Seasonal uptake of 15N-nitrate and distribution of absorbed nitrogen in peach trees

The absorption and distribution of N was measured monthly throught a calendar year in 3-year old peach trees (Prunus persica (L) c.v. Maycrest) grafted on Nemaguard rootstock. Plants were grown on siliceous sand in 500-L pots and fertilized with a solution containing ¹⁵N enriched KNO₃. During flowering and fruit set (March) approximately 7% of N found in new growth came from the fertilizer and the remainder came from the N stored in the old organs. Maximum N absorption took place during the periods of fruit ripening and maximal vegetative growth (May to August). This nitrogen was relocated from leaves to woody tissues and stored as reserve-N before leaf fall. In the following growth season reserve-N was used for flower development and new shoot growth. The N absorbed during plant dormancy was quite low and remained in the stem bark and roots mainly as soluble-N.     

Partitioning of nitrogen from biological fixation and fertilizer in Phaseolus vulgaris

Nitrogen uptake, distribution and remobilization in the vegetative and reproductive parts of the plant were studied in bean (Phaseolus vulgaris L.) cultivars Negro Argel and Rio Tibagi inoculated with either Rhizobium strain C05 or 127 K-17. Greenhouse grown plants were supplied with 2.5 mg N (plant)⁻¹ day⁻¹ as KNO₃ or K¹⁵NO₃ and the relative contribution to total plant nitrogen of mineral and symbiotically fixed nitrogen was determined. Control plants included those entirely dependent on fixed nitrogen as well as uninoculated plants supplied with 10 mg N (plant)⁻¹ day⁻¹. No differences were observed between inoculated treatments in total nitrate reductase activity and in the amount of mineral nitrogen absorbed, but there were considerable differences in the contribution of fixed nitrogen. Nitrogen fixation supplied from 58 to 72% of the total nitrogen assimilated during the bean growth cycle and the symbiotic combinations fixed most of their nitrogen (66 to 78% of total nitrogen) after flowering. Maximum uptake of mineral nitrogen was in the 15-day-period between flowering and mid-podfill (47 to 58% of total mineral nitrogen). Nitrogen partitioning varied with Rhizobium strains, and inoculation with strain C05 increased the nitrogen harvest index of both cultivars. Applied mineral nitrogen had a variable effect and in cv. Negro Argel was more beneficial to vegetative growth, resulting in smaller nitrogen harvest indices. Seed yield was not increased by heavy nitrogen fertilization. In contrast, cv. Rio Tibagi always benefited from nitrogen applications. Among the various nitrogen sources supplying the grain, the most important one was the fixed nitrogen translocated directly from nodules or after a rapid transfer through leaves, representing from 60 to 64% of the total nitrogen incorporated into the seeds.     

Fruit Regulates Bud Sprouting and Vegetative Growth in Field-Grown Loquat Trees (Eriobotrya japonica Lindl.): Nutritional and Hormonal Changes

The effects of fruit on bud sprouting and vegetative growth were compared on fruiting and defruited loquat trees from fruit set onward. Carbohydrate and nitrogen content in leaves and bark tissues and hormone concentrations were studied during the fruit development and vegetative growth periods. On defruited trees, a significant proportion of buds sprouted in winter, whereas buds from fruiting trees sprouted only in the spring when fruit reached its final size. Furthermore, when panicles were completely removed in autumn, the buds also sprouted. In addition, fruit directly affected vegetative growth by reducing shoot length. An effect of sink removal (flower or fruit) promoting bud sprouting, regardless of the season, was then demonstrated. Neither soluble sugar concentration nor nitrogen fraction concentration in leaves or bark tissues was related to bud sprouting, but a certain nutritional imbalance was observed during the most active period of fruit development. Moreover, fruit sink activity significantly modified hormone content by increasing indole-3-acetic acid (IAA) and reducing zeatin concentrations, resulting in a higher IAA/zeatin ratio parallel to the lower bud sprouting intensity. Therefore, these changes caused by fruit removal are all related to vegetative growth, but there is no evidence that they are responsible for bud burst.     

Gibberellic acid causes earlier flowering and synchronizes fruit ripening of coffee

The effect of 100 mgl^–1 gibberellic acid (GA₃) on flowering and fruit ripening synchrony, fruit set, fruit fresh weight, and vegetative growth were studied for different size classes of coffee (Coffea arabica L. cv. Guatemalan) flower buds. Flower buds that were > 4 mm, but not developed to the candle stage at the time of GA₃ treatment, reached anthesis 20 days earlier than the controls, and their development was independent of precipitation, unlike the controls. Fruit from buds that were treated with GA₃ at the candle stage showed earlier and more synchronous ripening than the control, although no differences in flowering were found during anthesis. Buds that were smaller than 4 mm at the time of treatment did not respond to GA₃ applications. Treatment with GA₃ did not affect fruit set, fresh weight of fruits, or vegetative shoot growth.     

Maximum Vegetative Growth Potential and Seasonal Patterns of Resource Dynamics during Peach Growth

The maximum vegetative growth potential of two peach [Prunuspersica (L.) Batsch] cultivars that differ in the timing ofresource demand for reproductive growth was determined in termsof stem extension, stem and leaf dry weight accumulation, andtrunk radial increment on defruited trees. The maximum vegetativegrowth potentials were similar on the two cultivars indicatingthat the greater partitioning of dry weight to vegetative growthfrequently observed on early maturing cultivars compared tolate maturing cultivars is the result of a shorter period ofcompetition between reproductive and vegetative growth, ratherthan a genetic difference in vegetative growth potential. Onboth cultivars, stem extension and leaf dry weight accumulationceased in mid-summer, however stem dry weight accumulation andtrunk radial increment increase continued through the autumn. The presence of fruit did not have a detectable effect on thefinal stem length, stem dry weight or leaf dry weight on theearly maturing cultivar, but it reduced final stem length anddry weight by 43 and 56%, respectively on the late maturingcultivar. The presence of fruit did decrease stem length, stemdry weight and leaf dry weight on the early maturing cultivarfor 1 month prior to and 1 month after fruit harvest. Fruitdecreased final trunk radial increment by 42 and 77% on theearly and late maturing cultivars, respectively. These reductionsin vegetative growth indicate that resource partitioning tovegetative growth was reduced by competition with fruit growth. Comparison of stem relative extension rates and stem and leafrelative growth rates on fruited and defruited trees indicatedthat vegetative growth was resource-limited shortly after vegetativebud break on fruited trees of both cultivars. This period ofresource-limited vegetative growth corresponded to a periodof resource-limited fruit growth identified in an earlier study.During the period of resource-limited vegetative growth, assimilatesupply was low due to low leaf area index, and carbohydratedemand was relatively high due to high vegetative and reproductivegrowth potentials, creating resource-limited growth conditions.Copyright1995, 1999 Academic Press Maximum vegetative growth potential, carbon economy, partitioning, resource availability, resource limitation, source-limited growth, growth analysis, relative growth rate, peach, Prunus persica (L.) Batsch     

Fitness implications of late bud break and time of burning in Lannea edulis (Sond.) Engl. (Anacardiaceae)

Many woody plants of savannas have massive underground parts (“lignotubers”) and diminutive aboveground parts with phenologies that are triggered by fire. Lannea edulis (Anacardiaceae) represents this life form and is widely distributed in south central Africa. The phenology of L. edulis was monitored on 42 permanently marked shoots over a 3-year period, from 2002 to 2004, and under three fire treatments (early and middle dry season burning, and fire protection) to determine whether (i) fire affected time of bud break and (ii) time of fruit ripening affected seed germination. Statistical analyses revealed that shoot reproductive status and fire treatments significantly affected time of bud break and the lag between bud break and leaf production. Shoot reproductive status explained 27% (P<0.001) while the interaction between reproductive status and fire treatments explained 34% (P<0.0001) of the variation in time at bud break. The appearance of the first leaf was delayed by 4 weeks in reproductive shoots compared with vegetative shoots. Shoot reproductive status explained 28% (P<0.0001) of the variation in the lag between bud break and appearance of the first leaf suggesting the existence of resource competition between reproduction and vegetative growth. However, reproductive status and fire treatments did not affect shoot size and leaves produced because replacement shoots after dieback due to fire were as long as shoots surviving from previous years due to insignificant annual shoot extension among the latter. There was high autocorrelation in the germination rate of seed-lots with seeds from fruits ripening early having a significantly higher germination rate (47% in 2002 and 89% in 2004) than those from fruits ripening later (3% in 2002 and 53% in 2004). Since time at bud break and fruit ripening were linked, it is proposed that late bud break results in reduced fitness in L. edulis because of reduced seed germination rate. Early and late dry season fires that delay bud break and destroy reproductive structures, respectively, also reduce this measure of fitness.     

Using trunk diameter sensors for regulated deficit irrigation scheduling in early maturing peach trees

The aim of this paper was to test the possibility of scheduling regulated deficit irrigation (RDI) using exclusively maximum daily trunk shrinkage (MDS) measurements, and that RDI strategies can be applied in early maturing peach trees reducing significantly the seasonal water use. During three growing seasons, 6-year-old peach trees (Prunus persica (L.) Batsch cv. Flordastar) grafted on P. persica × P. amygdalus GF-677 peach rootstock were submitted to different drip irrigation treatments. Control (T0) plants were irrigated above the estimated crop evapotranspiration level (≈130% ET_C) and T1 plants were submitted to RDI, which were irrigated in order to maintain MDS signal intensity (SI) values close to unity (no irrigation-related stress) from the fruit thinning stage to 2 weeks after harvest, at MDS SI values close to 1.3 during the early postharvest period, and at MDS SI values of 1.6 during the late postharvest period. The RDI strategy assayed reduced the seasonal water applied by 35-42% with respect to estimated ET_C without affecting yield efficiency components or the distribution of different peach fruit categories, while improving water productivity. The only vegetative growth component affected by RDI was pruning weight, indicating that vigor regulation as a result of RDI may decrease the competition for assimilates between vegetative apexes and reserve tissues. Also, the absence of any significant effect of RDI on the ratio between yield and the increase in trunk cross sectional area suggested similar carbon partitioning schemes during fruit growth. To improve the precision of MDS SI-driven schedule in RDI strategies changes in the irrigation protocol should be considered so that the scheduled water deficit levels are attained more rapidly. For this, when it is necessary to change from a MDS SI threshold value to a higher one, the daily irrigation rate should be decreased by more than 3%.     

Effect of mineral nitrogen on nitrogen nutrition and biomass partitioning between the shoot and roots of pea (Pisum sativum L.).

The effect of mineral N availability on nitrogen nutrition and biomass partitioning between shoot and roots of pea (Pisum sativum L., cv Baccara) was investigated under adequately watered conditions in the field, using five levels of fertiliser N application at sowing (0, 50, 100, 200 and 400 kg N ha^–1). Although the presence of mineral N in the soil stimulated vegetative growth, resulting in a higher biomass accumulation in shoots in the fertilised treatments, neither seed yield nor seed nitrogen concentration was affected by soil mineral N availability. Symbiotic nitrogen fixation was inhibited by mineral N in the soil but it was replaced by root mineral N absorption, which resulted in optimum nitrogen nutrition for all treatments. However, the excessive nitrogen and biomass accumulation in the shoot of the 400 kg N ha^–1 treatment caused crop lodging and slightly depressed seed yield and seed nitrogen content. Thus, the presumed higher carbon costs of symbiotic nitrogen fixation, as compared to root mineral N absorption, affected neither seed yield nor the nitrogen nutrition level. However, biomass partitioning within the nodulated roots was changed. The more symbiotic nitrogen fixation was inhibited, the more root growth was enhanced. Root biomass was greater when soil mineral N availability was increased: root growth was greater and began earlier for plants that received mineral N at sowing. Rooting density was also promoted by increased mineral N availability, leading to more numerous but finer roots for the fertilised treatments. However, the maximum rooting depth and the distribution of roots with depth were unchanged. This suggested an additional direct promoting effect of mineral N on root proliferation.     

The development and effects of nitrogen deficiency in field-grown kiwifruit (Actinidia deliciosa) vines

The development and effects of nitrogen (N) deficiency in kiwifruit (Actinidia deliciosa Hayward) vines planted at three densities (25.0, 12.5 and 8.33 m² vine^–1) were examined in a long term (1982 to 1989) field experiment in which N was applied at rates from 0 to 200 kg N ha^–1 year^–1. The rate of applied N significantly affected leaf N concentrations every year from 1985 onwards, and the average leaf N concentrations declined throughout the experiment. Fruit N concentrations varied significantly with the level of applied N as early as 1986. The average fruit N concentrations varied strongly between years, and were inversely proportional to the fruit number (per m²), indicating that, after fruit set, growth of individual fruit was relatively insensitive to the vine N status. Effects of N supply on fruit yields resulted mostly from changes in fruit number (per m²). For vines planted at the high density, fruit yields responded significantly to the level of applied N each season from 1986 onwards. In any year, maximum fruit yields for vines planted at the high density were associated with leaf N concentrations (20 weeks after bud burst) of at least 1.8 mmol g^–1. For vines planted at low density, significant yield responses to the level of applied N were not recorded until 1988, and maximum yields in that year were associated with leaf N concentrations of at least 1.4 mmol g^–1. The delayed expression of effects of N deficiency on fruit yields for vines planted at low density appeared to follow a shift in partitioning of resources in favour of fruit growth. This shift in partitioning did not appear to be sustainable, and by 1989 the fruit yield response to applied N continued to the highest N level tested. In that year, the leaf N concentration associated with maximum yield was 1.8 mmol g^–1, the same as that recorded throughout the experiment for the vines planted at high density. In the last two seasons of the experiment, leaf necrosis developed extensively on vines receiving less than the highest rate of N. This necrosis appeared to be premature senescence resulting from N deficiency. Leaf chloride (Cl) concentrations increased significantly with increasing severity of N deficiency, but were never more than those associated with Cl toxicity. While N supply significantly affected fruit firmness immediately post-harvest, there were no significant effects on fruit firmness after 12–20 weeks storage.     

The effect of autumn N supply on the architecture of young peach (Prunus persica L.) trees

Irrigation and fertilisation were recently considered as useful tools to control tree shape, and reduce pruning costs. The role of the N reserves, which determined spring growth, was considered to be essential. We intended therefore to evaluate its effects on peach tree architecture. Four levels of N fertilisation were applied on 1-year-old trees, from the end of shoot growth to leaf fall. In subsequent spring, each bud fell into one of the ten classes of positions previously defined within the crown. Its development was followed weekly from burst to June. Fertilisation promoted growth until a threshold level, since no differences were evidenced between the three highest N treatments. Fall N did not affect burst but the further transformation of the buds into rosettes, proleptic or ramificated axes. Crown base was little affected. Fall N increased the number of proleptic axes on most median and upper positions. Axes lengthening and thickening were limited on the median positions, promoted at crown top. The variations concerned the mean internodes lengths, not the number of phytomers per axis. Sylleptic ramification was limited to the crown outer parts, and decreased with fall N. Treatment did neither affect the fruit dry weights, nor the ratio between the number of leaves and the number of fruits. Fruit number was proportioned to vegetative growth by blossoming and fruit set. We conclude that a moderate autumn fertilisation improved orchard productivity, but favoured vegetative growth in the crown outer parts. Additional pruning may therefore be required to control tree shape.     

Timing of nitrogen uptake affects winter storage and spring remobilisation of nitrogen in nectarine (Prunus persica var. nectarina) trees

Two-year old nectarine trees (Prunus persica, Batsch, var. nectarina, cv. Starkredgold on GF305 rootstock) planted in pots each received five applications of 1.0 g ¹⁵N labelled urea either from mid May to mid July (early uptake) or from mid August to the beginning of October (late uptake). All trees were supplied with a corresponding amount of unlabelled urea when they did not receive the labelled N. In autumn, all abscised leaves were collected and during winter randomly selected trees were harvested and divided into main organs. The remaining trees were transplanted into similar pots filled with sand; they received no N fertiliser and were harvested in May to evaluate the remobilisation of N. Total N and ¹⁵N abundance were determined in each organ. Nectarine trees took up similar amounts of N in the 'early' and in the 'late' period; however, more labelled nitrogen was recovered in the perennial organs during the winter when trees received the labelled N in the 'late' than in the 'early' period. Some 73–80% of the N present in the dormant trees was stored in the roots, which contained almost twice the amount of labelled N taken up 'late' than that absorbed 'early'. Nitrogen for spring growth was remobilised predominantly from the roots and accounted for some 43–49% of the labelled N recovered in the tree during winter. Results suggest that the nitrogen taken up 'late' in the season is preferentially stored in roots and used by peach trees to sustain new growth the following spring. This revised version was published online in June 2006 with corrections to the Cover Date.     

Utilization of nitrogen from storage and current-year uptake in walnut spurs during the spring flush of growth

[¹⁵N]-depleted (NH₄)₂SO₄ applied to the soil in 1985 resulted in residual labeling of about 16% of the storage nitrogen (N) pool of mature walnut ( Juglans regia L. cv. Serr) trees in 1987. Application of [¹⁵N]-depleted (NH₄)₂SO₄ fertilizer to a different set of mature walnut trees in 1987 allowed monitoring of the kinetics and utilization of N from current year uptake in 1987 and resulted in >20% labeling of fruit N following completion of leaf expansion. Redistribution of storage N to the new growth predominated during the spring flush of growth although N derived from the soil during current-year uptake contributed increasingly during leaf expansion. Labeled N from current year uptake accumulated preferentially in the leaves as compared with reproductive organs during leaf expansion but subsequent to leaf expansion, fruit were more highly labeled with N derived from current-year uptake than leaves. Pistillate flower abortion was coincident with an apparent competition for N among developing vegetative and reproductive organs and preceded the period of significant N contribution from current-year uptake.     

Regulation of the expression of lipoxygenase genes in <Emphasis Type="Italic">Prunus persica</Emphasis> fruit ripening

Three genes of the lipoxygenase (LOX) family in peach (Prunus persica var. compressa cv. Ruipan 4) were cloned, and their expression patterns during fruit ripening were analyzed using real-time quantitative PCR. All of the three peach LOX genes had been expressed during fruit ripening; however, their expression patterns were significantly different. During the normal ripening of peach fruits, the expression levels of PpLox1, PpLox2 and PpLox3 increased in varying degrees accompanying upsurge of ethylene evolution. After treated by methyl jasmonic acid (MeJA), the peak of ethylene releasing occurred in advance, and the declining rate of fruit hardness was accelerated, the expression level of the three peach LOX genes in fruits markedly enhanced at the early stage of storage, but significantly decreased at the late storage stage. So, it could be suggested that all three LOXs relate to fruit ripening; however, their functions might be different. PpLox1 expression increase along with the upsurge of ethylene evolution in both control and MeJA-treated peach fruits suggested that PpLox1 probably played a major role in the peach fruit ripening. Expression peak of PpLox2 appeared at the 1 DAH (days after harvest) in both control and MeJA-treated peach fruits, while obvious changes in ethylene evolution and fruit hardness was not observed, which suggested that the rise of PpLox2 expression can be induced by certain stimulation related to ripening, such as harvesting stress and MeJA treatment. The expression of PpLox3 kept a lower level in the natural ripening fruits, whereas raced up at the early stage of storage in the fruits treated with MeJA, which indicated that PpLox3 was expressed inductively and had minor roles during the normal ripening of peach fruits, but when encountered with external stimulation, its expression level would rapidly enhance and accelerate the ripening of peach fruit.     

Nitrogen and carbon partitioning in soybean under variable nitrogen supplies and acclimation to the prolonged action of elevated CO2

This study was conducted to determine reciprocal effects of low to high doses of nitrogenous fertilizer (N₃₀, N₄₀, N₅₀, N₆₀ and N₇₀ — 30, 40, 50, 60 and 70 kg ha⁻¹ respectively) and CO₂ enriched environment on C and N partitioning in soybean (Glycine max (L.) Merril cv JS-335). Plants were grown from seedling emergence to maturity inside open top chambers under ambient, AC (350±50 mol mol⁻¹) and elevated, EC (600±50 mol mol⁻¹) CO₂ and analyzed at seedling, vegetative, flowering, pod setting and maturity stages. Soybean responded to both CO₂ enrichment and N supply. Leaves, stem and root reserves at different growth stages were analyzed for total C and N contents. Consistent increase in the C contents of the leaf, stem and root was observed under EC than in AC. N contents in the different plant parts were found to be decreased under EC-grown plants specially at seedling and vegetative stage despite providing N doses to the soil. Significant increase observed for C to N dry mass ratio under EC in the root, stems and leaves at seedling and vegetative stage was decreased in the middle and later growth stages possibly due to combined impact of N doses to the soil and increased N₂ fixing activities due to EC conditions. Critical analysis of our findings reveals that the composition and partitioning of C and N of soybean under variable rates of N supply and CO₂ enrichment alter according to need under altered metabolic process. These changes eventually may lead to alteration in uptake of not only N but other essential nutrients also under changing atmosphere.     

Translocation of amino acids in the xylem of apple (Malus domestica Borkh.) trees in spring as a consequence of both N remobilization and root uptake

Nitrogen is remobilized from storage for the growth of Malus domestica leaves each spring. Seasonal patterns of N translocation in the xylem sap as a consequence of remobilization were determined in 2-year-old 'Golden delicious' trees grafted on M9 rootstocks. The trees were grown in sand culture and (15)NH(4)(15)NO(3) at 10.4 atom% abundance supplied during August-September. The following year no further N was supplied and destructive harvests were taken during bud burst and leaf growth to determine the patterns of N remobilization together with the isolation of xylem sap for an analysis of their amino acid profiles and (15)N enrichments by GC-MS. The concentration of amino acids in the xylem sap rose following bud burst, peaked at full bloom and then fell again during petal fall and fruit set. The peak in amino acid concentration corresponded with the period when the rate of N remobilization was the fastest. The majority of labelled N was recovered in Asn, Gln + Glu and Asp demonstrating that they were being translocated as a consequence of remobilization. In a second experiment, 8-year-old trees growing in an orchard were fertilized with N either in the autumn or spring. Xylem sap samples were collected in the spring and early summer and, by comparison with the amino acid profiles recovered in trees from both treatments, Asn was identified as the main compound translocated as a consequence of both remobilization and root uptake of N, although there was evidence that root uptake of N occurred later. The data are discussed in relation to quantifying the internal cycling of N in trees.     

Dynamics of biomass and N accumulation of alfalfa under three N fertilization rates

The dynamics of biomass and N accumulation following defoliation of alfalfa and the application of N fertilization has rarely been studied under field conditions, particularly in the seeding year. Our objectives were to determine the effect of N fertilization on the dynamics of biomass and N accumulation during the first regrowth of alfalfa in the seeding year, and to determine if a model describing critical N concentration developed for established stands could be used in the seeding year. In two separate experiments conducted in 1992 and 1993, the biomass and N accumulation of alfalfa grown with three N rates (0, 40 and 80 kg N ha^-1) were determined weekly. Maximum shoot growth was reached with 40 kg N ha^-1 in 1992, and maximum shoot growth was not reached with the highest N fertilization rate in 1993. Nitrogen fixation, root N reserves and soil inorganic N uptake when no N was applied were, therefore, not sufficient to ensure non-limiting N conditions, particularly when growth rates were the highest between 14 to 21 d after defoliation. Nitrogen fertilization increased shoot biomass accumulation in the first 21 d of regrowth, biomass partitioning to the shoots and shoot and taproot N concentrations. The model parameters of critical N concentration developed by Lemaire et al. (1985) for established stands of alfalfa were not adequate in the seeding year. The N requirements per unit of shoot biomass produced are greater in the seeding year than on established stands, and this was attributed to a greater proportion of leaves in the seeding year.     

Nitrogen uptake in relation to water availability in wheat

Nitrogen uptake and distribution in wheat (Triticum aestivum L.) are dependent on environmental conditions and in particular on the water regime. Under Mediterranean conditions, where high water stress at the end of the crop cycle is frequent, nitrogen uptake can be reduced, affecting yield and quality of the grain. To disclose these relations a field experiment was carried out in Central Portugal. Wheat was grown on a clay soil (Vertisol) at three water treatments: rainfed (WO), with 80 mm of irrigation (W1) and with 50 mm and 70 mm irrigations (W2). All treatments received 50 kg ha^–1 of N prior to sowing and were top-dressed with 140 kg ha^–1 of N, splitted in two applications, Kjeldahl N was determined in green leaves (GL), yellow leaves (YL), stems (ST), chaff (CH) and grain (GR). N uptake after anthesis was 40% of the total in W2, but was not noticeable in the other two treatments. N concentrations in the total above-ground plant dry matter, and in both YL and ST were not very different according to treatment, but water availability increased grain-N concentration. It seems, therefore, that grain protein concentration and N uptake can be substantially increased by late irrigations.