The Effect of Mineral Nutrition on the Distribution of Growth in Lolium perenne

Ramets of Lolium perenne from the same genotypes were grownin nutrient solutions of two concentrations. Additional mineralnutrition increased the rate of production of new tillers, therate of increase in size of tillers and the rate of productionof new roots, but not the rate of growth of individual mainroots. The genotypes differed considerably from each other intheir rates of growth, especially of shoot growth. When thegrowth-rate of the same population of genotypes was alteredby changing the environmental conditions it was found that thelower the mean rate of shoot growth, the greater its coefficientof variation. Variation in the rate of shoot growth, due tomineral nutrition and genetic constitution of the plants growingin a dilute nutrient solution, was accompanied by a similarbut smaller variation in the number of roots.     

Influence of Genotype and Mineral Nutrition on the Distribution of Growth within Plants of Lolium perenne L. grown in Soil

Genotypes of Lolium perenne were grown with two levels of fertilizerapplication. Using exponential growth-rates and parameters derivedfrom them, the rate of growth of each genotype was partitionedinto the rates of initiation of new roots and tillers, and thegrowth of the individual roots and tillers after initiation.The growth of the individual roots was further analysed by measuringchanges in diameter and length of the main root, and the growthin the branches of the main root. The genotypes varied in their response to additional mineralnutrition. The greater the increase in the rate of shoot growthfor a genotype, the greater was its increase in the rate oftiller initiation, the smaller was the increase in the sizeof its tillers, and the greater was the decrease in its rateof root relative to shoot growth. Within a population of genotypes growing with the same levelof mineral nutrition, the greater the rate of shoot growth ofa genotype, the greater was the rate of initiation of new tillersand, at a low level of mineral nutrition, the smaller the sizeof tillers. With a higher level of mineral nutrition, the higherthe rate of tiller production, the smaller or larger was tillersize, depending upon environmental factors other than mineralnutrition. At both levels of mineral nutrition, the greaterthe rate of shoot growth, the smaller was the rate of root growthrelative to shoot growth, due to relatively less growth takingplace in the branches of the main root.     

The Effect of the Prevention of the Production of Additional Root Axes upon the Growth of Plants of Lolium perenne

Plants were prevented from forming additional nodal root axesby raising the base of the shoot above the level of the surroundingsoil, so keeping the base dry. Shoot growth from one to threeweeks after new root axes ceased to be produced was slightlyreduced, but root growth was considerably decreased. Shoot regrowthfollowing repeated defoliation was reduced by lack of new rootaxes but not significantly so until after four defoliations:the regrowth had low calcium and phosphorus contents. The resultsare discussed in relation to the growth of the root and shootsystems and mineral nutrition.     

Investigations of Carbon Transport in Plants: I. THE USE OF CARBON-11 TO ESTIMATE VARIOUS PARAMETERS OF THE TRANSLOCATION PROCESS

A technique is described which enables several components ofthe translocation system to be measured routinely, in vivo andsimultaneously. Plants are exposed to a 1-min pulse of ¹¹CO₂and the movement of the ¹¹C pulse through the plant followedusing an array of scintillation counters. It is possible toestimate the time taken for the ¹¹C to enter the sieve tubes.In addition, the speed of translocation can be obtained frommeasurements of the arrival of the ¹¹C pulse at different positionsalong the translocation pathway. The increasing half-width ofthe pulse as it enters and moves through the sieve tubes givessome indication of the extent of the delays in the differentparts of the translocation system. The short half-life of the¹¹C allows the measurements to be repeated on the same plantseveral times per day. A technique is discussed whereby dataon the movement of ¹¹C could be combined with simultaneous measurementsof the rate of uptake of carbon dioxide to provide an estimateof the rate of movement of carbon.     

Real Time Studies of Carbon- 11 Translocation in Moonflower: III. FURTHER EXPERIMENTS ON THE EFFECTS OF A NITROGEN ATMOSPHERE, WATER STRESS, AND CHILLING; AND A QUALITATIVE THEORY OF STEM TRANSLOCATION

Translocation of naturally loaded carbon- 11 is studied in themoonflower Ipomoea alba L. and data are presented to show that:(i) source leaf export is momentarily inhibited by a suddenlyapplied water stress; (ii) pathway translocation appears toproceed by a MÜnch-like mechanism, but in a porous mediumrather than in an array of parallel, only slightly leaky pipes;and (iii) sink unloading seems to proceed normally in a nitrogenatmosphere. A qualitative model which incorporates these findingsis presented.     

The relationship between the relative growth rates of the shoot system, number of tillers and mean tiller size in Lolium perenne

The relative growth rate of the shoot system of Lolium perenne may be considered as being made up of two components, the relative growth rate of the increase in the number of tillers and the relative growth rate of the mean tiller. These three relative growth rates were calculated for twenty-two clones of Lolium perenne growing in twenty-eight environments. Analyses of variance showed that differences in the environment were responsible for a greater amount of variation than either differences between clones or the interaction between clonal and environmental influences.
For each clone it was possible to calculate relationships between the relative growth rate of the shoot and its two components as they varied with the environments. The relationships held irrespective of the environmental factor(s) which altered to cause the difference in relative growth rates. In all clones an increase in the relative growth rate of the shoot was found to be due to an increase in the relative growth rates of both components. In seventeen clones the relationship between the increments of the two components was constant. In five of the clones an increase in the relative growth rate of the shoot at low values was due more to an increase in the relative growth rate of the number of tillers than to an increase in the relative growth rate of the mean tiller. At high values the opposite occurred.
These results are discussed in relation to the theory of 'nutritive diversion' and in relation to the proportion of lateral buds which produce tillers.     

Investigations of Carbon Transport in Plants: II. THE EFFECTS OF LIGHT AND DARKNESS AND SINK ACTIVITY ON TRANSLOCATION

The use of ¹¹C as a tracer has allowed repetitive measurementsof the speed of assimilate translocation to be made on singlemaize plants throughout prolonged periods of light and darkness.The speed appeared to double when the light was switched on.The time required to achieve a maximum speed, usually about3·5 cm min^–1, depended on the duration of the previousdark period. When the plant was transferred to darkness thespeed immediately decreased by about 20 per cent and continuedto decrease over the next 20 h to values of 0·5 to 0·9cm min^–1. The mean speed of translocation in tomato in the light, andother C3 plants, was usually about 1 cm min^–1. It wasreduced by 15–30 per cent when the fruit was removed orcooled from 26 to 10°C.     

The Rate of Growth and Partitioning of Assimilates in Young Grass Plants: A Mathematical Model

A model describing the increase in weight with time of younggrass plants is formulated. The parameters are the relativegrowth rates of the root and shoot systems; k, the ratio ofthe relative growth rate of the root system relative to thatof the shoot system; b, the weight of the root system when thatof the shoot system is unity, and u the rate of increase inweight of the whole plant per unit of shoot system per unitof time, k and b are the constants in the allometric formula,r = bs^k where r and are the weights of the root and shoot systems.The model enables the effect of changes in the distributionof assimilates between the root and shoot systems upon the rateof growth of the plant to be assessed. Data from a number ofexperiments are analysed in this manner and the significanceof the results discussed.     

The Effect of Phosphorus Nutrition upon the Growth and Morphology of Young Plants of Lolium perenne L.

Genotypes of Lolium perenne were grown in soil of low phosphorusstatus, with and without additional phosphorus. Lack of phosphorusresulted in a great reduction in the number of main roots andin an increase in the length of each individual root. The numberof tillers was also reduced, but to a lesser extent than thenumber of main roots. The dry weight of the root and shoot systemwas reduced to a lesser extent than the numbers of roots andtillers. The effect on root relative to shoot growth variedwith the genotype.     

Real Time Studies of Carbon-11 Translocation in Moonflower: II. THE EFFECTS OF METABOLIC AND PHOTOSYNTHEIC ACTIVITY AND OF WATER STRESS

Naturally loaded carbon-11 was used to study in vivo the dynamicsof translocation. It was found that translocation displayedstrong short-term sensitivity to source chilling, source anoxia,disturbance of the osmotic balance of stem apoplast, and apexshading but that it seemed indifferent to metabolic inhibitorsand stem anoxia. Plant-wide water stress effected a long-termdisruption of translocation which was reversed only slowly whenthe stress was relieved. These experiments generally supporta mass flow theory, but indicate that there is a close couplingbetween translocation streams from different sources.