Allocation Of Assimilate Research Articles

Tripartite symbioses regulate plant–soil feedback in alder

Abstract Plant–soil feedbacks regulate plant productivity and diversity, but potential mechanisms underpinning such feedbacks, such as the allocation of recent plant assimilate, remain largely untested especially for plants forming tripartite symbioses. We tested how soils from under alder Alnus glutinosa and beneath other species of the same and different families affected alder growth and nutrition, and colonization of roots by nitrogen‐fixing Frankia bacteria and ectomycorrhizal fungi. We also measured how the soil environment affected carbon capture and allocation by pulse labelling seedlings with 13CO2. We then tested for linkages between foliar nutrient stoichiometry and carbon capture and allocation and soil origin using statistical modelling approaches. Performance of alder and nitrogen nutrition were best on home and birch Betula pendula soils (both Betulaceae), whereas performance on Douglas fir Pseudotsuga menziesii (Pinaceae) soil was poor. Plants growing in P. menziesii soil were virtually devoid of Frankia and ectomycorrhizas, and the natural abundance 15N signatures of leaves were more enriched indicating distinct nitrogen acquisition pathways. Seedlings in these soils also had smaller 13C fixation and root allocation rates, leading to smaller 13C respiration rates by microbes. Statistical models showed that the best predictors of foliar N concentration were 13C allocation rates to fine roots and net CO2 exchange from the mesocosms. The best predictors for foliar phosphorus concentration were net CO2 exchange from the mesocosms and soil origin; seedlings in home soils tended to have greater foliar phosphorus compared to birch soils while seedlings from Douglas fir soils were no different from the other treatments. Foliar phosphorus concentration was not correlated with plant available or total soil phosphorus for any of the soils. Home soils also resulted in distinct ectomycorrhizal communities on seedlings roots, which could be responsible for greater foliar phosphorus concentration. Our findings show how the association of alder with nitrogen‐fixing Frankia relieved nitrogen limitation in the seedling triggering a performance feedback loop. We propose that relief of nitrogen limitation likely increases plant phosphorus demand, which may promote the formation of ectomycorrhizas in nutrient‐deficient soils. The formation of tripartite symbioses therefore generates positive plant–soil feedbacks, which enables plants to acquire mineral nutrients otherwise inaccessible in trade for carbon. A free Plain Language Summary can be found within the Supporting Information of this article.

Growth Indices of Kimiya Cultivar of Lentil in Response to Drought Stress at Flowering and Pod Filling Stages under Greenhouse Conditions

Drought stress is one of the most important environmental factors which can limit the lentil production. To evaluate the effect of drought stress at flowering and pod filling stages on growth indices of lentil cultivar Kimiya (a new high yielding lentil cultivar for moderate cold and semi warm climate of Iran), an experiment was conducted at the research greenhouse of Higher Educational Complex of Saravan in completely randomized design with four replications. The drought stress was applied by withholding irrigation until the soil moisture reached to 20% of field capacity at stages of flowering and pod filling. In this experiment, we measured grain yield per plant, growth indices including plant leaf area (PLA), relative growth rate (RGR), plant growth rate (PGR), and net assimilation rate (NAR). Results showed that the flowering stage in lentil plant is more sensitive to drought as exhibited significant decline in PLA, RGR, PGR and NAR. PGR declined at the end of growing season when vegetative growth stop, senescence of leaves, the reduction of NAR, and the allocation of assimilate to the seeds.

Short-term effects of drought on tropical forest do not fully predict impacts of repeated or long-term drought: gas exchange versus growth.

Are short-term responses by tropical rainforest to drought (e.g. during El Niño) sufficient to predict changes over the long-term, or from repeated drought? Using the world's only long-term (16-year) drought experiment in tropical forest we examine predictability from short-term measurements (1–2 years). Transpiration was maximized in droughted forest: it consumed all available throughfall throughout the 16 years of study. Leaf photosynthetic capacity was maintained, but only when averaged across tree size groups. Annual transpiration in droughted forest was less than in control, with initial reductions (at high biomass) imposed by foliar stomatal control. Tree mortality increased after year three, leading to an overall biomass loss of 40%; over the long-term, the main constraint on transpiration was thus imposed by the associated reduction in sapwood area. Altered tree mortality risk may prove predictable from soil and plant hydraulics, but additional monitoring is needed to test whether future biomass will stabilize or collapse. Allocation of assimilate differed over time: stem growth and reproductive output declined in the short-term, but following mortality-related changes in resource availability, both showed long-term resilience, with partial or full recovery. Understanding and simulation of these phenomena and related trade-offs in allocation will advance more effectively through greater use of optimization and probabilistic modelling approaches.This article is part of a discussion meeting issue ‘The impact of the 2015/2016 El Niño on the terrestrial tropical carbon cycle: patterns, mechanisms and implications’.

Awns reduce grain number to increase grain size and harvestable yield in irrigated and rainfed spring wheat.

Genotypic variation in ear morphology is linked to differences in photosynthetic potential to influence grain yield in winter cereals. Awns contribute to photosynthesis, particularly under water-limited conditions when canopy assimilation is restricted. We assessed performance of up to 45 backcross-derived, awned-awnletted NILs representing four diverse genetic backgrounds in 25 irrigated or rainfed, and droughted environments in Australia and Mexico. Mean environment grain yields were wide-ranging (1.38-7.93 t ha(-1)) with vegetative and maturity biomass, plant height, anthesis date, spike number, and harvest index all similar (P >0.05) for awned and awnletted NILs. Overall, grain yields of awned-awnletted sister-NILs were equivalent, irrespective of yield potential and genetic background. Awnletted wheats produced significantly more grains per unit area (+4%) and per spike (+5%) reflecting more fertile spikelets and grains in tertiary florets. Increases in grain number were compensated for by significant reductions in grain size (-5%) and increased frequency (+0.8%) of small, shrivelled grains ('screenings') to reduce seed-lot quality of awnletted NILs. Post-anthesis canopies of awnletted NILs were marginally warmer over all environments (+0.27 °C) but were not different and were sometimes cooler than awned NILs at cooler air temperatures. Awns develop early and represented up to 40% of total spikelet biomass prior to ear emergence. We hypothesize that the allocation of assimilate to large and rapidly developing awns decreases spikelet number and floret fertility to reduce grain number, particularly in distal florets. Individual grain size is increased to reduce screenings and to increase test weight and milling quality, particularly in droughted environments. Despite the average reduction in grain size, awnless lines could be identified that combined higher grain yield with larger grain size, increased grain protein concentration, and reduced screenings.

Rhizosphere interactions, carbon allocation, and nitrogen acquisition of two perennial North American grasses in response to defoliation and elevated atmospheric CO2

Carbon allocation and N acquisition by plants following defoliation may be linked through plant-microbe interactions in the rhizosphere. Plant C allocation patterns and rhizosphere interactions can also be affected by rising atmospheric CO(2) concentrations, which in turn could influence plant and microbial responses to defoliation. We studied two widespread perennial grasses native to rangelands of western North America to test whether (1) defoliation-induced enhancement of rhizodeposition would stimulate rhizosphere N availability and plant N uptake, and (2) defoliation-induced enhancement of rhizodeposition, and associated effects on soil N availability, would increase under elevated CO(2). Both species were grown at ambient (400 μL L(-1)) and elevated (780 μL L(-1)) atmospheric [CO(2)] under water-limiting conditions. Plant, soil and microbial responses were measured 1 and 8 days after a defoliation treatment. Contrary to our hypotheses, we found that defoliation and elevated CO(2) both reduced carbon inputs to the rhizosphere of Bouteloua gracilis (C(4)) and Pascopyrum smithii (C(3)). However, both species also increased N allocation to shoots of defoliated versus non-defoliated plants 8 days after treatment. This response was greatest for P. smithii, and was associated with negative defoliation effects on root biomass and N content and reduced allocation of post-defoliation assimilate to roots. In contrast, B. gracilis increased allocation of post-defoliation assimilate to roots, and did not exhibit defoliation-induced reductions in root biomass or N content. Our findings highlight key differences between these species in how post-defoliation C allocation to roots versus shoots is linked to shoot N yield, but indicate that defoliation-induced enhancement of shoot N concentration and N yield is not mediated by increased C allocation to the rhizosphere.

The effect of nitrogen enrichment on the carbon sink in coniferous forests: Uncertainty and sensitivity analyses of three ecosystem models

Estimates of the global carbon sink induced by nitrogen enrichment range vary widely, from nearly zero to 2.3 Gt C year-1. It is necessary to reduce this uncertainty if we are to make accurate predictions of the future magnitude of the terrestrial carbon sink. Here, we present a Monte Carlo approach to uncertainty and sensitivity analysis of three ecosystem models, Century,BGCand Hybrid. These models were applied to a coniferous forest ecosystem in Sweden. The best estimate of the change in total carbon content of the ecosystem with the cumulative change in nitrogen deposition over 100 years, ΔCtotal/ΔNdeposition was 20.1 kg C (kg N)-1 using the pooled mean, with a pooled standard deviation of 13.8 kg C (kg N)-1. Variability in parameters accounted for 92% of the total uncertainty in ΔCtotal/ΔNdeposition, and only 8% was attributable to differences between models. The most sensitive parameters were those which controlled the allocation of assimilate between leaves, roots and stem. In particular, an increase in allocation to fine roots led to a large reduction in ΔCtotal/ΔNdeposition in all models, because the fine roots have a very high turnover rate, and extra carbon allocated there is soon lost through mortality and decomposition.

Effects of treatments potentially influencing the supply of assimilate on its partitioning in sugarcane

Two pot experiments and one field experiment were conducted on sugarcane to assess the effects of treatments expected to change total carbon assimilation on the partitioning of assimilate. In the first experiment pots of cultivars CP and N14 were arranged to simulate normal field spacing. At 5 months, plants were partially defoliated or left intact. In the subsequent four months, defoliation resulted in a small (not significant) decrease in total dry mass increment; it increased the proportional partitioning of assimilates to leaves in N14, whilst in CP it increased the proportional partitioning to stems. In both cultivars defoliation increased proportional allocation to non-structural dry matter, and thus sucrose, in the stem. In the second experiment pots of cv. CP were grown at normal spacing for 4 months, then left untreated, shaded, or placed further apart. During the subsequent four months shading decreased total dry matter increment, but increased proportional partitioning to the stems, and within stems to non-structural dry matter, and so sucrose. Widened spacing increased total assimilation, but decreased proportional allocation to stems; partitioning within the stems was not affected. In the field experiment plants of both cultivars were partially defoliated at 6 months, or left intact. Defoliation resulted in only a very small decrease in stem dry mass increment during the subsequent four months (leaves were not measured). Within the stem partial defoliation caused proportionally increased partitioning to non-structural dry matter, hence to sucrose. The results suggest that sucrose storage receives priority in the allocation of assimilate, rather than representing the accumulation of assimilate not required for vegetative growth.

Physiological responses of argentine peanut varieties to water stress.: Light interception, radiation use efficiency and partitioning of assimilates

In Argentina, peanut production is concentrated in areas where unpredictable and intermittent periods of water deficit occur almost every year especially, during the pod growth period. Florman INTA is the most popular variety among peanut producers, but it is highly sensitive to drought. Manfredi 393 INTA was released as a drought-tolerant variety. Differences between these varieties in radiation interception and crop mass accumulation relative to light levels, as well as in allocation of assimilate to economic yield under water deficit, have not been previously studied. An experiment was set with two different regimes of water supply. Half of the crop was irrigated (IRR) from sowing to maturity, while the other half received no water between 47 and 113 days after sowing. The fraction of PAR intercepted, ( f), leaf area, pod and vegetative above-ground biomass and leaf carbon dioxide exchange rate (CER) were measured periodically during the water deficit period. The leaf area index, degree of leaf folding, canopy extinction coefficient, radiation use efficiency (RUE), partitioning factor, ( p), and harvest index (HI) were calculated from the measurements. Under water stress, f was reduced in both varieties with respect to their controls, and the reduction was proportionally higher in Florman INTA as a consequence of a higher leaf area reduction and degree of leaf folding. However, f remained higher in Florman INTA than in Manfredi 393 INTA due to the enhanced capacity of the former to generate leaf area under non-limiting water supply. RUE values were higher in Manfredi 393 INTA than in Florman INTA, both under irrigation as well as under severe water deficit, where they were obtained using a two-parameter exponential model. The reason for the higher RUE values in Manfredi 393 INTA was its ability to maintain a higher leaf CER. Partitioning to pods under irrigation was greater in Manfredi 393 INTA than in Florman INTA, as a result of a longer pod filling period and higher p. Towards the end of podfill, there was a rapid increase of p in Florman INTA, but too late to improve its HI. Under water stress, the time course of p for both varieties was lower than in the IRR treatments and consequently, HI at harvest was reduced. Low HI values could be attributed to some extent to the mechanical impedance of the upper soil layer, caused by water deficit. Mechanical impedance alters the relation among p and HI values obtained under irrigation and water stress. However, even if it is accounted for, cultivars with high HI under IRR conditions usually have high HI under water deficit.

Allocation responses to CO2 enrichment and defoliation by a native annual plant Heterotheca subaxillaris

Among plants grown under enriched atmospheric CO2, root:shoot balance (RSB) theory predicts a proportionately greater allocation of assimilate to roots than among ambient-grown plants. Conversely, defoliation, which decreases the plant's capacity to assimilate carbon, is predicted to increase allocation to shoot. We tested these RSB predictions, and whether responses to CO2 enrichment were modified by defoliation, using Heterotheca subaxillaris, an annual plant native to south-eastern USA. Plants were grown under near-ambient (400 μmol mol−1) and enriched (700 μmol mol−1) levels of atmospheric CO2. Defoliation consisted of the weekly removal of 25% of each new fully expanded, but not previously defoliated, leaf from either rosette or bolted plants. In addition to dry mass measurements of leaves, stems, and roots, Kjeldahl N, protein, starch and soluble sugars were analysed in these plant components to test the hypothesis that changes in C:N uptake ratio drive shifts in root:shoot ratio. Young, rapidly growing CO2-enriched plants conformed to the predictions of RSB, with higher root:shoot ratio than ambient-grown plants (P < 0.02), whereas older, slower growing plants did not show a CO2 effect on root:shoot ratio. Defoliation resulted in smaller plants, among which both root and shoot biomass were reduced, irrespective of CO2 treatment (P < 0.03). However, H. subaxillaris plants were able to compensate for leaf area removal through flexible shoot allocation to more leaves vs. stem (P < 0.01). Increased carbon availability through CO2 enrichment did not enhance the response to defoliation, apparently because of complete growth compensation for defoliation, even under ambient conditions. CO2-enriched plants had higher rates of photosynthesis (P < 0.0001), but this did not translate into increased final biomass accumulation. On the other hand, earlier and more abundant yield of flower biomass was an important consequence of growth under CO2 enrichment.

Apical control of branch growth and angle in woody plants

Apical control is the inhibition of a lateral branch growth by shoots above it (distal shoots). If the distal shoots are cut off to remove apical control, the lateral branch can grow larger and may bend upwards. Apical control starts when new lateral buds grow after passing through a period of dormancy. Buds initially break and produce leaves, then apical control is exerted and the lower (proximal) laterals stop growing. Apical control also inhibits growth of large, old branches. Gravimorphism and restricted water and nutrient transport can inhibit branch growth, but they are not primary mechanisms of apical control. Apical control may reduce branch photosynthesis. Under apical control allocation of branch-produced assimilate to the stem is relatively high, so low assimilates in the branch may limit branch growth even though hormone levels are adequate for growth. Hormones appear to be involved in apical control, but it is not known how. One role of hormones may be to maintain the strength of the stem sink for branch-produced assimilate. Upward bending of a woody branch after release from apical control requires both new wood production and production of wood cells that can generate an upward bending moment. Apical control inhibits radial growth of branches and, in some species, may regulate the production of wood with an upward bending moment.

Experimental testing of dynamic energy budget models

1. Dynamic energy budget (DEB) models describing the allocation of assimilate to the competing processes of growth, reproduction and maintenance in individual organisms have been applied to a variety of species with some success. There are two contrasting model formulations based on dynamic allocation rules that have been widely used (net production and net assimilation formulations). However, the predictions of these two classes of DEB models are not easily distinguished on the basis of simple growth and fecundity data. 2. It is shown that different assumptions incorporated in the rules determining allocation to growth and reproduction in two classes of commonly applied DEB models predict qualitatively distinct patterns for an easily measured variable, cumulative reproduction by the time an individual reaches an arbitrary size. 3. A comparison with experimental data from Daphnia pulex reveals that, in their simplest form, neither model predicts the observed qualitative pattern of reproduction, despite the fact that both formulations capture basic growth features. 4. An examination of more elaborate versions of the two models, in which the allocation rules are modified to account for brief periods of starvation experienced in the laboratory cultures, reveals that a version of the net production model can predict the qualitative pattern seen for cumulative eggs as a function of mass in D. pulex. The analysis leads to new predictions which can be easily tested with further laboratory experiments.

Transient three-dimensional modeling of soil water and solute transport with simultaneous root growth, root water and nutrient uptake

A three-dimensional solute transport model was developed and linked to a three-dimensional transient model for soil water flow and root growth. The simulation domain is discretized into a grid of finite elements by which the soil physical properties are spatially distributed. Solute transport modeling includes passive and active nutrient uptake by roots as well as zero- and first-order source/sink terms. Root water uptake modeling accounts for matric and osmotic potential effects on water and passive nutrient uptake. Root age effects on root water and nutrient uptake activity have been included, as well as the influence of nutrient deficiency and ion toxicity on root growth. Examples illustrate simulations with different levels of model complexity, depending on the amount of information available to the user. At the simplest level, root growth is simulated as a function of mechanical soil strength only. Application of the intermediate level with root water and nutrient uptake simulates the influence of timing and amount of NO3 application on leaching. The most comprehensive level includes simulation of root and shoot growth as influenced by soil water and nutrient status, temperature, and dynamic allocation of assimilate to root and shoot.

GRAZPLAN: Decision support systems for Australian grazing enterprises. III. Pasture growth and soil moisture submodels, and the GrassGro DSS

This paper specifies the pasture growth module of a model for simulating grazing systems for ruminants and the soil moisture budget that drives pasture growth. Both modules operate at a daily time step. The pasture growth module is quite general in structure but recognises four functional groups of pasture plants: annual and perennial species are distinguished, as are grasses and forbs. Shoot tissue is classified as live, senescing, standing dead, or litter, and also according to its dry matter digestibility, thus enabling integration with diet selection and feed intake models. The phenological development of pasture plants is modelled, with the transitions between each stage governed by environmental variables (day length, temperature and soil moisture). Prereproductive and postreproductive phenostages of vernalisation and ‘summer dormancy’, respectively, are modelled in the appropriate cultivars. Functions predicting net primary production in response to light intercepted, mean daytime temperature, and available soil moisture, and also the process of maturation, are common to all functional groups. The model's treatment of the allocation of assimilate has a similarly general form. Seed and seedling dynamics are modelled for annual species only. GrassGro is a discrete computer package, developed for Microsoft Windows, ™ that combines the pasture growth module with a module for predicting the intake of herbage of ruminants and their productivity. This decision support system enables users to analyse simplified grazing systems in terms of pasture and animal production, gross margins, and year-to-year variability for any specified pasture cultivar, or combination of cultivars, at any specified site. The package may also be used to simulate forward from current pasture and animal conditions, for assessing the probability distribution of production outcomes, given the historical variability of weather conditions over the specified forward period.

Internodal Compartmentation of Stem‐Infused [14C]Sucrose in Sweet and Grain Sorghum

Stem infusion was evaluated for quantifying downward movement, intracellular allocation, and interorgan partitioning of assimilate in sweet and grain sorghum [Sorghum bicolor (L.) Moench] stems during mid‐grain fill and post‐black layer. Sucrose concentration did not vary below the site of infusion with [14C]sucrose, although gradients of intracellular 80%‐ethanol soluble and insoluble 14C‐components were established in the stem. Variation in gradient steepness between cultivars resulted from aspects of parenchymal uptake or phloem uptake of sucrose and appears related to sucrose‐concentrating ability. The introduced [14C]sucrose concentration gradient in stem tissue is useful for studying stem mechanisms that controls ink strength.

Developmental and Environmental Effects on Assimilate Partitioning in Canada Thistle (Cirsium arvense)

Under field conditions, more photoassimilate moved to roots of Canada thistle at the bolt than at the bud, flower, or postflower stages. Similarly, greater photoassimilate accumulated in roots of Canada thistle in the greenhouse at the rosette and bolt than at the flower bud stage. Growth chamber experiments indicated that environmental conditions typical of fall, and possibly early spring, favored photoassimilate movement to the root and superseded growth stage control of assimilate partitioning. Allocation of assimilate within the root was strongly influenced by growth stage, with most assimilate being utilized for growth at the rosette stage and for fructan reserves in bolt and flower bud stages.

The effects of liming on mycelial colonization and carbon allocation in ectomycorrhizal mycelia attached to Pinus silvestris plants

The effects of liming on ectomycorrhizal mycelial colonization and carbon allocation were assessed using Pinus silvestris plants grown in association with an ectomycorrhizal fungus. Plants were placed in perspex growth chambers divided by a central partition so that soils of different pH could be used on either side of the chambers. Differences between the growth form and growth rates of the fungi and allocation of plant assimilate were determined at different pH values.

A Carbon 14 Study of Metabolism in Tall Fescue Seedlings Acclimating to Growth at Low Temperatures

The youngest fully expanded leaves of young plants of tall fescue (Festuca arundinacea Schreb. cv. S 170) were allowed to assimilate 14C02 either (a) at the fifth leaf stage immediately before transfer from 17/14 °C to 7/4 °C (non-acclimated), or (b) after transfer from 17/14 °C to 7/4 °C at the fifth leaf stage, and further development in 7/4 °C of one or two more leaves (acclimation for one or two plastochrons). Controls were maintained in 17/14 °C and allowed to assimilate 14C02 at the corresponding (fifth, sixth, or seventh) leaf stages. Allocation of 14C amongst sinks and biochemical fractions was analysed during a subsequent period of growth at 7/4 °C (cold) or 17/14 °C (control). Allocation of assimilate to growing parts of the shoot was less than controls in the non-acclimated plants transferred to the cold and more than controls in plants acclimated for one plastochron. After the imbalance induced initially by transfer from 17/14 °C to 7/4 °C, acclimation for one or two plastochrons brought the allocation amongst sinks and amongst biochemical fates closer to the balance existing in controls. The main shoot and side tillers differed in the time during acclimation when they became more like the controls. The percentage of assimilate in the soluble carbohydrate fraction of non-acclimated plants and of plants acclimated for one plastochron, was higher than in controls. The percentage of assimilate in the cell wall fraction was lower in non-acclimated plants than in controls but the difference from controls after two plastochrons acclimation again was less. During the first plastochron after transfer to cold, diversion of assimilate to a reserve pool in sinks could be a factor limiting cell wall synthesis and growth and this limitation may be relieved when the reserve pool is 'full'. Low temperature reduced the percentage of assimilate in the protein fraction of growing parts of the shoot and the difference was found even after two plastochrons acclimation.

Partitioning of Assimilate Between Vegetative and Reproductive Growth in Soybean1

AbstractChanges in the proportion of the total biomass harvested have made an important contribution to the increase in yield in several grain crops. Field experiments were conducted for several years on Typic Argiudoll and Typic Paleudalf soils to investigate the effect of cultivars, growth habit, and environmental conditions on the partitioning of assimilate between vegetative and reproductive plant parts in soybean [Glycine max(L.) Merr.] during flowering and fruit set. The experiments included the following variables; cultivars from maturity group II to V, including both indeterminate and determinate growth habits, optimum and delayed plantings, and moisture stress. Data were collected from growth stage R1 to R6 on vegetative growth characteristics (nodes on main stem, total nodes, and plant height), pod development, and weight of vegetative and reproductive plant parts. Partitioning coefficients were calculated by dividing fruit weight by the total aboveground biomass. The nodes on the main stem and on the branches reached a maximum at R5 in all cases. Determinate cultivars produced fewer nodes on the main stem between R1 and R5; however, they produced more branch nodes and the total node production was greater than the indeterminate cultivars. The number of pods containing developing seed increased until approximately R6, suggesting that the production of new vegetative sinks (node production) in soybean stopped before the total fruit load was established. The partitioning coefficients increased rapidly from &lt; 5% at growth stage R3 to ≥ 30% at R6. The partitioning coefficient at any growth stage varied only slightly across the variables included in the experiments. This suggests that variation in fruit and seed number may be more closely related to variations in crop growth rate than to variations in the allocation of assimilate between vegetative and reproductive plant parts.

An appraisal of ear, leaf and stem 14CO2 assimilation, 14C‐assimilate distribution and growth in a reproductive seed crop of amenity Lolium perenne

SUMMARYIn seed crops of Lolium perenne, yield may be reduced by competition for a limited assimilate supply from sinks other than the ear. This study was undertaken to evaluate the priorities for allocation of assimilate within the crop from all photosynthetic sites on the main reproductive tiller after anthesis.Ear, stem and leaves were fed with 14CO2 on two occasions; the assimilatory efficiency of these sources and the magnitude and pattern of 14C‐assimilate export from each was determined. The growth of each part of the main tiller and subtending tillers was also measured.Stem elongation apparently dominated the current assimilate resource and the ear did not become a net importer of assimilate until this process had ceased. Assimilate allocation to the tillers was high throughout.The nature of any competition between these sinks is discussed. When crop growth was contrasted with that in a previous year, environmental factors were implicated as determinants of priority for assimilate allocation to each sink. Sources of carbon for seed filling are also discussed as is the relevance of these findings to seed crop management.

Seedling stage of two subalpineAbies species in distinction from sapling stage: A matter-economic analysis

A growth analytical study is made on the seedlings ofAbies mariesii Mast. andAbies veitchii Lindl. in the subalpine climaxAbies forests of the northern Yatsugatake Mountains, central Japan. Seedlings are distinguished from saplings by the absence of the fully expanded lateral branch system. The high dependence of assimilation on new needles characterizes the lives of seedlings. Leader shoots of seedlings, resembling not leader shoots but lateral branch shoots of saplings, have shoot characters adaptive for assimilation. Seedlings grow into saplings at 20 cm in height and 5 g in dry weight. The matter-economic analysis suggests the existence of a boundary growth rate below which an individual cannot maintain the needle amount requisite for its survival (called the critical growth rate) and that above which an individual can easily enter the sapling stage due to higher allocation of assimilate to roots and aged trunk stem (the capacity growth rate). Forest floor seedlings suffer, a high mortality during their initial several years and scarcely grow to enter the sapling stage, because of the scantiness of their matter production. In the regeneration patterns of subalpineAbies forests, both the seedling bank type and the sapling bank type are recognized.