant performance and ecosystem functioning. To evaluate the effects of elevated CO₂, soil heterogeneity and diversity (species richness and composition) on productivity, patterns of biomass allocation and root foraging precision, we conducted an experiment with grassland assemblages formed by monocultures, two- and three-species mixtures of Lolium perenne, Plantago lanceolata and Holcus lanatus. The experiment lasted for 90 days, and was conducted on microcosms built out of PVC pipe (length 38 cm, internal diameter 10 cm). When nutrients were heterogeneously supplied (in discrete patches), assemblages exhibited precise root foraging patterns, and had higher total, above- and belowground biomass. Greater aboveground biomass was observed under elevated CO₂. Species composition affected the below:aboveground biomass ratio and interacted with nutrient heterogeneity to determine belowground and total biomass. Species richness had no significant effects, and did not interact with either CO₂ or nutrient heterogeneity. Under elevated CO₂ conditions, the two- and three-species mixtures showed a clear trend towards underyielding. Our results show that differences among composition levels were dependent on soil heterogeneity, highlighting its potential role in modulating diversity–productivity relationships. Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible to authorized users.     

Applications of mineral nutrients to heavily N-fertilized Scots pine trees: Effects on arginine and mineral nutrient concentrations

The aim of the investigation was to study if improved nutrient status in Scots pine (Pinus sylvestris L) trees would be reflected in decreased concentrations of arginine in the needles. The studies trees had imbalanced mineral nutrient composition and elevated needle arginine concentrations caused by long-term fertilization with N. Concentrations of arginine and mineral nutrients in needles were followed over three consecutive years of additional fertilization with N alone or with P, K, Mg and micronutrients in combination with and without N.Analysis of needle mineral concentrations suggested that there were deficiencies only in K and Mg. The N concentration increased both in trees fertilized with N alone and in trees fertilized with N in combination with mineral nutrients. In the control treatment and in trees fertilized with mineral nutrients other than N the N concentration remained fairly constant. The highest Ca/N, K/N and P/N ratios were found in trees fertilized with mineral nutrients other than N while the lowest ratios were found in trees fertilized with N alone. Arginine concentrations in needles from trees fertilized with N alone remained at a high level throughout the experiment while arginine concentrations in trees given the other treatments decreased.The results show that the mineral nutrient balance can be improved with appropriate fertilization and that this improvement is reflected in decreasing arginine levels. Furthermore the study demonstrates that when N supply is reduced the arginine concentration also decreases also as an effect of reduced N supply per se. The study also indicates that arginine may be a better measure of the N status in pine trees than total N.     

Homeostatic gas-exchange parameters inferred from 13C/12C in tree rings of conifers

The CO₂ concentration of the atmosphere has increased by almost 30% in the past two centuries, with most of the increase (>5 Pa) during the past 60 years. Controlled environment studies of crop plants dependent on the C₃ photosynthetic pathway indicate that an increase of this magnitude would enhance net photosynthesis, reduce stomatal conductance, and increase the difference in CO₂ concentration across the stomata, i.e., CO₂ concentration outside the leaf to that within (c _a-c _i). Here we report evidence, based on stable isotope composition of tree rings from three species of field-grown, native conifer trees, that the trees have indeed responded. However, rather than increasing c _a-c _i, intercellular CO₂ concentrations have shifted upward to match the rise in atmospheric concentrations, holding c _a-c _i constant. No differences were detected among Douglas-fir (Pseudotsuga menziesii), ponderosa pine (Pinus ponderosa), or western white pine (Pinus monticola). The values of c _a-c _i were inferred from stable carbon isotope ratio (¹³C) of tree ring holocellulose adjusted for the 0.6–2.6 difference between holocellulose and whole sapwood. The cellulose extraction removed contaminants deposited in the tree ring after it formed and the adjustment corrected for the enrichment of cellulose relative to whole tissue. The whole sapwood values were then adjusted for bublished estimates of past atmospheric ¹³CO₂ and CO₂ concentrations. To avoid confounding tree age with CO₂, cellulose deposited by saplings in the 1980s was compared to cellulose deposited in the inner rings of nature trees when the mature trees were saplings, between 1910–1929 and 1941–1970; thus saplings were compared to saplings. In a separate analysis, the juvenile effect, which describes the tendency for ¹³C to increase in the first decades of a tree's life, was quantified independent of source CO₂ effects. This study provides evidence that conifers have undergone adjustments in the intercellular CO₂ concentration that have maintained c _a-c _i constant. Based on these results and others, we suggest that c _a-c _i, which has also been referred to as the intrinsic water-use efficiency, should be considered a homeostatic gas-exchange set point for these conifer species.     

RETRACTED ARTICLE: CO<Subscript>2</Subscript> effects on plant nutrient concentration depend on plant functional group and available nitrogen: a meta-analysis

Elevated CO₂ is expected to lower plant nutrient concentrations via carbohydrate dilution and increased nutrient use efficiency. Elevated CO₂ consistently lowers plant foliar nitrogen, but there is no consensus on CO₂ effects across the range of plant nutrients. We used meta-analysis to quantify elevated CO₂ effects on leaf, stem, root, and seed concentrations of B, Ca, Cu, Fe, K, Mg, Mn, P, S, and Zn among four plant functional groups and two levels of N fertilization. CO₂ effects on plant nutrient concentration depended on the nutrient, plant group, tissue, and N status. CO₂ reduced B, Cu, Fe, and Mg, but increased Mn concentration in the leaves of N₂ fixers. Elevated CO₂ increased Cu, Fe, and Zn, but lowered Mn concentration in grass leaves. Tree leaf responses were strongly related to N status: CO₂ significantly decreased Cu, Fe, Mg, and S at high N, but only Fe at low N. Elevated CO₂ decreased Mg and Zn in crop leaves grown with high N, and Mn at low N. Nutrient concentrations in crop roots were not affected by CO₂ enrichment, but CO₂ decreased Ca, K, Mg and P in tree roots. Crop seeds had lower S under elevated CO₂. We also tested the validity of a “dilution model.” CO₂ reduced the concentration of plant nutrients 6.6% across nutrients and plant groups, but the reduction is less than expected (18.4%) from carbohydrate accumulation alone. We found that elevated CO₂ impacts plant nutrient status differently among the nutrient elements, plant functional groups, and among plant tissues. Our synthesis suggests that differences between plant groups and plant organs, N status, and differences in nutrient chemistry in soils preclude a universal hypothesis strictly related to carbohydrate dilution regarding plant nutrient response to elevated CO₂.     

Temporal patterns of soil nutrients in a Panamanian moist forest revealed by ion-exchange resin and experimental irrigation

The effect of seasonal water availability on soil nutrients and soil N transformations was investigated by irrigating two large plots of mature tropical forest on Barro Colorado Island (BCI), Panama, during the dry season for five consecutive years. Methods included (i) nutrient accumulation by ion-exchange resins placed on the surface of the mineral soil for contiguous 21-day periods, (ii) monthly mineral soil (0–10 cm) extractions and incubations for inorganic N and P concentrations, and (iii) leaching loss of nutrients from leaf litter samples. Rates of nutrient accumulation by the resins showed a great deal of variation between sampling dates and among years in control plots; albeit, seasonal patterns were slight, except for the highest Ca values near the end of the wet season and inorganic P (P_i) and SO₄ values that peaked during the dry season. Irrigation had remarkably little effect on nutrient accumulation rates by resins, except for an increase in Mg and Na values, but did affect the timing in the temporal variation in K, Na, N_i and P_i values. In contrast, inorganic N (N_i) and P_i pools and N transformation rates in the mineral soil hardly varied among sampling dates and did not show any response to irrigation. We hypothesize that the timing of leaf litterfall and nutrient leaching from forest floor litter can set up temporal patterns in the levels of soil nutrient at the surface of the mineral soil, but the temporal patterns essentially disappear with depth in the mineral soil.     

Gas hold-up in converging-diverging tube airlift fermenter

Summary Fractional gas holdup study was carried out in two airlift fermenters: one having of conventional design, the other having an asymetric riser arm. Air flow rate was varied from 1.5 to 9.0 cm/sec and gas hold-up values compared. Fractional gas holdup, _G, was strongly dependent on superficial gas velocity and initial liquid height. The modified fermenter always showed a higher gas holdup than the conventionally designed one.Symbols ALF Airlift Fermenter - CDT Convergent-divergent Tube - UT Uniform Tube - U_G Superficial gas velocity, cm/s - h_i Initial liquid height in riser, cm - H_i Dispersed liquid height in riser, cm - H_O Dispersed liquid height in downcomer, cm - K,m,n Constant - a,a Constant - A_d Riser cross sectional area, cm^z - A_r Downcomer cross sectional area, cm^z - U_b Bubble rise velocity, cm/s - g Acceleration due to gravity, cm/s^z - d_B Bubble diameter, cm - R_ev Bubble's Reynolds number, dimensionless Greek Letters _G Fractional gas holdup, dimensionless - {ITG9}{INL} Liquid density, g/cc - {IT}{INL} Liquid viscosity, poise(g/cm.s) - {ITGS}{INL} Liquid surface tension, dyne/cm - porous plate pore diameter, cm     

Response ofStylosanthes guianensis to endomycorrhizal fungi inoculation as affected by lime and phosphorus applications

The nutrient concentration in the shoots ofStylosanthes guianensis (Aubl.) Sw. cultivated in a sterilized acid and dystrophic soil (Quartzipsament) amended with 4 levels of lime (0; 0.27; 0.63 and 1.10 meq Ca²⁺/100 g soil, as Ca(OH)₂), 2 levels of P (0 and 20 mg P kg^-1 soil, as KH₂PO₄) and not-inoculated or inoculated with 3 vesicular-arbuscular (VA) mycorrhizal fungi was evaluated under greenhouse conditions. The effectiveness of the different fungal species in increasing the nutrient concentration in the shoots varied with the different edaphic conditions. In general, mycorrhiza formation was associated with increases in the concentrations of most of the nutrients analyzed. Under the experimental conditions, the increments in nutrient concentration were higher overall in plants inoculated withAcaulospora scrobiculata. Inoculation ofS. guianensis with VA mycorrhizal fungi was also associated with alterations in the ratios of nutrients in the shoots, which might be important in understanding and explaining the tolerance of mycorrhizal plants to nutritional stresses such as Al and Mn toxicity.     

Mineral allocation to reproduction in Sorhum bicolor and Sorghum halepense in relation to parental nutrient supply

Summary This experiment investigated the effect of parental nutrient shortage on the allocation of five nutrients to seeds and rhizomes in Sorghum halepense, a perennial, noxious weed, and to seeds in Sorghum bicolor, an annual, cultivated species. Plants from both species were grown from seeds and supplied with fertilizer at three concentrations. The allocation of biomass and nutrients (N, P, K, Ca and Mg) to reproductive and vegetative parts was determined. Relative biomass allocation to reproduction (either sexual or vegetative) remained constant in S. halepense in spite of large differences in total plant weight. In S. bicolor, however, biomass allocation to sexual reproductive structures decreased significantly with decreasing nutrient supply. Individual seed weight was not modified by parental nutrient supply in S. halepense, but it increased with decreasing nutrient availability in S. bicolor. Important differences in mineral allocation to seeds were found between the two species. While S. bicolor seeds were largely buffered from the differences in parental nutrient status, concentration of nutrients in S. halepense seeds decreased significantly with decreasing supply for all the nutrients analyzed except Ca. However, mineral nutrient concentration in S. halepense rhizomes remained remarkably constant despite differences in the external supply, evincing the priority given to vegetative reproduction at the expense of sexual reproduction. Overall, the pattern of nutrient allocation in S. bicolor seeds under different nutrient supply resembled the pattern observed in S. halepense rhizomes, but it had little resemblance to the pattern of nutrient allocation in S. halepense seeds. The results are discussed in terms of differences and similarities in the reproductive strategy of these two species.     

林地覆盖经营对雷竹鞭根主要养分内循环的影响

为了给林地覆盖经营雷竹(Phyllostachys violascens)林可持续经营提供理论参考,探讨了休养式覆盖经营(覆盖3a后休养3a)、长期覆盖经营(覆盖6a)和不覆盖雷竹林(CK)2年生壮龄竹鞭及其1级、2级根N、P、K、Mg、Ca、Fe浓度和养分迁移、内循环率的差异。结果表明:不同覆盖经营年限雷竹林N、P、K、Mg、Ca和Fe浓度总体上1级根显著高于2级根。1级根和2级根中均存在N、P、K、Mg的养分内循环,且1级根养分内循环率大于2级根,Fe、Ca内循环不明显。N、P、K、Mg养分浓度与养分迁移速率随时间的推延,1级根为持续降低,2级根为先升高后降低。与不覆盖雷竹林相比,休养式林地覆盖经营总体上提高了1级、2级根的N、P、K、Ca的浓度和P、K、Mg的迁移速率、N、P、K的迁移量、P、K的养分内循环率以及1级根Mg的浓度和迁移量、2级根N的迁移速率和Mg的内循环率;长期林地覆盖经营虽提高了雷竹1级根N、K的浓度和N的迁移量及2级根N的浓度和内循环率,但总体上降低了1级根P、K、Mg和2级根N、P、Mg的迁移量与1级、2级根P、Mg的迁移速率及P、K、Mg的养分内循环率。研究表明:雷竹林鞭根中存在明显的养分内循环,且1级根对养分内循环的贡献较大。休养式林地覆盖经营利于雷竹林对养分的循环利用,而长期覆盖经营阻碍了根系对养分的平衡吸收,减弱了根系养分的内循环,不利于雷竹林的生长更新。     

Nutrient requirements of exotic tree species in Zimbabwe

Pot and field experiments were conducted in the greenhouse and at three field sites (Marondera, Domboshawa and Makoholi) in Zimbabwe to examine the effects of soils and fertilizers on nutrient uptake and growth of 6 exotic tree species (Eucalyptus camaldulensis, E. grandis, E. tereticornis, Leucaena leucocephala, Casuarina cunninghamiana, and Acacia holosericea). Plant growth, N and P contents of all species were increased by the application of N, P, K and micronutrient fertilizers. The effect of individual nutrients (N, P, K and micronutrients) and their combination on Eucalyptus species was further investigated in a pot experiment using soil from Domboshawa. Eucalyptus species responded only to N application and no significant interactions were found between N and the other elements. Nutrient uptake results showed that E. camaldulensis and E. tereticornis removed more cations than the N-fixing trees but only in the fertilized treatments. L. leucocephala and C. cunninghamiana were higher in P, but no clear trends were observed for N. Plant growth and nutrient uptake by E. camaldulensis. C. cunninghamiana and A. holosericea were assessed in the field at the three sites. Plant species grown in the Marondera site had greater height and diameter at breast height (DBH) than those in the two other sites. These results followed trends in soil nutrient contents. The analysis of foliage revealed differences in the nutrient concentration of leaves from different trees, but no effect of site was found. The interrelationships between plant characteristics, soil and foliage nutrients were examined. In a pot experiment, mineral N was the only variable correlated with growth response and nutrient uptake, while in the field the only significant correlation was obtained with soil pH.     

Phosphate transport across biomembranes and cytosolic phosphate homeostasis in barley leaves

Barley (Hordeum vulgare L.) plants were grown hydroponically with or without inorganic phosphate (P_i) in the medium. Leaves were analyzed for the intercellular and the intracellular distribution of P_i. Most of the leaf P_i was contained in mesophyll cells; P_i concentrations were low in the xylem sap, the apoplast and in the cells of the epidermis. The vacuolar concentration of P_i in mesophyll cells depended on P_i availability in the nutrient medium. After infiltrating the intercellular space of leaves with solutions containing P_i, P_i was taken up by the mesophyll at rates higher than 2.5 mol· (g fresh weight)^–1 · h^–1. Isolated mesophyll protoplasts did not possess a comparable capacity to take up P_i from the medium. Phosphate uptake by mesophyll protoplasts showed a biphasic dependence on P_i concentration. Uptake of P_i by P_i-deficient cells was faster than uptake by cells which had P_i stored in their vacuoles, although cytoplasmic P_i concentrations were comparable. Phosphate transport into isolated mesophyll vacuoles was dependent on their P_i content; it was stimulated by ATP. In contrast to the vacuolar P_i concentration, and despite different kinetic characteristics of the uptake systems for p_i of the plasmalemma and the tonoplast, the cytoplasmic p_i concentration was regulated in mesophyll cells within narrow limits under very different conditions of P_i availability in the nutrient medium, whereas vacuolar P_i concentrations varied within wide limits.Dedicated to Professor Wilhelm Simonis on the occasion of his 80th birthdayThis investigation was part of the research efforts of the Sonderforschungsbereich 176 of the Bayerische Julius-Maximilians-Universität Würzburg. We are grateful to Dr. Olaf Wolf for introducing us to the method for preparation of xylem sap of barley plants and to Mr. Yin Zuhua for fluorimetric experiments with the dye pyranine. T. Mimura is indebted to the Alexander-von-Humboldt-Stiftung for a postdoctoral research fellowship.     

不同配比施肥对马尾松幼苗生长特征的影响

为获得马尾松幼苗最佳施肥配方,该文以1年生马尾松幼苗为试验材料,采用L₁₆（4³）正交设计,并通过测定幼苗苗高、地径、生物量、叶绿素含量、叶片N、P、K含量,探讨不同N、P、K配比施肥对马尾松幼苗生长特征影响。结果表明：（1）不同配比施肥处理间马尾松幼苗苗高、地径、生物量、质量指数、叶绿素和养分含量存在显著差异,其中,处理12生物量、质量指数、叶绿素a和总叶绿素含量、隶属值最高。（2）施N对幼苗生长及生理指标均有极显著影响;施K对苗高、地径、地上生物量、总生物量有显著影响,对叶绿素和针叶养分有极显著影响;施P对叶绿素a、叶绿素b、针叶N和P含量有极显著影响,对苗高、地下生物量、总叶绿素含量有显著影响。（3）施N对苗高、地径、地上生物量、总生物量、质量指数、叶绿素a含量、总叶绿素含量和针叶N含量的影响最大,K次之,P最小。各因素对地下生物量和针叶P含量的影响均表现为N>P>K。（4）N3水平利于幼苗苗高地径的生长及生物量的积累,N4水平利于叶绿素a和总叶绿素含量及针叶N、P含量的积累,P4水平利于生物量、叶绿素含量和养分P含量的积累...     

Seasonal variation in nutrient concentration in leaves and branches of Quercus pyrenaica

Abstract. Seasonal variation in nutrient concentration in leaves and branches of Quercus pyrenaica was studied in natural Q. pyrenaica forest in the Sierra de Gata (Salamanca Province, Spain). Two permanent plots were established at the two extremes of a rainfall gradient in this area: annual mean precipitation from 720 mm at Fuenteguinaldo (granite bedrock) to 1580 mm at Navasfrias (schists and graywackes). Leaf and branch samples were collected every three weeks during the growing season from May to October, at three height levels of the tree canopy. Seasonal changes and internal nutrient dynamics were investigated for N, Ca, Mg, K, Na, Mn, Fe and P during a two-year period. The concentrations of all nutrients varied among the seasons; these variations were related to nutrient mobility and the annual physiological cycle. Nutrient concentrations decrease in the case of K and P, while the sparse mobile nutrients Ca, Mg, Mn and Fe gradually accumulated during each growing season. In Navasfrias a considerable resorption of P from senescing leaves was detected. Different patterns were found for the other nutrients studied (Na and N).     

The effects of nutrient supply,predominantly addition of iron,and rhizobial inoculation on the tolerance of Lupinus pilosus genotypes to a calcareous soil

Two glasshouse experiments were conducted to examine the effects of nutrient supply and rhizobial inoculation on the performance of Lupinus pilosus genotypes differing in tolerance to calcareous soils. In experiment 1, plants were grown for 84 days in a calcareous soil (50% CaCO₃; soil water content 90% of field capacity) at four nutrient treatments (no-added nutrients, added nutrients without Fe, added nutrients with soil applied FeEDDHA, added nutrients with foliar applied FeSO₄). In experiment 2, plants were grown for 28 days with supply of NH₄NO₃ without inoculation or inoculated with Bradyrhizobium sp. (Lupinus). Chlorosis in the youngest leaves was a good indicator of the relative tolerance of the genotypes to the calcareous soil in both experiments, except the treatment with FeEDDHA at 5 mg kg^–1 soil which was toxic to all genotypes. Chlorosis scores correlated with chlorophyll meter readings and chlorophyll concentrations. The foliar application of FeSO₄ did not fully alleviate chlorotic symptoms despite concentrations of active or total Fe in the youngest leaves being increased. Adding nutrients and chemical nitrogen did not change the severity of chlorosis or improve the growth of the plant. The nutrient supply did not alter the ranking of tolerance of genotypes to the calcareous soil. The results suggest that nutrient deficiency or poor nodulation was not a major cause of poor plant growth on calcareous soils and that bicarbonate may exert a direct effect on chlorophyll synthesis. The mechanism for tolerance is likely to be related to an ability to exclude bicarbonate or prevent its transport to the leaves.     

Changes in nutrient use efficiency, status and retranslocation in young post-fire regeneration Pinus halepensis in response to sudden N and P input, irrigation and removal of competing vegetation

The capacity of Mediterranean species to adapt to variable nutrient supply levels in a global change context can be a key factor to predict their future capacity to compete and survive in this new scenario. We aimed to investigate the capacity of a typical Mediterranean tree species, Pinus halepensis, to respond to sudden changes in N and P supply in different environmental conditions. We conducted a fertilisation, irrigation and removal of competing vegetation experiment in a calcareous post-fire shrubland with an homogeneous young (5 years old) population of P. halepensis in order to investigate the retranslocation and nutrient status for the principal nutrients (N, P, Mg, K, S, Ca and Fe), and the nutrient use efficiency (NUE) of the most important nutrients linked to photosynthetic capacity (N, P, Mg and K). P fertilisation increased P concentration in needles, P, N, Mg and K retranslocations, and NUE calculated as biomass production per unit of nutrient lost in the litterfall. The P fertilisation was able to increase the aboveground biomasses and P concentration 3 years after P fertiliser application. Those responses to P fertilisation were enhanced by the removal of competing vegetation. The N needle and litterfall concentration decreased after P fertilisation and this effect was greater when the P fertilisation was accompanied by removal of competing vegetation. The increase of P availability decreased the P-NUE and increased the N-NUE when these variables were calculated as aboveground biomass production per unit of P present in the biomass. Both P-NUE and N-NUE increased when calculated as total aboveground production per unit of nutrient loss. The results show that it is necessary to calculate NUE on a different basis to have a wider understanding of nutrient use. The irrigation did not change the needle nutrient concentrations and the litterfall production, but it significantly changed the nutrient litterfall concentrations and total aboveground contents (especially P and K). These results show a high capacity of P. halepensis to quickly respond to a limiting nutrient such as P in the critical phases of post-fire regeneration. The increase in P availability had a positive effect on growth and P concentrations and contents in aboveground biomass, thus increasing the capacity of growth in future periods and avoiding immediate runoff losses and leachate. This capacity also strongly depends on neighbour competition.     

Effect of crop residues on root growth and phosphorus acquisition of pearl millet in an acid sandy soil in Niger

The effect of long-term (1983–1988) applications of crop residues (millet straw, 2–4 t ha^-1 yr^–1) and/or mineral fertilizer (30 kg N, 13 kg P and 25 kg K ha^-1 yr^-1) on uptake of phosphorus (P) and other nutrients, root growth and mycorrhizal colonization of pearl millet (Pennisetum glaucum L.) was examined for two seasons (1987 and 1988) on an acid sandy soil in Niger. Treatments of the long-term field experiment were: control (–CR–F), mineral fertilizer only (–CR+F), crop residues only (+CR–F), and crop residues plus mineral fertilizer (+CR+F).In both years, total P uptake was similar for +CR–F and –CR+F treatments (1.6–3.5 kg P ha^-1), although available soil P concentration (Bray I P) was considerably lower in +CR–F (3.2 mg P kg^-1 soil) than in –CR+F (7.4) soil. In the treatments with mineral fertilizers (–CR+F; +CR+F), crop residues increased available soil P concentrations (Bray I P) from 7.4 to 8.9 mg kg^-1 soil, while total P uptake increased from 3.6 to 10.6 kg P ha^-1. In 1987 (with 450 mm of rainfall), leaf P concentrations of 30-day-old millet plants were in the deficiency range, but highest in the +CR+F treatment. In 1988 (699 mm), leaf P concentrations were distinctly higher, and again highest in the +CR+F treatment. In the treatments without crop residues (–CR–F; –CR+F), potassium (K) concentrations in the leaves indicated K deficiency, while application of crop residues (+CR–F; +CR+F) substantially raised leaf K concentrations and total K uptake. Leaf concentrations of calcium (Ca) and magnesium (Mg) were hardly affected by the different treatments.In the topsoil (0–30 cm), root length density of millet plants was greater for +CR+F (6.5 cm cm^-3) than for +CR–F (4.5 cm cm^-3) and –CR+F (4.2 cm cm^-3) treatments. Below 30 cm soil depth, root length density of all treatments declined rapidly from about 0.6 cm cm^-3 (30–60 cm soil depth) to 0.2 cm cm^-3 (120–180 cm soil depth). During the period of high uptake rates of P (42–80 DAP), root colonization with vesicular-arbuscular mycorrhizal (VAM) fungi was low in 1987 (15–20%), but distinctly higher in 1988 (55–60%). Higher P uptake of +CR+F plants was related to a greater total root length in 0–30 cm and also to a higher P uptake rate per unit root length (P influx). Beneficial effects of crop residues on P uptake were primarily attributed to higher P mobility in the soil due to decreased concentrations of exchangeable Al, and enhancement of root growth. In contrast, the beneficial effect of crop residues on K uptake was caused by direct K supply with the millet straw.     

Nitrogen allocation and carbon isotope fractionation in relation to intercepted radiation and position in a young Pinus radiata D. Don tree

The three dimensional distribution of intercepted radiation, intercellular CO₂ concentration (C_i) and late summer needle nitrogen (N) concentration were determined at the tips of all 54 branches in a 6·2-m-tall Pinus radiata D. Don tree growing in a New Zealand plantation. Measurements included above- and below-canopy irradiance, leaf stable carbon isotopic composition (δ¹³C) and tree canopy architecture. The radiation absorption component of the model, MAESTRO, was tested on site and then used to determine the branch tip distribution of intercepted radiation. We hypothesized that in branch tip needles: (i) the allocation of nitrogen and other nutrients would be closely associated with the distribution of intercepted radiation, reflecting carbon gain optimization theory, and (ii) C_i would predominantly reflect changes in photosynthetic rate (A) rather than stomatal conductance (g_s), indicating that the increase in A for a given increase in N concentration was larger than the corresponding increase in g_s. Needle nitrogen concentration was poorly related to intercepted radiation, regardless of the period over which the latter was calculated. At a given height, there was a large azimuthal variation in intercepted radiation but N concentration was remarkably uniform around the tree canopy. There was, however, a linear and positive correspondence between N concentration and δ¹³C and needle height above ground (r² = 0·73 and 0·68, respectively). The very strong linear correspondence between N concentration and C_i (r² = 0·71) was interpreted, using gas exchange measurements, as supporting our second hypothesis. Recognizing the strong apical control in P. radiata and possible effects of leaf nitrogen storage in an evergreen species, we propose that the tree leader must have constituted a very strong carbon sink throughout the growing season, and that the proximity of branch tip needles to the leader affected their photosynthetic capacity and nutrient concentration, independent of intercepted radiation. This implies an integrated internal determination of resource allocation within the tree and challenges the current convention that resources are optimally distributed according to the profile of intercepted radiation.     

Effect of five tree crops and a cover crop in multi-strata agroforestry at two fertilization levels on soil fertility and soil solution chemistry in central Amazonia

The spatio-temporal patterns of soil fertility and soil solution chemistry in a multi-strata agroforestry system with perennial crops were analysed as indicators for the effects of crop species and management measures on soil conditions under permanent agriculture in central Amazonia. The study was carried out in a plantation with locally important tree crop species and a leguminous cover crop at two fertilization levels on a xanthic Ferralsol. Soil fertility to 2 m soil depth was evaluated 3.5 years after the establishment of the plantation, and soil solution chemistry at 10, 60 and 200 cm soil depth was monitored over 2 years. Several soil fertility characteristics exhibited spatial patterns within the multi-strata plots which reflected the differing properties of the plant species and their management, including the fertilizer input. Significant differences between species could be detected to 150 cm depth, and between fertilization treatments to 200 cm depth. Favourable effects on nutrient availability in the soil were found for annatto (Bixa orellana) (P, K) and cupuaçu (Theobroma grandiflorum) (Ca, Mg) in comparison with peach palm (Bactris gasipaes) and Brazil nut (Bertholletia excelsa). Nutrient concentrations of the soil solution showed pronounced fluctuations in the topsoil, corresponding to fertilizer applications. Large nutrient concentrations in the soil solution were accompanied by increased concentrations of aluminium and low pH values, caused by exchange reactions between fertilizer and sorbed acidity and reinforced by the acidifying effect of nitrification. The soil solution under the leguminous cover crop Pueraria phaseoloides had relatively large N concentrations during periods when those under the tree crops were small, and this could partly explain why no yield responses to N fertilization were observed at this site.