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Because light conditions in the forest understory are highly heterogeneous, photosynthetic acclimation to spatially variable irradiance within a crown is important for crown-level carbon assimilation. The effect of variation in irradiance within the crown on leaf nitrogen content and photosynthetic rate was examined for pinnate compound leaves in saplings of Cedrela sinensis, a pioneer deciduous tree. Five shading treatments, in which 0, 25, 50, 75 and 100% of leaves were shaded, were established by artificial heavy shading using shade screen umbrellas with 25% transmittance. Although the nitrogen content of leaves was constant regardless of shading treatment, ribulose 1·5-bisphosphate carboxylase/oxygenase (Rubisco) content and light-saturated photosynthetic capacity were lower in shade leaves within partially shaded crowns than within fully shaded crowns. Shade leaves within partially shaded crowns contained higher amount of amino acids. Most shade leaves died in partially shaded crowns, whereas more than half of shade leaves survived in totally shaded crowns. Assumptions on photosynthetic acclimation to local light conditions cannot explain why shade leaves have different photosynthetic capacities and survival rates in between partially and totally shaded crowns. Irradiance heterogeneity within the crown causes a distinct variation in photosynthetic activity between sun and shaded leaves within the crown. [ABSTRACT FROM AUTHOR]

1 The morphological plasticity of sun and shade branches of Pinus sylvestris growing at the edge of a ‘tree-patch’ created in 1989, when surrounding trees were removed, was compared with that of branches of trees growing in the centre of the patch. 2 In 1992, we selected 10-year-old branches. Yearly growth increments (long-shoots) and emerging buds were individually marked, architectural parameters measured, the branch topology mapped, and the number of male and female cones counted. In 1993, the survival of growth increments and buds was recorded and the branches were harvested to determine dry mass of growth increments and needles. 3 The size of growth increments produced after 1989, i.e. their length, total dry mass and needle dry mass, decreased in the order sun branches of edge trees > branches of centre trees > shade branches of edge trees. Thus, the growth increments produced on the shade branches of trees that also had branches in the sun were consistently smaller than the growth increments on the branches of centre trees growing completely in the shade. 4 The number of new growth increments produced after 1989 was highest in sun branches and lowest in shade branches of edge trees. Survival of growth increments and buds was higher in edge than in centre trees; no difference was found between sun and shade branches of edge trees. 5 In shade branches of edge trees, branching angles between first- and second-order growth increments were highest and increased from older to younger growth increments. This was interpreted as ‘bending’ towards the edge of the patch. 6 Production of female cones was almost totally restricted to edge trees and higher in sun than in shade branches. 7 One prediction of an optimal foraging strategy, i.e. the production of more growth increments and buds in higher light, was supported by the data, whereas the other prediction, i.e. decreased length of growth increments, could only be supported when it was... [ABSTRACT FROM AUTHOR]

Root restriction may be of importance for productivity in both forestry and agriculture. To study the physiological effects of root restriction in European alder (Alnus glutinosa Gaertn.), seedlings were grown in aerated liquid culture under one of four root. volumes to induce the following levels of root restriction: 1.5, 6, 16 and 500 ml. Root restriction for 96 days reduced shoot elongation, plant dry weight, leaf area and chlorophyll, levels and increased leaf area/root dry weight ratio and correlative bud inhibition in seedlings. The initial reduction in root/shoot ratios of severely restricted seedlings was followed by a reduction in leaf water potential, the development of internal water deficits in the upper shoots, a reduction in stomatal opening and transpiration rates and, eventually, stomatal closure. Severe prolonged root restriction (1.5 ml root volume) resulted in a decline in seedling vigour and ultimately. senescence as determined by increased electrical impedance ratios, followed by visible leaf senescence and later, by whole plant senescence. Of the severely restricted seedlings, 40%. were dead after 96 days of restriction. The results suggest that imbalanced root/shoot ratios caused the development of internal water stress and the consequent reduction in stomatal aperture, culminating in leaf and whole plant senescence. [ABSTRACT FROM AUTHOR]

Indol-3yl-acetic acid (IAA) present in the rooting solution for 1-4 days appreciably decreased the number of roots subsequently formed in pea stem cuttings. Removal of the lowest 10 mm of the cutting base after IAA treatment abolished the inhibitory effect of IAA almost completely. The number of roots formed from the remaining part of the base internode after excision of the basal centimeter of the internode 4 days after the cuttings were taken was similar to that of the control. It is concluded that the first root primordia, which develop near the cut surface, have an inhibitory influence on development of further roots. The inhibitory effect of IAA may be explained as a strengthening of this dominance phenomenon. Addition of charcoal to the rooting solution delayed the appearance of roots but increased the number of roots developed during a standard rooting period. Adsorption of stimulatory and inhibitory compounds at the surface of the cutting base is believed to be the reason for these results as no evidence of accumulation of inhibitory compounds in the solution was obtained. Charcoal reversed the inhibitory effect of IAA if added after the IAA treatment. This reversal was almost complete if the IAA treatment lasted for one day only but decreased drastically if the IAA treatment was extended over 4 days. [ABSTRACT FROM AUTHOR]

Removing apical portions of current growth coppice shoots from field-grown, low-pruned stumps of mulberry (Morus alba L. cv. Shin-ichinose) caused sprouting of one or more upper main buds, almost concurrently with that of accessory buds. However, removal of the new sprouts, including those from accessory buds, slightly enhanced the sprouting of buds immediately below them, and did not affect buds lower down. In contrast, mature leaves inhibited the buds in their axils. Budless, leafy nodes on the upper part of pruned shoots tended to swell after treatment, perhaps due to the accumulation of substances translocated from the roots and possibly from the remaining leaves. Lateral buds at different positions along the shoot differed in their sprouting ability with buds lower on the shoot being more inhibited. This inhibition gradient dissappeared when all coppice shoots on one stump were pruned to the same bud position, suggesting inhibition from neighboring, actively growing shoots. These results demonstrate that acropetal influences are important in bud dominance relationships. [ABSTRACT FROM AUTHOR]

Plants of Pisum sativum var. arvense Poir. cv. Dun were grown with two equal shoots kept in different light conditions. In these plants a darkened shoot was inhibited and it eventually withered and died; it elongated and became etiolated only when the shoot in the stronger light was removed. A similar result was obtained in simulated ecological conditions, when the shoot in the inferior light was merely shaded: this shoot was severely inhibited, though it did survive. The inhibition of the shaded shoot was more pronounced when the plants were stressed by the removal of large parts of their cotyledonary reserves. These results demonstrate an integration of responses to the light environment with the correlative inhibition between shoots of the same plant. This integration enables the plant to use its developmental resources optimally in heterogeneous environments, rather than merely growing where conditions are 'appropriate'. [ABSTRACT FROM AUTHOR]

It was postulated that the release of lateral buds from apical dominance is triggered by the immediate increase in apoplastic water potential (hydrostatic pressure) that is produced by shoot decapitation and that is rapidly transmitted throughout the plant. In experiments conducted to test this hypothesis the use of a strain gauge transducer capable of measuring bud growth with an accuracy of ± 0.1 μm, showed that growth of the inhibited lateral bud at the primary leaf node of Phaseolus vulgaris (L.) ev. Canadian Wonder was initiated within 1 to 5 s following shoot decapitation or excision of the primary leaves. When only the apical bud was excised the lateral bud showed a brief, transitory growth response of ca 1 min duration, but the axillary buds of the first and second trifoliate leaves were released from inhibition. Decapitation of the shoot just below the first trifoliate leaf induced a lateral bud response characterized by three distinct stages: a) a rapid initial growth response with a mean duration of 4.9 min b) a period of arrested growth, which varied in duration from 2 min to 4 h and c) the subsequent resumption of growth. Excision of both primary leaves induced a rapid but transitory bud response of considerably greater duration than that induced by apical bud excision. Excision of the primary leaves prior to decapitation of the shoot eliminated the phase of arrested growth, which characterized the bud response to decapitation of the intact plant. The rapidity of the bud response to both shoot decapitation and leaf excision and the interaction between the effect of these two treatments are consistent with the hypothesis that competition for water plays a major role in the correlative inhibition of lateral buds. [ABSTRACT FROM AUTHOR]

A plant has a great excess of buds each with the potential of developing an entire shoot system. The general question tackled was to what extent shoot size and time of bud development are important for bud hierarcy. Pea seedlings with two shoots, which were either equal or unequal in size, were obtained by the early removal of the seminal shoot. When these two shoots were also removed, one of the two cotyledon buds next to the basis of the shoots developed into the new shoot system. The determination of which of the buds became dominant was studied as a function of the relative sizes of the two primary cotyledonary shoots, of differences in the timing of the removal of these shoots and of the size of the buds. The bud that became dominant was not necessarily the larger shoot. Instead, it was usually the bud that was inhibited for a shorter period by the shoot next to it. It is suggested that the fate of a bud is predominantly determined by developmental parameters, for example time of release, which are correlated with its developmental status and not necessarily with its physical size or with the past development of its shoot. [ABSTRACT FROM AUTHOR]

Roots are known to respond to favourable nutrient conditions by increased initiation and growth of lateral roots. The problem studied here was to what extent does this local developmental response depend on the environments of other roots on the same plant. Such dependence could a How for an optimal allocation of resources required for root growth in unpredictable, heterogeneous soils. Pea seedlings (Pisum sativum var. arvense cv. Dun) were pruned and grown to have two equal root systems, each in an individual container. As expected, these roots responded by increased development to a wide range of nutrient solution concentrations. The local development of these roots, expressed by their dry weight, was a function of the relative rather than the absolute conditions in which they were grown: roots in a given environment developed more rapidly if other roots on the same plant were in poorer than if they were in richer nutrient conditions. The number of lateral initials doubled within 3d after the roots were exposed to optimal nutrient conditions, before any dry weight differences could be detected. This rapid root initiation was also a function of the conditions other roots of the same plant were in. These results mean that root development and especially lateral root initiations depends on the integrated effects of the local environment and the internal correlative relations between the roots. [ABSTRACT FROM AUTHOR]