The influence of severe shoot pruning on growth,carbon and nitrogen status in young peach trees (Prunus persica)

One-year-old peach trees (Prunus persica (L.) Batsch) were severely pruned in July by removing 60% of the shoots. Tree responses were analyzed in terms of architecture and nutritional status. Tree growth was recorded from July to September by nondestructive (leaf production, thickening and branching of the remaining secondary axes) and destructive measurements (biomass partitioning and concentrations of total nitrogen (N) and nonstructural carbohydrates (NC) in specific tissues). The dry weights of pruned trees were lower than those of control trees at the end of the growing season (i.e., 2.5 months after pruning), whereas shoot:root ratios were restored to the initial values. Tree response occurred in two stages. During the first 24 days following pruning, the growth components of the remaining secondary axes were similar to the control, and new secondary axes were produced. During the next 17 days, increases in both diameter and branching of secondary axes contributed to the maintenance of pruned tree growth rate (similar to that of control trees) and restoration of initial shoot:root ratios. No significant effect of pruning was observed on NC concentrations, whereas N concentrations increased in several organs of the pruned trees during the first growth period. The transient increase in internal N availability contributed to the initiation of new axes and the restoration of a more functional biomass partitioning between shoots and roots.     

Leaf senescence and late-season net photosynthesis of sun and shade leaves of overstory sweetgum (Liquidambar styraciflua) grown in elevated and ambient carbon dioxide concentrations

We examined the effects of elevated CO2 concentration ([CO2]) on leaf demography, late-season photosynthesis and leaf N resorption of overstory sweetgum (Liquidambar styraciflua L.) trees in the Duke Forest Free Air CO2 Enrichment (FACE) experiment. Sun and shade leaves were subdivided into early leaves (formed in the overwintering bud) and late leaves (formed during the growing season). Overall, we found that leaf-level net photosynthetic rates were enhanced by atmospheric CO2 enrichment throughout the season until early November; however, sun leaves showed a greater response to atmospheric CO2 enrichment than shade leaves. Elevated [CO2] did not affect leaf longevity, emergence date or abscission date of sun leaves or shade leaves. Leaf number and leaf area per shoot were unaffected by CO2 treatment. A simple shoot photosynthesis model indicated that elevated [CO2] stimulated photosynthesis by 60% in sun shoots, but by only 3% in shade shoots. Whole-shoot photosynthetic rate was more than 12 times greater in sun shoots than in shade shoots. In senescent leaves, elevated [CO2] did not affect residual leaf nitrogen, and nitrogen resorption was largely unaffected by atmospheric CO2 enrichment, except for a small decrease in shade leaves. Overall, elevated [CO2] had little effect on the number of leaves per shoot at any time during the season and, therefore, did not change seasonal carbon gain by extending or shortening the growing season. Stimulation of carbon gain by atmospheric CO2 enrichment in sweetgum trees growing in the Duke Forest FACE experiment was the result of a strong stimulation of photosynthesis throughout the growing season.     

Changes in fine root production and longevity in relation to water and nutrient availability in a Norway spruce stand in northern Sweden

The PEACH computer simulation model of reproductive and vegetative growth of peach trees (Grossman and DeJong 1994) was adapted to estimate seasonal nitrogen (N) dynamics in organs of mature peach (Prunus persica (L.) Batsch cv. O'Henry) trees grown with high and low soil N availability. Seasonal N accumulation patterns of fruits, leaves, stems, branches, trunk and roots of mature, cropping peach trees were modeled by combining model predictions of organ dry mass accumulation from the PEACH model with measured seasonal organ N concentrations of trees that had been fertilized with either zero or 200 kg N ha(-1) in April. The results provided a comparison of the N use of perennial and annual organs during the growing season for trees growing under both low and high N availability. Nitrogen fertilization increased tree N content by increasing organ dry masses and N concentrations during the fruit growing season. Dry mass of current-year vegetative growth was most affected by N fertilization. Whole-tree N content of fertilized trees was almost twice that of non-fertilized trees. Although N use was higher in fertilized trees, calculated seasonal N accumulation patterns were similar for trees in both treatments. Annual organs exhibited greater responses to N fertilization than perennial organs. Estimated mean daily N use per tree remained nearly constant from 40 days after anthesis to harvest. The calculations indicated that fertilized trees accumulated about 1 g N tree(-1) day(-1), twice that accumulated by non-fertilized trees. Daily N use by the fertilized orchard was calculated to be approximately 1 kg N ha(-1), whereas it was approximately 0.5 kg N ha(-1) for the non-fertilized trees. During the first 25-30 days of the growing season, all N use by growing tissues was apparently supplied by storage organs. Nitrogen release from storage organs for current growth continued until about 75 days after anthesis in both N treatments.     

Phenology and photosynthetic traits of short shoots and long shoots in Betula grossa

Leaf phenology, growth irradiance (i.e., photosynthetic photon flux (PPF) at the leaf surface) and photosynthetic capacity (A(area); measured at a PPF of 1000 micro mol m(-2) s(-1) and expressed on a leaf area basis) were investigated in early leaves (ELs) and late leaves (LLs) of Betula grossa Siebold & Zucc. trees. Early leaves first appeared on morphologically distinct long shoots and short shoots. The appearance of ELs, which was restricted to the bud break period, was followed by the successive appearance of LLs on long shoots only. Late leaves appeared successively until the middle of the growing season. Late leaves started to abscise around the middle of the growing season, whereas ELs on both long and short shoots did not abscise until near the end of the growing season. Solar irradiance was higher at the surface of LLs of late appearance than at the surface of either LLs of early appearance or ELs. Solar irradiance at the surface of ELs decreased after LLs appeared. In both long and short shoots, A(area) of ELs increased and then remained stable for 65-80 days before starting to decrease. Although A(area) was higher in LLs than in ELs for a short time in August, it started to decrease earlier in LLs than in ELs. Area-based nitrogen concentration (N(area)) was higher in LLs than in ELs after August. Although N(area) decreased slowly in ELs after August, it did not decrease in LLs. In both ELs and LLs, A(area)/N(area) decreased with time. The crown was thus characterized by a rapidly growing surface with young LLs having high A(area) and by shaded inner parts with ELs having stable low A(area).     

Carbon allocation and nitrogen acquisition in a developing Populus deltoides plantation

We established Populus deltoides Bartr. stands differing in nitrogen (N) availability and tested if: (1) N-induced carbon (C) allocation could be explained by developmental allocation controls; and (2) N uptake per unit root mass, i.e., specific N-uptake rate, increased with N availability. Closely spaced (1 x 1 m) stands were treated with 50, 100 and 200 kg N ha(-1) year(-1) of time-release balanced fertilizer (50N, 100N and 200N) and compared with unfertilized controls (0N). Measurements were made during two complete growing seasons from May 1998 through October 1999. Repeated nondestructive measurements were carried out to determine stem height and diameter, leaf area and fine-root dynamics. In October of both years, above- and belowground biomass was harvested, including soil cores for fine-root biomass. Leaves were harvested in July 1999. Harvested tissues were analyzed for C and N content. Nondestructive stem diameter and and fine-root dynamic measurements were combined with destructive harvest data to estimate whole-tree biomass and N content at the end of the year, and to estimate specific N-uptake rates during the 1999 growing season. Shoot growth response was greater in fertilized trees than in control trees; however, the 100N and 200N treatments did not enhance growth more than the 50N treatment. Root biomass proportions decreased over time and with increasing fertilizer treatment. Fertilizer-induced changes in allocation were explained by accelerated development. Specific N-uptake rates increased during the growing season and were higher for fertilized trees than for control trees.     

Frost hardiness, bud phenology and growth of containerized Picea mariana seedlings grown at three nitrogen levels and three temperature regimes

We studied the influence of temperature and near- and sub- optimal mineral nutrition of black spruce seedlings (Picea mariana [Mill.] B.S.P.) during their second growing period on bud set, bud development, growth, mineral content and cold tolerance. Bud break and growth after bud break were also studied. Seedlings were grown for 106 d in growth chambers under three temperature regimes in combination with three concentrations of a fertilizer. They were then cold hardened for 56 d and dehardened for 66 d.Under these near- and sub-optimal N levels, bud formation occurred during the growing season. Bud formation was accelerated with decreasing fertilization, but was not affected by temperature treatments. Needles from seedlings with 0.64% N (dry mass basis) before hardening did not harden. Those with 0.87% N showed a lesser degree of hardiness than those with 1.28% N. Stem diameter increased at the beginning of the hardening period. During this acclimation period, shoot dry mass decreased with time at a constant rate and at the same rate over time for all treatments whereas root dry mass was more variable. Total number of needle primordia was low and no difference was observed among growing conditions. Bud break was similar in all treatments. Following bud break, shoot height and stem diameter increases were small but their magnitude varied with the nutritional regimes applied during the previous growing period. During hardening, nitrogen concentration of shoot tissues first increased and then decreased; phosphorus concentration first increased and then remained stable; potassium concentration remained stable. Concentration of these three elements generally decreased in the roots during this hardening.     

Nutrition and bud removal affect biomass and nutrient allocation in Douglas-fir and western red cedar

Seedlings of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) and western red cedar (Thuja plicata J. Donn ex D. Don) were grown at high (250 mg l(-1)) and low (20 mg l(-1)) nitrogen (N) supply for a year. Before the second growing season, half of the seedlings in each nutrient treatment were allocated to the other treatment. Half of the seedlings in each nutrient treatment then had all growing points removed. Biomass and N, phosphorus (P) and potassium (K) concentrations of old and new shoots and roots were measured three times in the second year to test the interaction of current-year and previous-year nutrient supply on biomass and nutrient allocation in these two species with different growth habits. Pruned seedlings served as controls. Unpruned seedlings of both species increased in height throughout the second growing season, except for Douglas-fir in the N250 --> N20 treatment. Repeated pruning did not prevent new shoot growth, but resulted in a 12 to 52% reduction in biomass of new shoots and new and old roots. Seedlings receiving a low N supply in the first growing season were more severely affected by pruning than seedings receiving a high N supply. Growth was reduced more by pruning in western red cedar than in Douglas-fir. Concentrations of N, P and K were higher in pruned seedlings than in unpruned seedlings. Although dry weights of all plant parts in all treatments increased throughout the second growing season, some retranslocation of N, P and K was observed from old shoots of both species in the N250 --> N20 and N20 --> N20 treatments after August. Quantities of N, P and K retranslocated were greatest in seedlings grown the previous year in the high-N treatment.     

白刺幼苗芽库及枝系构型对不同氮添加水平的响应

[目的]研究不同氮添加梯度下白刺幼苗芽库组成及空间结构的差异,探讨了幼苗的养分限制、氮素利用以及根系和插穗的品质与芽库的关联,阐明了白刺芽库响应氮素有效性所采取的适应性策略。[方法]本研究通过盆栽控制实验,对唐古特白刺幼苗的芽库特征进行了测量分析。[结果]氮添加显著增加了白刺幼苗芽和营养枝数量,显著降低了休眠芽和休眠枝数量,并对二级枝和三级枝出芽率具有明显促进作用;随着氮添加量的递增,营养枝有从基部向顶端移动趋势;氮平衡指数与白刺幼苗出芽强度、分枝强度、二级枝和三级枝出芽率均呈二次非线性正相关关系;植株氮含量、氮积累量和地下部分形态特征分别与芽和营养枝数量呈正相关关系,与休眠芽和休眠枝数量呈负相关关系。[结论]氮添加影响幼苗芽库容量。随着氮添加水平的提高,各指标多数在N3和N4处理达到最大值后逐渐降低,因此6个氮添加水平中36 mmol·L-1和48 mmol·L-1是白刺幼苗最适氮添加量。氮添加对幼苗芽库内组分的相对位置产生了不同影响趋势,所以白刺幼苗可以通过改变芽库容量和空间分布来响应养分有效性变化。     

Root-shoot relationships of Fraxinus mandchurica

IntroductionRootsystemsofplantsplaycruciaIrolesinabovegroundgroWth,competitionbetweenthesameordifferentspecies,fluxesofenergyandnutrientscy-cIinginecosystems(Fogel1985,Faheyetal1988,1994).DuringtheevolutionofterrestrialplantstheirrootSandshootsbecameprogressivelyspeciaIizedtoexpIoitdifferentfacetsoftheirenvironments(Russell1979).Shootsentra9solarradiationandthroughphotosynthesis,eIaboratethemetabolitesonwhichallgroWthdepends,rootsanchortheplantinthesoilandabsorbwaterandnutrients.But,histo…     

Characterization of a type II chlorophyll a/b-binding protein gene (Lhcb2*Pp1) in peach. II. mRNA abundance in developing leaves exposed to sun or shade

Leaf development of shoots exposed to full sunlight and shoots shaded by the canopy was followed in field-grown, mature peach trees (Prunus persica (L.) Batsch, cv. Loring) during the first half of the 1995 growing season. The architecture and size of shaded shoots and sun-exposed shoots differed significantly. Total number of leaves produced on shaded shoots was significantly less than on sun-exposed shoots throughout the season, and differences in leaf number between light conditions increased as the season progressed. The overall patterns of leaf development along sun-exposed and shaded shoots were qualitatively similar. The expression pattern of the type II chlorophyll a/b-binding protein gene, Lhcb2*Pp1, determined by RNA abundance in leaves at different positions along the shoot, was also similar between the two light conditions. The major difference between sun-exposed and shaded leaves was a lower abundance of Lhcb2*Pp1 RNA in mature, shaded leaves compared with sun-exposed leaves. Although the number of fruit per shoot was significantly lower on shaded shoots than on sun-exposed shoots, the rate of fruit drop was not substantially different during the growing season, indicating that quantitative differences in leaf initiation and growth caused by differences in light exposure did not adversely affect fruit retention. However, based on comparison with a previous study of leaf development in non-fruiting trees, reproductive development slowed the rate of vegetative growth without affecting the overall pattern of leaf development along the shoots.     

Wachstum,Mykorrhiza und Frostresistenz von Fichtenjungpflanzen bei Düngung mit verschiedenen Stickstoffgaben

Growth, mycorrhiza and frost resistance of Picea abies seedlings following fertilization with different levels of nitrogen . NPK fertilization with varying levels of nitrogen causes increased growth of spruce seedlings and faster flushing in spring. During the growing season, the frost resistance of all organs of the plants, especially new needles and shoots is the lower, the more nitrogen the plants have received. Consequently, spruce plantations, especially at high altitudes, may be liable to late frost damage.     

Soil temperature and plant growth stage influence nitrogen uptake and amino acid concentration of apple during early spring growth

In spring, nitrogen (N) uptake by apple roots begins about 3 weeks after bud break. We used 1-year-old 'Fuji' Malus domestica Borkh on M26 bare-root apple trees to determine whether the onset of N uptake in spring is dependent solely on the growth stage of the plant or is a function of soil temperature. Five times during early season growth, N uptake and total amino acid concentration were measured in trees growing at aboveground day/night temperatures of 23/15 degrees C and belowground temperatures of 8, 12, 16 or 20 degrees C. We used (15NH4)(15NO3) to measure total N uptake and rate of uptake and found that both were significantly influenced by both soil temperature and plant growth stage. Rate of uptake of 15N increased with increasing soil temperature and changed with plant growth stage. Before bud break, 15N was not detected in trees growing in the 8 degrees C soil treatment, whereas 15N uptake increased with increasing soil temperatures between 12 and 20 degrees C. Ten days after bud break, 15N was still not detected in trees growing in the 8 degrees C soil treatment, although total 15N uptake and uptake rate continued to increase with increasing soil temperatures between 12 and 20 degrees C. Twenty-one days after bud break, trees in all temperature treatments were able to acquire 15N from the soil, although the amount of uptake increased with increasing soil temperature. Distribution of 15N in trees changed as plants grew. Most of the 15N absorbed by trees before bud break (approximately 5% of 15N supplied per tree) remained in the roots. Forty-six days after bud break, approximately one-third of the 15N absorbed by the trees in the 12-20 degrees C soil temperature treatments remained in the roots, whereas the shank, stem and new growth contained about two-thirds of the 15N taken up by the roots. Total amino acid concentration and distribution of amino acids in trees changed with plant growth stage, but only the amino acid concentration in new growth and roots was affected by soil temperature. We conclude that a combination of low soil temperature and plant developmental stage influences the ability of apple trees to take up and use N from the soil in the spring. Thus, early fertilizer application in the spring when soil temperatures are low or when the aboveground portion of the tree is not actively growing may be ineffective in promoting N uptake.     

Root produced DHZR-, ZR- and IPA-like cytokinins in xylem sap in relation to coppice shoot initiation and growth in cloned trees of Betula pubescens

Six-year-old cloned Betula pubescens Ehrh. trees, grown outdoors at 65 degrees 01' N, were cut on six dates during the growing season to study coppice shoot development in relation to root-produced cytokinin-like compounds. Bleeding sap was collected over timed intervals for two days after cutting, and endogenous cytokinin-like compounds were measured by ELISA assay in HPLC-purified fractions of xylem sap. Initiation and development of coppice shoots on the clonally propagated plants were comparable to those in seedlings. Coppice shoot initiation was affected by the time of cutting, diminishing significantly after June. Of the cytokinin-like compounds detected in the xylem sap, zeatin riboside-like (ZR) compounds were present in the highest concentrations, and the concentrations of dihydrozeatin riboside-like (DHZR) and isopentenyladenoside-like (IPA) compounds were approximately one third and one eighth of the ZR concentrations, respectively. The concentration of cytokinin-like compounds was positively correlated with xylem sap flow rate. The export of cytokinin-like compounds, especially DHZR- and ZR-types, was positively correlated with the initiation and elongation rate of coppice shoots, the number of lateral branches, and the radial growth of the more slowly growing coppice shoots. The export of cytokinin-like compounds collected immediately after cutting may represent the basal value for each tree. This value is probably affected by the size and activity of the root system and may be a relevant estimate for predicting the success of coppicing.     

Biomass and nutrient allocation in Douglas-fir and amabilis fir seedlings: influence of growth rate and nutrition

Allocation of biomass and nutrients to shoots and roots was followed for three years in fast and slow growing populations of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco), a fast growing pioneer species, and amabilis fir (Abies amabilis Dougl. ex J. Forbes), a slow growing shade-tolerant species. Seedlings were grown for three seasons in five nutrient treatments containing varying proportions of nitrogen and phosphorus (N:P). In both species, growth was greatest in the 250:20 N:P treatment followed by the 100:60 and 100:20 treatments. Vector analysis showed that, in both species, relative to the 100:20 treatment, seedlings in the 20:20 treatment were N deficient and seedlings in the 100:4 treatment were P deficient, i.e., where deficiency is defined to mean that an increase in nutrient supply increases nutrient content, nutrient concentration and plant dry weight. Seedlings in the 100:60 treatment had a higher P content than seedlings in the 100:20 treatment but the same dry weight, indicative of what Timmer and Armstrong (1987) termed luxury consumption. No nutrient retranslocation was observed in either species until the third growing season. In Douglas-fir, the greatest percentage of nutrients was exported from one-year-old shoots between May and July of the third growing season to support new growth. The total amount and percent of nutrients retranslocated was higher in Douglas-fir than in amabilis fir. Amabilis fir seedlings also exported N and P from older shoots, but this was later partially replenished. In both species, P retranslocation was greatest in treatments with a high N:P ratio. Nitrogen retranslocation was greatest in amabilis fir seedlings in treatments with a low N:P ratio, and greatest in Douglas-fir seedlings in the 250:20 and 100:60 treatments. Potassium retranslocation was correlated with seedling size. Douglas-fir retranslocated more of its shoot N reserves into new growth at the expense of older needles when soil fertility was high and sinks were strong. Otherwise, both species preferentially translocated the elements in short supply. Thus, retranslocation varied with the ecological characteristics of species, the relative availability of soil nutrients and sink strength.     

Nitrogen availability, local light regime and leaf rank effects on the amount and sources of N allocated within the foliage of young walnut (Juglans nigra x regia) trees

Early season leaf growth depends largely on nitrogen (N) provided by remobilization from storage, and many studies have tested the effect of N availability to roots on the amount of N provided for new leaf development by remobilization. Although it is well known that the light regime experienced by a leaf influences the amount of N per unit leaf area (LA), the effect of the local light regime on the amount of N derived either directly from root uptake or from remobilization for early season leaf growth has never been tested at an intra- canopy scale. The objective of this study was to quantify the relative importance of (1) N availability to roots, (2) local light regime experienced by the foliage (at the shoot scale) and (3) leaf rank along the shoot, on the total amount of N allocated to leaves and on the proportions of N provided by remobilization and root uptake. To quantify the importance of N uptake and remobilization as sources of leaf N, potted hybrid walnut trees (Juglans nigra L. x regia L.) were grown outdoors in sand and fed with a labeled ((15)N) nutrient solution. By removing the apical bud, the trees were manipulated to produce only two shoots. The experimental design had two factors: (1) high (HN; 8 mol N m(-3)) and low (LN; 2 mol N m(-3)) N availability; and (2) high (HL; 90% of incident photosynthetically active photon flux (PPF)) and low (LL; 10% of incident PPF) light. Total leaf N per tree was unaffected by either N availability or irradiance. The HN treatment increased the amount of leaf N derived from root uptake at the whole-tree scale (typically around 8 and 2% in the HN and LN treatments, respectively). Nitrogen allocation within foliage of individual trees was controlled by the local light regime, which strongly affected individual leaf characteristics as leaf mass per unit LA and area- based amount of leaf (N(a)). Decreasing the light availability to a branch decreased the amount of N allocated to it, benefiting the less shaded branches. In contrast, shading of the lower branch did not affect the fraction of total leaf N remobilized for either the lower, shaded branch or the upper, unshaded branch. The relevance of these findings for tree growth modeling is discussed.     

不同发育阶段白刺群落的结构特征及分布格局

对民勤境内沙质草地发育成熟期和发育中期两种不同条件下白刺群落的结构特征及分布格局进行对比分析。结果表明:(1)不同发育阶段白刺群落的结构特征差异不明显,均呈现植被稀疏,结构单一的特征,几乎没有其他的灌木物种分布,零星伴有芦苇、刺蓬、骆驼蓬等草本植物,建群种白刺优势明显。(2)不同发育阶段群落白刺的生长状况差异明显,发育成熟期群落白刺的密度及盖度高于发育中期群落;发育中期群落白刺在整个生长季都有较高的生长量,而发育成熟期群落白刺在整个生长季生长量很小,已基本没有生长能力。(3)不同发育阶段白刺群落长势均较稳定,但更新苗很少,在没有人为干预促进更新的状况下,随着植株的逐渐增长并老化,白刺群落将走向衰败,最终导致草地沙化。     

Root-shoot relationships ofFraxinus mandchurica

In this paper, root-shoot relationships of seedlings of Manchurican ash (Fraxinus mandchurica) in pots is studied in green house. The results show that roots and shoots have the co-ordination of growth and roots and shoots of ash have the same growth dynamics. There are very close relationships between total root mass and total shoot mass, between fine root mass and leaf mass in this experiments. At the end growing season, ash root-shoot mass ratio and fine root-leaf mass ratio are 1.85 and 2.01 respectively. These ratios are difference during growth season. There are larger roots than shoots on seedling stage. Low nitrogen and phosphorus produce higher root-shoot ratio, and high nutrient concentrations decrease the ratios. This project is supported by National Natural Science Foundation of P. R. China (No.39570586) (Responsible Editor: Chai Ruihai)     

Growth, allocation and tissue chemistry of Picea abies seedlings affected by nutrient supply during the second growing season

One-year-old Norway spruce (Picea abies (L.) Karst.) seedlings were grown hydroponically in a growth chamber to investigate the effects of low and high nutrient availability (LN; 0.25 mM N and HN; 2.50 mM N) on growth, biomass allocation and chemical composition of needles, stem and roots during the second growing season. Climatic conditions in the growth chamber simulated the mean growing season from May to early October in Flakaliden, northern Sweden. In the latter half of the growing season, biomass allocation changed in response to nutrient availability: increased root growth and decreased shoot growth led to higher root/shoot ratios in LN seedlings than in HN seedlings. At high nutrient availability, total biomass, especially stem biomass, increased, as did total nonstructural carbohydrate and nitrogen contents per seedling. Responses of stem chemistry to nutrient addition differed from those of adult trees of the same provenance. In HN seedlings, concentrations of alpha-cellulose, hemicellulose and lignin decreased in the secondary xylem. Our results illustrate the significance of retranslocation of stored nutrients to support new growth early in the season when root growth and nutrient uptake are still low. We conclude that nutrient availability alters allocation patterns, thereby influencing the success of 2-year-old Norway spruce seedlings at forest planting sites.     

核桃主要器官氮素含量及分配的动态变化规律

对核桃主要器官中氮素含量及器官间氮素的分配比例的动态变化规律进行了研究。结果表明:氮素在核桃各器官中的变化规律与其自身的生长规律相吻合,在整个生育期中,以树体萌芽期各营养器官的氮素含量最高,雌花或幼果的氮素含量也相对较高;在枝条旺盛生长及果实的速长期,各主要器官的氮素含量呈下降趋势;在核桃种仁充实期,果实中的氮素含量急剧上升,而叶片和枝条中的氮素含量继续下降。不同生育期主要器官间氮素的分配比例有差异,5月中旬至7月上旬氮素的分配比例排序为叶片>果实 >果枝>营养枝;7月中旬至9月上旬氮素的分配比例排序为果实>叶片>果枝>营养枝。     

An experimental test of a nitrogen uptake and partitioning model for young trees

Simulation models of nitrate uptake and total nitrogen partitioning during the exponential growth phase of one-year-old peach trees (Prunus persica (L.) Batsch.) were tested in an experiment with 88 plants grown in soil-filled containers. Plants were fertilized with (15)N-NO(3) (-) and nitrate uptake estimated by periodic destructive analysis of plants for excess (15)N. Partitioning of N within the trees was followed by the analysis of plant parts for total N and (15)N. The nitrate uptake model, which provides one of the main inputs to the partitioning model, is based on a simplified form of the Michaelis-Menten equation adapted to describe uptake by roots growing in soil layers. The nitrogen partitioning model considers each plant part (e.g., roots, trunk, shoots, leaves) as either a sink or a source for nitrogen. The model uses a flow equation, which is the same for all plant parts, to model the dynamics of nitrogen partitioning in the tree using increases in dry matter of various plant parts as driving force variables. The experiment demonstrated an error in the compartment organization of the partitioning model as a result of which the model failed to simulate changes in root N. A modification of the partitioning model structure to take account of the importance of trunk nitrogen reserves for root growth at the beginning of the growing season, which was indicated by the (15)N data, greatly improved prediction of root N. This modification is discussed in relation to the modeling approach.